Design,fabrication and testing of a piezoelectric energy microgenerator

This article presents the design, fabrication and characterization of a micromachined energy harvester utilizing aluminium nitride (AlN) as a piezoelectric thin film material for energy conversion of random vibrational excitations. The harvester was designed and fabricated using silicon micromachining technology where AlN is sandwiched between two electrodes on top of a silicon cantilever beam which is terminated by a silicon seismic mass. The harvester generates electric power when subjected to mechanical vibrations. The generated electrical response of the device was experimentally evaluated at various acceleration levels. A maximum power of 34.78 μW was obtained for the device with a seismic mass of 5.6 × 5.6 mm² at an acceleration value of 2 g. Various fabricated devices were tested and evaluated in terms of the generated electrical power as well as the resonant frequency.     

Directed transport and location-designated rotation of nanowires using ac electric fields

The motion control of individual nanowires is essential for effective nanowire manipulation strategies. In this paper, we demonstrate a simple and general method to dynamically control the motion of a chemically untreated nanowire in a quadrupole electrode structure. The motion of single nanowires was determined by positive dielectrophoresis and orientational torque, which were induced by optionally exerting ac signals onto specific electrodes for regulating the electric field distribution in real time. A silver nanowire was guided to transform postures and transport directionally in a working regime of about 115 μm × 115 μm. The selected nanowire was then transported to a region of weak gradients and forced to rotate at the designated location subsequently. The behavior of the nanowires, including their posture, cornering time, linear displacement and location-designated rotation, was dynamically monitored and regulated. A simple analytical model was developed to derive the driving forces and torques on the nanowire.     

Fabrication of micro-capacitive inclination sensor by resin molding

Capacitive inclination sensors have the advantage that they can easily provide a linear analog output with respect to inclination. Although inclination sensors featuring this advantages are already commercially available, they are generally too large. We fabricated a micro-capacitive inclination sensor by a combination of a resin forming method and a mold. Electrodes of the sensor are 40 μm in a gap and 12 mm² in area. The sensor detects difference of capacitance, which varies with movement of silicone oil accompanying with inclination of the sensor. Since the dimensions of the sensing region are 5 × 5 × 3 mm³ this inclination sensor is expected to be widely used in fields where efficient and reliable position control is a primary factor to be considered. The use of resins is also expected to contribute to a reduction in the costs of materials. We successfully fabricated a micro inclination sensor as a molded product. In future, we will wire up the device to complete this inclination sensor, and will then conduct performance evaluations. If techniques using resin-molded parts are introduced to the low-cost mass-production of Micro Electro Mechanical Systems devices, the range of applications will further expand to new areas of technology and industry.     

Evaluation of low-acceleration MEMS piezoelectric energy harvesting devices

Microelectromechanical systems-based piezoelectric energy harvesting device research is continuing to increase due to high demands in powering wireless sensor networks. This paper compares three different cantilever structures that have been the most widely used designs in MEMS energy harvesting devices. The cantilever structures consist of a wide beam, narrow beam, and trapezoidal beam structure. Aluminium nitride was used as the piezoelectric material because of its CMOS compatibility. Finite element modelling was used to investigate the theoretical outputs of the devices prior to fabrication. The three different structures were fabricated using standard micro-fabrication techniques on SOI wafers in order to verify the results experimentally. The finite element modelling results agree with the experimental results. The AlN deposited on the experimental wafers had a (002) FWHM rocking curve value of 1.7°. The power density based on the volume of space needed to fabricate the structures was 2.5, 0.78, and 0.65 mW/cm³/g² at resonant frequency for the wide, trapezoidal, and narrow beam structures respectively. The bandwidth of the devices is also an important parameter when selecting the cantilever structure. An array of the cantilevers over a 4 cm² area resulted in a bandwidth of was 4.8, 9, and 26.4 Hz for the wide, trapezoidal, and narrow beam structures respectively.     

Impact of thermal contact resistances on micro-gap heat losses for microthermionic power generators

Thermionic power generation is a safe and clean energy source that allows for converting heat into electrical energy using thermionic electrons. The miniaturization is an advantage of this technology that led to the recent development of micro-gap thermionic power generators. In this work, thermal contact resistances between the micro-gap insulators and the emitter as well as between the micro-gap insulators and the collector are measured. A thermal resistance of 48.6 K/W is obtained by downsizing the insulators until 60 × 45 μm² of contact area with the emitter, demonstrating a high impact for decreasing the micro-gap conduction heat loss density from the emitter to the collector from 28 W/cm² (theoretical value obtained without considering contact resistances) to 5.6 W/cm². Downsizing the contact area between the insulators and the emitter from 320 × 300 to 60 × 45 μm² leads to an increase of the power conversion efficiency from 9.1 × 10^?5 until 1.5 × 10^?3.     

Fabrication of AFM probe with CuO nanowire formed by stress-induced method

A novel method has been proposed to fabricate an atomic force microscope (AFM) probe using CuO nanowire and a stress-induced method that can form the nanowire easily. By heating a commercial AFM probe with a film coating of Ta and Cu, a Cu hillock with CuO nanowires on its surface could be formed at the end of the probe. The thickness of the coating films, the heating temperature, and the heating time were investigated to obtain CuO nanowires with a high aspect ratio for use as an AFM probe tip. It was found that a suitable probe tip can be fabricated using the a Cu film thickness of 700 nm, a heating temperature of 380 °C and a heating time of 6 h. Probe tips (~5 μm high) and nanowires of ~25 nm diameter were obtained successfully. In the range evaluated, the measurement resolution of the CuO nanowire probe was slightly worse than that of a commercial AFM probe. However, both probes had almost the same dimensional measurement precision.     

Improving particle detection sensitivity of a microfluidic resistive pulse sensor by a novel electrokinetic flow focusing method

A novel and simple method of improving the particle detection sensitivity of a microfluidic resistive pulse sensor was presented in this paper. This novel electrokinetic flow focusing method utilizes a focusing solution (with high resistivity) flowing from the upstream focusing channel to the downstream focusing channel. The focusing solution in the sensing gate works like a virtual insulation wall that greatly narrows the gate and thus improves the detection sensitivity. An equation was derived to relate the magnitude of the output signal to the resistivity and the width of the focusing solution. The width of the focused particle solution under different voltages was numerically predicted. The results show that the magnitude of output signal increases with the decrease in the width of the focused particle stream. More importantly, the detection sensitivity can be improved by decreasing the space occupied by the focusing solution in the upstream and downstream channels as much as possible. Detection of 1 μm particle with a sensing gate of 30 × 40 × 10 μm (width × length × height) was successfully achieved. The proposed method is simple and advantageous in detecting smaller particles without fabricating a small sensing gate.     

A facile strategy to integrate robust porous aluminum foil into microfluidic chip for sorting particles

High efficiency integration of functional microdevices into microchips is crucial for broad microfluidic applications. Here, a device-insertion and pressure sealing method was proposed to integrate robust porous aluminum foil into a microchannel for microchip functionalization which demonstrate the advantage of high efficient foil microfabrication and facile integration into the microfluidic chip. The porous aluminum foil with large area (10 × 10 mm²) was realized by one-step femtosecond laser perforating technique within few minutes and its pores size could be precisely controlled from 3 μm to millimeter scale by adjusting the laser pulse energy and pulse number. To verify the versatility and flexibility of this method, two kinds of different microchips were designed and fabricated. The vertical-sieve 3D microfluidic chip can separate silicon dioxide (SiO₂) microspheres of two different sizes (20 and 5 μm), whereas the complex stacking multilayered structures (sandwich-like) microfluidic chip can be used to sort three different kinds of SiO₂ particles (20, 10 and 5 μm) with ultrahigh separation efficiency of more than 92%. Furthermore, these robust filters can be reused via cleaning by backflow (mild clogging) or disassembling (heavy clogging).     

Micro solar energy harvesting using thin film selective absorber coating and thermoelectric generators

The use of a nanometer-scale solar selective absorber coating to enhance the performance of a thermoelectric generation (TEG) module in solar thermal energy harvesting is presented. The thin film coating is fabricated by electrochemical deposition of a bimetallic layer of tin and nickel on copper substrate. The coating has a dendrite structure with grain size of 100 nm. Testing indicates the ability of these collectors to transform incident radiation into thermal energy. The collectors utilizing the selective coating achieved a final temperature 10 °C higher than the baseline copper device. More importantly, the coating demonstrates the ability to collect and transmit over 90 % of the available heat flux. The harvested thermal energy is applied to drive a TEG module for useful power generation. The device utilized with selective absorber coating shows an output power 4.5 times more than the baseline device. Overall area of the collector plate is 16 cm².     

A printed circuit board capacitive sensor for air bubble inside fluidic flow detection

This paper presents a three-electrode capacitive fluidic sensor for detecting an air bubble inside a fluidic channel such as blood vessels, oil or medical liquid channels. The capacitor is designed and fabricated based on a printed circuit board (PCB). The electrodes are fabricated by using copper via structure through top to bottom surface of the PCB. A plastic pipe is layout through the capacitive sensor and perpendicular to the PCB surface. Capacitance of sensor changes when an air bubble inside fluidic flow cross the sensor. The capacitance change can be monitored by using a differential capacitive amplifier, a lock-in amplifier, filter and an NI acquisition card. Signal is processed and calculated on a computer. Air bubble inside the liquid flow are detected by monitor the unbalance signal between the three electrode potential voltages. Output voltage depends on the volume of the air bubble due to dielectric change between capacitor’s electrodes. Output voltage is up to 53 mV when an 2.28 mm³ air bubble crosses the sensing channel. Air bubble velocity can be estimated based on the output pulse signal. This proposed fluidic sensor can be used for void fraction detection in medical devices and systems; fluidic characterization; and water–gas, oil–water and oil–water–gas multiphase flows in petroleum technology. That structure also can apply to the micro-size for detecting in microfluidic to monitor and control changes in microfluidic channels.     

Nonlinear behaviour of membrane type electromagnetic energy harvester under harmonic and random vibrations

In this paper, the fabrication and characterization of a vibration-based polydimethylsiloxane (PDMS) membrane type electromagnetic energy harvester (EMEH) is reported. The harvester is suitable for generating electric energy from low level sinusoidal and narrow band random vibrations. Under acceleration levels greater than 0.1 g the behaviour of the EMEH is nonlinear, exhibiting sharp jump and hysteresis phenomena during frequency sweeps. Under sinusoidal excitations (0.1–3 g), the device produces a maximum of 88.8 mV load voltage and 39.4 μW power. At a matching load impedance of 10.1 Ω and when excited at its resonant frequency of 108.4 Hz and 3 g base acceleration, it generates a power of 68.0 μW, which corresponds to a power density of 30.22 μW/cm³. The nonlinear behaviour of the EMEH is exploited to harvest energy under narrow band random excitations. At higher acceleration levels of narrow band (50–150 Hz) random excitations, the device exhibits a broadening of the load voltage spectrum in comparison to the response under relatively low acceleration levels of narrow band (5–150 Hz) random excitations. The results show that the nonlinear behaviour of the PDMS membrane can be utilized to enhance the bandwidth of the harvester under narrow band random excitations and provides a simple alternative to other bandwidth broadening methods such as beam prestress, resonance tuning, or stopper impacts.     

An efficient energy harvesting circuit for batteryless IoT devices

A new energy harvesting circuit for battery-less IoT beacon tags is developed herein to maximize power conversion efficiency as well as high throughput power with a wide input–output range. This design energy harvest (EH) circuit incorporates a charge pump (CP) with shoot-through current suppression, a body selector circuit, a maximum power point tracking circuit (MPPT), a timing control circuit, a hysteresis control circuit and a low dropout regulator. Also in this MPPT circuit is a gated clock tuned in a self-adaptive fashion to match the input impedance of the EH circuit to the output impedance of the photovoltaic (PV) panel, thus achieving successfully maximum power point. The circuit is implemented in an integrated chip in an area of 1.2 mm² via the TSMC 0.18 process. Experiments on the chip are conducted and the results show that the input voltage range is allowed from 0.55 to 1.7 V to effectively harvest the solar power from a flexible dye-sensitized solar cell. The achieved peak power conversion efficiency (PCE) is 77% at the input power of 52 μW. For a wide range of lighting luminance (300–1300 lx,) the achieved average PCE is more than 70%. The achieved wide input–output range and the maximum throughput power of 200 μW is much larger than others reported, while the 77% of PCE is close to that best power conversion efficiency reported.

     

Dean flow focusing and separation of small microspheres within a narrow size range

Rapid, selective particle separation and concentration within the bacterial size range (1–3 μm) in clinical or environmental samples promises significant improvements in detection of pathogenic microorganisms in areas including diagnostics and bio-defence. It has been proposed that microfluidic Dean flow-based separation might offer simple, efficient sample clean-up: separation of larger, bioassay contaminants to prepare bioassay targets including spores, viruses and proteins. However, reports are limited to focusing spherical particles with diameters of 5 μm or above. To evaluate Dean flow separation for (1–3 μm) range samples, we employ a 20 μm width and depth, spiral microchannel. We demonstrate focusing, separation and concentration of particles with closely spaced diameters of 2.1 and 3.2 μm, significantly smaller than previously reported as separated in Dean flow devices. The smallest target, represented by 1.0 μm particles, is not focused due to the high pressures associated with focussing particles of this size; however, it is cleaned of 93 % of 3.2 μm and 87 % of 2.1 μm microparticles. Concentration increases approaching 3.5 times, close to the maximum, were obtained for 3.2 μm particles at a flow rate of 10 μl min^?1. Increasing concentration degraded separation, commencing at significantly lower concentrations than previously predicted, particularly for particles on the limit of being focused. It was demonstrated that flow separation specificity can be fine-tuned by adjustment of output pressure differentials, improving separation of closely spaced particle sizes. We conclude that Dean flow separation techniques can be effectively applied to sample clean-up within this significant microorganism size range.     

Analytical study on cantilever resonance type magnet-integrated sensor device for micro-magnetic field detection

A beam-shaped cantilever resonance type magnetic sensor device has been proposed with a micro magnet. Two structural designs, named as design 1 and design 2, have been comparatively analyzed using ANSYS in order to obtain larger frequency shifts (higher magnetism sensitivity) due to the applied exterior magnetic field. The analytical results show that, in the range of 0–10 mT, the frequency shifts are small, while under 100 mT, a relatively larger frequency shift of about 30 Hz can be theoretically obtained. The power consumption of the proposed devices has been further theoretically studied for preliminary understanding. Using the well-known displacement equations, the estimated power consumption is around 0.21 μW, which is very lower than that of the reported magnetic field sensors. This implies that it is possible to fabricate higher sensitive magnetic field sensor with lower power consumption.     

Transparent thin thermoplastic biochip by injection-moulding and laser transmission welding

Recently microfluidic devices have emerged as a viable technology for the miniaturization of high throughput tools for analytical tasks related to structural biology such as screening of crystallization conditions and structural analysis. This work reports the manufacture of microfluidic chips in transparent thermoplastic polymers [poly(methylmethacrylate) (PMMA), and cyclic olefin copolymer (COC)] using two complementary technologies, injection moulding for the fabrication of the fluidic level and laser transmission welding for the sealing of the cover. A steel mould insert was produced by laser micro caving using a solid state laser radiation source (Nd:YAG, wavelength 1,064 nm). Fluidic chips of ~670 μm thickness comprising channels of 50 μm depth and width down to 50 μm were injection moulded in PMMA and COC. Joining of transparent thin cover film to the micro-injected fluidic level was performed by laser transmission welding using high power diode laser radiation (wavelength 940 nm) and an intermediate thin absorbing layer with a thickness of about several nanometers.     

A new high detectivity room temperature linear thermopile array with a D* greater than 2 × 109 cmHz1/2/W based on organic membranes

We present a newly designed high-detectivity thermoelectric linear array, based on an organic membrane for use in the room temperature range. The sensor array has 64 individual readable channels and was designed and developed for IR spectroscopy. This detector may be used to infer the condition of lubricants and coolants within a mechanical system, so that they can be replaced when needs be, e.g. determining the age of technical oils of wind power plants in real time. Thus valuable resources can be saved and costly damage to equipment avoided. In order to achieve a D* greater than 2 × 10⁹ cmHz^1/2/W, the sensor was designed and optimized to be operated under vacuum conditions. To minimize the thermal cross talk between individual pixels, the pixels are separated from each other by a 50 μm slit in the self-supporting organic membrane made of SU-8.     

Simultaneous monitoring of oxygen consumption and acidification rates of a single zebrafish embryo during embryonic development within a microfluidic device

A microfluidic device with a light modulation system was developed to simultaneously measure the oxygen consumption rate (OCR) and acid extrusion rate (AER) of a single zebrafish embryo during embryonic development. The device combines two components: an array of acrylic microwells containing two sensing layers as the dual luminescent sensor for oxygen (O₂) and acid (pH) detection, and a microfluidic module with pneumatically actuated glass lids to controllably seal the microwells. The continuous blue LED and modulated UV LED lights were simultaneously used to excite the dual luminescent sensor, with the emission detected by a single photodetector. The detection signals were then split into DC and AC components to measure the time variations in fluorescence intensity and phosphorescence lifetime for pH and O₂ detection, respectively. We have successfully measured the OCR and AER of a single developing zebrafish embryo inside a sealed microwell from the blastula stage (3 h post-fertilization, 3 hpf) through the hatching stage of 48 hpf. We also demonstrated the measurement of the OCR and AER of a single 48 hpf zebrafish that experienced acute hypoxia by using our device to monitor the transition between aerobic and anaerobic metabolism. We observed that the AER began to significantly increase, while the OCR rapidly decreased after 20 min of hypoxia, indicating the time point of transition where the non-mitochondrial metabolism subsequently dominated the energy production. Our proposed methodology provides the potential for studying the bioenergetic metabolism in a developing organism that relates mitochondrial physiology and disease.     

Highly integrated polymeric microliquid flow controller for droplet microfluidics

Microfluidic applications demand accurate control and measurement of small fluid flows and volumes, and the majority of approaches found in the literature involve materials and fabrication methods not suitable for a monolithic integration of different microcomponents needed to make a complex Lab-on-a-Chip (LoC) system. The present work leads to a design and manufacturing approach for problem-free monolithic integration of components on thermoplastics, allowing the production of excellent quality devices either as stand-alone components or combined in a complex structures. In particular, a polymeric liquid flow controlling system (LFCS) at microscale is presented, which is composed of a pneumatic microvalve and an on-chip microflow sensor. It enables flow regulation between 30 and 230 μl/min with excellent reproducibility and accuracy (error lower than 5%). The device is made of a single Cyclic Olefin Polymer (COP) piece, where the channels and cavities are hot-embossed, sealed with a single COP membrane by solvent bonding and metalized, after sealing, to render a fully functional microfluidic control system that features on-chip flow sensing. In contrast with commercially available flow control systems, the device can be used for high-quality flow modulation in disposable LoC devices, since the microfluidic chip is low cost and replaceable from the external electronic and pneumatic actuators box. Functionality of the LFCS is tested by connecting it to a microfluidic droplet generator, rendering highly stable flow rates and allowing generation of monodisperse droplets over a wide range of flow rates. The results indicate the successful performance of the LFCS with significant improvements over existing LFCS devices, facing the possibility of using the system for biological applications such as generating distinct perfusion modes in cell culture, novel digital microfluidics. Moreover, the integration capabilities and the reproducible fabrication method enable straightforward transition from prototype to product in a way that is lean, cost-effective and with reduced risk.     

Numerical simulation of the capillary flow in the meander microchannel

Pumping in microfluidic devices is an important issue in actuating fluid flow in microchannel, especially that capillary force has received more and more attractions due to the self-driven motion without external power input. However, less 2D simulation was done on the capillary flow in microchannel especially the meander microchannel which can be used for mixing and lab-on-a-chip (LOC) application. In this paper, the numerical simulation of the capillary flow in the meander microchannel has been studied using computer fluid dynamic simulation software CFD-ACE⁺. Different combinations of channel width in the X-direction denoted as W_x and Y-direction denoted as W_y were designed for simulating capillary flow behavior and pressure drop. The designed four types of meander microchannels (W_x × W_y) were 100 × 100 μm, 100 × 200 μm, 50 × 200 μm, and 50 × 400 μm. In this simulation results, it is found that the capillary pumping speed is highly depending on the channel width. The large speed change occurs at the turning angle of channel width change from W_x to W_y. The fastest pumping effect is found in the meander channel of 100 × 100 μm, which has an average pumping speed of 0.439 mm/s. The slowest average flow speed of 0.205 mm/s occurs in the meander channel of 50 × 400 μm. Changing the meander channel width may vary the capillary flow behavior including the pumping speed and the flow resistance as well as pressure drop which will be a good reference in designing the meander microchannels for microfluidic and LOC application.     

A microbial fuel cell powering an all-digital piezoresistive wireless sensor system

Microbial fuel cells (MFCs) are energy sources, which generate electrical charge thanks to bacteria metabolism. We report on a full custom pressure wireless sensor node especially designed to operate with MFCs, comprising an ultra-low-power Impulse-Radio Ultra-Wide-Band Transmitter operating in the low 0–960 MHz band, a nanostructured piezoresistive pressure sensor connected to a discrete component digital read-out circuit, and an MFC energy supply system. The sensor device comprises an insulating matrix of polydimethylsiloxane and nanostructured multi-branched copper microparticles as conductive filler. Our prototype system comprises two MFCs connected in series to power both the UWB transmitter, which consumes 40 μW, and the read-out circuit. The two MFCs generate an open circuit voltage of 1.2 ± 0.1 V. Each MFC prototype has a total volume of 0.34 L and comprises two circular poly(methyl methacrylate) chambers (anode and cathode) separated by a cation exchange membrane. The paper reports measurements on a fully working prototype that enables the separate transmission of pressure information and MFC voltage level at the same time. The complete sensor node powered by the MFC, thanks to its nature can be located either in harsh environments where there is no connection to energy grids, or in environments where the MFC, hence the complete node, can self-sustain.