Ultrasonics - Methods for the characterization of the ultrasonic properties of materials

IEC TS 63081:2019:
• defines key quantities relevant to ultrasonic materials characterization;
• specifies methods for direct measurement of many key ultrasonic materials parameters.
This document is applicable to all measurements of properties of passive acoustic materials under drive conditions that are not subject to nonlinear acoustic propagation. Whilst there are materials properties that may be of interest in a nonlinear drive regime, these are currently outside the scope of this document.

General Information

Status
Published
Publication Date
10-Dec-2019
Technical Committee
Current Stage
PPUB - Publication issued
Completion Date
11-Dec-2019
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IEC TS 63081
Edition 1.0 2019-12
TECHNICAL
SPECIFICATION
colour
inside
Ultrasonics – Methods for the characterization of the ultrasonic properties
of materials
IEC TS 63081:2019-12(en)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC TS 63081
Edition 1.0 2019-12
TECHNICAL
SPECIFICATION
colour
inside
Ultrasonics – Methods for the characterization of the ultrasonic properties
of materials
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.140.50 ISBN 978-2-8322-7643-3

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

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC TS 63081:2019 ® IEC 2019
CONTENTS

FOREWORD ........................................................................................................................... 4

INTRODUCTION ..................................................................................................................... 6

1 Scope .............................................................................................................................. 7

2 Normative references ...................................................................................................... 7

3 Terms and definitions ...................................................................................................... 7

4 List of symbols .............................................................................................................. 10

5 Overview ....................................................................................................................... 12

5.1 General principles ................................................................................................. 12

5.2 Sample preparation ............................................................................................... 12

5.2.1 Fluid samples ................................................................................................ 12

5.2.2 Solid samples ................................................................................................ 13

5.2.3 Sample geometry ........................................................................................... 13

5.2.4 Sample stabilization ....................................................................................... 13

5.3 Source and receiver transducers ........................................................................... 14

5.4 Transmission versus reflection measurements ...................................................... 14

5.5 Transducer excitation signal ................................................................................. 15

5.5.1 Frequency dependence of quantities ............................................................. 15

5.5.2 CW and quasi-CW methods ........................................................................... 15

5.5.3 Frequency modulated pulses and time delay spectrometry ............................ 16

5.5.4 Impulse methods ........................................................................................... 18

6 Insertion loss measurement ........................................................................................... 19

7 Longitudinal wave speed measurements ........................................................................ 22

7.1 General ................................................................................................................. 22

7.2 Transducers immersed within fluid material ........................................................... 22

7.3 Transducers and sample immersed in a coupling fluid .......................................... 23

8 Absorption coefficient measurements ............................................................................ 24

8.1 Single sample through transmission method ......................................................... 24

8.2 Double sample through transmission method ........................................................ 26

9 Echo reduction (ER) measurement ................................................................................. 27

9.1 Normal incidence .................................................................................................. 27

9.2 Oblique incidence ................................................................................................. 29

10 Backscatter coefficient measurement............................................................................. 29

Bibliography .......................................................................................................................... 31

Figure 1 – Schematic showing diffractive spreading between source and receiving

transducers ........................................................................................................................... 14

Figure 2 – Illustration of a typical TDS system ...................................................................... 17

Figure 3 – Development and signal processing for a compensated frequency

modulated signal ................................................................................................................... 17

Figure 4 – Pulse dispersion in absorbing media .................................................................... 19

Figure 5 – The additional diffractive spreading encountered in through transmission

measurements ...................................................................................................................... 21

Figure 6 – Source and receiving transducers immersed in a fluid medium to be

characterized ........................................................................................................................ 22

Figure 7 – Source, receiver and sample all immersed in a coupling fluid ............................... 24

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IEC TS 63081:2019 © IEC 2019 – 3 –

Figure 8 – Multiple echoes that are clearly separated in time ................................................ 25

Figure 9 – Multiple reflection and transmission phenomena occurring at the surfaces of

a sample ............................................................................................................................... 26

Figure 10 – Schematic presentation of a measurement set-up used to determine the

echo reduction of a test material ........................................................................................... 27

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– 4 – IEC TS 63081:2019 ® IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ULTRASONICS – METHODS FOR THE CHARACTERIZATION OF THE
ULTRASONIC PROPERTIES OF MATERIALS
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

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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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rights. IEC shall not be held responsible for identifying any or all such patent rights.

The main task of IEC technical committees is to prepare International Standards. In exceptional

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• the required support cannot be obtained for the publication of an International Standard,

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• the subject is still under technical development or where, for any other reason, there is the

future but no immediate possibility of an agreement on an International Standard.

Technical Specifications are subject to review within three years of publication to decide

whether they can be transformed into International Standards

IEC TS 63081, which is a Technical Specification, has been prepared by IEC technical

committee 87: Ultrasonics
The text of this Technical Specification is based on the following documents:
DTS Report on voting
87/718/DTS 87/725/RVDTS
---------------------- Page: 6 ----------------------
IEC TS 63081:2019 © IEC 2019 – 5 –

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.

Words in bold in the text are defined in Clause 3. Symbols and formulae are in Times New Roman

+ Italic.

The committee has decided that the contents of this document will remain unchanged until the

stability date indicated on the IEC website under "http://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.
A bilingual version of this publication may be issued at a later date.

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.

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– 6 – IEC TS 63081:2019 ® IEC 2019
INTRODUCTION

Many ultrasonic measurement standards contain requirements for the properties of acoustic

materials to be used to construct the measurement equipment relied upon within those

documents. The following are examples of such standards.

• IEC 61161 specifies amplitude reflection factor and acoustic energy absorption for reflecting

targets and absorbing targets and specifies amplitude transmission coefficient for anti-

streaming foils.
• IEC 61391-1 discusses reflection coefficient.

• IEC 61689 defines echo reduction and specifies limits upon its values. The terms reflection

loss and transmission loss are also used, and values specified.
• IEC TS 62306 specifies transmission loss and reflection amplitude reduction.
• IEC 62359 specifies reflection coefficient and absorption.
• IEC 60601-2-37 specifies reflectance and absorption coefficient.

As the list above suggests, a wide range of terms is used to specify the properties of an acoustic

material, and these terms are not used consistently across IEC documents. Furthermore, there

is a degree of duplication with multiple names for the same quantity. This is further confused

since there is no document within the IEC ultrasonics portfolio that defines the methods by

which those properties are measured.
This document seeks to address the shortcomings by providing:

• a clear unambiguous definition of the key quantities of interest during materials

characterization;
• a discussion of similar terms and how they may relate to the key quantities;
• recommended experimental methods for determining the values of key quantities.
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IEC TS 63081:2019 © IEC 2019 – 7 –
ULTRASONICS – METHODS FOR THE CHARACTERIZATION OF THE
ULTRASONIC PROPERTIES OF MATERIALS
1 Scope
This document:
• defines key quantities relevant to ultrasonic materials characterization;

• specifies methods for direct measurement of many key ultrasonic materials parameters.

This document is applicable to all measurements of properties of passive acoustic materials

under drive conditions that are not subject to nonlinear acoustic propagation. Whilst there are

materials properties that may be of interest in a nonlinear drive regime, these are currently

outside the scope of this document.
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
absorption per unit length

component of the attenuation coefficient (IEC 60050-801:1994, 801-23-35) that does not arise

from scattering and is due only to absorption of acoustic energy within the sample

αα= f (1)
where
α is the absorption constant (dB/(MHz m));
f is the frequency in MHz;
y is the frequency exponent (in general not an integer).

Note 1 to entry: For absorption, y = 2 for water, and in general y is between 1 and 2 for fluids, soft tissues and

tissue mimicking materials.

Note 2 to entry: Absorption per unit length is expressed in units of decibel per metre (dB/m).

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– 8 – IEC TS 63081:2019 ® IEC 2019
3.2
amplitude reflection coefficient

ratio of the pressure amplitude of an acoustic wave reflected from an interface separating two

media to the pressure amplitude of a plane wave incident on that interface
(2)
R =
where

p is the pressure amplitude of the reflected longitudinal wave, at the reflection angle θ ;

r r

p is the pressure amplitude of the incident longitudinal wave, at the incident angle θ

i i

Note 1 to entry: Care should be taken with the term reflection coefficient as both amplitude and intensity forms

appear in common scientific parlance. This can be particularly problematic when equations involve reflection

coefficient terms, since both are dimensionless, but one varies as the square of the other. Intensity forms of reflection

coefficient are more common in optics.

Note 2 to entry: In general, the equation shown can apply to reflections of different types, each at different reflection

angles but all governed by Snell’s law.

Note 3 to entry: Amplitude reflection coefficient is dimensionless as it is a ratio of quantities. It does not require

the use of a calibrated receiver since measurements are relative in nature.
3.3
amplitude transmission coefficient

ratio of the pressure amplitude of an acoustic wave transmitted through an interface separating

two media, to the pressure amplitude of a plane wave incident on that interface
T = (3)
where
p is the pressure amplitude of the transmitted longitudinal wave;
p is the pressure amplitude of the incident longitudinal wave

Note 1 to entry: Care should be taken with the term transmission coefficient as both amplitude and intensity forms

appear in common scientific parlance. This can be particularly problematic when equations involve transmission

coefficient terms, since both are dimensionless, but one varies as the square of the other. Intensity forms of

transmission coefficient are more common in optics.

Note 2 to entry: In general, the equation shown can apply to transmissions of different types. For example, a

longitudinal wave incident from fluid to solid at an angle will generate two transmitted waves at non-normal incidence,

a shear wave and a longitudinal wave, each at different refraction angles. Each of the transmitted waves is governed

by Snell’s law.

Note 3 to entry: Amplitude transmission coefficient is dimensionless as it is a ratio of quantities. It does not

require the use of a calibrated receiver since measurements are relative in nature.

3.4
backscatter coefficient

differential scattering cross-section per unit volume as a function of frequency for a scattering

angle of 180°
−1 −1

Note 1 to entry: Backscatter coefficient is expressed in units of one per second per steradian (s Sr ).

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IEC TS 63081:2019 © IEC 2019 – 9 –
3.5
density
mass density

at a given point within a three-dimensional domain of quasi-infinitesimal volume dV, scalar

quantity equal to the mass dm within the domain divided by the volume dV
ρ = dm/dV

Note 1 to entry: Mass density is an intensive quantity describing a local property of a substance.

Note 2 to entry: The concept of mass density may also be applied to the mass m in a domain D with a volume V,

m 1
leading to the average density .
ρ ρvd
V V

Note 3 to entry: Mass density is expressed in units of kilogram per metre cubed (kg/m ).

[SOURCE: IEC 60050-113:2011, 113-03-07]
3.6
echo reduction

reduction in pressure amplitude of an ultrasonic plane wave resulting from its reflection from an

interface between two media
p
ER=−20 log dB
i (4)
=−20 log R dB
( )
10 p
where
p is the pressure amplitude of the reflected longitudinal wave;
p is the pressure amplitude of the incident longitudinal wave

Note 1 to entry: In general, the reflected waves are governed by elastic Snell’s laws and the reduction in pressure

amplitude is a function of the angle of the incidence of the plane-wave on the surface.

Note 2 to entry: Echo reduction is expressed in decibels (dB).
3.7
group velocity

velocity in the direction of propagation of a characteristic feature of the envelope of a pulse

Note 1 to entry: Group velocity is commonly defined in terms of angular frequency ω and wavenumber k as

v =
and differs from phase velocity only in a dispersive medium.

Note 2 to entry: Group velocity is ordinarily the velocity of propagation of the energy associated with the

disturbance.
Note 3 to entry: Group velocity is expressed in units of metre per second (m/s).

[SOURCE: IEC 60050-801:1994, 801-23-21, modified – In the definition, "non-sinusoidal

disturbance" has been replaced by "pulse".]
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– 10 – IEC TS 63081:2019 ® IEC 2019
3.8
insertion loss

reduction in pressure amplitude of an ultrasonic plane wave resulting from the insertion of a

sample in the acoustic path
(5)
IL=−20 log dB
ns
where

p is the amplitude of the received pressure wave with the sample in the path (with sample);

p is the amplitude of the received pressure wave without the sample in the path (no sample)

Note 1 to entry: Care should be taken as insertion loss is sometimes incorrectly labelled transmission loss.

However, transmission loss is a more general term describing loss of signal between a source and a receiver.

IEC 60050-801:1994, 801-23-39 defines transmission loss as "reduction in sound pressure level between two

designated locations in a sound transmission system, one location often being at a reference distance from the

source". As such it can include contributions from the directivity functions of both source and receiver as well as

acoustic spreading. These are functions of the experimental configuration and not the material under investigation.

Note 2 to entry: Insertion loss is expressed in decibels (dB).
3.9
longitudinal wave speed
magnitude of the velocity of a free progressive longitudinal wave

Note 1 to entry: Longitudinal wave speed is expressed in units of metre per second (m/s).

3.10
phase velocity
velocity in the direction of propagation of a surface of constant phase

Note 1 to entry: Phase velocity is commonly defined as where ω is the angular frequency and k is the

v =
wave number.
Note 2 to entry: Phase velocity is expressed in units of metre per second (m/s).
[SOURCE: IEC 60050-801:1994, 801-23-20]
4 List of symbols
A toneburst amplitude in single sample absorption coefficient measurements
A , A amplitude of nth and mth echoes in single sample absorption coefficient
n m
measurements
A area of a transducer aperture
B bandwidth of time delay spectrometry (TDS) tracking filter
c longitudinal wave speed in the coupling fluid
c longitudinal wave speed
e excitation signal used with compensated frequency modulation (CFM)
CFM
E spectral modulus of CFM signal
CFM
ER echo reduction
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IEC TS 63081:2019 © IEC 2019 – 11 –
f frequency
F focal length of a transducer
H frequency spectrum of transducer used in calculation of CFM signal
IL insertion loss
k wave number
p(x,t) pressure signal as a function of time, measured at position x
P(x,f ) Fourier transform of p(x,t)
p pressure amplitude of the incident longitudinal wave
p amplitude of the received pressure wave without the sample in the path
pressure amplitude of the reflected longitudinal wave
p pressure amplitude of the reflected longitudinal wave, corrected for imperfect
reflector
p amplitude of the received pressure wave with the sample in the path
p pressure amplitude of the transmitted longitudinal wave

q(x,t) pressure signal as a function of time after delay applied, measured at position x

Q(x,f ) Fourier transform of q(x,t)
R amplitude reflection coefficient
t time
S sweep rate of TDS source signal
T amplitude transmission coefficient
x distance/position
y frequency exponent of absorption per unit length
Z acoustic impedance
v group velocity
v phase velocity
α absorption per unit length
Δx thickness (either of sample or vessel wall)
Δt change in time
Δφ change in phase
η backscatter coefficient
φ phase
ρ density
τ time delay
angular frequency
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– 12 – IEC TS 63081:2019 ® IEC 2019
5 Overview
5.1 General principles

It is important when measuring materials characteristics that the equipment set-up environment

and method have as little effect on the results as possible. Clause 5 discusses some of the set-

up issues and items to be noted when performing these measurements.

The application of a consistent and well understood protocol is the key to deriving meaningful

measurements that are reproducible and transportable. Controlling as much of the test

environment as possible, from temperature to sample preparation and conditioning, has an

important impact on the measurement quality and confidence.

Having water-filled tanks where the temperature can be controlled and measured to the desired

accuracy is important. Similarly, other aspects of the water quality employed for the

measurements (dissolved gas content and conductivity) may be important subject to the applied

technique.

In addition, measurements should be repeated at different conditions (distance, orientation

driving signal) depending on the property to be measured, in order to understand and minimize

set-up and instrumentation effects. To this end, once the type of measurement has been

selected for the particular parameter, sources of uncertainty should be investigated and

quantified [1]. Type A uncertainties can be quantified by repeating measurements and building

up an appropriate uncertainty budget. Type B sources of uncertainty will require modelling or

parallel/confirmatory validation studies.
5.2 Sample preparation
5.2.1 Fluid samples

When working with fluids, immersing the test transducers in the fluid is ideal. However,

practically fluids often need to be housed within a container which is immersed within a test

tank. Such containers are typically either rigid walled vessels (such as a parallel walled cell

culture flasks) or have an acoustically thin membrane at either end of the acoustic path through

the material.

Rigid-walled vessels are likely to have the benefit that they have parallel walls, and therefore

maintain a uniform thickness of sample. However, the material used to construct the walls of

the flask is likely to be acoustically mismatched to water, leading to significant reflections at the

interfaces. Additionally, they can exhibit acoustic absorption and dispersion.

Whilst membranes may be thin relative to the acoustic wavelength, their influence on the

determination of ultrasonic power as part of the radiation force balance measurement is well

documented [2],[3], and such effects need to be avoided. Care should also be taken to avoid

expansion of the membrane during the process of filling the measurement vessel with the fluid

under test. Particularly if the vessel is surrounded by air during filling, membranes can expand

to a convex shape and thus the vessel might become an acoustic lens which further perturbs

the measurement. It is best practice to use flat restraining plates in contact with the membrane

to minimize expansion during filling.

Given the possible artefacts introduced by a measurement vessel, measurements should be

conducted in a manner that separates the properties of the fluid under test from those of the

vessel containing i
...

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