Milliwatt-Level Electromagnetic Induction-Type MEMS Air Turbine Generator

In this chapter, an electromagnetic induction-type MEMS air turbine generator that combined with the MEMS technology and the multilayer ceramic technology is proposed. Three types of MEMS air turbine generators that included the different bearing systems, shape of the rotor and shape of the magnetic circuits are discussed to achieve the high output power. In the MEMS air turbine, the purpose is to achieve high-speed rotational motion. As a result of the comparison between the different structures, a rim-type rotor and a miniature ball bearing system showed the high rotational speed than a flat-type rotor and a fluid dynamic bearing system. The maximum rotational speed of the fabricated air turbine was 290,135 rpm. Moreover, it is important to introduce the magnetic flux to the magnetic circuit. By the multilayer ceramic technology, the three-dimensional coil in miniature monolithic structure was fabricated. The magnetic core that was designed to introduce the magnetic flux showed the low magnetic flux loss. The fabricated MEMS air turbine and the multilayer ceramic magnetic circuit were combined, and the miniature electromagnetic induction-type generator was achieved. The output power was 2.41 mVA, when the load resistance and the output voltage were 8 Ω and 139 mV, respectively

MEMS-based Micro-scale Wind Turbines as Energy Harvesters of the Convective Airflows in Microelectronic Circuits

As an alternative to conventional batteries and other energy scavenging techniques, this paper introduces the idea of using micro-turbines to extract energy from wind forces at the microscale level and to supply power to battery-less microsystems. Fundamental research efforts on the design, fabrication, and test of micro-turbines with blade lengths of just 160 μm are presented in this paper along with analytical models and preliminary experimental results. The proof-of-concept prototypes presented herein were fabricated using a standard polysilicon surface micro-machining silicon technology (PolyMUMPs) and could effectively transform the kinetic energy of the available wind into a torque that might drive an electric generator or directly power supply a micro-mechanical system. Since conventional batteries do not scale-down well to the microscale, wind micro-turbines have the potential for becoming a practical alternative power source for microsystems, as well as for extending the operating range of devices running on batteries

Micromechanics for energy generation

The emergence and evolution of energy micro-generators during the last two decades has delivered a wealth of energy harvesting powering solutions, with the capability of exploiting a wide range of motion types, from impulse and low frequency irregular human motion, to broadband vibrations and ultrasonic waves. It has also created a wide background of engineering energy microsytems, including fabrication methods, system concepts and optimal functionality. This overview presents a simple description of the main transduction mechanisms employed, namely the piezoelectric, electrostatic, electromagnetic and triboelectric harvesting concepts. A separate discussion of the mechanical structures used as motion translators is presented, including the employment of a proof mass, cantilever beams, the role of resonance, unimorph structures and linear/rotational motion translators. At the mechanical-to-electrical interface, the concepts of impedance matching, pre-biasing and synchronised switching are summarised. The separate treatment of these three components of energy microgenerators allows the selection and combination of different operating concepts, their co-design towards overall system level optimisation, but also towards the generalisation of specific approaches, and the emergence of new functional concepts. Industrial adoption of energy micro-generators as autonomous power sources requires functionality beyond the narrow environmental conditions typically required by the current state-of-art. In this direction, the evolution of broadband electromechanical oscillators and the combination of environmental harvesting with power transfer operating schemes could unlock a widespread use of micro-generation in microsystems such as micro-sensors and micro-actuators

Piezoelectric and Magnetoelectric Thick Films for Fabricating Power Sources in Wireless Sensor Nodes

In this manuscript, we review the progress made in the synthesis of thick film-based piezoelectric and magnetoelectric structures for harvesting energy from mechanical vibrations and magnetic field. Piezoelectric compositions in the system Pb(Zr,Ti)O3–Pb(Zn1/3Nb2/3)O3 (PZNT) have shown promise for providing enhanced efficiency due to higher energy density and thus form the base of transducers designed for capturing the mechanical energy. Laminate structures of PZNT with magnetostrictive ferrite materials provide large magnitudes of magnetoelectric coupling and are being targeted to capture the stray magnetic field energy. We analyze the models used to predict the performance of the energy harvesters and present a full system description

A Comparative Study of Electromagnetic Generator via Finite Element Element Analysis

Energy scavenging from ambient sources is an attractive alternative to batteries because of an almost unlimited lifetime and is environmentally safe

AN INTEGRATED ELECTROMAGNETIC MICRO-TURBO-GENERATOR SUPPORTED ON ENCAPSULATED MICROBALL BEARINGS

This dissertation presents the development of an integrated electromagnetic micro-turbo-generator supported on encapsulated microball bearings for electromechanical power conversion in MEMS (Microelectromechanical Systems) scale. The device is composed of a silicon turbine rotor with magnetic materials that is supported by microballs over a stator with planar, multi-turn, three-phase copper coils. The micro-turbo-generator design exhibits a novel integration of three key technologies and components, namely encapsulated microball bearings, incorporated thick magnetic materials, and wafer-thick stator coils. Encapsulated microball bearings provide a robust supporting mechanism that enables a simple operation and actuation scheme with high mechanical stability. The integration of thick magnetic materials allows for a high magnetic flux density within the stator. The wafer-thick coil design optimizes the flux linkage and decreases the internal impedance of the stator for a higher output power. Geometrical design and device parameters are optimized based on theoretical analysis and finite element simulations. A microfabrication process flow was designed using 15 optical masks and 110 process steps to fabricate the micro-turbo-generators, which demonstrates the complexity in device manufacturing. Two 10 pole devices with 2 and 3 turns per pole were fabricated. Single phase resistances of 46Ω and 220Ω were measured for the two stators, respectively. The device was actuated using pressurized nitrogen flowing through a silicon plumbing layer. A test setup was built to simultaneously measure the gas flow rate, pressure, rotor speed, and output voltage and power. Friction torques in the range of 5.5-33µNm were measured over a speed range of 0-16krpm (kilo rotations per minute) within the microball bearings using spin-down testing methodology. A maximum per-phase sinusoidal open circuit voltage of 0.1V was measured at 23krpm, and a maximum per-phase AC power of 10µW was delivered on a matched load at 10krpm, which are in full-agreement with the estimations based on theoretical analysis and simulations. The micro-turbo-generator presented in this work is capable of converting gas flow into electricity, and can potentially be coupled to a same-scale combustion engine to convert high-density hydrocarbon energy into electrical power to realize a high-density power source for portable electronic systems

Piezoelectric energy harvesting utilizing metallized poly-vinylidene fluoride (PVDF)

The primary objective of the enclosed thesis was to identify and develop a viable concept for an autonomous sensor system that could be implemented onto the surface of a road. This was achieved by an analysis of combinations of materials, sensing methods, power sources, microsystems, energy storage options, and wireless data transmission systems; the sub-systems required for an autonomous sensor. Comparison of sensing methods for the application of an on-road, autonomous sensor yielded a piezoelectric material as the ideal choice. A 52μm thin film of poly- vinylidene fluoride (PVDF) was chosen and coated with Ag electrodes on both sides.This was due to many constraints imposed by the intended environment including: physical, electrical, thermal, and manufacturing characteristics. One major hurdle in providing an autonomous sensor is the power source for the sensing, encoding, and transmission of data. Research involved determining the option best suited for providing a power source for the combination of sensors and wireless telemetry components. An energy budget of 105μJ was established to determine an estimate of energy needed to wirelessly transmit data with the selected RF transmitter. Based on these results, several candidates for power sources were investigated, and a piezoelectric energy harvesting system was identified to be the most suitable. This is an ideal case as the sensor system was already based on a piezoelectric material as the sensing component. Thus, a harvesting circuit and the sensor can be combined into one unit, using the same material. By combining the two functions into a single component, the complexity, cost and size of the unit are effectively minimized. In order to validate the conclusions drawn during this sensor system analysis and conceptual research, actual miniaturized systems were designed to demonstrate the ability to sense and harvest energy for the applications in mind. This secondary aspect of the research was a proof-of-concept, developing two prototype energy harvesting/sensing systems. The system designed consisted of a PVDF thin film with a footprint of 0.2032 m x 0.1397m x 52μm. This film was connected to an energy-harvesting prototype circuit consisting of a full-wave diode bridge and a storage capacitor. Two prototypes were built and tested, one with a 2.2μF capacitor, the other with a 0.1mF capacitor. The film was first connected to an oscilloscope and impulsed in an open circuit condition to determine the sensor response to a given signal. Secondly, the energy harvesting circuits were tested in conjunction with the film to test the energy supply component of the system. Lastly, the film and both energy-harvesting systems underwent full scale testing on a road using a vehicle as the stimulus. Both systems showed excellent rectification of the double polarity input with an evident rise in voltage across the capacitor, meaning energy was harvested. Typical results from the tests yielded 600-800mV across the 2.2μF capacitor, harvesting only a few μJ of energy. The 0.1mF capacitor system yielded approximately 4V per vehicle axle across the capacitor, harvesting 400-800μJ of energy. This equates to 4-8 times the required energy for wireless data transmission of the measurement data, which was estimated by other research groups to be on the order of 105μJ for the given system, and therefore proves the concept both, for bench-top and full-scale on-road experiments under controlled laboratory conditions

Thermal and Mechanical Energy Harvesting Using Lead Sulfide Colloidal Quantum Dots

The human body is an abundant source of energy in the form of heat and mechanical movement. The ability to harvest this energy can be useful for supplying low-consumption wearable and implantable devices. Thermoelectric materials are usually used to harvest human body heat for wearable devices; however, thermoelectric generators require temperature gradient across the device to perform appropriately. Since they need to attach to the heat source to absorb the heat, temperature equalization decreases their efficiencies. Moreover, the electrostatic energy harvester, working based on the variable capacitor structure, is the most compatible candidate for harvesting low-frequency-movement of the human body. Although it can provide a high output voltage and high-power density at a small scale, they require an initial start-up voltage source to charge the capacitor for initiating the conversion process. The current methods for initially charging the variable capacitor suffer from the complexity of the design and fabrication process. In this research, a solution-processed photovoltaic structure was proposed to address the temperature equalization problem of the thermoelectric generators by harvesting infrared radiations emitted from the human body. However, normal photovoltaic devices have the bandgap limitation to absorb low energy photons radiated from the human body. In this structure, mid-gap states were intentionally introduced to the absorbing layer to activate the multi-step photon absorption process enabling electron promotion from the valence band to the conduction band. The fabricated device showed promising performance in harvesting low energy thermal radiations emitted from the human body. Finally, in order to increase the generated power, a hybrid structure was proposed to harvest both mechanical and heat energy sources available in the human body. The device is designed to harvest both the thermal radiation of the human body based on the proposed solution-processed photovoltaic structure and the mechanical movement of the human body based on an electrostatic generator. The photovoltaic structure was used to charge the capacitor at the initial step of each conversion cycle. The simple fabrication process of the photovoltaic device can potentially address the problem associated with the charging method of the electrostatic generators. The simulation results showed that the combination of two methods can significantly increase the harvested energy