Energy harvesting from human and machine motion for wireless electronic devices

Published versio

Energy harvesting by vibration using piezoceramic materials (PZT-4)

M. Sc. Eng. University of KwaZulu-Natal, Durban 2014.The concept of energy harvesting in the ambient environment is of great interest. Energy harvesting is the process of drawing out a small amount of energy from the ambient environment. The ambient environment is characterized by various available sources of energy such as solar, wind, vibration, gas, liquid flows, etc., which can be converted to usable energy. Vibration energy harvesting is a mechanical process of gathering ambient energy from vibrating sources that can be converted into electrical energy using different techniques of conversion. Vibration energy is available in the urban and industrial environment, but it is often overlooked as a source of power to be scavenged and to provide electricity. There are various techniques for conversion of harvesting ambient energy found in nature. The main harvesting techniques are electromagnetic conversion, electrostatic conversion and piezoelectric conversion. In this context, this research study is concerned with finding a way to harvest electrical energy from vibration. Piezoelectric conversion is able to produce high electrical energy unlike electromagnetic and electrostatic conversion. Piezoelectric materials have a large capacity for conversion of energy due to their inherent ability to detect vibration sources. This conversion of mechanical energy to electrical energy through the use of piezoelectric materials is an exciting and rapidly developing area of research with a widening range of applications constantly materializing. The experiments for this study were performed at the Vibration Research and Testing Centre (VRTC) laboratory of the University of KwaZulu-Natal, Durban. An electrodynamic vibration (shaker) connected to the prototype (cantilever beam plus piezoelectric material, i.e. ceramic plate PZT-4) was used to simulate ambient vibration to collect the data. The experiments were designed to optimise power output of the prototype by estimating the output voltage. Two setups of prototype were used: a cantilever beam with a tip mass at the end and a cantilever beam without tip mass at the end. Data from the experiment was compared and analysed using MatLab. The results showed that the power output of the prototype with the tip mass was greater than the power output without the tip mass. The results of this study contribute to the development of piezoelectric power generation as a viable source of electrical energy with minimal environment impac

A gravitational torque energy harvesting system for rotational motion

This thesis describes a novel, single point-of-attachment, gravitational torque energy harvesting system powered from rotational motion. The primary aim of such a system is to scavenge energy from a continuously rotating host in order to power a wireless sensor node. In this thesis, a wireless tachometer was prototyped. Most published work on motion-driven energy harvesters has used ambient vibrations in the environment as the energy source. However, none of the reported devices have been designed to harvest energy directly from continuous ambient rotation. There are important applications such as tire pressure sensing and condition monitoring of machinery where the host structure experiences continuous rotation. In this work, it is shown that in many applications, a rotational energy harvester can offer significant improvements in power density over its vibration-driven counterparts. A prototype single point-of-attachment rotational energy harvester was conceived using a simple direct-current generator. The rotational source was coupled to the stator and an offset mass was anchored on the rotor to create a counteractive gravitational torque. This produces a relative angular speed between rotor and stator which causes power to be generated. Power transfer from the generator to a load was maximised by enforcing an input impedance match between the generator’s armature resistance and the input impedance of a boost converter which in this case, functioned as a resistance emulator. Energy storage and output voltage regulation were implemented using supercapacitors and a wide-input buck regulator respectively. When excess power was generated, it was stored in the supercapacitors and during low source rotation speeds, i.e. insufficient harvested power, the supercapacitors will discharge to maintain operation of the interface electronics. A detailed optimisation procedure of a boost converter was conducted in Matlab in order to minimise the power loss, resulting in a maximum voltage gain of 11.1 and measured circuit efficiency of 96 %. A state-space control model of the harvester electronics was developed in the analogue domain using classical control techniques and this showed the system to be closed-loop stable. A final prototype of the rotational energy harvesting system was built and this comprised an input impedance controller, wireless transmitter and tachometer. The entire system has a measured end-to-end efficiency which peaked at 58 % from a source rotation of 1400 RPM with the generator producing 1.45 W under matched load conditions