Air-coupled Nondestructive Evaluation Research Articles

Air-Coupled Nondestructive Evaluation Dissected

This work develops a two-dimensional theoretical model to simulate the behavior of a fully non-contact air-coupled nondestructive evaluation system for a thin isotropic plate. The model is divided into transmission, guided wave propagation and reception phase. The validation of the complete model was carried out by modeling the same system by means of finite element method using a Multiphysics software. In addition, the dependency of the generated Lamb waves on different transmitter’s parameters and incidence angle is thoroughly investigated. The results of the acoustic pressure excited by the transducer, the out-of-plane velocity amplitudes for the generated first antisymmetric Lamb wave mode, and the radiated pressure from the plate caused by the leaky Lamb wavefield were all compared between the two models and a reasonable degree of similarity was found.

Enhancing the bandwidth of piezoelectric composite transducers for air-coupled non-destructive evaluation

This paper details the development of a novel method for increasing the operational bandwidth of piezocomposites without the need for lossy backing material, the aim being to increase fractional bandwith by geometrical design. Removing the need for lossy backing materials, should in turn increase the transmit efficiency in the desired direction of propagation. Finite element analysis has been employed to determine the mode of operation of the new piezocomposite devices and shows good correlation with that derived experimentally. Through a series of practical and analytical methods it has been shown that additional thickness mode resonances can be introduced into the structure by a simple machining process. The shaped composites described in this paper offer increased operational bandwidth. A simple example of a two step thickness design is described to validate and illustrate the principle. A more complex conical design is presented that illustrates a possible tenfold increase in bandwidth from 30kHz to 300kHz, operating in air without backing. An illustration of the applicability of this type of transducer technology for frequency agile guided mode non-destructive evaluation is then presented.

English

Capacitance micromachined ultrasonic transducers (CMUTs) have become an attractive alternative to the piezoelectric transducers, especially in air-coupled nondestructive evaluation (NDE) and ultrasound medical imaging flow metering, micro/nanoelectronics, and industrial cleaning, etc. These are similar to other capacitance transducers as these employ a vibrating membrane to send and receive ultrasound in air and water. This paper describes the theory and design of a circular micromachined ultrasonic transducer which could lead to a CMUT with many advantages, including less loading effect. The software programs (Intellisuite 8.2 and MATLAB 7.0) were used to model a single cell of CMUT. The simulations-based studies of the critical parameters like collapse voltage and snapback voltage, which influence the operation of the CMUTs to a large extent, has been discussed. Small signal equivalent circuit model for the circular CMUT has been discussed and the program (SPICE) has been used for the simulation of the small signal equivalent circuit. Defence Science Journal, 2009, 59(6), pp.627-633 , DOI:http://dx.doi.org/10.14429/dsj.59.1568