Research On Liquid Detection Based On Surface Acoustic Wave Technology

Acoustic wave sensor has the advantages of high sensitivity,fast response,low loss and so on.It is suitable for liquid sensing and has wide applications in biomedicine,chemical industry,smart home and other fields.In this dissertation,the theoretical analysis,modeling,practical manufacture,system design and experimental test were studied.The design and manufacture of shear-horizontal surface acoustic wave sensors and corresponding reader were completed.And the typical problems in the field of liquid detection such as residue detection of detergents,the rapid identification of liquid speciesis and multi-parameter parallel detection of liquid were studied.In the aspect of theoretical analysis and modeling,the full matrix with boundary condition method and perturbation theory were used to analyze and simulate the sensor's liquid sensing mechanism.In this dissertation,a double-terminal dual delay line sensor structure was designed,the model between the sensor dimension parameters and the transmission characteristics was established by using the coupled-mode theory.The effects of the the number of electrode,aperture and center distance of the inter-digital transducer were analyzed,the design parameters of the sensor were optimized.And the finite element simulation software COMSOL was used to compare the time domain simulation results of the sensor,the sensor with liquid well and the sensors with liquid in the well.In terms of sensor manufacture,three kinds of sensors were made in this paper,the performance of the sensors were tested by using vector network analyzer and were compared with the simulation results of coupled-mode model.In the liquid detection experiment,the integrated sensor,thermostat water bath,pipettor and other detection devices were used to test various liquid samples such as detergent and glycerin.The objective function,principal component analysis and artificial neural network are used in data processing respectively.The results showed that the sensor could detect the detergent with a range of 0-240 ppm and a resolution of ±30ppm.The rapid identification of detergent,glycerin,juice,alcohol and milk could been realized.And the maximum relative error for the multiparameter parallel detection of the density,viscosity,dielectric constant and conductivity of the liquid were 0.44%,7.42%,0.85%,and 4.30%.In order to realize the practical use of the liquid detection system,the reader was designed and manufactured.The transmit chain used direct digital frequency synthesizer and phase-locked loop to generate high-frequency sweeping pulse signal,while the receive chain adapted the scheme of downconversion intermediate frequency sampling technique and digital quadrature demodulation.Although the effect of the reader was slightly worse than the vector network analyzer,it could also realize the detection of the detergent residue,the rapid identification of the liquid types and the multi-parameter parallel detection of liquid.