IEC TS 63001:2024
(Main)Measurement of cavitation noise in ultrasonic baths and ultrasonic reactors
Measurement of cavitation noise in ultrasonic baths and ultrasonic reactors
IEC TS 63001:2024 provides a technique of measurement and evaluation of ultrasound in liquids for use in cleaning devices, equipment, and ultrasonic reactors. It specifies
- the cavitation measurement at frequencies between harmonics of the operating frequency f0,
- the cavitation measurement derived by integrating broadband cavitation noise energy,
- the cavitation measurement by extraction of broadband spectral components.
This document covers the measurement and evaluation of cavitation, but not its secondary effects (cleaning results, sonochemical effects, etc.). Further details regarding the generation of cavitation noise in ultrasonic baths and ultrasonic reactors are provided in Annex A.
IEC TS 63001:2024 cancels and replaces the first edition published in 2019. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition:
a) addition of a new method of measurement: the measurement of integrated broadband cavitation energy between two frequency bounds.
General Information
Relations
Overview
IEC TS 63001:2024 - Measurement of cavitation noise in ultrasonic baths and ultrasonic reactors specifies standardized techniques to measure and evaluate ultrasound-induced cavitation in liquids used for cleaning devices, equipment and ultrasonic reactors. This second edition (2024) cancels and replaces IEC TS 63001:2019 and introduces a significant technical change: a new method to measure integrated broadband cavitation energy between two frequency bounds. The specification addresses cavitation noise measurement methods and instrumentation, but does not cover secondary effects such as cleaning results or sonochemical outcomes.
Key Topics
- Measurement methods
- Cavitation measurement at frequencies between harmonics of the operating frequency f0.
- Cavitation measurement derived by integrating broadband cavitation noise energy (new in 2024).
- Cavitation measurement by extraction of broadband spectral components from the acoustic spectrum.
- Instrumentation and requirements
- Use and calibration of hydrophones, analyser selection and calibration, and hydrophone-environment compatibility.
- Procedures for analyser settings covering transient and stable cavitation spectra.
- Controls for temperature, liquid chemistry and electrical interference during measurements.
- Measurement procedures
- Reference and in-situ monitoring measurement workflows, environmental control, and validation steps.
- Normative and informative annexes with worked examples and background on cavitation noise generation (Annex A).
- Normative annexes (examples): methods at specific spectral positions (e.g., 2.25 f0), broadband integration, and spectral component extraction.
Applications
IEC TS 63001:2024 is practical for:
- Manufacturers of ultrasonic baths and ultrasonic reactors validating device cavitation performance.
- Test and calibration laboratories performing acoustic and cavitation characterization.
- R&D teams and acoustic engineers optimizing transducers, power settings and bath geometry.
- Quality control and process engineers using in‑situ monitoring to ensure consistent cavitation energy during production cleaning.
- Regulatory bodies and standards committees referencing objective cavitation measurement methods.
The standard enables reproducible measurement of cavitation noise for device comparison, lifecycle testing, and process control - without making claims about cleaning efficacy or chemical effects.
Related Standards
- IEC TC 87 Ultrasonics publications (related technical committee) - see IEC webstore for related device and measurement standards.
- Refer to the normative references listed in IEC TS 63001:2024 for calibration and acoustic measurement practice.
Keywords: IEC TS 63001:2024, cavitation noise, ultrasonic baths, ultrasonic reactors, hydrophone, broadband cavitation energy, acoustic spectrum, cavitation measurement, in‑situ monitoring.
Standards Content (Sample)
IEC TS 63001 ®
Edition 2.0 2024-02
TECHNICAL
SPECIFICATION
colour
inside
Measurement of cavitation noise in ultrasonic baths and ultrasonic reactors
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IEC TS 63001 ®
Edition 2.0 2024-02
TECHNICAL
SPECIFICATION
colour
inside
Measurement of cavitation noise in ultrasonic baths and ultrasonic reactors
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.140.01; 17.140.50 ISBN 978-2-8322-8118-5
– 2 – IEC TS 63001:2024 © IEC 2024
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 List of symbols . 11
5 Measurement equipment . 12
5.1 Hydrophone . 12
5.1.1 General . 12
5.1.2 Calibration of hydrophone sensitivity . 12
5.1.3 Hydrophone properties . 12
5.1.4 Hydrophone compatibility with environment . 13
5.2 Analyser . 13
5.2.1 General considerations . 13
5.2.2 Specific measurement method: inertial cavitation spectrum
measurement at frequencies between harmonics of f . 14
5.2.3 Specific measurement method: Measurement of integrated broadband
cavitation noise energy between two frequency bounds . 14
5.2.4 Specific measurement method: cavitation noise measurement by
extraction of broadband spectral components . 15
5.3 Requirements for equipment being characterized . 15
5.3.1 Temperature and chemistry compatibility with the hydrophone . 15
5.3.2 Electrical interference . 15
6 Measurement procedure . 15
6.1 Reference measurements . 15
6.1.1 Control of environmental conditions for reference measurements . 15
6.1.2 Measurement procedure for reference measurements . 16
6.2 In-situ monitoring measurements . 16
Annex A (informative) Background . 17
A.1 Cavitation in ultrasonic cleaning . 17
A.2 Practical considerations for measurements . 19
A.3 Measurement procedure in the ultrasonic bath . 20
A.4 Characterization methods that do not utilize the acoustic spectrum . 21
Annex B (normative) Cavitation noise measurement between harmonics of f . 22
B.1 General . 22
B.2 Measurement method . 22
Annex C (informative) Example of cavitation noise measurement between harmonics
of f . 26
Annex D (normative) Measurement of integrated broadband cavitation noise energy
between two frequency bounds . 27
D.1 General . 27
D.2 Measurement frequency range . 27
D.3 Definition of integrated broadband cavitation noise energy. 27
Annex E (informative) Example of measurement of integrated broadband cavitation
noise energy between two frequency bounds . 28
Annex F (normative) Cavitation noise measurement by extraction of broadband
spectral components . 31
F.1 Compensation for extraneous noise . 31
F.2 Features of the acoustic pressure spectrum . 31
F.3 Identification of the operating frequency f and direct field acoustic pressure . 32
F.3.1 Identification of the operating frequency f . 32
F.3.2 Fit to primary peak (direct field) . 32
F.3.3 Determination of RMS direct field acoustic pressure . 32
F.3.4 Validation . 32
F.4 Identification of cavitation noise components . 32
F.4.1 Subtraction of direct field component of spectrum . 32
F.4.2 Determination of non-broadband cavitation component . 32
F.4.3 Determination of broadband cavitation component . 33
F.4.4 Validation . 33
Bibliography . 34
Figure A.1 – Typical setup of an ultrasonic cleaning device . 17
Figure A.2 – Spatial distribution of the acoustic pressure level in water in front of a
35 kHz transducer with reflections on all sides of the water bath (0,12 m × 0,3 m ×
0,25 m) . 18
Figure A.3 – Typical Fourier spectrum for sinusoidal ultrasound excitation above the
cavitation threshold at an operating frequency of 35 kHz . 18
Figure A.4 –Photograph of cavitation structure under the water surface at an operating
frequency of 25 kHz . 19
Figure A.5 – Typical rectangular ultrasound signal with a frequency of 25 kHz and
50 Hz double half wave modulation . 20
Figure B.1 – Block diagram of the measuring method of the cavitation noise level L . 24
CN
Figure C.1 – Power dependency of the cavitation noise level L . 26
CN
Figure C.2 – Diagram with example of spectral acoustic pressure of an ultrasonic bath
with an operating frequency of 46 kHz and its harmonics and sub-harmonics . 26
Figure E.1 – Schematic of the cylindrical cavitation hollow cavitation sensor [27], [28] . 28
Figure E.2 – High-frequency spectra obtained from the cavitation sensor of the type
shown in Figure E.1 [28] for a commercial ultrasonic cleaning vessel operating at
40 kHz whose nominal power setting has been changed from 5 % to 95 % of its full
operating power . 29
Figure E.3 – Variation in the integrated broadband cavitation energy derived using the
cylindrical cavitation sensor, from the acoustic spectra shown in Figure E.2 . 30
Figure E.4 – Raster scan covering a commercial ultrasonic cleaning vessel with four
transducers operating at 40 kHz . 30
Figure F.1 – Schematic representation of acoustic pressure spectrum pf() . 31
RMS
– 4 – IEC TS 63001:2024 © IEC 2024
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MEASUREMENT OF CAVITATION NOISE IN ULTRASONIC BATHS
AND ULTRASONIC REACTORS
FOREWORD
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IEC TS 63001 has been prepared by IEC technical committee 87: Ultrasonics. It is a
Technical Specification.
This second edition cancels and replaces the first edition published in 2019. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) addition of a new method of measurement: the measurement of integrated broadband
cavitation energy between two frequency bounds.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
87/804/DTS 87/822A/RVDTS
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Specification is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement,
available at www.iec.ch/members_experts/refdocs. The main document types developed by
IEC are described in greater detail at www.iec.ch/publications.
Terms in bold in the text are defined in Clause 3.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates that it
contains colours which are considered to be useful for the correct understanding of its
contents. Users should therefore print this document using a colour printer.
– 6 – IEC TS 63001:2024 © IEC 2024
INTRODUCTION
Ultrasonically induced cavitation is used frequently for immersion cleaning in liquids. There
are two general classes of ultrasonically induced cavitation. Inertial cavitation is the rapid
collapse of bubbles. Non-inertial cavitation refers to persistent pulsation of bubbles as a
result of stimulation by an ultrasonic field. Both inertial cavitation and non-inertial
cavitation can create significant localized streaming effects that contribute to cleaning.
Inertial cavitation additionally causes a localized shock wave that can contribute to cleaning
and or damage of parts. Both types of cavitation create acoustic signals (cavitation noise)
which can be detected and measured with a hydrophone. This document provides techniques
to measure and evaluate the degree of cavitation in support of validation efforts for ultrasonic
cleaning tanks, cleaning equipment, and reactors, as used, for example, for the purposes of
industrial process control or for hospital sterilization.
MEASUREMENT OF CAVITATION NOISE IN ULTRASONIC BATHS
AND ULTRASONIC REACTORS
1 Scope
This document, which is a Technical Specification, provides a technique of measurement and
evaluation of ultrasound in liquids for use in cleaning devices, equipment, and ultrasonic
reactors. It specifies
• the cavitation measurement at frequencies between harmonics of the operating
frequency f ,
• the cavitation measurement derived by integrating broadband cavitation noise energy,
• the cavitation measurement by extraction of broadband spectral components.
This document covers the measurement and evaluation of cavitation, but not its secondary
effects (cleaning results, sonochemical effects, etc.). Further details regarding the generation
of cavitation noise in ultrasonic baths and ultrasonic reactors are provided in Annex A.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
averaging time for cavitation measurement
t
av
length of time over which a signal is averaged to produce a measurement of cavitation
Note 1 to entry: Averaging time for cavitation is expressed in seconds (s).
Note 2 to entry: As cavitation is a stochastic process, integrating over a sufficiently large t can be necessary to
av
generate stability of the readings. An example is given in Annex B under Formula (B.4).
3.2
cavitation
formation of vapour cavities in a liquid
3.3
cavitation noise
acoustic signals as measured by a hydrophone, arising from the presence of cavitation in a
liquid, or the interaction of cavitation with the direct field acoustic pressure signal
– 8 – IEC TS 63001:2024 © IEC 2024
3.4
inertial cavitation
sudden collapse of a bubble in a liquid in response to an externally applied acoustic field,
such that an acoustic shock wave is created
3.5
non-inertial cavitation
oscillation in size or shape of a bubble in a liquid in response to an externally applied acoustic
field that is sustained over multiple cycles of the driving frequency
3.6
end-of-cable loaded sensitivity
M ( f )
L
quotient of the Fourier transformed
hydrophone voltage-time signal (u (t)) at the end of any integral cable or output connector
L
of a hydrophone or hydrophone assembly, when connected to a specific electric load
impedance, to the Fourier transformed acoustic pulse waveform (p(t)) in the undisturbed
free field of a plane wave in the position of the reference centre of the hydrophone if the
hydrophone were removed, at a specified frequency
ut
()
( )
L
Mf( )=
L
pt
( ())
Note 1 to entry: The Fourier transform is in general a complex-valued quantity but for this document only the
modulus is considered, and is expressed in units of volt per pascal, V/Pa,
Note 2 to entry: The term "response" is sometimes used instead of "sensitivity".
[SOURCE: IEC 62127-3:2022, 3.7, modified – Only the modulus is considered, Note 1 to entry
has been exchanged and Note 2 to entry has been added.] [2]
3.7
end-of-cable loaded sensitivity level
Lf
( )
M
L
twenty times the logarithm to the base 10 of the
ratio of the modulus of the end-of-cable loaded sensitivity M to a reference sensitivity of
L
M
ref
M f
( )
L
Lf = 20log dB
( )
M 10
L
M
ref
Note 1 to entry: A commonly used value of the reference sensitivity M is 1 V/µPa.
ref
Note 3 to entry: The end-of-cable loaded sensitivity level is expressed in decibels (dB).
[SOURCE: IEC 62127-1:2022, 3.26, modified – In the definition, a different symbol is used
and "quotient" has been replaced with "ratio".
3.8
hydrophone
transducer that produces electric signals in response to pressure fluctuations in water
[SOURCE: IEC 60050-801:2021, 801-32-26] [1]
3.9
hydrophone assembly
combination of hydrophone and hydrophone pre-amplifier
[SOURCE: IEC 62127-3:2022, 3.13] [2]
3.10
number of averages
N
av
number of waveforms captured and averaged in a cavitation measurement
3.11
operating frequency
f
driving frequency of ultrasound generator
Note 1 to entry: Operating frequency is expressed in hertz (Hz).
3.12
relative cavitation noise measurements
measurements made for purposes of comparison between two different cleaning
environments or different locations within a cleaning environment, such that the end-of-cable
loaded sensitivity of the hydrophone can be assumed to be identical in both cases
3.13
sampling frequency
f
s
number of points per second captured by a digital waveform recorder
Note 1 to entry: Sampling frequency is expressed in hertz (Hz).
3.14
size of the capture buffer
N
cap
total number of points captured at a time by a digital waveform recorder
3.15
capture time
t
cap
length of time to capture N points at a sampling frequency of f
cap s
Note 1 to entry: Capture time is expressed in seconds (s).
3.16
cavitation noise level
L
CN
level calculated from the cavitation noise at frequencies between harmonics of f
Note 1 to entry: Cavitation noise is expressed in decibels (dB).
3.17
integrated broadband cavitation noise energy
E
IBCN
and f
cavitation noise energy integrated between two identified frequency bounds, f
u l
2 -1
Note 1 to entry: Commonly expressed in units of V s .
3.18
reference sound pressure
p
ref
sound pressure, conventionally chosen, equal to 20 μPa for gases and to 1 μPa for liquids
and solids
Note 1 to entry: Reference sound pressure is expressed in pascals (Pa).
– 10 – IEC TS 63001:2024 © IEC 2024
[SOURCE: IEC 60050-801:1994, 801-21-22] [1]
3.19
averaged power spectrum
P f
( )
power spectrum of the instantaneous acoustic pressure averaged over N measurements
av
Note 1 to entry: Averaged power spectrum is expressed in units of Pa .
3.20
median of acoustic pressure
P
n
median value of amplitude values of spectral lines within B
f
Note 1 to entry: Median of acoustic pressure is expressed in pascals (Pa).
3.21
band filter
B
f
band filter located at a centre frequency which is between harmonics of f
Note 1 to entry: Band filter is expressed in hertz (Hz).
3.22
centre frequency
f
c
centre frequency of the band filter B
f
Note 1 to entry: Centre frequency is expressed in hertz (Hz).
3.23
direct field acoustic pressure
P
portion of the RMS acoustic pressure signal arising directly from the ultrasonic driving
excitation, at the operating frequency of the device
Note 1 to entry: RMS direct field acoustic pressure is expressed in pascals (Pa).
3.24
spectral acoustic pressure
P( f )
discrete Fourier transform of the hydrophone voltage divided by the end-of-cable loaded
sensitivity
Note 1 to entry: Spectral acoustic pressure is expressed in pascals (Pa).
3.25
non-broadband cavitation component
P
nb
portion of the RMS acoustic pressure signal arising from non-inertial cavitation
Note 1 to entry: The non-inertial cavitation component is expressed in pascals (Pa).
3.26
broadband cavitation component
P
b
portion of the RMS acoustic pressure signal arising from inertial cavitation
Note 1 to entry: The inertial cavitation component is expressed in pascals (Pa).
3.27
voltage
u(t)
instantaneous voltage measured by analyser
Note 1 to entry: Voltage is expressed in volts (V).
3.28
voltage spectrum
U(f)
discrete Fourier transform of the voltage
Note 1 to entry: Voltage spectrum is expressed in volts (V).
3.29
window function
w(n)
amplitude weighting function used in the discrete Fourier transform
3.30
frequency spacing
∆f
distance of spectrum samples of a discrete Fourier transform
Note 1 to entry: Frequency spacing is expressed in hertz (Hz).
4 List of symbols
f frequency
f operating frequency
f lower frequency limit used on the calculation of the integrated broadband
l
cavitation noise energy
f sampling frequency
s
f upper frequency limit used on the calculation of the integrated broadband
U
cavitation noise energy
E integrated broadband cavitation noise energy
IBCN
M ( f ) end-of-cable loaded sensitivity
L
N number of averages
av
N number of points captured in a waveform
cap
t capture time
cap
P( f ) spectral acoustic pressure (a function of frequency)
P ( f ) direct field acoustic pressure
P ( f ) non-broadband cavitation component
nb
P ( f ) broadband cavitation component
b
u(t) voltage (a function of time)
U( f ) voltage spectrum (a function of frequency)
L cavitation noise level
CN
p reference sound pressure
ref
Pf averaged power spectrum
( )
P median of acoustic pressure
n
B band filter
f
– 12 – IEC TS 63001:2024 © IEC 2024
f centre frequency
c
t averaging time for cavitation measurement
av
∆f frequency spacing
w(n) window function
5 Measurement equipment
5.1 Hydrophone
5.1.1 General
It is assumed throughout this document that a hydrophone is a device which produces an
output voltage waveform in response to an acoustic wave. Specifically, for the case of a
sinusoidal acoustic wave, the hydrophone shall produce an output voltage proportional to the
acoustic pressure integrated over its electro-acoustically active surface area. Assuming that
spatial variations in the acoustic pressure field over this active surface area are negligible, the
hydrophone can then be assumed to be a point sensor and the acoustic field pressure can
be described by Formula (1):
Pf()= U()f / M ()f
(1)
L
where Pf() is the spectral acoustic pressure, Uf() is the amplitude of the voltage, and M (f)
L
is the end-of-cable loaded sensitivity of the hydrophone (defined also as an amplitude for
purposes of this document). All parameters are expressed as a function of frequency and
follow the convention of only designating the magnitude of frequency-dependent quantities,
disregarding their phase angle.
NOTE The traditional concept of the hydrophone is of a nominally point-like measurement device which responds
both to the direct field and the signals generated from cavitation bubbles. However, alternative devices have been
used and will possibly be developed in future where the details of the construction of the device have been
designed to specifically measure the cavitation signal. An example of this device is covered in Annex D, where an
implementation for measurement of the integrated broadband cavitation noise energy is described. For such
devices, it is possible that concepts of hydrophone sensitivity and directional response are not directly
transferrable.
5.1.2 Calibration of hydrophone sensitivity
The hydrophone shall be calibrated such that M (f), the end-of-cable loaded sensitivity of
L
the hydrophone, is known for any frequency or frequency component for which an acoustic
pressure value is reported.
NOTE In some cases cavitation measurements can be made in relative terms, in which case a calibration to
determine M (f) is not necessary. See 5.2.1.4.
L
5.1.3 Hydrophone properties
5.1.3.1 Acoustic pressure range
The hydrophone and any associated electronics shall be suitable for the maximum pressure
of the environment, and shall be at minimum suitable for an RMS acoustic pressure up to
600 kPa.
5.1.3.2 Bandwidth of the hydrophone
The bandwidth of the hydrophone should be in accordance with 5.1.2, such that variations in
(f), the end-of-cable loaded sensitivity of the hydrophone, can be compensated for by
M
L
the cavitation measurement scheme, such as in 5.2.1.4.
5.1.3.3 Directional response
The hydrophone shall have an approximately spherical directivity. In order to achieve this,
for an operating frequency below 100 kHz the hydrophone should have an effective
diameter less than a quarter wavelength. This guideline may be relaxed above 100 kHz
because of the potential difficulty in achieving such a small effective diameter in a package
that can withstand the cleaning environment; however, there is the corresponding increase in
measurement uncertainty and the user should attempt to account for it.
5.1.3.4 Cable length
A connecting cable of a length and characteristic impedance which ensure that electrical
resonance in the connecting cable does not affect the defined bandwidth of the hydrophone
or hydrophone assembly shall be chosen. The cable shall also be terminated appropriately.
To minimize the effect of resonance in the connecting cable located between the
hydrophone’s sensitive element and a preamplifier or waveform digitizer input, the numerical
+ W ) where f is
value of the length of that cable in metres shall be much less than 50/(f
0 20 0
the operating frequency in megahertz and W is the −20 dB bandwidth of the hydrophone
signal in megahertz. Attention should be paid to the appropriateness of the output impedance
of the hydrophone and amplifier in relation to the input impedance of the connected
measuring device.
5.1.3.5 Measurement system linearity
The user shall ensure that the voltage output of any preamplifier or amplifier is linear over the
range used. This shall be done by obtaining the maximum voltage output within which the
response is linear within 10 %, and providing necessary adjustments to gain, such as can be
available from gain control settings on the preamplifier or amplifier.
5.1.4 Hydrophone compatibility with environment
Environmental conditions such as temperature or the chemistry of the environment shall be
within the hydrophone manufacturer’s stated range of operating conditions.
Differences between the calibration conditions for the hydrophone and the measurement
conditions shall be considered to the extent that they can affect the measurements. For
example, for relative cavitation noise measurements made at the same temperature with
hydrophones of identical construction, it can be unnecessary to determine how the sensitivity
of the hydrophone changes between the calibration and measurement conditions. However,
for absolute measurements the change in hydrophone sensitivity with temperature shall be
known, and corrected for in accordance with IEC 62127-3:2022.
5.2 Analyser
5.2.1 General considerations
5.2.1.1 General
The analyser is an instrument that converts u(t), the time-domain voltage waveform provided
by the hydrophone, to a measurement of cavitation activity. 5.2.1 describes several
considerations that are independent of the measuring method. Following that, several
independent methods are described in 5.2.2 to 5.2.4.
5.2.1.2 General considerations: sampling rate
If the analyser utilizes digital recording of u(t), let u[t ] designate this sampling with t
m m
designating the discrete points in time captured, with m = 1, …, N where N is the size of
cap cap
the capture buffer. The interval in time between successive samples shall be uniform, and
the sampling frequency f shall be at least a factor of two (2) higher than the highest
s
frequency component of interest in the signal. Consideration should be taken of any
– 14 – IEC TS 63001:2024 © IEC 2024
shockwave components of the signal in assessing the sampling frequency. An anti-aliasing
filter with a cutoff frequency of at most half of the sampling frequency shall be used to filter
out higher frequency components.
The size of the capture buffer (N ) shall also be known (the duration of waveform capture
cap
in units of seconds is then N /f ).
cap s
5.2.1.3 General considerations: averaging time
t , the period of time over which the analyser averages results to report cavitation activity,
av
shall be known either from a user-defined setting on the analyser or obtained from the
manufacturer. For an analyser utilizing digital recording of a waveform t NN× / f .
av av cap s
See Annex B for examples.
5.2.1.4 General considerations: calibration
For relative cavitation noise measurements performed with the same or identical
hydrophones, the measurements may be in terms of voltage only. For all other cases, the
measurement shall take account of M(f), the end-of-cable loaded sensitivity of the
hydrophone, in one of two ways.
1) If variation in M (f) is expected to be negligible throughout the frequency range of interest,
L
(f ), where f is the operating frequency of the
results shall be scaled by a factor of M
L 0 0
ultrasound. In this case, the user shall assess the uncertainty in the measurement due to
residual deviations in M (f) from M (f ) across the frequency range of the measurement.
L L 0
) shall be digitally recorded if Lf varies by more than 2 dB over the reported
2) u(t ( )
m M
L
bandwidth of the cavitation signal. , the voltage spectrum as computed from its
Uf()
m
N
cap
discrete Fourier transform (DFT), shall be computed and digitally stored for
m<
(only the single-sided spectrum is saved). Formula (2) shall then be used to calculate the
spectral acoustic pressure P( f ):
m
(2)
Pf()= U()f / M ( f )
mm L
NOTE For purposes of this document only the magnitude of the discrete Fourier transform is used.
5.2.2 Specific measurement method: inertial cavitation spectrum measurement at
frequencies between harmonics of f
In this method, the DFT of u(t) is computed as in 5.2.1.4. The operating frequency f is
scanned in the spectrum. The noise in a frequency band between the harmonics of the
operating frequency f is analysed and a cavitation noise level L is calculated. The centre
0 CN
n
frequency f of the frequency band is defined as ff= × + 0,25 , where n is an integer.
c c0
The cavitation noise level L is an indication of inertial cavitation activity. Further details
CN
are provided in Annex B.
5.2.3 Specific measurement method: Measurement of integrated broadband
cavitation noise energy between two frequency bounds
In this method, the DFT of u(t) is computed, and the energy between two specific frequency
limits, f and f , is integrated and, following subtraction of noise, used to derive a value of the
l u
integrated broadband cavitation noise energy (E ). Through appropriate choice of the
IBCN
upper and lower frequency limits of the spectral integration, this quantity is primarily related to
=
the degree of inertial cavitation activity. Further details of this measurement can be found in
Annex D.
NOTE With knowledge of the variation in the sensitivity of the device between f and f , the integrated
l u
2 −1
broadband cavitation noise energy can be converted to Pa s .
5.2.4 Specific measurement method: cavitation noise measurement by extraction of
broadband spectral components
In this method the DFT of u(t) is computed, noise is subtracted, and a broadband calibration
of the hydrophone provides a broadband determination of P(f) using Formula (2). A computer
algorithm then determines the relative RMS contributions of the direct field acoustic
pressure, broadband cavitation component, and non-broadband cavitation component
to the acoustic pressure spectrum, and reports these as P , P , and P , respectively. Further
0 b nb
details are provided in Annex F.
5.3 Requirements for equipment being characterized
5.3.1 Temperature and chemistry compatibility with the hydrophone
The cleaning environment shall be checked to make sure that its expected temperature range
and chemistry are compatible with the hydrophone specifications.
5.3.2 Electrical interference
The user shall perform reasonable checks that electrical interference is not significantly
affecting the measurements. These checks should include comparing the signal when the
hydrophone is outside of the cleaning solution to when it is inside the solution. If the signal
outside in air is significant compared to the signal with the hydrophone in the tank, there is
significant electrical interference.
NOTE It is also possible to check for electrical interference by shielding the hydrophone from acoustic signals
with an acoustically absorbing shell while leaving a water path for electrical conduction in a tank.
6 Measurement procedure
6.1 Reference measurements
6.1.1 Control of environmental conditions for reference measurements
Reference measurements are performed under controlled conditions in order to monitor the
stability of an ultrasonic system. Critical environmental conditions shall be documented and
reproduced, including:
• settings of the equipment under test;
• water quality – cavitation activity is known to depend on the level of impurities and
dissolved gases;
• temperature;
• position and angular orientation of the hydrophone;
• water height and position of any objects within the cleaning tank;
• ultrasonic settling time, i.e. the time that the ultrasound has been on (generally expected
to be at least five minutes);
• the type and quantity of any additives added to promote wetting of the surfaces of the
ultrasonic system and hydrophone in order to aid degassing.
In general, the user shall determine tolerances for each of these conditions when establishing
a baseline for future reference measurements. This shall be done by observing the variation
of cavitation measurements with variation in these parameters, and specifying the tolerances
based on the required repeatability of reference measurements. In the case of hydrophone
– 16 – IEC TS 63001:2024 © IEC 2024
position and water height, it is expected that reproducibility within a quarter wavelength at the
operating frequency will be sufficient. Although ideally position repeatability within 1/10 of a
wavelength should be achieved, in many cases practical considerations such as oscillations of
the water surface justify a relaxation of this recommendation
NOTE Higher tolerances can occur when objects are inside of a cleaning vessel.
6.1.2 Measurement procedure for reference measurements
1) The hydrophone shall be positioned at the documented user-defined locations and
angular orientations for the reference measurement.
2) Analyser settings for the reference measurement shall be reproduced based on
documented settings.
3) Cavitation activity shall be measured in accordance with one of the methods of 5.2.2 to
5.2.4 and recorded.
6.2 In-situ monitoring measurements
In-situ monitoring measurements are performed to monitor cavitation while a cleaning tank is
in use for cleaning. Uses can include research, process development, or documentation.
The level of control is not expected to be as high as in reference measurements. Nevertheless
the following general procedure should be applied.
1) Document cleaning system settings, analyser settings, and ultrasonic settling time.
2) Document position and angular orientation of the hydrophone.
3) Measure cavitation activity in accordance with one of the methods of 5.2.2 to 5.2.4 and
record results.
Annex A
(informative)
Background
A.1 Cavitation in ultrasonic cleaning
Acoustic cavitation is one of the main components of the ultrasonic cleaning action and is
used, for example, for the cleaning of hard surfaces in ultrasonic baths with a setup such as
shown in Figure A.1 or in ultrasonic reactors [3].
Figure A.1 – Typical setup of an ultrasonic cleaning device
A tank is equipped with ultrasonic transducers, which are driven by an electrical generator
with an operating frequency adapted to the resonance frequency of the transducers. The
tank is filled with a liquid cleaning medium. The temperature of the medium can be influenced
by heating elements. Due to the vibration of the transducers, a sound field develops inside the
tank.
– 18 – IEC TS 63001:2024 © IEC 2024
Figure A.2 – Spatial distribution of the acoustic pressure level in water
in front of a 35 kHz transducer with reflections on all sides
of the water bath (0,12 m × 0,3 m × 0,25 m)
The linear sound field of a small ultrasonic transducer element corresponds approximately to
the field of a piston radiator. The radiated waves are totally reflected on the water surface and
the tank walls. This results in a three-dimensional standing wave field (Figure A.2) [4]. At the
places where the modulus of the rarefactional acoustic pressure exceeds the threshold for
inertial cavitation, cavities can collapse violently. In this case the maximum bubble radius is
three times the initial radius at least and the velocity of the bubble wall is higher than the
speed of sound. At lower
...
IEC TS 63001 ®
Edition 2.0 2024-02
REDLINE VERSION
TECHNICAL
SPECIFICATION
colour
inside
Measurement of cavitation noise in ultrasonic baths and ultrasonic reactors
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IEC TS 63001 ®
Edition 2.0 2024-02
REDLINE VERSION
TECHNICAL
SPECIFICATION
colour
inside
Measurement of cavitation noise in ultrasonic baths and ultrasonic reactors
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.140.01; 17.140.50 ISBN 978-2-8322-8272-4
– 2 – IEC TS 63001:2024 RLV © IEC 2024
CONTENTS
FOREWORD . 4
INTRODUCTION . 2
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 List of symbols . 8
5 Measurement equipment . 12
5.1 Hydrophone . 12
5.1.1 General . 12
5.1.2 Calibration of hydrophone sensitivity . 13
5.1.3 Hydrophone properties . 13
5.1.4 Hydrophone compatibility with environment . 14
5.2 Analyser . 14
5.2.1 General considerations . 14
5.2.2 Specific measurement method: transient cavitation spectrum at f =
2,25 f
0 .
5.2.3 Specific measurement method: broadband transient and stable
cavitation spectra .
5.2.2 Specific measurement method: inertial cavitation spectrum
measurement at frequencies between harmonics of f . 15
5.2.3 Specific measurement method: Measurement of integrated broadband
cavitation noise energy between two frequency bounds . 15
5.2.4 Specific measurement method: cavitation noise measurement by
extraction of broadband spectral components . 16
5.3 Requirements for equipment being characterized . 15
5.3.1 Temperature and chemistry compatibility with the hydrophone . 16
5.3.2 Electrical interference . 16
6 Measurement procedure . 16
6.1 Reference measurements . 16
6.1.1 Control of environmental conditions for reference measurements . 16
6.1.2 Measurement procedure for reference measurements . 17
6.2 Measurement procedures for In-situ monitoring measurements In-situ
monitoring measurements . 17
Annex A (informative) Background . 18
A.1 Cavitation in ultrasonic cleaning . 18
A.2 Practical considerations for measurements . 21
A.3 Measurement procedure in the ultrasonic bath . 22
A.4 Characterization methods that do not utilize the acoustic spectrum . 22
Annex B (normative) Cavitation measurement at 2,25 f .
Annex C (informative) Example of cavitation measurement at 2,25 f .
Annex B (normative) Cavitation noise measurement between harmonics of f . 28
B.1 General . 28
B.2 Measurement method . 28
Annex C (informative) Example of cavitation noise measurement between harmonics
of f . 32
Annex D (normative) Measurement of integrated broadband cavitation noise energy
between two frequency bounds . 33
D.1 General . 33
D.2 Measurement frequency range . 33
D.3 Definition of integrated broadband cavitation noise energy. 33
Annex E (informative) Example of measurement of integrated broadband cavitation
noise energy between two frequency bounds . 34
Annex F (normative) Cavitation noise measurement by extraction of broadband
spectral components . 37
F.1 Compensation for extraneous noise . 37
F.2 Features of the acoustic pressure spectrum . 37
F.3 Identification of the operating frequency f and direct field acoustic pressure . 39
F.3.1 Identification of the operating frequency f . 39
F.3.2 Fit to primary peak (direct field) . 39
F.3.3 Determination of RMS direct field acoustic pressure . 39
F.3.4 Validation . 39
F.4 Identification of stable and transient cavitation noise components . 39
F.4.1 Subtraction of direct field component of spectrum . 39
F.4.2 Determination of stable non-broadband cavitation component . 39
F.4.3 Determination of transient broadband cavitation component . 40
F.4.4 Validation . 40
Bibliography . 41
Figure A.1 – Typical setup of an ultrasonic cleaning device . 18
Figure A.2 – Spatial distribution of the acoustic pressure level in water in front of a 25
35 kHz transducer with reflections on all sides of the water bath (0,12 m × 0,3 m ×
0,25 m) . 19
Figure A.3 – Typical Fourier spectrum for sinusoidal ultrasound excitation above the
cavitation threshold at an operating frequency of 35 kHz . 20
Figure A.4 – Sketch Photograph of cavitation structure under the water surface at an
operating frequency of 25 kHz . 21
Figure A.5 – Typical rectangular ultrasound signal with a frequency of 25 kHz and
50 Hz double half wave modulation . 21
Figure B.1 – Block diagram of the measuring method of the cavitation noise level L . 30
CN
Figure C.1 – Power dependency of the cavitation noise level L . 32
CN
Figure C.2 – Diagram with example of spectral acoustic pressure of an ultrasonic bath
with an operating frequency of 46 kHz and its harmonics and sub-harmonics . 32
Figure E.1 – Schematic of the cylindrical cavitation hollow cavitation sensor [27], [28] . 34
Figure E.2 – High-frequency spectra obtained from the cavitation sensor of the type
shown in Figure E.1 [28] for a commercial ultrasonic cleaning vessel operating at
40 kHz whose nominal power setting has been changed from 5 % to 95 % of its full
operating power . 35
Figure E.3 – Variation in the integrated broadband cavitation energy derived using the
cylindrical cavitation sensor, from the acoustic spectra shown in Figure E.2 . 36
Figure E.4 – Raster scan covering a commercial ultrasonic cleaning vessel with four
transducers operating at 40 kHz . 36
Figure F.1 – Schematic representation of acoustic pressure spectrum pf() . 38
RMS
– 4 – IEC TS 63001:2024 RLV © IEC 2024
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MEASUREMENT OF CAVITATION NOISE IN ULTRASONIC BATHS
AND ULTRASONIC REACTORS
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
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This redline version of the official IEC Standard allows the user to identify the changes
made to the previous edition IEC TS 63001:2019. A vertical bar appears in the margin
wherever a change has been made. Additions are in green text, deletions are in
strikethrough red text.
IEC TS 63001 has been prepared by IEC technical committee 87: Ultrasonics. It is a
Technical Specification.
This second edition cancels and replaces the first edition published in 2019. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) addition of a new method of measurement: the measurement of integrated broadband
cavitation energy between two frequency bounds.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
87/804/DTS 87/822A/RVDTS
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Specification is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement,
available at www.iec.ch/members_experts/refdocs. The main document types developed by
IEC are described in greater detail at www.iec.ch/publications.
Terms in bold in the text are defined in Clause 3.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates that it
contains colours which are considered to be useful for the correct understanding of its
contents. Users should therefore print this document using a colour printer.
– 6 – IEC TS 63001:2024 RLV © IEC 2024
INTRODUCTION
Ultrasonically induced cavitation is used frequently for immersion cleaning in liquids. There
are two general classes of ultrasonically induced cavitation. Transient Inertial cavitation is
the rapid collapse of bubbles. Stable Non-inertial cavitation refers to persistent pulsation of
bubbles as a result of stimulation by an ultrasonic field. Both transient inertial cavitation
and stable non-inertial cavitation may can create significant localized streaming effects that
contribute to cleaning. Transient Inertial cavitation additionally causes a localized shock
wave that may can contribute to cleaning and /or damage of parts. Both types of cavitation
create acoustic signals (cavitation noise) which may can be detected and measured with a
hydrophone. This document provides techniques to measure and evaluate the degree of
cavitation in support of validation efforts for ultrasonic cleaning tanks, cleaning equipment,
and reactors, as used, for example, for the purposes of industrial process control or for
hospital sterilization.
MEASUREMENT OF CAVITATION NOISE IN ULTRASONIC BATHS
AND ULTRASONIC REACTORS
1 Scope
This document, which is a Technical Specification, provides a technique of measurement and
evaluation of ultrasound in liquids for use in cleaning devices, equipment, and ultrasonic
reactors. It specifies
• the cavitation measurement at 2,25 f in the frequency range 20 kHz to 150 kHz, and
• the cavitation measurement by extraction of broadband spectral components in the
frequency range 10 kHz to 5 MHz.
• the cavitation measurement at frequencies between harmonics of the operating
frequency f ,
• the cavitation measurement derived by integrating broadband cavitation noise energy,
• the cavitation measurement by extraction of broadband spectral components.
This document covers the measurement and evaluation of cavitation, but not its secondary
effects (cleaning results, sonochemical effects, etc.). Further details regarding the generation
of cavitation noise in ultrasonic baths and ultrasonic reactors are provided in Annex A.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
averaging time for cavitation measurement
t
av
length of time over which a signal is averaged to produce a measurement of cavitation
Note 1 to entry: Averaging time for cavitation is expressed in seconds (s).
Note 2 to entry: As cavitation is a stochastic process, integrating over a sufficiently large t can be necessary to
av
generate stability of the readings. An example is given in Annex B under Formula (B.4).
3.2
cavitation
formation of vapour cavities in a liquid
3.3
cavitation noise
acoustic signals as measured by a hydrophone, arising from the presence of cavitation in a
liquid, or the interaction of cavitation with the direct field acoustic pressure signal
– 8 – IEC TS 63001:2024 RLV © IEC 2024
3.4
transient cavitation
inertial cavitation
sudden collapse of a bubble in a liquid in response to an externally applied acoustic field,
such that an acoustic shock wave is created
3.5
stable non-inertial cavitation
oscillation in size or shape of a bubble in a liquid in response to an externally applied acoustic
field that is sustained over multiple cycles of the driving frequency
3.6
end-of-cable loaded sensitivity
( f )
M
L
M ( f )
L
modulus quotient of the Fourier transformed
output voltage U( f ) hydrophone voltage-time signal (u (t)) at the end of any integral cable
L
or output connector of a hydrophone or hydrophone assembly, when connected to a
specific electric load impedance, to the Fourier transformed acoustic pressure P(f ) acoustic
pulse waveform (p(t)) in the undisturbed free field of a plane wave in the position of the
reference centre of the hydrophone if the hydrophone were removed, at a specified
frequency
ut
( ( ))
L
Mf =
( )
L
pt
( ( ))
Note 1 to entry: The Fourier transform is in general a complex-valued quantity but for this document only the
modulus is considered, and is expressed in units of volt per pascal, V/Pa,
Note 2 to entry: The term "response" is sometimes used instead of "sensitivity".
[SOURCE: IEC 62127-3:2022, 3.7, modified – Only the modulus is considered, Note 1 to entry
has been exchanged and Note 2 to entry has been added.] [2]
3.7
end-of-cable loaded sensitivity level
M
L.dB
Lf
( )
M
L
twenty times the logarithm to the base 10 of the
M
ratio of the modulus of the end-of-cable loaded sensitivity M ( f ) to a reference
L
L
sensitivity of M
ref
M
L
M = 20log dB
Note 1 to entry: .
L,dB 10
M
ref
Note 2 to entry: The value of reference sensitivity M is 1 V/Pa.
ref
M f
( )
L
Lf( ) = 20log dB
M 10
L
M
ref
Note 1 to entry: A commonly used value of the reference sensitivity M is 1 V/µPa.
ref
Note 3 to entry: The end-of-cable loaded sensitivity level is expressed in decibels (dB).
[SOURCE: IEC 62127-1:2022, 3.26, modified – In the definition, a different symbol is used
and "quotient" has been replaced with "ratio".
3.8
hydrophone
transducer that produces electric signals in response to waterborne acoustic signals pressure
fluctuations in water
[SOURCE: IEC 60050-801:19942021, 801-32-26] [1]
3.9
hydrophone assembly
combination of hydrophone and hydrophone pre-amplifier
[SOURCE: IEC 62127-3:20072022, 3.13] [2]
3.10
number of averages
N
av
number of waveforms captured and averaged in a cavitation measurement
3.8
operating volume
part of the liquid volume where cavitation effects are intended
3.11
operating frequency
f
driving frequency of ultrasound generator
Note 1 to entry: Operating frequency is expressed in hertz (Hz).
3.12
relative cavitation noise measurements
measurements made for purposes of comparison between two different cleaning
environments or different locations within a cleaning environment, such that the end-of-cable
loaded sensitivity of the hydrophone may can be assumed to be identical in both cases
Note 1 to entry: Care should be taken to ensure that changes in hydrophone sensitivity do not affect the
measurement.
3.13
sampling frequency
f
s
number of points per second captured by a digital waveform recorder
Note 1 to entry: Sampling frequency is expressed in hertz (Hz).
3.14
size of the capture buffer
N
cap
total number of points captured at a time by a digital waveform recorder
3.15
capture time
t
cap
length of time to capture N points at a sampling frequency of f
cap s
Note 1 to entry: Capture time is expressed in seconds (s).
– 10 – IEC TS 63001:2024 RLV © IEC 2024
3.16
cavitation noise level
L
CN
level calculated from the cavitation noise at a frequency of 2,25 f frequencies between
harmonics of f
Note 1 to entry: Cavitation noise is expressed in decibels (dB).
3.17
integrated broadband cavitation noise energy
E
IBCN
cavitation noise energy integrated between two identified frequency bounds, f and f
u l
2 -1
Note 1 to entry: Commonly expressed in units of V s .
3.18
reference sound pressure
p
ref
sound pressure, conventionally chosen, equal to 20 μPa for gases and to 1 μPa for liquids
and solids
Note 1 to entry: Reference sound pressure is expressed in pascals (Pa).
[SOURCE: IEC 60050-801:1994, 801-21-22] [1]
3.19
averaged power spectrum
P f
( )
power spectrum of the instantaneous acoustic pressure averaged over N measurements
av
Note 1 to entry: Averaged power spectrum is expressed in units of Pa .
3.20
median of acoustic pressure
P
n
median value of amplitude values of spectral lines within B
f
Note 1 to entry: Median of acoustic pressure is expressed in pascals (Pa).
3.21
band filter
B
f
band filter located at a centre frequency of 2,25 f which is between harmonics of f
0 0
Note 1 to entry: Band filter is expressed in hertz (Hz).
3.22
centre frequency
f
c
centre frequency of the band filter B
f
Note 1 to entry: Centre frequency is expressed in hertz (Hz).
3.23
direct field acoustic pressure
P
portion of the RMS acoustic pressure signal arising directly from the ultrasonic driving
excitation, at the operating frequency of the device
Note 1 to entry: RMS direct field acoustic pressure is expressed in pascals (Pa).
3.24
spectral acoustic pressure
P( f )
Fast discrete Fourier transform of the hydrophone voltage divided by the end-of-cable
loaded sensitivity
Note 1 to entry: Spectral acoustic pressure is expressed in pascals (Pa).
3.25
stable non-broadband cavitation component
P
s
P
nb
portion of the RMS acoustic pressure signal arising from stable non-inertial cavitation
Note 1 to entry: The stable non-inertial cavitation component is expressed in pascals (Pa).
3.26
transient broadband cavitation component
P
t
P
b
portion of the RMS acoustic pressure signal arising from transient inertial cavitation
Note 1 to entry: The transient inertial cavitation component is expressed in pascals (Pa).
3.27
voltage
u(t)
instantaneous voltage measured by analyser
Note 1 to entry: Voltage is expressed in volts (V).
3.28
voltage spectrum
U(f)
Fast discrete Fourier transform of the voltage
Note 1 to entry: Voltage spectrum is expressed in volts (V).
3.29
window function
w(n)
amplitude weighting function used in the discrete Fourier transform
3.30
frequency spacing
∆f
distance of spectrum samples of a Fast discrete Fourier transform
Note 1 to entry: Frequency spacing is expressed in hertz (Hz).
3.26
indexed frequency
f
k
frequency of index k at which the Fast Fourier Transform is evaluated
Note 1 to entry: f (k – 1) ∆f, where k = 1, 2, …, N .
k cap
4 List of symbols
f frequency
f indexed frequency
k
– 12 – IEC TS 63001:2024 RLV © IEC 2024
f operating frequency
f lower frequency limit used on the calculation of the integrated broadband
l
cavitation noise energy
f sampling frequency
s
f upper frequency limit used on the calculation of the integrated broadband
U
cavitation noise energy
E integrated broadband cavitation noise energy
IBCN
M ( f ) end-of-cable loaded sensitivity
L
N number of averages
av
N number of points captured in a waveform
cap
t capture time
cap
P( f ) spectral acoustic pressure (a function of frequency)
P ( f ) direct field acoustic pressure
P P ( f ) stable non-broadband cavitation component
s nb
P P ( f ) transient broadband cavitation component
t b
u(t) voltage (a function of time)
U( f ) voltage spectrum (a function of frequency)
L cavitation noise level
CN
p reference sound pressure
ref
Pf averaged power spectrum
( )
P median of acoustic pressure
n
B band filter
f
f centre frequency
c
T t averaging time for cavitation measurement
av av
∆f frequency spacing
w(n) window function
5 Measurement equipment
5.1 Hydrophone
5.1.1 General
It is assumed throughout this document that a hydrophone is a device which produces an
output voltage waveform in response to an acoustic wave. Specifically, for the case of a
sinusoidal acoustic wave, the hydrophone shall produce an output voltage proportional to the
acoustic pressure integrated over its electro-acoustically active surface area. Assuming that
spatial variations in the acoustic pressure field over this active surface area are negligible, the
hydrophone may can then be assumed to be a point sensor and the acoustic field pressure
may can be described by Formula (1):
Pf() = U()f / M ()f
(1)
L
where Pf() is the amplitude of the spectral acoustic field pressure, Uf() is the amplitude of
the voltage, and M (f) is the end-of-cable loaded sensitivity of the hydrophone (defined
L
also as an amplitude for purposes of this document). All parameters are expressed as a
function of frequency and follow the convention of only designating the magnitude of
frequency-dependent quantities, disregarding their phase angle.
NOTE The traditional concept of the hydrophone is of a nominally point-like measurement device which responds
both to the direct field and the signals generated from cavitation bubbles. However, alternative devices have been
used and will possibly be developed in future where the details of the construction of the device have been
designed to specifically measure the cavitation signal. An example of this device is covered in Annex D, where an
implementation for measurement of the integrated broadband cavitation noise energy is described. For such
devices, it is possible that concepts of hydrophone sensitivity and directional response are not directly
transferrable.
5.1.2 Calibration of hydrophone sensitivity
The hydrophone shall be calibrated such that M (f), the end-of-cable loaded sensitivity of
L
the hydrophone, is known for any frequency or frequency component for which an acoustic
pressure value is reported.
NOTE In some cases cavitation measurements can be made in relative terms, in which case a calibration to
determine M (f) is not necessary. See 5.2.1.4.
L
5.1.3 Hydrophone properties
5.1.3.1 Acoustic pressure range
The hydrophone and any associated electronics shall be suitable for the maximum pressure
of the environment, and shall be at minimum suitable for an RMS acoustic pressure up to
600 kPa.
5.1.3.2 Bandwidth of the hydrophone
The bandwidth of the hydrophone should be in accordance with 5.1.2, such that variations in
M (f), the end-of-cable loaded sensitivity of the hydrophone, may can be compensated for
L
by the cavitation measurement scheme, such as in 5.2.1.4.
5.1.3.3 Directional response
The hydrophone shall have an approximately spherical directivity. In order to achieve this,
for an operating frequency below 100 kHz the hydrophone should have an effective
diameter less than a quarter wavelength. This guideline may be relaxed above 100 kHz
because of the potential difficulty in achieving such a small effective diameter in a package
that can withstand the cleaning environment; however, there is the corresponding increase in
measurement uncertainty and the user should attempt to account for it.
5.1.3.4 Cable length
A connecting cable of a length and characteristic impedance which ensure that electrical
resonance in the connecting cable does not affect the defined bandwidth of the hydrophone
or hydrophone assembly shall be chosen. The cable shall also be terminated appropriately.
To minimize the effect of resonance in the connecting cable located between the
hydrophone’s sensitive element and a preamplifier or waveform digitizer input, the numerical
value of the length of that cable in metres shall be much less than 50/(f + BW W ) where f
0 20 20 0
is the operating frequency in megahertz and BW W is the −20 dB bandwidth of the
20 20
hydrophone signal in megahertz. Attention should be paid to the appropriateness of the
output impedance of the hydrophone/ and amplifier in relation to the input impedance of the
connected measuring device.
5.1.3.5 Measurement system linearity
The user shall ensure that the voltage output of any preamplifier or amplifier is linear over the
range used. This shall be done by obtaining the maximum voltage output within which the
– 14 – IEC TS 63001:2024 RLV © IEC 2024
response is linear within 10 %, and providing necessary adjustments to gain, such as may can
be available from gain control settings on the preamplifier or amplifier.
5.1.4 Hydrophone compatibility with environment
Environmental conditions such as temperature or the chemistry of the environment shall be
within the hydrophone manufacturer’s stated range of operating conditions.
Differences between the calibration conditions for the hydrophone and the measurement
conditions shall be considered to the extent that they may can affect the measurements. For
example, for relative cavitation noise measurements made at the same temperature with
hydrophones of identical construction, it may not can be necessary unnecessary to determine
how the sensitivity of the hydrophone changes between the calibration and measurement
conditions. However, for absolute measurements the change in hydrophone sensitivity with
temperature shall be known, and corrected for in accordance with IEC 62127-3:20072022.
5.2 Analyser
5.2.1 General considerations
5.2.1.1 General
The analyser is an instrument that converts u(t), the time-domain voltage waveform provided
by the hydrophone, to a measurement of cavitation activity. 5.2.1 describes several
considerations that are independent of the measuring method. Following that, several
independent methods are described in 5.2.2 to 5.2.4.
5.2.1.2 General considerations: sampling rate
If the analyser utilizes digital recording of u(t), let u[t ] designate this sampling with t
m m
where N is the size of
designating the discrete points in time captured, with m = 1, …, N
cap cap
the capture buffer. The interval in time between successive samples shall be uniform, and
the sampling frequency f shall be at least a factor of two (2) higher than the highest
s
frequency component of interest in the signal. Consideration should be taken of any
shockwave components of the signal in assessing the sampling frequency. An anti-aliasing
filter with a cutoff frequency of at most half of the sampling frequency shall be used to filter
out higher frequency components.
The size of the capture buffer (N ) shall also be known (the duration of waveform capture
cap
in units of seconds is then N /f ).
cap s
5.2.1.3 General considerations: averaging time
T t , the period of time over which the analyser averages results to report cavitation
av av
activity, shall be known either from a user-defined setting on the analyser or obtained from
the manufacturer. For an analyser utilizing digital recording of a waveform T NN× / f
av av cap s
t NN× / f
. See Annex B for examples.
av av cap s
5.2.1.4 General considerations: calibration
For relative cavitation noise measurements performed with the same or identical
hydrophones, the measurements may be in terms of voltage only. For all other cases, the
measurement shall take account of M M(f), the end-of-cable loaded sensitivity of the
L
hydrophone, in one of two ways.
1) If variation in M (f) is expected to be negligible throughout the frequency range of interest,
L
results shall be scaled by a factor of M (f ), where f is the operating frequency of the
L 0 0
ultrasound. In this case, the user shall assess the uncertainty in the measurement due to
residual deviations in M (f) from M (f ) across the frequency range of the measurement.
L L 0
=
=
2) u(t ) shall be digitally recorded if M (f) Lf varies by more than 2 dB over the
( )
m L,dB M
L
reported bandwidth of the cavitation signal. Uf(), the voltage spectrum as computed
m
from its Fast Fourier transform (FFT) discrete Fourier transform (DFT), shall be computed
N
cap
and digitally stored for (only the single-sided spectrum is saved). Formula (2)
m <
shall then be used to calculate the spectral acoustic pressure P( fm ):
(2)
Pf() = U()f / M ( f )
mm L
NOTE For purposes of this document only the magnitude of the Fast discrete Fourier transform is used.
5.2.2 Specific measurement method: transient cavitation spectrum at f = 2,25 f
In this method, the FFT of u(t) is computed as in 5.2.1.4. The operating frequency f is
scanned in the spectrum. The noise in a frequency band at the 2,25 fold of the operating
frequency f is analysed and a cavitation noise level L is calculated. The cavitation
0 CN
noise level L is an indication of transient cavitation activity. Further details are provided
CN
in Annex B and Annex C.
5.2.3 Specific measurement method: broadband transient and stable cavitation
spectra
In this method the FFT of u(t) is computed, noise is subtracted, and a broadband calibration of
the hydrophone provides a broadband determination of P(f) using Equation (2). A computer
algorithm then determines the relative RMS contributions of the applied field, transient
cavitation, and stable cavitation to the acoustic pressure spectrum, and reports these as P ,
P , and P , respectively. Further details are provided in Annex D.
t s
5.2.2 Specific measurement method: inertial cavitation spectrum measurement at
frequencies between harmonics of f
In this method, the DFT of u(t) is computed as in 5.2.1.4. The operating frequency f is
scanned in the spectrum. The noise in a frequency band between the harmonics of the
operating frequency f is analysed and a cavitation noise level L is calculated. The centre
0 CN
n
frequency f of the frequency band is defined as ff= × + 0,25 , where n is an integer.
c0
c
The cavitation noise level L is an indication of inertial cavitation activity. Further details
CN
are provided in Annex B.
5.2.3 Specific measurement method: Measurement of integrated broadband
cavitation noise energy between two frequency bounds
In this method, the DFT of u(t) is computed, and the energy between two specific frequency
limits, f and f , is integrated and, following subtraction of noise, used to derive a value of the
l u
integrated broadband cavitation noise energy (E ). Through appropriate choice of the
IBCN
upper and lower frequency limits of the spectral integration, this quantity is primarily related to
the degree of inertial cavitation activity. Further details of this measurement can be found in
Annex D.
NOTE With knowledge of the variation in the sensitivity of the device between f and f , the integrated
l u
2 −1
broadband cavitation noise energy can be converted to Pa s .
– 16 – IEC TS 63001:2024 RLV © IEC 2024
5.2.4 Specific measurement method: cavitation noise measurement by extraction of
broadband spectral components
In this method the DFT of u(t) is computed, noise is subtracted, and a broadband calibration
of the hydrophone provides a broadband determination of P(f) using Formula (2). A computer
algorithm then determines the relative RMS contributions of the direct field acoustic
pressure, broadband cavitation component, and non-broadband cavitation component
to the acoustic pressure spectrum, and reports these as P , P , and P , respectively. Further
0 b nb
details are provided in Annex F.
5.3 Requirements for equipment being characterized
5.3.1 Temperature and chemistry compatibility with the hydrophone
The cleaning environment shall be checked to make sure that its expected temperature range
and chemistry are compatible with the hydrophone specifications.
5.3.2 Electrical interference
The user shall perform reasonable checks that electrical interference is not significantly
affecting the measurements. These checks should include comparing the signal when the
hydrophone is outside of the cleaning solution to when it is inside the solution. If the signal
outside in air is significant compared to the signal with the hydrophone in the tank, there is
significant electrical interference.
NOTE It may is also be possible to check for electrical interference by shielding the hydrophone from acoustic
signals with an acoustically absorbing shell while leaving a water path for electrical conduction in a tank.
6 Measurement procedure
6.1 Reference measurements
6.1.1 Control of environmental conditions for reference measurements
Reference measurements are performed under controlled conditions in order to monitor the
stability of an ultrasonic system. Significant care must be taken to document and reproduce
Critical environmental conditions shall be documented and reproduced, including:
• settings of the equipment under test;
• water quality – cavitation activity is known to depend on the level of impurities and
dissolved gases;
• temperature;
• position and angular orientation of the hydrophone;
• water height and position of any objects within the cleaning tank;
• ultrasonic settling time, i.e. the time that the ultrasound has been on (generally expected
to be at least five minutes);
• the type and quantity of any additives added to promote wetting of the surfaces of the
ultrasonic system and hydrophone in order to aid degassing.
In general, the user shall determine tolerances for each of these conditions when establishing
a baseline for future reference measurements. This shall be done by observing the variation
of cavitation measurements with variation in these parameters, and specifying the tolerances
based on the required repeatability of reference measurements. In the
...
Frequently Asked Questions
IEC TS 63001:2024 is a technical specification published by the International Electrotechnical Commission (IEC). Its full title is "Measurement of cavitation noise in ultrasonic baths and ultrasonic reactors". This standard covers: IEC TS 63001:2024 provides a technique of measurement and evaluation of ultrasound in liquids for use in cleaning devices, equipment, and ultrasonic reactors. It specifies - the cavitation measurement at frequencies between harmonics of the operating frequency f0, - the cavitation measurement derived by integrating broadband cavitation noise energy, - the cavitation measurement by extraction of broadband spectral components. This document covers the measurement and evaluation of cavitation, but not its secondary effects (cleaning results, sonochemical effects, etc.). Further details regarding the generation of cavitation noise in ultrasonic baths and ultrasonic reactors are provided in Annex A. IEC TS 63001:2024 cancels and replaces the first edition published in 2019. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: a) addition of a new method of measurement: the measurement of integrated broadband cavitation energy between two frequency bounds.
IEC TS 63001:2024 provides a technique of measurement and evaluation of ultrasound in liquids for use in cleaning devices, equipment, and ultrasonic reactors. It specifies - the cavitation measurement at frequencies between harmonics of the operating frequency f0, - the cavitation measurement derived by integrating broadband cavitation noise energy, - the cavitation measurement by extraction of broadband spectral components. This document covers the measurement and evaluation of cavitation, but not its secondary effects (cleaning results, sonochemical effects, etc.). Further details regarding the generation of cavitation noise in ultrasonic baths and ultrasonic reactors are provided in Annex A. IEC TS 63001:2024 cancels and replaces the first edition published in 2019. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: a) addition of a new method of measurement: the measurement of integrated broadband cavitation energy between two frequency bounds.
IEC TS 63001:2024 is classified under the following ICS (International Classification for Standards) categories: 17.140.01 - Acoustic measurements and noise abatement in general; 17.140.50 - Electroacoustics. The ICS classification helps identify the subject area and facilitates finding related standards.
IEC TS 63001:2024 has the following relationships with other standards: It is inter standard links to IEC TS 63001:2019. Understanding these relationships helps ensure you are using the most current and applicable version of the standard.
You can purchase IEC TS 63001:2024 directly from iTeh Standards. The document is available in PDF format and is delivered instantly after payment. Add the standard to your cart and complete the secure checkout process. iTeh Standards is an authorized distributor of IEC standards.
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