Piezoelectric wafer active sensors

Figure 16.5 Coupling between piezoelectric wafer active sensors and Lamb waves in a thin-wall structure, (a) Symmetric mode (b) antisymmetric mode.

Figure 16.6 Piezoelectric wafer active sensors (PWAS) installation, (a) 7 mm PWAS on a metallic structure (b) 7 mm round and square PWAS on a composite structure.

Figure 16.7 Use of piezoelectric wafer active sensors (PWAS) for damage detection with ]MDpagating and standing guided waves in thin-waU structures, (a) pitch-catch (b) pulse-echo (c) thickness mode (d) impact and acoustic emission (AE) detection (e) electromechanical (E/M) impedance (f) PWAS phased array.

Giurgiutiu V. Structural health monitoring with piezoelectric wafer active sensors. Elsevier Academic Press 2008. 

Giurgiutiu V, Yu LY, Kendall JR, Jenkins C. In situ imaging of crack growth with piezoelectric-wafer active sensors. AIAA J 2007 45(11) 2758—69. http //dx.doi.org/ 10.2514/1-30798. 

Yu L, Giurgiutiu V. In situ 2-D piezoelectric wafer active sensors arrays for guided wave damage detection. Ultrasonics 2008 48(2) 117—34. http //dx.doi.0rg/lO.lOl6/ j.ultras.2007.10.008. 

Cue A, Giurgiutiu V, Joshi S, Tidwell Z. Structural health monitoring with piezoelectric wafer active sensors for space applications. AIAA J 2007 45(12) 2838—50. http // dx.doi.org/10.2514/1.26141. 

Giurgiutiu V, Harries K, Petrou M, Bost J, Quattlehaum JB. Disbond detection with piezoelectric wafer active sensors in RC structures strengthened with FRP composite overlays. Earthq Eng Eng Vib 2003 2(2) 213—24. 

For thin shell structures, the most promising methods are those based in the analysis of the propagation of elastic waves. The wave propagation methods have often used piezoelectric wafer active sensors (PWAS) as transmitters to generate waves and simultaneously as receivers to measure the echo signals due to the defects. A time-frequency analysis allows an estimation of crack size on the basis of the relationship between new and baseline response. The sensitivity of Lamb waves to defects depends largely on the frequency, and for complex structures the dispersive Lamb waves interact with reinforcements with partial reflections and refractions. These systems have not reached the level of maturity required for industrial applications. A full discussion with alternatives is presented in the book by Giurgiutiu (2008). 

Giurgiutiu V. (2008), Structural Health Monitoring with Piezoelectric Wafer Active Sensors. Amsterdam, Boston Academic Press... 

Giurgiutiu, V. Embedded Ultrasonics NDE with Piezoelectric Wafer Active Sensors. Journal Instrumentation, Mesure, Metrologie, Lavoisier Pub., Paris, Prance, RS series 12M, Vol. 3, No. 3-4 (2003), pp. 149-180... 

With the aid of a particular class of materials (thin-film piezoelectrics), incorporation of AW devices and conventional integrated circuit components on the same silicon substrate is in fact possible. Under the proper conditions, a number of piezoelectric materials can be deposited in thin-film form, typically by RF sputtering, and retain their piezoelectric nature. For this to occur, the crystallites that grow during deposition must be predominantly oriented in a single, piezo-electrically active crystallographic direction. Two such materials are 2 0 and AIN the former has been used as an overlayer on Si wafers to fabricate all of the FPW devices studied for sensor applications to date, and also for SAW resonators. Because extremely thin piezoelectric films are readily fabricated, both ZnO and AIN have been used to make bulk resonators that operate at much higher... 

Fiber optics based monitoring of PMC includes, eg, strain (161), temperature, acoustic emission signals, and other measurements (162). Electromagnetic resistance measurements yield information on strain changes and defect acciunu-lation (101-104). Even carbon nanotubes are now investigated as strain sensors in PMC (163). Piezoelectric thin wafers or plates (164) or active fiber composites made from piezoelectric fibers (165) also yield, eg, strain and acoustic emission signals. The performance of fiber optics and piezoelectric sensors for detection of microdamage in CFRP is compared in Reference 166. 

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