Abstract
We present a comprehensive study of a magnetic sensor system that benefits from a new technique to substantially increase the magnetoelastic coupling of surface acoustic waves (SAW). The device uses shear horizontal acoustic surface waves that are guided by a fused silica layer with an amorphous magnetostrictive FeCoSiB thin film on top. The velocity of these so-called Love waves follows the magnetoelastically-induced changes of the shear modulus according to the magnetic field present. The SAW sensor is operated in a delay line configuration at approximately 150 MHz and translates the magnetic field to a time delay and a related phase shift. The fundamentals of this sensor concept are motivated by magnetic and mechanical simulations. They are experimentally verified using customized low-noise readout electronics. With an extremely low magnetic noise level of ≈100 pT/sqrt{{rm{Hz}}}, a bandwidth of 50 kHz and a dynamic range of 120 dB, this magnetic field sensor system shows outstanding characteristics. A range of additional measures to further increase the sensitivity are investigated with simulations.
Highlights
Magnetic field sensing is an important task for many applications ranging, e.g., from positioning and navigation to electronic stability programs, electrical current sensors to biomagnetic field detection[1,2,3]
Ultra-low limit of detection (LOD) for magnetic field sensing in combination with ambient temperature operation and sufficient spatial resolution have been reported for orthogonal fluxgate magnetometers[6], sensors employing the giant magnetoimpedance effect[7], atomic magnetometers[8], magnetoresistive devices[9], and, most recently, for sensors using the ΔE-effect[10]
The design of a novel Love wave-type magnetic field surface acoustic waves (SAWs) sensor will be outlined with an emphasis on finite element modeling (FEM) simulations to work out the advantages of using a dedicated guiding layer
Summary
Anne Kittmann[1], Phillip Durdaut 2, Sebastian Zabel[1], Jens Reermann[2], Julius Schmalz[2], Benjamin Spetzler[1], Dirk Meyners[1], Nian X. The device uses shear horizontal acoustic surface waves that are guided by a fused silica layer with an amorphous magnetostrictive FeCoSiB thin film on top The velocity of these so-called Love waves follows the magnetoelastically-induced changes of the shear modulus according to the magnetic field present. Very demanding specifications arise in terms of the dynamic magnetic field range and the frequency bandwidth in case of a current sensor[4] as well as in a limit of detection (LOD) in the pT/ Hz to fT Hz range in case of sensors for biomagnetic signals[5] Both applications require the detection of DC or very low frequency magnetic fields, which is especially challenging if 1/f (f: frequency) noise is present.
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