Effects of magnetic-elastic anisotropy on magnetoelectric gyrator with ferrite/PZT/ferrite laminate for enhancement of power conversion efficiencies

Highlights

• An effective method is presented for further improving the PE in ME gyrators.

• Approximately 1.69 times enhancement in PE is obtained at θ = 75˚ and H = 98Oe.

• Anisotropic magneto-elastic variations account for PE variations along θ rotations.

Abstract

Effects of magnetic-elastic anisotropy on ferrite/lead zirconate titanate (PZT)/ferrite magnetoelectric (ME) gyrators were investigated for power conversion efficiency further improvement, and a methodology was introduced by changing the direction of applied magnetic field (H_DC). Simulation by using finite element method provides a clear evolution of magnetic flux density distribution in ferrite as H_DC rotates. Consequently, enhanced ME coupling as well as power conversion efficiency (PE) was achieved under a certain angle with maximum effective magnetic field applied especially at intensive magnetic fields. Experimental results show that current (I)-voltage (V) versus directional angle (θ) between H_DC direction and longitudinal direction of ME sample and PE vs θ data can essentially track the dynamic piezomagnetic coefficient (DPMC) vs θ profile, indicating that the H_DC rotation induced anisotropic magneto-elastic variations are responsible for the eventual PE improvement. For higher H_DC = 98Oe, PE reaches its maximum of 76.5% at θ = 75˚ relative to its counterpart of 47.6% at θ = 0˚, exhibiting an approximately 1.69 times higher enhancement. Therefore, the feasibility of an efficient approach was verified by the obtained results, providing possibilities for PE further improvement and enhanced flexibilities for ME gyrator design.

Introduction

An ideal non-reciprocal electronic device prototype of gyrator with passive, linear and lossless merits was conjectured by Tellegen based on transduction of magnetic flux and electric charge in 1948, which was recognized as the fifth missing fundamental component circuit with two-port four-wire configuration[1]. Capacitor-to-inductor mutation function accomplished by an ideal gyrator terminated with a capacitor behaves like an inductor, which is useful for the design of inductor filters[2], [3]. In the last decades, the research revival of magnetoelectric (ME) has propelled the gyrator realization to move forward, and ME-coil configuration can fulfill the requirements of gyrator basic constraints[4]. In ME gyrators, the power transfer of ME gyrator is from electric to magnetic energies via the coil or vice versa, and then the magnetic field was converted to elastic strain due to magnetostrictive effect, and finally a conversion from the elastic strain to electric through piezoelectricity[5], [6]. Therefore, concrete evidence has been provided that the ME composite plays a vital role in gyrator scheme involving magnetic and electric mutation conversions, whereby significant ME couplings mediated by strain between magnetostrictive and piezoelectric phase under external magnetic/electric field application [7], [8]. In this case, flourishing research on controlling and improving elastic strain coupling of voltage (V)-current (I)/I-V ME gyrators are actively conducted[9], [10], [11]. Pioneer work of ME gyrator was proposed by Dong et al. in 2006, taking advantage of magnetic-elastic/elastic-electric conversion a theoretical estimation of I-V conversion coefficient up to 2500 V/A in the vicinity of resonance was predicted by equivalent circuit method[12], [13]. Nevertheless, the research on ME gyrator was stagnant in the following years, since effective approaches on improving the weak ME coupling induced by magnetic-elastic conversion are extremely scarce. A surge revival of ME gyrator studies emerged in 2016, and studies were focused on ones with enhanced stability and power conversion efficiency (PE) implemented by improving magnetic-strain conversion via structural and parametric optimizations [14], [15], [16]. In 2017, Leung et al. reported the influence of topical optimum parameters including thickness ratio n, load resistance R_L and magnitude of bias field H_DC on PE in layered ME laminates, and the enhanced magnetic-strain conversion of the NZFO ferrite layer was employed to explain the increased power drive in ME gyrators[17], [18]. Moreover, the progress in ME gyrator has been advanced to aim at magneto-elastic strain couplings then PE enhancement by means of rare earth doping in spinel ferrites, and built-in magnetization grading induced by various ion doping on magnetostrictive materials lead to stronger magnetic-elastic conversion and then generate to higher PE at optimum magnitude of H_DC under low input[19], [20], [21]. Very recently, versatile methodologies including high mechanical quality factor (Q) materials selection, minimizing geometrical demagnetization effect and different polarized/magnetized schemes have successively been reported for improving PE and reducing power consumption in ME gyrators, and the experiment results show that the enhanced magneto-elastic strain coupling by using high Q material is responsible for achievable higher PE at optimum bias[22], [23], [24]. Efforts so far have primarily focused on improving isotropic dynamic magneto-elastic strain to further enhance PE in ME gyrator[25]. However, actually the ME coupling can also be effectively improved by the anisotropic dynamic magneto-elastic strain caused via altering direction of H_DC, thereby reducing energy loss in magneto-elastic-electric conversion.

Therefore, research on the impact of anisotropic magneto-elastic strain seems necessary for PE improvement in ME gyrators, anticipating achievable higher PE and reduced power dissipation in ME gyrator.

In this work, an effective approach is proposed to enhance PE in ME-coil gyrators consisting of tri-layer ferrite/PZT-8/ferrite with anisotropic magneto-elastic strain induced by H_DC direction. Compared with the previous reports, endeavors have contributed to improving the magneto-elastic-electric conversion in the power transfer process. Anisotropic magneto-elastic strain induced by changing H_DC direction was systemically investigated, and the optimal H_DC direction was found to transfer more vibrating energy at the resonance condition, thereby mitigating the energy dissipation in the magneto-elastic-electric conversion process. In this case, the dynamic anisotropic magneto-elastic behaviors in magnetostrictive phase were characterized under various H_DC vectors, followed by the characterizations of ME gyrator including I-V conversion ratios, inductance-capacitance conversion characteristics and PE under various H_DC vectors. Optimum direction of H_DC existed as expected to increase the PE under extremely low input power density, especially in intensive magnetic field. Therefore, certain non-zero H_DC directional angle might facilitate magneto-elastic-electric energy transfer efficiency due to the anisotropic magneto-elastic behaviors of spinel ferrites.