Hydrogels are biomimetic materials widely used in the area of biomedical engineering and biosensing. Ferrogels (FG) are magnetic composites capable of functioning as magnetic field sensitive transformers and field assisted drug deliverers. FG can be prepared by incorporating magnetic nanoparticles (MNPs) into chemically crosslinked hydrogels. The properties of biomimetic ferrogels for multifunctional biosensor applications can be set up by synthesis. The properties of these biomimetic ferrogels can be thoroughly controlled in a physical experiment environment which is much less demanding than biotests. Two series of ferrogels (soft and dense) based on polyacrylamide (PAAm) with different chemical network densities were synthesized by free-radical polymerization in aqueous solution with N,N’-methylene-diacrylamide as a cross-linker and maghemite Fe₂O₃ MNPs fabricated by laser target evaporation as a filler. Their mechanical, electrical and magnetic properties were comparatively analyzed. We developed a giant magnetoimpedance (MI) sensor prototype with multilayered FeNi-based sensitive elements deposited onto glass or polymer substrates adapted for FG studies. The MI measurements in the initial state and in the presence of FG with different concentrations of MNPs at a frequency range of 1–300 MHz allowed a precise characterization of the stray fields of the MNPs present in the FG. We proposed an electrodynamic model to describe the MI in multilayered film with a FG layer based on the solution of linearized Maxwell equations for the electromagnetic fields coupled with the Landau-Lifshitz equation for the magnetization dynamics.

In the development of any type of magnetic field sensor based on magnetic films, special consideration must be given to the magnetic layer component. The presented work investigates the use of scalable flux closing magnetostrictive multilayers for inverse magnetoelectric sensors. In such a type of magnetic field sensor, highly sensitive AC and DC field detection relies on strong excitation of the incorporated magnetic layers by piezoelectrically driven cantilever oscillation at mechanical resonances. The provoked periodic flux change is influenced by the magnetic field to be measured and is picked up by a coil, which generates the measured output. The multilayered inverse magnetoelectric sensor is investigated with regard to linearity, noise behavior, and detection limit of DC and AC signals. A significant advancement for inverse magnetoelectric thin film sensors is demonstrated in this study. Using exchange bias stabilized magnetic multilayers with flux closure structures, detection limits are improved by an order of magnitude to less than 8 pT/Hz1/2 at 10 Hz and 18 pT/Hz1/2 at DC.

Intrinsic magnetic noise limits the functionality of all magnetic field sensors and related devices using magnetic films as sensing elements. A novel origin of magnetic noise due to ferromagnetic material's magnetostriction is revealed by implementing a comprehensive multi‐level signal‐noise model and thoroughly validating it experimentally on magnetoelectric composite ΔE‐effect sensors. From electrical measurements and operando magnetic domain visualization, magnetic contributions are shown to dominate the noise floor and limit the overall performance of multi‐domain magnetoelastic sensors. The newly introduced noise contribution is correlated with the nonlinearity of the magnetostrictive properties. The effect on sensor output is particularly pronounced in magnetoelastic and magnetoelectric composite devices, but the results generally apply to all sensor devices incorporating magnetic materials. Therefore, the identified magnetic noise source makes a significant contribution to understanding the limitations of magnetic sensors and provides important guidelines for optimizing future magnetic sensors for low detectivity.

Amorphous and nanocrystalline soft magnetic materials have attracted much attention in the area of sensor applications. In this work, the magnetoimpedance (MI) effect of patterned soft ferromagnetic meander-shaped sensor elements has been investigated. They were fabricated starting from the cobalt-based amorphous ribbon using the lithography technique and chemical etching. Three-turn (S1: spacing s = 50 μm, width w = 300 μm, length l = 5 mm; S2: spacing s = 50 μm, width w = 400 μm, length l = 5 mm) and six-turn (S3: s = 40 μm, w = 250 μm, length l = 5 mm; S4: s = 40 μm, w = 250 μm and l = 8 mm) meanders were designed. The ‘n’ shaped meander part was denominated as “one turn”. The S4 meander possesses a maximum MI ratio calculated for the total impedance ΔZ/Z ≈ 250% with a sensitivity of about 36%/Oe (for the frequency of about 45 MHz), and an MI ratio calculated for the real part of the total impedance ΔR/R ≈ 250% with the sensitivity of about 32%/Oe (for the frequency of 50 MHz). Chemical etching and the length of the samples had a strong impact on the surface magnetic properties and the magnetoimpedance. A comparative analysis of the surface magnetic properties obtained by the magneto-optical Kerr technique and MI data shows that the designed ferromagnetic meander-shaped sensor elements can be recommended for high frequency sensor applications focused on the large drop analysis. Here we understand a single large drop as the water-based sample to analyze, placed onto the surface of the MI sensor element either by microsyringe (volue range 0.5–500 μL) or automatic dispenser (volume range 0.1–50 mL).

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.

Delta-E effect sensors developed for detecting small amplitude and low-frequency magnetic fields have shown potential for miniaturization. However, a comprehensive signal-and-noise analysis of such miniaturized sensors is lacking. Here, we present an in-depth study of the key performance characteristics of sub-millimeter-sized delta-E effect sensors with a double-wing resonator geometry. Several resonance modes are evaluated for their sensitivity, noise, and limit of detection (LoD) as functions of the excitation voltage amplitude and magnetic bias flux density. We identify and discuss the optimal conditions for sensor operation and compare the performance to that of the reported macroscopic devices. While all investigated resonance modes behave qualitatively similar, quantitative differences in signal and noise lead to an almost sevenfold difference in LoD s. The performance is limited by magnetic noise at large excitation amplitudes and, unlike reported macroscopic delta-E effect sensors, by noise from the excitation signal and charge amplifier at low excitation amplitudes. The best performance is achieved in the third resonance mode excited at 683 kHz with a LoD≤7.4±3 nT/Hz between 10 and 1000 Hz and a minimum of 2.8 nT/Hz at 195 Hz. This demonstrates an improvement over previously reported values for miniaturized delta-E effect sensors in this frequency range. Moreover, the sensors show a −3 dB bandwidth of ≈440 Hz, which is significantly wider compared to macroscopic delta-E effect sensors. Reducing electronic noise and employing advanced magnetic multilayers can further improve the LoD, making these miniaturized sensors promising candidates for compact arrays.