Measurement of cavitation noise in ultrasonic baths and ultrasonic reactors

IEC TS 63001:2019 provides a technique of measurement and evaluation of ultrasound in liquids for use in cleaning devices and equipment. It specifies
• the cavitation measurement at 2,25 f0 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.
IEC TS 63001:2019 covers the measurement and evaluation of the cavitation, but not its secondary effects (cleaning results, sonochemical effects, etc.).

General Information

Status
Published
Publication Date
15-Jan-2019
Technical Committee
Current Stage
PPUB - Publication issued
Completion Date
16-Jan-2019
Ref Project

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IEC TS 63001
Edition 1.0 2019-01
TECHNICAL
SPECIFICATION
colour
inside
Measurement of cavitation noise in ultrasonic baths and ultrasonic reactors
IEC TS 63001:2019-01(en)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC TS 63001
Edition 1.0 2019-01
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 978-2-8322-6410-2

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC TS 63001:2019 © IEC 2019
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 ............................................................................................... 11

5.1 Hydrophone .......................................................................................................... 11

5.1.1 General ......................................................................................................... 11

5.1.2 Calibration of hydrophone sensitivity ............................................................. 12

5.1.3 Hydrophone properties .................................................................................. 12

5.1.4 Hydrophone compatibility with environment ................................................... 12

5.2 Analyser ............................................................................................................... 13

5.2.1 General considerations .................................................................................. 13

5.2.2 Specific measurement method: transient cavitation spectrum at f =

2,25 f ............................................................................................................ 14

5.2.3 Specific measurement method: broadband transient and stable

cavitation spectra .......................................................................................... 14

5.3 Requirements for equipment being characterized .................................................. 14

5.3.1 Temperature and chemistry compatibility with the hydrophone ....................... 14

5.3.2 Electrical interference .................................................................................... 14

6 Measurement procedure ................................................................................................ 14

6.1 Reference measurements ..................................................................................... 14

6.1.1 Control of environmental conditions for reference measurements .................. 14

6.1.2 Measurement procedure for reference measurements ................................... 15

6.2 Measurement procedures for in-situ monitoring measurements ............................. 15

Annex A (informative) Background ....................................................................................... 16

A.1 Cavitation in ultrasonic cleaning ............................................................................ 16

A.2 Practical considerations for measurements ........................................................... 18

A.3 Measurement procedure in the ultrasonic bath ...................................................... 19

A.4 Characterization methods that do not utilize the acoustic spectrum ....................... 20

Annex B (normative) Cavitation measurement at 2,25 f ....................................................... 21

B.1 General ................................................................................................................. 21

B.2 Measurement method ........................................................................................... 21

Annex C (informative) Example of cavitation measurement at 2,25 f ................................... 24

Annex D (normative) Cavitation measurement by extraction of broadband spectral

components ................................................................................................................... 25

D.1 Compensation for extraneous noise ...................................................................... 25

D.2 Features of the acoustic pressure spectrum .......................................................... 25

D.3 Identification of the operating frequency f and direct field acoustic pressure ....... 26

D.3.1 Identification of the operating frequency f .................................................... 26

D.3.2 Fit to primary peak (direct field) ..................................................................... 26

D.3.3 Determination of RMS direct field acoustic pressure ...................................... 26

D.3.4 Validation ...................................................................................................... 26

D.4 Identification of stable and transient cavitation component .................................... 26

D.4.1 Subtraction of direct field component of spectrum .......................................... 26

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IEC TS 63001:2019 © IEC 2019 – 3 –

D.4.2 Determination of stable cavitation component ................................................ 26

D.4.3 Determination of transient cavitation component ............................................ 26

D.4.4 Validation ...................................................................................................... 27

Bibliography .......................................................................................................................... 28

Figure A.1 – Typical setup of an ultrasonic cleaning device .................................................. 16

Figure A.2 – Spatial distribution of the acoustic pressure level in water in front of a 25

kHz transducer with reflections on all sides of the water bath (0,12 m × 0,3 m × 0,25 m) ...... 17

Figure A.3 – Typical Fourier spectrum for sinusoidal ultrasound excitation above the

cavitation threshold at an operating frequency of 35 kHz ...................................................... 17

Figure A.4 – Sketch of cavitation structure under the water surface at an operating

frequency of 25 kHz .............................................................................................................. 18

Figure A.5 – Typical rectangular ultrasound signal with a frequency of 25 kHz and 50

Hz double half wave modulation ............................................................................................ 19

Figure B.1 – Block diagram of the measuring method of the cavitation noise level L ........ 22

Figure C.1 – Power dependency of the cavitation noise level L ........................................ 24

Figure D.1 – Schematic representation of acoustic pressure spectrum ................... 25

Pf()
RMS
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– 4 – IEC TS 63001:2019 © IEC 2019
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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Technical Specifications are subject to review within three years of publication to decide

whether they can be transformed into International Standards.

Technical Specification IEC 63001 has been prepared by IEC technical committee 87:

Ultrasonics.
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IEC TS 63001:2019 © IEC 2019 – 5 –
The text of this Technical Specification is based on the following documents:
Draft TS Report on voting
87/681/DTS 87/693A/RVDTS

Full information on the voting for the approval of this Technical Specification can be found in

the report on voting indicated in the above table.

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

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

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the specific document. At this date, the document will be
• transformed into an International Standard,
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• amended.
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colour printer.
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– 6 – IEC TS 63001:2019 © IEC 2019
INTRODUCTION

Ultrasonically induced cavitation is used frequently for immersion cleaning in liquids. There

are two general classes of ultrasonically induced cavitation. Transient cavitation is the rapid

collapse of bubbles. Stable cavitation refers to persistent pulsation of bubbles as a result of

stimulation by an ultrasonic field. Both transient cavitation and stable cavitation may create

significant localized streaming effects that contribute to cleaning. Transient cavitation

additionally causes a localized shock wave that may contribute to cleaning and/or damage of

parts. Both types of cavitation create acoustic signals which may 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 and cleaning

equipment, as used, for example, for the purposes of industrial process control or for hospital

sterilization.
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IEC TS 63001:2019 © IEC 2019 – 7 –
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 and equipment. 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.

This document covers the measurement and evaluation of the cavitation, but not its

secondary effects (cleaning results, sonochemical effects, etc.).
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

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).
3.2
cavitation
formation of vapour cavities in a liquid
3.2.1
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
3.2.2
stable 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
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– 8 – IEC TS 63001:2019 © IEC 2019
3.3
end of cable loaded sensitivity
M ( f )

modulus quotient of the Fourier transformed

output voltage U( f ) at the end of any integral cable 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 ) 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

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 volt per pascal, V/Pa,
Note 2 to entry: The term ‘response’ is sometimes used instead of ‘sensitivity’.
3.4
end of cable loaded sensitivity level
L.dB

twenty times the logarithm to the base 10 of the ratio of the modulus of the end of cable

loaded sensitivity M ( f ) to a reference sensitivity of M .
L ref
Note 1 to entry: M = 20log dB .
L,dB 10
ref
Note 2 to entry: The value of reference sensitivity M is 1 V/Pa.
ref
3.5
hydrophone

transducer that produces electric signals in response to waterborne acoustic signals

[SOURCE: IEC 60050-801:1994, 801-32-26] [1]
3.6
hydrophone assembly
combination of hydrophone and hydrophone pre-amplifier
[SOURCE: IEC 62127-3: 2007, 3.10] [2]
3.7
number of averages
number of waveforms captured and averaged in a cavitation measurement
3.8
operating volume
part of the liquid volume where cavitation effects are intended
3.9
operating frequency
driving frequency of ultrasound generator
Note 1 to entry: Operating frequency is expressed in hertz (Hz).
3.10
relative cavitation 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 be assumed to be identical in both cases

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IEC TS 63001:2019 © IEC 2019 – 9 –

Note 1 to entry: Care should be taken to ensure that changes in hydrophone sensitivity do not affect the

measurement.
3.11
sampling frequency
number of points per second captured by a digital waveform recorder
Note 1 to entry: Sampling frequency is expressed in hertz (Hz).
3.12
size of the capture buffer
cap
total number of points captured at a time by a digital waveform recorder
3.13
capture time
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).
3.14
cavitation noise level
level calculated from the cavitation noise at a frequency of 2,25 f
Note 1 to entry: Cavitation noise is expressed in decibels (dB).
3.15
reference sound pressure
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]
3.16
averaged power spectrum
P f
( )

power spectrum of the instantaneous acoustic pressure averaged over N measurements

Note 1 to entry: Averaged power spectrum is expressed in Pa .
3.17
median of acoustic pressure
median value of amplitude values of spectral lines within B
Note 1 to entry: Median of acoustic pressure is expressed in pascals (Pa).
3.18
band filter
band filter located at a centre frequency of 2,25 f
Note 1 to entry: Band filter is expressed in hertz (Hz).
---------------------- Page: 11 ----------------------
– 10 – IEC TS 63001:2019 © IEC 2019
3.19
direct field acoustic pressure

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).

3.20
spectral acoustic pressure
P( f )

Fast 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).
3.21
stable cavitation component
portion of the RMS acoustic pressure signal arising from stable cavitation
Note 1 to entry: The stable cavitation component is expressed in pascals (Pa).
3.22
transient cavitation component
portion of the RMS acoustic pressure signal arising from transient cavitation

Note 1 to entry: The transient cavitation component is expressed in pascals (Pa).

3.23
voltage
u(t)
instantaneous voltage measured by analyser
Note 1 to entry: Voltage is expressed in volts (V).
3.24
voltage spectrum
U(f)
Fast Fourier Transform of the voltage
Note 1 to entry: Voltage spectrum is expressed in volts (V).
3.25
frequency spacing
distance of spectrum samples of a Fast Fourier Transform
Note 1 to entry: Frequency spacing is expressed in hertz (Hz).
3.26
indexed frequency
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
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IEC TS 63001:2019 © IEC 2019 – 11 –
4 List of symbols
f frequency
f indexed frequency
f operating frequency
f sampling frequency
M ( f ) end-of-cable loaded sensitivity
N number of averages
N number of points captured in a waveform
cap
t capture time
cap
P( f ) spectral acoustic pressure (a function of frequency)
( f ) direct field acoustic pressure
P ( f ) stable cavitation component
P ( f ) transient cavitation component
u(t) voltage (a function of time)
U( f ) voltage spectrum (a function of frequency)
L cavitation noise level
P reference sound pressure
ref
P f averaged power spectrum
( )
P median of acoustic pressure
B band filter
T averaging time for cavitation measurement
∆f frequency spacing
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 then be assumed to be a point sensor and the acoustic field pressure may

be described by Equation (1):
Pf()= U()f / M ()f (1)

where Pf() is the amplitude of the acoustic field pressure, Uf() is the amplitude of the

voltage, and M (f) is the end-of-cable loaded sensitivity of the hydrophone (defined also as

an amplitude for the 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.
---------------------- Page: 13 ----------------------
– 12 – IEC TS 63001:2019 © IEC 2019
5.1.2 Calibration of hydrophone sensitivity

The hydrophone shall be calibrated such that M (f), the end-of-cable loaded sensitivity of

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 5.2.1.3.
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
(f),

The bandwidth of the hydrophone should be according to 5.1.2, such that variations in M

the end-of-cable loaded sensitivity of the hydrophone, may be compensated for 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

+ BW ) 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 BW 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/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 may 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.
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IEC TS 63001:2019 © IEC 2019 – 13 –

Differences between the calibration conditions for the hydrophone and the measurement

conditions shall be considered to the extent that they may affect the measurements. For

example, for relative cavitation measurements made at the same temperature with

hydrophones of identical construction, it may not be necessary 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 62127-3:2007.
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
...

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