Magnetic field sensors using magnetoelectric (ME) effects in planar ferromagnetic-piezoelectric heterostructures convert a magnetic field into an output voltage. The parameters of ME sensors are ...determined by characteristics of the magnetic constituent. In this work, the low-frequency ME effects in heterostructures comprising a layer of antiferromagnetic hematite α-Fe
O
crystal with easy-plane anisotropy and a piezoelectric layer are studied. The effects arise due to a combination of magnetostriction and piezoelectricity because of mechanical coupling of the layers. The field dependences of magnetization and magnetostriction of the hematite crystal are measured. The resonant ME effects in the hematite-piezopolymer and hematite-piezoceramic structures are studied. The strong coupling between magnetic and acoustic subsystems of hematite results in a tuning of the acoustic resonance frequency by the magnetic field. For the hematite layer, the frequency tuning was found to be ~37% with an increase in the bias field up to 600 Oe. For the hematite-PVDF heterostructure, the frequency tuning reached ~24% and the ME coefficient was 58 mV/(Oe∙cm). For the hematite-piezoceramic heterostructure, the frequency tuning was ~4.4% and the ME coefficient 4.8 V/(Oe∙cm). Efficient generation of the second voltage harmonic in the hematite-piezoceramic heterostructure was observed.
A voltage transformer employing the magnetoelectric effect in a composite ceramic heterostructure with layers of a magnetostrictive nickel–cobalt ferrite and a piezoelectric lead zirconate–titanate ...is described. In contrast to electromagnetic and piezoelectric transformers, a unique feature of the presented transformer is the possibility of tuning the voltage transformation ratio K using a dc magnetic field. The dependences of the transformer characteristics on the frequency and the amplitude of the input voltage, the strength of the control magnetic field and the load resistance are investigated. The transformer operates in the voltage range between 0 and 112 V, and the voltage transformation ratio K is tuned between 0 and 14.1 when the control field H changes between 0 and 6.4 kA/m. The power at the transformer output reached 63 mW, and the power conversion efficiency was 34%. The methods for calculation of the frequency response, and the field and load characteristics of the transformer are proposed. The ways to improve performance characteristics of magnetoelectric transformers and their possible application areas are discussed.
A sensor of dc magnetic fields using the magnetoelectric effect in a planar ferromagnetic-piezoelectric composite structure is described. It is shown that introduction in the sensor circuit a ...negative feedback, which contains a current amplifier, a voltage divider, and a compensation coil, results in a widening of the sensor magnetic field region and linearization of its characteristic. The width of the sensor field region depends on the compensation coil parameters and feedback coefficient and can be increased by a factor of tens. A prototype of the sensor based on the metglas-piezofiber composite-metglas structure was fabricated. The prototype had a linear output voltage versus magnetic field dependence within the field region from 0.1 Oe to 72 Oe and a sensitivity of 29 mV/Oe.
The direct magnetoelectric (ME) effect is investigated in a planar structure comprising mechanically coupled layers of a magnetostrictive fibrous composite (MFC) and a piezoelectric ceramics (lead ...zirconate titanate, PZT). The MFC is an array of Ni-wires with a diameter of 200 μm that are aligned parallel to each other in a single layer. The wires are separated by a distance of 250 or 500 μm and fixed in a polyamide matrix. The structure was placed in a tangential constant field H and was excited by an alternating magnetic field h parallel to H, while the voltage generated by the PZT layer was measured. The resulting field dependences of the magnetization M(H) and the magnetostriction λ(H) were determined by the orientation of the field H in the plane of the structure and the distance between the Ni-wires. The ME coupling coefficient of the structure decreased from 4.8 to 0.25 V/A when the orientation of H was changed from parallel to perpendicular to Ni-wires. With an increase in the excitation field amplitude h, a nonlinear ME effect in the output voltage, namely frequency doubling, was observed. The frequency and field dependences of the efficiency of the ME transduction in the MFC-piezoelectric heterostructure are well described by the existing theory.
A wideband ac magnetic field sensor using the nonlinear magnetoelectric effect of magnetic fields mixing in a planar structure consisting of a piezoelectric langatate and an amorphous ferromagnet has ...been described. The measured and pumping fields mix due to nonlinearity of the ferromagnetic layer magnetostriction. The voltage of the total frequency generated by the langatate layer is recorded at the frequency of the structure planar acoustic oscillations that provide both frequency selectivity and enhancement of the voltage by Q ≈ 1400. The maximum sensitivity of the sensor is 1.8 V/Oe, which is ~320 times higher than the sensitivity of the sensor using the linear magnetoelectric effect, but ~4 times lower than the sensitivity of the linear sensor at the resonance. The sensor operates without a dc bias magnetic field and allows registration of fields as low as ~10 -5 Oe in the frequency band of 1-70 kHz with a frequency resolution of ~50 Hz.
Magnetoelectric (ME) effects in composite ferromagnet-piezoelectric (FM/PE) heterostructures realize the mutual transformation of alternating magnetic and electric fields, and are used to create ...magnetic field sensors, actuators, inductors, gyrators, and transformers. The ME effect in composite structures is excited by an alternating magnetic field, which is created using volumetric electromagnetic coils. The coil increases the size, limits the operating frequencies, and complicates the manufacture of devices. In this work, we propose to excite the ME effect in composite heterostructures using a new coil-free excitation system, similar to a “magnetic capacitor”. The system consists of parallel electrodes integrated into the heterostructure, through which an alternating current flows. Modeling and measurements have shown that the excitation magnetic field is localized mainly between the electrodes of the magnetic capacitor and has a fairly uniform spatial distribution. Monolithic FM/PE heterostructures of various designs with FM layers of amorphous Metglas alloy or nickel-zinc ferrite and PE layers of lead zirconate titanate piezoceramic were fabricated and investigated. The magnitude of the ME effect in such structures is comparable to the magnitude of the ME effect in structures excited by volumetric coils. However, the low impedance of the coil-free excitation system makes it possible to increase the operating frequency, reducing the size of ME devices and the power consumption. The use of coil-free excitation opens up the possibility of creating planar ME devices, and accelerates their integration into modern electronics and microsystem technology.
The correlation between the direct magnetoelectric (ME) effect and the magnetization of planar ferromagnetic (FM)-piezoelectric composite structures has been demonstrated. It is experimentally proved ...that for unsaturated layers of FM galfenol, permendur, amorphous alloy, and nickel, the magnetostriction is the quadratic function of the magnetization. Using a langatate-nickel structure with magnetic hysteresis as an example, it has been shown that the dc magnetic field dependence of ME interaction efficiency can be calculated and predicted using magnetization curves for the FM layer.
The results of magnetoelectric effect experimental studies in two different structures based on piezoelectric semiconductor gallium arsenide are presented. The monolithic structure consisted of a ...gallium arsenide substrate with deposited nickel layer (GaAs-Ni), and the composite structure contained a semiconductor substrate with an amorphous magnetic alloy (GaAs-Metglas) ribbon glued on one side. A quality factor
Q
≈ 23500 and magnetoelectric coefficient of 316 V/Oe.cm were achieved at the frequency of planar acoustic oscillations for GaAs-Ni structure at room temperature.
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