Menghui Li

An Extremely Low Equivalent Magnetic Noise Magnetoelectric Sensor

As a result of the coupling between their dual order parameters, multiferroic materials exhibit unusual physical properties and, in turn, promise new device applications. [ 1 , 2 ] Of particular interest is the existence of a cross-coupling between the magnetic and electric orders, termed the magnetoelectric (ME) effect. [ 3–5 ] Because no single-phase material has been put forward demonstrating a practical capacity for such coupling at room temperature, [ 8 ] many of the most promising applications offered by the ME effect, including magnetic fi eld sensors and electric write-magnetic read memory devices, have not been forthcoming. [ 6 , 7 ] Furthermore, the exploitation of high magnetic fi eld sensitivity in two-phase ferromagnetic/ferroelectric composites requires development and identifi cation of end users. [ 7 ]

Giant magnetoelectric effect in self-biased laminates under zero magnetic field

A giant magnetoelectric (ME) effect in self-biased annealed Metglas/Pb(Zr,Ti)O3/Metglas laminates under zero magnetic bias is reported. The remanent magnetization was increased by annealing Metglas, which generated an internal bias field. This shifted the M-H hysteresis loops, yielding large values for the ME voltage coefficient of αME = 12 V/cm·Oe and 380 V/cm·Oe at 1 kHz and electromechanical resonance under zero magnetic bias, respectively. This self-biased laminate is shown to have a high sensitivity to ac magnetic fields.

A review on equivalent magnetic noise of magnetoelectric laminate sensors

Since the turn of the millennium, multi-phase magnetoelectric (ME) composites have been subject to attention and development, and giant ME effects have been found in laminate composites of piezoelectric and magnetostrictive layers. From an application perspective, the practical usefulness of a magnetic sensor is determined not only by the output signal of the sensor in response to an incident magnetic field, but also by the equivalent magnetic noise generated in the absence of such an incident field. Here, a short review of developments in equivalent magnetic noise reduction for ME sensors is presented. This review focuses on internal noise, the analysis of the noise contributions and a summary of noise reduction strategies. Furthermore, external vibration noise is also discussed. The review concludes with an outlook on future possibilities and scientific challenges in the field of ME magnetic sensors.

Theoretical and experimental investigation of magnetoelectric effect for bending-tension coupled modes in magnetostrictive-piezoelectric layered composites

In this paper, we discuss a theoretical model with experimental verification for the resonance enhancement of magnetoelectric (ME) interactions at frequencies corresponding to bending-tension oscillations. A dynamic theory of arbitrary laminated magneto-elasto-electric bars was constructed. The model included bending and longitudinal vibration effects for predicting ME coefficients in laminate bar composite structures consisting of magnetostrictive, piezoelectric, and pure elastic layers. The thickness dependence of stress, strain, and magnetic and electric fields within a sample are taken into account, as such the bending deformations should be considered in an applied magnetic or electric field. The frequency dependence of the ME voltage coefficients has obtained by solving electrostatic, magnetostatic, and elastodynamic equations. We consider boundary conditions corresponding to free vibrations at both ends. As a demonstration, our theory for multilayer ME composites was then applied to ferromagnetic-f...

Evaluation of Applied Axial Field Modulation Technique on ME Sensor Input Equivalent Magnetic Noise Rejection

By using nonlinearity effects in magnetostrictive -piezoelectric laminated sensors, modulation techniques can transfer low-frequency signals to higher frequencies. Theory predicts that the transfer ability depends mainly on the amplitude of the carrier signal and the sensor nonlinearity. This was confirmed by our experiments. We present the first analysis on a ME noise model associated to a modulation technique. Furthermore, the overall equivalent magnetic noise was analyzed, and shown to be dominated only by the signal transfer ability and the output electrical noise level appearing around the carrier frequency.

Magnetoelectric nonlinearity in magnetoelectric laminate sensors

A nonlinearity in the magnetoelectric coefficient, αMENonlin, of Metglas/Pb(Zr,Ti)O3 (PZT) and Metglas/Pb(Mg1/3,Nb2/3)O3-PbTiO3 (PMN-PT) laminate sensors has been observed. This nonlinearity was found to be dependent on the dc magnetic bias (Hdc) and frequency of the ac drive field (Hac). The maximum value of αMENonlin for both types of composites was found near the electromechanical resonance. For Metglas/PZT laminates, the maximum occurred under a finite bias of Hdc ≈5 Oe; whereas, for Metglas/PMN-PT, the maximum was found near zero dc bias. One application for αMENonlin is a cross-modulation scheme that can shift low frequency signals to higher frequency to achieve lower noise floor. For Metglas/PMN-PT, αMENonlin has another application: removal of the necessity of a dc bias, which helps to design high-sensitivity sensor arrays and gradiometers.

Theoretical model for geometry-dependent magnetoelectric effect in magnetostrictive/piezoelectric composites

A quasistatic theoretical model including geometry effect is presented for predicting the magnetoelectric (ME) coefficients in a ME multilayer composite consisting of magnetostrictive and piezoelectric layers. The model is developed based on average-field method considering the geometry effect. The model characterizes the ME coefficient in terms of not only the parameters of two composite components and the thickness fraction but also the length and width fractions for the piezoelectric or magnetostrictive components. Analytical predictions indicate that the width and length fractions strongly influence the maximum ME coefficient and the corresponding thickness fraction also. Clearly, geometry effects cannot be ignored in predicting ME coefficient. Theoretical ME coefficients are also compared to experimental test data, demonstrating excellent agreement.

Control of magnetic and electric responses with electric and magnetic fields in magnetoelectric heterostructures

This paper reports on the tuning of both magnetic and electric responses with electric and magnetic fields for metglas-Pb (Zr,Ti)O3 based magnetoelectric (ME) heterostructures that can be promising for communication and sensor applications. The hysteresis loop results indicate a change in the in-plane magnetization due to application of voltages that leads to a tuning of the ferromagnetic resonance frequency by up to about 210 MHz with electric field. Furthermore, these structures show a high ME voltage coefficient that results in the detection of a 2 nT ac magnetic field and a low noise floor.

Enhanced magnetoelectric effect in self-stressed multi-push-pull mode Metglas/Pb(Zr,Ti)O3/Metglas laminates

Two methods to effectively induce self-stress on Metglas/Pb(Zr,Ti)O3/Metglas laminate are presented: (i) applying a dc magnetic field to the Metglas layers or (ii) applying a dc electric field to the core piezoelectric composites. An optimum self-stress enhances the magnetoelectric (ME) effect in the laminates. With a 20 Oe dc magnetic bias, the value of αME for the self-stressed laminate was enhanced to 31.4 V/cm · Oe, which was by a factor of 1.24× compared to the laminate without self-stress. Furthermore, the equivalent magnetic noise floor was reduced by the self-stress at low frequencies.

Ultralow equivalent magnetic noise in a magnetoelectric Metglas/Mn-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure

An ultralow equivalent magnetic noise of 6.2 pT/√Hz at 1 Hz was obtained in a bimorph heterostructure sensor unit consisting of longitudinal-magnetized Metglas layers and a transverse-poled 1 mol. % Mn-doped Pb(Mg1/3Nb2/3)O3-29PbTiO3 (PMN-PT) single crystal. Furthermore, the equivalent magnetic noise was ≤1 pT/√Hz at 10 Hz. Compared with previously reported multi-push-pull configuration Metglas/PMN-PT sensor units, the current heterostructure exhibits a higher magnetoelectric coefficient of 61.5 V/(cm × Oe), a similar equivalent magnetic noise at 1 Hz and a lower noise floor at several hertz range. The ultralow equivalent magnetic noise in this sensor unit is due to the low tangent loss and ultrahigh piezoelectric properties of Mn-doped PMN-PT single crystals.