This International Standard is applicable to:-
hydrophones used for measurements made in water and in the ultrasonic frequency range
up to 40 MHz;
NOTE - Although some physiotherapy medical applications of medical ultrasound are developing which operate in the frequency range 40 kHz - 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 [1].

hydrophones employing circular piezoelectric sensor elements, designed to measure the
pulsed and continuous-wave ultrasonic fields generated by ultrasonic equipment;
NOTE - Some hydrophones may have non-circular active elements, arising from slight deviations from circular structure caused, for example, by electrode structure, or conversely, the active elements may actually be squares.
The Clauses within this document remain valid, although, in these cases, special attention cases should be paid to the directional response, and the effective radii of the active element through various axes of rotation.
hydrophones with or without a hydrophone pre-amplifier

This International Standard specifies
absolute hydrophone calibration methods;
relative (comparison) 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 International Standard.