oSIST prEN ISO 25222-2:2026

SLOVENSKI STANDARD
01-april-2026
Neporušitvene preiskave - Karakterizacija in preverjanje ultrazvočne opreme
sklopljene z zrakom (ISO/DIS 25222-2:2026)
Non-destructive testing - Characterization and verification of ultrasonic air-coupled
equipment - Part 2: Probes (ISO/DIS 25222-2:2026)
Zerstörungsfreie Prüfung - Charakterisierung und Verifizierung von Prüfausrüstung für
luftgekoppelten Ultraschall - Teil 2: Prüfköpfe (ISO/DIS 25222-2:2026)
Essais non destructifs - Caractérisation et vérification des équipements de contrôle par
ultrasons à couplage par air - Partie 2: Traducteurs (ISO/DIS 25222-2:2026)
Ta slovenski standard je istoveten z: prEN ISO 25222-2
ICS:
19.100 Neporušitveno preskušanje Non-destructive testing
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 25222-2
ISO/TC 135/SC 3
Non-destructive testing —
Secretariat: DIN
Characterization and verification of
Voting begins on:
ultrasonic air-coupled equipment —
2026-02-16
Part 2:
Voting terminates on:
2026-05-11
Probes
ICS: 19.100
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
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RECIPIENTS OF THIS DRAFT ARE INVITED
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NOTIFICATION OF ANY RELEVANT PATENT
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PROVIDE SUPPORTING DOCUMENTATION.
Reference number
ISO/DIS 25222-2:2026(en)
DRAFT
ISO/DIS 25222-2:2026(en)
International
Standard
ISO/DIS 25222-2
ISO/TC 135/SC 3
Non-destructive testing —
Secretariat: DIN
Characterization and verification of
Voting begins on:
ultrasonic air-coupled equipment —
Part 2:
Voting terminates on:
Probes
ICS: 19.100
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2026
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
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Published in Switzerland Reference number
ISO/DIS 25222-2:2026(en)
ii
ISO/DIS 25222-2:2026(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 3
5 General requirements of conformity . 4
6 Technical information for probes . 4
6.1 General .4
6.2 Probe data sheet . .4
6.3 Probe test report .4
7 Test equipment . 6
7.1 Electronic equipment .6
7.2 Other equipment .7
7.3 Ambient conditions.8
8 Performance requirements for probes . 9
8.1 Physical aspects.9
8.1.1 Evaluation procedure . .9
8.1.2 Acceptance criterion .9
8.2 Measurement setup .9
8.2.1 General .9
8.2.2 Pulse-echo measurement .10
8.2.3 Transmission measurements .11
8.2.4 Characterization of transmitter using a microphone . 12
8.2.5 Characterization of transmitter using a laser Doppler vibrometer . 12
8.2.6 Refractovibrometry .14
8.3 Pulse properties .14
8.3.1 General .14
8.3.2 Pulse duration.14
8.3.3 Sensitivity . 15
8.3.4 Burst excitation saturation .18
8.3.5 Dead time after transmitter pulse.19
8.3.6 Frequency spectrum . 20
8.4 Soundfield properties .21
8.4.1 General .21
8.4.2 Scanning procedures .21
8.4.3 Near-field length, focal distance and focal length . 22
8.4.4 Focal width .24
8.4.5 Beam divergence . 26
Annex A (informative) Characterization of receiver probes using thermoacoustic excitation .28
Bibliography .29

iii
ISO/DIS 25222-2:2026(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO 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, ISO [had/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
www.iso.org/patents.ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO /TC 135, Non-destructive testing, Subcommittee
SC 3. Ultrasonic testing.
A list of all parts in the ISO 25222 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
ISO/DIS 25222-2:2026(en)
Introduction
This document was drafted following and complementing ISO 22232-2:2020 to include air-coupled ultrasonic
transducers.
This document is based on the guideline DGZfP US-08E which was originally prepared by members of
German Society for Non-Destructive Testing (DGZfP), Committee Ultrasonic Testing, Subcommittee Air-
coupled Ultrasonic Testing.
v
DRAFT International Standard ISO/DIS 25222-2:2026(en)
Non-destructive testing — Characterization and verification
of ultrasonic air-coupled equipment —
Part 2:
Probes
1 Scope
This document specifies the characteristics of probes used for non-destructive air-coupled ultrasonic testing
with centre frequencies from 10 kHz to 3 MHz, with focusing or without focusing means. This document
refers to probes based on the piezoelectric effect. Air-coupled probes based on other physical principles
can be characterized according to this guideline if it is judged as appropriate, but adaption of tests can be
necessary.
This document covers tests under standard environmental conditions. The procedures given in the standard
can be applied to extended environmental conditions e.g. higher air pressures, but additional tests can be
necessary.
This document excludes periodic tests for probes.
If parameters specified in this document are to be verified during the probe’s lifetime, as agreed upon by the
contracting parties, the procedures of verification for these parameters can be selected from those given in
this document.
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.
ISO 5577:2017, Non-destructive testing — Ultrasonic testing — Vocabulary
ISO 9613-2:2024, Acoustics — Attenuation of sound during propagation outdoors — Part 2: Engineering method
for the prediction of sound pressure levels outdoors
ISO/IEC 17050-1:2004, Conformity assessment — Supplier's declaration of conformity — Part 1: General
requirements
ISO 22232-1:2020, Non-destructive testing — Characterization and verification of ultrasonic test equipment —
Part 1: Instruments
ISO 22232-2:2020, Non-destructive testing — Characterization and verification of ultrasonic test equipment —
Part 2: Probes
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5577:2017, as well as 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/DIS 25222-2:2026(en)
— ISO Online browsing platform: available at http:// www .iso .org/ obp
3.1
target
reflector used in pulse–echo technique or a microphone or any other type of sensor applied for determination
of the exerted sound pressure
3.2
peak-to-peak amplitude
difference between the highest positive and the lowest negative amplitude in a pulse
Note 1 to entry: See Figure 1 .
Key
A amplitude
L pulse duration
s time
h peak-to-peak amplitude
Figure 1 — Typical ultrasonic pulse with pulse duration L and peak-to-peak amplitude h
3.3
probe data sheet
document giving manufacturer's technical specifications of the same type of probes, i.e. probes manufactured
in series
Note 1 to entry: The data sheet does not necessarily need to be a test certificate of performance.
Note 2 to entry: For individually designed or manufactured probes, some parameters might not be accurately known
before manufacturing.
[Source: ISO 22232-2:2020, 3.3]
3.4
probe test report
document showing compliance with this document giving the measured values of the required parameters
of one specific probe, including test equipment and conditions
[Source: ISO 22232-2:2020, 3.4]
3.5
dead time after transmitter pulse
time interval following the start of the transmitter pulse during which the amplifier is unable to respond to
incoming signals, when using the pulse-echo technique, because of saturation by the transmitter pulse
[Source: ISO 22232-1:2020, 3.3]

ISO/DIS 25222-2:2026(en)
4 Symbols
Table 1 — Symbols
Symbol Unit Meaning
A Amplitude
L µs Pulse duration
h V Peak-to-peak amplitude
f Hz Center frequency
c
f Hz Upper cut-off frequency
u
f Hz Lower cut-off frequency
l
Δf Hz Bandwidth
Δf % Relative bandwidth
rel
n number of burst cycles
dB Pulse-echo or transmission sensitiv-
S
ity
dB Sensitivity in the frequency domain
S Pa/V Sensitivity of a transmitter probe
transmitter
S V/Pa Sensitivity of a receiver probe
receiver
T °C Temperature
t s Time of flight
U V Peak-to-peak voltage of the input
in
signal
U V Peak-to-peak voltage of the output
out
signal
V Magnitude of the FFT of the excitation
signal
V Magnitude of the FFT of the received
signal
d mm Dead zone
D
t s Dead time after transmitter pulse
D
z mm Distance to focal point from sound
F
exit point
d mm Distance to focal point from probe
F
face
v m/s Sound velocity
z , z mm Boundaries of the focal zone
1 2
Δz mm Length of focal zone
F
Δx mm Focal width on x-axis
F
Δy mm Focal width on y-axis
F
Δx mm Beam width on x-axis at the further
end of the focal zone
Δy mm Beam width on y-axis at the further
end of the focal zone
Ω ° Angle of beam divergence in x-direc-
x
tion
Ωy ° Angle of beam divergence in y-direc-
tion
ISO/DIS 25222-2:2026(en)
5 General requirements of conformity
An ultrasonic probe complies with this document if it fulfils all of the following requirements:
a) the probe shall comply with Clause 8;
b) a declaration of conformity according to ISO/IEC 17050-1:2004 shall be available;
c) the ultrasonic probe shall be clearly marked to identify the manufacturer, and carry a unique serial
number or show a permanent reference number from which information can be traced to the datasheet
and probe test report;
d) a probe data sheet corresponding to the ultrasonic probe shall be available, which defines the
performance criteria for the items given in Clause 8 ;
e) a probe test report shall be delivered together with the probe, which includes at least the test results
given in Clause 8 .
Table 2 summarises the tests to be performed on air-coupled ultrasonic probes.
Table 2 — List of tests for air-coupled ultrasonic probes
Title of the test Probe type applicable Subclause
Physical aspects transmitter and receiver 8.1
Pulse properties transmitter 8.3
Pulse duration transmitter 8.3.2
Sensitivity receiver 8.3.3
Saturation receiver 8.3.4
Dead time after transmitter pulse receiver 8.3.5
Frequency spectrum transmitter and receiver 8.3.6
Soundfield properties transmitter and receiver 8.4
Focal distance and focal length transmitter and receiver 8.4.3
Focal width transmitter and receiver 8.4.4
Beam divergence transmitter and receiver 8.4.5
6 Technical information for probes
6.1 General
The test conditions and the equipment used for the evaluation of the probe parameters shall be listed (see
Table 3).
For individually designed or manufactured probes some parameters may not be accurately known prior to
manufacturing. In that case the measured values shall be used as reference values.
6.2 Probe data sheet
The probe data sheet gives the list of information to be reported for all probes within the scope of this
document (see Table 3).
6.3 Probe test report
The probe test report gives the measured values of the required parameters of one specific probe and other
information from the probe data sheet (see Table 3). The probe test report shall include the unique serial
number or the permanent reference number to provide a unique assignment between the specific probe and
the probe test report.
ISO/DIS 25222-2:2026(en)
Table 3 — List of information to be given in a probe data sheet and a probe test report
Information to be Probe type applica- Probe data sheet Probe test report Clause
given ble
Manufacturer‘s name transmitter and I I —
receiver
Probe type transmitter and I I —
receiver
Probe serial number transmitter and — I —
receiver
Probe housing dimen- transmitter and I I —
sions receiver
Probe weight transmitter and I I —
receiver
Type of focus transmitter and I I —
receiver
Transducer material transmitter and I I —
receiver
Shape and size of transmitter and I I —
transducer receiver
Type of connectors transmitter and I I —
receiver
Operating tempera- transmitter and I I —
ture range receiver
Storage temperature transmitter and I I —
range receiver
Room temperature transmitter and I M —
during measurements receiver
Measurement setup transmitter and I I 8.2
receiver
Transmitter–receiver transmitter and I I 8.2.6
distance receiver
Transmitter pulse transmitter I I 7.1 b)
type
Transmitter pulse transmitter I I 7.1 b), c)
voltage
Pulser output imped- transmitter I I 7.1 c)
ance
Preamplifier band- receiver I I 7.1 e)
width
Preamplifier input receiver I I 7.1 e)
impedance
Preamplifier gain receiver I I 7.1 e)
Probe cable specifi- transmitter and I I 7.1
cation receiver
Matching device spec- transmitter and I I 7.1
ification receiver
Oscilloscope/ Digitiz- transmitter and I I 7.1 f)
er specification receiver
Spectrum analyzer transmitter and I I 7.1 f)
specification receiver
I: Information, M: Measurement

ISO/DIS 25222-2:2026(en)
TTabablele 3 3 ((ccoonnttiinnueuedd))
Information to be Probe type applica- Probe data sheet Probe test report Clause
given ble
Thermoacoustic receiver I I 7.1 h)
transmitter specifi-
cation
Microphone specifi- transmitter I I 7.1 i)
cation
Microphone effective transmitter I I 8.2.4
aperture
Laser Doppler vibro- transmitter I I 7.1 j)
meter specification
Received pulse shape receiver I M 8.3.1
Received pulse dura- receiver I M 8.3.2
tion
Sensitivity receiver I M 8.3.3
Cycle # of burst satu- I M 8.3.4
ration
Dead time after trans- receiver I M 8.3.5
mitter pulse
Center frequency receiver I M 8.3.6
Bandwidth receiver I M 8.3.6
Focal distance, near- transmitter and I M 8.4.3
field length receiver
Focal length transmitter and I M 8.4.3
receiver
Focal width transmitter and I M 8.4.4
receiver
Angles of divergence transmitter and I M 8.4.5
receiver
I: Information, M: Measurement
7 Test equipment
7.1 Electronic equipment
The ultrasonic instrument (or laboratory pulser/receiver) used for the tests specified in Clause 8 shall be
of the type designated on the probe data sheet and shall comply with ISO 22232-1:2020 as applicable. The
following modifications apply to ISO 22232-1:2020:
a) The frequency range of the instrument shall cover the bandwidth of the air-coupled ultrasonic probe
under test.
b) A unipolar or bipolar rectangular tone burst pulser or a bipolar sine wave pulser or a spike pulser may
be used.
c) The pulser shall provide sufficient pulse power to ensure that each rectangular pulse of a tone burst
meets the nominal voltage. Output impedance of the pulser shall be documented.
d) The length of the unipolar rectangular pulse shall be adjustable to the nominal frequency of the probe.
e) Preamplifiers shall be used as required by the equipment. The bandwidth, the input impedance and the
preamplifier gain shall be documented.

ISO/DIS 25222-2:2026(en)
Where more than one type of ultrasonic instrument is designated, the tests shall be repeated with each of
the additional designated types.
Testing shall be carried out with the probe cables and electrical matching devices specified on the probe
data sheet for use with the particular type of ultrasonic instrument. The specifications of the probe cables
and electrical matching devices shall be documented.
In addition to the ultrasonic instrument or laboratory pulser/receiver, the items of equipment essential to
assess probes in accordance with this document are as follows:
f) an oscilloscope or digitizer with a minimum sampling frequency equal to 10 times the expected upper
cut-off frequency f of the transmitter or receiver probe, whichever is greater;
u
g) a frequency spectrum analyser with a minimum sampling frequency of 10 times the expected upper
cut-off frequency f , or an oscilloscope/digitiser or computer capable of performing discrete Fourier
u
transforms (DFT).
h) a thermoacoustic broadband transmitter providing transient single pulses without ringdown. The pulse
bandwidth shall cover the expected bandwidth of the tested probe (this may depend on the distance
and position of the measurement).
i) a broadband microphone such that the bandwidth of the microphone and the amplifier covers the
bandwidth of the probe under test.
j) a laser Doppler vibrometer with a minimum sampling frequency of 2,5 times probe center
frequency if a Fast Fourier transform (FFT) measurement is done or a minimum sampling
frequency of 10 times probe center frequency, if a time measurement (measuring real displacement or
velocity) is used. The bandwidth of the laser Doppler vibrometer shall cover the bandwidth of the probe
under test.
The specifications of applied items shall be recorded.
7.2 Other equipment
For measuring distances, a ruler or a measurement tool with a similar accuracy shall be used.
The following reflectors shall be used:
a) A steel ball or rod with a hemispheric ended smooth reflective surface. For each frequency range the
diameter of the ball or the rod to be used is given in Table 4.
b) A large planar and smooth steel reflector. The reflector’s lateral size shall be at least ten times wider
than the beam width of the probe under test measured at the end of the focal zone, as defined in 8.4.5.
Table 4 — Steel ball or rod diameters for different frequencies
Probe center frequency f (kHz) Diameter d of ball or rod (mm)
C
10 ≤ f ≤ 120 5 ≤ d ≤ 15
C
120 < f ≤ 700 3 ≤ d ≤ 5
C
f > 700 d ≤ 3
C
A setup with a manual or automated scanning mechanism or a robot with at least these five free axes shall
be used:
— three linear axes x, y, z;
— two angular axes.
ISO/DIS 25222-2:2026(en)
The scanning mechanism used should be able to maintain alignment between the reflector and the probe in
the x- and y-directions within ±0,1 mm at 100 mm distance in the z-direction, where z is the direction of the
acoustical axis.
If the amplitudes of ultrasonic signals are recorded automatically, the system shall have sufficient accuracy.
In particular, consideration shall be given to the effects of the system bandwidth, spatial resolution, data
processing and data storage on the accuracy of the results.
Typical setups to measure the pulse properties and the soundfield properties of air-coupled probes are
specified in 8.2.
7.3 Ambient conditions
Where values for wave propagation in air are specified in this document, they are based on a sound velocity
of 343,21 m/s and a characteristic acoustic impedance of 413,3 Pa s/m, which are valid for standard
temperature 20 °C and standard pressure 101 325 Pa. For deviating temperature T (in °C) the approximation
given in Formula (1) can be used for the sound velocity:
(1)
The dependence of the sound velocity on frequency and pressure are normally insignificant. However, the
acoustic impedance, which is the product of the speed of sound and the density, depends on atmospheric
pressure, because the air density depends on pressure. Air density will decrease by about 1 % for a decrease
of 10 hPa in pressure or 3 °C increase in temperature.
Variations in temperature and pressure as well as air draft shall be prevented. The air temperature shall not
deviate by more than ±2 °C during the characterization of air-coupled probes. The room temperature and air
pressure shall be measured and reported in the probe test report.
The room surrounding the test setup should be large compared to the measurement distance. It shall be
ensured that the air-coupled ultrasound is not reflected by any walls, obstacles or parts of the test setup.
Care should be taken about the influence of sound attenuation in air, which, at high frequencies, causes
a downshift of the measured center frequency when using broadband probes (see Table 5). The sound
attenuation in air and its dependence on frequency are described in ISO 9613-2:2024.
For example, if a 250 kHz probe with a relative bandwidth of 15 % is characterized, at the distance of 200 mm
the resulting spectrum would have a maximum at 249 kHz. However, if the relative bandwidth is 0,38, the
maximum would be at 243 kHz.
Table 5 — Downshift of the measured center frequency due to attenuation in air
Distance Center frequency for Δf = 15 % Center frequency for Δf = 38 %
rel rel
mm kHz kHz
0 50 250 500 1000 50 250 500 1000
50 50 250 498 982 50 248 486 904
100 50 249 495 966 50 246 473 844
200 50 249 491 942 50 243 452 780
500 50 247 480 906 50 234 411 714
NOTE The measurement result depends on the distance, the actual center frequency of the transducer and the transducer
relative bandwidth . The given bandwidth is the -3 dB bandwidth as measured directly in front of the transducer using a
broadband microphone. The values in this table were calculated assuming a parabolic function for the spectrum directly in front
of the transducer and a perfectly broadband microphone.

ISO/DIS 25222-2:2026(en)
8 Performance requirements for probes
8.1 Physical aspects
8.1.1 Evaluation procedure
The outside of the probe shall be visually inspected for correct identification, correct assembly and for
physical damage which can influence its current or future reliability.
8.1.2 Acceptance criterion
No visible damage of the probe surface used for transmitting and receiving ultrasound is allowed.
8.2 Measurement setup
8.2.1 General
This and the following clauses describe the measurement setups to find pulse properties described in8.3,
and beam properties described in 8.4. Pulse properties are all measured at a fixed distance and position
(stationary measurements), except for the measurements of the dead zone. Beam properties are measured
with the help of a positioning system described in 7.2 (scanning measurements).
Five different measurement setups are possible, depending on the type of probe:
a) Characterization using pulse-echo technique,
b) characterization of pairs of probes using through-transmission technique,
c) characterization of transmitters using a microphone,
d) characterization of transmitters using a laser Doppler vibrometer,
e) characterization of receivers using thermoacoustic or some other broadband excitation.
These five setups are described in 8.2.2, 8.2.3, 8.2.4, 8.2.5 and Annex A, respectively.
Many air-coupled probes are designed to be used both as transmitter and receiver. Such probes can be
characterized using pulse-echo technique in setup a), but also using setups b) to e). Air-coupled probes
designed as either transmitter or receiver cannot be characterized using pulse-echo technique. For these
probes, one of the measurement setups b) to e) shall be applied.
There are several options to drive a transmitter probe:
f) with unipolar rectangular pulses or unipolar rectangular tone bursts,
g) with bipolar rectangular pulses or bipolar rectangular tone bursts,
h) with bipolar sine wave tone bursts;
i) with a spike pulse, if applicable.
The transmitter probe shall be driven as recommended by the manufacturer, depending on the intended
use. The type of excitation (voltage, pulse length, burst signal length etc.) can have a strong influence on the
recorded signals and on the sound field. For example, burst excitation reduces the bandwidth of the recorded
signal. The choice of experimental equipment can have a significant influence too, because of the influence
of the electrical coupling conditions like impedances of the pulser, probe, cables, and receiver. Therefore, the
type of the excitation including all parameters describing the excitation as well as the used equipment shall
be reported together with the applied setup.

ISO/DIS 25222-2:2026(en)
8.2.2 Pulse-echo measurement
Pulse-echo measurements can be performed with probes which can be used both as transmitter and
receiver, only. The setup for pulse-echo measurements (see Figure 2 and Figure 3) includes a probe, which
transmits and receives ultrasonic signals and a target, which reflects the ultrasonic signal. The reflecting
target is described in 7.2.
The setup for stationary measurements (which are used to evaluate pulse parameters) and for the evaluation
of the dead zone contains a large flat reflector as a target placed at the focal distance or the near-field length
of the probe (see Figure 2). If the dead zone is larger than the focal distance, the distance between the probe
and the reflector shall be selected to be larger than the dead zone and specified in the probe test report. The
orientation of the probe shall be adjusted to maximize the received signal. If the focal distance is not known,
the distance between the probe and the reflector shall be selected to maximize the reflected signal. This
procedure is legitimate because for most probes the distance of the maximum signal is approximately equal
to the focal distance.
The setup for scanning measurements (for the evaluation of soundfield parameters) includes a ball or a rod
as a target. The target properties are described in 7.2. For these measurements the probe shall be moved
relatively to the target (see Figure 3).
Key
1 ultrasonic instrument
2 PC
3 documentation
4 manipulator control
5 manipulator
6 probe
7 target
Figure 2 — Setup for pulse-echo measurements using a large flat reflecting target

ISO/DIS 25222-2:2026(en)
Key
1 ultrasonic instrument
2 PC
3 documentation
4 manipulator control
5 manipulator
6 probe
7 ball reflector or rod
Figure 3 — Setup to measure the soundfield parameters of air-coupled probes using a ball or a rod
as a target
8.2.3 Transmission measurements
This sub-clause describes characterization of pairs of probes. It can be applied to any pair of probes if one
probe is applicable as a transmitter and the other one as a receiver.
For a characterization of a pair of probes, a setup as illustrated in Figure 4 shall be used. The distance between
the two probes shall be equal to the sum of their focal distances or near-field lengths. The orientation of
both probes shall be adjusted to maximize the received signal. If the focal distances or the near-field lengths
are not known, the distance between the probes shall be selected to maximize the received signal.
Key
1 ultrasonic instrument
2 PC
3 documentation
4 manipulator control
5 manipulator
6 probe
7 transmitter probe
Figure 4 — Setup to measure the soundfield parameters of two air-coupled probes used as a pair

ISO/DIS 25222-2:2026(en)
8.2.4 Characterization of transmitter using a microphone
Characterization with a microphone can be performed only with probes which can be used as transmitter.
In a setup for stationary measurements (which are measurements of pulse parameters, see 8.3) using a
microphone as a target, the microphone shall be placed in the middle of the focus of the probe, i.e. at the focal
distance or near-field length on the acoustical axis. This position shall be found by maximizing the received
signal starting from large distances to avoid optimization within the near-field. This setup is illustrated in
Figure 5.
In a setup for scanning measurements (performed for the evaluation of the beam properties, see 8.4) using a
microphone as a target, the the sound field of the probe shall be relatively moved to the microphone using a
positioning system satisfying the requirements described in 7.2.
Care should be taken of the microphone effective aperture, which shall be reported, because its size
influences the lateral resolution of the sound field image.
Key
1 pulse generator
2 PC
3 documentation
4 oscilloscope
5 manipulator control
6 manipulator
7 probe
8 microphone
Figure 5 — Setup for measurements with a microphone
8.2.5 Characterization of transmitter using a laser Doppler vibrometer
Setups based on laser vibrometry can be used instead of a microphone to characterize transmitter probes.
The advantage is the smooth spectrum. The disadvantages are the higher complexity of the measurement
and its evaluation.
The measurement setup (see Figure 6) includes a thin light-reflecting membrane in the xy-plane whose
velocity is measured using a laser doppler vibrometer. The sound pressure p at that point at the membrane

ISO/DIS 25222-2:2026(en)
is calculated from the measured velocity v taking into account the frequency-dependent influence of the
Foil
[1]
membrane as given inFormula (2) :
(2)
where
is the angular frequency;
Z is the specific acoustic impedance of air;
Air
j is ;
m is the areal density of the membrane (kg/m ); and
Foil
d is the thickness of the membrane.
Foil
v velocity
v measured velocity in the membrane
Foil
In a setup for scanning measurements (performed for the evaluation of the soundfield parameters, see
8.4) using a laser Doppler vibrometer as a target, the probe shall be relatively moved to the foil using a
positioning system satisfying the requirements described in 7.2.
Key
1 pulse generator
2 PC
3 documentation
4 oscilloscope / velocity decoder
5 manipulator control
6 manipulator
7 transmitter probe
8 membrane
9 laser Doppler vibrometer
Figure 6 — Setup for measurements of sound pressure using a laser Doppler vibrometer
As an alternative, it is also possible to measure the surface velocity directly on the surface of the transmitter
probe using a laser Doppler vibrometer and to compute the sound field using a validated computational
method, for example point source synthesis or finite elements method. In this case it is possible to
quantitatively determine the sound field without any artifacts due to the receiver characteristic, which
normally influences the sound field measurement.
Another application of laser vibrometry is refractovibrometry. The sound waves in air change its local
density. The refractive index of air is a function of density. Changes in the speed of light caused by changing
the refractive index can be measured with a scanning laser vibrometer. The transmitter probe is excited with
a continuous wave excitation and the laser Doppler vibrometer scans the entire sound field of the transducer
point by point. With this method, an image of the pressure distribution in front of the transmitter probe can
be generated.
ISO/DIS 25222-2:2026(en)
8.2.6 Refractovibrometry
Another application of laser vibrometry is refractovibrometry. The sound waves in air change its local
density. The refractive index of air is a function of density. Changes in the speed of light caused by changing
the refractive index can be measured with a scanning laser vibrometer. The transmitter probe is excited
with a continuous wave excitation and the laser Doppler vibrometer scans the entire sound field of the
transducer point by point (seeFigure 7). With this method, an image of the pressure distribution in front of
the transmitter probe can be generated.
Key
1 pulse generator
2 PC
3 documentation
4 oscilloscope / velocity decoder
5 manipulator control
6 transmitter probe
7 reflector
8 laser Doppler vibrometer
Figure 7 — Setup for measurements of pressure distrution using a laser Doppler vibrometer and
refractovibrometry
8.3 Pulse properties
8.3.1 General
The following sub-clauses describe the evaluation of measurements to evaluate the pulse properties such as
duration, sensitivity, burst excitation saturation, dead time after transmitter pulse and frequency spectrum
properties for transmitter and receiver. The measurements are performed using stationary measurement
setups as described in 8.2.
The pulse properties are all measured at a fixed distance and position, with the exception of the
measurements for the determination of the dead zone, see 8.3.4.
The measured unrectified signal (also called RF signal) shall be recorded. It is recommended to plot and
document the transmitter pulse shape.
8.3.2 Pulse
...