Microwave ferrite acceleration sensors

This paper presents a new and potentially simple method of producing a frequency shift proportional to sensed acceleration in a passive microwave device. Magnetostriction effects in microwave ferrite rods are employed to convert an applied stress (acceleration) to a shift in resonant frequency. Equations for the ferrite effective permeability are derived in terms of the internal field component. Experimental verification was obtained by placing the resonant cavity on a rotatable test stand and using the earth's gravitational field as the accelerating field 0 to 1 g being applied to the device. A SHF signal generator excites the cavity, while a spectrum analyzer and digital frequency counter monitor the resonant frequency. Correction was made for spurious frequency shifts due to lead component movements. A net, non-linear frequency shift characterized by the value +1.064 kHz per gravity was obtained. Agreement as to sign and general magnitude of theory and experiment was encouraging. Magnesium-manganese ferrites have small magnetostriction coefficients, yet even the frequency shifts with these ferrites were easily detectable. This effect or application is certainly worthy of additional interest and exploration.