Research On Miniaturized Mechanical Antennas

Antenna miniaturization has gradually become a research hotspot in the antenna fields.Many applications like 5G,Internet of things,biomedical devices,and wearable devices demand higher performance with smaller feature size.Compared with conven-tional antennas,the miniature antennas with the advantage of compact structures can have good performance in the limited space.Due to the limitation of traditional electromag-netic radiation theory,in the case of low frequency band or limited space,the antennas with depth miniaturization will face some fundamental difficulties such as low radiation efficiency and difficult impedance matching.Since the traditional miniaturization tech-nologies cannot solve the problem,a new radiation mechanism of mechanical antennas is proposed based on the basic principle of electromagnetic radiation generated by the ac-celerated motions of charges.The working principles of mechanical antennas are introduced in this thesis.The strain powered antennas are taken as the main research objects,and the radiation mecha-nisms of the magnetoelectric and piezoelectric antennas are analyzed.The strain powered antenna is compared with a metallic dipole antenna of the same size.The mechanical antenna technology breaks the limitation of the electromagnetic wavelength to the an-tenna size and further improves the miniaturization degree of the antennas.In gen-eral,main contributions of this thesis are listed as follows:1.There exist two basic types of mechanical antennas,namely,mechanical moving antennas and strain powered antennas.The equivalent radiation sources and electromag-netic field distributions of the mechanical moving antennas are studied.In addition,the resonant modes and radiation efficiency of the strain powered antennas are studied by the mechanical vibration models.2.The electromagnetic radiation of magnetostrictive/piezoelectric laminated com-posites is studied.The solutions of the M-P-M magnetoelectric composite model are com-pleted in COMSOL Multiphysics,and the acoustic resonance and magnetoelectric cou-pling are mainly studied.Meanwhile,the reactive near field of the magnetoelectric an-tenna is analyzed through the simulation method.Its radiation characteristics are similar to those of a magnetic dipole.Based on the Q factor theory of electrically small antennas,the radiation Q of the magnetoelectric antenna is calculated,which proves that it can reach the theoretical lower limit of electrically small antennas.The magnetoelectric antenna is composed of M-P-M laminated composite material with a length of 50?m,a width of 11?m and a thickness of 3.0076?m.The simulation results show that the acoustic resonance frequency of the magnetoelectric antenna is 19.65 MHz under the excitation of RF voltage.Compared with the metallic loop antenna of the same size,the radiation efficiency of the magnetoelectric antenna is 4 orders of magnitude higher than that of the loop antenna.3.A viable approach for calculating the electromagnetic radiation of piezoelectric devices is proposed.The simulation analysis of piezoelectric devices is realized,and the radiation characteristics of the electric dipole are confirmed.Then,the input impedance and radiation efficiency of the two antennas are analyzed by comparing with the short dipole antenna of the same size.Finally,an experimental platform is built to verify the resonant characteristics and radiation effect of the piezoelectric crystal.The length of the Li Nb O₃ crystal is 9.6 cm and the width of the bottom surface is 2.2 cm.The experimental results show that the series resonant frequency is 34.20 k Hz and the input impedance is38.22 k?,which are in good agreement with the simulation results.Under the same input power,the signal intensity emitted by the piezoelectric crystal is much stronger than that of the whip antenna,whose electric length is 4 times that of the piezoelectric crystal.