Ultrasonics - Power measurement - Radiation force balances and performance requirements

IEC 61161:2013 specifies a method of determining the total emitted acoustic power of ultrasonic transducers based on the use of a radiation force balance; establishes general principles for the use of radiation force balances in which an obstacle (target) intercepts the sound field to be measured; establishes limitations of the radiation force method related to cavitation and temperature rise; establishes quantitative limitations of the radiation force method in relation to diverging and focused beams; provides information on estimating the acoustic power for diverging and focused beams using the radiation force method; and provides information on assessment of overall measurement uncertainties. This International Standard is applicable to the measurement of ultrasonic power up to 1 W based on the use of a radiation force balance in the frequency range from 0,5 MHz to 25 MHz; the measurement of ultrasonic power up to 20 W based on the use of a radiation force balance in the frequency range 0,75 MHz to 5 MHz; the measurement of total ultrasonic power in well-collimated, diverging and focused ultrasonic fields; and to the use of radiation force balances of the gravimetric type or force feedback type. This third edition cancels and replaces the second edition published in 2006. It constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
- whereas the second edition tacitly dealt with circular transducers only, the present edition as far as possible deals with both circular and rectangular transducers, including a number of symbols for rectangular transducers;
- attention is paid to focused cases and the influence of scanning has been added;
- the method of calibrating the radiation force balance now depends on whether the set-up is used as a primary or as secondary measurement tool;
- and Annex B (basic formulae) has been updated and in Annex C the buoyancy change method is mentioned (see also future IEC 62555).

Ultrasons - Mesurage de puissance - Balances de forces de rayonnement et exigences de fonctionnement

La CEI 61161:2013 spécifie une méthode pour déterminer la puissance acoustique totale émise par des transducteurs ultrasonores, basée sur l'usage d'une balance de forces de rayonnement; établit les principes généraux pour utiliser les balances de forces de rayonnement dans lesquelles un obstacle dénommé cible intercepte le champ acoustique à mesurer; établit des limitations de la méthode de forces de rayonnement relatives à la cavitation et à l'élévation de la température; établit des limitations quantitatives de la méthode de forces de rayonnement par rapport aux faisceaux divergents et focalisés; fournit des informations concernant l'évaluation de la puissance acoustique pour les faisceaux divergents et focalisés par la méthode de la force de rayonnement; et fournit des informations concernant l'évaluation des incertitudes de mesure globales. La présente Norme internationale est applicable au mesurage de la puissance ultrasonore jusqu'à 1 W par utilisation d'une balance de forces de rayonnement dans la plage de fréquences de 0,5 MHz à 25 MHz; au mesurage de la puissance ultrasonore jusqu'à 20 W par utilisation d'une balance de forces de rayonnement dans la plage de fréquences de 0,75 MHz à 5 MHz; au mesurage de la puissance ultrasonore totale de transducteurs dans des champs ultrasonores possédant une bonne collimation, divergents et focalisés; et à l'utilisation de balances de forces de rayonnement de type gravimétrique ou à retour de force. Cette troisième édition annule et remplace la deuxième édition publiée en 2006. Elle constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
- alors que la deuxième édition a implicitement traité des transducteurs circulaires uniquement, la présente édition traite dans la mesure du possible des transducteurs circulaires et rectangulaires et inclut également un certain nombre de symboles destinés aux transducteurs rectangulaires;
- une plus grande d'attention est accordée aux cas focalisés et l'influence du balayage a été ajoutée;
- la méthode d'étalonnage de la balance de forces de rayonnement dépend désormais de l'utilisation ou non de la configuration comme outil de mesure primaire ou secondaire;
- et l'Annexe B (formules fondamentales) a été actualisée et l'Annexe C fait mention de la méthode de changement de flottabilité (voir aussi la future CEI 62555).

General Information

Status
Published
Publication Date
29-Jan-2013
Technical Committee
Current Stage
PPUB - Publication issued
Start Date
30-Jan-2013
Completion Date
30-Jan-2013
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IEC 61161
Edition 3.0 2013-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Ultrasonics – Power measurement – Radiation force balances and performance
requirements
Ultrasons – Mesurage de puissance – Balances de forces de rayonnement et
exigences de fonctionnement
IEC 61161:2013
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 61161
Edition 3.0 2013-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Ultrasonics – Power measurement – Radiation force balances and performance
requirements
Ultrasons – Mesurage de puissance – Balances de forces de rayonnement et
exigences de fonctionnement
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX X
ICS 17.140.50 ISBN 978-2-83220-617-1

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

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – 61161 © IEC:2013
CONTENTS

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

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

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

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

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

4 List of symbols ................................................................................................................. 9

5 Requirements for radiation force balances ........................................................................ 9

5.1 General ................................................................................................................... 9

5.2 Target type ............................................................................................................ 10

5.2.1 General ..................................................................................................... 10

5.2.2 Absorbing target ........................................................................................ 10

5.2.3 Reflecting target ........................................................................................ 10

5.3 Target diameter ..................................................................................................... 11

5.4 Balance/force measuring system ........................................................................... 11

5.5 System tank .......................................................................................................... 11

5.6 Target support structures ...................................................................................... 11

5.7 Transducer positioning .......................................................................................... 11

5.8 Anti-streaming foils ................................................................................................ 11

5.9 Transducer coupling .............................................................................................. 12

5.10 Calibration ............................................................................................................. 12

6 Requirements for measuring conditions .......................................................................... 12

6.1 Lateral target position ............................................................................................ 12

6.2 Transducer/target separation ................................................................................. 12

6.3 Water .................................................................................................................... 12

6.4 Water contact ........................................................................................................ 13

6.5 Environmental conditions ...................................................................................... 13

6.6 Thermal drifts ........................................................................................................ 13

7 Measurement uncertainty ............................................................................................... 13

7.1 General ................................................................................................................. 13

7.2 Balance system including target suspension .......................................................... 13

7.3 Linearity and resolution of the balance system ...................................................... 13

7.4 Extrapolation to the moment of switching the ultrasonic transducer ....................... 14

7.5 Target imperfections .............................................................................................. 14

7.6 Reflecting target geometry .................................................................................... 14

7.7 Lateral absorbers in the case of reflecting target measurements ........................... 14

7.8 Target misalignment .............................................................................................. 14

7.9 Ultrasonic transducer misalignment ....................................................................... 14

7.10 Water temperature ................................................................................................ 14

7.11 Ultrasonic attenuation and acoustic streaming ....................................................... 14

7.12 Foil properties ....................................................................................................... 14

7.13 Finite target size .................................................................................................... 15

7.14 Plane-wave assumption ......................................................................................... 15

7.15 Scanning influence ................................................................................................ 15

7.16 Environmental influences ...................................................................................... 15

7.17 Excitation voltage measurement ............................................................................ 15

7.18 Ultrasonic transducer temperature ......................................................................... 15

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61161 © IEC:2013 – 3 –

7.19 Nonlinearity ........................................................................................................... 15

7.20 Acceleration due to gravity .................................................................................... 15

7.21 Other sources ........................................................................................................ 16

Annex A (informative) Additional information on various aspects of radiation force

measurements ................................................................................................................ 17

Annex B (informative) Basic formulae .................................................................................. 30

Annex C (informative) Other methods of ultrasonic power measurement .............................. 36

Annex D (informative) Propagation medium and degassing .................................................. 37

Annex E (informative) Radiation force measurement with diverging ultrasonic beams .......... 38

Annex F (informative) Limitations associated with the balance arrangements ....................... 42

Bibliography .......................................................................................................................... 46

Figure 1 – Section through an absorbing target ..................................................................... 16

Figure 2 – Linearity check: balance readout as a function of the input quantity ..................... 16

Figure E.1 – Piston result (oscillating curve) for P/cF as a function of ka ............................... 39

Figure E.2 – P/cF as a function of ka for four different pseudo-trapezoidal amplitude

distributions .......................................................................................................................... 39

Figure E.3 – Ratio of the radiation conductance G as obtained using a convex-conical

reflecting target to an absorbing target versus the value of ka [29] ........................................ 41

Figure F.1 – Arrangement A .................................................................................................. 42

Figure F.2 – Arrangement B, with convex-conical reflecting target ........................................ 43

Figure F.3 – Arrangement B, with absorbing target ............................................................... 43

Figure F.4 – Arrangement C, with absorbing target ............................................................... 43

Figure F.5 – Arrangement E, with absorbing (a) or concave-conical reflecting (b) target ....... 43

Figure F.6 – Arrangement F, with convex-conical reflecting target ........................................ 44

Figure F.7 – Arrangement F with absorbing target ............................................................... 44

Table F.1 – Advantages and disadvantages of different arrangements .................................. 45

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– 4 – 61161 © IEC:2013
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ULTRASONICS – POWER MEASUREMENT –
RADIATION FORCE BALANCES AND PERFORMANCE REQUIREMENTS
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

international co-operation on all questions concerning standardization in the electrical and electronic fields. To

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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

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

International Standard IEC 61161 has been prepared by IEC technical committee 87:

Ultrasonics.

This third edition cancels and replaces the second edition published in 2006. It constitutes a

technical revision.

This edition includes the following significant technical changes with respect to the previous

edition:

– whereas the second edition tacitly dealt with circular transducers only, the present edition

as far as possible deals with both circular and rectangular transducers, including a number

of symbols for rectangular transducers;

– attention is paid to focused cases and the influence of scanning has been added;

– the method of calibrating the radiation force balance now depends on whether the set-up

is used as a primary or as secondary measurement tool;

– Annex B (basic formulae) has been updated and in Annex C the buoyancy change method

is mentioned (see also future IEC 62555).
---------------------- Page: 6 ----------------------
61161 © IEC:2013 – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
87/520/FDIS 87/528/RVD

Full information on the voting for the approval of this standard can be found in the report on

voting indicated in the above table.

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

NOTE The following print types are used:
• Requirements: in Arial 10 point
• Notes: in Arial 8 point
• Words in bold in the text are defined in Clause 3
• Symbols and formulae: Times New Roman + Italic.

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

the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data

related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
---------------------- Page: 7 ----------------------
– 6 – 61161 © IEC:2013
INTRODUCTION

A number of measuring methods exist for the determination of the total emitted power of

ultrasonic transducers ([1], [2], [3] , see also Annex C). The purpose of this International

Standard is to establish standard methods of measurement of ultrasonic power in liquids in

the lower megahertz frequency range based on the measurement of the radiation force using

a gravimetric balance. The great advantage of radiation force measurements is that a value

for the total radiated power is obtained without the need to integrate field data over the cross-

section of the radiated sound beam. This standard identifies the sources of errors and

describes a systematic step-by-step procedure to assess overall measurement uncertainty as

well as the precautions that should be undertaken and uncertainties that should be taken into

account while performing power measurements.

Basic safety requirements for ultrasonic physiotherapy devices are identified in IEC 60601-2-5

and make reference to IEC 61689, which specifies the need for acoustic power measurements

with an uncertainty better than ± 15 % at a level of confidence of 95 %. Considering the usual

degradation of accuracy in the practical application of this standard, reference measurement

methods need to be established with uncertainties better than ± 7 %. Ultrasonic diagnostic

device declaration requirements including acoustic power are specified in other IEC standards,

as for example in IEC 61157.

The measurement of acoustic power accurately and repeatably using a radiation force

balance as defined in this standard is influenced by a number of practical problems. As a

guide to the user, additional information is provided in Annex A using the same section and

clause numbering as the main body.
—————————
Numbers in square brackets refer to the Bibliography.
---------------------- Page: 8 ----------------------
61161 © IEC:2013 – 7 –
ULTRASONICS – POWER MEASUREMENT –
RADIATION FORCE BALANCES AND PERFORMANCE REQUIREMENTS
1 Scope
This International Standard

• specifies a method of determining the total emitted acoustic power of ultrasonic

transducers based on the use of a radiation force balance;

• establishes general principles for the use of radiation force balances in which an obstacle

(target) intercepts the sound field to be measured;

• establishes limitations of the radiation force method related to cavitation and temperature

rise;

• establishes quantitative limitations of the radiation force method in relation to diverging

and focused beams;

• provides information on estimating the acoustic power for diverging and focused beams

using the radiation force method;
• provides information on assessment of overall measurement uncertainties.
This International Standard is applicable to:

• the measurement of ultrasonic power up to 1 W based on the use of a radiation force

balance in the frequency range from 0,5 MHz to 25 MHz;

• the measurement of ultrasonic power up to 20 W based on the use of a radiation force

balance in the frequency range 0,75 MHz to 5 MHz;

• the measurement of total ultrasonic power in well-collimated, diverging and focused

ultrasonic fields;

• the use of radiation force balances of the gravimetric type or force feedback type.

(See also Clause A.1)

NOTE 1 A focused beam is converging in the pre-focal range and diverging beyond focus.

NOTE 2 Ultrasonic power measurement in the high intensity therapeutic ultrasound (HITU) range, i.e. beyond 1 W

or 20 W, respectively, is dealt with in the future IEC 62555.
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and

are indispensable for its application. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any
amendments) applies.

IEC 61689, Ultrasonics – Physiotherapy systems – Field specifications and methods of

measurement in the frequency range 0,5 MHz to 5 MHz
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
---------------------- Page: 9 ----------------------
– 8 – 61161 © IEC:2013
3.1
acoustic streaming
bulk fluid motion initiated by a sound field
3.2
free field

sound field in a homogeneous isotropic medium whose boundaries exert a negligible effect on

the sound waves

[SOURCE: IEC 60050-801:1994, definition 801-23-28, modified – the term no longer contains

“sound”]
3.3
output power

time-average ultrasonic power emitted by an ultrasonic transducer into an approximately

free field under specified conditions in a specified medium, preferably water
Note 1 to entry: Output power is expressed in watt (W).
3.4
radiation force
acoustic radiation force

time-average force acting on a body in a sound field and caused by the sound field, excluding

the component due to acoustic streaming; or, more generally: time-average force (excluding

the component due to acoustic streaming) in a sound field, appearing at the boundary

surface between two media of different acoustic properties, or within a single attenuating

medium

Note 1 to entry: Radiation force, acoustic radiation force, is expressed in newton (N).

3.5
radiation pressure
acoustic radiation pressure
radiation force per unit area

Note 1 to entry: This term is widely used in the literature. However, strictly speaking, the radiation force per unit

area is a tensor quantity [4] and it should be referred to as the acoustic radiation stress tensor when a strict

scientific terminology is to be used. The integral quantity "acoustic radiation force" is generally preferred in this

International Standard. Whenever at some places, the term "acoustic radiation pressure" appears it is to be

understood as the negative value of the normal radiation stress in the direction of the field axis.

Note 2 to entry: Radiation pressure, acoustic radiation pressure, is expressed in pascal (Pa).

3.6
target

device specially designed to intercept substantially all of the ultrasonic field and to serve as

the object which is acted upon by the radiation force
3.7
ultrasonic transducer

device capable of converting electrical energy to mechanical energy within the ultrasonic

frequency range and/or reciprocally of converting mechanical energy to electrical energy

3.8
radiation conductance
ratio of the acoustic output power and the squared RMS transducer input voltage

Note 1 to entry: It is used to characterize the electrical to acoustical transfer of ultrasonic transducers.

---------------------- Page: 10 ----------------------
61161 © IEC:2013 – 9 –
Note 2 to entry: Radiation conductance is expressed in siemens (S).
4 List of symbols
a radius of a circular ultrasonic source transducer

b and b half-dimensions of a rectangular ultrasonic source transducer in x and y direction,

x y
respectively (so that 2 b and 2 b are the transducer's side lengths)
x y
c speed of sound (usually in water)

d and d geometrical focal lengths of a focusing ultrasonic transducer in the x-z and the

x y
y-z plane, respectively
d geometrical focal length of a focusing ultrasonic transducer in the case of
d = d = d
x y
F radiation force on a target in the direction of the incident ultrasonic wave
g acceleration due to gravity
G radiation conductance
2 2 1/2
h half the diagonal of a rectangular transducer, h = (b + b )
d d x y
h harmonic mean of b and b , h = 2 / (1/b + 1/b )
h x y h x y
k circular wavenumber, k = 2 π / λ
P output power of an ultrasonic transducer
s normalized distance from a circular ultrasonic transducer, s = z λ / a
z distance between an ultrasonic transducer and a target
α amplitude attenuation coefficient of plane waves in a medium (usually water)

β and β focus (half-)angles of a rectangular focusing ultrasonic transducer in the x-z

x y
and the y-z plane, respectively; β = arctan(b /d ), β = arctan(b /d ) if the
x x x y y y
transducer is planar and the focal lengths are counted from the planar
transducer surface

γ focus (half-)angle of a circular focusing ultrasonic transducer; γ = arcsin(a / d)

if the transducer is spherically curved and the focal length is counted from the

"bottom" of the "bowl"; γ = arctan(a / d) if the focal length is counted from the

plane defined by the rim of the active part of the "bowl" or if the transducer is

planar

θ angle between the direction of the incident ultrasonic wave and the normal to a

reflecting surface of a target
λ ultrasonic wavelength in the sound-propagating medium (usually water)
ρ (mass) density of the sound-propagating medium (usually water)

NOTE 1 The direction of the incident wave mentioned above under F and θ is understood to be the direction of

the field axis, i.e., it is understood in a global sense rather than in a local sense.

NOTE 2 Strictly speaking, in the case of a focusing transducer, the focusing details and the transducer shape are

independent of each other, i.e. a circular transducer, too, can have two different focus (half-)angles. With regard to

ultrasound practice, however, this standard restricts to the two cases of a circular transducer with one focus (half-)

angle and of a rectangular transducer with two focus (half-)angles (which can, of course, be equal to each other).

5 Requirements for radiation force balances
5.1 General

The radiation force balance shall consist of a target which is connected to a balance. The

ultrasonic beam shall be directed vertically upwards or downwards or horizontally on the

target and the radiation force exerted by the ultrasonic beam shall be measured by the

---------------------- Page: 11 ----------------------
– 10 – 61161 © IEC:2013

balance. The ultrasonic power shall be determined from the difference between the force

measured with and without ultrasonic radiation. Guidance is contained in Annex B. Calibration

can be carried out by means of small precision weights of known mass.

NOTE Different possible radiation force measurement set-ups are presented in Figures F.1 to F.7. Each

measurement set-up has it
...

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