Johan Arbustini

Non-invasive monitoring of magnetic nanoparticles (MNPs) is gaining increasing importance in the biomedical field. Applications such as drug delivery, contrast imaging, and protein detection require the development of precise and robust experimental setups that closely replicate realistic and physiological conditions. In this study, we investigate the detection and quantification of MNPs under dynamic flow conditions using an unshielded and portable gradiometer setup designed for potential in-vivo applications. With its large possible detection area, the setup provides a versatile and adaptable platform for evaluating MNP behavior also in physiologically relevant environments, offering strong potential for translation into diverse in-vivo magnetic sensing applications. For testing, MNPs are moved as a bolus through a plastic tube in the sensing area of the setup. An AC susceptibility technique was employed to excite the MNPs using a weak alternating magnetic field of 100 μT, while the resulting low MNPs magnetization induced a signal detected by two pick-up coils arranged in a differential configuration on one side of the sensing area. Through appropriate calibration of the setup, the magnetic moment of each sample was estimated. The resulting magnetic field was calculated as a function of the sample’s "depth", i.e., distance from the first coil. For MNPs bolus velocities of 10 mm/s, the experimental curves follow the theoretical trend derived from the Biot–Savart law for the magnetic field generated by a single magnetic dipole. 50 μg MNP droplets are detected with a magnitude of 4 nT and a SNR of 8 dB at a distance of 10mm. The gradiometer sensor is capable of quantifying a 500 μg MNP sample at depths up to 24mm.

This letter presents a pilot evaluation of a microelectromechanical-system (MEMS) cantilever resonator with monolithically integrated NdFeB magnets at its tip for compact generation of a time-dependent magnetic field. By applying a low-amplitude sinusoidal voltage with a predefined frequency to a piezoelectric layer, the cantilever is driven at its mechanical resonance, causing the embedded magnets to oscillate in space, resulting in a time-varying magnetic flux density. A prototype device is characterized for the first time by a superconducting quantum interference device magnetometer inside a magnetically shielded room only for evaluation purposes. A magnetic performance factor is introduced, which relates device design aspects to experimental observables and allows for the comparison of different devices. The results enable us to outline optimization steps toward robust, low-power MEMS-based magnetic field markers for biomagnetic sensing applications, industrial sensing, and magnetic measurement platforms where conventional coil-based systems are impractical.

Optimizing sensor readout schemes and integrated circuit designs for both open-loop and closed-loop implementations requires precise modeling and simulation strategies. This study introduces a novel two-port impedance model to estimate the behavior of a converse Magnetoelectric (cME) sensor. This model provides a possible framework for calculating transfer functions and simulating magnetometer behavior in both continuous- and discrete-time simulation environments, and it is also possibly transferable to other magnetometer types. Common S-parameters were measured experimentally using an impedance analyzer and converted to Z-parameters to create a transfer function for system-level simulations. The model was validated through an analysis of output-related noise using MATLAB and LTSpice simulations to optimize the noise of the analog circuit parts of the system. The simulation results were compared with experimental measurements using a Zurich Instruments lock-in amplifier and the custom-designed low-noise printed circuit board (PCB) under model considerations. The proposed methodology derives noise considerations and the transfer function of a magnetometer. These are essential for readout schemes for mixed-signal circuit design. This allows low-noise electronics to be designed and extended to other sensor interface electronics, broadening their applicability in high-performance magnetic sensing.

Objectives: This study evaluates micro-electro-mechanical systems (MEMS) devices comprising cantilever piezoelectric resonators with powder-based permanent magnets (micromagnets) at the tip. Fabricated using a well-known PowderMEMS process given by the Fraunhofer Institute for Silicon Technology, these devices function as magnetic field sensors based on the magnetic torque detection principle, which arises from the interaction between the given micromagnets’ dipole moment and the to-be-measured magnetic field. The study investigates how the magnetic state of the micromagnets influences the overall sensitivity of the provided Prototype MEMS-devices. Methods: The performance of the first prototypes of this narrow-band magnetic field sensor was evaluated using two approaches: (1) a Vibrating Sample Magnetometer (VSM) to analyze the magnetic hysteresis loop and (2) sensitivity measurements at resonance frequency to determine the provided sensitivity under a predefined external magnetic flux density. Results: Among the four prototypes analyzed, the device with the highest remanence and coercivity demonstrated superior sensing performance, achieving a sensitivity of 1,090 kV/T at the resonance frequency. The analysis showcased substantial variations in noise amplitude spectral density, and sensitivity, emphasizing the importance of magnetic hysteresis properties in sensor performance. Conclusions: These findings highlight the potential of MEMS-devices with enhanced coercivity and remanence for enhanced sensing capabilities in compact sensor designs, particularly useful for array sensor configurations in narrow-bandwith medical applications.

Reconstructing an Amplitude-modulated (AM) signal with a modulation index below 0.01 is a significant challenge for conventional and established direct and digital demodulation methods. This work examines the importance of appropriate demodulation techniques and methods for analyzing and evaluating their performance using the sensing principle of electrically modulated Magnetoelectric (ME) sensors. These magnetic field sensors produce a double-sideband amplitude-modulation with carrier (DSB-AM-WC) signal at the sensor output, and their ultra-low modulation index often limits an accurate recovery of magnetic signal information. Addressing this limitation requires optimized demodulation strategies to realize the full potential of this ME sensor system for use in biomedical applications. This study assesses signal integrity during frequency conversion and defines detection limits for an analog demodulator designed for DSB-AM-WC signals with an ultra-low modulation index, which is explicitly designed for this sensor concept. The proposed low-cost demodulation system converts the 500 kHz (Radio Frequency, RF) DSB-AM-WC sensor output to an Intermediate Frequency (IF), allowing subsequent analog-to-digital for digitization. This work analyzes the analog signal path of electrically modulated ME Sensors and develops a sensor emulator setup for controlled testing of analog demodulation schemes. The emulator can generate AM signals (500 kHz carrier, Sideband ranging from 10 Hz–12 kHz, modulation index from 0.00001–1) while primarily considering electrical noise contributions from the hardware at room temperature, thus bridging the gap between theoretical analysis and practical implementation. Experimental results demonstrate that the proposed analog demodulation system, featuring a double-balanced frequency mixer (SRA-8+, Mini-Circuits, Brooklyn, NY), achieves an ultra-low noise input-referred noise of 10 nV/ √ Hz , enabling the recovery of modulation indices as low as 0.000249, delivers an signal-to-noise ratio (SNR) of 20 dB, and provides a stable dynamic range of 64 dB at output. The results confirm the effectiveness of the developed low-cost demodulation system while highlighting limitations, including the effect of input power and the phase shift available in diode-based mixers on maintaining signal integrity for low modulation index AM signals. The results identified the first possible guidelines for optimizing analog front-end systems for ME sensors. Future work will focus on investigating the signal output of real ME sensor prototypes, benchmarking the proposed system against state-of-the-art technologies, and considering additional environmental factors influencing performance.

Converse magnetoelectric sensors enable the detection of low‐frequency and low‐amplitude magnetic fields over a bandwidth of several kilohertz by combining the electrical excitation of a magnetoelectric resonator via a piezoelectric layer with an inductive readout. Here, a comprehensive sensor model is presented to further foster the development of this promising sensor concept. The model relates the output signal to the device characteristics, taking into account the magnetoelastic and electromechanical properties, the resonator geometry, and operating conditions. The sensor system is thoroughly experimentally analyzed to validate the model. Based on the analysis, the sensor concept is explained in detail, including the origin of its loss and bandwidth and their connection with the magneto‐mechanical loss in the magnetostrictive layer. Significant advances have been made in the comprehensive understanding of converse magnetoelectric sensors, providing a solid basis for future improvements in magnetoelectric sensor systems.

Some magnetoelectric sensors require predefined external magnetic fields to satisfy optimal operation depending on their resonance frequency. While coils commonly generate this external magnetic field, a microelectromechanical systems (MEMS) resonator integrated with permanent magnets could be a possible replacement. In this proof-of-concept study, the interaction of a MEMS resonator and the ME sensor is investigated and compared with the standard approach to achieve the best possible sensor operation in terms of sensitivity. The achievable sensor sensitivity was evaluated experimentally by generating the magnetic excitation signal by a coil or a small-sized MEMS resonator. Moreover, the possibility of using both approaches simultaneously was also analysed. The MEMS resonator operated with 20V_ppat 1.377 kHz has achieved a sensor sensitivity of 221.21mV/T. This sensitivity is comparable with the standard approach, where only a coil for sensor excitation is used. The enhanced sensitivity of 277.0mV/T could be identified by generating the excitation signal simultaneously by a coil and the MEMS resonator in parallel. In conclusion, these MEMS resonator methods can potentially increase the sensitivity of the ME sensor even further. The unequal excitation frequency of the MEMS resonator and the resonance frequency of the ME sensor currently limit the performance. Furthermore, the MEMS resonator as a coil replacement also enables the complete sensor system to be scaled down. Therefore, optimizations to match both frequencies even better are under investigation.