Roszaidi Ramlan

On the performance of a dual-mode non-linear vibration energy harvesting device

The research trend for harvesting energy from the ambient vibration sources has moved from using a linear resonant generator to a non-linear generator in order to improve on the performance of a linear generator; for example, the relatively small bandwidth, intolerance to mistune and the suitability of the device for low-frequency applications. This article presents experimental results to illustrate the dynamic behaviour of a dual-mode non-linear energy-harvesting device operating in hardening and bi-stable modes under harmonic excitation. The device is able to change from one mode to another by altering the negative magnetic stiffness by adjusting the separation gap between the magnets and the iron core. Results for the device operating in both modes are presented. They show that there is a larger bandwidth for the device operating in the hardening mode compared to the equivalent linear device. However, the maximum power transfer theory is less applicable for the hardening mode due to occurrence of the maximum power at different frequencies, which depends on the non-linearity and the damping in the system. The results for the bi-stable mode show that the device is insensitive to a range of excitation frequencies depending upon the input level, damping and non-linearity.

Normal Incidence of Sound Transmission Loss of a Double-Leaf Partition Inserted with a Microperforated Panel

A double-leaf partition in engineering structures has been widely applied for its advantages i.e. in terms of its mechanical strength as well as its lightweight property. In noise control, the double-leaf also serves to be an effective noise barrier. Unfortunately at low frequency, the sound transmission loss reduces significantly due to the coupling between the panels and the air between them. This paper studies the effect of a micro-perforated panel (MPP) inserted inside a double-leaf partition on the sound transmission loss performance of the system. The MPP insertion is proposed to provide a hygienic double-leaf noise insulator replacing the classical abrasive porous materials between the panels. It is found that the transmission loss improves at the troublesome mass-air-mass resonant frequency if the MPP is located closer to the solid panel. The mathematical model is derived for normal incidence of acoustic loading.

A Combined Softening and Hardening Mechanism for Low Frequency Human Motion Energy Harvesting Application

This paper concerns the mechanism for harvesting energy from human body motion. The vibration signal from human body motion during walking and jogging was first measured using 3-axes vibration recorder placed at various places on the human body. The measured signal was then processed using Fourier series to investigate its frequency content. A mechanism was proposed to harvest the energy from the low frequency-low amplitude human motion. This mechanism consists of the combined nonlinear hardening and softening mechanism which was aimed at widening the bandwidth as well as amplifying the low human motion frequency. This was realized by using a translation-to-rotary mechanism which converts the translation motion of the human motion into the rotational motion. The nonlinearity in the system was realized by introducing a winding spring stiffness and the magnetic stiffness. Quasi-static and dynamic measurement were conducted to investigate the performance of the mechanism. The results show that, with the right degree of nonlinearity, the two modes can be combined together to produce a wide flat response. For the frequency amplification, the mechanism manages to increase the frequency by around 8 times in terms of rotational speed.

On the optimum parameters of a device for harvesting energy from running and walking

This paper investigates the feasibility of using an energy harvesting device tuned such that its natural frequency coincides with higher harmonics of the input to capture energy from walking or running human motion more efficiently. The paper starts by reviewing the concept of a linear resonant generator for a tonal frequency input and then derives an expression for the power harvested for an input with several harmonics. The amount of power harvested is estimated numerically using measured data from human subjects. Assuming that the input is periodic, the signal is reconstructed using a Fourier series before being used in the simulation. It is found that although the power output depends on the input frequency, the choice of tuning the natural frequency of the device to coincide with a particular higher harmonic is restricted by the amount of damping that is needed to maximize the amount of power harvested, as well as to comply with the size limit of the device. It is also found that it is not feasible to tune the device to match the first few harmonics when the size of the device is small, because a large amount of damping is required to limit the motion of the mass.

A broadband vibration energy harvesting model for multiple cantilever beams

Conventional vibration energy harvesters are required to function only on sole resonant frequency and to harvest energy on a restricted bandwidth. In this paper, a novel mathematical model of a energy harvester is proposed to confront the problem and to harvest energy in a broader spectrum of frequency. Simulation results show that the proposed model is able to generate broadband energy with suitable optimized parameters. Furthermore, it is observed that by reducing the frequency ratio between cantilever beams, the ripples effect in the energy bandwidth can be reduced.

Characterisation of Structure-Borne Sound Source Using Reception Plate Method

A laboratory-based experiment procedure of reception plate method for structure-borne sound source characterisation is reported in this paper. The method uses the assumption that the input power from the source installed on the plate is equal to the power dissipated by the plate. In this experiment, rectangular plates having high and low mobility relative to that of the source were used as the reception plates and a small electric fan motor was acting as the structure-borne source. The data representing the source characteristics, namely, the free velocity and the source mobility, were obtained and compared with those from direct measurement. Assumptions and constraints employing this method are discussed.

Translation to Rotary Frequency-Up Conversion Vibration Based Energy Harvesting Device for Human Body Motion

This paper presents some preliminary studies on the frequency-up conversion method for low frequency application energy vibration based harvesting device, mainly from human body motion, by employing the translation to rotary mechanism. Vibration signals from different parts of the human body were first measured when the human subject was walking at 5 km/h. The signals obtained from the measurement were then reconstructed using Fourier Transform and it was found that frequency content of human body motion was in the range of 1 Hz 25 Hz. A preliminary experiment was conducted to check on the ability of the mechanism to amplify the low excitation frequency. Although the experiment was not optimized, it is found that the device was able to amplify input frequency up to 3.6 times.

Vibration Strength Estimation of a Structure-Borne Source: Case Study for a Reception Beam

This paper presents the estimation of vibration strength obtained from reception structure method. It describes a laboratory-based measurement procedure, which determines the strength of a vibration source in terms of its total squared free velocity. The source used in the experiment is a small electric fan motor. Here instead of using the usual flat rectangular plate, a thin stainless steel beam was used as the reception structure. The aim is to validate the data obtained from the reception method with that from the direct measurement. A good agreement is found between the two results, although small discrepancies occur due to the modal behavior of the beam.

Sensitivity Study of Surface Curvature in Characterisation Of Cartilage Mechanical Properties

The mechanical properties of articular cartilage serve as important measures of tissue function or degeneration, and are known to change significantly with asteoarthritis. In previous computational studies, the cartilage surface of axisymmetric models was assumed to be flat in order to evaluate the cartilage behaviour. This assumption was inappropriate since the synovial joint possessed curvature geometrical shape and may contribute to the inaccurate in characterising the cartilage properties. Therefore, this study aims to examine the sensitivity of cartilage surface curvature of characterized cartilage biphasic properties using a combination of experimental and computational methods. Axisymmetric biphasic poroelastic finite element models were generated to measure cartilage surface radius and thickness. Based on the results, the smaller cartilage surface of 20 mm radius produced higher difference of the characterised properties where its generate 9% difference in the permeability and 5% difference in the elastic modulus, compared to the flat cartilage. Based on these results, it may indicate that the cartilage curvature will affect the characterised cartilage biphasic properties of elastic modulus and permeability.