Compact and High-Efficiency Rectenna for Wireless Power-Harvesting Applications

A compact, single-layer microstrip rectenna for dedicated far-field RF wireless power-harvesting applications is presented. The proposed rectenna circuit configurations including multiband triple L-Arms patch antenna with diamond slot ground are designed to resonate at 10, 13, 17, and 26 GHz with 10 dB impedance bandwidths of 0.67, 0.8, 2.45, and 4.3 GHz, respectively. Two rectifier designs have been fabricated and compared, a half wave rectifier with a shunted Schottky diode and a voltage doubler rectifier. The measured and simulated maximum conversion efficiencies of the rectifier using the shunted diode half-wave rectifier are 41%, and 34%, respectively, for 300 Ω load resistance, whereas they amount to 50% and 43%, respectively, for voltage doubler rectifier with 650 Ω load resistance. Compared to the shunted rectifier circuit, it is significant to note that the voltage doubler rectifier circuit has higher efficiency. Both rectifier’s circuits presented are tuned for a center frequency of 10 GHz and implemented using 0.81 mm thick Rogers (RO4003c) substrate. The overall size of the antenna is 16.5 × 16.5 mm2, and the shunted rectifier is only 13.3 × 8.2 mm2 and 19.7 × 7.4 mm2 for the voltage doubler rectifier. The antenna is designed and simulated using the CST Microwave Studio Suite (Computer Simulation Technology), while the complete rectenna is simulated using Agilent’s ADS tool with good agreement for both simulation and measurements.

Autocharging Techniques for Implantable Medical Applications

Implantable devices have successfully proven their reliability and efficiency in the medical field due to their immense support in a variety of aspects concerning the monitoring of patients and treatment in many ways. Moreover, they assist the medical field in disease diagnosis and prevention. However, the devices’ power sources rely on batteries, and with this reliance, comes certain complications. For example, their depletion may lead to surgical interference or leakage into the human body. Implicit studies have found ways to reduce the battery size or in some cases to eliminate its use entirely; these studies suggest the use of biocompatible harvesters that can support the device consumption by generating power. Harvesting mechanisms can be executed using a variety of biocompatible materials, namely, piezoelectric and triboelectric nanogenerators, biofuel cells, and environmental sources. As with all methods for implementing biocompatible harvesters, some of them are low in terms of power consumption and some are dependent on the device and the place of implantation. In this review, we discuss the application of harvesters into implantable devices and evaluate the different materials and methods and examine how new and improved circuits will help in assisting the generators to sustain the function of medical devices.

Piezoelectric ceramic for energy harvesting from ambient vibration

Direct piezoelectric conversion is very popular in generating power from mechanical stress. There is continuous progress in power harvesting from mechanical vibration. In this article, experimental tests on a piezoelectric circular plate, to evaluate the electric power produced by the piezoelectric conversion at low acceleration over a wide range of ambient vibration frequency, are presented. The experimental analysis is presented and discussed. The results demonstrate the potentiality of using low-cost piezoelectric diaphragms to harvest energy from ambient vibration. Under low acceleration (5.36 m/s2), the vibration frequency was varied in the range of 10– 200 Hz and the generated power was measured. Under a very small dynamic force (less than 0.06 N), the output power of 1.5 mW was obtained with an 8.5 mm drum harvester across a load resistance of 17.8 kΩ at a frequency of 173 Hz.

Evaluation of the Negative Stiffness Mechanism on the Performance of a Hinged Wave Energy Converter

This paper presents the numerical and experimental study of a new spring mechanism adapted to a cone-shaped point absorber wave energy converter (WEC). The WEC is intended to be hinged to a floating wind platform with a long arm to create a combined wind and wave harvesting concept. The main objective of the spring mechanism is to improve the platform restoring moments against the wind thrust forces, generated by the wind turbine while contributing to wave energy harvesting. However, the study is presented for the case where the WEC dynamics is investigated outside the platform and attached to a fixed frame, to validate the mathematical model of the WEC concept. Moreover, the impact on the power harvesting performance is investigated with and without negative springs in this scenario.

Ground Effect on Current Energy Harvesting From a Freely-Oscillating Circular Cylinder at Low Reynolds Number

This paper investigates the potential of current energy harvesting from a freely-oscillating circular cylinder, with a focus on near-ground effects. Energy can be harvested by converting the oscillatory motion of a cylinder excited by water current into electricity. The boundary shear layer, created by the ground surface, interacts with the cylinder vortices and consequently affects the force behavior and power harvesting performance. The problem is simulated in a two-dimensional turbulent flow, using the Finite Volume (FV) solver and the dynamic motion module, inherited in OpenFOAM. Ground effects on the power generation capacity of an oscillating cylinder operating in river current velocity at Reynolds number of 3 × 104 are studied at varying depths. Vortex-induced vibration is studied to observe the ground boundary layer influence on the structural response, vortex structure, hydrodynamic forces, and gained power. The results shed physical insight into the understanding of the flow behavior of the oscillating cylinder near the ground. Simulations show that the ground effect appears when the distance between the cylinder and the ground is less than three times the cylinder’s diameter. Decreasing the gap distance between the cylinder and the ground suppresses the vortices behind the oscillating cylinder, causing an increase in the harvested energy. Further, the optimal-power harvesting distance between the ground and the freely-oscillating cylinder is two and half times the cylinder’s diameter, because of the high oscillating frequency, causing higher power relative to shorter distances.

Automated tuning of a piezoelectric power harvesting cantilever beam via the application of an axial load

This thesis deals with automatic tuning of piezoelectric power harvesters. A prototype was constructed to verify the effect of the application of an axial load on a cantilever beam and the effectiveness of increasing the power harvested from a piezoelectric beam via axial loading. It was shown, experimentally, that the natural frequency of a piezoelectric beam harvester can be changed over a range of 25Hz. From the experimental results it was shown that the power can increase up to seven times when tuned in comparison to unturned. Computer simulations were used to demonstrate a closed loop tuning system’s ability to apply an axial load effectively onto a piezoelectric cantilever beam in response to ambient vibrations. The closed loop tuning system is a viable option for tuning and can lead to increased power when applying the axial load suggested by the tuning system.

Automated tuning of a piezoelectric power harvesting cantilever beam via the application of an axial load

This thesis deals with automatic tuning of piezoelectric power harvesters. A prototype was constructed to verify the effect of the application of an axial load on a cantilever beam and the effectiveness of increasing the power harvested from a piezoelectric beam via axial loading. It was shown, experimentally, that the natural frequency of a piezoelectric beam harvester can be changed over a range of 25Hz. From the experimental results it was shown that the power can increase up to seven times when tuned in comparison to unturned. Computer simulations were used to demonstrate a closed loop tuning system’s ability to apply an axial load effectively onto a piezoelectric cantilever beam in response to ambient vibrations. The closed loop tuning system is a viable option for tuning and can lead to increased power when applying the axial load suggested by the tuning system.

Flexible Smart Material With Excellent Energy Harvesting

The field of power harvesting has experienced significant growth over the past few years due to the ever-increasing desire to produce portable and wireless electronics with extended lifespans. The present work aims to introduce an approach to harvesting electrical energy from a mechanically excited piezoelectric element and investigates a power analytical model generated by a smart structure of type polyvinylidene fluoride(PVDF) that can be stuck onto fabrics and flexible substrates, although we report the effects of various substrates and investigates the sticking of these substrates on the characterization of the piezoelectric material.