A wireless micro-sensor for simultaneous measurement of pH, temperature, and pressure

In response to a magnetic field impulse, magnetostrictive magnetoelastic sensors mechanically vibrate. These vibrations can be detected in several ways: optically from the amplitude modulation of a reflected laser beam, acoustically using a microphone or hydrophone, and by using a pickup coil to detect the magnetic flux emitted from the sensor. Earlier work has shown that the resonant frequency of a magnetoelastic sensor shifts in response to different environmental parameters, including temperature, pressure, fluid flow velocity and mass loading, with each parameter determined in an otherwise constant environment. To extend the utility of the sensor technology in this work we report on the fabrication and application of a miniaturized array of four magnetoelastic sensors that enable the simultaneous remote query measurement of pH, temperature, and pressure from a passive, wireless platform. (Some figures in this article are in colour only in the electronic version; see www.iop.org)