Research On Loss Mechanism Of Bulk Acoustic Wave Antenna

The rapid development of modern communication technology has put forward higher and higher requirements for antenna size,efficiency,and other indicators.The size of conventional antennas has always been limited by the wavelength of electromagnetic waves.Bulk Acoustic Wave(BAW)antennas use acoustic resonance instead of electromagnetic resonance,which provides a solution for antenna miniaturization.However,antenna radiation efficiency and operating bandwidth will be limited by the Chu Harrington limit.An effective way to improve antenna operating efficiency is to reduce loss.In this paper,the loss mechanism of BAW antenna is deeply studied,the causes of magnetic loss,dielectric loss,and mechanical loss are analyzed.The analytical modeling and analysis of BAW antenna loss are carried out from both electromagnetic field radiation and equivalent circuit.The optimization of antenna design can meet the demand for subminiature antennas in implantable medical devices,wireless communication systems,and other systems.The main research work is as follows:A stress source radiation model based on the finite-difference time-domain method is constructed,and it is proposed to use stress as the equivalent radiation source of the antenna to analyze the radiation power and energy of the antenna.From the perspective of electromagnetic field radiation,the typical high-frequency loss of BAW antennas,eddy current loss,was mainly discussed.Based on the simultaneous solution of the two curl equations in Maxwell’s equations and the constitutive relationship of the magnetostrictive layer,an eddy current loss model is constructed.The influence of eddy current loss on the total energy and average radiation power of magnetic thin films was analyzed.The eddy current loss factor has been defined to describe the impact of eddy current on antenna performance.This provides a theoretical basis for suppressing eddy current losses.The equivalent circuit model of BAW antenna is constructed,and three main loss mechanisms,namely dielectric loss,magnetic loss,and mechanical loss,are introduced.Using the complex forms of dielectric constant,permeability,and stiffness,the loss factors are introduced to accurately analyze the coupling performance of BAW antenna.By the Advanced Design System(ADS),the resonant characteristic curves of piezoelectric/piezomagnetic phase are obtained,which are basically consistent with the finite element simulation results,preliminarily verifying the reliability of the equivalent circuit model.The magnetoelectric voltage gain is calculated using Kirchhoff’s current law,and a conclusion is obtained that the optimal thickness ratio of the piezoelectric phase to the piezomagnetic phase for the BAW antenna is 1:1.In order to assist engineers in impedance matching the BAW antenna during system development,the input and output impedance are also calculated,which is basically consistent with the ADS simulation results.A low-frequency BAW antenna prototype is fabricated using multiferrous materials(Terfenol-D and PZT).The impedance characteristic curve of the BAW antenna is obtained and the effectiveness of the equivalent circuit model is verified.Five sets of BAW antenna prototypes with different thickness ratios were prepared simultaneously.The experimental results show that when the thickness ratio of piezoelectric and magnetic phases is about 1:1,the internal energy conversion efficiency of BAW antenna is the highest.This provides theoretical support for the design of BAW antenna.