Progress of the development and calibration of needle-type ultrasonic hydrophone

To evaluate the sound field characteristic of ultrasonic diagnostic and therapy equipment and industrial ultrasonic transducer, ultrasonic hydrophone such as needle-type hydrophone, membrane hydrophone and fiber optic hydrophone are always needed. The needle-type hydrophone has been widely used for its property of small size, high signal to noise ratio, good directivity, wide frequency response, ability for near field continuous acoustic measurement. Firstly this paper presents the development progress of the needle-type hydrophone in details, including structure and its improvement, focusing on the development of needle-type hydrophone sensing element and the evolving structure progress. Secondly the calibration methods of needle hydrophone, including reciprocity method, field scanning method, optical interfereometry method, are compared and analyzed. Currently hydrophone calibration capability of National Institute of Metrology China is introduced in the last section.