IEC 60565-1-2020 Underwater acoustics – Hydrophones – Calibration of hydrophones – Part 1: Procedures for free-field calibration of hydrophones.
3.1 5 hydrophone
electroacoustic transducer that produces electrical voltages in response to water borne pressure signals
Note 1 to entry: A hydrophone is designed to respond principally to underwater sound pressure. Note 2 to entry: In general, a hydrophone may also produce a signal in response to non-acoustic pressure
fluctuations (for example, those existing in a turbulent boundary layer during conditions of high water flow).
Note 3 to entry: Hydrophone types include reference hydrophones and measuring hydrophones. Measuring hydrophones are used in general measurements of sound fields, and reference hydrophones are principally used for calibration purposes (for example in comparison calibrations with measuring hydrophones).
Note 4 to entry: Hydrophones are principally used as listening devices, but in reciprocity calibration, a hydrophone is used as reciprocal transducer, not only acting as a hydrophone, but also as a projector (sound source).
Note 5 to entry: A hydrophone which is integrated with a digital acquisition system is sometimes termed a “digital hydrophone”, but the combination is best considered as a measuring system, not a hydrophone alone.
Note 6 to entry: If a hydrophone is connected to a charge amplifier, the sensitivity of the hydrophone is sometimes described in terms of charge sensitivity, which is related to the voltage sensitivity of the hydrophone by its electrical capacitance.
[SOURCE: IEC 60500:201 7, 3.1 7, modified – In the definition, “signals” has been replaced by “voltages”.]
3.1 6 signal
specified time-varying field quantity of interest, such as electric current, voltage, sound pressure, sound particle velocity, or other quantity
[SOURCE: ISO 1 8405:201 7, 3.1 .5.8]
3.1 7 directional response
directivity directivity pattern normalized variation in transducer sensitivity with angle, applying to both receive and transmit sensitivity of an electroacoustic transducer
Note 1 to entry: The sensitivity value used for normalization is the sensitivity in a specified reference direction, most commonly the sensitivity in the direction of the principal axis of the transducer (as defined in IEC 60500:201 7).
Note 2 to entry: If the transducer is reciprocal, the normalized directional response is the same in both transmit and receive modes.
Note 3 to entry: The response is sometimes expressed as normalized directional response level in decibels.
Note 4 to entry: Directional response can be specified in a two-dimensional space in one plane only.
Conventionally, the two-dimensional directional response is specified in the three planes defined for the transducer coordinate system defined in IEC 60500:201 7 (XY, XZ, YZ). In three dimensions, a transducer directional response can be specified in all planes through the reference centre.IEC 60565-1 pdf download.