A passive, wireless strain sensor using a microfabricated magnetoelastic beam element

This paper describes a resonant wireless strain sensor fabricated from a magnetoelastic alloy. The sensor consists of a doubly-clamped suspended structure comprised of a resonant strip and a strain attenuating spring. Strain causes a shift in magnetoelastic resonant frequency in the longitudinal mode of the sensor, which is detected wirelessly using pick-up coils. The sensor is fabricated from a 28 μm thick foil of Metglas™ 2826MB (Fe₄₀Ni₃₈Mo₄B₁₈), a ferromagnetic magnetoelastic alloy, using micro-electrodischarge machining (μEDM). The sensor has an active area of 7×2 mm² and operates at a resonance frequency of 227.4 kHz. It has a sensitivity of 4300 ppm/mstrain; the dynamic range is 0.2-2.8 mstrain. The sensor geometry can be modified to accommodate differing sensitivity and dynamic range requirements.