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.

The behavior of strain-coupled composite magnetoelectric cantilever sensors under excitation with an inhomogeneous magnetic field is investigated. We consider a local excitation generated by a ring-shaped copper coil with one winding, variably positioned around the sensor. 3D finite-element-method simulations of the sensitivity along the longitudinal sensor axis are conducted and compared to the experimental results. The investigated sensor consists of a 2 µm thick magnetostrictive layer [(Fe₉₀Co₁₀)₇₈Si₁₂B₁₀] and a 2 µm thick AlN piezoelectric layer on the opposite sides of a 350 µm thick silicon cantilever of 26.25 mm length and 2.45 mm width. The sensitivity along the sensor axis is investigated for three different frequencies—one below the resonance frequency, one at resonance, and one above resonance. A rich position-dependent sensitivity behavior is observed in simulations and experiments with a maximum sensitivity at ∼4 mm from the fixed end of the cantilever for all three frequencies. Below and at the resonance frequency, a monotonously decreasing sensitivity is observed toward the free end of the cantilever. For the frequency above resonance, we observe a position of zero sensitivity at ∼17 mm from the fixed end and a subsequent second maximum of sensitivity. We attribute the zero sensitivity to the destructive interference of local excitation and resonance effects.

Magnetoelectric (ME) magnetic field sensors are novel sensing devices of great interest in the field of biomagnetic measurements. We investigate the influence of magnetic crosstalk and the linearity of the response of ME sensors in different array and excitation configurations. To achieve this aim, we introduce a combined multiscale 3D finite-element method (FEM) model consisting of an array of 15 ME sensors and an MRI-based human head model with three approximated compartments of biological tissues for skin, skull, and white matter. A linearized material model at the small-signal working point is assumed. We apply homogeneous magnetic fields and perform inhomogeneous magnetic field excitation for the ME sensors by placing an electric point dipole source inside the head. Our findings indicate significant magnetic crosstalk between adjacent sensors leading down to a 15.6% lower magnetic response at a close distance of 5 mm and an increasing sensor response with diminishing crosstalk effects at increasing distances up to 5 cm. The outermost sensors in the array exhibit significantly less crosstalk than the sensors located in the center of the array, and the vertically adjacent sensors exhibit a stronger crosstalk effect than the horizontally adjacent ones. Furthermore, we calculate the ratio between the electric and magnetic sensor responses as the sensitivity value and find near-constant sensitivities for each sensor, confirming a linear relationship despite magnetic crosstalk and the potential to simulate excitation sources and sensor responses independently.

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.

In recent years, thin-film magnetoelectric (ME) magnetic-field sensors have emerged as novel and advantageous devices for biomagnetic measurements. These ME sensors promise contactless readings of the magnetic fields generated by the human body, e.g., in magnetocardiography, with added benefits such as operation at room temperature without magnetic shielding [1]. The ME sensors considered here are based on strain-coupled thin-film magnetostrictive and piezoelectric layers on a cantilever. An incident magnetic field deforms the magnetostrictive layer which is coupled to a deformation of the piezoelectric layer giving a voltage signal. Previous studies often characterize the sensor performance under simplified homogeneous magnetic-field conditions. We have demonstrated that these sensors show a significantly different behavior under inhomogeneous magnetic-field excitation [2]. Here, we discuss a multiscale simulation approach using a joint sensor and simplified human head model for evaluation of sensor performance at different positions and orientations.