MEMS-BASED PIEZOELECTRIC ENERGY HARVESTER FOR POWERING WIRELESS SENSOR NODES

Microelectromechanical systems (MEMS) embody, an advanced semiconductor technology, which encompasses moving components as well as electronics on a single chip. Over the years, MEMS-based devices, such as sensors, accelerometers have become pervasive appearing in all types of applications ranging from consumer electronics to automotive to the medical devices sector. One other area that is also proliferating is the energy harvesting application using MEMS-fabricated piezoactuators. Energy harvesting (EH) is the process of converting energy from ambient sources into electricity to make devices or systems more self-sufficient. Energy harvesting technologies use energy generated from the environment or from humans to enable devices or systems to be powered directly without having to rely on batteries. MicroGen Systems LLC, based in Ithaca, NY, has introduced a MEMS-fabricated piezoelectric energy harvester called BOLT micropower generator that includes a piezoelectric layer that generates electric charge in response to an external stimuli mainly vibration.

MicroGen Systems used Infinite Power Solutions’ (Littleton, Colorado) new IPS-EVAL-EVH-01 energy harvesting evaluation kit to power a wireless temperature sensor supplied by Texas Instruments at the recently held Sensors Expo and Tradeshow 2011 in Rosemont, Illinois. The energy harvesting kit by Infinite Power Solution comes with a complete microelectronic circuit system that enables harvesting the energy from BOLT transducer and stores it in the EH kit’s THINERGY MEC 101 microenergy cell. MicroGen’s BOLT060 energy harvesting device has a resonant frequency of 60 hertz (Hz), while BOLT120 has a fundamental resonant frequency of 120 Hz. In the demo, the BOLT060 was vibrated at 60 Hz frequency and with an acceleration amplitude of 0.7 g (g = 9.8 meter per second square [m/s²]). The generated energy was stored in the thin-film battery ‘THINERGY’ solid-state micropower cell. BOLT devices are approximately 1.0 cm² in area and can generate up to 200 milliwatt (mW). Due to the advantage of using MEMS fabrication technique, BOLT micropower generator can be scaled further. The advantage of using the IPS-EVAL-EVH-01 energy harvesting kit apart from the award winning thin film battery is the presence of an energy harvesting power management integrated circuit supplied by Maxim Integrated Products. The power management circuit can help boost the voltage when required and can also be programmed to regulate the output voltage that goes from the circuit to power the wireless temperature sensor.

According to MicroGen Systems, BOLT micropower generator is the first commercially available piezoelectric-based energy harvesting solution. Further according to Robert Andosca, CEO of MicroGen, BOLT is well positioned to power wireless sensor nodes and systems and will help eliminate the need to replace dead batteries in these systems or help extend the life of lithium batteries 6-fold in WSN applications. MicroGen projects that its device could be useful in a number of applications ranging from automotive to civil infrastructure and military applications. In addition to BOLT060 and BOLT120, MicroGen also provides BOLT050 and BOLT100 with a vibrational resonant frequency of 50 Hz and 100 Hz, respectively. MicroGen has the ability to custom build BOLT micropower generators for vibrational resonant frequencies ranging from 30 Hz to 1.5 kHz. MicroGen is partly funded by New York State Energy Research and Development Authority. MicroGen carries out its product development at Cornell Nanoscale Science and Technology Facility.

NEW BUTANE-POWERED MICRO THERMOPHOTOVOLTAIC SYSTEM--NEXT GENERATION POWER SUPPLY SYSTEM FOR PORTABLE CONSUMER ELECTRONICS

Photovoltaics (PVs) known as solar cells are considered as one of the most significant means of tapping solar energy. PV cells are devices that trap solar energy to convert it into electricity. They are made from semiconducting material such as silicon and gallium. A PV cell mainly has two functions namely, photogeneration of charge carriers in a light absorbing material and separation of charge carriers to a conductive contact that converts it into electricity. Recently, researchers have shown that apart from solar energy, other forms of heat can be used to generate electricity. This new generation of photovoltaic cells is called thermophotovoltaics. It is a highly efficient and reliable system that can use concentrated sun light, nuclear power, fossil fuel, or a radioisotope heat source to heat an intermediate thermal emitter due to which the emitter emits electromagnetic radiation that eventually illuminates the photo cells which in turn converts the incident radiation/light to electricity. 

Using this principle, researchers from the Massachusetts Institute of Technology (MIT) have developed a new button-sized thermophotovoltaic system that could potentially replace rechargeable lithium-ion batteries used in consumer electronic devices such as laptops and cell phones. The newly developed button-sized micro power generators use butane as the fuel input, and have silicon-based microreactors as the central system of the micro power generator. Cylindrical tube inlets supplies butane fuel and oxygen to the microreactor containing photonic crystals on the surface of the reactors. The microreactor converts the fuel inputs to heat and the waste is discarded through another external outlet tube. In order to increase the efficiency of converting light to electricity compared to previous systems, the researchers etched the surface of the photonic crystals to create billions of tiny pits, giving the photonic crystals an ability to emit light at wavelengths matching those wavelengths of light at which the photovoltaic cells are at their best in converting the incident light to electricity. The photonic crystals were made out of tungsten, as this material was identified to give the best results on matching wavelengths. The photovoltaic cells were mounted against the face of the microreactors with a tiny gap so as to facilitate this conversion of light to electricity. 

The research team led by Marin Soljacic, professor of physics at MIT, used the silicon microreactor created by Klavs Jensen, the Warren K. Lewis Professor of Chemical Engineering, at the Microsystems Technology Laboratories of MIT and borrowed the idea of engineering nanoscale pits to emit a completely different spectrum of light from a research by John D. Joannopoulos, the Francis Wright Davis Professor of Physics at MIT and others. According to MIT researchers, the principle of using nanoscale pits has been successfully used to create more efficient light-emitting diodes, lasers, and optical fibers. According to the creators of the photovoltaic conversion system, this new micropower generator system could be highly beneficial for powering portable power electronics as butane can run three times longer than a traditional lithium-ion battery of same size and weight. Also, the new system can be refueled instantly by simply replacing the cartridge containing a fresh supply of butane. However, the photovoltaic system is still in research stage and the MIT researchers are now seeking partners and collaborating with other researchers to create new electricity generating devices. Even though in its nascent stage with no set commercialization date, MIT researchers have shown that this new research initiative can potentially have a huge implication on the multibillion dollar power supply market for consumer electronic devices. The immediate application of this could be in the military for powering soldier’s gadgets, which require batteries that last longer and can be recharged instantly. 

NOVEL WAVEGUIDE CONCEPT FOR NONRECIPROCAL LIGHT PROPAGATION

Silicon photonics has received significant attention in the recent years as a technology, which could enable high-speed performance at low cost and power requirements. The technology is expected to bring significant performance gains in areas such as communication, high-performance computing, and photovoltaics. However, to make this technology feasible for market adoption, it is crucial to ensure that photonic components can be fabricated at low cost, and also ensure that they use processes compatible with CMOS (complimentary metal oxide semiconductor) equipment. Currently, there are numerous academic and industry initiatives focusing on producing different building blocks of optical interconnects. The goal is to achieve a single all-silicon circuit, which integrates both electronic and photonic components, and also achieve high-volume manufacturing at low costs.
As a result of a cooperative research conducted at the California Institute of Technology and the University of California, San Diego, a new method has been proposed for radically limiting the back-reflection of light signals at silicon chip-integrated waveguides. This new optical isolator enables nonreciprocal light propagation on a silicon photonic chip without the need for integrating conventional methods based on magnetic field or nonlinear optical materials. The team has fabricated the silicon waveguide with metal spots along the sides, which interacts with the propagating light wave differently depending on its propagation direction. The metallic-silicon pattern enables light to travel freely in one direction, but dissipates it when it travels in the opposite direction. In this regard, the structure resembles an electrical diode, which in conventional electronics systems enables the signal to travel in only one direction. The waveguide, which is 0.8-micrometers-wide, has been incorporated into a prototype device, and tested using at a 0.55 micrometer-wavelength. The advantage of the proposed concept is that while it offers breakthrough performance, the device can be manufactured using standard CMOS processing, which ensures ease of integration into existing production flow.
The significance of the proposed optical isolator is that in holds promise for improving the performance of silicon photonics chips by limiting the interference of reflected light beams with optical components, such as light sources. This feature is critical to enable the integration of multiple photonic components on the single chip, and as a result bring photonic chips closer to commercial reality. The proposed optical isolator is still in the experimental stage. However, future work will be focused on integrating this technology into a fully operational integrated circuit.

ACTIVE LED THERMAL MANAGEMENT

The use of light-emitting diodes (LEDs) as a lighting source is gaining interest due to the demand for low-powered lighting sources. LED is a form of solid state lighting (SSL). Hence, LED devices have inherently better power consumption and reliability compared to traditional energy-saving lights, such as, compact fluorescent lamp (CFL) lights. However, due to the use of physical electronics to generate light in a LED device, heat dissipation becomes an issue. Heat sinks have been traditionally used to dissipate excess heat from the device and to avoid overheating.
With this view in mind, Nuventix, a company based in Austin, Texas, has a novel approach of using active cooling to reduce the heat build up on LED devices. The company has developed its patented SynJet technology, which utilizes an active cooling approach that forces air over the heat sinks for better heat dissipation. According to sources from Nuventix, the SynJet technology is expected to match or exceed current LED device reliability performance, which could make it attractive for LED manufacturers.
The SynJet approach begins by integrating together both a heat sink with the SynJet blower module to provide the active cooling component. The blower module contains a vibrating diaphragm, which moves up and down to provide air movement. This air movement is funneled through a nozzle system, which accelerates the air into a high-velocity pulse. This pulse of air is then channeled across the heat sink to draw away heat. Due to the design of the nozzle, the air pulse that is ejected from the nozzle is at high velocity and draws additional air flow behind the jet stream. This is due to the momentum generated by the initial air pulse and the subsequent low pressure zone behind the high velocity air pulse. Nuventix believes that this additional stream could provide up to ten times the original air volume from the initial pulse, which increases the overall air streaming across the heat sink. Furthermore, the airflow is twisted to provide a turbulent air flow, which is claimed to provide better heat transfer coefficient as the air travels along the heat sink fins.
The company believes that utilizing its technology could allow SSL manufacturers to design LED devices, which can provide greater light output with the same amount of space. The SynJet design can be customized to meet specific customer shapes to optimize the cooling capacity. Since there is no bearing involved in the oscillating diaphragm, Nuventix believes the system could last up to 100000 hours of operation. Further to this, the device consumes less than 1 W of power, making it a feasible cooling solution for LED designers wanting to increase their output power and yet maintain a low-foot print design. Existing designs could even reduce their heat sink footprint size as a result of using this active air flow cooling method.
Nuventix sources believe that with the use of their SynJet technology, higher lumen LED designs could be introduced, making the adoption of SSL devices as a means of primary lighting more attractive. According to them, there exists a trend for the usage of LED devices in accent lighting and also in general illumination purposes. By allowing a brighter device at reasonable cost and size, SSL could be a valid option for mass scale adoption worldwide as a device for lighting. With a recent $10 million venture funding, Nuventix hopes to be able to ramp up its technology research to support the proliferation of SSL devices.

CONTACTLESS METAL-TO-METAL ELECTRONIC CONNECTIONS

The performance of future electronic systems is limited by interconnect bandwidth, power, performance, and other fundamental physical limitations (such as mechanical reliability, thermal constraints, and overall system form factor). In particular, the interconnects in an embedded chip limits the overall system performance in consumer electronics, high-speed connector, high-speed memory interface, and future network-on-chip. Therefore, the interconnect system should possess ultrahigh-data rates, a reliable interconnect fabric, be scalable, re-configurable, and highly compact.
Based on emerging 60GHz EHF technology, California-based WaveConnex leverages a decade of research using deep submicron complementary metal oxide semiconductor (CMOS) to make millimeter-wave technology a practical and cost-effective reality. The company has developed its products to serve as replacements for metal-to-metal interconnections currently used in nearly all electronic systems. These new products will have the potential to overcome the limitations of current connectors in terms of performance, reliability, and size.
Spun out from the University of California, Los Angeles’ (UCLA) Engineering Institute for Technology Advancement, and incorporated in 2009, WaveConnex has licensed its millimeter wave radio technology from the university.
Built to function like a connector with bandwidth exceeding 10 Gb/s, a tiny silicon chip replaces the function of a connector in a new yet familiar form. Smaller than the connector it replaces and assembled like any other surface-mount component, the company’s product eliminates the need for direct contact typical of a conventional connector and the liabilities associated with such a connector. Since contactless connections allow data to be exchanged between electronic devices without them being in actual physical contact with one other, the technology being developed by WaveConnex will potentially enable wide-ranging applications in the areas of database transfer, internet infrastructure and entertainment electronics, among others.
One of the potential applications being envisoned are pocket-sized "smart cards" that contain embedded integrated circuits which store and process large amounts of data without ever coming into direct contact with another device. The smart card can contain information such as medical history and records in encrypted form, including medications, X-rays, and MRI (magnetic resonance imaging) results. Subsequently, it enables a doctor to access an accurate medical profile, giving them detailed information for the prescription of treatments and also enabling them to update a profile.
While such applications are feasible today through means of alternate technologies, they remain highly impractical due to the limitations in speed and size of these technologies. The new technology being developed by WaveConnex will help make this practical by enabling substantially faster transfer of large databases. WaveConnex received initial sponsorship from the Institute for Technology Advancement (ITA) of the UCLA Henry Samueli School of Engineering and Applied Science (HSSEAS).

MICROFLUIDIC CHIP-BASED 3D IMAGING TECHNIQUE TO CHARACTERIZE LIVE CELLS

New products entail research for new materials. The advent of newer composite materials, probiotic and prebiotics, anti-oxidants and various other particulates and microbials for key applications in food, cosmetics, and healthcare have pushed the boundaries of imaging technologies to higher levels, thereby enabling imaging at nanometer resolutions. This has led to new developments in electron microscopy and high-resolution fluorescence imaging due to these technologies’ ability to look at subcellular architectures and also 3D live cell imaging capabilities. Developments in new techniques, such as stimulated emission depletion microscopy (STED), photo activated localization microscopy (PALM), and stochastic optical reconstruction microscopy (STORM) are progressing at a rapid pace and commercial instruments are beginning to surface from leading vendors such as Leica Microsystems, Carl Zeiss, and Nikon.
Toward this end, researchers from the Vanderbilt University, led by Neils de Jonge, an assistant professor at Vanderbilt University are developing a new imaging technique called liquid/wet scanning transmision electron microscopy (STEM) or Liquid STEM, for imaging live cells. In STEM, a narrow beam incident on a sample scans the entire sample. Each pixel is programmed to detect the number of electrons scattered to create an image. STEM enables 3D imaging. In the new technique termed liquid/wet STEM, the researchers led by Neils de Jonge developed a new microfluidic specimen holder made of silicon substrate comprising of electron transparent windows. The sample cells labeled with gold nanoparticles are enclosed in the microfluidic channel between the electron transparent windows in a liquid solution. The microfluidic chip is placed in the vacuum of an electron microscope. An electron beam is scanned across the cells and a dark field detector detects the scattered electrons. Transmission electron microscope (TEM) and scanning electron microscope (SEM) only image cells in vacuum, making it impossible for live cell imaging. Liquid STEM addresses this challenge by using a silicon microfluidic chip with micrometer-sized channels and electron transparent windows to enable 3D live cell imaging. The research group has used a 200 kV Hitachi HD2000, developed by Hitachi High Technologies America Inc.
The research group has spun-off a company called Protochips Inc, based in Raleigh, North Carolina, to commercialize microfluidic chips for liquid STEM applications. Liquid STEM technology itself is currently under development and thus yet to be proven for commercial use at a larger scale. Some challenges that needs to be addressed are with respect to background noise and artifacts (contaminants) arising from liquid solution or the transparent windows that can reduce the signal to noise ratio in addition to the technology challenges associated with STEM such as image darkening (less material residing in the path of the electron beam). According to Niels de Jonge, the new Liquid STEM technique offers the potential to combine the ultrahigh resolution of electron microscopy while maintaining much of the functionality of a light microscope. Neisl De Jonge’s research group collaborated with Vanderbilt Institute of Integrative Biosystem and Research to develop the microfluidic chip, and also collaborated with Oakridge National Laboratory for the electron microscopy.

SEMICONDUCTOR NANOWIRES TO CONTROL LIGHT EMISSION FROM LIGHT-EMITTING DIODES

Driven by the strong industry focus to enhance capabilities and efficiency of LEDs, the LED market is constantly growing. The technology is tapping new market opportunities and expanding its presence from computer and consumer electronics to control lights in cars and lighting applications. However, while in some applications the broad angular light emission is a strong advantage; it is at the same time a limiting factor in other possible uses.

Interesting conclusions on the possibility of enhancing the performance of LED devices are provided as a result of the research conducted at the Institute of Photonic Sciences (ICFO), Spain. The project, aimed at examining the propagation of light through layers of semiconductor nanowires and nanorods, has demonstrated that it is possible to control the emission of light from arrays of nanowires by growing such structures in a specific pattern. In addition, it is possible to optimize the emission of light by placing the emitting segment at a specific position along the nanowires.

Arrays of heterostructured InP-InAsP-InP nanowires have been fabricated using the vapor-liquid-solid (VLS) growth mechanism by metal-organic vapor phase epitaxy (MOVPE). In the next step, the period arrangement of the nanowires, which form a 2D photonic crystal slab, is achieved by the means of nanoimprint lithography. These nanowires come in a diameter of 90 nanometers, and a lattice constant of 510 nanometers. Silke Diedenhofen, postdoctoral researcher at ICFO, told Technical Insights,"The nanowires are grown in a bottom-up process that requires a metal catalyst particle. The metal particles are structured by nanoimprint lithography. Nanoimprint lithography allows patterning of structures on wafer-scale in a cost-efficient manner. By choosing an optimum structure of the metal particles, the nanowires can be grown such that the emission of light has the preferred direction. By growing the emitting segment at a specific height of the nanowires, the emission of light can be further maximized."
The proposed technology is interesting as it provides a base for future improvement in the efficiency and directionality of LED emission. Diedenhofen said, "Our work is fundamental research aiming to understand light emission from nanostructures. There is still need for long-term nanowire research, before a nanowire LED will enter the market. For fabricating LEDs based on nanowires, not only the optical, but also the optoelectronic function has to be optimized." The proposed concept has a strong potential to be applied in a design of nanowire-based LEDs and single-photon sources with significantly enhanced capabilities.  

INNOVATIVE HIGH-SIGNAL-TO-NOISE RATIO OPTICAL AMPLIFIERS PROMISES EFFICIENT AND ENHANCED DATA REACH

The rapid proliferation of data and voice communications has begun to put strain on fiberoptic networks, and in turn on service providers to expand their capabilities to deliver larger amounts of data at faster speed to remote locations with increased quality. Although fiberoptic networks have stepped up to the challenge of delivering more and faster, with the ever increasing data heavy applications such as mobile TV, gaming and other applications it becomes imperative that the technology needs to keep evolving to handle these situations as well. Ideally, we need robust amplifiers to take noise free signals from the origin to the destination at rapid speeds. Currently, semiconductor optical amplifiers do the job of amplifying any optical signal that comes from either fiber and transmit an amplified version of the signal out of the second fiber. However, drawbacks of these amplifiers include high-coupling loss and also low signal-to-noise ratio.


To address these drawbacks, researchers from the Chalmers Institute of Technology in Gothenburg, Sweden, have developed new optical amplifiers that can help increase the reach of signals from current distance of 1000 km to 4000 km in turn setting the stage for low-noise data communications that can reach remote locations. The new amplifier technology can help in connecting countries or continents more efficiently, as the new optical amplifier will enable placing amplification hubs at bigger intervals compared to existing amplification hubs according to Peter Andrekson, who has codeveloped the low-noise amplifier together with his research group in fiberoptics at Chalmers Institute of Technology. The research paper was recently published in the journal, Nature Photonics. According to the research paper, authors claim that their phase sensitive amplifier can improve the signal to noise ratio by 6 db when compared to the conventional optical amplifiers, which can theoretically improve the signal to noise ratio only by 3db. Further, the researchers experimentally demonstrated an optic-fiber -based non-degenerate phase-sensitive amplifier link consisting of a phase-insensitive parametric copier followed by a phase-sensitive amplifier (PSA). The researchers attribute the success of achieving a low-noise signal to the copier--PSA cascade.

Researchers suggest using highly nonlinear fibers (HNLF) or silicon for the gain media due to their high efficiency and low-coupling loss. HNLFs were also used to create PSA. Although still in experimental stages, the new technology certainly promises a drastic improvement in increasing the reach of data, which is the need of the day. According to Peter Andrekson, the technology is also scalable to other wavelengths such as visible or infrared radiation, thus could find applications in spectroscopy, laser radar technology apart from the main telecommunication market. Commercialization can be achieved through active participation of private companies who are in need of this technology. To develop the current prototype, funding was provided by the European project--PHASORS, and the Swedish Research Council (VR). Participating partners in the EU project include University of Southampton, University College Cork, University of Athens, Eblana, OFS, One-Five Photonics, and EXFO Sweden AB.

Details: Peter Andrekson, Professor of Photonics, Chalmers Institute of Technology, SE-412 96 Gothenburg, Sweden. Phone: +46-31-772-16-06. E-mail: peter.andrekson@chalmers.se. 4. ENERGY-EFFICIENT POWER CONVERSION

The trend in consumer electronics is toward increased functionality and greater circuit density, which requires power supply ICs with power management functions that minimize power consumption while maintaining the necessary functions to protect the system from external interference. Power management ICs (PMICs) are used in electronic applications or devices to manage the voltage and current. These circuits can incorporate multiple functions for power management such as battery management, voltage regulation, charging and digital current to digital current (DC-DC) converters, among other functions.

Initially, power management was confined to linear power supplies, which are 30% to 40% efficient, bulky, hot, and unmanageable. Then came switch-mode power supplies (SMPS) with introduction to the pulse-frequency modulation (PFM) controller and pulse-width modulation (PWM) controller with hysteric control topology. As the complexity of a system climbs up the ladder, with as many as five voltage rails per processor, and with multiple processors per printed circuit board, power supply complexity goes up. These systems need tracking, sequencing and margining, coupled with tighter voltage regulations on voltage rails.

Spun out of Cambridge University, UK-based Cambridge Semiconductor Ltd., (CamSemi) is a developer of integrated circuits for advanced power management and conversion in energy storage and lighting applications. The company was founded to help manufacturers to find better, lower cost solutions to designing more energy-efficiency power conversion products. Its products aim to improve conversion efficiencies and reduce no-load values, as well as bring down system costs and component counts.

Flyback and self-excited converter (ringing choke converter [RCC]) are the two most common SMPS products, suitable for all regional input chargers and adapters. These products meet the market demand for energy, but are not ideal for low-cost and mass production of products. In particular, audio, cordless phones, and network equipment need a high level of design capability. Hence, many consumer electronics manufacturers do not want to introduce SMPS topology. However, with the emergence of CamSemi’s Resonant Discontinuous Forward Converter (RDFC), the device consumes less than 60 Watts. With a low-cost structure, such as a bridge, it can provide high efficiency, low-standby power consumption. In addition, the device has very low-electromagnetic interference (EMI) and the small footprint transformers reduce the demand for copper and steel.

CamSemi's products are based on its portfolio of patented and proprietary technologies including intelligent control architectures and ultrahigh voltage (UHV) process technology. These breakthrough approaches can benefit multiple markets, although initial products are targeted at the switch mode power supply and lighting sectors.
CamSemi believes that the next big wave in the offline-power-conversion space will be in lighting. Incandescent lamps are only 5% efficient, and will be phased out over the next five to 10 years. The company has accelerated the development of stand-alone controllers to bring those to market first while the intention of launching integrated products remains in the pipeline.