IEC 62127-2:2007/AMD2:2017

IEC 62127-2 ®
Edition 1.0 2017-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
A MENDMENT 2
AM ENDEMENT 2
Ultrasonics – Hydrophones –
Part 2: Calibration for ultrasonic fields up to 40 MHz

Ultrasons – Hydrophones –
Partie 2: Etalonnage des champs ultrasoniques jusqu’à 40 MHz

IEC 62127-2:2007-08/AMD2:2017-03(en-fr)

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IEC 62127-2 ®
Edition 1.0 2017-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
A MENDMENT 2
AM ENDEMENT 2
Ultrasonics – Hydrophones –
Part 2: Calibration for ultrasonic fields up to 40 MHz

Ultrasons – Hydrophones –
Partie 2: Etalonnage des champs ultrasoniques jusqu’à 40 MHz

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.140.50 ISBN 978-2-8322-3904-9

– 2 – IEC 62127-2:2007/AMD2:2017
© IEC 2017
FOREWORD
This amendment has been prepared by IEC technical committee 87: Ultrasonics.
The text of this amendment is based on the following documents:
CDV Report on voting
87/612/CDV 87/639/RVC
Full information on the voting for the approval of this amendment can be found in the report
on voting indicated in the above table.
The committee has decided that the contents of this amendment and the base publication will
remain unchanged until the stability date indicated on the IEC website under
"http://webstore.iec.ch" in the data related to the specific publication. At this date, the
publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
_____________
2 Normative references
Add the following new reference:
IEC 61689, Ultrasonics – Physiotherapy systems – Field specifications and methods of
measurement in the frequency range 0,5 MHz to 5 MHz
3 Terms, definitions and symbols
3.26
derived instantaneous intensity
(added by Amendment 1)
Delete the following text below the term:
"approximation of the instantaneous intensity"
Replace the existing four lines before Equation (1) by the following:
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

© IEC 2017
4 List of symbols
Replace:
ρc specific acoustic impedance
by
ρc characteristic acoustic impedance of the measurement liquid (water)
Add the following new symbols:
d distance between the auxiliary transducer and the reflector measured along the axis of
symmetry
d distance between the auxiliary transducer and the active element of the hydrophone
h
measured along the axis of symmetry
d distance between the auxiliary transducer and the last minimum of the acoustic
m
pressure amplitude along the axis of symmetry of the auxiliary transducer
R amplitude reflection coefficient for the reflector/water interface
RT
Z characteristic acoustic impedance of the reflector
RT
J reciprocity coefficient for plane waves
p
*
S apparent transmitting current response of an auxiliary transducer
t
*
M apparent receiving voltage response of an auxiliary transducer
t
p acoustic pressure generated by a transducer at its surface
a
p acoustic pressure incident on a transducer surface
i
p acoustic pressure incident on the hydrophone surface
h
I transmitting current driven to a transducer
t
U voltage generated by a transducer in the receiving mode
t
G correction that accounts for the diffraction in the propagation field and is related to the
th
waveform generation by the transducer and the reception by the hydrophone
G correction that accounts for the diffraction in the propagation field and is related to the
tt
generation and the reception by the transducer
U voltage measured with the transducer coupled to the system
load
I current measured over a short circuit jumper replacing the transducer
sc
9 Free field reciprocity calibration
9.1 General
Replace the existing text by the following:
This clause specifies the primary reference measurement procedure (see JCGM 200:2012,
2.8 [79]) calibration of hydrophones under free field conditions using the principle of
reciprocity.
Add the following new note:
NOTE The free field condition can be achieved in a confined water space by following any of a variety of
measurement procedures, such as with the use of tone-burst (time-gated sine wave – see 10.5.3), time-delay
spectrometry [63, 68], frequency modulated chirp [80, 81] or other techniques [82].

– 4 – IEC 62127-2:2007/AMD2:2017
© IEC 2017
9.4 Two-transducer reciprocity calibration method
9.4.1 Apparatus
Replace the existing subclause title and text by the following:
9.4.1 Auxiliary transducers
Circularly plane piston auxiliary transducers should be used to generate the ultrasonic field in
the frequency range of interest, limited to the maximum range between 1 MHz and 15 MHz.
The effective radiation area (A ) shall be determined, according to IEC 61689, for each
ER
transducer and at all frequencies the transducer is intended to be used. If a frequency
modulated chirp is to be used as excitation signal, the A shall be determined at least in the
ER
minimum, maximum and one intermediate frequency in the range of interest.
The position of the last minimum of acoustic pressure amplitude along the axis of symmetry,
d , shall be determined with an uncertainty not larger than 1 mm. It shall be done as an on-
m
axis line scan, according to IEC 61689, at the same frequencies the A was determined. The
ER
near field distance produced by the auxiliary transducer is defined as N = a /λ, where λ is
1 t
the ultrasonic wavelength in water at the frequency of operation and a = 2λd +λ is the
t m
effective radius of the ultrasonic transducer.
NOTE Focusing auxiliary transducers can be used, but several corrections need to be applied, and this document
is only intended for plane-piston transducers. A detailed implementation of a reciprocity-based calibration method
using focusing transducers can be found in [84].
The effective radiation area (A ) is used in the equations of Annex K to properly assess the
ER
diffraction correction and the reciprocity coefficient for plane waves, whilst the last minimum
) is used to indirectly define the near
of pressure amplitude along the axis of symmetry (d
m
field distance (N ), being N = (2λd + λ )/λ. Although both quantities A and d are directly
1 1 m ER m
linked for ideal transducers, both shall be determined experimentally according to IEC 61689.
9.4.2 Procedure
Replace the existing subclause title and text by the following:
9.4.2 Reflector
The reflector should comprise a flat surface whose smallest linear dimension shall be at least
four times the effective radius of the ultrasonic transducer a . The reflector shall also be flat to
t
±10 μm, with a surface finish good to ±5 μm (surface roughness: R < 5 μm; R < 5 μm;
v p
R < 1 μm). The thickness of the reflector shall be such that the first reflection from the rear
a
surface will not interfere with that directly from the front surface for any of the excitation
signals to be used. Special attention shall be given for long burst or low-rate frequency
modulated chirps, mainly at the lowest frequencies of interest.
The amplitude reflection coefficient for the reflector/water interface R shall be
RT
experimentally determined, for instance by the relation R = (Z – ρc)/(Z + ρc), were ρc
RT RT RT
is the characteristic acoustic impedance of the water and Z is the characteristic acoustic
RT
impedance of the reflector.
NOTE R is the maximum valley depth, R is the maximum peak height and R is the arithmetic average
v p a
describing the reflector profile roughness amplitude parameters.
Add the following new subclauses:
9.4.3 Measurement field
As both the auxiliary transducer and the hydrophone have finite apertures, a diffraction
pattern is present in the ultrasonic field. To minimize uncertainties due to the analytical or

© IEC 2017
numerical corrections to be applied to the measurement quantities, the nearest measurement
shall be performed at least at 0,9 × N , and the furthest distance shall not be larger than
2,2 × N . Water-air surface and tank walls shall be far enough from the ultrasonic path such
that any reflected waveform will not interfere with the direct waveform at the measurement
spot.
If any structure is too close to the direct ultrasonic waveform path, it shall be covered with
absorbing lining to minimize the interference with the measurement signal, and concern about
that interference shall be included in the uncertainty budget.
9.4.4 Reciprocity approach
Reciprocity can be established as a primary hydrophone calibration method provided some
practical and theoretical details are adopted. Annex K depicts the fundamentals of the
reciprocity approach.
9.4.5 Measurement procedure
Several distinct setups (see Annex K [83, 84, 85]) could be used regarding the positioning of
the three main elements of the two-transducer reciprocity calibration method: auxiliary
transducer, reflector and hydrophone.
Regardless of the configuration adopted, the self-calibration of the auxiliary transducer is the
first step, and it is done to quantify the acoustic pressure generated by the transducer in a
defined spot in the ultrasonic field.

– 6 – IEC 62127-2:2007/AMD2:2017
© IEC 2017
Annex K
(informative)
Two-transducer reciprocity calibration method
Replace the existing Annex K, added by Amendment 1, by the following:
K.1 General
The two-transducer reciprocity method involves the assessment of the acoustic pressure in a
defined spot in the ultrasonic field. To accomplish that, the first step is to assess the
ultrasonic field generated by an auxiliary transducer. The second step is to place the active
element of the hydrophone to be calibrated in a defined spot for which the acoustic pressure
can be defined as precisely as possible.
K.2 Fundamentals of reciprocity
*
A reversible transducer has an apparent transmitting current response S (ω) and apparent
t
*
receiving voltage response M (ω) defined as
t
p (ω) U(ω)
* 0 * t
S = and M = (K.1)
t t
I(ω) p(ω)
t i
where p is the acoustic pressure generated by the auxiliary transducer at its surface, I is the
t
transmitting current of the transducer, p is the acoustic pressure incident on the transducer
i
surface and U is the voltage generated by the transducer in the receiving mode.
t
NOTE The term ‘acoustic pressure’ is used in Annex K, although it is recognized that in any practical situation
this quantity will vary spatially. Similarly, the electrical output of transducer devices used in reception mode will be
dependent on the acoustic pressure spatially-averaged on their active surface.
*
If the transducer is reciprocal, the reciprocity coefficient for plane waves J relates S (ω) and
p t
*
M (ω) as follows:
t
*
M (ω)
t
J = (K.2)
p
*
S (ω)
t
2A
ER
By definition, J = .
p
ρ c
If the wave generated by a reciprocal transducer propagates in water and reflects off with a
normal incidence at a reflector distant d from the transducer surface placed on its axis of
symmetry, it produces an incident wave whose acoustic pressure can be measured by the
reciprocal transducer. Relating the definition by Equation (K.3)
−2α d
p(ω)= p (ω) R e G (K.3)
0 RT tt
i
where α is the amplitude attenuation coefficient of plane waves in water and G is the
tt
correction due to the fact that the returning waveform is generated and measured by a finite
transducer, i.e. it accounts for the diffraction in the propagation field and is related to the
generation and reception by the transducer. Combining Equations (K.1), (K.2) and (K.3), the

© IEC 2017
acoustic pressure generated by a reciprocal transducer at its surface is related to electrical
and geometrical quantities as follows:
ρ c
p (ω)= U (ω)I (ω) . (K.4)
t t
−2α d
2A R e G
ER RT tt
A normal incidence reflection on the reflector is necessary for the self-calibration. This is
ensured by maximizing the waveform reflection from the reflector as measured by the
transducer. The driven electrical current I is measured with the auxiliary transducer in the
t
output mode. The input voltage U is measured when the auxiliary transducer is in the input
t
mode. It should be an open-circuit voltage, and electrical corrections should be applied to the
measured current and voltage.
In sequence, the hydrophone active element is placed in a determined spot in the ultrasonic
field, and the acoustic pressure is maximized in order to assure the alignment of the
hydrophone active element symmetry axis and the transducer symmetry axis. The acoustic
pressure at this point is calculated using the following expression:
−α d
h
( ) ( ) (K.5)
p ω = p ω e G
0 th
h
where p is the measured acoustic pressure incident on the hydrophone’s active element if
h
the hydrophone were removed, d is the distance from the transducer surface to the active
h
hydrophone element measured on the symmetry axis, and G is the correction that accounts
th
for the diffraction in the propagation field and is related to the generation transducer and the
reception by the hydrophone.
The open-circuit voltage from the hydrophone U should be measured with p incident on its
h h
active element. The end of cable sensitivity is therefore given as
U (ω)
h
M(ω)= (K.6)
p (ω)
h
K.3 Electrical quantities
The transmitting current, I , shall be measured as precisely as possible, which can be
t
performed in many different ways. Measuring the voltage drop across a calibrated impedance
or using a current probe are typical electrical setups.
The output voltage from the transducer in the receiving mode, U , shall be measured unloaded
t
by the transducer, i.e. as an open circuit voltage. One way to perform that is to measure the
current over a short circuit replacing the transducer. The open circuit voltage is
I (ω)
sc
U (ω)= U (ω) (K.7)
t load
I (ω)
t
where U is the voltage measured with the transducer coupled to the system and I is the
load sc
current measured over a short circuit jumper replacing the transducer.
In the case of a constant load assumed throughout the calibration process, corrections
described in Annex C could be applied directly to the final assessed sensitivity.

– 8 – IEC 62127-2:2007/AMD2:2017
© IEC 2017
K.4 Diffraction correction and loss due to nonlinear sound propagation
Due to the finite size of auxiliary transducers and hydrophones, a diffraction pattern
develops in the ultrasonic field. In the two-transducer reciprocity method, two diffraction
corrections are applied: G , correction that accounts for the diffraction in the propagation
th
field and is related to the waveform generation by the transducer and the reception by the
hydrophone, and G , correction due the generation and the reception by the transducer.
tt
Many references can be used to theoretically describe the diffraction loss in ultrasonic fields
[83, 86, 87], and a numerical implementation of diffraction corrections can be applied [88, 89,
90, 91].
K.5 Ultrasonic field
For the two-transducer reciprocity calibration, the ultrasonic field is shaped by the influence of
many aspects, mainly:
• diffraction pattern for both the auxiliary transducer and hydrophone (see K.3);
• signal type (see Annex G and [8, 80]);
• reflector reflection coefficient (see 9.4.2);
• water path attenuation (see [92]);
• speed of sound (see [36]).
The amplitude attenuation coefficient for plane ultrasonic waves, α, in the megahertz
frequency range is proportional to f  , and should be taken from a polynomial fit as a function
of temperature T in the temperature range from 0 °C to 60 °C [92]:
1 0
 
5,685⋅10 − 3,025⋅10 {T }
 
2  −1 2 −3 3 −15 −2 −1
α / f = + 1,174⋅10 {T } − 2,954⋅10 × {T } ×10 Hz ⋅ m (K.8)
 
−5 4 −7 5
 
+ 3,970⋅10 {T } − 2,111⋅10 {T }
 
NOTE 1 {T} denotes the numerical value of the temperature in °C.
-1 -1
NOTE 2 If the amplitude attenuation coefficient in m is going to be given in dB m , its numerical value should
be multiplied by 20·log (e) = 8,69.
The speed of sound is presented in tables in [36], and polynomial fits are available for
different accuracies, temperature ranges, and barometric pressures. The contribution for the
uncertainty budget should be taken into account regarding the formula used to assess the
speed of sound.
a) Temperature range: 0 °C to 100 °C at atmospheric pressure; accuracy better than
-1
0,02 ms (see [93])
 
1402,39+ 5,03836 {T }− 0,0581173 {T }
 
 −4 3 −6 4 −1
c= + 3,34638⋅10 {T } − 1,48260⋅10 {T } m⋅ s (K.9)
 
−9 5
 
+ 3,16585⋅10 {T }
 
b) Temperature range: 10 °C to 40 °C at atmospheric pressure; accuracy better than
-1
0,18 ms (see [93])
2 −1
c=(1405,03+ 4,624 {T }− 0,0383 {T } )m⋅ s (K.10)

© IEC 2017
c) Temperature range: 15 °C to 35 °C at atmospheric pressure; accuracy better than
-1
0,20 ms (see [94])
2 −1
( ) (K.11)
c= 1404,3+ 4,7 {T }− 0,04 {T } m⋅ s
For the atmospheric pressure dependence of the speed of sound, see [95].
K.6 Experimental setup
K.6.1 General
Different experimental arrangements have been proposed to perform the two-transducer
reciprocity calibration. Regardless of the electrical setup, the main concern in the
experimental preparation comprises the positioning of the auxiliary transducer, reflector, and
hydrophone. Three experimental setups are shown, each of them presenting advantages and
drawbacks.
K.6.2 Twisting reflector
Figure K.1 depicts an arrangement in which the reflector is twisted between the two steps of
the calibration procedure. Care should be taken to avoid a large angle of rotation of the
reflector. A maximum of 10° would be acceptable, but the uncertainty of the hydrophone
voltage measurement due to non-normal reflection should be considered. Moreover, for large
membrane hydrophones, it could be a negative issue to set the rotation angle small. Another
negative aspect of this arrangement is that it may not be simple to rotate large and heavy
stainless steel reflectors with appropriate accuracy.
Auxiliary
transducer
Hydrophone
d
d – d
h 1
Reflector
IEC
Figure K.1 – Experimental setup with a twisting reflector [83]
K.6.3 Translational reflector
Figure K.2 discloses an arrangement in which the reflector is inserted in the path between the
auxiliary transducer and the hydrophone.

– 10 – IEC 62127-2:2007/AMD2:2017
© IEC 2017
Reflector
Auxiliary
transducer
Hydrophone
d
d
h
IEC
Figure K.2 – Experimental setup with a translational reflector [84]
K.6.4 Translational auxiliary transducer
In Figure K.3, the hydrophone and the reflector remain still during the measurement
procedure, and the moving element is the transducer.
d
Transducer
Plane reflector
d
h
Hydrophone
IEC
Figure K.3 – Experimental setup with a translational auxiliary transducer [85]

© IEC 2017
Bibliography
Add the following references:
[79] BIPM JCGM 200:2012, International vocabulary of metrology – Basic and general
concepts and associated terms (VIM).
[80] ISAEV, A.E. and Matveev A.N. Calibration of Hydrophones in a Field with Continuous
Radiation in a Reverberating Pool. Acoustical Physics, 2009, vol. 55, no. 6, p. 762-
770.
[81] COSTA-FELIX, R.P.B. and MACHADO, J.C. Output bandwidth enhancement of a
pulsed ultrasound system using a flat envelope and compensated frequency-
modulated input signal: Theory and experimental applications. Measurement, 2015,
vol. 69, p. 146-154.
[82] ISAEV, A.E. A Quality Criterion for Obtaining Free-Field Conditions when Calibrating a
Hydroacoustic Receiver in a Water Tank with Reflecting Sides. Measurement
Techniques, 2014, vol. 57, no. 5, p. 549-556.
[83] BRENDEL, K., LUDWIG, G. Calibration of Ultrasonic Standard Probe Transducers.
Acustica, 1976, vol. 36, p. 203.
[84] SHOU W, DUAN S, HE P, XIA R, QIAN D. Calibration of a Focusing Transducer and
Miniature Hydrophone As Well As Acoustic P
...