Micro Power Generator Research Articles

Multi-mode vibration based electromagnetic type micro power generator for structural health monitoring of bridges

This article presents the development of multi-mode vibration based electromagnetic type micro power generator (MPG). Along the stainless steel planar spring (SPS) and magnet assembly, a movable coil (MC) is a novel addition to the resonant frequencies of the device. The design with MCs on either side of the magnet provide higher power generation for the same footprint of the device at multiple modes. Computer numerical control (CNC) milling machine, wire-cut electric discharge machine (EDM) and 3D printer are used to fabricate the MCs, SPS and spacers respectively to yield a MPG with an overall volume of 29.03 cm3. The developed MPG is characterized to generate power at four different resonant frequencies below 100 Hz. At 3rd mode (82 Hz) the developed MPG is able to produce a maximum 33 mV open circuit voltage, 14.5 mV load voltage and a power of 68.4 μW. Furthermore, the present development and experimentation of the MPG with a yielded power density of 2.35 μW/cm3 at 2 g acceleration can be regarded as guidelines for multi-mode devices.

Experimental and numerical study of premixed propane/air combustion in the micro-planar combustor with a cross-plate insert

Over the past decade, the micro-thermophotovoltaic (MTPV) system has aroused widely public attention. Micro-combustor is an important part, which can determine the working performance of this micro-power generator. In this paper, experimental investigations as well as a three-dimensional CFD simulation have been carried out to study the performance of propane/air premixed combustion in a new kind of cross-plate micro-planar combustor. Benefited from the heat transfer enhancement by the setting up of cross-plate, the average wall temperature of the new combustor is increased by more than 90 K, which results in the growth of radiation efficiency. Besides, the blowout limit is apparently extended in the cross-plate combustor. Compared to the single-channel combustor, the blowout limit of propane/air in the cross-plate combustor can be raised by 0.4 m/s at equivalence ratio 0.7. It is also found that the cross-plate length can significantly affect the flame shape in the micro-channel and temperature distribution of the external wall. In contrast, the dimensionless plate length of 5/9 is suggested as the optimal structure parameter for the micro-combustor, which is due to the highest radiation efficiency.

Improving the performance of galloping micro-power generators by passively manipulating the trailing edge

Recent trends in distributed sensing networks have generated significant interest in the design of scalable micro-power generators. One such device exploits the galloping oscillations of a prism to harness energy from a moving fluid. Performance of galloping harvester's depends on the flow patterns around the prism, which, in turn, depend on its geometry and the Reynolds number of the flow. In this letter, we demonstrate that the useful range of the galloping instability can be extended by attaching a rigid splitter plate to the rear face of the prism. The plate provides a secondary flow reattachment point, which serves to improve the oscillation amplitude and power output of the generator. Experimental results demonstrate as much as 67% power enhancement for some prism geometries and a significant reduction in the cut-in wind speed of the generator.

Discontinuous Galerkin Finite Element Investigation on the Fully-Compressible Navier–Stokes Equations for Microscale Shock-Channels

Microfluidics is a multidisciplinary area founding applications in several fields such as the aerospace industry. Microelectromechanical systems (MEMS) are mainly adopted for flow control, micropower generation and for life support and environmental control for space applications. Microflows are modeled relying on both a continuum and molecular approach. In this paper, the compressible Navier–Stokes (CNS) equations have been adopted to solve a two-dimensional unsteady flow for a viscous micro shock-channel problem. In microflows context, as for the most gas dynamics applications, the CNS equations are usually discretized in space using finite volume method (FVM). In the present paper, the PDEs are discretized with the nodal discontinuous Galerkin finite element method (DG–FEM) in order to understand how the method performs at microscale level for compressible flows. Validation is performed through a benchmark test problem for microscale applications. The error norms, order of accuracy and computational cost are investigated in a grid refinement study, showing a good agreement and increasing accuracy with reference data as the mesh is refined. The effects of different explicit Runge–Kutta schemes and of different time step sizes have also been studied. We found that the choice of the temporal scheme does not really affect the accuracy of the numerical results.

Viability study of implementing cross flow helical turbine for Micropower generation in India

The proposed study investigates the viability of implementing vertical flow helical turbine (which are known for its self-starting capability) for power generation from tidal/River sources. A micropower system is proposed to provide incessant power on the order of 20 Watts in general, so a system comprises of 30 to 40 individual units each producing approximately 0.6 Watts

Rational Design Approach for Enhancing Higher-Mode Response of a Microcantilever in Vibro-Impacting Mode.

This paper proposes an approach for designing an efficient vibration energy harvester based on a vibro-impacting piezoelectric microcantilever with a geometric shape that has been rationally modified in accordance with results of dynamic optimization. The design goal is to increase the amplitudes of higher-order vibration modes induced during the vibro-impact response of the piezoelectric transducer, thereby providing a means to improve the energy conversion efficiency and power output. A rational configuration of the energy harvester is proposed and it is demonstrated that the new design retains essential modal characteristics of the optimal microcantilever structures, further providing the added benefit of less costly fabrication. The effects of structural dynamics associated with advantageous exploitation of higher vibration modes are analyzed experimentally by means of laser vibrometry as well as numerically via transient simulations of microcantilever response to random excitation. Electrical characterization results indicate that the proposed harvester outperforms its conventional counterpart (based on the microcantilever of the constant cross-section) in terms of generated electrical output. Reported results may serve for the development of impact-type micropower generators with harvesting performance that is enhanced by virtue of self-excitation of large intensity higher-order mode responses when the piezoelectric transducer is subjected to relatively low-frequency excitation with strongly variable vibration magnitudes.

A triple hybrid micropower generator with simultaneous multi-mode energy harvesting

This study presents a triple hybrid energy harvesting system that combines harvested power from thermoelectric (TE), vibration-based electromagnetic (EM) and piezoelectric (PZT) harvesters into a single DC supply. A power management circuit is designed and implemented in 180 nm standard CMOS technology based on the distinct requirements of each harvester, and is terminated with a Schottky diode to avoid reverse current flow. The system topology hence supports simultaneous power generation and delivery from low and high frequency vibrations as well as temperature differences in the environment. The ultra-low DC voltage harvested from TE generator is boosted with a cross-coupled charge-pump driven by an LC oscillator with fully-integrated center-tapped differential inductors. The EM harvester output was rectified with a self-powered and low drop-out AC/DC doubler circuit. The PZT interface electronics benefits from peak-to-peak cycle of the harvested voltage through a negative voltage converter followed by synchronous power extraction and DC-to-DC conversion through internal switches, and an external inductor. The hybrid system was tested with a wearable in-house EM energy harvester placed wrist of a jogger, a commercial low volume PZT harvester, and DC supply as the TE generator output. The system generates more than 1.2 V output for load resistances higher than 50 kΩ, which corresponds to 24 μW to power wearable sensors. Simultaneous multi-mode operation achieves higher voltage and power compared to stand-alone harvesting circuits, and generates up to 110 μW of output power. This is the first hybrid harvester circuit that simultaneously extracts energy from three independent sources, and delivers a single DC output.

Power density optimization for MEMS piezoelectric micro power generator below 100 Hz applications

In piezoelectric based micro-power generator (PMPG), electrical energy is generated from mechanical vibration by gaining on the piezoelectric effects. This study concentrates on optimization of the output power density of PMPG at an extremely low frequency (ELF) range below 100 Hz. Taguchi method with eight control parameters and signal-to-noise ratios are utilized in design optimization, COMSOL Multiphysics ver. 4.2 was used for PMPG simulation at optimized parameter. Both Taguchi and S/N ratio analyses show that piezoelectric material selected and its dimensions have the most influence on the generated electric energy density. The simulated PMPG resulting output root mean square voltage was 2.47 V, and power density was 0.376 W/cm3. The PMPG design was fabricated with MEMS technology producing 0.29 W/cm3 power density and supplying 2.19 V DC to the final load. The modeling, simulation and fabricated design show that the PMPG is capable of replacing traditional Lithium Iodide (Li-Ion) batteries powering small electronic gadgets, such as biomedical implant and wearable electronics in frequency range of 25–27 Hz.

A Papertronic, On‐Demand and Disposable Biobattery: Saliva‐Activated Electricity Generation from Lyophilized Exoelectrogens Preinoculated on Paper

Portable, on‐demand micropower generation is provided by developing paper‐based biobatteries that can deliver on‐chip energy to the next generation of point‐of‐care (POC) diagnostic platforms. This work creates a low‐cost, disposable, long shelf life and eco‐friendly micropower source that can be easily integrated in paper‐based POC devices and be readily activated by one drop of saliva, which is readily available in any challenging area. A high‐performance, paper‐based, bacteria‐powered battery is created by building microbial fuel cells with inactive, lyophilized (or freeze‐dried) exoelectrogenic cells, allowing for a long shelf life, which generates power within minutes of adding saliva. An oxygen‐tight interface and engineered conductive paper reservoir achieve significant performance boosts from maximized microbial electron transfer efficiency. Exoelectrogenic bacteria preinoculated in the paper battery is freeze‐dried for long‐term storage (in this work, the bacteria cells are stored for up to four months) and can be readily rehydrated for on‐demand power generation. Sixteen microbial fuel cells are incorporated on a single sheet of paper while all are connected in series with two electrical switches mounted on a paper circuit board, which produce more than enough electrical energy to power an on‐chip, light‐emitting diode.

Development and characterisation of polyvinylidene fluoride-polyaniline films for piezoelectric power generation

Piezoelectric polymer nanocomposites are prepared to improve the dielectric properties of polyvinylidene fluoride (PVDF) as micropower generators. Polyaniline (PANI) was chosen as a filler material to prepare the nanocomposites. PVDF-PANI nanocomposite films were prepared using the solvent cast method with different volume fractions of PANI varying from 0.04 to 0.06%. The films were then characterised for structural, mechanical and surface morphological properties using X-ray diffraction, differential scanning calorimeter, Raman spectra, Infrared spectra, tensile testing and scanning electron microscopy. X-ray diffraction analysis shows that the prepared PVDF-PANI films were in beta-phase. DSC scans indicate that the degree of crystallinity in PVDF-PANI has improved. Raman and Infrared spectrum further confirm the presence of beta-phase in PVDF-PANI film. Tensile properties of PVDF-PANI films show good mechanical properties. The surface feature shows that PANI is uniformly distributed in PVDF and also results in the disappearance of spherulites. The influence of volume fractions of PANI in PVDF on the dielectric properties were analysed. The results showed that the dielectric permittivity of PVDF-PANI (137.36) was much higher than that of PVDF (12). The sensitivity of these films were studied by the application of pressure, and it was observed that the voltage response of the film sensor is 12.4 V pk–pk, which is steady with the constant application of 1.85 kg weight. PVDF-PANI film sensor shows higher sensitivity with a longer period of time. These films were tested to use as micropower generators when coupled with supercapacitors.

Out-of-Plane Continuous Electrostatic Micro-Power Generators.

This paper presents an out-of-plane electrostatic micro-power generator (MPG). Electret-based continuous MPGs with different gaps and masses are fabricated to demonstrate the merits of this topology. Experimental results of the MPG demonstrate output power of 1 mW for a base acceleration amplitude and frequency of 0.08 g and 86 Hz. The MPGs also demonstrate a wideband harvesting bandwidth reaching up to 9 Hz. A free-flight and an impact mode model of electrostatic MPGs are also derived and validated by comparison to experimental results.

Self-sustaining, solar-driven bioelectricity generation in micro-sized microbial fuel cell using co-culture of heterotrophic and photosynthetic bacteria

Abstract Among many energy harvesting techniques with great potential, microbial fuel cell (MFC) technology is arguably the most underdeveloped. Even so, excitement is building, as microorganisms can harvest electrical power from any biodegradable organic source (e.g. wastewater) that is readily available in resource-limited settings. Nevertheless, the requirement for endless introduction of organic matter imposes a limiting factor to this technology, demanding an active feeding system and additional power. Here, we demonstrated self-sustaining bioelectricity generation from a microliter-scale microbial fuel cell (MFC) by using the syntrophic interaction between heterotrophic exoelectrogenic bacteria and phototrophs. The MFC continuously generated light-responsive electricity from the heterotrophic bacterial metabolic respiration with the organic substrates produced by photosynthetic bacteria. Without additional organic fuel, the mixed culture in a 90-μL-chamber MFC generated self-sustained current for more than 13 days, while the heterotrophic culture produced current that decreased dramatically within a few hours. The current from the mixed culture was about 70 times greater than that of the device with only photosynthetic bacteria. The miniaturization provided a short start-up time, a well-controlled environment, and small internal resistance. Those advantages will become the general design platform for micropower generation.

Design optimization of a fully integrated charge-pump with LC tank oscillator for ultra-low voltage energy harvesting

Model based optimization of a novel integrated interface circuit topology is presented for low voltage DC-DC step-up conversion. A cross-coupled charge pump is implemented in standard 0.18µm CMOS technology using an integrated LC tank oscillator to enable a compact, low cost, self-starting solution with maximum efficiency at ultra-low input voltage levels available from embedded micro-power generators. The voltage doubling oscillator can start up with input as low as 0.10V. Full system can step 0.2V up to 1.7V to supply >400μW to 6kΩ load with 46.5% efficiency based on post-layout simulations. The minimum simulated input voltage is 0.11V, which is boosted up to 1.0V under open circuit conditions. The optimized system thorough the established model improves output power and efficiency more than 30% compared to the alternatives. The compact LC tank leads to 17% area reduction compared to the conventional VCO with four planar inductors.

INFLUENCE OF MODIFIED AIR ON COMBUSTION CHARACTERISTICS IN MESO-SCALE VORTEX COMBUSTOR

The need to supply power for miniaturized mechanical devices opens exciting new opportunities for combustion, especially in the field of micro-power generation. Because of the need for power supply devices with high-specific energy (small-size, low weight, long duration) and power. Meso/micro scale combustion has been considered as a potential solution for many small-volumes and energy demanding systems, such as power supplies for portable device. In this study the structure of turbulent diffusion flames in a meso scale combustor with different oxygen concentration has been investigated using a new design of vortex combustor. Methane gas was used as a fuel. Numerical investigations have been performed on the temperature distribution, swirl number, heat loss, and emitter efficiency in vortex combustion. The results have been obtained for various O2 concentrations in the air as oxidizer. The results shows that thermal flame behaves depend strongly on the oxygen content in the oxidizer. When the oxygen concentration increases from 15% to 30%, the flame temperature of the meso-combustion rises in all cases. Emitter efficiency is very high in the meso-combustor with high O2 concentration in oxidizer.

Gold particles growth on carbon felt for efficient micropower generation in a hybrid biofuel cell

In this study, homogeneously dispersed gold particles growth onto carbon felt were fabricated by electrodeposition method followed by a thermal treatment at 1000°C under nitrogen. The thermal treatment induced the dewetting of gold and the formation of well-crystallized gold particles that exhibited large surface area. The structural properties of the resulted Au@CF material were evaluated by SEM, XRD and TGA. We studied the electrocatalytic properties of this new gold material through the abiotic glucose oxidation in alkaline medium and the enzymatic dioxygen electroreduction by the enzyme bilirubin oxidase. Finally, we showed the potentiality of the resulting Au@CF material to build a 3-dimensional glucose hybrid biofuel cell by assemblying an abiotic anode with an enzymatic cathode. The system exhibited high electrochemical performance with an open circuit voltage of 0.71V and a maximum power density of 310μWcm−2 at 352mV (by taking into account the projected surface area), in spite of a low gold loading (0.2wt%). The advance presented in this work is the efficiency of the synthesis technique to get a new free-standing material for electrocatalysis based on gold particles with high reactive surface area for electron transfer and macropores for diffusion transport.

Thermodynamic assessment of integrated biogas-based micro-power generation system

In this paper, a thermodynamic modelling of an integrated biogas (60%CH4+40%CO2) micro-power generation system for electricity generation is reported. This system involves a gas turbine cycle and organic Rankine cycle (ORC) where the wasted heat of gas turbine cycle is recovered by closed ORC. The net output power of the micro-power generation system is fixed at 1.4MW includes 1MW power generated by GT and 0.4MW by ORC. Energy and exergy assessments and related parametric studies are carried out, and parameters that influence on energy and exergy efficiency are evaluated. The performance of the system with respect to variation of design parameters such as combustion air inlet temperature, turbine inlet temperature, compressor pressure ratio, gas turbine isentropic efficiency and compressor isentropic efficiency (from the top cycle) and steam turbine inlet pressure, and condenser pressure (from bottoming cycle) is evaluated. The results reveal that by the increase of gas turbine isentropic efficiency, the outlet temperature of gas turbine decreases which incurs negative impacts on the performance of air preheater and heat exchanger, however the energy and exergy efficiency increases in the whole system. By the increase of air compressor pressure ratio, the energy and exergy of the combined cycle decreases. The exergy efficiency of ORC alters by the variation of gas turbine parameters which can be attributed to the variation of temperature discrepancy between gas turbine exhaust temperature and ORC working fluid. Both first and second law efficiency of the combined cycle increases with the enhancement of inlet pressure of ORC turbine due to the mitigation of exergy destruction in heat exchanger. The rate of power generation in ORC increases by the enhancement of ORC turbine inlet pressure, however overall exergy destruction of the cycle decreases slightly.

Analysis, design and experimental characterization of diode‐less transducers for DC-to-DC multiplication

Voltage multiplication is often needed both to perform accurate measurement of both DC and AC voltages and in the energy accumulation section of transducers used for energy scavenging. Classical voltage multipliers are based on electronic circuits that require a voltage supply in order to guarantee the desired behavior; this in turn creates a disadvantage in terms of power consumption that could affect the overall power budget in very low power systems and energy harvesting devices. Moreover the presence of diodes poses a limit, due to their inherent voltage threshold, to the minimum level of the voltage that can be multiplied, which inhibits the use of voltage multipliers in micro-power generators with ultra-low voltage output. The device proposed here implements a “vibration driven” DC-to-DC voltage multiplication; it uses capacitors and cantilevers to realize mechanical switches. Active switches and diodes are not used, therefore, neither a power budget has to be accounted for the operation of the device nor any limiting threshold has to be considered as starting level for the voltage to be multiplied. The proposed solution has been first analytically modeled and numerically studied. A prototype device has been realized and an extensive experimental measurement campaign has been performed in order to validate the concepts.

Design Optimization of a Micro-Combustor for Lean, Premixed Fuel-Air Mixtures

Present technology has been shifting towards miniaturization of devices for energy production for portable electronics. Micro-combustors, when incorporated into a micro-power generation system, create the energy desired in the form of hot gases to power such technology. This creates the need for a design optimization of the micro-combustor in terms of geometry, fuel choice, and material selection. A total of five micro-combustor geometries, three fuels, and three materials were computationally simulated in different configurations in order to determine the optimal micro-combustor design for highest efficiency. Inlet velocity, equivalence ratio, and wall heat transfer coefficient were varied in order to test a comprehensive range of micro-combustor parameters. All simulations completed for the optimization study used ANSYS Fluent v16.1 and post-processing of the data was done in CFD Post v16.1. It was found that for lean, premixed fuel-air mixtures (φ = 0.6 - 0.9) ethane (C2H6) provided the highest flame temperatures when ignited within the micro-combustor geometries. An aluminum oxide converging micro-combustor burning ethane and air at an equivalence ratio of 0.9, an inlet velocity of 0.5 m/s, and heat transfer coefficient of 5 W/m2-K was found to produce the highest combustor efficiency, making it the optimal choice for a micro-combustor design. It is proposed that this geometry be experimentally and computationally investigated further in order to determine if additional optimization can be achieved.

Design and Development of Micro-Power Generating Device for Biomedical Applications of Lab-on-a-Disc.

The development of micro-power generators for centrifugal microfluidic discs enhances the platform as a green point-of-care diagnostic system and eliminates the need for attaching external peripherals to the disc. In this work, we present micro-power generators that harvest energy from the disc’s rotational movement to power biomedical applications on the disc. To implement these ideas, we developed two types of micro-power generators using piezoelectric films and an electromagnetic induction system. The piezoelectric-based generator takes advantage of the film’s vibration during the disc’s rotational motion, whereas the electromagnetic induction-based generator operates on the principle of current generation in stacks of coil exposed to varying magnetic flux. We have successfully demonstrated that at the spinning speed of 800 revolutions per minute (RPM) the piezoelectric film-based generator is able to produce up to 24 microwatts using 6 sets of films and the magnetic induction-based generator is capable of producing up to 125 milliwatts using 6 stacks of coil. As a proof of concept, a custom made localized heating system was constructed to test the capability of the magnetic induction-based generator. The heating system was able to achieve a temperature of 58.62°C at 2200 RPM. This development of lab-on-a-disc micro power generators preserves the portability standards and enhances the future biomedical applications of centrifugal microfluidic platforms.

Two-dimensional simulation of premixed laminar flame at microscale

Microcombustion is one of the most essential topics in the development of micropower generators for portable devices, microaerial vehicles and sensors. Although one-dimensional numerical modelling of combustion has been developed, maturing a lot during the last forty years, two-dimensional numerical modelling of combustion, particularly at very small scales has only started in the last decade. In this particular study, two-dimensional numerical simulations of premixed, laminar, lean methane–air flames at atmospheric pressure formed in a 2mm diameter microcombustor are performed. A skeletal mechanism consisting of 16 species and 41 reactions is employed. This study shows the importance of applying low target residuals for convergence in CFD, which plays a critical role in obtaining an accurate solution in the numerical modelling of microcombustion. The main focus of this work is to investigate the effect of preheating the reactants on the flame structure and stability with adiabatic and non-adiabatic combustor walls. The flame in the 2mm diameter circular microcombustor under adiabatic wall conditions shows a laminar Bunsen type flame behaviour. On the other hand, under the non-adiabatic wall conditions, a cone shaped high temperature flame zone is observed. Preheating the reactants widens the flame stability at high incoming flow velocities under both conditions, however, under non-adiabatic wall conditions, at low incoming flow velocities and/or low mass flow rates, preheating the reactants contributes neither to flame stability nor combustion characteristics. On the contrary, it results in low combustor exit temperature. Finally, the effects of convective heat transfer coefficients and heat loss, with and without radiation, on the microcombustion are analysed.