INVESTIGATION OF EFFECT OF USING NANO COATING ON WOODEN SHEDS ON DYNAMIC PARAMETERS

In this article, the dynamic parameters (frequencies, mode shapes, damping ratios) of the uncoated wooden shed and the coated by silicon dioxide are compared using the operational modal analysis method. Ambient excitation was provided from micro tremor ambient vibration data on ground level. Enhanced frequency domain decomposition (EFDD) was used for output. Very best correlation was found between mode shapes. Nano-SiO2 gel applied to the entire outer surface of the red oak shed has an average of 14.54% difference in frequency values and 13.53% in damping ratios, proving that nanomaterials can be used to increase internal rigidity in wooden slabs. High adherence of silicon dioxide to wooden surfaces was observed as another important result of this study.

Enhanced low-frequency vibration energy harvesting with inertial amplifiers

Piezoelectric vibration energy harvesters have demonstrated the potential for sustainable energy generation from diverse ambient sources in the context of low-powered micro-scale systems. However, challenges remain concerning harvesting more power from low-frequency input excitations and broadband random excitations. To address this, here we propose a purely mechanical approach by employing inertial amplifiers with cantilever piezoelectric vibration energy harvesters. The proposed mechanism can achieve inertial amplification amounting to orders of magnitude under certain conditions. Harmonic, as well as broadband random excitations, are considered. Two types of harvesting circuits, namely, without and with an inductor, have been employed. We explicitly demonstrate how different parameters describing the inertial amplifiers should be optimally tuned to maximise harvested power under different types of excitations and circuit configurations. It is possible to harvest five times more power at a 50% lower frequency when the ambient excitation is harmonic. Under random broadband ambient excitations, it is possible to harvest 10 times more power with optimally selected parameters.

Mechanism of Principal Component Analysis in Structural Dynamics under Ambient Excitation

Principal component analysis (PCA) is a classical dimensionally reduction method having been widely applied in structural health monitoring (SHM) systems. However, it usually works as a “black-box” in most applications, i.e. the outputs of PCA only make sense statistically without physical meaning. This problem causes the difficulty to estimate the stability of the current PCA-based SHM methods, due to the unclear physical essence in engineering. This paper aims to propose a physical interpretation of PCA when it is applied to the response data from a multi-freedom system under ambient excitation. Both non-damping and damping cases are analyzed theoretically and verified by both numerical and laboratory experiments. The results indicate there is a close connection between the outputs of PCA and dynamical parameters: PCA can reveal information about the mode shape and modal participation of the structure. This work gives a theoretical foundation of the current PCA-based SHM method under ambient excitation, leading to the possibility of further advancement.

Adaptive Electromagnetic Energy Harvester for Mobile Devices

<div>Advances in design and development of light-weight and low power wearable and mobile devices open up the possibility of lifetime extension of these devices from ambient sources through energy harvesting devices as opposed to periodically recharge the batteries. The most commonly available ambient energy source for mobile devices is Kinetic energy harvesters (KEH). The major drawback of the energy harvesters is limited effectiveness of harvesting mechanism near a fixed resonant frequency. It is difficult to harvest a reliable amount of energy from every forms of device motions with different excitation frequencies. To overcome this drawback, in this paper we propose an adaptive electromagnetic energy harvester which utilises spring characteristics to adapt its resonant frequency to match the ambient excitation frequency. This paper presents a prototype design and analysis of an adaptive electromagnetic energy harvester both in simulation and real. The harvester has tested using a specially designed experimental setup and compared with numerical simulations. The proposed solution generates 3.5 times higher maximum power over the default power output and 2.4 times higher maximum frequency compared to a fixed resonant frequency electromagnetic energy harvester.</div>