MagnetoMyoGraphy (MMG) with superconducting quantum interference devices (SQUIDs) enabled the measurement of very weak magnetic fields (femto to pico Tesla) generated from the human skeletal muscles during contraction. However, SQUIDs are bulky, costly and require working in a temperature-controlled environment, limiting wide-spread clinical use. We introduce a low-profile magnetoelectric (ME) sensor with analog frontend circuitry that has sensitivity to measure pico-Tesla MMG signals at room temperature. It comprises magnetostrictive and piezoelectric materials, FeCoSiB/AlN. Accurate device modelling and simulation are presented to predict device fabrication process comprehensively using the finite element method (FEM) in COMSOL Multiphysics®. The fabricated ME chip with its readout circuit was characterized under a dynamic geomagnetic field cancellation technique. The ME sensor experiment validate a very linear response with high sensitivities of up to 378 V/T driven at a resonance frequency of ${f_{res}}$ = 7.76 kHz. Measurements show the sensor limit of detections of down to 175 pT/Hz at resonance, which is in the range of MMG signals. Such a small-scale sensor has the potential to monitor chronic movement disorders and improve the end-user acceptance of human-machine interfaces.

A surface-acoustic-wave (SAW) magnetic-field sensor utilizing fundamental, first- and second-order Love-wave modes is investigated. A $4.5 \mathsf{\mu }\mathrm{m}$ SiO₂ guiding layer on an ST-cut quartz substrate is coated with a 200 $\mathrm{n}$ $\mathrm{m}$ (Fe₉₀Co₁₀)₇₈Si₁₂B₁₀ magnetostrictive layer in a delay-line configuration. Love-waves are excited and detected by two interdigital transducers (IDT). The delta-E effect in the magnetostrictive layer causes a phase change with applied magnetic field. A sensitivity of 1250 ${}^{°}$ / $\mathrm{m}$ $\mathrm{T}$ is measured for the fundamental Love mode at 263 $\mathrm{M}$ $\mathrm{Hz}$ . For the first-order Love mode a value of 45 ${}^{°}$ / $\mathrm{m}$ $\mathrm{T}$ is obtained at 352 $\mathrm{M}$ $\mathrm{Hz}$ . This result is compared to finite-element-method (FEM) simulations using one-dimensional (1D) and two-and-a-half-dimensional (2.5 D) models. The FEM simulations confirm the large drop in sensitivity as the first-order mode is close to cut-off. For multi-mode operation, we identify as a suitable geometry a guiding layer to wavelength ratio of $h_{\mathrm{GL}}/\lambda \approx 1.5$ for an IDT pitch of $p=12 \mathsf{\mu }\mathrm{m}$ . For this layer configuration, the first three modes are sufficiently far away from cut-off and show good sensitivity.

In this theoretical study, we explore the enhancement of sensing capabilities in surface acoustic wave (SAW)-based magnetic field sensors through the integration of engineered phononic crystals (PnCs). We particularly focus on amplifying the interaction between the SAW and magnetostrictive materials within the PnC structure. Through comprehensive simulations, we demonstrate the synchronization between the SAWs generated by IDTs and the resonant modes of PnCs, thereby leading to an enhancement in sensitivity. Furthermore, we investigate the ΔE effect, highlighting the sensor’s responsiveness to changes in external magnetic fields, and quantify its magnetic sensitivity through observable changes in the SAW phase velocity leading to phase shifts at the end of the delay line. Notably, our approach yields a magnetic field sensitivity of approximately $S~138\frac{°}{mT}$ for a delay line length of only 77 µm in homogeneous magnetic fields. Our findings underline the potential of PnCs to advance magnetic field sensing. This research offers insights into the integration of engineered materials for improved sensor performance, paving the way for more effective and accurate magnetic field detection solutions.

Magnetoelectric thin-film cantilevers consisting of strain-coupled magnetostrictive and piezoelectric layers are promising candidates for magnetic field measurements in biomedical applications. In this study, we investigate magnetoelectric cantilevers that are electrically excited and operated in a special mechanical mode with resonance frequencies above 500 kHz. In this particular mode, the cantilever bends in the short axis, forming a distinctive U-shape and exhibiting high-quality factors and a promising limit of detection of 70$\mathrm{p}$$\mathrm{T}$/$\mathrm{Hz}$^1/2 at 10 $\mathrm{Hz}$. Despite this U mode, the sensors show a superimposed mechanical oscillation along the long axis. The induced local mechanical strain in the magnetostrictive layer results in magnetic domain activity. Due to this, the mechanical oscillation may cause additional magnetic noise, deteriorating the limit of detection of such sensors. We compare finite element method simulations with measurements of magnetoelectric cantilevers in order to understand the presence of oscillations. From this, we identify strategies for eliminating the external effects that affect sensor operation. Furthermore, we investigate the influence of different design parameters, in particular the cantilever length, material parameters and the type of clamping, on the amplitude of the undesired superimposed oscillations. We propose design guidelines to minimize the unwanted oscillations.

We investigate a coupled multiscale 3D finite element model consisting of an orthogonal array of thin-film cantilever magnetoelectric magnetic field sensors and a simplified human head model. Electric point dipole sources are placed inside the head to generate an electromagnetic field. This field propagates through the tissue layers and outside of the head, where it reaches the sensor array. The investigated sensors are based on a 300 μm thick silicon substrate layer of 26.25 mm length and 2.45 mm width, with a 20 μm thick AlN layer and a 20 μm thick FeCoSiB layer as piezoelectric and magnetostrictive materials, respectively, located on opposite sides of the substrate. We position three sensors orthogonally to obtain a vector field sensor. The head model is based on the three-shell approach and consists of concentric spheres representing white matter, skull, and skin. All three layers are assigned specific conductivity and relative permittivity values from literature, aiming to approximate the propagation of electromagnetic fields through the different tissue types. We observe propagation of an electric field generated by the dipole source and subsequent induction of a magnetic field inside the head structure, propagating outwards to the sensor array, where the generated voltage in the piezoelectric layer is evaluated for different magnetoelectric sensor array and source positions and orientations. We show different behaviors of the sensors for a dipole source inside the head tissue versus a simple air environment, highlighting benefits in accuracy and specificity of a combined head and sensor model with realistic material parameters.

Magnetoelectric cantilevers consisting of strain-coupled magnetostrictive and piezoelectric (PE) layers are applicable to magnetic-field sensing. For the first bending mode, the magnetic field-induced stress distribution is of equal sign along the cantilever length. Thus, a plate-capacitor electrode configuration encompassing the complete PE layer may be used for collecting the strain-induced charge. For higher order modes, stress regions of the opposite sign occur in the cantilever length direction. To prevent charge cancellation and to harvest the piezoelectric induced charge efficiently, segmented electrodes are employed. This study investigates the effect of the electrode configuration on the signal-to-noise ratio (SNR) for higher order bending modes. The charges collected by the electrodes are calculated using a finite element method simulation considering the mechanical, electrical, and magnetic properties of the cantilever. By combination with an analytic noise model, taking into account the sensor and amplifier noise sources, the SNR is obtained. We analyze a 3 mm long, 1 mm wide, and 50 $\mathrm{\mu }$ m thick silicon cantilever with layers of 2 $\mathrm{\mu }$ m magnetostrictive soft amorphous metal (FeCoSiB) and 2 $\mathrm{\mu }$ m piezoelectric aluminum nitride. We demonstrate that an SNR-optimized electrode design yields an SNR improvement by 2.3 dB and 2.4 dB for the second and third bending modes compared to a signal optimized design.