Magnetoacoustic remote query temperature and humidity sensors

In response to an externally applied time-varying magnetic field, freestanding sensors made of magnetoelastic thick or thin films mechanically oscillate. These oscillations are strongest at the characteristic resonant frequency of the sensor. Depending upon the physical geometry and the surface roughness of the magnetoelastic sensor, these mechanical deformations launch an acoustic wave that can be detected remotely from the test area by a microphone. By monitoring changes in the characteristic resonant frequency of a magnetoacoustic sensor, multiple environmental parameters can be measured. In this work we report on the application of magnetoacoustic sensors for the remote query measurement of temperature, the monitoring of phase transitions and, in combination with a humidity-responsive mass-changing Al2O3 ceramic thin film, the in situ measurement of humidity levels.