Impedance characteristics of magnetoelectric antennas

Abstract

Mechanical antenna, a novel scheme for realizing very low frequency (VLF) and portable transmitters, has been investigated recently. In this work, the impedance characteristics of 1-1 type of and 2-1 type of magnetoelectric (ME) mechanical antennas are systematically studied and compared with each other. Based on the measured frequency-impedance curves and the corresponding modified Butterworth-van Dyke (MBVD) model, three characteristic frequency points, i.e. the minimum impedance frequency <inline-formula><tex-math id="M5">\begin{document}$ {f}_{\rm{m}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20220591_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20220591_M5.png"/></alternatives></inline-formula>, the series resonance frequency <inline-formula><tex-math id="M6">\begin{document}$ {f}_{\rm{s}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20220591_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20220591_M6.png"/></alternatives></inline-formula>, and the resonance frequency <inline-formula><tex-math id="M7">\begin{document}$ {f}_{\rm{r}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20220591_M7.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20220591_M7.png"/></alternatives></inline-formula> are obtained and discussed. On this basis, the influence of driving voltage, bias magnetic field, and the quality factor (<i>Q</i> value) on ME antenna impedance characteristics are experimentally explored. Finally, the reactance components of both 1-1 type of and 2-1 type of ME antenna are collected by referring to the actual working frequency <inline-formula><tex-math id="M8">\begin{document}$ {f}_{\rm{d}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20220591_M8.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20220591_M8.png"/></alternatives></inline-formula>. Experimental results prove that the resonant ME antennas are basically pure resistive vibrators, while an ME antenna with high <i>Q</i> value normally fails to support high driving field because of the low resistance (< 100 Ω) and the strong nonlinearity. Thus, the field radiation capability in 2-1 type of ME antenna is higher than that in 1-1 typed one. This work provides the ideas for choosing <i>Q</i> value and further optimizing a magnetoelectric antenna based on the understanding of its impedance characteristics.