【作者】 陈剑；

【导师】 文玉梅；

【作者基本信息】 重庆大学 ， 仪器科学与技术， 2002， 硕士

【摘要】 无源、无线声表面波传感器不但能测量多种物理量或化学量，而且具有：抗干扰能力强、耐用性高、能忍受恶劣的环境，微型化、无源化、无线遥测等多种优点，从而引起了人们的重视。信号处理是该类传感器的核心之一，也是它的重要研究内容。本文研究了用数字信号处理的方法从无源、无线单端对谐振器型声表面波传感器的响应信号即无线查询的回波信号中提取出包含被测量信息的特征频率。本文首先分析了该类传感器输出的传感信号的特点和主要组成，为测量随被测量改变的特征频率，阐明了直接或间接测量谐振频率的两种方法和相应的信号处理任务；并设计了一种频域与时域相结合的信号检测算法；在信号检测后，针对不同特征量的测量采用了不同的数字信号处理算法。本文采用陷波、数字相敏检波、基于多分辨率分析的硬阈值去噪算法和FFT、频率校正等算法，估计出回波信号中调制信号的主频。它反映了激励信号的频率和谐振频率之差，从而实现对谐振频率的间接测量。在信号预处理中，采用陷波器抑制固定干扰信号；采用数字相敏检波算法从陷波后的输出信号中提取出回波信号的包络幅值，并推导了数字相敏检波后输出信号的主频与回波信号中调制信号主频的关系；分析了经陷波、数字相敏检波，重采样后的输出信号中“噪声”的组成；采用基于多分辨率分析的硬阈值去噪算法减小或抑制这些“噪声”；最后采用FFT、频率校正算法从去噪后的输出信号中估计出调制信号的主频。在实现这些算法时，具体分析了它们在处理信号前后对信号的要求或影响，并始终为估计出回波信号中的调制信号主频设计了一些具体的参数或算法，最后分析了上述算法对调制信号主频测量结果的影响。处理结果表明采用上述算法从较高信噪比的回波信号中估计出调制信号主频是可行的。本文根据电子计数器测频的原理，用软件的方法测量回波信号载波的频率，实现对谐振频率的直接测量。分析了软件测频的频率分辨率，并采用软件内插的算法提高了频率分辨率和测量的精度，而且在LabVIEW6i平台上建立了基于软件测频的虚拟仪器系统。比较本文采用的两种测量谐振频率的算法，即估计回波信号中调制信号主频和测量回波信号载频的算法，测量回波信号载频的算法更简单，较易实用化，而估计回波信号中调制信号主频的算法复杂，运算量大，实时性不好，从而限制了<WP=5>它的实用化。更多还原

【Abstract】 Wireless Passive SAW sensors can not only measure various physical and chemical quantities, but also hold such excellence as resisting interference, durability, bearing hostile environment, minisize, passive wireless measurement etc. So people are interested in it. Signal processing is one of the kernels of this kind of sensors and the main aspect of effectiveness. Digital signal processing is studied and used to extract the characteristic frequency of the measurand from the response of wireless passive sensors using SAW resonators, that is the echo to RF interrogation signal. At first, the response of the sensors is analyzed, and its characteristic and primary components are discussed. It illuminates two methods of direct and indirect measurement for resonant frequency and the tasks of signal processing corresponding to them, for measuring the characteristic quantity varying with the measurand varied. An algorithm of signal detection combinedly based on time domain and frequency domain is designed. While the signal is detected, the algorithm of signal processing varying with the characteristic quantity to be extracted is different. Algorithms such as notch filtering, digital phase detection, denoising with hard threshold based on multiresolution analysis, FFT, and rectifying frequency etc., are used to evaluate the primary frequency of modulation signal, which shows the difference between the carrier frequency of exciting signal and resonant frequency, realizing the indirect measurement for resonant frequency. While preprocessing, notch filter is used to eliminate the exciting frequency interference. Digital phase detection (DPSD) is used to extract the echo envelope. The relation between the primary frequency of the output by digital phase detection and that of modulation signal from the echo is derived. The components of ’noises’ in the decimation output are analyzed. Denoising with hard threshold based on multiresolution analysis is used to decrease or eliminate these ’noises’. Finally, the primary frequency of the modulation signal is evaluated by using FFT and the algorithm of rectifying frequency from the denoised output. These algorithms being implemented, the requirements and effects for using them are analyzed. And in order to evaluate the primary frequency of the modulation signal, some arguments are selected and the algorithms are designed corresponding to the sensing<WP=7>signal features. Finally, the effects on the primary frequencies of the modulation signal by the above algorithms are analyzed. The processed results show that the algorithms can evaluate the primary frequency of modulation signal from the echo with higher signal-noise ratio. According to the principle of frequency measurement in an electronic counter, the frequency measurement by a software method is used to measure the carrier frequency of the echo, realizing direct measurement of the resonant frequency. The frequency resolution for this method is analyzed, and the interpolation by software method is used to improve the frequency resolution and frequency precision. A virtual instrument implementing this measurement is developed in LabVIEW6i. Comparing the algorithm to evaluate the primary frequency of the modulation signal with the algorithm to measure the carrier frequency of the echo, the direct measurement is simpler and more practical, while the indirect measurement is complex, and computed with a great deal of time. Consequently the indirect measurement is difficult to be implemented in realtime.更多还原