Simultaneous gas and magnetic sensing using a single heated micro-resonator

In this paper, we propose a single device for simultaneous measurement of in-plane magnetic field and gas concentration. The concept is based on tracking simultaneously the resonant frequency of the first two symmetric and anti-symmetric modes of an electrothermally actuated out-of-plane buckled micro-beam. First, the Lorentz-force magnetic sensing was investigated at different electrothermal voltages in air. Powered with 3.78 mW, the magnetic sensor achieves a sensitivity of 0.0867 /T at the second mode with good linearity lower than 0.1%. On the other hand, the gas-sensing technique is based on the thermal conductivity mechanism. We simultaneously measure the frequencies shift of the first and the second modes while changing the gas concentration and the magnetic field (Bx). At Bx = 55 mT, Helium (He) and Argon (Ar) sensing yield the highest sensitivity of 4.15%/%He in the range of 2.5–10% He and 2.22%/%Ar in the range of 10–20%Ar. Additionally, the results show a response/recovery time of 200 s/180 s (He) and 580 s/320 s (Ar). Herein, for the first time, we experimentally demonstrate the potential for employing a multimode micro-resonator for magnetic field and gas sensing. The proposed multi-sensing device has the characteristics of simple design, low cost, small size, and good linearity, making it suitable for smart environmental monitoring applications.