Novel thick-foam ferroelectret with engineered voids for energy harvesting applications

This work reports a novel thick-foam ferroelectret which is designed and engineered for energy harvesting applications. We fabricated this ferroelectret foam by mixing a chemical blowing agent with a polymer solution, then used heat treatment to activate the agent and create voids in the polymer foam. The dimensions of the foam, the density and size of voids can be well controlled in the fabrication process. Therefore, this ferroelectret can be engineered into optimized structure for energy harvesting applications

A new 2-D model of a thin annular disk using a modified assumption

The work describes an improved 2-D model for a thin annulus by using a modified assumption with regard to coupled vibration. With this approach, the impedance spectrum and displacements due to radial modes, both in radial and thickness direction of a thin ring, are obtained. Bending displacement is investigated by finite element analysis (FEA) and matches our model. The bending in the thickness direction is coupled to radial modes and shows several node circles in the high radial overtone frequency range. The model is validated by FEA with excellent agreement between the new theory and FEA result

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

Design and experimental characterization of a tunable vibration-based electromagnetic micro-generator

Vibration-based micro-generators, as an alternative source of energy, have become increasingly significant in the last decade. This paper presents a new tunable electromagnetic vibration-based micro-generator. Frequency tuning is realized by applying an axial tensile force to the micro-generator. The dimensions of the generator, especially the dimensions of the coil and the air gap between magnets, have been optimized to maximize the output voltage and power of the micro-generator. The resonant frequency has been successfully tuned from 67.6 to 98 Hz when various axial tensile forces were applied to the structure. The generator produced a power of 61.6–156.6 µW over the tuning range when excited at vibrations of 0.59 ms-2. The tuning mechanism has little effect on the total damping. When the tuning force applied on the generator becomes larger than the generator’s inertial force, the total damping increases resulting in reduced output power. The resonant frequency increases less than indicated from simulation and approaches that of a straight tensioned cable when the force associated with the tension in the beam becomes much greater than the beam stiffness. The test results agree with the theoretical analysis presented

Photoresist patterned thick-film piezoelectric elements on silicon

A fundamental limitation of screen printing is the achievable alignment accuracy and resolution. This paper presents details of a thick-resist process that improves both of these factors. The technique involves exposing/developing a thick resist to form the desired pattern and then filling the features with thick film material using a doctor blading process. Registration accuracy comparable with standard photolithographic processes has been achieved resulting in minimum feature sizes of <50 ?m and a film thickness of 100 ?m. Piezoelectric elements have been successfully poled on a platinised silicon wafer with a measured d 33 value of 60 pCN?1

PDMS/PVA composite ferroelectret for improved energy harvesting performance

This paper address the PDMS ferroelectret discharge issue for improved long- term energy harvesting performance. The PDMS/PVA ferroelectret is fabricated using a 3D-printed plastic mould technology and a functional PVA composite layer is introduced. The PDMS/PVA composite ferroelectret achieved 80% piezoelectric coefficient d33 remaining, compared with 40% without the proposed layer over 72 hours. Further, the retained percentage of output voltage is about 73% over 72 hours

High density p-type Bi0.5Sb1.5Te3 nanowires by electrochemical templating through ion-track lithography

High density p-type Bi0.5Sb1.5Te3 nanowire arrays are produced by a combination of electrodeposition and ion-track lithography technology. Initially, the electrodeposition of p-type wBi(0.5)Sb(1.5)Te(3) films is investigated to find out the optimal conditions for the deposition of nanowires. Polyimide-based Kapton foils are chosen as a polymer for ion track irradiation and nanotemplating Bi0.5Sb1.5Te3 nanowires. The obtained nanowires have average diameters of 80 nm and lengths of 20 mu m, which are equivalent to the pore size and thickness of Kapton foils. The nanowires exhibit a preferential orientation along the {110} plane with a composition of 11.26 at.% Bi, 26.23 at.% Sb, and 62.51 at.% Te. Temperature dependence studies of the electrical resistance show the semiconducting nature of the nanowires with a negative temperature coefficient of resistance and band gap energy of 0.089 +/- 0.006 eV

Screen Printed PZT Thick Films Using Composite Film Technology

A spin coating composite sol gel technique for producing lead zirconate titanate (PZT) thick films has been modified for use with screen printing techniques. The resulting screen printing technique can be used to produce 10 ?m thick films in a single print. The resultant films are porous but the density can be increased through the use of repeated sol infiltration/pyrolysis treatments to yield a high density film. When fired at 710°C the composite screen printed films have dielectric and piezoelectric properties comparable to, or exceeding, those of films produced using a 'conventional' powder/glass frit/oil ink and fired at 890°C

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