Characterization Of Thermophysical Properties Of Materials Based On Chirped Photoacoustic Piezoelectric Technology

Thermophysical property is one of the important physical properties of materials.Its size reflects the speed of material heat propagation.The measurement and research of material thermal diffusivity is particularly important in the fields of material research,electronic information,aerospace and so on.Photoacoustic piezoelectric technology is applied to the measurement of material thermal diffusivity because of its high sensitivity,wide detection frequency response,simple and reliable system.At present,the thermal diffusivity measurement method based on photoacoustic piezoelectric technology has some limitations in measurement speed.In this paper,the measurement of photoacoustic piezoelectric electrothermal diffusivity based on chirp modulation and matched filter method is carried out to realize the rapid and high-precision measurement of material thermal diffusivity.The main research contents are as follows:Firstly,the time domain measurement theory of chirped photoacoustic piezoelectric thermal diffusivity based on chirped modulated laser excitation and matched filter signal processing is established.Chirp modulation and matched filtering are used to replace the single frequency modulation and phase-locked demodulation in the traditional frequencydomain photoacoustic piezoelectric thermal diffusivity measurement technology.Based on the frequency-domain photoacoustic piezoelectric response of single frequency laser excitation,the time-domain photoacoustic piezoelectric signal excited by chirped（multi frequency）laser is deduced,and the theoretical model of chirp modulation time-domain photoacoustic piezoelectric is established.At the same time,the matched filtering signal processing method based on correlation detection is used to process the chirped timedomain photoacoustic piezoelectric signal,The inversion method of chirped photoacoustic pressure electrothermal diffusivity is formed.Secondly,based on the chirped photoacoustic piezoelectric model,the simulation of various parameters affecting the measurement of material thermal diffusivity is carried out.Through sensitivity analysis,the effects of laser modulation frequency,sample thermal diffusivity and thickness on the sensitivity of thermal diffusivity measurement based on photoacoustic piezoelectric phase signal in single frequency modulation frequency domain photoacoustic piezoelectric model are theoretically simulated.Based on this,the chirp start and end frequency,chirp duration effects of sample thermal diffusivity and thickness on the sensitivity of thermal diffusivity measurement based on chirped time domain photoacoustic piezoelectric signal.The results show that in the chirped photoacoustic piezoelectric model,the closer the thermal diffusion length range caused by each parameter is to a certain depth within the sample thickness,the more sensitive the thermal diffusivity measurement based on chirped time-domain photoacoustic piezoelectric signal,which lays a foundation for optimizing the parameters affecting the thermal diffusivity measurement.Thirdly,a chirped time-domain photoacoustic piezoelectric thermal diffusivity measurement system is established,and the experimental research on the measurement of thermal diffusivity of metal materials is carried out.Based on the chirped photoacoustic piezoelectric model,thermal diffusivity inversion method and thermal diffusivity measurement sensitivity analysis,the thermal diffusivity measurement experimental system is established and the parameters of the system are optimized.The chirped timedomain photoacoustic piezoelectric Signals of red copper and aluminum samples are measured.The thermal diffusivity values of red copper and aluminum are obtained through signal processing and inversion.Compared with the reference value,the relative error is less than 3%.The results show that the chirped time-domain photoacoustic pressure electrothermal diffusivity measurement system can effectively measure the thermal diffusivity of metal materials.The research of thesis shows that the photoacoustic piezoelectric thermal diffusivity measurement technology based on chirp modulation and matched filter method can quickly and effectively measure the thermal diffusivity of metal materials,and can provide a means for the measurement of thermophysical parameters of materials.