From Structural Health Monitoring with Piezoelectric Wafer Active Sensors

11.2 PHASED-ARRAYS IN CONVENTIONAL ULTRASONIC NDE

The phased array principle was introduced into ultrasonic testing because of its multiple advantages (Krautkramer, 1990; Rose, 1999; Ahmad et al., 2005). Some of the advantages of phased arrays over conventional ultrasonic transducers are high inspection speed, flexible data processing capability, improved resolution, and the capability of scanning without requiring mechanical movement, i.e., dynamic beam steering and focusing (Wooh and Shi, 1998). The backscattered ultrasonic signals can be analyzed and then mapped into an image. By using an ultrasonic phased array, the ultrasonic wave front can be focused in a certain point or steered in a specific direction; the inspection of a wide area can be achieved by electronically sweeping and/or refocusing without physically manipulating the transducers. Damage, which can be characterized as a local change in impedance, is diagnosed by using the echoes received from the propagating ultrasonic waves. However, in comparison to sonar and medical phased arrays, ultrasonic NDE phased arrays encounter several aspects that are of special concerns (i) the wave speed in solids is much higher than in water and tissues; (ii) the wave propagation is much more complicated, since dispersive and multi-mode waves may be present. For these reasons, the electronics required for ultrasonic phased array implementation may be rather complicated and sophisticated.

Current ultrasonic phased array technology mostly employs pressure waves generated through normal impingement on the material surface. Such phased arrays have shown clear advantages in the inspection of very thick specimens and in the sidewise inspection...


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Ultrasonic Linear Position Sensors and Switches
Ultrasonic linear position sensors and switches use ultrasonic waves in combination with light and frequency readings for position and displacement sensing.
Pulser-Receivers
Pulser-receivers generate ultrasonic pulses, which are propagated into materials for NDT testing.
Beam Steerers
Beam steerers are optical tools that allow the user to easily change a laser beam's optical axis height or direction.
Ultrasonic Horns and Boosters
Ultrasonic horns and ultrasonic boosters are used with ultrasonic transducers and converters. Boosters or velocity transformers amplify ultrasonic vibrations. Ultrasonic horns, sonotrodes, anvils, blades or probes contact and transmit ultrasonic vibration.

Topics of Interest

11.3 1-D LINEAR PWAS PHASED ARRAYS We will start our analysis of the PWAS phased array with the simplest configuration: we will discuss the 1-D, a.k.a. linear, phased array (Fig. 11.3). Arrays are...

11.11 SUMMARY AND CONCLUSIONS This chapter has dealt with the use of PWAS transducers to achieve in-situ phased arrays for active structural health monitoring. The chapter started with a review of...

10.1 INTRODUCTION This chapter deals with the use of piezoelectric wafer active sensors (PWAS) to detect structural damage using wave propagation techniques. This application of PWAS technology...

Overview Lester W. Schmerr Jr. Center for Nondestructive Evaluation and the Dept. of Aerospace Engineering Iowa State University Ames, Iowa 50011 lschmerr@cnde.iastate.edu It will be shown that it is...

There are many ways to alter the characteristics of ultrasonic waves in a liquid contained in a tank. The ultrasonic waves can be frequency modulated (FM) by varying the output frequency of the...

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