Magnetic Field Sensing by Exploiting Giant Nonstrain-Mediated Magnetodielectric Response in Epitaxial Composites

A Comprehensive Study on Magnetoelectric Transducers for Wireless Power Transfer Using Low-Frequency Magnetic Fields

Magnetoelectric (ME) transducers, comprising of layered magnetostrictive and piezoelectric materials, are more efficient than inductive coils in converting low-frequency magnetic fields into electric fields, particularly in applications that require miniaturized devices such as biomedical implants. Therefore, ME transducers are an attractive candidate for wireless power transfer (WPT) using low-frequency magnetic fields, which are less harmful to the human body and can penetrate easily through different lossy media. The literature lacks a comprehensive study on the ME transducer as a power receiver in a WPT link. This paper studies the impact of different ME design parameters on the WPT link performance. An accurate analytical model of the ME transducer, operating in the longitudinal-transverse mode, is presented, describing both temporal and spatial deformations. Nine ME transducers with different sizes (ME volume: 5-150 mm³) were fabricated with Galfenol and PZT-5A as magnetostrictive and piezoelectric layers, respectively. Through the modeling and measurement of these ME transducers, the effects of the ME transducer dimension, DC bias magnetic field, loading (R_L), and operation frequency on the resonance frequency, quality factor, and received power (P_L) of the ME transducer are determined. In measurements, a 150 mm³ ME transducer achieved > 10-fold higher P_L for a wide R_L range of 500 Ω to 1 MΩ at 95.5 kHz, compared to an optimized coil with comparable size and operation frequency.

Optical properties of Pb0.52Zr0.48TiO3 nanorod arrays: second harmonic generation and multiphoton carrier dynamics

Nonlinear optical properties of poled and unpoled, lead zirconate-titanate (Pb0.52Zr0.48TiO3) nanorod arrays, grown on Pt-coated Si with ∼200 nm diameter and ∼600 nm height, were investigated. Clear signatures of second harmonic generations (SHG), from 490–525 nm (2.38–2.53 eV) at room temperature, were observed. Furthermore, time resolved differential reflectivity measurements were performed to study dynamical properties of photoexcited carriers in the range of 690–1000 nm where multiphoton processes were responsible for the photo-excitations. We compared this excitation scheme, which is sensitive mainly to the surface states, to when the photoexcited energy (∼3.1 eV) was close to the band gap of the nanorods. Our results offer promises for employing these nanostructures in nonlinear photonic applications.

High-resolution magnetic sensors in ferrite/piezoelectric heterostructure with giant magnetodielectric effect at zero bias field

A dielectric AC magnetic sensor in layered ferrites/piezoelectric composites was fabricated and developed, whereby its high magnetodielectric (MDE) effects, the typical magnetic-sensing parameters, were systematically characterized at zero bias. Polycrystalline ferrites were synthesized by the solid-state sintering technique with a composition of Ni_0.7Zn_0.3Tb_0.02Fe_1.98O₄, and the desired spinel structure and soft magnetic properties were confirmed by x-ray diffraction and VSM, respectively. The field-induced charge order insulating state in piezoelectric ceramics accounts for the suppressed permittivity, which enables the possibility of a highly sensitive magnetic sensor at zero bias field. Experimental results exhibit that a small variation in H as low as 100 mOe can be clearly distinguished with a favorable nonlinearity of 2.24%. Meanwhile, the output stability of the presented sensor under 2h of constant and continuous excitation was tested within a favorable fluctuating tolerance range of 6.14-6.28 nF, and the estimated uncertainty of ∼0.063 038 nF was verified by statistical analysis. The presented ferrite/piezoelectric magnetic sensors exhibiting a high MDE response without the requirement for an external magnetic bias are of importance for use in bio-magnetic field detection due to metrics of miniaturization, high sensitivity, and favorable stabilities.