Advances in sensor hardware, software, power management, and networking are propelling wireless communications technology to new heights. Unfortunately, with these advances technical and economic issues have emerged and need to be addressed if the technology is to continue gaining speed. Self-powered wireless-sensor network nodes would be the holy grail of wireless communications. Until then, designers must figure out how to manage sensor power at ultra-low levels. Energy-scavenging is a popular solution to minimize power consumption, if not eliminate it altogether. There’s no “one size fits all” solution for all of the industries that can benefit from energy-harvesting—fortunately, there are numerous designers taking strides in all sorts of ingenious ways, as revealed at the Sensors Expo & Conference, held June 11-13 at the Rosemont Convention Center in Illinois. Creating an efficient wireless node is a true tightrope for designers. First they have to choose a winning combination of wireless mesh technology and protocols. Then they have to integrate this into viable solutions to suit different markets like industrial, commercial, medical, building automation, transportation, avionics, military, and automotive applications. But that’s not without a silver lining. Market analyst firm Wicht Technologie Consulting (WTC) predicts a $200 million worldwide market for energy scavengers in 2009, and to the victor goes the spoils. Energy management and conservation Before they can spread to these markets, wireless networks need to improve the bottom-line by getting them to operate using less energy and function more efficiently. For example, there are two parallel efforts heavily embedded in the industry and academia to improve energy consumption in tire-pressure management systems (TPMSs). One track seeks the development of more efficient and longer-lasting batteries, while the other chases greater use of energy harvesting. Sometimes these technologies are used in combination. According to Dr. Jeremy E. Frank, president of KCF Technologies, the typical battery life for wireless sensors varies between three and 18 months, depending on the application. He estimates life-cycle cost savings for present-day wireless sensing are at least three-times higher than the installed sensor’s cost, estimated at $1000 to $3000. KCF is currently working to develop low-cost vibration power harvesting for industrial wireless sensors through the U.S. Department of Energy’s (DOE) Small Business Technology Transfer Research (STTR) project. KCF works closely with several Penn State University teams including the Power Electronics Lab and Center for Acoustic Vibration as well as G.E. Global Research and Omega Piezo. Other major development teams such as GE, Honeywell, and Eaton are also working with the DOE to develop products for energy and cost savings through wireless sensors. KCF completed the design of its first line, the VPH100 (Vibration Power Harvester), and has moved on to testing its vibration-scavenging technology and engineer a second generation product. First- and second-generation demonstrations were performed working with Johnson Controls, RLW Inc., and ExxonMobil. KCF’s latest pet, being third-generation VPH technology, will supplement current VPH technology next year (take a look at VPH technology here ). Harvesting around the horn MicroStain Inc., a supplier of smart wireless microminiature displacement, orientation, and strain sensor modules recently demonstrated the first successful flight test of energy-harvesting wireless sensor nodes for rotating helicopter parts and other critical components. The sensors help engineers track damage on these parts. Kavlico/Schneider has studied different energy scavenging techniques and concludes that it is very application-specific (see the table). They believe that good low-power sensor designs working in conjunction with a specific energy-scavenging and harvesting method may be the answer. An example of this design approach is the company's sCap3 battery-less capacitive digital-output MEMS-based pressure sensor for TPMSs. It consumes just 60 µW. In the Netherlands, energy harvesting is a serious objective. Working with the Netherlands Organisation for Applied Scientific Research Building and Construction Research (TNO), semiconductor giant IMEC created the Holst Centre to investigate self-powered wireless sensing technology. The institute’s Wireless Autonomous Transducer Solutions program includes ultra-low-power dissipation electronics, ultra-low-power DSP technology, micropower sensors and actuators, and integration and implementation of IC functions among its goals. Philippe Mattelaer, Holst Centre’s business development manager, says that advances in battery densities have not kept pace with other relevant technologies for wireless communications (To see the chart, click here ). The centre has demonstrated successful approaches to electrostatic and piezoresistive energy-harvesting approaches (take a look at the technology here ). One of the most advanced developments at the Holst Centre has been the demonstration of a moderately complex biomedical sensor that’s fully powered by body heat using thermoelectric energy scavenging from a wrist-mounted thermoelectric generator. The researchers devised a self-powered wireless pulse oxymeter system that draws an average of 62 µW and works from 89 µW from its generator source. It uses a commercial finger sensor that measures the user’s pulse. The Georgia Institute of Technology has been working intensively with nanotechnology as a solution to energy harvesting. Researchers there recently demonstrated a prototype nanometer-scale generator that produces continuous dc power by harvesting power from mechanical motion, ultrasonic waves, and even blood flow. Based on arrays of vertically aligned zinc-oxide nanowires that move inside an electrode with a zig-zag pattern, the generator can produce nano-amperes of current (view the technology here ). The researchers expect the device, when optimized, to produce as much as 4 W/cm3. EnOcean, Ubiware, Powercast, Perpetuum, and other firms are developing a variety of energy-scavenging techniques—some with commercial products on the market and others with products in the testing, pilot, or developmental stages. Better battery technology? Lithium battery companies like Tadiran, Varta, and EaglePicher are eager to answer these demands by developing newer battery technologies with micro levels of power consumption and longer lifetimes. Invariably, though, batteries must be replaced—and that means maintenance costs. Steve Simon, engineering vice president for R&D at mPhase Technologies Inc., believes that battery technology advances aren’t keeping up to meet the needs of new applications in electronics. His firm is working on a silicon-based nano-battery that uses silicon dioxide, zinc, and a hydrophobic coating (view the technology here ). This battery’s long list of favorable features includes a long shelf life as well as high power and energy densities. It also can be selectively activated for primary, rechargeable, and reserve battery applications. It is easily scalable, and can be easily integrated with other electronic devices. Also, it can be mass-produced with existing equipment, and it can be assembled using a wide range of chemistries.