Design of a Carrier Wave for Capacitive Transducer with Large Dynamic Range Capacitive transducers are widely used in fundamental physics experiments, seismology, Earth or planetary observations, and space scientific and technical applications because of their high precision, simple structure, and compatibility with various measurements. However, in real applications, there is a tradeoff between their resolution and dynamic range. Therefore, this paper is aimed at enlarging the dynamic range while ensuring high resolution. In this paper, a noise analysis of a capacitive transducer is presented, which shows that the amplitude noise of the carrier wave is the main limiting factor. Hence, a new method of generating a carrier wave with loweramplitude noise is proposed in the paper. Based on the experimental verification, it is found that the carrier wave produced through the new method performed significantly better than the typical digital carrier wave when they were compared in the same sensing circuit. With the carrier wave produced through the new method, the dynamic range of the capacitive transducer can reach 120.7 dB, which is 18.3 dB greater than for the typical direct digital synthesis (DDS) method. In addition, the resolution of the carrier wave is mainly limited by the voltage reference components.

Circumferential SH Wave Piezoelectric Transducer System for Monitoring CorrosionLike Defect in LargeDiameter Pipes The fundamental circumferential shear horizontal (CSH0) wave is of practical importance in monitoring corrosion defects in largediameter pipes due to its virtually nondispersive characteristics. However, so far, there have been limited CSH0 wave transducers which can be used to constitute a structural health monitoring (SHM) system for pipes. Moreover, the CSH0 wavexe2x80x99s capability of sizing the corrosionlike defect has not yet been confirmed by experiments. In this work, firstly, the mechanism of exciting CSH waves was analyzed. A method based on our previously developed bidirectional SH wave piezoelectric transducers was then proposed to excite the pure CSH0 mode and first order circumferential shear horizontal (CSH1) mode. Both finite element simulations and experiments show that the bidirectional transducer is capable of exciting pure CSH0 mode traveling in both circumferential directions of a 1  mm thick steel pipe from 100 to 300 kHz. Moreover, this transducer can also serve a sensor to detect CSH0 mode only by filtering circumferential Lamb waves over a wide frequency range from 100 to 450 kHz. After that, a method of sizing a rectangular notch defect by using CSH0 wave was proposed. Experiments on an 11  mm thick steel pipe show that the depth and circumferential extent of a notch can be accurately determined by using the proposed method. Finally, experiments were performed to investigate the reflection and transmission characteristics of CSH0 and CSH1 waves from notches with different depths. It was found that transmission coefficients of CSH0 mode decrease with the increasing of notch depth, which indicates that it is possible to monitor the depth change of corrosion defects by using CSH0 wave.