Compact, single-device gyrator attains “Highest ever reported” power-conversion efficiency

Nearly 70 years after the gyrator—a device that, among other useful feats, can convert voltage to current and vice-versa—was first proposed, Virginia Tech researchers and collaborators from the University of Colorado and Oakland University have devised a compact, solid-state version that achieves the highest ever reported power-conversion efficiency: 85 percent under low-power conditions and 80 percent at high power.

As described in Applied Physics Letters, the new trilayer device exploits the giant magnetoelectric coupling effect and measures 470mm³—smaller than half of a typical dice cube. It has the potential to unlock the door to an array of energy-efficient power-processing technologies, including better photovoltaics, energy-harvesting devices, wireless power transfer, and passive current sensors without the need for integrators, according to authors.

The team’s magnetoelectric gyrator consists of the ceramic piezoelectric Pb(Zr,Ti)O₃ (PZT) sandwiched between layers of Mn-doped Ni_0.8Zn_0.2Fe₂O₃ (NZFO), magnetostrictive composite. Copper-wire coils form inductive and capacitive ports. An applied current in the coil generates a magnetic field that changes the shape of the magnetostrictive NZFO layers, causing stress-strain vibrations that are transferred to the PZT layer, which, in turn, generates charge or voltage. Conversely, applying voltage to the piezoelectric layer will induce current in the coil.

Measured under a 70-oersted magnetic field, power conversion efficiency rose with increasing frequency, jumping dramatically and peaking at fundamental resonance—a 600-fold enhancement from sub-resonance to resonance frequencies. First author Chung Ming Leung says two material properties are key to achieving even better conversion efficiencies: a high mechanical quality factor, which characterizes the sharpness of the resonance spectrum, and the strength of the coupling between the piezoelectric and magnetostrictive layers. In fact, Leung and colleagues predict that the maximum power conversion achievable with a NZFO/PZT magnetoelectric gyrator is 96.7 percent.

Source: “Highly efficient solid state magnetoelectric gyrators,” by Chung Ming Leung, Xin Zhuang, Daniel Friedrichs, Jiefang Li, Robert W. Erickson, V. Laletin, M. Popov, G. Srinivasan, and D. Viehland, Applied Physics Letters (2017). The article can be accessed at https://doi.org/10.1063/1.4996242 .