###### Abstract  
In recent years, with the continuing progress of aging social infrastructures such as bridges and tunnels, there has been high demand for the assessment of deterioration of their performance and conditions. Since current inspection methods for those structures have mainly relied on human resources, it is important to reduce their increasing maintenance cost. One of the key methods for achieving effective maintenance without expensive human costs is to use sensors to discriminate between healthy and unhealthy conditions. In this paper, a MEMS (micro electro mechanical systems) wideband frequency sensor, which is referred to as a super acoustic (SA) sensor, is evaluated through the pencil lead break (PLB) test. Due to its wideband frequency characteristics, the SA sensor is expected to be a promising alternative to the existing vibration sensors, including acoustic emission (AE) sensors. Several PLB signals were generated on an aluminum plate (5 mm thick), and propagating Lamb waves were detected by both AE and SA sensors. SA sensors were able to identify the location of PLB sources on the plate by measuring time differences between each sensor. By comparing the wave spectrums of both the AE and SA sensors analyzed by wavelet transform, the applicability of SA sensor for AE measurement is verified. acoustic emission; MEMS sensor; acoustic emission sensor; elastic wave; source location Article  
Elastic Wave Measurement Using a MEMS AE Sensor  
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cost and size of the sensors are issues that need to be resolved. On the other hand, MEMS (micro electro mechanical systems) sensors are widely used as acceleration sensors. Almost every smartphone has several MEMS accelerometers, and the cost of these sensors is quite reasonable. Compared to the piezoelectric sensors, MEMS sensors have beneficial characteristics such as low cost as a result of mass production, and smaller size. SA sensors are a type of MEMS sensor, and have a broad frequency bandwidth [3; 4; 5]. Taking advantage of this characteristic, SA sensors can be used as a multifunctional vibration sensor to measure several frequency ranges conventionally measured by multiple sensors. It is also expected that SA sensors can be manufactured at relatively low cost, compared to commercial AE sensors. Although there are different type of transduction principles, such as optics, MEMS vibration sensors-including AE sensors-consist of three types of major transduction methods; piezoresistive, capacitive and piezoelectric. Capacitive- and resonant-type MEMS AE sensors have been actively researched in the academic field [6; 7; 8; 9; 10]. Capacitive MEMS sensors have moving electrodes parallel to the fixed ones manufactured by surface micromachining processes. The distance between electrode pairs varies when an external vibration places inertial force on the electrodes. Because of the nature of the sensing method, which adopts moving electrodes supported by elastic springs, capacitive sensors inherently become resonant-type. Piezoelectric MEMS sensors have also been developed, but the difficulty of forming stable PZT (lead zirconium titanate) membranes with micromachining make it hard to apply in numerous applications compared to other principles. Film-type is frequently employed as a basic structure [11; 12]. However, this type is typically made with polymer processes such as PVDF (polyvinylidene difluoride), rather than with a micromachining process. Piezoresistive MEMS sensors have been adopted in many commercial and academic fields, such as accelerometers, pressure sensors and force sensors [13; 14]. In our previous work, piezoresistive MEMS AE transducers with broad frequency characteristics were developed.