Magnetoelastic microsensors for environmental monitoring

This paper reports on the operational characteristics, and application, of a new passive wireless micro-sensor platform based on magnetoelastic materials. We have used micro-electro-discharge machining (micro-EDM) to fabricate magnetoelastic micro-sensor arrays. In response to a time varying magnetic field, amorphous ferromagnetic magnetoelastic thin films efficiently convert magnetic energy into elastic energy. The elastic waves mechanically deform the sensor which, for ribbon shaped elements, has a characteristic mechanical resonant frequency that is a function of its length, elasticity, and material density. Since the magnetoelastic material is also magnetostrictive, as the sensor mechanically deforms it generates magnetic flux that extends remotely about the device, which can be detected by a pickup coil. The remote query capability of this sensor technology enables a host of new monitoring applications including in-situ and in-vivo experiments. The bare sensor is capable of measuring ambient temperature and pressure, liquid density, liquid viscosity, and fluid flow velocity. The sensor platform can be used for chemical sensing when used in combination with mass-changing chemically responsive layers. Using an array of the magnetoelastic sensors one can determine multiple environmental conditions simultaneously.