Lorentz-force hydrophone characterization

Abstract

Abstract-A Lorentz-force hydrophone consists of a thin wire placed inside a magnetic field. When under the influence of an ultrasound pulse, the wire vibrates and an electrical signal is induced by the Lorentz force that is proportional to the pulse amplitude. In this study a compact prototype of such a hydrophone is introduced and characterized, and the hydrodynamic model previously developed is refined. It is shown that the wire tension has a negligible effect on the measurement of pressure. The frequency response of the hydrophone reaches 1 MHz for wires with a diameter ranging between 70 and 400 µm. The hydrophone exhibits a directional response such that the signal amplitude differs by less than 3dB as the angle of the incident ultrasound pulse varies from -20 o and +20 o . The linearity of the measured signal is confirmed across the 50 kPa to 10 MPa pressure range, and an excellent resistance to cavitation is observed. This hydrophone is of interest for high pressure ultrasound measurements including High Intensity Focused Ultrasound (HIFU) and ultrasonic measurements in difficult environments.

Design of a Superconducting Magnet for Lorentz Force Electrical Impedance Tomography

“…2. A practical Halbach magnet was tested experimentally to generate a uniform field for a Lorentz-force hydrophone [10]. Therefore, a reasonable idea is sparked: it could use superconducting coils to build an electromagnet that operating below its critical temperature, which is essentially equivalent to the Halbach Array based on permanent magnets.…”