Davresh Hasanyan

Pull-In Instabilities in Functionally Graded Microthermoelectromechanical Systems

We study pull-in instabilities in a functionally graded microelectromechanical system (MEMS) due to the heat produced by the electric current. Material properties of two-phase MEMS are assumed to vary continuously in the thickness direction. It is shown that the pull-in voltage strongly depends upon the variation through the thickness of the volume fractions of the two constituents. It is probably the first work to consider Joules heating, dependence of the electric conductivity upon the temperature, and the gradation of material properties in studying the pull-in instability in micro-thermo-electro-mechanical plates.

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...

NONLINEAR MAGNETOTHERMOELASTICITY OF ANISOTROPIC PLATES IMMERSED IN A MAGNETIC FIELD

A geometrically nonlinear theory of magnetothermoelasticity of electroconductive anisotropic plates in a magnetic field is developed. In this context, the Kirchhoff hypothesis is adopted for the plate modeling and the geometrical nonlinearities are considered in the von Kármán sense. In addition, the assumptions related to the distribution of electric and magnetic field disturbances through the plate thickness as proposed by Ambartsumyan and his collaborators are adopted. Based on the electromagnetic equations (i.e., the ones by Faraday, Ampère, Ohm, Maxwell, and Lorentz), on the modified Fourier law of heat conduction, and elastokinetic field equations, the three-dimensional coupled problem is reduced to an equivalent two-dimensional one appropriate to the theory of plates. The theory developed herein enables one to investigate the interacting effects among the magnetic, thermal, and elastic fields in orthotropic thin plates. As a special case, the problem of the free vibration of simply supported plate strips immersed in a transversal magnetic field is considered. Effects of the directionality property of the constituent material, magnetic and temperature fields, and electric conductivity, as well as thermal expansion coefficients, on the characteristics of vibrational behavior of the plate strips are investigated.

Electromagnetically conducting elastic plates in a magnetic field: modeling and dynamic implications

Abstract The basic field equations and boundary conditions necessary for the dynamic approach of electromagnetically conducting flat plates subjected to an external magnetic field are derived. Whereas the structural equations include the geometrical non-linearities of elastic isotropic plates, the electromagnetic equations are used in a linearized form that is obtained from their non-linear counterpart by applying the small disturbance concept. In this context, it was shown that the governing equations involve the bending–stretching coupling arising from both the geometrical non-linear approach of the problem and the inclusion of the Lorentz ponderomotive forces that are reduced to a 2-D plate counterpart. A number of special cases are considered, implications of the external magnetic field on non-linear/linear eigenfrequencies are highlighted, and pertinent conclusions are outlined.

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.

Shear-mode magnetostrictive/piezoelectric composite with an enhanced magnetoelectric coefficient

A magnetoelectric (ME) laminate heterostructure consisting of two shear-mode piezoelectric Pb(Mg1/3Nb2/3)O3-30PbTiO3 (PMN-PT) single crystal layers, a longitudinally magnetized magnetostrictive Tb0.3Dy0.7Fe1.92 alloy plate, and a mechanical clamping brass substrate has been demonstrated that has a notably superior ME effect relative to previous laminate configurations of these two materials. A giant ME coefficient of 7.5 V/(cm Oe) at low frequencies under an optimal dc magnetic bias of ∼400 Oe was found. The superior ME effects originate from the nature of heterostructure design, which allows the PMN-PT single crystals to operate in a shear mode that has maximum electro-mechanical coupling (i.e., d15 = 6800 pC/N).

Thermoelastic Cracked Plates Carrying Nonstationary Electrical Current

ABSTRACT Problems related to the distribution of electromagnetic field and of the Joule heating along/around the cracks in a thermo- and electroconductive plate are addressed. It is assumed that the plate carries a nonstationary electrical current and contains two finite collinear cracks that are located perpendicular to the current direction. The cracks are free of mechanical loads. The formulated problem is reduced to a system of singular integral equations with Cauchy-type singular kernels and solved numerically. The influence of interaction of the cracks as well as non-stationarity of the current on the distribution of current and Joule heating are clarified. The results are instrumental toward arrest and de-acceleration of crack propagation in electro-conductive material structures.

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.

Giant resonant magnetoelectric effect in bi-layered Metglas/Pb(Zr,Ti)O3 composites

In this paper, giant resonant magnetoelectric (ME) effect in an unsymmetrical bi-layered Metglas/Pb(Zr,Ti)O3 ME composites with multi-push pull configuration that can be significantly tuned was investigated experimentally and theoretically. The actual measured and predicted results present the similar resonant frequency shifting behaviors for such ME composites: The resonant frequency can be varied from 70 Hz to 220 Hz by tip mass loading, where the ME voltage coefficients were over 250 V/cm-Oe. Moreover, the giant frequency-tunable resonant effect allowed us to design a 60 Hz magnetic field energy harvester to be capable of harvesting energy generated by electronic instruments working on a 60 Hz ac power supply.