Ultrasound velocity mapping with Lorentz force hydrophone

Abstract

In previous work [Grasland-Mongrain et al. 2013], a Lorentz force hydrophone consisting of a cylindrical arrangement of magnets around a thin metallic wire has been presented. An ultrasonic wave vibrates the wire inside a magnetic field, which induces an electrical current. The ultrasound velocity map is then tomographically reconstructed by recording the current amplitude after translation and rotation of the wire. A hydrodynamic model provides a relationship between the velocity and the measured tension. Wire tension influence, electrical output characteristics, frequency response, sensitivity, directionality, and robustness to cavitation were characterized. A multi-wires hydrophone was also fabricated and tested. Results show that tension of the wire has negligible influence on the signal. No peak of electrical impedance was observed from 0.15 to 10 MHz. The signal was linear over pressure from 50 kPa to 15 MPa. The hydrophone was robust even when cavitation activity occurred. The directivity is explained with the Lorentz force expression. The multi-wire hydrophone could work only at low frequencies. Such hydrophone could be of interest for high intensity acoustic field characterization.