IEC 61828:2020

IEC 61828 ®
Edition 2.0 2020-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Ultrasonics – Transducers – Definitions and measurement methods
regarding focsusing for the transmitted fields

Ultrasons – Transducteurs – Définitions et méthodes de mesure
pour la focalisation des champs transmis

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IEC 61828 ®
Edition 2.0 2020-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Ultrasonics – Transducers – Definitions and measurement methods

regarding focsusing for the transmitted fields

Ultrasons – Transducteurs – Définitions et méthodes de mesure

pour la focalisation des champs transmis

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.140.50 ISBN 978-2-8322-9019-4

– 2 – IEC 61828:2020 © IEC 2020
CONTENTS
FOREWORD . 6
INTRODUCTION . 8
1 Scope . 9
2 Normative references . 9
3 Terms and definitions . 10
4 Symbols . 41
5 Independent measurement of total acoustic output power . 44
6 Acoustic field measurement: equipment . 44
6.1 Hydrophone . 44
6.1.1 General . 44
6.1.2 Sensitivity of a hydrophone . 44
6.1.3 Directional response of a hydrophone . 45
6.1.4 Effective hydrophone radius . 45
6.1.5 Choice of the size of a hydrophone active element . 45
6.1.6 Hydrophone pressure limits . 46
6.1.7 Hydrophone intensity limits . 46
6.1.8 Hydrophone cable length and amplifiers . 47
6.2 Requirements for positioning and water baths . 47
6.2.1 General . 47
6.2.2 Positioning systems . 47
6.2.3 Water bath . 48
6.3 Requirements for data acquisition and analysis systems . 49
6.4 Requirements and recommendations for ultrasonic equipment being
characterized . 50
7 Measurement procedure . 50
7.1 General . 50
7.2 Preparation and alignment . 50
7.2.1 General drive and field conditions . 50
7.2.2 Initial adjustment to driving voltage . 51
7.2.3 Preparation of source transducer . 52
7.2.4 Aligning an ultrasonic transducer and hydrophone . 52
7.2.5 Finding the beam axis . 53
7.2.6 Measurements to determine field level conditions . 55
7.2.7 Determining if transducer is focusing . 56
7.2.8 Measuring other beamwidth parameters of a focusing transducer . 57
7.2.9 Measuring the beam area parameters . 58
7.2.10 Measuring additional beam maximum based parameters . 59
7.2.11 Alternative: calculation of focal parameters using numerical projection . 60
7.2.12 Plane wave transmitted fields . 61
7.2.13 Steered plane waves . 61
7.2.14 Measurements of high intensity therapeutic ultrasound fields . 61
7.2.15 Calculation of I . 62
sa
7.2.16 Further evaluation for sidelobes and pre-focal maxima . 63
7.3 Considerations for scanning transducers and transducers with multiple
sources . 65
7.3.1 Automatic scanning transducers . 65

7.4 Spatial impulse response and beamplots . 65
7.4.1 General . 65
7.4.2 Point target . 66
7.4.3 Beamplots and beam contour plots . 66
7.5 Plane wave compounding . 66
Annex A (informative) Background for the transmission/ Characteristics of focusing
transducers . 67
A.1 General . 67
A.2 Field of piston source . 68
A.3 Focusing with a lens . 68
A.4 Focusing with a concave transducer . 71
A.5 Geometric focusing gains . 73
A.6 Beamwidth estimation . 74
Annex B (informative) Rationale for focusing and nonfocusing definitions . 79
B.1 Overview. 79
B.1.1 Background information . 79
B.1.2 General . 79
B.1.3 Focusing transducers . 79
B.1.4 Focusing methods . 80
B.1.5 Known and unknown focusing transducers . 81
B.1.6 Focusing and beamwidth . 81
B.1.7 Focusing parameter definitions . 82
B.1.8 Applications of focusing definitions . 82
B.1.9 Relation of present definitions to physiotherapy transducers (treatment
heads) . 82
B.1.10 Relation of present definitions to therapeutic transducers . 82
B.2 System and measurement requirements . 83
B.2.1 General . 83
B.2.2 Transmitted pressure waveforms . 83
B.2.3 Transmitted fields . 83
B.2.4 The scan plane and the steering of beams . 83
B.2.5 Pulse echo field measurements . 84
Annex C (informative) Methods for determining the beam axis for well-behaved beams . 94
C.1 Comparisons of beam axis search methods . 94
C.2 Beamwidth midpoint method . 95
Annex D (informative) Methods for determining the beam axis for beams that are not
well behaved . 97
Annex E (informative) Uncertainties . 99
E.1 General . 99
E.2 Overall (expanded) uncertainty . 99
E.3 Common sources of uncertainty . 99
Annex F (informative) Transducer and hydrophone positioning systems . 101
Annex G (informative) Planar scanning of a hydrophone to determine acoustic output
power . 102
G.1 Overview. 102
G.2 General principle . 102
G.3 Hydrophone scanning methodology. 103
G.3.1 General methodology . 103
G.3.2 Particular considerations for implementation for HITU fields . 104

– 4 – IEC 61828:2020 © IEC 2020
G.4 Corrections and sources of measurement uncertainty . 104
G.4.1 Uncertainty in the hydrophone calibration . 104
G.4.2 Planar scanning . 104
G.4.3 Attenuation factor of water: unfocusing transducers . 104
G.4.4 Attenuation factor of water: focusing transducers . 105
G.4.5 Received hydrophone signal . 105
G.4.6 Integration . 105
G.4.7 Finite size of the hydrophone . 106
G.4.8 Partial extent of integration . 106
G.4.9 Non-linear propagation . 106
G.4.10 Directional response . 106
G.4.11 Noise . 107
G.4.12 Intensity approximated by derived intensity . 107
Annex H (informative) Properties of water . 108
H.1 General . 108
H.2 Attenuation coefficient for propagation in water . 109
Bibliography . 110

Figure A.1 – Beam contour plot: contours at −6 dB, −12 dB, and −20 dB for a 5 MHz
transducer with a radius of curvature of D = 50 mm centred at location 0,0 (bottom
centre of graph) . 76
Figure A.2 – Types of geometric focusing . 76
Figure A.3 – Transducer options . 77
Figure A.4 – Parameters for describing a focusing transducer of known geometry . 78
Figure A.5 – Path difference parameters for describing a focusing transducer of known
geometry . 78
Figure B.1 – Electronic focusing along z by transmit beamforming in the scan plane xz . 84
Figure B.2 – Field parameters for a nonfocusing transducer of known geometry. For
example, for a circularly symmetric geometry, transducers have a diameter 2a and a

beam axis along z . 85
Figure B.3 – Phased array geometry and construction for electronic focusing in the
azimuth plane and mechanical lens focusing in the elevation plane . 85
Figure B.4 – Field parameters for a focusing transducer of known geometry . 86
Figure B.5 – Definitions for pressure-based field measurements for an unknown
transducer geometry . 86
Figure B.6 – Beamwidth focus for transducers of known and unknown geometry . 87
Figure B.7 – Beam maximum parameters . 88
Figure B.8 – Pressure focus for a transducer of known geometry (design case) . 88
Figure B.9 – Pressure focus for a transducer of unknown geometry (measurement

case) . 89
Figure B.10 – Beam area parameters . 89
Figure B.11 – Beam axis parameters: pulse-pressure-squared-integral level relative to
the beam maximum in decibels (dB) plotted against axial distance . 90
Figure B.12 – Beamplot parameters . 91
Figure B.13 – Schematic diagram of the different planes and lines in an ultrasonic field
for a rectangular transducer . 92
Figure B.14 – Schematic diagram of the different planes and lines in an ultrasonic field

for a circular transducer . 93

Figure C.1 – x-axis scan at 9 cm depth for the first focal zone with beam centre . 95
Figure C.2 – x-axis scan at 4,4 cm depth for the second focal zone . 95
Figure D.1 – Asymmetric beam showing relative acoustic pressure versus sample
number for the beamwidth midpoint method . 98
Figure F.1 – Schematic diagram of the ultrasonic transducer and hydrophone degrees
of freedom . 101

Table C.1 – Standard deviations for x and y scans using three methods of determining
the centre of the beam . 94
Table C.2 – Decibel beamwidth levels for determining midpoints . 96
Table H.1 – Speed of sound, c, and characteristic acoustic impedance, ρ c, as a
function of temperature, for propagation in water . 108

– 6 – IEC 61828:2020 © IEC 2020
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ULTRASONICS –TRANSDUCERS – DEFINITIONS AND MEASUREMENT
METHODS REGARDING FOCUSING 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
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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.
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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 second edition cancels and replaces the first edition published in 2001. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Clause 6 on Measurement procedures has been replaced by Clause 6: "Acoustic field
measurement: equipment" and Clause 7: "Measurement procedure" and related definitions.
b) Reorganization of definitions and measurement section to accommodate specific sets of
measurements for focusing, nonlinearity, beam axis alignment, beam area, beam maximum,
numerical projection, plane wave, high intensity therapeutic ultrasound, multiple sources,
spatial impulse response and compound plane waves. Clause 3 has been moved to
Annex B.
c) The normative references have been updated and the Bibliography has been expanded from
8 to 40 references.
d) Twelve figures have been updated and seven new figures (B.1, B.3, B.7, B.10, B.11, B.12,
B.13, B.14) have been added to facilitate measurements and be consistent with
measurement terminology.
e) New measurements have been added for time delays, arrays, plane waves and spatial
impulse response.
f) Annex A has been expanded to provide general guidance on pulsed waves, system
responses, focusing gains and minimum beamwidth estimation.
g) New annexes have been added:
• Annex B (informative) Rationale for focusing and nonfocusing definitions
• Annex E (informative) Uncertainties;
• Annex F (informative) Transducer and hydrophone positioning systems;
• Annex G (informative) Planar scanning of a hydrophone to determine acoustic output
power;
• Annex H (informative) Properties of water;
In addition, Annex A was reorganized and new Clauses A.1, A.5 and A.6 were added.
h) Guidelines for remaining within the manufacturer’s pressure and intensity hydrophone limits
and the determination of the extent of nonlinearity in the field have been added.
The text of this International Standard is based on the following documents:
FDIS Report on voting
87/746/FDIS 87/749/RVD
Full information on the voting for the approval of this International 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 1 The following print types are used:
– Requirements: in roman type.
– Notes: small roman type.
– Words in bold in the text are defined in Clause 3.
NOTE 2 There are some inconsistencies in font type for symbols and formulae between some of the normative
references and this document. They will be resolved in a future revision of the normative references.
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.
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.

– 8 – IEC 61828:2020 © IEC 2020
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. This document 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 document, 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 and field characterization measurements are given for both
focusing and nonfocusing transducers.

ULTRASONICS –TRANSDUCERS – DEFINITIONS AND MEASUREMENT
METHODS REGARDING FOCUSING FOR THE TRANSMITTED FIELDS

1 Scope
This document
– provides definitions for the transmitted field characteristics of focusing and nonfocusing
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 field characteristics of focusing and
nonfocusing transducers;
– specifies beam axis alignment methods appropriate for focusing and nonfocusing
transducers.
This document 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 can 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 transmitted 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. This document 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 document incorporates definitions from other related standards where possible, and
supplies more specific terminology, both for defining focusing characteristics and for providing
a basis for measurement of these characteristics.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 61689:2013, Ultrasonics – Physiotherapy systems – Field specifications and methods of
measurement in the frequency range 0,5 MHz to 5MHz
IEC 62127-3:2007, Ultrasonics – Hydrophones – Part 3: Properties of hydrophones for
ultrasonic fields up to 40 MHz
IEC 62127-3:2007/AMD1:2013
IEC TS 62556:2014, Ultrasonics – Field characterization – Specification and measurement of
field parameters for high intensity therapeutic ultrasound (HITU) transducers and systems
IEC 61161, Ultrasonics – Power measurement – Radiation force balances and performance
requirements
– 10 – IEC 61828:2020 © IEC 2020
IEC 62555, Ultrasonics – Power measurement –High intensity therapeutic ultrasound (HITU)
transducers and systems
ISO/IEC Guide 98-3:2008, Uncertainty of measurement – Part 3: Guide to the expression of
uncertainty in measurement (GUM:1995)
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
acoustic pulse waveform
temporal waveform of the instantaneous acoustic pressure at a specified position in an acoustic
field and displayed over a period sufficiently long to include all significant acoustic information
in a single pulse, a single tone-burst, or one cycle of a continuous wave
Note 1 to entry: In some cases such as an amplitude-modulated pulse, the overall pulse train can appear as a group
of nearly contiguous pulses with spacings much smaller than the overall pulse repetition time.
3.2
annular array
ultrasonic transducer element group having radiating elements in the same plane or curved
surface and consisting of concentric elements which are electrically phased to control the
characteristics of an acoustic beam
3.3
acoustic frequency
acoustic-working frequency
frequency of an acoustic signal based on the observation of the output of a hydrophone placed
in an acoustic field at the position corresponding to the spatial-peak temporal-peak acoustic
pressure
Note 1 to entry: The signal is analysed using either the zero-crossing acoustic-working frequency technique or
a spectrum analysis method.
Note 2 to entry: In a number of cases the present definition is not very helpful or convenient, especially for
broadband transducers. In that case a full description of the frequency spectrum should be given in order to enable
any frequency-dependent correction to the signal.
Note 3 to entry: Acoustic frequency is expressed in hertz (Hz).
[SOURCE: IEC 62127-1:2007, 3.3]
3.3.1
zero-crossing acoustic-working frequency
number, n, of consecutive half-cycles (irrespective of polarity) divided by twice the time between
the commencement of the first half-cycle and the end of the n-th half-cycle
Note 1 to entry: None of the n consecutive half-cycles should show evidence of phase change.
Note 2 to entry: This frequency is intended for continuous-wave systems only.
[SOURCE: IEC 62127-1:2007/AMD1:2013, 3.3.1, modified – NOTE 2 and NOTE 3 have been
deleted.]
3.3.2
arithmetic-mean acoustic-working frequency

f
awf
arithmetic mean of the most widely separated frequencies f and f , within the range of three
1 2
times f , at which the magnitude of the acoustic pressure spectrum is 3 dB below the peak
magnitude
Note 1 to entry: This frequency is intended for pulse-wave systems only.
Note 2 to entry: It is assumed that f < f .
1 2
Note 3 to entry: If f is not found within the range < 3 f , f is to be understood as the lowest frequency above this
2 1 2
range at which the spectrum magnitude is 3 dB below the peak magnitude.
Note 4 to entry: See IEC 62127-1 for methods of determining the arithmetic-mean acoustic-working frequency.
[SOURCE: IEC 62127-1:2007 and IEC 62127-1:2007/AMD1:2013, 3.3.2, modified – Note 4 to
entry has been added.]
3.4
aperture path difference
Δ
difference in path lengths from a specified geometric focus to the periphery of the transducer
aperture and to the intersection of the beam axis with the transducer aperture plane for a
specified longitudinal plane and for an unsteered beam
SEE: Figure A.5.
Note 1 to entry: Δ is expressed in metres, m.
3.5
apodization
amplitude weighting or shading of the transducer aperture
3.6
axial field-point path difference
Δ′
difference in path lengths from a specified field point on the beam axis to the periphery of the
transducer aperture and to the intersection of the beam axis with the transducer aperture
plane
SEE: Figure A.5.
Note 1 to entry: It is specified in the same longitudinal plane as the aperture path difference.
Note 2 to entry: Δ′ is expressed in metres, m.
3.7
azimuth axis
axis formed by the junction of the azimuth plane and the source aperture plane
(measurement) or transducer aperture plane (design)
SEE: Figure B.3, Figure B.13 and Figure B.14.
Note 1 to entry: The selection of this axis is arbitrary for a circularly-symmetric HITU transducer without a hole in
its centre but is perpendicular to the elevation axis.
Note 2 to entry: If a HITU transducer has a hole in its centre, within which is a diagnostic imaging transducer, then
this axis is aligned with the azimuth axis of the imaging transducer.

– 12 – IEC 61828:2020 © IEC 2020
3.8
azimuth plane
plane containing the beam axis and the line of the minimum full width half maximum
beamwidth
Note 1 to entry: For an ultrasonic transducer array, this is the imaging plane.
Note 2 to entry: For a single ultrasonic transducer with spherical or circular symmetry, it is any plane containing
the beam axis.
SEE: Figure B.3, Figure B.13 and Figure B.14.
3.9
bandwidth
BW
difference in the most widely separated frequencies f and f at which the magnitude of the
1 2
acoustic pressure spectrum becomes 3 dB below the peak magnitude, at a specified point in
the acoustic field
Note 1 to entry: Bandwidth is expressed in hertz (Hz).
[SOURCE: IEC 62127-1:2007, 3.6]
3.10
beam area
A , A , A
b,6 b,12 b,20
area in a specified plane perpendicular to the beam axis consisting of all points at which the
pulse-pressure-squared integral is greater than a specified fraction of the maximum value of
the pulse-pressure-squared integral in that plane
Note 1 to entry: If the position of the plane is not specified, it is the plane passing through the point corresponding
to the maximum value of the pulse-pressure-squared integral in the whole acoustic field.
Note 2 to entry: In a number of cases, the term pulse-pressure-squared integral is replaced everywhere in the
above definition by any linearly related quantity, e.g.:
a) in the case of a continuous wave signal the term pulse-pressure-squared integral is replaced by mean square
acoustic pressure as defined in IEC 61689;
b) in cases where signal synchronization with the scanframe is not available the term pulse-pressure-squared
integral can be replaced by temporal-average intensity.
Note 3 to entry: Some specified fractions are 0,25 and 0,01 for the −6 dB and −20 dB beam areas, respectively.
Note 4 to entry: Beam area is expressed in square metres (m ).
[SOURCE: IEC 62127-1:2007 and IEC 62127-1:2007/AMD1:2013, 3.7, modified – The symbol
A has been added.]
b,12
3.11
beam area focal depth
distance along beam axis from source aperture plane to beam area focus
SEE: Figure B.10.
3.12
beam area focal plane
plane perpendicular to the beam axis and containing the beam area focus
SEE: Figure B.10.
3.13
beam area focus
point on the beam axis at which the −6 dB beam area is a minimum
SEE: Figure B.10.
3.14
beam axis
straight line that passes through the beam centrepoints of two planes perpendicular to the line
which connects the point of maximal pulse-pressure-squared integral with the centre of the
external transducer surface plane
SEE: Figure B.3, Figure B.13 and Figure B.14.
Note 1 to entry: The location of the first plane is the location of the plane containing the maximum
pulse-pressure-squared integral or, alternatively, is one containing a single main lobe which is in the postfocal
zone. The location of the second plane is as far as is practicable from the first plane and parallel to the first with the
same two orthogonal scan lines (x and y axes) used for the first plane.
Note 2 to entry: In a number of cases, the term pulse-pressure-squared integral is replaced in the above definition
by any linearly related quantity, e.g.:
a) in the case of a continuous wave signal the term pulse-pressure-squared integral is replaced by mean square
acoustic pressure as defined in IEC 61689;
b) in cases where signal synchronization with the scanframe is not available the term pulse-pressure-squared
integral can be replaced by temporal-average intensity.
Note 3 to entry: Refer to Annex C and Annex D.
[SOURCE: IEC 62127-1:2007, 3.8, modified – In the definition, "external transducer aperture"
has been replaced by "external transducer surface plane".]
3.15
beam centrepoint
position determined by the intersection of two lines passing through the beamwidth midpoints
of two orthogonal planes, xz and yz
3.16
beam maximum
bm
maximum measured pulse-pressure-squared integral on the beam axis
SEE: Figure B.7.
[SOURCE: IEC TS 62556:2014, 3.10]
3.17
beam maximum depth
L
bm
smallest distance between two points on the beam axis where the pulse-pressure-squared
integral falls below its maximum on the beam axis by 6 dB
SEE: Figure B.7.
Note 1 to entry: In a number of cases, the term pulse-pressure-squared integral is replaced in the above definition
by any linearly related quantity, e.g.: in the case of a continuous wave signal the term pulse-pressure-squared
integral is replaced by mean square acoustic pressure as defined in IEC 61689.
Note 2 to entry: Beam maximum depth is expressed in metres (m).
[SOURCE: IEC TS 62556:2014, 3.11]

– 14 – IEC 61828:2020 © IEC 2020
3.18
beam maximum length
z
p
distance from the source aperture plane to the position on the beam axis where the maximum
pulse-pressure-squared integral is measured
SEE: Figure B.7.
Note 1 to entry: In a number of cases, the term pulse-pressure-squared integral is replaced in the above definition
by any linearly related quantity, e.g.: in the case of a continuous wave by the mean square acoustic pressure as
defined in IEC 61689.
Note 2 to entry: Beam maximum length is expressed in metres (m).
...