Battery-less PWAS-based wireless Acoustic Emission sensor Md Mazharul Islam 1 , Farshad Zahedi 1 , and Haiying Huang 1* 1 Dept. of Mechanical and Aerospace Engineering, University of Texas at Arlington, 500 W. First Street, WH211, Arlington, TX USA 76019 ABSTRACT Battery-less wireless transmission of acoustic emission (AE) signal acquired using a PWAS is demonstrated in this paper. The wireless AE sensor is equipped with a passive wireless transponder that receives a microwave carrier signal and up-converts the AE signal to microwave frequencies for wireless transmission. A low voltage ultrasound amplifier was designed, fabricated, and tested to amplify the AE signal and to provide a better impedance matching between the PWAS and the 50 Ω wireless transponder. A light-based energy harvester was adopted to drive the low-power voltage amplifier so that no battery is needed at the wireless sensor node. The energy harvesting devices and the amplifier were characterized using ultrasound pitch-catch and pencil lead break experiments. The design, implementation, and characterization of the wireless AE sensing system are described. Keywords: Acoustic Emission, Light Energy Harvesting, Wireless Sensor, PWAS, Wireless Transmission. 1. INTRODUCTION Structural Health Monitoring (SHM) of civil and mechanical structures that are designed to operate for prolonged periods of time improves reliability, safety, and efficient usage of the structures. In general, damage detecting techniques widely used for SHM can be categorized as global or local monitoring techniques. Global monitoring technique detects damages based on its effects on the global structural parameters such as mass, stiffness, damping, resonant frequency shifts, and/or mode shapes 1, 2 . The limitations of global monitoring techniques are that they cannot provide the location of the damage and they are not sensitive to small damages in the structures 3 . Moreover, unwanted sources or interferences such as friction, backlash, and external forces etc. could lead to false predictions of structural damages 4 . Therefore, SHM techniques that are capable of detecting local damages were investigated. Strain and temperature are the most widely used parameters for local damage detection 5 . The disadvantage of the local monitoring techniques is that a large number of sensors are needed to cover a large area due to the limited detection range of these sensors. Acoustic Emission (AE) monitoring may be the only SHM technique that has a large detection range yet is sensitive to small damages. AE refers to the transient elastic waves, i.e. stress waves, resulting from a rapid release of strain energy due to the deformation or damage of the structure 6 . These AE signals can propagate in the structure over a long distance without much attenuation. As a result, AE sensors can detect damage formation occurring far away from the sensor. Moreover, installing several AE sensors on the structure enables damage localization through triangulation algorithms. Conventionally, AE monitoring has been carried out using wired transducers. Despite of the tremendous efforts on wireless sensor research, very few are related to wireless AE sensors 7-9 . This is due to the fundamental incompatibilities between the high frequency and large bandwidth of the AE signals and the limited throughput of the conventional wireless sensor configurations. Even though several researchers have attempted to develop wireless AE sensors 10 , they have to resort to processing the data on board and only transmitting the feature information wirelessly. Because on- board data processing usually consumes a lot of power, on-board processing of the AE signals could drastically reduce the battery-life of these wireless AE sensors. H. Huang, huang@uta.edu, Phone 1 817 272-0563; fax 1 817 272-5010 astl.uta.edu