Study On Wireless Testing Technology Of Passive Magnetoelectric Surface Acoustic Wave Sensors

Magnetic field sensors are wildly applied in industrial production,biomedicine,and national defense,etc.As an ermerging technique,magnetoelectric surface acoustic wave(M SAW)sensors not only have the advantages of miniaturization,high sensitivity,and high reliability,but also are passive devices,allowing wireless reading in a wide field range,and are easy to maintain.So far,it is the only wireless passive magnetic sensor.Therefore,study on the fabrication and wireless detection techniques of MSAW sensors are of particular importance.The main work of this thesis is as follows:First,one-port MSAW resonators are fabricated by magnetron sputtering multilayered(FeCoSiB/SiO2)n films directly on top of interdigital tranducers(IDTs).A thin SiO2 layer was used as insulator between the IDT and the magnetic multilayer.In order to investigate the effect of magnetic anisotropy on the acoustic response,we have prepared three types of MSAW resonators with and withno different induced magnetic anisotropy along different directions.The measured resonance frequency(fR)exhibits either a butterfly-like or loop-like dependence on the external field,which can be attributed to the competition between the magnetic field-induced anisotropy and the stress-induced or shape anisotropy.Secondly,this thesis designs a wireless interrogation system matched with MSAW sensors.The transmitting end of the system adopts DDS to drive PLL to multiply the low-frequency signal.The power amplifier amplifies the frequency multiplication signal to transmit a narrow-band pulse excitation signal.The receiving end uses a down-conversion structure,including a low-noise amplifier(LNA),a mixer,a local oscillator phase-locked loop circuit,and an ADC sampling circuit.The FFT algorithm module based on FPGA processes the ADC sampling signal in the frequency domain and extracts the frequency value of the difference frequency signal.The design and functional simulation are completed through the With ADS(Advanced Design System)and Multisim software,we simulate each module of the transceiver circuit and complete the transceiver circuit design.This thesis implements SPI interface and RF switch control,and builds a signal processing module using FFT IP based on FPGA.Using Verilog HDL builds the simulation environment,and verifies the function of each FPGA module.Finally,tune each module of the system to build a complete wireless test system.The power amplifier at the transmitter can achieve a gain of 14 dB and output a maximum power of 15 dBm excitation signal.This thesis tests the power attenuation of the excitation signal at different distances.The RF switch used in the wireless system can achieve-40 dB isolation in the operating band.The designed receiver LNA can provide a gain of 15 dB for the echo signal;the local oscillator circuit can stably output the drive signal without clutter.The mixer,combined with the low-pass filter,implements the down-conversion function better.This paper verifies the functional integrity of the wireless interrogation system using a surface acoustic wave resonator.