Review of energy harvesting techniques and applications for microelectronics

The trends in technology allow the decrease in both size and power consumption of complex digital systems. This decrease in size and power gives rise to new paradigms of computing and use of electronics, with many small devices working collaboratively or at least with strong communication capabilities. Examples of these new paradigms are wearable devices and wireless sensor networks. Currently, these devices are powered by batteries. However, batteries present several disadvantages: the need to either replace or recharge them periodically and their big size and weight compared to high technology electronics. One possibility to overcome these power limitations is to extract (harvest) energy from the environment to either recharge a battery, or even to directly power the electronic device. This paper presents several methods to design an energy harvesting device depending on the type of energy available.Peer Reviewe

Design and Analysis of a Mechanical Driveline with Generator for an Atmospheric Energy Harvester

The advent of renewable energy as a primary power source for microelectronic devices has motivated research within the energy harvesting community over the past decade. Compact, self-contained, portable energy harvesters can be applied to wireless sensor networks, Internet of Things (IoT) smart appliances, and a multitude of standalone equipment; replacing batteries and improving the operational life of such systems. Atmospheric changes influenced by cyclical temporal variations offer an abundance of harvestable thermal energy. However, the low conversion efficiency of a common thermoelectric device does not tend to be practical for microcircuit operations. One solution may lie in a novel electromechanical power transformer integrated with a thermodynamic based phase change material to create a temperature/pressure energy harvester. The performance of the proposed harvester will be investigated using both numerical and experimental techniques to offer insight into its functionality and power generation capabilities. The atmospheric energy harvester consists of a ethyl chloride filled mechanical bellows attached to an end plate and constrained by a stiff spring and four guide rails that allow translational motion. The electromechanical power transformer consists of a compound gear train driven by the bellows end plate, a ratchet-controlled coil spring to store energy, and a DC micro generator. Nonlinear mathematical models have been developed for this multi-domain dynamic system using fundamental engineering principles. The initial analyses predicted 9.6 mW electric power generation over a 24 hour period for ±1°C temperature variations about a nominal 22°C temperature. Transfer functions were identified from the lumped parameter models and the transient behavior of the coupled thermal-electromechanical system has been studied. A prototype experimental system was fabricated and laboratory tested to study the overall performance and validate the mathematical models for the integrated energy harvester system. The experimental results agree with the numerical analyses in behavioral characteristics. Further, the power generation capacity of 30 mW for a representative electrical resistance load and emulated rack input which correspond to 50 cyclic bidirectional temperature variations (~175 hours of field operation) validated the simulation models. This research study provides insight into the challenges of designing an electromechanical power transformer to complement an atmospheric energy harvester system. The mathematical models estimated the behavior and performance of the integrated harvester system and establishes a foundation for future optimization studies. The opportunity to power microelectronic devices in the milliwatt range for burst electric operation or with the use of supercapacitors/batteries enables global remote operation of smart appliances. This system can assist in reducing/eliminating the need for batteries and improving the operational life of a variety of autonomous equipment. Future research areas have been identified to improve the overall system capabilities and implement the harvester device for real-world applications

THERMAL ENERGY HARVESTING IN WIRELESS SENSOR NODES USED FOR CONDITION MONITORING

Presently, wireless sensor notes (WSN) are widely investigated and used in condition monitoring on industrial process monitoring and control, based on their inherent advantages of lower maintenance cost, easy installation and the ability to be installed in places not reached easily. However, current WSN based monitoring system still need dedicated power line or regular charging / replacing the batteries, which not only makes it difficult to deploy it in the fields but also degrades the operational reliability. This PhD research focuses on an investigation into energy harvesting approaches for powering WSN so as to develop a cost-effective, easy installation and reliable wireless measurement system for monitoring mission critical machinery such as multistage gearbox. Among various emerging energy harvest approaches such as vibrations, inductions, solar panels, thermal energy harvesting is deemed in this thesis to be the most promising one as almost all machines have frictional losses which manifest in terms of temperature changes and more convenient for integration as the heat sources can be close to wireless nodes. In the meantime, temperature based monitoring is adopted as its changes can be more sensitive to early health conditions of a machine when its tribological behaviour is starting to be degraded. Moreover, it has much less data output and more suitable for WSN application compared the mainstream vibration based monitoring techniques. Based on these two fundamental hypothesis, the research has been carried out according to two main milestones: the development of a thermoelectric harvesting (TEH) module and the evaluation of temperature based monitoring performances based on an industrial gearbox system. The first one involves the designing, fabricating and optimising the thermal EH module along with a WSN based temperature node and the second investigates the analysis methods to detect the temperature changes due to various faults associated with tribological mechanisms in the gearbox. In completing the first milestone, it has successfully developed a TEH module using cost-effective thermoelectric generator (TEG) devices and temperature gradient enhancement modules (heat sinks). Especially, the parameters such as their sizes and integration boundary conditions have been configured optimally by a proposed procedure based on the fine element (FE) analysis and the heat generation characteristics of machines to be monitored. The developed TEG analytic models and, FE models along with simulation study show that three different specifications of heat sinks with a Peltier TEG module are able to produce power that are consistently about 85% of the experimental values from offline tests, showing the good accuracy in predicting power output based on different applications and thus the reliability of the models proposed. And further investigation shows that a Peltier TEG module based that the thermal energy harvesting system produces is nearly 10 mW electricity from the monitored gearbox. This power is demonstrated sufficient to drive the WSN temperature node fabricated with low power consumption BLE microcontroller CC2650 sensor tags for monitoring continuously the temperature changes of the gearbox. Moreover, it has developed model based monitoring using multiple temperature measurements. The monitoring system allows two common faults oil shortages and mechanical misalignment to be detected and diagnosed, which demonstrates the specified performance of the self-power wireless temperature system for the purpose of condition monitoring

SUSTAINABLE ENERGY HARVESTING TECHNOLOGIES – PAST, PRESENT AND FUTURE

Chapter 8: Energy Harvesting Technologies: Thick-Film Piezoelectric Microgenerato

Optical wireless data transfer for rotor detection and diagnostics

A special application of optical wireless data transfer, namely on-line monitoring and diagnostic of rotors in turbines and engines, has been considered in this thesis. In this application, to maintain line of sight, i.e. data transfer, between a sensor placed on a rotating component inside the turbine and a monitoring point placed in a fixed position outside the turbine, a periodic fast fading channel is generated, which gives the transceivers more flexibility regarding their mounting location. The communication in such a channel is affected by the intermittency and variation of the signal power, which produces a unique channel condition that influences the performance of the optical transceiver. To investigate the channel condition and the error rate of the periodic fast fading channel with signal fluctuation, a model is developed to simulate the optical channel by considering the variation of signal power as a result of the change in the relative position of the photodiode with respect to the Lambertian radiation pattern of the LED, in a simplified linear geometry. The error rate is estimated using the Saddlepoint approximation on a specific threshold strategy. The results show that the channel can afford the sensor data transmission and the performance can be improved by modifying several parameters, such as geometrical distance, transmitter power and load resistor. Compared to a normal channel, a higher load resistor on the photodiode front end has the advantage of decreasing the noise level and increasing the data capacity in the fast fading channel. The analysis of the automatic gain control amplifier indicates that a higher load resistor needs a lower loop gain and from the model of the Transimpedance amplifier (TIA), the bandwidth extension from the amplifier is more significant for a higher resistor. In addition to the theoretical model, an experimental setup is built to emulate the channel in practice. The degree of similarity between the experimental setup and the theoretical model of the channel is estimated from the comparison of the generated communication windows. Since it has been found that differences exist in the duration of the communication window and the variation of the signal power, scaling factors to ensure their compatibility have been derived. Transceiver hardware which implemented the modelled functionality has been developed and a protocol to establish the communication with the required error rate has been proposed. Using the hardware implementation, a detection method for both rising and falling edges of the signal pulses and a threshold strategy have been demonstrated. The device power consumption is also estimated. What is more, the electromagnetic environment of a squirrel cage motor is simulated using the finite element method to investigate the interference and the possibility of providing power to the IR communication devices using power scavenging. In the conclusion, the key findings of the thesis are summarised. A solution is proposed for sensor data transfer using an optical channel for rotor monitoring applications, which involves the design of the IR transceiver, the implementation of the developed protocol and the power consumption estimation

Energy Neutral Design of Embedded Systems for Resource Constrained Monitoring Applications

Automatic monitoring of environments, resouces and human processes are crucial and foundamental tasks to improve people's quality of life and to safeguard the natural environment. Today, new technologies give us the possibility to shape a greener and safer future. The more specialized is the kind of monitoring we want to achieve, more tight are the constraints in terms of reliability, low energy and maintenance-free autonomy. The challenge in case of tight energy constraints is to find new techniques to save as much power as possible or to retrieve it from the very same environment where the system operates, towards the realization of energy neutral embedded monitoring systems. Energy efficiency and battery autonomy of such devices are still the major problem impacting reliability and penetration of such systems in risk-related activities of our daily life. Energy management must not be optimized to the detriment of the quality of monitoring and sensors can not be operated without supply. In this thesis, I present different embedded system designs to bridge this gap, both from the hardware and software sides, considering specific resource constrained scenarios as case studies that have been used to develop solutions with much broader validity. Results achieved demonstrate that energy neutrality in monitoring under resource constrained conditions can be obtained without compromising efficiency and reliability of the outcomes

Antenna and rectifier designs for miniaturized radio frequency energy scavenging systems

With ample radio transmitters scattered throughout urban landscape, RF energy scavenging emerges as a promising approach to extract energy from propagating radio waves in the ambient environment to continuously charge low power electronics. With the ability of generating power from RF energy, the need for batteries could be eliminated. The effective distance of a RF energy scavenging system is highly dependent on its conversion efficiency. This results in significant limitations on the mobility and space requirement of conventional RF energy scavenging systems as they operate only in presence of physically large antennas and conversion circuits to achieve acceptable efficiency. This thesis presents a number of novel design strategies in the antenna and rectifier designs for miniaturized RF energy scavenging system. In the first stage, different energy scavenging systems including solar energy scavenging system, thermoelectric energy scavenging system, wind energy scavenging system, kinetic energy scavenging system, radio frequency energy scavenging system and hybrid energy scavenging system are investigated with regard to their principle and performance. Compared with the other systems, RF energy scavenging system has its advantages on system size and power density with relatively stable energy source. For a typical RF energy scavenging system, antenna and rectifier (AC-DC convertor) are the two essential components to extract RF energy and convert to usable electricity. As the antenna occupies most of the area in the RF energy scavenging system, reduction in antenna size is necessary in order to design a miniaturized system. Several antennas with different characteristics are proposed in the second stage. Firstly, ultra-wideband microstrip antennas printed on a thin substrate with a thickness of 0.2 mm are designed for both half-wave and full-wave wideband RF energy scavenging. Ambient RF power is distributed over a wide range of frequency bands. A wideband RF energy scavenging system can extract power from different frequencies to maximize the input power, hence, generating sufficient output power for charging devices. Wideband operation with 4 GHz bandwidth is obtained by the proposed microstrip antenna. Secondly, multi-band planar inverted-F antennas with low profile are proposed for frequency bands of GSM 900, DCS 1800 and Wi-Fi 2.4 GHz, which are the three most promising frequency bands for RF energy scavenging. Compared with previous designs, the triple band antenna has smaller dimensions with higher antenna gain. Thirdly, a novel miniature inverted-F antenna without empty space covering Wi-Fi 2.4 GHz frequency band is presented dedicated for indoor RF energy scavenging. The antenna has dimensions of only 10 × 5 × 3.5 mm3 with appreciable efficiency across the operating frequency range. In the final stage, a passive CMOS charge pump rectifier in 0.35 μm CMOS technology is proposed for AC to DC conversion. Bootstrapping capacitors are employed to reduce the effective threshold voltage drop of the selected MOS transistors. Transistor sizes are optimized to be 200/0.5 μm. The proposed rectifier achieves improvements in both power conversion efficiency and voltage conversion efficiency compared with conventional designs. The design strategies proposed in this thesis contribute towards the realization of miniaturized RF energy scavenging systems

Piezoelectric Energy Harvesting: Enhancing Power Output by Device Optimisation and Circuit Techniques

Energy harvesting; that is, harvesting small amounts of energy from environmental sources such as solar, air flow or vibrations using small-scale (≈1cm 3 ) devices, offers the prospect of powering portable electronic devices such as GPS receivers and mobile phones, and sensing devices used in remote applications: wireless sensor nodes, without the use of batteries. Numerous studies have shown that power densities of energy harvesting devices can be hundreds of µW; however the literature also reveals that power requirements of many electronic devices are in the mW range. Therefore, a key challenge for the successful deployment of energy harvesting technology remains, in many cases, the provision of adequate power. This thesis aims to address this challenge by investigating two methods of enhancing the power output of a piezoelectric-based vibration energy harvesting device. Cont/d

Transpiration as a Mechanism for Mechanical and Electrical Energy Conversion.

Devices that scavenge power by utilizing energy present in their environment are of interest to researchers for powering sensors in areas where hard-wired connections are not feasible and battery maintenance is costly. Researchers have made of use vibrations, temperature, and other environmental stimuli. In this thesis, transpiration is researched as a mechanism for mechanical and electrical energy conversion. Two energy scavenging devices inspired by the transpiration mechanism in plants were developed and tested. The first is a class of mechanical actuators that operate via the evaporation of water to generate forces per unit length of 5.75 - 67.75 mN/m, angular rotations of 330o and tip deflections of 3.5 mm. The actuators were also studied as a way to achieve bottom-up self assembly by programming deflection profiles into materials using geometric parameters. These actuators can be used in applications for an evaporation-powered and controlled self-assembly of micro components. The experimental work is coupled with the development of an accurate theoretical model based on the principle of virtual work. The second type of devices developed in this thesis use an evaporation-induced flow within leaf-like microvasculature networks to drive the movement of gas bubbles through capacitor plates. This motion allows the charge pumping of an energy conversion circuit. Evaporation-driven flow was enhanced by using porous materials at the fluidic channel outlets to achieve a maximum flow velocity of 1.5 cm/s. Changes in capacitance measured at 1 MHz were between 8 - 10 pF and greater than 30 pF at lower frequencies for each bubble. Current generated by capacitance change was measured to reach up to 1 nA. Using the conversion circuit, voltage outputs up to 5 microvolts were measured for each water to air interface. A theoretical bound of the scavenged power density was calculated as a function of the size of the storage capacitor. Theoretical analysis and simulation results are presented to describe how the circuit can be modified to suit the energy harvesting application. The primary contribution of this thesis is the demonstration that the transpiration mechanism of plants can be mimicked in microscale devices to provide mechanical and electrical energy.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/61555/1/rborno_1.pd