Investigation into the impedance characteristics of magnetoelectric antennas

Mechanical antenna is recently considered a novel scheme for realizing very low frequency (VLF) and portable transmitters. In this paper, the impedance characteristics of 1-1 typed and 2-1 typed magnetoelectric (ME) mechanical antennas are systematically studied and compared. Based on measured frequency-impedance curves and the corresponding MBVD (Modified Butterworth-Van Dyke) model, three characteristic frequency points, i.e., the minimum impedance frequency f_m, the series resonance frequency f_s and the resonance frequency f_r are obtained and discussed. On this basis, the influence of driving voltage, bias magnetic field, and the quality factor (Q value) on ME antenna impedance characteristics is experimentally explored. Finally, the reactance components of both 1-1 typed and 2-1 typed ME antenna are collected by referring to the actual working frequency f_d. Experimental results prove that resonant ME antennas are basically pure resistive vibrators, while a ME antenna with high Q value normally fails to support high driving field because of the low resistance (< 100Ω) and the strong nonlinearity. Thus, the field radiation capability in 2-1 typed ME antenna is higher than that of 1-1 typed one. This work provides perspectives for Q value selection and further optimization of a magnetoelectric antenna based on the understanding of its impedance characteristics.