| Low frequency communication benefits from the strong penetration ability of low frequency signal,and is mainly used in ground-penetration and underwater communication.Frequency-Shift Keying(FSK)modulation is often used for medium and low speed data transmission.Because FSK has the advantages of strong anti-noise ability and good anti-attenuation performance.At present,inductive magnetic antennas are commonly used to receive low frequency signal,but their size and mass are relatively large.In order to realize the miniaturization of receiving antennas,this paper studies a high sensitivity,low noise,low frequency communication magnetoelectric antenna based on magnetoelectric effect.Compared with the existing direct antenna modulated magnetoelectric antenna,this paper mainly studies the magnetoelectric receiving antenna for FSK modulation low frequency communication.First,a magnetoelectric receiving antenna with a parallel structure is studied.The antenna obtains two resonance peaks with different frequencies through two sheets of layered magnetoelectric materials in parallel,which are used to receive FSK carriers signal carrying binary signals "0" and "1" respectively.The influence of the length of the piezomagnetic material on the resonance frequency is analyzed through theoretical and experimental means.The results show that the carrier frequency of FSK can be adapted by changing the length of the piezomagnetic material.Two pieces of multi-push-pull(MPP)magnetoelectric materials based on Metglas piezomagnetic material and PZT piezoelectric material were prepared.The output of the electrical composite material is connected in parallel,and the resonant frequency of the magnetoelectric receiving antenna is 24.6 k Hz and 29.8 k Hz.The limit of detection(LOD)at the resonant frequency is 0.25 p T and 0.35 p T,respectively.The test results show that it can effectively receive FSK modulation signal.In addition,a magnetoelectric receiving antenna with a cantilever beam structure is studied.This structure uses the characteristics of the cantilever beam's multi-order bending vibration to realize FSK communication,which is conducive to the miniaturization of the receiving antenna.The first to fourth order vibration models of the cantilever beam model are analyzed by theoretical and simulation methods,and the results show that the cantilever beam structure has multiple resonance peaks that could be used for FSK communication.A magnetoelectric receiving antenna with a cantilever beam structure based on Metglas and PZT was prepared,in which the Nd Fe B magnet was used as the free-end mass.Experiments show that the resonant frequency of the antenna can be changed by changing the length of the piezomagnetic phase.When the piezomagnetic phase length is 75 mm,there are four resonance peaks within 1 k Hz,namely 20 Hz,90 Hz,350 Hz and 650 Hz,and the corresponding limit of detection are 0.6 n T,0.4 n T,110 p T and 70 p T.The test results show that the four resonance peaks of the structure do not interfere with each other when receiving signals,and can realize multiple FSK communication modes such as 2FSK,3FSK and 4FSK.Finally,a test system for the magnetoelectric receiving antenna was established,which realized the demodulation of the FSK received signal,and tested the influence of various noises on the signal demodulation process.The FSK signal received by the magnetoelectric antenna is demodulated by the quadrature multiplication algorithm,and the modulated signal is accurately restored to a binary signal.Facing a variety of common noises in practical applications,the effects of power frequency noise,vibration noise and Gaussian white noise on the signal demodulation algorithm were tested respectively.In the case of co-frequency interference,the data is preprocessed through the z-score algorithm to remove the offset of the data,normalize the data,and reduce the impact of co-frequency noise. |
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