Fundamental Noise Limits and Sensitivity of Piezoelectrically Driven Magnetoelastic Cantilevers

Abstract

Magnetoelastic sensors for the detection of lowfrequency and low-amplitude magnetic fields are in the focus of research for more than 30 years. In order to minimize the limit of detection (LOD) of such sensor systems, it is of high importance to understand and to be able to quantify the relevant noise sources. In this contribution, cantilever-type electromechanical and magnetoelastic resonators, respectively, are comprehensively investigated and mathematically described not only with regard to their phase sensitivity but especially to the extent of the sensor-intrinsic phase noise. Both measurements and calculations reveal that the fundamental LOD is limited by additive phase noise due to thermal-mechanical noise of the resonator, i.e. by thermally induced random vibrations of the cantilever, and by thermal-electrical noise of the piezoelectric material. However, due to losses in the magnetic material parametric flicker phase noise arises, limiting the overall performance. In particular, it is shown that the LOD is virtually independent of the magnetic sensitivity but is solely determined by the magnetic losses. Instead of the sensitivity, the magnetic losses, represented by the material's effective complex permeability, should be considered as the most important parameter for the further improvement of such sensors in the future. This implication is not only valid for magnetoelastic cantilevers but also applies to any type of magnetoelastic resonator.

Phase Noise of SAW Delay Line Magnetic Field Sensors

“…If one considers the magnetic quality factor with values of up to about 25 or the relative magnetic loss factor with values slightly below (each for ) comparable values can be found in literature [ 66 , 78 ]. In fact, a similar value for the relative magnetic loss factor of has recently been found for a resonant magnetic field sensor with a magnetostrictive thin-film of the same alloy utilized here [ 79 ].…”

Magnetoelastic Coupling and Delta-E Effect in Magnetoelectric Torsion Mode Resonators

“…Additional simulations show that further optimization of the electrode design and reduction in the parasitic capacity from bond pads and wires could improve of TM1 to . Alternatively, the parasitic effect of the sensor capacitance could be neutralized with additional electronics to utilize the phase-modulated signal for magnetic field detection [ 48 ]. A further improvement by a factor of two could be obtained by exciting both electrodes and , phase shifted by 180°.…”

“…Consequently, the ac magnetic field to be measured causes an amplitude modulation (am) and phase modulation (pm) of the current through the sensor. Detailed information on the operation and read-out can be found elsewhere [ 46 , 47 , 48 ]. The linearized change of and with the magnetic field can be described by the amplitude sensitivity and the phase sensitivity [ 49 ], respectively.…”

Roadmap on Magnetoelectric Materials and Devices

“…The detectivity in the ME sensors discussed so far is limited by different noise sources. A fundamental limitation comes from thermal-mechanical noise of the resonator [383,434] and thermal-electrical noise of the piezoelectric material, where applicable. Yet, theoretical and experimental analysis shows that magnetic losses or hysteresis effects, mostly as a result of magnetic domain wall processes, are the dominating contributions to sensor noise in ME structures.…”