A key longstanding objective of the Structural Health Monitoring (SHM) research community is to enable the embedment of SHM systems in high value assets like aircraft to provide on-demand damage detection and evaluation. As against traditional non-destructive inspection hardware, embedded SHM systems must be compact, lightweight, low-power and sufficiently robust to survive exposure to severe in-flight operating conditions. Typical Commercial-Off-The-Shelf (COTS) systems can be bulky, costly and are often inflexible in their configuration and/or scalability, which militates against in-service deployment. Advances in electronics have resulted in ever smaller, cheaper and more reliable components that facilitate the development of compact and robust embedded SHM systems, including for Acousto-Ultrasonics (AU), a guided plate-wave inspection modality that has attracted strong interest due mainly to its capacity to furnish wide-area diagnostic coverage with a relatively low sensor density. This article provides a detailed description of the development, testing and demonstration of a new AU interrogation system called the Acousto Ultrasonic Structural health monitoring Array Module+ (AUSAM+). This system provides independent actuation and sensing on four Piezoelectric Wafer Active Sensor (PWAS) elements with further sensing on four Positive Intrinsic Negative (PIN) photodiodes for intensity-based interrogation of Fiber Bragg Gratings (FBG). The paper details the development of a novel piezoelectric excitation amplifier, which, in conjunction with flexible acquisition-system architecture, seamlessly provides electromechanical impedance spectroscopy for PWAS diagnostics over the full instrument bandwidth of 50 KHz–5 MHz. The AUSAM+ functionality is accessed via a simple hardware object providing a myriad of custom software interfaces that can be adapted to suit the specific requirements of each individual application.

A new acoustic sensing capability, consisting of a flexible high-density linear piezoelectric sensor array coupled to a high-bandwidth interrogation device, is developed and applied to in situ wavenumber–frequency modal decomposition of acoustic emissions in plates. An experimental assessment of the capability is undertaken using acoustic emissions generated by a ball-drop impact on aluminium and composite panels. A new method for acoustic source localisation based on this new sensor array is described, and it is shown to be more accurate than a conventional multilateration technique using single-point piezoelectric receivers. The potential of this new capability for acoustic emission detection, location and possible quantification is discussed.

Lamb waves provide arguably the best prospect for achieving a structural health monitoring (SHM) capability with broad diagnostic coverage at sensor densities that are not impractically high. The traditional approach in Lamb wave SHM is to employ a single mode, typically one of the fundamental modes, in a non-dispersive and easily excited regime, which is done largely to simplify the interpretation of the elastic wave dynamics. However, the diagnostic value of an interrogation conducted using only the fundamental modes is limited. In general, higher order modes offer potential for greater sensitivity to structural damage and greater scope for discriminating between different failure mechanisms. This paper reports on experimental work demonstrating an in-situ fibre Bragg grating (FBG) sensing capability for Lamb waves at frequencies of up to 2MHz, an achievement that represents an important step toward developing a more robust and versatile approach to Acousto-Ultrasonic SHM.

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