Sensor applications that normally rely on battery power, especially wireless sensors, are limited by the battery's life or its need for recharging. Using power available from the environment, such as mechanical energy from vibration and wind, sunlight, or temperature differences, several companies are changing the rules for system design.
Energy harvesting, or scavenging as it is frequently called, relies on conversion techniques that include piezoelectric, RF, inductive coupling, thermo-electric and photo-voltaic cells, and wind-powered generators. Although some techniques have been used for many years, the need for alternate energy sources for both high power applications and for much lower micro-power applications (replacing or supplementing batteries in wireless sensing and monitoring) has spurred considerable interest.
In its "Energy Harvesting, Micro Batteries and Power Management ICs" report, Darnell Research, a provider of strategic information regarding power electronics, forecasts that the total global market potential for energy harvesting in sensing and other applications in the automotive, home and industrial automation, medical, and military/aerospace industries could grow from13.5 million units in 2008 to 164.1 million units in 2013.
Structural health monitoring for bridges and aircraft has garnered considerable attention recently. Other industrial applications, such as machinery condition monitoring, also can benefit by harvesting energy to power wireless sensors. Automotive is perhaps one of the largest single markets for energy harvesting. This should be no surprise since automotive has been one of the largest markets for sensors for many years. Wicht Technology Consulting (part of the market research firm iSuppli), in its market briefing #7, predicts that energy harvesting in tire pressure monitoring systems (TPMS) will grow from 100,000 units in 2011 to 60 million units in 2015.
Active research in the area of energy harvesting by the U.S. government and many universities could propel the technology into many different applications. Geothermal, solar (including photovoltaic technology), and wind power are part of the National Renewable Energy Laboratory's (NREL) research efforts. Other national labs, such as Los Alamos National Laboratory are exploring applications and evaluating technologies for Structural Health Monitoring (SHM) and other uses.
Researchers at Georgia Institute of Technology are investigating the use of fiber-based nanotechnology in clothing. Pairs of textile fibers covered with nanowires, when woven into a shirt or jacket, could allow body movement to power a range of portable electronic devices. Current estimates indicate that a square meter of fabric made from the special fibers could theoretically generate as much as 80 mW.
Advanced research is not confined to government and universities. Researchers at independent research center IMEC and IMEC-NL at the Holst Centre are also active in the energy harvesting area and have generated 40 µW from a micromachined piezoelectric energy harvester.
Energy harvesting is already a reality in one of the newest consumer products: the photovoltaic cell in Iqua's 603 Sun Bluetooth headset uses available light from the sun and indoor lighting to power the transducer and extend the operation time of the headset.
Energy Harvesting Systems
The energy conversion technique is the key ingredient but not the only one in an energy harvesting sensor system. In addition to low-power sensors, products rely on low-power parts, such as microcontrollers and RF components.
At Sensors Expo 2008, the Energy Harvesting Symposium will explore energy harvesting techniques, associated circuitry, and sensing applications in addition to examining existing real-world products. With input from companies active in making energy harvesting an enabling technology—including KCF Technologies, Inc., Advanced Cerametrics, Inc., Perpetuum Ltd, Smart Material, Corp., GreenPeak Technologies, Microchip Technology Inc., MicroStrain, Inc., IMEC, Enocean, Wicht Technologie Consulting—this session should provide attendees several ideas for improving next generation products or creating new ones.
Session Organizer Randy Frank is President of Randy Frank & Associates, Ltd., a consultancy that focuses on sensors, power and automotive electronics. Randy is a Society of Automotive Engineers (SAE) and an IEEE Fellow, author of the book Understanding Smart Sensors, 2nd Edition, and former board member of the IEEE Power Electronics Society.