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Description
Previous research reported a resonance phenomenon due to the propagation of laser-induced shock waves through polyurea-based laminated composite structures. Specifically, the output stress waves were found to be two orders of magnitude higher than the input waves despite the absence of additional sources of energy beside the mechanical work done by the ultrahigh strain rate loading. The objective of this research is to leverage the reported resonance phenomena to synthesize a novel energy-free mechanical amplifier for sensors used to detect and report mechanical vibrations, especially those used in biomedical applications. A significant difference in the current research is the focus on propagation of stress waves in the acoustic frequency range (below 100 kHz) with the expectation that similar amplification phenomena persists. Acrylic/Polyurea/Acrylic (AC/PU/AC) samples with 25.4mm x 25.4mm square and various thicknesses were created using spin coating and hand layup techniques. Electrical and mechanical experimental testing were used to characterize all samples. The electrical response investigation was accomplished by utilizing piezoelectric (PZT) plates to drive input sinusoidal ultrasonic waves between 1-100Hz into each sample while another PZT plate was used as a sensor to measure the response. The results from the electrical characterization showed amplified responses for all AC/PU/AC samples on the order of twenty times higher than the input. The mechanical response analysis was conducted by measuring the out-of-plane free surface displacement using laser ultrasonic, which also resulted in amplified responses between a range of 0.8-4.95. Finally, a lumped parameters model based on treating each layer of the composite as a mass-spring-dampener was created to estimate and predict the amplification phenomena, which also resulted in amplified responses. The amplification effect may be attributed to Stoneley waves, which are adding to the transmitted wave through the interlayer material to produce an amplified resultant wave. This amplification effect is observed when the interlayer thickness strategically lies in the range of 30um for polyurea bonding and 1-3um for acrylic bonding.
