Combined hydrophone secondary calibration and directional response measurement setup

A combined measurement setup was developed for secondary hydrophone sensitivity calibration and hydrophone directional response measurements. The Setup comprises a mechanical hydrophone positioning and scanning system with five motorizes axes, a water basin, a pulse generator, a positioning controller, ultrasonic transducers and a computer with software. Sensitivity calibrations are based on comparison of the device under test with a reference membrane hydrophone calibrated primarily beforehand. Nonlinear broadband ultrasonic pulses are applied for characterization in wide frequency ranges from 1 MHz to 50 MHz. To simplify the rotational axis alignment needs for directional response measurements, an iterative rotational axis mismatch compensation method was developed. Hydrophone characterization examples are provided and the results are compared with independent measurements. For sensitivity, good agreement was found with deviations below 0.5 dB. Hydrophone effective sizes were determined preferably in the far field of a planar source transducer rather than in a focused field.