Ultrasonics - Focusing transducers - Definitions and measurement methods for the transmitted fields

EN following parallel vote

Ultraschall - Fokusierende Wandler - Definitionen und Messverfahren für die erzeugten Felder

Ultrasons - Transducteurs focaliseurs - Définitions et méthodes de mesure des champs transmis

La présente Norme internationale spécifie: - des définitions des caractéristiques du champ transmis de transducteurs focalisants pour des applications ultrasonores médicales; - la relation entre ces définitions et les descriptions théoriques, la conception et le mesurage des champs transmis par des transducteurs focalisants; - des méthodes de mesurage pour l'obtention de caractéristiques définies de transducteurs focalisants; - des méthodes d'alignement de l'axe du faisceau adaptées aux transducteurs focalisants. La présente Norme internationale se réfère à des transducteurs ultrasonores focalisants fonctionnant dans la plage de fréquences appropriée pour des applications ultrasonores médicales (soit de 0,5 MHz à 40 MHz) aussi bien thérapeutiques que diagnostiques. La présente norme montre comment les caractéristiques du champ transmis par les transducteurs peuvent être décrites du point de vue de la conception et mesurées par une personne n'ayant aucune connaissance préalable des détails de construction d'un appareil spécifique. Le champ ultrasonore émis pour une excitation spécifiée est mesuré par un hydrophone soit dans un milieu d'essai standard (par exemple de l'eau), soit dans un autre milieu donné. La Norme s'applique uniquement à des milieux où le comportement du champ est essentiellement similaire à celui constaté dans un fluide (c'est-à-dire où l'influence des ondes de cisaillement et de l'anisotropie élastique est faible), cela comprenant les tissus mous et les gels imitant un tissu. Tous les aspects du champ affectant leur description théorique ou qui sont importants pour la conception sont aussi inclus. Ces définitions peuvent être utiles dans des communications scientifiques, pour la conception d'appareils et pour la description du rendement et de la sécurité de systèmes utilisant ces dispositifs.

Ultrasonics - Focusing transducers - Definitions and measurement methods for the transmitted fields (IEC 61828:2001)

General Information

Status
Published
Publication Date
31-Aug-2002
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
01-Sep-2002
Due Date
01-Sep-2002
Completion Date
01-Sep-2002

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SLOVENSKI STANDARD
SIST EN 61828:2002
01-september-2002
Ultrasonics - Focusing transducers - Definitions and measurement methods for
the transmitted fields (IEC 61828:2001)
Ultrasonics - Focusing transducers - Definitions and measurement methods for the
transmitted fields

Ultraschall - Fokusierende Wandler - Definitionen und Messverfahren für die erzeugten

Felder

Ultrasons - Transducteurs focaliseurs - Définitions et méthodes de mesure des champs

transmis
Ta slovenski standard je istoveten z: EN 61828:2001
ICS:
11.040.55 'LDJQRVWLþQDRSUHPD Diagnostic equipment
17.140.50 Elektroakustika Electroacoustics
SIST EN 61828:2002 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN 61828:2002
---------------------- Page: 2 ----------------------
SIST EN 61828:2002
EUROPEAN STANDARD EN 61828
NORME EUROPÉENNE
EUROPÄISCHE NORM October 2001
ICS 17.140.50
English version
Ultrasonics -
Focusing transducers -
Definitions and measurement methods
for the transmitted fields
(IEC 61828:2001)
Ultrasons - Ultraschall -
Transducteurs focaliseurs - Fokusierende Wandler -
Définitions et méthodes de mesure Definitionen und Messverfahren
des champs transmis für die erzeugten Felder
(CEI 61828:2001) (IEC 61828:2001)

This European Standard was approved by CENELEC on 2001-09-01. CENELEC members are bound to

comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European

Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on

application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other

language made by translation under the responsibility of a CENELEC member into its own language and

notified to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Czech Republic,

Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands,

Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2001 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 61828:2001 E
---------------------- Page: 3 ----------------------
SIST EN 61828:2002
EN 61828:2001 - 2 -
Foreword

The text of document 87/196/FDIS, future edition 1 of IEC 61828, prepared by IEC TC 87, Ultrasonics,

was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as EN 61828 on

2001-09-01.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2002-06-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2004-09-01
Annexes designated "normative" are part of the body of the standard.
Annexes designated "informative" are given for information only.
In this standard, annex ZA is normative and annexes A, B and C are informative.
Annex ZA has been added by CENELEC.
__________
Endorsement notice

The text of the International Standard IEC 61828:2001 was approved by CENELEC as a European

Standard without any modification.

In the official version, for Bibliography, the following notes have to be added for the standards

indicated:
IEC 61161:1992 NOTE: Harmonized as EN 61161:1994 (not modified).
IEC 62092:2001 NOTE: Harmonized as EN 62092:2001 (not modified).
__________
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SIST EN 61828:2002
- 3 - EN 61828:2001
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

This European Standard incorporates, by dated or undated reference, provisions from other

publications. These normative references are cited at the appropriate places in the text and the

publications are listed hereafter. For dated references, subsequent amendments to or revisions of any

of these publications apply to this European Standard only when incorporated in it by amendment or

revision. For undated references, the latest edition of the publication referred to applies (including

amendments).

NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant

EN/HD applies.
Publication Year Title EN/HD Year
IEC 60050-801 1994 International Electrotechnical --
Vocabulary (IEV) -
Chapter 801: Acoustics and
electroacoustics
IEC 61102 1991 Measurement and characterisation of EN 61102 1993
ultrasonic fields using hydrophones in
the frequency range 0,5 MHz to 15 MHz
IEC 61157 1992 Requirements for the declaration of the EN 61157 1994
acoustic output of medical diagnostic
ultrasonic equipment
IEC 61689 1996 Ultrasonics - Physiotherapy systems - EN 61689 1996
Performance requirements and methods
of measurement in the frequency range
0,5 MHz to 5 MHz
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SIST EN 61828:2002
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SIST EN 61828:2002
NORME CEI
INTERNATIONALE
IEC
61828
INTERNATIONAL
Première édition
STANDARD
First edition
2001-05
Ultrasons – Transducteurs focalisants –
Définitions et méthodes de mesurage
pour les champs transmis
Ultrasonics – Focusing transducers –
Definitions and measurement methods
for the transmitted fields
 IEC 2006 Droits de reproduction réservés  Copyright - all rights reserved

Aucune partie de cette publication ne peut être reproduite ni No part of this publication may be reproduced or utilized in any

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électronique ou mécanique, y compris la photocopie et les photocopying and microfilm, without permission in writing from

microfilms, sans l'accord écrit de l'éditeur. the publisher.

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Pour prix, voir catalogue en vigueur
For price, see current catalogue
---------------------- Page: 7 ----------------------
SIST EN 61828:2002
61828  IEC:2006 – 3 –
CONTENTS

FOREWORD...........................................................................................................................7

INTRODUCTION...................................................................................................................11

1 Scope.............................................................................................................................13

2 Normative references .....................................................................................................13

3 General ..........................................................................................................................15

3.1 Focusing transducers ............................................................................................15

3.2 System and measurement requirements................................................................19

3.3 General focused field descriptions.........................................................................21

4 Focusing definitions........................................................................................................25

4.1 Background information.........................................................................................25

4.2 Definitions .............................................................................................................25

5 List of symbols ...............................................................................................................51

6 Measurement procedures ...............................................................................................53

6.1 General .................................................................................................................53

6.2 Finding the beam axis ...........................................................................................53

6.3 Determining if transducer is focusing.....................................................................57

6.4 Measuring other focal parameters of a focusing transducer ...................................59

Annex A (informative) Background for the transmission/ Characteristics of focusing

transducers ....................................................................................................................81

Annex B (informative) Methods for determining the beam axis for well-behaved

beams ............................................................................................................................91

Annex C (informative) Methods for determining the beam axis for beams that are not

well-behaved ..................................................................................................................99

Bibliography........................................................................................................................103

Figure 1 – Transducer options – Top: Transducer with a radius of curvature R and a focal

length equal to R – Middle: Transducer with a plano-concave lens – Bottom: Transducer

with a plano-convex lens.......................................................................................................63

Figure 2 – Definitions for focusing measurements when the transducer geometry is

unknown ...............................................................................................................................65

Figure 3 – Field parameters for non-focusing and focusing transducers ................................67

Figure 4 – Beam contour plot – Contours at –6, –12, and –20 dB for a 5 MHz transducer

with a diameter of 25 mm and a radius of curvature of 50 mm centred at location 0,0

(bottom centre of graph) .......................................................................................................69

Figure 5 – Parameters for describing a focusing transducer of a known geometry.................71

Figure 6 – Path difference parameters for describing a focusing transducer of a known

geometry ..............................................................................................................................73

Figure 7 – Beamwidth focus in a principal longitudinal plane.................................................75

Figure 8 –Types of geometric focusing..................................................................................77

Figure 9 – Pressure focus in a principal longitudinal plane....................................................79

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SIST EN 61828:2002
61828  IEC:2006 – 5 –

Figure B.1 – X-axis scan at 9 cm depth for the first focal zone with beam centre ..................93

Figure B.2 – X-axis scan at 4,4 cm depth for the second focal zone......................................95

Figure C.1 – Asymmetric beam showing beamwidth midpoint method .................................101

Table B.1 – Standard deviations for x and y scans using three methods of determining

the centre of the beam ..........................................................................................................93

Table B.2 – –dB beamwidth levels for determining midpoints ...............................................97

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SIST EN 61828:2002
61828  IEC:2006 – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ULTRASONICS – FOCUSING TRANSDUCERS –
DEFINITIONS AND MEASUREMENT METHODS
FOR THE TRANSMITTED FIELDS
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

this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,

Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC

Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested

in the subject dealt with may participate in this preparatory work. International, governmental and non-

governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely

with the International Organization for Standardization (ISO) in accordance with conditions determined by

agreement between the two organizations.

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

consensus of opinion on the relevant subjects since each technical committee has representation from all

interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

misinterpretation by any end user.

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

transparently to the maximum extent possible in their national and regional publications. Any divergence

between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in

the latter.

5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any

equipment declared to be in conformity with an IEC Publication.

6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

Publications.

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 61828 has been prepared by IEC technical committee 87:

Ultrasonics.
This bilingual version (2006-07) replaces the English version.
The text of this standard is based on the following documents:
FDIS Report on voting
87/196/FDIS 87/204/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.
The French version of this standard has not been voted upon.

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

---------------------- Page: 10 ----------------------
SIST EN 61828:2002
61828  IEC:2006 – 9 –

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

the maintenance result 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: 11 ----------------------
SIST EN 61828:2002
61828  IEC:2006 – 11 –
INTRODUCTION

Focusing transducers are essential in medical applications for obtaining high-resolution

images, Doppler and flow data and for concentrating ultrasonic energy at desired sites for

therapy. Present terminology for focusing transducers is inadequate for communicating

precisely the characteristics of the focused fields of the wide variety of transducers and

transducer array types and focusing means in common usage.

This International Standard provides specific definitions appropriate for describing the

focused field from a theoretical viewpoint for transducers with known characteristics intended

by design. Other specific definitions included in this standard, based on measurement

methods, provide a means of determining focusing properties, if any, of a transducer of

unknown field characteristics. The measurement method and definitions provide criteria for

determining if the transducer is focusing, as well as a means of describing the focusing

properties of the field. Beam axis alignment methods are given for focusing transducers.

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SIST EN 61828:2002
61828  IEC:2006 – 13 –
ULTRASONICS – FOCUSING TRANSDUCERS –
DEFINITIONS AND MEASUREMENT METHODS
FOR THE TRANSMITTED FIELDS
1 Scope
This International Standard

− provides definitions for the transmitted field characteristics of focusing transducers for

applications in medical ultrasound;

− relates these definitions to theoretical descriptions, design, and measurement of the

transmitted fields of focusing transducers;

− gives measurement methods for obtaining defined characteristics of focusing transducers;

− specifies beam axis alignment methods appropriate for focusing transducers.

This International Standard relates to focusing ultrasonic transducers operating in the

frequency range appropriate to medical ultrasound (0,5 MHz to 40 MHz) for both therapeutic

and diagnostic applications. It shows how the characteristics of the transmitted field of

transducers may be described from the point of view of design, as well as measured by

someone with no prior knowledge of the construction details of a particular device. The

radiated ultrasound field for a specified excitation is measured by a hydrophone in either a

standard test medium (for example, water) or in a given medium. The standard applies only to

media where the field behaviour is essentially like that in a fluid (i.e. where the influence of

shear waves and elastic anisotropy is small), including soft tissues and tissue-mimicking gels.

Any aspects of the field that affect their theoretical description or are important in design are

also included. These definitions would have use in scientific communications, system design

and description of the performance and safety of systems using these devices.

This standard incorporates definitions from other related standards where possible, and

supplies new, more specific terminology, both for defining focusing characteristics and for

providing a basis for measurement of these characteristics.
2 Normative references

The following referenced documents are indispensable for the application of this document.

For dated references, only the edition cited applies. For undated references, the latest edition

of the referenced document (including any amendments) applies.

IEC 60050(801):1994, International Electrotechnical Vocabulary (IEV) – Chapter 801:

Acoustics and electroacoustics

IEC 61102:1991, Measurement and characterization of ultrasonic fields using hydrophones in

the frequency range 0,5 MHz to 15 MHz
___________
Specifically, IEC 61102 and IEC 61157 (see clause 2).
---------------------- Page: 13 ----------------------
SIST EN 61828:2002
61828  IEC:2006 – 15 –

IEC 61157:1992, Requirements for the declaration of the acoustic output of medical

diagnostic ultrasonic equipment

IEC 61689:1996, Ultrasonics – Physiotherapy systems – Performance requirements and

methods of measurement in the frequency range 0,5 MHz to 5 MHz
3 General

The information contained in this clause is an introduction to the definitions given in clause 4

and the measurement methods given in clause 6.
3.1 Focusing transducers
The term "focusing transducer" is commonly used for a device which has a smaller

beamwidth in some regions of the field than a device which is "non-focusing". A "non-

focusing transducer" can still have a natural focus, so it is necessary to distinguish a

focusing transducer as having a greater concentration of pressure amplitude (for a given

power output) than a non-focusing transducer at its natural focus. For example, a non-

focusing transducer made of a simple disc of uniformly poled piezoelectric material has a

beam whose intensity at its natural focus can be as much as four times the average intensity

at the source, and whose –6 dB beamwidth can be approximately half of that at the source. A

definition of a focusing transducer is given in 4.2.33 to make a quantitative distinction

between focusing and non-focusing transducers.
3.1.1 Focusing methods

The simplest means of intentionally focusing an ultrasonic transducer, borrowed from

analogous optical principles, is that of shaping the ultrasonic transducer into a concave form

or adding to it a physical lens as illustrated in figure 1. In the top part of this figure, a

transducer curved with a radius R is shown focusing to the centre of curvature, where R is

positive by convention. By the geometrical-optics approximation, the focal length F is equal to

R and hence is also positive. In the middle of figure 1 is shown a transducer with a plano-

concave lens made of a material with longitudinal velocity, c , which is curved on one side

with a radius, R , and radiates into a medium in which the velocity is c . In acoustics, c

LENS W W

is typically less than c , i.e., the index of refraction n (equal to c /c ) is less than 1. When

L W L

this is true, the radius is considered to be negative and the focal length, given by the

geometric-acoustics approximation as R divided by (n – 1), is positive. At the bottom of

LENS

the figure, for comparison, the typical situation for a convex lens in optics is shown: n is

greater than 1 and the radius is considered to be positive, so the focal length is positive.

3.1.2 Known and unknown focusing transducers

For ultrasonic transducers currently used in medical ultrasound applications, it is difficult to

determine from physical observation if an ultrasonic transducer is focusing, because

additionally many other focusing methods such as geometric shaping and arrangement,

reflectors, arrays with electronic phasing and delay, Fresnel lenses, shading, etc. may be

used singly or in combination. Because of inherent natural focusing and the potential

complexity of additional focusing means used, any generally useful definition of a focusing

transducer must be in terms of its field rather than its construction. If a focusing source were

to be defined in terms of its pressure field, then this would be relatively easy to apply in

practice, since the pressure can be measured directly with a hydrophone.
___________
Terms in bold print are defined in clause 4.
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SIST EN 61828:2002
61828  IEC:2006 – 17 –

A distinction is also made between ultrasonic transducers whose construction is known and

transducers about which very little information is available. For the first category of ultrasonic

transducers, certain theoretical definitions, such as geometric focal length, are useful for

describing and modelling focusing characteristics. Ultrasonic transducers falling in the

second category function as an unknown "black box" and only the field may be accessible.

In the latter case, and in general, focusing parameters are determined from measurements,

and the measurement procedures of clause 6 are appropriate. In clause 6, measurement

methods are given for determining if a transducer system radiating into known propagation

media under specified excitation conditions is "focusing". Because of the lack of knowledge of

ultrasonic transducer construction and limited access to the ultrasonic transducer field, the

focusing definitions shown in figure 2 are required. These definitions are given in clause 4

and their use is explained in 3.1.5.
3.1.3 Focusing and beamwidth

Previously, hydrophone measurements of beam characteristics were based on regions of axial

peak pressure. For example, definitions for a depth-of-field were based on the fall-off in

intensity on either the near side or the far side of an axial peak on the beam axis. For axially

symmetric beams, this axial peak can be related to the geometric focal length. For typical

rectangular arrays, azimuthal plane electronic focusing and elevational plane mechanical lens

focusing can cause peaks of axial pressure at different locations along a beam axis. These

individual peaks can be dealt with separately by beamwidth measurements made in the

corresponding orthogonal planes: therefore, new definitions are based on beamwidths in a

specified longitudinal plane (refer to figure 7). Focusing definitions must also distinguish

between natural and intentional focusing.
3.1.4 New focusing parameter definitions

This document introduces new focusing parameters and provides more specific contexts for

existing terminology. For example, the terms "near field" and "far field" are often misapplied

to focusing transducers, though they have traditionally been defined for non-focusing

transducers only. The definitions near Fresnel zone, far Fresnel zone and focal

Fraunhofer zone, apply to focusing transducers. These definitions, explained in more detail

in 3.3 and derived from annex A, are illustrated in figure 3b and are applied to a strongly

focusing circular aperture in figure 4. Other concepts such as focusing in a particular plane

are also necessary to reduce ambiguity in usage.

For the purposes of this document, the following definitions for a focusing transducer will be

used.

For ultrasonic transducers of known construction (refer to figure 5 for transducer geometry

and terms), a focusing transducer is an electro-acoustic device that produces, at any

distance less than one-half of the transition distance from the transducer aperture, a –6 dB

beamwidth in a longitudinal plane that is less than half the transducer aperture width in

that plane. For measurement purposes and cases (see figure 2) where the geometry of the

ultrasonic transducer is not known or where there is no direct access to the ultrasonic

transducer (because of the device being used in some stand-off arrangement), a definition of

focusing based on data is more appropriate. For this second case, a focusing transducer is

an electro-acoustic device that produces, at any distance less than half of the transition

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SIST EN 61828:2002
61828  IEC:2006 – 19 –

distance from the source aperture, a –6 dB beamwidth in a longitudinal plane that is less

than one-half the –20 dB source aperture width (measured in a plane as close as possible to

the ultrasonic transducer) in that plane. For arrays with a rectangular geometry, a specified

longitudinal plane is either an xz or yz plane with z along the beam axis. Non-focusing

transducers are those not meeting the conditions specified above.
3.1.5 Applications of focusing definitions
Two definitions of focusing are given in 3.1.4, which apply in two cases.

a) For transducers for which the construction is known, an ideal definition is given for

describing, modeling or design purposes.

b) A second definition applies to measurements of the focusing characteristics of real

transducers which either have an unknown construction or imperfect realization.

Use of the first definition is not a substitute for actual measurement. Whether or not a

transducer is focusing in practice must be determined by the second definition for transducers

of unknown construction and by the measurement procedures of clause 6. Knowledge about

the transducer (first definition) may be helpful in guiding measurements. If measurements

meet the criteria of the second definition, the transducer is focusing, irrespective of whether

focusing was intentional or accidental.

3.1.6 Relation of present definitions to physiotherapy transducers (treatment heads)

The definition of focusing in the present document is not related to the definitions of

“divergent, collimated and convergent” beams as described in IEC 61689. The definition of

beam type is based on energy and area considerations that are more important for

physiotherapy transducers. The definition of focusing in the present document is based on a

different parameter: –6 dB beamwidth. This definition is useful in identifying the existence and

location of the highest field concentrations. When the current document is applied to

physiotherapy transducers, focusing can be understood to correspond to high-beam non-

uniformity ratio “hot-spot” transducers.
3.2 System and measurement requirements
In 3.1 it was shown that the radiating device has to be considered as a who
...

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