SIST EN IEC 62127-3:2023

SLOVENSKI STANDARD
01-april-2023
Ultrazvok - Hidrofoni - 3. del: Lastnosti hidrofonov za ultrazvočna polja (IEC 62127-
3:2022)
Ultrasonics - Hydrophones - Part 3: Properties of hydrophones for ultrasonic fields (IEC
62127-3:2022)
Ultraschall - Hydrophone - Teil 3: Eigenschaften von Hydrophonen zur Verwendung in
Ultraschallfeldern (IEC 62127-3:2022)
Ultrasons - Hydrophones - Partie 3: Propriétés des hydrophones pour les champs
ultrasoniques (IEC 62127-3:2022)
Ta slovenski standard je istoveten z: EN IEC 62127-3:2023
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 62127-3

NORME EUROPÉENNE
EUROPÄISCHE NORM January 2023
ICS 17.140.50 Supersedes EN 62127-3:2007; EN 62127-3:2007/A1:2013
English Version
Ultrasonics - Hydrophones - Part 3: Properties of hydrophones
for ultrasonic fields
(IEC 62127-3:2022)
Ultrasons - Hydrophones - Partie 3: Propriétés des Ultraschall - Hydrophone - Teil 3: Eigenschaften von
hydrophones pour les champs ultrasoniques Hydrophonen zur Verwendung in Ultraschallfeldern
(IEC 62127-3:2022) (IEC 62127-3:2022)
This European Standard was approved by CENELEC on 2023-01-23. 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
© 2023 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 62127-3:2023 E

European foreword
The text of document 87/818/FDIS, future edition 2 of IEC 62127-3, prepared by IEC/TC 87
"Ultrasonics" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2023-10-23
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2026-01-23
document have to be withdrawn
This document supersedes EN 62127-3:2007 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 62127-3:2022 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 standard indicated:
IEC 60565-1 NOTE Approved as EN IEC 60565-1
IEC 60565-2 NOTE Approved as EN IEC 60565-2
Annex A
(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.cenelec.eu.
Publication Year Title EN/HD Year
IEC 62127-1 - Ultrasonics - Hydrophones - Part 1: EN IEC 62127-1 -
Measurement and characterization of
medical ultrasonic fields
IEC 62127-2 - Ultrasonics - Hydrophones - Part 2: EN 62127-2 -
Calibration for ultrasonic fields up to 40
MHz
IEC 62127-3 ®
Edition 2.0 2022-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Ultrasonics – Hydrophones –
Part 3: Properties of hydrophones for ultrasonic fields

Ultrasons – Hydrophones –
Partie 3: Propriétés des hydrophones pour les champs ultrasoniques

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.140.50 ISBN 978-2-8322-6210-8

– 2 – IEC 62127-3:2022 © IEC 2022
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms, definitions and symbols. 7
4 List of symbols . 11
5 Hydrophone characteristics . 11
5.1 General . 11
5.2 Basic information . 11
5.3 Sensitivity . 12
5.4 Frequency response . 13
5.4.1 Stated frequency band . 13
5.4.2 Frequency dependence . 13
5.5 Directional response . 13
5.5.1 General . 13
5.5.2 Determination of the directional response . 13
5.5.3 Symmetry of directional response . 14
5.6 Effective hydrophone size . 15
5.6.1 General . 15
5.6.2 Model of directional response . 15
5.6.3 Fitting of experimental response to theoretical predictions . 16
5.7 Dynamic range, linearity and electromagnetic interference . 16
5.8 Electric output characteristics . 17
5.8.1 Hydrophone without pre-amplifier . 17
5.8.2 Hydrophone assembly . 18
5.8.3 Output lead configuration . 18
5.9 Environmental aspects . 18
5.9.1 Temperature range . 18
5.9.2 Water tightness . 18
5.9.3 Water properties and incompatible materials . 18
5.9.4 Exposed material . 18
5.10 Guidance manual . 19
5.11 List of hydrophone characteristics . 19
Annex A (informative) Examples of information on hydrophone properties . 20
A.1 General . 20
A.2 Basic information . 20
A.3 Sensitivity and frequency response . 20
A.4 Directional response . 23
A.5 Effective dimension . 23
A.6 Dynamic range, linearity and electromagnetic interference . 25
A.6.1 Lower dynamic limit . 25
A.6.2 Upper dynamic limit . 25
A.7 Electric output characteristics . 25
A.8 Environmental aspects . 25
Annex B (informative) Rationale . 27

IEC 62127-3:2022 © IEC 2022 – 3 –
B.1 General . 27
B.2 Changes to the determination of directional response . 27
B.3 Changes to the determination of effective radius . 27
Annex C (informative) Membrane hydrophone directivity model . 29
C.1 General . 29
C.2 Details of model . 29
Bibliography . 30

Figure A.1 – Frequency response of 0,2 mm needle hydrophone in the range 1 MHz to
40 MHz . 21
Figure A.2 – Frequency response of 0,2 mm needle hydrophone in the range 100 kHz
to 1 MHz . 22
Figure A.3 – Directional response of 0,2 mm needle hydrophone . 23
Figure A.4 – Effective radius of 0,2 mm needle hydrophone . 24
Figure A.5 – Comparison of modelled and experimentally derived directional response . 24

Table A.1 – Example of basic information for 0,2 mm needle hydrophone assembly . 20

– 4 – IEC 62127-3:2022 © IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ULTRASONICS – HYDROPHONES –
Part 3: Properties of hydrophones 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
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 itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
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.
IEC 62127-3 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 and
Amendment 1:2013. 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) Procedures to determine the effective hydrophone size have been changed according to the
rationale outlined in Annex B.
d) Requirements on the frequencies for which the effective hydrophone size shall be provided
have been changed to achieve practicality for increased frequency bands.
e) The new Annex B and Annex C have been added.

IEC 62127-3:2022 © IEC 2022 – 5 –
f) Annex A has been updated to reflect the changes of the normative parts.
The text of this International Standard is based on the following documents:
Draft Report on voting
87/818/FDIS 87/824/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 Words 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,
• replaced by a revised edition, or
• amended.
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.

– 6 – IEC 62127-3:2022 © IEC 2022
INTRODUCTION
The spatial and temporal distribution of acoustic pressure in an ultrasonic field in a liquid
medium is commonly determined using miniature ultrasonic hydrophones. The properties of
these hydrophones have been dealt with in a number of IEC standards in various aspects. The
purpose of this document is to bring together all these specifications and to establish a common
standard on the properties of ultrasonic hydrophones. The main hydrophone application in
this context is the measurement of ultrasonic fields emitted by medical diagnostic equipment in
water. Other medical applications are field measurements for therapy equipment such as that
used in lithotripsy, high-intensity focused ultrasound (HIFU) and physiotherapy. Hydrophones
are also used extensively in non-medical applications for both product development and quality
control including:
– mapping of the ultrasound field within ultrasonic cleaning baths;
– characterization of acoustic fields used in transmission measurement systems
(e.g. ultrasonic spectrometers, ultrasonic attenuation meters and velocimeters);
– characterization of acoustic fields used in reflection measurement systems (e.g. Doppler
flowmeters).
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 ultrasonics and, in particular, to quantitatively characterize the field structure of
medical diagnostic instruments. 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 properties will have to be dealt with in a revised version of
this document or in a separate one.
Underwater hydrophones as covered by IEC 60500, IEC 60565-1, and IEC 60565-2 are not
included in this document, although there is an overlap in the frequency ranges. Underwater
hydrophones are used in natural waters, even in the ocean, and this leads to different technical
concepts and requirements. In addition, the main direction of acoustic incidence in underwater
applications is at various angles and often at right angles to the hydrophone axis, whereas in
this document it is assumed that the main direction of acoustic incidence is in the direction of
the hydrophone axis.
Historically, ultrasonic hydrophones were used almost exclusively as amplitude sensors.
However, the complex-valued nature of a hydrophone’s system response function is well
understood and IEC 62127-1:2022 makes use of this within the deconvolution procedures it
contains. In this document, requirements are specified for the amplitude aspect of the
hydrophone sensitivity and recommendations are provided for the phase aspect which can be
derived either via calibration, or via calculation methods that are discussed in
IEC 62127-1:2022.
IEC 62127-3:2022 © IEC 2022 – 7 –
ULTRASONICS – HYDROPHONES –
Part 3: Properties of hydrophones for ultrasonic fields

1 Scope
This part of IEC 62127 specifies relevant hydrophone characteristics.
This document is applicable to:
– hydrophones employing piezoelectric sensor elements, designed to measure the pulsed
and continuous wave ultrasonic fields generated by ultrasonic equipment;
– hydrophones used for measurements made in water;
– hydrophones with or without an associated pre-amplifier.
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 62127-1, Ultrasonics – Hydrophones – Part 1: Measurement and characterization of
medical ultrasonic fields
IEC 62127-2, Ultrasonics – Hydrophones – Part 2: Calibration for ultrasonic fields up to 40 MHz
3 Terms, definitions and symbols
For the purposes of this document, the terms and definitions given in IEC 62127-1, IEC 62127-2
and the following 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 or tone-burst, or one or more cycles in a continuous wave
Note 1 to entry: Temporal waveform is a representation (e.g. oscilloscope presentation or formula) of the
instantaneous acoustic pressure.
[SOURCE: IEC 62127-1:2022, 3.1]

– 8 – IEC 62127-3:2022 © IEC 2022
3.2
directional response
description of the response of a hydrophone, as a function of direction of propagation of the
incident plane sound wave, in a specified plane through the reference centre and at a specified
frequency
Note 1 to entry: Although directional response is a complex-valued function, it is generally the modulus of
directional response that is of most interest and this is commonly presented graphically.
[SOURCE: IEC 60565:2006, 3.5, modified – In the definition, ", generally presented
graphically," has been deleted; "electro-acoustic transducer" has been replaced by
"hydrophone"; and "radiated or incident sound" has been replaced by "incident plane sound
wave,".]
3.3
effective hydrophone size
a
h
size of a theoretical receiver hydrophone that has a predicted directional response function
with an angular width equal to the observed angular width
Note 1 to entry: The size is usually a function of frequency. For representative experimental data, see [1].
Note 2 to entry: The effective hydrophone size is expressed in metres (m).
Note 3 to entry: For hydrophones with a circular geometry, the effective hydrophone size is a radius.
Note 4 to entry: For hydrophones with a rectangular geometry, the effective hydrophone size is the half of the
largest value of the length or width.
[SOURCE: IEC 62127-1:2022, 3.20]
3.4
electric load impedance
Z
L
complex electric input impedance (consisting of a real and an imaginary part) to which the
hydrophone unit output cable is connected or is intended to be connected
Note 1 to entry: The electric load impedance is expressed in ohms (Ω).
[SOURCE: IEC 62127-1:2022, 3.22]
3.5
end-of-cable
relating to the end of the
integral output cable
3.6
end-of-cable
relating to the output
connector firmly connected with the hydrophone or hydrophone assembly and not to an extra
cable
3.7
end-of-cable loaded sensitivity
M (f)
L
quotient of the Fourier transformed hydrophone
voltage-time signal (u (t)) at the end of any integral cable or output connector of a
L
hydrophone or hydrophone assembly, when connected to a specified electric load
impedance, to the Fourier transformed acoustic pulse waveform (p(t)) in the undisturbed

IEC 62127-3:2022 © IEC 2022 – 9 –
free field of a plane wave in the position of the reference centre of the hydrophone if the
hydrophone were removed
 ut
()
( )
L
Mf( )=
(1)
L
 pt
( ())
Note 1 to entry: The end-of-cable loaded sensitivity is a complex-valued parameter. Its modulus is expressed in
units of volt per pascal (V/Pa), its phase angle is expressed in degrees, and represents the phase difference between
the electrical voltage and the sound pressure.
3.8
end-of-cable open-circuit sensitivity
M (f)
c
quotient of the Fourier transformed hydrophone open-circuit voltage-time
(u (t)) at the end of any integral cable or output connector of a hydrophone to the
signal
c
Fourier transformed acoustic pulse waveform (p(t)) in the undisturbed free field of a plane
wave in the position of the reference centre of the hydrophone if the hydrophone were
removed
 ut
( ())
c
Mf =
( ) (2)
c
 pt
()
( )
Note 1 to entry: The end-of-cable open-circuit sensitivity is a complex-valued parameter. Its modulus is
expressed in units of volt per pascal (V/Pa), its phase angle is expressed in degrees, and represents the phase
difference between the electrical voltage and the sound pressure.
3.9
end-of-cable loaded sensitivity level
Lf
( )
M
L
twenty times the logarithm to the base 10 of the
quotient of the modulus of the end-of-cable loaded sensitivity |M (f)| to a reference sensitivity
L
M
ref
M ( f)
L
Lf = 20log dB (3)
( )
M 10
L
M
ref
Note 1 to entry: Commonly used values of the reference sensitivity M are 1 V/µPa or 1 V/Pa.
ref
Note 2 to entry: The end-of-cable loaded sensitivity level is expressed in decibels (dB).
3.10
free field
sound field in a homogeneous and isotropic medium in which the effects of boundaries are
negligible
[SOURCE: IEC 60565:2006, 3.13]

– 10 – IEC 62127-3:2022 © IEC 2022
3.11
hydrophone geometrical size
geometrical size of a hydrophone active element
a
g
size defined by the lateral extents of the active element of a hydrophone
Note 1 to entry: The hydrophone geometrical size is expressed in metres (m).
Note 2 to entry: For hydrophones with a circular geometry, the hydrophone geometrical size is a radius.
Note 3 to entry: For hydrophones with a rectangular geometry, the hydrophone geometrical size is a half of the
largest value of the length or width.
3.12
hydrophone
transducer that produces electric signals in response to pressure fluctuations in water
[SOURCE: IEC 60050-801:2021, 801-32-26]
3.13
hydrophone assembly
combination of hydrophone and hydrophone pre-amplifier
3.14
hydrophone axis
nominal symmetry axis of the hydrophone active element
Note 1 to entry: Unless stated otherwise (explicitly and quantitatively) by the manufacturer, it is understood for the
purposes of this document that this is given by the apparent geometrical symmetry axis of the hydrophone.
3.15
hydrophone pre-amplifier
active electronic device connected to, or to be connected to, a particular hydrophone and
reducing its output impedance
Note 1 to entry: A hydrophone pre-amplifier requires a supply voltage (or supply voltages).
Note 2 to entry: The hydrophone pre-amplifier may have a forward voltage transmission factor of less than one,
i.e. it need not necessarily be a voltage amplifier in the strict sense.
3.16
reference centre
point on or near a hydrophone about which its acoustic receiving sensitivity is defined
Note 1 to entry: Unless stated otherwise (explicitly and quantitatively) by the manufacturer, it is understood for the
purposes of this document that this is given by the geometrical centre of the front surface of the hydrophone active
element.
[SOURCE: IEC 60565:2006, 3.25, modified – In the definition, "transducer" has been replaced
by "hydrophone" and "transmitting responses" has been omitted. The note has been replaced.]
3.17
uncertainty
parameter, associated with the result of a measurement, that characterizes the dispersion of
the values that could reasonably be attributed to the measurand
Note 1 to entry: See ISO/IEC Guide 98-3:2008 [2], 2.2.3.
[SOURCE: IEC 62127-1:2022, 3.92]

IEC 62127-3:2022 © IEC 2022 – 11 –
4 List of symbols
a hydrophone geometrical size
g
a effective hydrophone size
h
c speed of sound in a medium
D model function used during the determination of effective hydrophone size from a
H
measured directional response of a hydrophone
f frequency
k wavenumber, equal to 2π/λ
Lf
( )
end-of-cable loaded sensitivity level
M
L
M general symbol for the complex hydrophone sensitivity, M = M being its modulus
and arg(M) being its argument (equal to phase angle)
M end-of-cable open-circuit sensitivity
c
M end-of-cable loaded sensitivity
L
Z complex electric output impedance of a hydrophone or hydrophone assembly
h
Z electric load impedance
L
θ angle of incidence of an ultrasonic wave with respect to the hydrophone axis
5 Hydrophone characteristics
5.1 General
For a full characterization of the hydrophone performance in the frequency range of this
document, the following information is required. Examples of information on hydrophone
characteristics are provided in Annex A.
NOTE Determination methods are covered in IEC 62127-2.
5.2 Basic information
The following shall be briefly stated:
– the basic physical principles of the transduction process, the type of sensor material
involved, the form and geometrical dimensions (diameter, thickness) of the hydrophone
active element and the needle diameter in case of a needle hydrophone;
– the configuration and design of the hydrophone;
– whether or not a pre-amplifier is associated with the hydrophone; if the pre-amplifier can
be disconnected from the hydrophone, clear information shall be given as to which pre-
amplifier type belongs to which hydrophone type;
– the nominal direction of ultrasonic incidence in relation to the hydrophone.
NOTE The last point is important, as it has been found in the literature [3] that even with membrane hydrophones,
the response can change upon reversal of the ultrasonic propagation direction in relation to the hydrophone.
The following should be briefly stated:
– the lateral and thickness dimensions of the hydrophone active element;
– the frequency of the fundamental thickness resonance of the hydrophone active element;
– the size and mass of the hydrophone;
___________
Numbers in square brackets refer to the Bibliography.

– 12 – IEC 62127-3:2022 © IEC 2022
– the recommended directional response model (see 5.6.2) appropriate for the hydrophone;
– in the case of a membrane hydrophone, the acoustic reflection and transmission factor
(preferably as a function of frequency);
– information on preamplifier roll-off at low frequencies outside the hydrophone calibration
range, if applicable, to support appropriate calibration data extrapolation in accordance with
IEC 62127-1:2022.
General note relating to 5.3 and 5.4: if phase information is available, the phase angle (which
equals the argument of the complex hydrophone sensitivity) should be stated in addition to the
sensitivity (which equals the modulus of the complex hydrophone sensitivity), as well as the
frequency dependence of the phase angle in addition to the frequency dependence of the
sensitivity.
5.3 Sensitivity
The modulus of the end-of-cable sensitivity of the hydrophone or hydrophone assembly shall
be stated in units of volt per pascal (V/Pa) or in decimal submultiples, or as a logarithmic level
in decibels (dB) with reference to a stated sensitivity value.
NOTE 1 Refer to 3.9 regarding the definition of the end-of-cable loaded sensitivity level.
If a pre-amplifier contributes to the sensitivity value given, this shall be stated.
It shall be stated whether the sensitivity value given is understood as the end-of-cable open-
circuit sensitivity or as the end-of-cable loaded sensitivity. In the latter case, the relevant
electric loading conditions shall be stated, i.e. the electric load impedance, in order to obtain
the stated sensitivity.
The uncertainty of the stated sensitivity shall be given.
The frequency interval over which the sensitivity is given and over which the uncertainty
applies shall be stated. For the purposes of this document, sensitivity and uncertainty values
may be given separately for several frequency intervals.
The methods by which the sensitivity and its uncertainty have been obtained shall be
described.
The temperature dependence of the sensitivity shall be given. The hydrophone sensitivity shall
be stated as a function of the water temperature, at least over the temperature range 19 °C to
25 °C, or the particular water temperature to which the stated sensitivity relates shall be stated
together with the temperature coefficient of the sensitivity.
A recommended calibration period shall be provided in the instructions for use. This
recommendation applies unless otherwise stated by specific device application standards.
NOTE 2 A calibration period of one year will be appropriate in most cases.
The reference centre shall be stated if the sensitivity does not relate to the geometrical centre
of the front surface of the hydrophone active element.
NOTE 3 This is particularly important for any phase considerations.
The direction of acoustic incidence shall be stated if the sensitivity does not relate to an
incidence in the direction of the hydrophone axis.

IEC 62127-3:2022 © IEC 2022 – 13 –
5.4 Frequency response
5.4.1 Stated frequency band
The frequency band claimed for the hydrophone or hydrophone assembly shall be stated by
giving the lower frequency limit and the upper frequency limit. The modulus of the end-of-cable
sensitivity of the hydrophone or hydrophone assembly shall be constant over the stated
frequency band with a tolerance which shall also be stated.
5.4.2 Frequency dependence
The modulus of the end-of-cable sensitivity or sensitivity level of the hydrophone or
hydrophone assembly as a function of frequency shall be stated either graphically or as a list
of values and over a frequency range containing at least the frequency band claimed under
5.4.1. If it is given as a list of values or as discrete points in a graph, the frequency distance
between adjacent points should be low enough so that all important details of the frequency
dependence are shown and the sensitivity level does not vary by more than ±1 dB between
adjacent points.
The frequency response may be given in terms of absolute sensitivity values or in a relative
representation, relative with reference to the absolute sensitivity of the hydrophone or
hydrophone assembly at a certain frequency. In the case of the relative representation, the
reference sensitivity and the frequency to which it applies shall be stated.
The phase of the end-of-cable sensitivity may be given as a function of frequency either
graphically or as a list of values.
The statement of the frequency response shall refer to the same conditions (i.e. loaded or open-
circuit output of the hydrophone or hydrophone assembly) as the sensitivity statement in
accordance with 5.3.
If the uncertainty of the sensitivity values in the frequency response representation differs from
the uncertainty assessment of 5.3, this shall be clearly stated and the new or additional
uncertainty shall be given.
If the frequency response is given as a list of absolute sensitivity values (end-of-cable, loaded
or open-circuit), the sensitivity statement in accordance with 5.3 may be omitted.
NOTE 1 The frequency response can depend on the electric load conditions.
NOTE 2 If, in a practical application, the hydrophone or hydrophone assembly is used with subsequent electronic
components such as an amplifier, oscilloscope, etc., the frequency response of the whole system will also be, of
course, influenced by the frequency response of these additional components.
5.5 Directional response
5.5.1 General
Directional response, and quantities derived from it, are subject to numerous changes relative
to the first edition of IEC 62127-3. Details for the rationale behind these changes can be found
in Annex B.
5.5.2 Determination of the directional response
The directional response of the hydrophone shall be stated at a minimum of three frequencies
where the lowest and highest frequencies are as widely separated as possible.
– The lowest frequency at which the directional response of the hydrophone has been
determined should be the lower limit of the frequency band claimed under 5.4.1. If not, the
reason(s) for variation shall be stated.

– 14 – IEC 62127-3:2022 © IEC 2022
– The highest frequency at which the directional response of the hydrophone has been
determined should be the upper limit of the frequency band claimed under 5.4.1. If not, the
reason(s) for variation shall be stated.
NOTE Experimental determination of directional response becomes increasingly challenging as frequency
increases. Consequently, the highest frequency at which it is practical to determine the directional response
of the hydrophone can be lower than the upper frequency band claimed under 5.4.1. However, effective
hydrophone size becomes asymptotic as frequency increases. Therefore, it is likely that there is negligible
variation in effective hydrophone size at frequencies above the highest frequency at which directional
response has been evaluated.
– The midpoint frequency that is within ±15 % of the geometric mean of the lowest and highest
frequencies at which directional response of the hydrophone has been determined is the
third frequency at which the directional response shall be stated. If not, the reason(s) for
variation shall be stated.
– If the hydrophone has a fundamental thickness resonance within range of the lowest and
highest frequencies in this subclause 5.5.2, the directional response at this frequency shall
also be stated. If not, the reason(s) for variation shall be stated.
The directional response should be measured by rotating the hydrophone about an axis,
which passes through the reference centre and which is perpendicular to the hydrophone
axis, at least from −35° up to +35° (with the hydrophone axis as reference), or at least from
the first left-hand minimum to the first right-hand minimum, whichever of the angular spans is
the smaller. If this method is used, this shall be done twice, namely about two rotational axes
perpendicular to each other. If, in the plane perpendicular to its axis, a hydrophone has a
certain distinct direction (for example that of the electric leads in the case of a membrane
hydrophone), the rotational axes should be in this direction and perpendicular to it. If the active
element is non-circular, one of the rotational axes shall be in the direction of the largest
dimension. The directions of the rotational axes shall be identified on the hydrophone using a
mark or in the accompanying literature.
The angular increment shall be chosen to ensure that the variation between adjacent points in
the directional response is not more than 1 dB.
The measurement of the directional response shall be carried out in a quasi-planar wave
ultrasonic field.
If the active element is irregular in shape, or has more than two symmetry axes, the directional
response should be measured around additional axes.
Each of the resulting directional responses obtained from the measurements shall be stated.
5.5.3 Symmetry of directional response
If, in any of the directional response results obtained, the angle between the direction of
maximum response and the hydrophone axis is greater than one tenth of the angular
difference between the left-hand −6 dB direction and the right-hand −6 dB direction, this shall
be stated and the deviation-of-axis angle shall be given. The sensitivity level in the direction of
the hydrophone axis shall be not lower than the maximum in any other direction minus 2 dB.
The symmetry of any directional response should be such that if a normalized sensitivity level
of −6 dB occurs for some particular direction subtending a certain angle to the direction of
maximum sensitivity (0 dB), then the sensitivity level measured on the opposite side subtending
the same angle to the direction of maximum sensitivity shall be −6 dB ± 3 dB.
NOTE Problems in field measurement practice will arise if the direction of maximum hydrophone response varies
significantly with frequency.
IEC 62127-3:2022 © IEC 2022 – 15 –
5.6 Effective hydrophone size
5.6.1 General
From the directional response
...