Cost-effective and reliable damage detection is critical for the utilization of composite materials. This paper presents part of an experimental and analytical survey of candidate methods for in-situ damage detection of composite materials. Experimental results are presented for the application of Lamb wave techniques to quasiisotropic graphite/epoxy test specimens containing representative damage modes, including delamination, transverse ply cracks and through-holes. Linear wave scans were performed on narrow laminated specimens and sandwich beams with various cores by monitoring the transmitted waves with piezoceramic sensors (PZT). Optimal actuator and sensor configurations were devised through experimentation, and various types of driving signals were explored. These experiments provided a procedure capable of easily and accurately determining the time-of-flight of a Lamb wave pulse between an actuator and sensor. Lamb wave techniques provide more information about damage presence and severity than previously tested methods (frequency response techniques), and provide the possibility of determining damage location due to their local response nature. These methods may prove suitable for structural health monitoring applications since they travel long distances and can be applied with conformable piezoelectric actuators and sensors that require little power.

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fever with or without chills, chest tightness, dry cough, and shortness of breath, while developing patchy to diffuse infiltration of the lungs, as shown radiographically in Figure 1. Identifying and monitoring SARS-CoV-2 infection has become crucially important. A recent projection of the transmission dynamics of SARS-CoV-2 [2] showed that longitudinal serological studies are desperately needed to determine the extent and duration of immunity to SARS-CoV-2. Even in the event of apparent elimination, maintenance of SARS-CoV-2 surveillance is still needed because of a possible resurgence of contagion. In the past, notable viruses have emerged suddenly from obscurity or anonymity, provoking concern from the point of view of immunology regarding their sustained epidemic transmission in naive human populations. More than 70% of these infections have been zoonotic, entering either directly from wild animal reservoirs or indirectly via an intermediate domestic animal host. [3] Ebola virus, avian influenza, human immunodeficiency virus (HIV), and SARS are all examples of zoonoses that have emerged from wild animals, presenting an increasingly serious threat to human health and economies worldwide. Figure 2 shows the trend in the number of people infected with SARS-CoV-2. [4] The spread of the severe acute respiratory syndrome coronavirus has changed the lives of people around the world with a huge impact on economies and societies. The development of wearable sensors that can continuously monitor the environment for viruses may become an important research area. Here, the state of the art of research on biosensor materials for virus detection is reviewed. A general description of the principles for virus detection is included, along with a critique of the experimental work dedicated to various virus sensors, and a summary of their detection limitations. The piezoelectric sensors used for the detection of human papilloma, vaccinia, dengue, Ebola, influenza A, human immunodeficiency, and hepatitis B viruses are examined in the first section; then the second part deals with magnetostrictive sensors for the detection of bacterial spores, proteins, and classical swine fever. In addition, progress related to early detection of COVID-19 (coronavirus disease 2019) is discussed in the final section, where remaining challenges in the field are also identified. It is believed that this review will guide material researchers in their future work of developing smart biosensors, which can further improve detection sensitivity in monitoring currently known and future virus threats.

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