IEC 62127-2:2025

Ultrasonics - Hydrophones - Part 2: Calibration for ultrasonic fields

IEC 62127-2:2025 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 the frequency range covered by this document.
This document is applicable to
- hydrophones used for measurements made in water and in the ultrasonic frequency range 50 kHz to 100 MHz;
- hydrophones employing piezoelectric sensor elements, designed to measure the pulsed wave and continuous wave ultrasonic fields generated by ultrasonic equipment;
- hydrophones with or without a hydrophone pre-amplifier.
IEC 62127-2:2025 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;
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.

Ultrasons - Hydrophones - Partie 2: Etalonnage des champs ultrasoniques

L'IEC 60601-2-40:2025 s'applique à la SECURITE DE BASE et aux PERFORMANCES ESSENTIELLES des ELECTROMYOGRAPHES et des APPAREILS A POTENTIEL EVOQUE, désignés ci-après sous le terme APPAREILS EM.
Si un article ou un paragraphe est spécifiquement destiné à être applicable uniquement aux APPAREILS EM, ou uniquement aux SYSTEMES EM, le titre et le contenu de cet article ou de ce paragraphe l’indiquent. Si cela n’est pas le cas, l’article ou le paragraphe s’applique à la fois aux APPAREILS EM et aux SYSTEMES EM, selon le cas.
Les APPAREILS EM suivants sont exclus de la liste:
- APPAREILS EM destinés à une application thérapeutique;
- APPAREILS EM destinés à être utilisés avec les neurostimulateurs électriques transcutanés et les stimulateurs musculaires électriques (APPAREILS EM couverts par l'IEC 60601-2-10).
L'IEC 60601-2-40:2024 annule et remplace la deuxième édition parue en 2016. Cette édition constitue une révision technique.
Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) des exigences relatives aux stimulateurs à tension constante ont été ajoutées;
b) des exigences relatives aux STIMULATEURS VISUELS ont été clarifiées.
L'IEC 62127-2:2024 spécifie:
- les méthodes d'étalonnage absolues de l'hydrophone;
- les méthodes d'étalonnage (comparatives) relatives de l'hydrophone.
Des recommandations et des références à des documents validés sont indiquées pour les différentes méthodes d'étalonnage relatif et absolu dans la plage de fréquences couverte par le présent document.
Le présent document s'applique:
- aux hydrophones utilisés pour des mesurages réalisés dans l'eau et dans la plage de fréquences ultrasonores comprise entre 50 kHz et 100 MHz;
- aux hydrophones qui utilisent des capteurs piézoélectriques, conçus pour mesurer les champs ultrasoniques à ondes pulsées et entretenues, générés par les équipements à ultrasons;
- aux hydrophones avec ou sans préamplificateur d'hydrophone.
L'IEC 62127-2:2025 annule et remplace la première édition parue en 2007, l'Amendement 1:2013 et l'Amendement 2:2017. Cette édition constitue une révision technique.
Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) la limite de fréquence supérieure de 40 MHz a été supprimée;
b) les définitions de la sensibilité de l'hydrophone ont été modifiées afin de reconnaître les sensibilités comme des grandeurs à valeur complexe;
c) les procédures de mesure de la réponse directionnelle et de détermination de la taille efficace ont été mises à jour au 12.5.1 pour s'aligner sur les modifications récentes de l'IEC 62127-3;
d) l'Annexe F a été modifiée pour inclure une technique d'étalonnage pour l'étalonnage à haute fréquence à valeurs complexes;
e) la description de la méthode par réciprocité de l'Annexe K a été élargie pour comprendre également les transducteurs à focalisation.

General Information

• Status: Published
• Publication Date: 06-Jan-2025
• ICS: 17.140.50 - Electroacoustics
• Technical Committee: TC 87 - Ultrasonics
• Drafting Committee: WG 8 - TC 87/WG 8
• Current Stage: PPUB - Publication issued
• Start Date: 07-Jan-2025
• Completion Date: 13-Dec-2024

Relations

• Revises: IEC 62127-2:2007/COR1:2008 - Corrigendum 1 - Ultrasonics - Hydrophones - Part 2: Calibration for ultrasonic fields up to 40 MHz
• Effective Date: 05-Sep-2023
• Revises: IEC 62127-2:2007/AMD1:2013 - Amendment 1 - Ultrasonics - Hydrophones - Part 2: Calibration for ultrasonic fields up to 40 MHz
• Effective Date: 05-Sep-2023
• Revises: IEC 62127-2:2007 - Ultrasonics - Hydrophones - Part 2: Calibration for ultrasonic fields up to 40 MHz
• Effective Date: 05-Sep-2023
• Revises: IEC 62127-2:2007/AMD2:2017 - Amendment 2 - Ultrasonics - Hydrophones - Part 2: Calibration for ultrasonic fields up to 40 MHz
• Effective Date: 05-Sep-2023

Overview

IEC 62127-2:2025 is the latest international standard developed by the International Electrotechnical Commission (IEC) focusing on ultrasonics hydrophone calibration for ultrasonic fields. This standard is a comprehensive technical revision of previous editions and amendments, providing up-to-date calibration methodologies that apply to hydrophones used in water-based ultrasonic measurements. It covers both absolute and relative calibration methods within the ultrasonic frequency range of 50 kHz to 100 MHz.

This standard specifically addresses hydrophones equipped with piezoelectric sensor elements, designed to measure pulsed or continuous ultrasonic waves. It applies to hydrophones with or without pre-amplifiers, making it relevant for a wide range of ultrasonic measurement equipment.

Key Topics

• Calibration Methods
  IEC 62127-2:2025 specifies detailed procedures for both absolute calibration, which establishes a direct reference measurement of hydrophone sensitivity, and relative (comparative) calibration, which compares a hydrophone against a calibrated standard.

• Frequency Range Extension
  The updated standard removes the previous upper frequency limit of 40 MHz, extending effective calibration and measurement capabilities up to 100 MHz. This broad frequency coverage enables applications in advanced ultrasonic testing and research.

• Complex-Valued Sensitivity
  Sensitivity definitions now recognize hydrophone sensitivity as a complex quantity, reflecting both magnitude and phase, essential for accurate characterization of ultrasonic fields.

• Directional Response and Effective Size
  Updated procedures for measuring the hydrophone directional response and its effective size ensure precise field characterization, enhancing measurement reliability.

• Reciprocity Calibration Methods
  Refinements include enhanced descriptions for the reciprocity calibration method, extended to focus on transducers that can concentrate ultrasonic energy, improving calibration accuracy for high-intensity ultrasonic fields.

Applications

IEC 62127-2:2025 is critical in ensuring reliable and accurate ultrasonic field measurements used in multiple applications:

• Medical Ultrasound Equipment Testing
  Calibrated hydrophones are essential for validating the performance and safety of diagnostic and therapeutic ultrasound devices.

• Non-Destructive Testing (NDT)
  Precise hydrophone calibration supports the detection and characterization of flaws in materials through ultrasonic inspection.

• Underwater Acoustics and Sonar
  Accurate ultrasonic field measurements contribute to sonar system calibration and underwater communication technologies.

• Industrial Ultrasonics
  Applications include precise measurement for cleaning, welding, and processing equipment involving high-frequency ultrasonic fields.

• Research and Development
  Enables ultrasonics researchers to carry out high-precision experiments benefiting from standardized calibration procedures and calibrated instrumentation.

Related Standards

• IEC 62127-1 - General requirements for hydrophones used in ultrasonic measurements.
• IEC 62127-3 - Methods for measuring directional response of hydrophones, which align closely with updates introduced in IEC 62127-2:2025.
• IEC 61161 - Ultrasonic field characterization methods, providing complementary techniques supporting hydrophone calibration.
• ISO/IEC 17025 - General requirements for the competence of testing and calibration laboratories, relevant for labs implementing IEC 62127-2 procedures.

---

Implementing IEC 62127-2:2025 ensures that ultrasonic measurement systems using hydrophones deliver high accuracy, traceability, and repeatability of results, meeting the rigorous demands of medical, industrial, and research applications worldwide. This standard serves as a key reference for engineers, calibration laboratories, and instrument manufacturers aiming for the highest standards in ultrasonic hydrophone calibration.

Standards Content (Sample)

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
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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

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

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
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

– 8 – IEC 62127-2:2025 © IEC 2025
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ULTRASONICS – HYDROPHONES –
Part 2: Calibration for ultrasonic fields

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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;

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.

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 the frequency range covered by this document.
This document is applicable to
• hydrophones used for measurements made in water and in the ultrasonic frequency range
50 kHz to 100 MHz;
NOTE 1 Although some physiotherapy medical applications of medical ultrasound are developing which operate
in the frequency range 40 kHz to 100 kHz, the primary frequency range of diagnostic imaging remains above
2 MHz. It has recently been established that, even in the latter case, the hydrophone response at substantially
lower frequencies can influence measurements made of key acoustic parameters [4].
NOTE 2 Calibration methods for underwater acoustics hydrophones applicable in the frequency range from
200 Hz to 1 MHz are available in IEC 60565-1 [2], and for frequencies from 0,01 Hz to several kilohertz in
IEC 60565-2 [3].
• hydrophones employing piezoelectric sensor elements, designed to measure the pulsed
wave and continuous wave ultrasonic fields generated by ultrasonic equipment;
NOTE 3 Some hydrophones can have non-cir
...