A Contactless DC Current Sensor Based on Thin-Film Lithium Niobate S0-Mode Lamb Wave Resonator

This paper present a novel contactless DC current sensor based on a high frequency S0-mode Lamb wave resonator fabricated on a lithium niobate on insulator (LNOI) substrate, which offers high sensitivity and high Q-value. This current sensor is constructed by mounting a self-aligned micro-magnet on a microcantilever, which also integrates a thin-film Lamb wave resonator serving as a strain sensor. In this design, the magnetic force exerted on the permanent magnet by the DC-current excited magnetic field results in strain on the microcantilever structure. This strain is then detected through the frequency shift of the Lamb wave resonator, allowing for accurate measurement of the current magnitude. The Lamb wave resonator and the microcantilever was fabricated on a LNOI wafer through electrode lift-off and a two-step back-etching process. A 2-μm nickel layer was patterned on the tip of the microcantilever, allowing for the self-alignment of the magnet on the microstructure through the attractive force. The thin-film S0-mode Lamb wave resonator operates at 371.2 MHz with a Q-factor as high as 1432, enabling highly sensitive current measurement. Experimental results show the current sensor achieved a sensitivity of 325 Hz/mA. This sensor holds promising potential for applications in smart meters, electric vehicle charging stations, and other energy systems.