EN IEC 62127-2:2025

SLOVENSKI STANDARD
01-april-2025
Ultrazvok - Hidrofoni - 2. del: Kalibracija za ultrazvočna polja (IEC 62127-2:2025)
Ultrasonics - Hydrophones - Part 2: Calibration for ultrasonic fields (IEC 62127-2:2025)
Ultraschall - Hydrophone - Teil 2: Kalibrierung für Ultraschallfelder (IEC 62127-2:2025)
Ultrasons - Hydrophones - Partie 2: Etalonnage des champs ultrasoniques (IEC 62127-
2:2025)
Ta slovenski standard je istoveten z: EN IEC 62127-2:2025
ICS:
11.040.01 Medicinska oprema na Medical equipment in general
splošno
17.140.50 Elektroakustika Electroacoustics
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 62127-2

NORME EUROPÉENNE
EUROPÄISCHE NORM February 2025
ICS 17.140.50 Supersedes EN 62127-2:2007; EN 62127-
2:2007/A1:2013; EN 62127-2:2007/A2:2017
English Version
Ultrasonics - Hydrophones - Part 2: Calibration for ultrasonic
fields
(IEC 62127-2:2025)
Ultrasons - Hydrophones - Partie 2: Etalonnage des Ultraschall - Hydrophone - Teil 2: Kalibrierung für
champs ultrasoniques Ultraschallfelder
(IEC 62127-2:2025) (IEC 62127-2:2025)
This European Standard was approved by CENELEC on 2025-02-11. 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 CEN-CENELEC
Management Centre 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 CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 62127-2:2025 E

European foreword
The text of document 87/878/FDIS, future edition 2 of IEC 62127-2, prepared by TC 87 "Ultrasonics"
was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as EN IEC 62127-
2:2025.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2026-02-28
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2028-02-29
document have to be withdrawn
This document supersedes EN 62127-2:2007 and all of its amendments and corrigenda (if any).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 62127-2:2025 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following note has to be added for the standard indicated:
IEC 61828:2020 NOTE Approved as EN IEC 61828:2021 (not modified)
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
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.
NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 61161 -  Ultrasonics - Power measurement - EN 61161 -
Radiation force balances and performance
requirements
IEC 61689 -  Ultrasonics - Physiotherapy systems - Field EN IEC 61689 -
specifications and methods of
measurement in the frequency range 0,5
MHz to 5 MHz
IEC 62127-1 -  Ultrasonics - Hydrophones - Part 1: EN IEC 62127-1 -
Measurement and characterization of
medical ultrasonic fields
IEC 62127-3 2022 Ultrasonics - Hydrophones - Part 3: EN IEC 62127-3 2023
Properties of hydrophones for ultrasonic
fields
IEC 62127-2 ®
Edition 2.0 2025-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Ultrasonics – Hydrophones –
Part 2: Calibration for ultrasonic fields

Ultrasons – Hydrophones –
Partie 2: Etalonnage des champs ultrasoniques

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.140.50 ISBN 978-2-8327-0091-4

– 2 – IEC 62127-2:2025 © IEC 2025
CONTENTS
FOREWORD . 8
INTRODUCTION . 10
1 Scope . 11
2 Normative references . 11
3 Terms and definitions . 12
4 List of symbols . 21
5 Overview of calibration procedures . 24
5.1 Principles . 24
5.2 Summary of calibration procedures . 25
5.3 Reporting of results . 26
5.4 Recommended calibration periods . 28
6 Generic requirements of a hydrophone calibration system . 28
6.1 Mechanical positioning . 28
6.1.1 General . 28
6.1.2 Accuracy of the axial hydrophone position . 28
6.1.3 Accuracy of the lateral hydrophone position . 29
6.2 Temperature measurements and temperature stability . 29
6.3 Hydrophone size . 29
6.4 Measurement vessel and water properties . 30
6.5 Measurement of output voltage . 30
7 Electrical considerations . 30
7.1 Signal type . 30
7.2 Earthing . 31
7.3 Measurement of hydrophone output voltage . 31
7.3.1 General . 31
7.3.2 Electrical loading by measuring instrument . 31
7.3.3 Electrical loading by extension cables . 31
7.3.4 Noise . 32
7.3.5 Cross-talk (radio-frequency rf pick-up) and acoustic interference . 32
7.3.6 Integral hydrophone pre-amplifiers . 32
8 Preparation of hydrophones . 32
8.1 General . 32
8.2 Wetting . 32
8.3 Hydrophone support . 32
8.4 Influence of cable . 33
9 Free field reciprocity calibration . 33
9.1 General . 33
9.2 Object . 33
9.3 General principles . 33
9.3.1 General . 33
9.3.2 Three-transducer reciprocity calibration method . 33
9.3.3 Self-reciprocity calibration method . 34
9.3.4 Two-transducer reciprocity calibration method . 34
9.4 Two-transducer reciprocity calibration method . 34
9.4.1 General . 34
9.4.2 Auxiliary transducers . 34

IEC 62127-2:2025 © IEC 2025 – 3 –
9.4.3 Reflector . 35
9.4.4 Measurement field . 35
9.4.5 Reciprocity approach . 35
9.4.6 Measurement procedure . 35
10 Free field calibration by planar scanning . 35
10.1 General . 35
10.2 Object . 36
10.3 General principle . 36
10.4 Procedural requirements . 38
10.4.1 Hydrophone scanning . 38
10.4.2 Power measurement . 38
10.4.3 Transducer mounting . 38
10.4.4 Measurement conditions . 38
10.4.5 Measurements . 39
10.5 Corrections and sources of uncertainty . 39
11 Free field calibration by optical interferometry . 39
11.1 General . 39
11.2 Principle . 39
12 Calibration by comparison using a standard hydrophone . 39
12.1 General . 39
12.2 Object . 39
12.3 Principle . 40
12.4 Procedural requirements . 40
12.4.1 Source transducer . 40
12.4.2 Source transducer drive signal . 40
12.4.3 Measurement system . 40
12.5 Procedure . 41
12.5.1 Measurements (Type I): determination of the directional response of a
hydrophone . 41
12.5.2 Measurements (Type II): calibration by comparison using a standard
hydrophone . 42
12.6 Maximum hydrophone size . 42
Annex A (informative) Assessment of uncertainty in free field calibration of
hydrophones . 43
A.1 General . 43
A.2 Overall (expanded) uncertainty . 43
A.3 Common sources of uncertainty . 43
Annex B (informative) Behaviour of PVDF polymer sensors in high-intensity ultrasonic
fields . 45
B.1 General . 45
B.2 Theoretical background . 45
B.3 Tests . 45
B.4 Results . 46
B.5 Conclusions . 47
Annex C (informative) Electrical loading corrections . 48
C.1 General . 48
C.2 Corrections using complex impedance . 48
C.3 Corrections using only capacitances . 49

– 4 – IEC 62127-2:2025 © IEC 2025
Annex D (informative) Absolute calibration of hydrophones using the planar scanning
technique . 50
D.1 Overview. 50
D.2 Hydrophone scanning methodology. 50
D.3 Corrections and sources of measurement uncertainty . 51
D.3.1 Total power . 51
D.3.2 Received hydrophone signal . 51
D.3.3 Integration . 52
D.3.4 Directional response . 52
D.3.5 Finite size of the hydrophone . 53
D.3.6 Noise . 53
D.3.7 Nonlinear propagation . 54
D.3.8 Planar scanning . 55
D.3.9 Intensity proportional to pressure squared . 55
D.4 Rationale behind the planar scanning technique for calibrating hydrophones . 56
D.4.1 General . 56
D.4.2 Relationship between hydrophone and transducer effective radii . 56
D.4.3 Justification for al/ ≤ 0,5 . 56
t
D.4.4 Derivation of Formula (D.2). 57
D.4.5 Effect of nonlinear propagation, D.3.7 . 58
Annex E (informative) Properties of water . 60
E.1 General . 60
E.2 Attenuation coefficient for propagation in water . 61
Annex F (informative) The absolute calibration of hydrophones by optical
interferometry . 62
F.1 Overview. 62
F.2 Present position . 62
F.2.1 "Magnomic" or nonlinear propagation-based method . 62
F.2.2 Optical interferometry . 63
F.2.3 High-frequency implementations of optical interferometry . 63
Annex G (informative) Waveform concepts . 78
G.1 Overview. 78
G.2 Temporal waveform, frequency concepts and hydrophone positioning for
comparison calibrations of hydrophones . 78
G.3 Temporal waveform and frequency coverage concepts . 79
G.3.1 Using a narrow-band tone-burst (concept a) . 79
G.3.2 Using a broadband waveform resulting from a narrow-band tone-burst
after nonlinear propagation (concept b) . 80
G.3.3 Using a broadband pulse (concept c) . 80
G.3.4 Using a continuous wave frequency sweep with time delay spectrometry
(concept d) . 81
G.3.5 Continuous wave frequency sweep with TGFA (concept e) . 81
G.4 Hydrophone position concepts . 81
G.4.1 Near-field hydrophone position (concept A) . 81
G.4.2 Far field hydrophone position (concept B) . 81
G.4.3 Far field hydrophone position with special reference to a long
propagation path in order to achieve nonlinear distortion (concept C) . 82
G.4.4 Geometric spherical focus position with focusing source transducer (low
voltage or linear excitation) (concept D) . 82

IEC 62127-2:2025 © IEC 2025 – 5 –
G.4.5 Geometric spherical focus position with focusing source transducer and
high voltage excitation in order to achieve nonlinear distortion (concept
E) . 82
G.5 Special considerations for calibrations close to the face of a transducer . 83
G.5.1 General requirement . 83
G.5.2 Influence of edge waves . 83
G.5.3 Potential influence of head waves . 84
G.5.4 Treatment of head waves close to the transducer . 84
G.5.5 Statements on the usable paraxial plane wave region in the case of a
near-field hydrophone position, considering both edge wave and head
wave contributions . 86
Annex H (informative) Time delay spectrometry – Requirements and a brief review of
the technique . 87
H.1 General . 87
H.2 Calibration and performance evaluation of ultrasonic hydrophones using

time delay spectrometry . 87
H.2.1 Ultrasonic field parameter measured . 87
H.2.2 Ultrasonic frequency range over which the technique is applicable . 87
H.2.3 Ultrasonic field configuration for which the technique is applicable . 87
H.2.4 Spatial resolution . 88
H.2.5 Sensitivity of the technique . 88
H.2.6 Range over which the sensitivity is measured . 88
H.2.7 Reproducibility . 88
H.2.8 Impulse response . 88
H.2.9 Procedure for performing measurements . 88
H.3 Measurement procedure for sensitivity intercomparison . 89
H.4 Measurement procedure (reciprocity calibration) . 89
H.5 Limitations . 89
Annex I (informative) Determination of the phase response of hydrophones . 90
I.1 Overview. 90
I.2 Coherent time delay spectrometry . 91
I.2.1 Principle of operation . 91
I.2.2 Example results . 91
I.2.3 Uncertainties . 92
I.2.4 Limitations . 93
I.3 Pulse calibration technique with optical multilayer hydrophone . 93
I.3.1 Principle of operation . 93
I.3.2 Example of results . 93
I.3.3 Uncertainties . 94
I.3.4 Limitations . 94
I.4 Nonlinear pulse propagation modelling . 95
I.4.1 Principle of operation . 95
I.4.2 Limitations . 95
Annex J (informative) Maximum size considerations for the active element of a
hydrophone . 96
J.1 Maximum hydrophone size in the near field case (Annex G – hydrophone
position concept A) . 96
J.2 Maximum hydrophone size in the far field case (Annex G – hydrophone
position concept B) . 96

– 6 – IEC 62127-2:2025 © IEC 2025
J.3 Maximum hydrophone size in the far field case with special reference to a
long propagation path in order to achieve nonlinear distortion (Annex G –
hydrophone position concept C) . 96
Annex K (informative) Two-transducer reciprocity calibration method . 98
K.1 General . 98
K.2 Fundamentals of reciprocity . 98
K.3 Electrical quantities . 99
K.4 Diffraction correction and loss due to nonlinear sound propagation . 100
K.5 Ultrasonic field . 100
K.6 Experimental set-up . 101
K.6.1 General . 101
K.6.2 Twisting reflector . 101
K.6.3 Translational reflector . 102
K.6.4 Translational auxiliary transducer . 102
K.7 Hydrophone calibration using a calibrated spherically curved auxiliary

transducer based on the self-reciprocity method . 103
Bibliography . 107

Figure F.1 – Experimental set-up of the interferometric foil technique . 65
L
Figure F.2 – End-of-cable open-circuit sensitivity level of a coplanar membrane
M
c
hydrophone . 67
Figure F.3 – Experimental set-up of the heterodyne vibrometer technique . 69
Figure F.4 – Measured frequency-dependent radial profiles of the acoustic pulse field . 71
Figure F.5 – Experimentally determined spatial averaging correction versus frequency
for hydrophones of different effective element diameter, d . 72
eff
Figure F.6 – End-of-cable loaded sensitivity level and sensitivity phase of a coplanar
membrane hydrophone assembly at 50 Ω termination . 73
Figure F.7 – Hydrophone waveform generated by a 9 µm coplanar membrane
hydrophone positioned at the focus of a 5 MHz transducer (focal length 51 mm). 74
Figure F.8 – Interferometer displacement waveform generated with the pellicle
positioned at the focus of the 5 MHz transducer (focal position 51 mm) . 75
Figure F.9 – Frequency spectrum of the displacement waveform (lower curve) and the
differentiated displacement waveform (upper curve) . 75
Figure F.10 – Sensitivity of a 0,2 mm active element diameter of a 9 µm bilaminar
membrane hydrophone determined at 5 MHz intervals over the frequency range 5 MHz
to 60 MHz . 76
Figure G.1 – Coordinates of a field point P in the near field of a plane-circular source

transducer of radius a . 84
t
Figure I.1 – Phase of end-of-cable open-circuit sensitivity for two membrane
hydrophones . 92
Figure I.2 – Phase of end-of-cable open-circuit sensitivity for a 0,2 mm diameter
needle hydrophone . 94
Figure K.1 – Experimental set-up with a twisting reflector [22] . 102
Figure K.2 – Experimental set-up with a translational reflector [23] . 102
Figure K.3 – Experimental set-up with a translational auxiliary transducer [24] . 103
Figure K.4 – Relationship of G and θ (°) for several values of ka . 105
c m h
IEC 62127-2:2025 © IEC 2025 – 7 –
Table 1 – List of typical uncertainty values (for 95 % coverage) obtained by the
calibration methods specified in this document and for the frequency range listed . 26
Table E.1 – Speed of sound c [54],[55] and specific acoustic impedance, ρc, as a

function of temperature, for propagation in water . 60
Table G.1 – Temporal waveform and hydrophone position concepts described in
Annex G . 78
Table I.1 – Example of uncertainties (where a coverage factor, k = 2, is used) for a
HTDS phase calibration of a needle hydrophone with a diameter of 0,2 mm, expressed
at a confidence level of 95 % . 92
Table K.1 – Values of the correction coefficient G (ka , θ ) for the spatial average
c h m
effect of the free-field acoustic pressure over the hydrophone surface if it were
removed . 105

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INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ULTRASONICS – HYDROPHONES –
Part 2: Calibration for ultrasonic 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
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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6) All users should ensure that they have the latest edition of this publication.
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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) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
may be required to implement this document. However, implementers are cautioned that this may not represent
the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC 62127-2 has been prepared by IEC technical committee 87: Ultrasonics. It is an
International Standard.
This second edition cancels and replaces the first edition published in 2007, Amendment 1:2013
and Amendment 2:2017. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) the upper frequency limit of 40 MHz has been removed;
b) hydrophone sensitivity definitions have been changed to recognize sensitivities as complex-
valued quantities;
c) directional response measurement and effective size determination procedures have been
updated in 12.5.1 to align with recent changes in IEC 62127-3;

IEC 62127-2:2025 © IEC 2025 – 9 –
d) Annex F has been amended to comprise a calibration technique for high-frequency complex-
valued calibration;
e) the reciprocity method description in Annex K was extended to also comprise focusing
transducers;
The text of this International Standard is based on the following documents:
Draft Report on voting
87/878/FDIS 87/884/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts of IEC 62127 series, published under the general title Ultrasonics –
Hydrophones, can be found on the IEC website.
NOTE Terms in bold in the text are defined in Clause 3.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
IMPORTANT – The "colour inside" logo on the cover page of this document 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.

– 10 – IEC 62127-2:2025 © IEC 2025
INTRODUCTION
The spatial and temporal distribution of acoustic pressure in an ultrasonic field in a liquid
medium is commonly determined using miniature ultrasonic hydrophones. These devices are
not absolute measurement instruments and it is important that they are calibrated. This part of
IEC 62127 specifies the calibration methods to use in determining the response of a
hydrophone in the ultrasonic range, i.e. above 50 kHz. The main hydrophone application in
this context lies in the measurement of ultrasonic fields emitted by medical diagnostic
equipment in water. It is important to understand hydrophone behaviour over a wide frequency
band in order to reliably characterize the acoustic parameters of the applied acoustic field. In
particular, the frequency range above 15 MHz is important to fully characterize this equipment,
primarily due to the increased appearance of high-frequency components in the ultrasonic
signals, caused by nonlinear propagation. In addition, the number of medical ultrasonic systems
that use frequencies above 15 MHz, particularly intra-operative probes, is growing. It has turned
out in recent years that the hydrophone response below 0,5 MHz is also important in order to
reliably determine the peak-negative (rarefactional) acoustic pressure.
While the term "hydrophone" can be used in a wider sense, it is understood here as referring
to miniature piezoelectric hydrophones. It is this instrument type that is used today in various
areas of medical ultrasonics and, in particular, to characterize quantitatively the field structure
of medical diagnostic instruments [1] . With regard to other pressure sensor types, such as
those based on fibre optics, some of the requirements of this document are applicable to these
as well but others are not. If in the future these other "hydrophone" types gain more importance
in field measurement practice, their characteristics and calibration will be dealt with in a future
edition of IEC 62127-2 or in a separate part of IEC 62127.
NOTE 1 This document covers the ultrasonic frequency range, from 50 kHz to an upper frequency of 100 MHz.
Not all techniques described are applicable to the full frequency range. Standards dealing with hydrophone
properties (IEC 62127-3) and hydrophone use (IEC 62127-1) are being maintained in parallel. This will eventually
lead to unified standards covering the whole field of practical hydrophone application.
NOTE 2 Hydrophone calibration in the lower ultrasonic and in the underwater sound frequency range is particularly
addressed in the IEC 60565 series [2],[3].

___________
Numbers in square brackets refer to the Bibliography.

IEC 62127-2:2025 © IEC 2025 – 11 –
ULTRASONICS – HYDROPHONES –
Part 2: Calibration for ultrasonic fields

1 Scope
This part of IEC 62127 specifies:
• absolute hydrophone calibration methods;
• relative (comparative) hydrophone calibration methods.
Recommendations and references to accepted literature are made for the various relative and
absolute calibration methods in
...