用于声子晶体检测的外差测量信号处理研究

Study on the Processing of the Heterodyne Interference Signal for Phononic Crystal Detections

为了满足声子晶体谐振频率测量要求,即测量出其振动形式且可连续测量,该文运用光外差测量技术测得光电信号,声子晶体激励采用压电激励方式。由于光电信号很微弱,故用自动增益控制电路对光电信号放大,然后运用锁相混频技术,解调出振动信息。本系统中自动增益控制电路,使系统对实验台倾斜等原因造成的连续测量时光电信号大幅变化带来的困难得以解决。该系统实现了对微弱振动的实时、灵敏度及信噪比均高的精确连续测量,对于声子晶体在线、连续检测具有重要意义。

To satisfy the demands for the resonance frequency detection of the phononic crystal,that is to get the form of vibration of the phononic crystals （PCs）, which include the amplitude and the phase information of the vibration continually,we use the optical heterodyne interference technique to detect the vibration so as to get the photocurrent which contains the information we need to process. The phononic crystal was excited by the piezoelectric excitation. As the photocurrent is weak,we use the auto-gain-control （AGC） circuit to enlarge it,and then we use the phase-locked-loop （PLL） frequency-mixing method to demodulate the signal which reflects the vibration amplitude and the phase. The AGC circuit used in this system has overcome the difficulties of the large-scale variation of the photocurrent caused by the incline of the test-bed and other factors,thus we can realize the accurate and continuous detection of the weak vibration in time. Its anti-jamming ability, quick response, and high signal to noise ratio （SNR） ,make this method more important to the on-line and continuous detection of the phononic crystal.