>> “Near static strain measurement with piezoelectric films” appeared in Sensors & Actuators

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A fundamental challenge that prevents the implementation of piezoelectric sensors for measuring extremely low frequency (<1 mHz) events, such as aerodynamic pressure measurements, earthquake detection, and physiological monitoring, is their inability to measure static or very low frequency signals. To enable near static measurements, we present a low-noise, differential charge amplifier topology that performs real-time cancellation of drift in the output voltage while simultaneously increasing the gain of a conventional charge amplifier. A sensing frequency range from 0.01 mHz to 310 kHz with a voltage drift reduction of up to 95% is demonstrated. A theoretical sensitivity increase of up to 30 dB is achieved with the proposed topology compared to a basic charge amplifier with the same component tolerances, time constant, and allowable drift rate. The proposed circuit is interfaced with a piezoelectric PVDF film for evaluation of performance in the time and frequency domains. The measured voltage from uniaxial near DC strain measurements stays within 3% over a measurement period of 500 s. The paper further describes a linear piezoelectric strain sensor model and the various factors that influences the charge output, loading effect, and lateral cross-sensitivity of the sensor. The calculated strain–voltage relation-ship or the gage sensitivity agrees well with the measurements with a linearity error of less than 5% up to 1 millistrain.

A. RAMANATHAN, L.M. Headings, and M.J. Dapino, “Near static strain measurement with piezoelectric films,” Sensors & Actuators: A. Physical. Vol. 301, 111654, 2020. doi:10.1016/j.sna.2019.111654

>> “Detection of crack initiation and growth using fiber Bragg grating sensors embedded into metal structures through ultrasonic additive manufacturing” published in Sensors 2019

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Structural health monitoring (SHM) is a rapidly growing field focused on detecting damage in complex systems before catastrophic failure occurs. Advanced sensor technologies are necessary to fully harness SHM in applications involving harsh or remote environments, life-critical systems, mass-production vehicles, robotic systems, and others. Fiber Bragg Grating (FBG) sensors are attractive for in-situ health monitoring due to their resistance to electromagnetic noise, ability to be multiplexed, and accurate real-time operation. Ultrasonic additive manufacturing (UAM) has been demonstrated for solid-state fabrication of 3D structures with embedded FBG sensors. In this paper, UAM-embedded FBG sensors are investigated with a focus on SHM applications. FBG sensors embedded in an aluminum matrix 3 mm from the initiation site are shown to resolve a minimum crack length of 0.286 ± 0.033 mm and track crack growth until near failure. Accurate crack detection is also demonstrated from FBGs placed 6 mm and 9 mm from the crack initiation site. Regular acrylate-coated FBG sensors are shown to repeatably work at temperatures up to 300 °C once embedded with the UAM process.

S.K. CHILELLI, J.J. SCHOMER, and M.J. Dapino, “Detection of crack initiation and growth using fiber Bragg grating sensors embedded into metal structures through ultrasonic additive manufacturing,” Sensors 2019, 19(22), 4917. 2019. doi:10.3390/s19224917