| Magnetoelastic resonance sensors, of the type considered in this work, are elements of magnetostrictive material that exhibit a mechanical resonance. The mechanical resonance of a magnetoelastic sensor can be stimulated and detected magnetically on a remote query basis (wireless, passive) and the sensors in this work are measured by monitoring the impedance of a solenoid with the sensor elements inside the core. The resonance frequency and peak amplitude depend on the applied magnetic biasing field due to the DeltaE effect. This work examines the sensitivity of the resonance frequency and amplitude to fluid viscosity and density, and mass loading, as a function of the bias condition and DeltaE effect. Scaling issues, the effect of sensor shape and size on the frequency sensitivity, and DeltaE effect, are investigated to determine optimal operating conditions. Free-floating and mounted sensors are compared along with fabrication methods for creating multi-sensor arrays. The effects of measuring multiple sensors, each with their own identifiable resonance frequency, within the same solenoid are addressed. An equivalent circuit for the impedance measuring technique is derived and the limitations imposed by overdriving the sensors into nonlinear regimes are investigated. The physical arrangement of single-element and multi-sensor arrays is investigated to facilitate practical application of the sensor technology. |
