A resonant magnetic field sensor is developed by using a piezoelectric quartz crystal double-ended tuning fork (DETF), two FeGa thin plates, and four quartz spacers. The double ends of the DETF are bonded to the ends of the magnetostrictive thin plates through four spacers with adhesive, allowing the magnetostrictive force to be converted into the longitudinal force in the DETF which leads to an increase of the resonant frequency of the DETF. This design brings the advantage of field-independent damping, i.e., the quality factor (Q-factor) of the sensor is found to be independent on the dc field, with an average value of about 3318 in the air due to the low internal loss in quartz. After an initially slow increase before the field reaching ~50 Oe, the resonant frequency of the sensor increases linearly with the increase of the applied dc field before reaching 280 Oe. The total frequency shift, sensitivity of the frequency shift per magnetic field, and field resolution in the linear region are 2.12% (~808.3 Hz), 3.5 Hz/Oe and 8 mOe, respectively. The results demonstrate a possibility and promising to realize a highly sensitive magnetic sensor with high-Q-factor quartz crystal as well as direct digital frequency output.

A static/quasi-static magnetic field sensor is developed by using a double ended trip-beam tuning fork (TBTF), a TbxDy1-xFe2-y plate and several piezoelectric Pb(Zr1−xTix)O3 (PZT) plates. The TBTF is boned horizontally across two ceramic supports which are fixed on the ends of the TbxDy1-xFe2-y plate. The magnetostrictive stress induces an axial force in the TBTF, which causes the resonance frequency of the TBTF to increase. The theoretical analysis shows that the magnetostrictive stress increases approximately linearly with the increase of the external DC field, and so does the resonance frequency shift of the TBTF. The magnetostrictive stress can get to 32.65MPa at the field of 1000Oe, and the total frequency shift respectively achieves 2.97% and 16.67% under the assumption of 10% and 60% transmission efficiencies (as the sectional area of the magnetostrictive plate being 6mm×1mm). A Be-bronze TBTF based sensor was fabricated, and the frequency shift of 2.1% was obtained by applying a DC magnetic field in the range of 0–1000Oe. The magneto-mechanical damping in the magnetostrictive plate has no influence on the quality factor of the TBTF which is found to be relatively constant after an initial increase. The results show the great potential to realize a high sensitivity magnetic sensor featuring high quality factor and digital frequency output

Cable current detection plays a vital role in power grids toward improving transmission efficiency, relieving power congestion, and ensuring grid reliability. However, the sensors in existing current detection systems either are wired with measurement instruments or are wireless yet require batteries, which is inconvenient for monitoring overhead powerlines. Inspired by RF sensing tags, which are widely used for applications such as temperature and humidity measurements, in this article, we propose a distinctive cable current detection system that can avoid the constraint of wires and batteries. By detecting the ambient magnetic field produced by ac current flowing through a cable, the proposed system realizes a minimal measurement range of 5–17.5 A at 50/60 Hz with a maximum wireless distance of 5.2 m. This prototype can detect cable current with an extendable measurement range, providing a promising strategy for passive and wireless current detection.

The existing detection device for unexploded ordnance (UXO) based on geomagnetic anomaly and electromagnetic induction suffers from issues such as functional separation, large size, and low efficiency due to the constraints of sensors. The centimeter-sized magnetostrictive/piezoelectric composite demonstrates static and dynamic wideband frequency response capabilities for measuring magnetic fields. Here, a novel dual-mode detection method is proposed for receiving magnetic anomalies and transient electromagnetic responses in parallel by the FeNiMoSiB/PZT-5A composite. The transient primary field generated by a transmitting coil can not only cause the target to induce a secondary field, but also drive the operation of the magnetoelectric (ME) composite. The FeNiMoSiB layer excited by a high amplitude field generates nonlinear magnetostriction. Under the magnetic-mechanical-electrical conversion, the ME composite driven by the transient primary field undergoes a step response to output oscillating voltage. Due to the nonlinear ME effect, the oscillating voltage is modulated by the magnetic anomaly, resulting in an amplitude change. The magnetic anomaly information can be obtained by demodulating the resonant voltage signal. After the voltage oscillation ends, it begins to decay. Moreover, the dominant secondary field will hinder the voltage attenuation, and its information can be obtained by analyzing the late attenuation voltage signal. In the experiment, the ferromagnetic metal targets at different depths are detected, and the maximum detection depth is about 1.2m. In field environments, the targets buried at a depth of 0.5m in the soil are successfully located along the survey line, demonstrating good positioning performance.

Filmed planar coils have obvious advantages for miniaturization, micro-fabrication, and circuit integration. Amorphous and nanocrystalline films exhibit extremely large permeabilities and are extensively used to film planar coils for inductance enhancement. In this paper, we analyze aspects in designing a soft magnetic film/planar coil multilayer structure. It is pointed out that when the inductance of a filmed coil varies with the film permeability, it may get saturated before the permeability reaches its maximum. The saturation and variable tendency are closely related to the filmed inductor geometry. It is the ratios of the film dimensions and gap to the coil conductor width that determine the variation rate and saturated value. In addition, the film aspect ratio must be considered to produce suitable effective permeability as the inductance actually responds to the effective permeability instead of the nominal material permeability. Experimental and simulation data demonstrate the validity of the analysis.

A type of differential resonant magnetic field sensor is developed by employing the composite elements of FeGa plates, piezoelectric quartz crystal double-ended tuning forks (DETFs) and bias permanent magnets. The model and analysis show that the differential design brings the benefits of doubled sensitivity, increased linearity and low temperature drift. Importantly, a small and compact magnetic circuit containing a pair of permanent magnets and dual FeGa plates ensures the generation of differential actuation, which not only reduces the leakage flux but also improve the filed-sensitivity and resolution. The magnetic circuit model based on the “lumped parameters” method is established. As an important aid, the distribution of magnetic flux density along the longitudinal direction of the FeGa alloy is simulated by finite element analysis software. In order to avoid the prediction error caused by parameter errors, simulations in different conditions are carried out for comparative analysis. This method ensures the magnetic circuit provides qualified magnetic field. The experimental results show that the differential resonant magnetic field sensor with frequency readout has the characteristics of high sensitivity of 4.4 Hz/Oe, high resolution of <3. 04 × 10-4Oe, low temperature drift and excellent linear (non-linearity error of 1.3%FS) and low hysteresis (1.5%FS) over its measurement full scale (FS) of ±100Oe.