BOOK_CONTENT
From Structural Health Monitoring with Piezoelectric Wafer Active Sensors

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 made up of a number of elements, usually identical in size and arranged along a line, at uniform pitch. The wave pattern generated by the phased array is the result of the superposition of the waves generated by each individual element. By sequentially firing the individual elements of an array transducer at slightly different times, the ultrasonic wavefront can be focused or steered in a specific direction. Thus, inspection of a wide zone can be achieved by electronically sweeping and/or refocusing without physical manipulating the array.


Figure 11.3: Uniform linear array of M omni-directional PWAS transducers spaced at pitch d.

Once the beam steering and focusing have been established, the detection of internal flaws is done with the pulse-echo method (Fig. 11.4). A pulse, consisting of a smooth-windowed tone-burst of duration t p, is transmitted toward the target. The target reflects the signal and creates an echo, which is detected by the radar. By analyzing the phased-array signal in the interval ( t p , t p + t 0), one identifies the delay, ?, representing the time-of-flight (TOF) taken by the wave to travel to the target and back. Knowing TOF and wave speed allows one to precisely determine the target position.


Figure 11.4: The pulse-echo method: (a) the transmitted pulse, s
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Topics of Interest

11.4 FURTHER EXPERIMENTS WITH LINEAR PWAS ARRAYS 11.4.1 EUSR DETECTION STUDIES Extensive experiment were carried out to verify the detection ability of 1-D linear EUSR algorithm using the setup...

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...

11.6 GENERIC PWAS PHASED-ARRAY FORMULATION The 1-D phased array algorithm employed in many applications uses the parallel-rays approximation. This assumption greatly simplifies the beamforming...

11.7 2-D PLANAR PWAS PHASED ARRAY STUDIES In the previous section, we have explored the capabilities of 1-D linear arrays of PWAS transducers and have shown that they can successfully detect the...

11.9 DAMAGE DETECTION EXPERIMENTS USING RECTANGULAR PWAS ARRAY To verify the damage detection ability of the 2D-EUSR algorithm, two rectangular PWAS arrays (a 4 8 array and an 8 8 array) were used.