Energy harvesting technology has only become commercially available in the last few years and is enabling entirely new, energy saving applications in building and industrial automation. The first requirement for designing self-powered wireless products was the ability to scavenge energy from the surrounding environment. Energy harvesting has been around for centuries: after all, windmills, tide mills and water turbines have been extracting raw energy from the environment to generate power since ancient times. The second requirement was to use this energy for efficient communication between different devices. Again, likely solutions have been assumed for some time, with low power radio systems such as Bluetooth or Wi-Fi.
Bringing these two needs together was the challenge that researchers in Siemens laboratories took up in the late 1990s, when they turned their attention to scavenging tiny amounts of energy to power wireless systems. It was apparent from the start that existing technologies were not efficient enough to make them work reliably. What was needed was to bring three key elements together: effective energy converters, sophisticated electronics and software.
Having successfully identified the opportunity and potential solutions, in 2001 a new company –EnOcean- was established out of Siemens in order to exploit the new technology. EnOcean's wireless technology harvests the required power from the energy resources in the surroundings: motion, light or differences in temperature. The amount of energy obtained in this way is enough to transmit a wireless signal and turn on a light, for instance. These radio telegrams, just one millisecond in duration, use an optimum data rate of 125 kilobits per second. To eliminate transmission errors, each telegram is typically repeated twice in the space of 30 milliseconds. Furthermore, data packets are transmitted at random intervals, so the probability of collision is extremely small. Using the 868 MHz and 315 MHz frequency bands, this technology can be used just about anywhere in the world.
Wireless transmission distances can reach approximately 300m in the open and up to 30m inside buildings. A refinement with new self-powered wireless modules is their individually attributed 32-bit identification number, which provides over 4 billion unique IDs, to exclude any possibility of overlap with other wireless devices. Power conversion and radio transmission are complemented by sophisticated electronics and, most importantly, by intelligent software stacks that make it simple and straightforward to integrate the technology across a large variety of user applications.
In 2003, EnOcean commercialized its first generation of energy harvesting radio sensors based on piezoelectric powered modules. The second generation in 2007, which consolidated energy transducers, electronics and software, added the option of a new, more efficient means of mechanical power conversion – this time using miniature magnetic coils instead of piezoelectric devices. In the next few months, EnOcean is going to market with its third generation of mechanical converter (ECO 200), with further improvements in the efficiency of energy conversion, in noise emission and fully automated manufacturing. Here, the magnetic flux permeating a coil is abruptly reversed as soon as a spring mechanism reaches a snap-over point and causes iron parts to move.
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