Energy harvesting (EH) technologies to power small sized electronic devices are attracting great attention. Wasted energy in a vehicle’s rotating tire has a great potential to enable self-powered tire pressure monitoring sensors (TPMS). Piezoelectric type energy harvesters can be used to collect vibrational energy and power such systems. Due to the presence of harsh acceleration in a rotating tire, a design tradeoff needs to be studied to prolong the harvester’s fatigue life as well as to ensure sufficient power generation. However, the design by traditional deterministic design optimization (DDO) does not show reliable performance due to the lack of consideration of various uncertainty factors (e.g., manufacturing tolerances, material properties, and loading conditions). In this study, we address a new EH design formulation that considers the uncertainty in car speed, dimensional tolerances and material properties, and solve this design problem using reliability-based design optimization (RBDO). The RBDO problem is formulated to maximize compactness and minimize weight of a TPMS harvester while satisfying power and durability requirements. A transient analysis has been done to measure the time varying response of EH such as power generation, dynamic strain, and stress. A conservative design formulation is proposed to consider the expected power from varied speed and stress at higher speed. When compared to the DDO, the RBDO results show that the reliability of EH is increased significantly by scarifying the objective function. Finally, experimental test has been conducted to demonstrate the merits of RBDO design over DDO.

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The complicated transfer path relationship between the vibrations of a seat and the noise at the locations of the driver’s ears was estimated from the residual spectrum. For accurate quantitative estimation of the rattle noise at the locations of the driver’s ears, in particular the partial coherence function of the pure inputs to the output was modelled by considering the correlation between the inputs and the input–output. Whenever a coherence analysis was performed with the noise sources in close proximity selected as the inputs and the noise at the locations of the driver’s ears modelled as the output, the partially coherent output spectrum as a quantitative contribution of the inputs to the output was determined. In this study, we applied a coherence analysis technique to identify the sources of the rattle noise of a seat by visualizing the noise sources with an acoustic camera while excitation of the seat was carried out using a hydraulic exciter. We were able to generate the rattle noise from the headrest stay, the recliner and the front part of the slide while excitation of the seat was obtained using a hydraulic exciter with white noise. We observed that the noise was generated by utilizing a hydraulic six-axis exciter positioned at the driver’s seat of a middle-sized manual transmission vehicle. We determined that the noise measured at the locations of the driver’s ears had a frequency of 58 Hz using acoustic visualization and a coherence technique. It was selected in particular as the target frequency since the 58 Hz resonant frequency caused by the twisting mode of the seat back was identical with the frequency of the rattle noise. Finally, it was verified through a modal test that the rattle noise at 58 Hz was generated by the vibration characteristics of the seat, which depended on gaps between the headrest stay and the guide.