FOREWORD

INTRODUCTION

1 Scope

2 Normative references

3 Terms and definitions

4 List of symbols

5 Overview of calibration procedures

5.1 Principles

5.2 Summary of calibration procedures

5.3 Reporting of results

5.4 Recommended calibration periods

6 Generic requirements of a hydrophone calibration system

6.1 Mechanical positioning

6.1.1 General

6.1.2 Accuracy of the axial hydrophone position

6.1.3 Accuracy of the lateral hydrophone position

6.2 Temperature measurements and temperature stability

6.3 Hydrophone size

6.4 Measurement vessel and water properties

6.5 Measurement of output voltage

7 Electrical considerations

7.1 Signal type

7.2 Earthing

7.3 Measurement of hydrophone output voltage

7.3.1 General

7.3.2 Electrical loading by measuring instrument

7.3.3 Electrical loading by extension cables

7.3.4 Noise

7.3.5 Cross-talk (radio-frequency rf pick-up) and acoustic interference

7.3.6 Integral hydrophone pre-amplifiers

8 Preparation of hydrophones

8.1 General

8.2 Wetting

8.3 Hydrophone support

8.4 Influence of cable

9 Free field reciprocity calibration

9.1 General

9.2 Object

9.3 General principles

9.3.1 General

9.3.2 Three-transducer reciprocity calibration method

9.3.3 Self-reciprocity calibration method

9.3.4 Two-transducer reciprocity calibration method

9.4 Two-transducer reciprocity calibration method

9.4.1 General

9.4.2 Auxiliary transducers

9.4.3 Reflector

9.4.4 Measurement field

9.4.5 Reciprocity approach

9.4.6 Measurement procedure

10 Free field calibration by planar scanning

10.1 General

10.2 Object

10.3 General principle

10.4 Procedural requirements

10.4.1 Hydrophone scanning

10.4.2 Power measurement

10.4.3 Transducer mounting

10.4.4 Measurement conditions

10.4.5 Measurements

10.5 Corrections and sources of uncertainty

11 Free field calibration by optical interferometry

11.1 General

11.2 Principle

12 Calibration by comparison using a standard hydrophone

12.1 General

12.2 Object

12.3 Principle

12.4 Procedural requirements

12.4.1 Source transducer

12.4.2 Source transducer drive signal

12.4.3 Measurement system

12.5 Procedure

12.5.1 Measurements (Type I): determination of the directional response of a hydrophone

12.5.2 Measurements (Type II): calibration by comparison using a standard hydrophone

12.6 Maximum hydrophone size

Annex A (informative) Assessment of uncertainty in free field calibration of hydrophones

Annex B (informative) Behaviour of PVDF polymer sensors in high-intensity ultrasonic fields

Annex C (informative) Electrical loading corrections

Annex D (informative) Absolute calibration of hydrophones using the planar scanning technique

Annex E (informative) Properties of water

Annex F (informative) The absolute calibration of hydrophones by optical interferometry

Annex G (informative) Waveform concepts

Annex H (informative) Time delay spectrometry - Requirements and a brief review of the technique

Annex I (informative) Determination of the phase response of hydrophones

Annex J (informative) Maximum size considerations for the active element of a hydrophone

Annex K (informative) Two-transducer reciprocity calibration method

Bibliography

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IEC 62127-2:2025

Gulf StandardGSO IEC 62127-2:2026

GSO IEC 62127-2:2026Gulf Standard

GSO IEC 62127-2:2026

IEC 62127-2:2025

مواصفة قياسية خليجية

الموجات فوق الصوتية-السماعات المائية - (الهيدروفونات) - الجزء 2: معايرة مجالات الموجات فوق الصوتية

Gulf Standard

Ultrasonics - Hydrophones - Part 2: Calibration for ultrasonic fields

ICS:

17.140.50

English Language – اللغةالإنجليزيةEdition 1 – 14/04/2026 – 1 الطبعة

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إدارة التواصل، قسم إدارة المعرفة

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Gulf StandardGSO IEC 62127-2:2026

GSO IEC 62127-2:2026Gulf Standard

Gulf Foreword

GCC Standardization Organization (GSO) is a regional organization which consists of the national standardization bodies of GCC member states. One of GSO main functions is to issue gulf standards and technical regulations through specialized technical committees.

GSO Technical Council in its meeting number (62) held on 26/10/1447 H, which corresponds to 14/04/2026, has approved Gulf Standard GSO IEC 62127-2:2026 titled "Ultrasonics - Hydrophones - Part 2: Calibration for ultrasonic fields" in English language which was studied and adopted from International Electrotechnical Commission Standard IEC 62127-2:2025 without any technical modifications through the technical program of GSO Technical Committee for Metrology (TC04) in QATAR schedule .

تقديم خليجي

هيئة التقييس لدول مجلس التعاون لدول الخليج العربية هيئة إقليمية تضم في عضويتها أجهزة التقييس الوطنية في الدول الأعضاء ، ومن مهام الهيئة إعداد المواصفات القياسية واللوائح الفنية الخليجية بواسطة لجان فنية متخصصة.

قرر المجلس الفني لهيئة التقييس لدول مجلس التعاون لدول الخليج العربية في الاجتماع الـ (62) بتاريخ 1447/10/26 هـ ،الموافق 2026/04/14م اعتماد المواصفة القياسية الخليجية رقم GSO IEC 62127-2:2026 وعنوانها "الموجات فوق الصوتية-السماعات المائية - (الهيدروفونات) - الجزء 2: معايرة مجالات الموجات فوق الصوتية" باللغة الانجليزية التي تم دراستها وتبنيها عن اللجنة الدولية الكهروتقنية رقم IEC 62127-2:2025 بدون إدخال تعديلات فنية عليها ضمن برنامج عمل اللجنة الفنية الخليجية لمواصفات المقاييس (TC04) المدرجة في خطة دولة قطر .

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– –

IEC 62127-2:2025 ED2 © IEC 2025

Gulf StandardGSO IEC 62127-2:2026

GSO IEC 62127-2:2026Gulf Standard

IEC 62127-2

	INTERNATIONAL STANDARD	Edition 2.0 2025-01


	Ultrasonics – Hydrophones – Part 2: Calibration for ultrasonic fields

INTERNATIONAL

ELECTROTECHNICAL

COMMISSION

ICS 17.140.50ISBN 9782832700914

Warning! Make sure that you obtained this publication from an authorized distributor.

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GSO IEC 62127-2:2026Gulf Standard

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IEC 62127-2:2025 ED2 © IEC 2025

Gulf StandardGSO IEC 62127-2:2026

GSO IEC 62127-2:2026Gulf Standard

CONTENTS

FOREWORD

INTRODUCTION

1 Scope

2 Normative references

3 Terms and definitions

4 List of symbols

5 Overview of calibration procedures

5.1 Principles

5.2 Summary of calibration procedures

5.3 Reporting of results

5.4 Recommended calibration periods

6 Generic requirements of a hydrophone calibration system

6.1 Mechanical positioning

6.1.1 General

6.1.2 Accuracy of the axial hydrophone position

6.1.3 Accuracy of the lateral hydrophone position

6.2 Temperature measurements and temperature stability

6.3 Hydrophone size

6.4 Measurement vessel and water properties

6.5 Measurement of output voltage

7 Electrical considerations

7.1 Signal type

7.2 Earthing

7.3 Measurement of hydrophone output voltage

7.3.1 General

7.3.2 Electrical loading by measuring instrument

7.3.3 Electrical loading by extension cables

7.3.4 Noise

7.3.5 Cross-talk (radio-frequency rf pick-up) and acoustic interference

7.3.6 Integral hydrophone pre-amplifiers

8 Preparation of hydrophones

8.1 General

8.2 Wetting

8.3 Hydrophone support

8.4 Influence of cable

9 Free field reciprocity calibration

9.1 General

9.2 Object

9.3 General principles

9.3.1 General

9.3.2 Three-transducer reciprocity calibration method

9.3.3 Self-reciprocity calibration method

9.3.4 Two-transducer reciprocity calibration method

9.4 Two-transducer reciprocity calibration method

9.4.1 General

9.4.2 Auxiliary transducers

9.4.3 Reflector

9.4.4 Measurement field

9.4.5 Reciprocity approach

9.4.6 Measurement procedure

10 Free field calibration by planar scanning

10.1 General

10.2 Object

10.3 General principle

10.4 Procedural requirements

10.4.1 Hydrophone scanning

10.4.2 Power measurement

10.4.3 Transducer mounting

10.4.4 Measurement conditions

10.4.5 Measurements

10.5 Corrections and sources of uncertainty

11 Free field calibration by optical interferometry

11.1 General

11.2 Principle

12 Calibration by comparison using a standard hydrophone

12.1 General

12.2 Object

12.3 Principle

12.4 Procedural requirements

12.4.1 Source transducer

12.4.2 Source transducer drive signal

12.4.3 Measurement system

12.5 Procedure

12.5.1 Measurements (Type I): determination of the directional response of a hydrophone

12.5.2 Measurements (Type II): calibration by comparison using a standard hydrophone

12.6 Maximum hydrophone size

Annex A (informative) Assessment of uncertainty in free field calibration of hydrophones

Annex B (informative) Behaviour of PVDF polymer sensors in high-intensity ultrasonic fields

Annex C (informative) Electrical loading corrections

Annex D (informative) Absolute calibration of hydrophones using the planar scanning technique

Annex E (informative) Properties of water

Annex F (informative) The absolute calibration of hydrophones by optical interferometry

Annex G (informative) Waveform concepts

Annex H (informative) Time delay spectrometry - Requirements and a brief review of the technique

Annex I (informative) Determination of the phase response of hydrophones

Annex J (informative) Maximum size considerations for the active element of a hydrophone

Annex K (informative) Two-transducer reciprocity calibration method

Bibliography

INTERNATIONAL ELECTROTECHNICAL COMMISSION

International StandardIEC 62127-2:2025 ED2

Ultrasonics - Hydrophones - Part 2: Calibration for ultrasonic fields

FOREWORD

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.

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.

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.

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.

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.

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

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.

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.

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:

the upper frequency limit of 40 MHz has been removed;

hydrophone sensitivity definitions have been changed to recognize sensitivities as complex-valued quantities;

directional response measurement and effective size determination procedures have been updated in 12.5.1 to align with recent changes in IEC 62127-3;

Annex F has been amended to comprise a calibration technique for high-frequency complex-valued calibration;

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.

NOTETerms 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.

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]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 1This 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 2Hydrophone calibration in the lower ultrasonic and in the underwater sound frequency range is particularly addressed in the IEC 60565 series [2],[3].

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GSO IEC 62127-2:2026Gulf Standard

International StandardIEC 62127-2:2025 ED2

Ultrasonics - Hydrophones - Part 2: Calibration for ultrasonic fields

1Scope

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 1Although 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 2Calibration 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 3Some hydrophones can have non-circular active elements, arising from slight deviations from a circular structure caused, for example, by electrode structure; or, conversely, the active elements can actually be squares. It is important in these cases to pay special attention to the directional response and to the effective radii of the active element through various axes of rotation.

•

hydrophones with or without a hydrophone pre-amplifier.

2Normative 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 61161, Ultrasonics - Power measurement - Radiation force balances and performance requirements

IEC 61689, Ultrasonics - Physiotherapy systems - Field specifications and methods of measurement in the frequency range 0,5 MHz to 5 MHz

IEC 62127-1, Ultrasonics - Hydrophones - Part 1: Measurement and characterization of medical ultrasonic fields

IEC 62127-3:2022, Ultrasonics - Hydrophones - Part 3: Properties of hydrophones for ultrasonic fields

3Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 62127-1, IEC 62127-3 and the following apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

•

IEC Electropedia: available at https://www.electropedia.org/

•

ISO Online browsing platform: available at https://www.iso.org/obp

3.1

acoustic centre

point on or near a transducer from which the spherically divergent sound waves emitted by the transducer, and observable at remote points, appear to diverge

Note 1 to entry: This point is the boundary between the near field and the far field.

Note 2 to entry: In this region, the sound field has plane wave fronts changing to spherical wave fronts with divergence.

3.2

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

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 focal Fraunhofer 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, for example

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,

in cases where signal synchronization with the scanframe is not available the term pulse-pressure-squared integral may be replaced by temporal average intensity.

Note 3 to entry: See IEC 62127-1:2022, Figure 1.

[SOURCE: IEC 62127-1:2022, 3.8, modified - In the definition, "aperture" has been replaced with "surface".]

3.3

beam centrepoint

position determined by the intersection of two lines in the same beam area plane xy passing through the beamwidth midpoints of two orthogonal planes, xz and yz, perpendicular to their respective beamwidth lines

[SOURCE: IEC 62127-1:2022, 3.9]

3.4

beamwidth

w6, w12, w20

greatest distance between two points on a specified axis perpendicular to the beam axis where the pulse-pressure-squared integral falls below its maximum on the specified axis by a specified amount

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, for example

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,

in cases where signal synchronization with the scanframe is not available the term pulse-pressure-squared integral may be replaced by temporal average intensity.

Note 2 to entry: Commonly used beamwidths are specified at −6 dB, −12 dB and −20 dB levels below the maximum. The decibel calculation implies taking 10 times the logarithm of the ratios of the integrals.

Note 3 to entry: Beamwidth is expressed in metres (m).

[SOURCE: IEC 62127-1:2022, 3.11]

3.5

beamwidth midpoint

linear average of the location of the centres of beamwidths in a plane

Note 1 to entry: The average is taken over as many beamwidth levels as given in IEC 61828:2020, Clause C.2 and Table C.2.

[SOURCE: IEC 61828:2020 [5], 3.22]

3.6

beam centre

point in a plane in the far field, usually perpendicular to the beam axis, at which the spatial-peak temporal-peak acoustic pressure occurs

3.7

derived instantaneous intensity

quotient of squared instantaneous acoustic pressure and characteristic acoustic impedance of the medium at a particular instant in time at a particular point in an acoustic field

mml-m1

I (t) = \frac{p {(t)}^{2}}{ρ c}

(1)

where:

p(t)	is the instantaneous acoustic pressure;
ρ	is the density of the medium;
c	is the speed of sound in the medium.

Note 1 to entry: For measurement purposes referred to in this document, the derived instantaneous intensity is an approximation of the instantaneous intensity.

Note 2 to entry: Increased uncertainty is expected to be taken into account for measurements very close to the transducer.

Note 3 to entry: Derived instantaneous intensity is expressed in units of watt per metre squared (W/m2).

[SOURCE: IEC 62127-1:2022, 3.14]

3.8

diametrical beam scan

set of measurements of the hydrophone output voltage made while moving the hydrophone in a straight line passing through a point on the beam axis and in a direction normal to the beam axis

Note 1 to entry: The diametrical beam scan can extend to different distances on either side of the beam axis.

[SOURCE: IEC 62127-1:2022, 3.15]

3.9

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 62127-3:2022, 3.2]

3.10

effective hydrophone size

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 the function of frequency. For representative experimental data, see [9].

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 half the greatest value of the length or width.

[SOURCE: IEC 62127-1:2022, 3.20]

3.11

effective radius of a non-focusing ultrasonic transducer

radius of a perfect disc piston-like ultrasonic source transducer that has a predicted axial acoustic pressure distribution approximately equivalent to the observed axial acoustic pressure distribution over an axial distance until at least the last axial maximum has passed

Note 1 to entry: The effective radius of a non-focusing ultrasonic transducer is expressed in metres (m).

[SOURCE: IEC 62127-1:2022, 3.21]

3.12

effective wavelength

λeff

longitudinal speed of sound in the propagation medium divided by the acoustic-working frequency

Note 1 to entry: The effective wavelength is expressed in metres (m).

Note 2 to entry: : Application dependent definitions of the acoustic-working frequency are given in IEC 62127-1:2022.

[SOURCE: IEC 61828:2020 [5], 3.46, modified - Note 2 to entry has been added.]

3.13

electric load impedance

ẔL

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]

3.14

end-of-cable loaded sensitivity

mml-m3

{\underline{M}}_{L} (f)

<of a hydrophone or hydrophone assembly> quotient of the Fourier transformed hydrophone voltage-time signal F (uL (t )) at the end of any integral cable or output connector of a hydrophone or hydrophone-assembly, when connected to a specified electric load impedance, to the Fourier transformed acoustic pulse waveform F (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

mml-m2

{\underline{M}}_{L} (f) = \frac{F (u_{L} (t))}{F (p (t))}

(2)

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.

[SOURCE: IEC 62127-1:2022, 3.25]

3.15

end-of-cable loaded sensitivity level

LML(f)

<of a hydrophone or hydrophone assembly> twenty times the logarithm to the base 10 of the quotient of the modulus of the end-of-cable loaded sensitivity mml-m4

| {\underline{M}}_{L} (f) |

to a reference sensitivity Mref

mml-m5

L_{M_{L}} (f) = 20 {log}_{10} \frac{| {\underline{M}}_{L} (f) |}{M_{ref}} dB

(3)

Note 1 to entry: Commonly used values of the reference sensitivity Mref are 1 V/µPa or 1 V/Pa.

Note 2 to entry: The end-of-cable loaded sensitivity level is expressed in decibels (dB).

[SOURCE: IEC 62127-1:2022, 3.26]

3.16

end-of-cable open-circuit sensitivity

mml-m7

{\underline{M}}_{c} (f)

<of a hydrophone> quotient of the Fourier transformed hydrophone open-circuit voltage-time signal ℱ (uc (t)) at the end of any integral cable or output connector of a hydrophone to the Fourier transformed acoustic pulse waveform ℱ (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

mml-m6

{\underline{M}}_{c} (f) = \frac{F (u_{c} (t))}{F (p (t))}

(4)

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.

[SOURCE: IEC 62127-1:2022, 3.27]

3.17

external transducer surface

external transducer aperture

part of the surface of the ultrasonic transducer or ultrasonic transducer element group assembly that emits ultrasonic radiation into the propagation medium

Note 1 to entry: This surface is assumed to be accessible for measurements using a hydrophone in a chosen propagation medium (usually water).

Note 2 to entry: This surface is either directly in contact with the patient or is in contact with a water or liquid path to the patient.

Note 3 to entry: See IEC 61828:2020 [5], Figure B.5.

[SOURCE: IEC 61828:2020 [5], 3.52]

3.18

far field

region of the field where mml-m8

z > z_{T}

aligned along the beam axis for planar non-focusing transducers

Note 1 to entry: In the far field, the sound pressure appears to be spherically divergent from a point on or near the radiating surface. Hence, the pressure produced by the sound source is approximately inversely proportional to the distance from the source.

Note 2 to entry: The term "far field" is used in this document only in connection with non-focusing source transducers. For focusing transducers, a different terminology for the various parts of the transmitted field applies (see IEC 61828 [5]).

Note 3 to entry: If the shape of the transducer aperture produces several transition distances, the one furthest from the transducer is used.

[SOURCE: IEC 62127-1:2022, 3.30]

3.19

free field

sound field in a homogeneous and isotropic medium in which the effects of boundaries are negligible

[SOURCE: IEC 60565:2006, 3.13]

3.20

hydrophone

transducer that produces electric signals in response to pressure fluctuations in water

Note 1 to entry: A hydrophone is principally a passive device designed and built to respond to sound pressure.

Note 2 to entry: In some applications, a hydrophone is used as an active device to transmit sound.

[SOURCE: IEC 60050-801:2021 [6], 801-32-26]

3.21

hydrophone assembly

combination of hydrophone and hydrophone pre-amplifier

[SOURCE: IEC 62127-3:2022, 3.13]

3.22

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.

[SOURCE: IEC 62127-3:2022, 3.14]

3.23

hydrophone geometrical size

geometrical size of a hydrophone active element

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 the greater value of the length or width.

Note 4 to entry: For fibre optic hydrophones, the hydrophone geometrical size is the radius of the light spot at the tip of the fibre.

[SOURCE: IEC 62127-3:2022, 3.11, modified - Note 4 to entry has been added.]

3.24

hydrophone pre-amplifier

active electronic device connected to, or intended 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 can have a forward voltage transmission factor of less than one, i.e. it need not necessarily be a voltage amplifier in the strict sense.

[SOURCE: IEC 62127-3:2022, 3.15]

3.25

instantaneous acoustic pressure

p (t)

pressure at a particular instant in time and at a particular point in an acoustic field, minus the ambient pressure

Note 1 to entry: Instantaneous acoustic pressure is expressed in pascals (Pa).

[SOURCE: IEC 60050-802:2011 [7], 802-01-03, modified - Note 1 to entry has been added.]

3.26

instantaneous intensity

I (t)

acoustic energy transmitted per unit time in the direction of acoustic wave propagation per unit area normal to this direction at a particular instant in time and at a particular point in an acoustic field

Note 1 to entry: Instantaneous intensity is the product of instantaneous acoustic pressure and particle velocity. It is difficult to measure intensity in the ultrasound frequency range. For the measurement purposes referred to in this document and under conditions of sufficient distance from the external transducer surface (at least one transducer diameter, or an equivalent transducer dimension in the case of a non-circular transducer) the instantaneous intensity can be approximated by the derived instantaneous intensity.

Note 2 to entry: Instantaneous intensity is expressed in units of watt per metre squared (W/m2).

[SOURCE: IEC 62127-1:2022, 3.36]

3.27

longitudinal plane

plane defined by the beam axis and a specified orthogonal axis

Note 1 to entry: See IEC 62127-1:2022, Figure 1.

[SOURCE: IEC 62127-1:2022, 3.39].]

3.28

near field

region of the field where mml-m9

z < z_{T}

aligned along the beam axis for planar non-focusing transducers

Note 1 to entry: For circular planar transducers, this is at a distance less than Aob/πλ, where Aob is the output beam area and λ is the wavelength of the ultrasound corresponding to the acoustic frequency.

Note 2 to entry: If the shape of the transducer aperture produces several transition distances, the one closest to the transducer is used.

[SOURCE: IEC 62127-1:2022, 3.41].]

3.29

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 62127-3:2022, 3.16]

3.30

source aperture plane

closest possible measurement plane to the external transducer surface plane that is perpendicular to the beam axis

Note 1 to entry: If the offset distance is zero, the source aperture plane can be coincident with the external transducer surface plane.

Note 2 to entry: See Figure B.5, Figure B.7, Figure B.9 and Figure B.10 in IEC 61828:2020 [5].

[SOURCE: IEC 61828:2020 [5], 3.135].]

3.31

source aperture width

LSA

<in a specified longitudinal plane> greatest −20 dB beamwidth along the line of intersection between the designated longitudinal plane and the source aperture plane

Note 1 to entry: See Figure B.5 and Figure B.6b in IEC 61828:2020 [5].

Note 2 to entry: Source aperture width is expressed in metres (m).

[SOURCE: IEC 61828:2020 [5], 3.136, modified - two Notes to entry on HITU transducers have been omitted.].]

3.32

transducer aperture width

LTA

full width of the transducer aperture along a specified axis orthogonal to the beam axis of the unsteered beam at the centre of the transducer

Note 1 to entry: See Figure 3 in IEC 62127-1:2022.

Note 2 to entry: Transducer aperture width is expressed in metres (m).

[SOURCE: IEC 62127-1:2022, 3.81].]

3.33

transition distance

aperture area divided by π times the effective wavelength λeff

[SOURCE: IEC 61828:2020 [5], definition 3.153, modified - In the definition, the words "the effective wavelength" have been added and a subscript has been added to the symbol for effective wavelength.]

3.33.1

transition distance for design

zTD

for a given longitudinal plane, the transducer aperture area ATA of the ultrasonic transducer divided by π times the effective wavelength λeff

mml-m10

z_{TD} = A_{TA} / (π λ_{eff})

(5)

Note 1 to entry: For design, for an unapodized ultrasonic transducer with circular symmetry about the beam axis, the source aperture area is mml-m11

π a_{e}^{2}

, where ae is the effective radius; therefore the transition distance is mml-m12

z_{T} = a^{2} / λ_{eff}

Note 2 to entry: For a spherically focusing transducer, the transition distance is approximately the same but more exactly it is mml-m13

z_{T} = 2 D^{2} (1 - \sqrt{1 - {(a / D)}^{2}}) / λ_{eff}

where D is the radius of curvature.

Note 3 to entry: For design, for an unapodized rectangular ultrasonic transducer which has a transducer aperture width, LTA1, in a specified longitudinal plane, the effective in-plane area is (LTA1)2. Therefore, for this plane, the transition distance is mml-m14

z_{T1} = {(L_{TA1})}^{2} / (π λ_{eff})

. The transition distance for the orthogonal longitudinal plane including the second transducer aperture width is mml-m15

z_{T2} = {(L_{TA2})}^{2} / (π λ_{eff})

Note 4 to entry: For apodized transducers with a symmetric even apodization or weighting function W (normalized to a maximum value of one for the particle velocity distribution), the transition distances are the following.
For circularly symmetric transducers with an active radius a: mml-m16

z_{T} = (\frac{2}{λ}) \int_{0}^{a} W (r) r d r

For a rectangular transducer with a physical aperture length L in a given longitudinal plane, for example, xz: mml-m17

z_{T} = (\frac{4}{π λ_{eff}}) {| \int_{0}^{L / 2} W (x) d x |}^{2}

Note 5 to entry: For symmetric shapes other than the most common cases of circular symmetry and rectangular geometry, the same definition of transition distance can be used. For example, for apertures with n-fold symmetry (n > 2) such as hexagons and octagons, the transition distance in a symmetry plane perpendicular to a side is equal to the area of the aperture divided by (πλeff). For annular arrays with several rings, the equivalent area is the total (all rings) area of the active aperture. For cases in which unique phasing is used such as annular arrays with alternate phase shifts (0° or 180°) in addition to intended focusing or for cases of apertures with unusual shapes and phasing, three-dimensional diffraction computation is employed to determine the minimum beamwidth corresponding to the appropriate transition distance.

Note 6 to entry: Transition distance for design is expressed in metres (m).

[SOURCE: IEC 61828:2020 [5], 3.153.1, modified - A subscript has been added to the symbol for effective wavelength and Note 6 to entry has been omitted.]

3.33.2

transition distance for measurement

zTM

for a given longitudinal plane, the source aperture area, ASAeff , of the ultrasonic transducer divided by π times the effective wavelength λeff

mml-m18

z_{TM} = A_{SAeff} / (π λ_{eff})

(6)

Note 1 to entry: For measurements in each specified longitudinal plane, the source aperture width in that plane is used, or mml-m19

z_{T1} = {(L_{SA1})}^{2} / (π λ_{eff})

; in the other orthogonal plane, mml-m20

z_{T2} = {(L_{SA2})}^{2} / (π λ_{eff})

Note 2 to entry: Transition distance for measurement is expressed in metres (m).

[SOURCE: IEC 61828:2020 [5], 3.153.2, modified - A subscript has been added to the symbol for effective wavelength.]

3.34

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 [10], 2.2.3.

3.35

wavelength

distance in the direction of propagation of a periodic wave between two successive positions at which the phase is the same

Note 1 to entry: The wavelength is expressed in metres (m).

[SOURCE: IEC 60050-845:2020 [8], 845-21-025, modified - Notes 1, 2, 3, 5 and 6 to entry have been omitted. Note 4 to entry has been renumbered Note 1 to entry and "or decimal submultiples of metre" has been deleted.]

30mm

20mm

15mm

10mm

17mm

– –

Gulf StandardGSO IEC 62127-2:2026

GSO IEC 62127-2:2026Gulf Standard

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1Numbers in square brackets refer to the Bibliography.