Research And Implementation On Non-contact Monitoring System Of Vital Signs Based On Microwave Technology

Vital signs are of great significance in early prevention and diagnosis of diseases,and it can be measured by the contact monitoring equipment and the non-contact monitoring equipment.The contact monitoring equipment could affect the body’s daily activities and bound activity space of human,besides it cannot monitor special people,such as infants,severely burned patients and seriously ill patient.Therefore,it is necessary to design a non-contact device to monitor human’s vital signs under the interference-free environment.This thesis designed a monitoring system for vital signs based on microwave technology,which works at the ISM frequency band.The followings are the main work and conclusions of this thesis:(1)A Yagi antenna printed in PCB was designed and some improvements were made,such as the two dipole elements were printed on the both sides of substrate instead of the phase inverter;Special microstrip took place of the Balun microstrip matching network,which reduced the size of antenna and increased the stability of Yagi antenna.The final designed antenna has a good radiation performance,S11=-22.87 dB at 2.45 GHz,the forward gain and the backward gain are 8.69 dB and-10.55 dB,respectively.(2)This thesis also designed a 2-unit,4-unit rectangular array antenna with good radiation performance and directivity.The design of the power divider achieved the average power distribution.There are two rectangular grooves in the rectangle radiation patch to adjust the radiation efficiency,and it is convenient to adjust the size of two rectangles to achieve impedance matching.(3)Transmitter and receiving circuits were integrated into one PCB board.RF signals were produced by writing code in the RF chip and though the Baiun circuit to achieve the highest efficiency of transmitting power.Circulator separated transmitted signal and received signal;Detection circuit and the subsequent analog signal processing circuit achieved the basic processing of echo signals,and finally the RF chip sampled and processed signals.(4)The vital signs were extracted by using trend analysis,normalization,FFT and wavelet transform based on the echo signal collected by the proposed non-contact system.Finally the respiratory rate and heart rate were extracted.(5)Compared with the existing contact system,this thesis performed a series of experiments to verify the designed system.The errors of heart rate and respiration rate of non-contact monitoring system based on Yagi antenna are ± 1.9 beat·min-1 and± 1 beat · min-1,respectively.The errors of heart rate and respiration rate of non-contact monitoring system based on rectangular array antenna are ± 0.6 beat · min-1,± 0.5 beat ·min-1.The accuracy of the system based on the rectangular array antenna is higher than the Yagi antenna at the same distance,but the Yagi antenna can monitor the signals of human body movements at the longer distance.