Low frequency calibration of hydrophones by self-mixing interferometry at UME

Realization and dissemination of the unit of sound pressure in water are carried out through calibration of hydrophones and underwater acoustic transducers. Different calibration methods applicable for different frequency ranges are available for this purpose. For calibration of reference hydrophones at low frequencies air-water pistonphone has been constructed at Turkish National Metrology Institute (UME). One of the main parts of the calibration system is optical interferometer. Two different interferometer types were used for the precise displacement measurements. The hydrophone calibrations performed by using air-water pistonphone both with homodyne Michelson interferometer and diode laser based self-mixing interferometer, ECDL.