Cunzheng Dong’s PhD Proposal Review

“Acoustically Actuated Magnetoelectric Antennas for VLF Communication and Magnetic Sensing”

Committee Members:
Prof. Nian Sun (Advisor)
Prof. Yongmin Liu
Prof. Hossein Mosallaei

Abstract:
Since the discovery of strong magnetoelectric (ME) coupling in two-phase ME laminate composites, strain-mediated ME heterostructures have attracted a great deal of attention from academic and industrial research groups for their potential usage in magnetic sensors, voltage tunable inductors, magnetic tunable filters, and miniaturized mechanical antennas, etc. Acoustically actuated ME antennas have recently been demonstrated as a promising solution for very low frequency (VLF) communications and magnetic fields detection, for their 2-3 orders of reduced dimensions, outstanding sensitivity at resonance, and robust immunity to electrical interferences than conventional electric antennas. Their performance and noise analysis are deeply investigated and discussed in this proposal review.

Firstly, A portable VLF communication system using one pair of ME antennas operating at their electromechanical resonance (EMR) is presented. The measured near-field radiation pattern reveals ME antennas are equivalent to magnetic dipole antennas. The magnetic field radiated by the ME transmitter has been predicted along with distance from near-field to far-field. The measured magnetic field distribution coincided well with the prediction, and the maximum communication distance of 120 m has been achieved by single antenna unit. Antenna arrays are widely used as an effective approach to enhance radiation field intensity. By tunning all the driving signal for each antenna unit at the same frequency and in phase, the total radiation field strength has been linearly enhanced by one order with 12 antenna arrays. Furthermore, nonlinear antenna modulation (NAM) has also been successfully demonstrated on the ME antennas.

Secondly, a Metglas/Quartz based ME resonator as magnetic sensor for reception of VLF magnetic signals is presented. Metglas is a highly permeable magnetostrictive material which can effectively concentrate the magnetic fields. Moreover, the high magnetostriction and low coercivity of Metglas can generate a distinct strain change in response to subtle magnetic fields. Piezoelectric single crystal Quartz is often used as electronic oscillators due to their extremely high Q factor with low noise and high stability. The combined properties of these two materials provide ME sensors an extremely high sensitivity and low magnetic noise of less than 10 fT at the EMR frequency. The VLF signal reception capability of the proposed ME sensor was also compared with a conventional VLF loop antenna and the PZT-5A based ME sensor.

Lastly, a compact and sensitive system was developed to characterize the magnetomechanical properties, such as the saturation magnetostriction, piezomagnetic coefficient, delta-E effect and magnetomechanical coupling factor of magnetic thin films. These magnetomechanical properties are critical in determining the performance of ME antennas. For saturation magnetostriction and piezomagnetic coefficient measurement, a high precision optical probe was harnessed to measure the deflection of the magnetic thin film/Si cantilever due to strain change induced by domain rotation. The same cantilever samples were used for delta-E effect and magnetomechanical coupling factor characterization, the DC bias magnetic field induced cantilever resonance frequency shift was used for calculating the change of elastic modulus.