An investigation of PDMS structures for optimized ferroelectret performance

This paper reports the ANSYS simulation and fabrication processes for optimising PDMS ferroelectret performance. The proposed model extends the previously published analytical models and compares this with simulation of individual void geometry. The ferroelectret material is fabricated from PDMS using 3D-printed plastic moulds. The analytical model and Ansys simulation results predict the variation in performance of the PDMS ferroelectret with the different void geometry and surface charge density. The theoretical maximum piezoelectric coefficient d33 achieved was about 220 pC/N. The experimental maximum d33 obtained was 172 pC/N

Thick-film Piezoelectric Vibration Harvesting –A HUMS Application

A vibration energy scavenger, manufactured entirely by thick-film construction, has been developed to power autonomous subsystems in an embedded health and useage system. The device is constrained to a 2mm thickness and has been designed for a specific helicopter application. The resulting power output is capable of powering an ‘off-the-shelf’ microcontroller based system

Strategies for increasing the operating frequency range of vibration energy harvesters: a review

This paper reviews possible strategies to increase the operational frequency range of vibration-based micro-generators. Most vibration-based micro-generators are spring-mass-damper systems which generate maximum power when the resonant frequency of the generator matches the frequency of the ambient vibration. Any difference between these two frequencies can result in a significant decrease in generated power. This is a fundamental limitation of resonant vibration generators which restricts their capability in real applications. Possible solutions include the periodic tuning of the resonant frequency of the generator so that it matches the frequency of the ambient vibration at all times or widening the bandwidth of the generator. Periodic tuning can be achieved using mechanical or electrical methods. Bandwidth widening can be achieved using a generator array, a mechanical stopper, non-linear (e.g. magnetic) springs or bi-stable structures. Tuning methods can be classified into intermittent tuning (power is consumed periodically to tune the device) and continuous tuning (the tuning mechanism is continuously powered). This paper presents a comprehensive review of the principles and operating strategies for increasing the operating frequency range of vibration-based micro-generators presented in the literature to date. The advantages and disadvantages of each strategy are evaluated and conclusions are drawn regarding the relevant merits of each approach

Scaling effects for piezoelectric energy harvesters

This paper presents a fundamental investigation into scaling effects for the mechanical properties and electrical output power of piezoelectric vibration energy harvesters. The mechanical properties investigated in this paper include resonant frequency of the harvester and its frequency tunability, which is essential for the harvester to operate efficiently under broadband excitations. Electrical output power studied includes cases when the harvester is excited under both constant vibration acceleration and constant vibration amplitude. The energy harvester analysed in this paper is based on a cantilever structure, which is typical of most vibration energy harvesters. Both detailed mathematical derivation and simulation are presented. Furthermore, various piezoelectric materials used in MEMS and non-MEMS harvesters are also considered in the scaling analysi

Vibration energy harvesting using the Halbach array

This paper studies the feasibility of vibration energy harvesting using a Halbach array. A Halbach array is a specific arrangement of permanent magnets that concentrates the magnetic field on one side of the array while cancelling the field to almost zero on the other side. This arrangement can improve electromagnetic coupling in a limited space. The Halbach array offers an advantage over conventional layouts of magnets in terms of its concentrated magnetic field and low-profile structure, which helps improve the output power of electromagnetic energy harvesters while minimizing their size. Another benefit of the Halbach array is that due to the existence of an almost-zero magnetic field zone, electronic components can be placed close to the energy harvester without any chance of interference, which can potentially reduce the overall size of a self-powered device. The first reported example of a low-profile, planar electromagnetic vibration energy harvester utilizing a Halbach array was built and tested. Results were compared to ones for energy harvesters with conventional magnet layouts. By comparison, it is concluded that although energy harvesters with a Halbach array can have higher magnetic field density, a higher output power requires careful design in order to achieve the maximum magnetic flux gradient

Electromagnetic vibration energy harvesting using an improved Halbach array

This paper reports an electromagnetic vibration energy harvester using an improved Halbach array. A Halbach array is a specific arrangement of permanent magnets that concentrates the magnetic field on one side of the array while cancelling the field on the other side to almost zero. Previous research showed that although the Halbach array has higher magnetic field density compared to normal magnet layouts, its magnetic flux gradient is not as high. Thus, output powers of energy harvesters with Halbach arrays were found to be less than those with normal magnet layouts. This paper proposes an improved Halbach array that achieves both high magnetic field strength and magnetic flux gradient. Test results showed that the improved Halbach array can increase the output power of energy harvesters by a factor of seven compared to the previous Halbach design and by a factor of 1.5 compared to the normal configuration

Multilayer ferroelectret-based energy harvesting insole

This paper reports a flexible energy harvesting insole made of multilayer ferroelectrets, and demonstrates that this insole can power a wireless signal transmission. We have previously studied the energy harvesting characteristics of single and 10-layer ferroelectrets under compressive forces with quantified amplitudes and frequencies. In this work, we fabricate a flexible insole using multilayer ferroelectrets, and increase the number of layers from 10 up to 80, then use this insole to harvest energy from footsteps. We use this insole to power a commercial ZigBee wireless transmitter, and successfully demonstrate that an 8-bit data transmission can be solely powered by the energy harvested from this insole for every 3 to 4 footsteps. It confirms the anticipation from our previous work that the multilayer ferroelectrets are capable of powering the start-up and transmission of a low-power chipset, and shows a potential of using this energy harvesting insole in wearable applications

Design optimization of a magnetically levitated electromagnetic vibration energy harvester for body motion

This paper presents a magnetically levitated electromagnetic vibration energy harvester based on magnet arrays. It has a nonlinear response that extends the operating bandwidth and enhances the power output of the harvesting device. The harvester is designed to be embedded in a hip prosthesis and harvest energy from low frequency movements (< 5 Hz) associated with human motion. The design optimization is performed using Comsol simulation considering the constraints on size of the harvester and low operating frequency. The output voltage across the optimal load 3.5k? generated from hip movement is 0.137 Volts during walking and 0.38 Volts during running. The power output harvested from hip movement during walking and running is 5.35 ?W and 41.36 ?W respectivel

Improving the dielectric and piezoelectric properties of screen-printed low temperature PZT/polymer composite using cold isostatic pressing

This paper reports an improvement in dielectric and piezoelectric properties of screen-printed PZT/polymer films for flexible electronics applications using Cold Isostatic Pressing (CIP). The investigation involved half and fully cured PZT/polymer composite pastes with weight ratio of 12:1 to investigate the effect of the CIP process on the piezoelectric and dielectric properties. It was observed that the highest dielectric and piezoelectric properties are achieved at pressures of 5 and 10 MPa for half and fully cured films respectively. The relative dielectric constants were 300 and 245 measured at 1 kHz for the half and fully cured samples. Using unoptimised poling conditions, the initial d33 values were 30 and 35 pC/N for the half and fully cured films, respectively. The fully cured sample was then poled using optimized conditions and demonstrated a d33 of approximately 44 pC/N which is an increase of 7% compared with non-CIP processed material