Solid-state, rechargeable thin-film energy storage devices are poised to significantly impact power-product OEM markets. Demand for this technology already exists, especially in wireless sensor networks where current battery technologies with limited service life and super capacitors with limited energy density and high leakage currents simply aren’t sufficient.
Necessity alone may not dictate the pace of invention, yet it does help provide funding and focus brilliant minds on overcoming immense technical challenges. That is certainly the case for this technology, and the year 2010 will mark the resolution of many of those technical challenges as commercial production of solid-state, thin-film batteries builds momentum. This will represent a huge step forward to the day of ubiquitous computing when electronic devices proliferate almost everywhere.
Many analysts agree that wireless sensor applications will be one of the first major markets for rechargeable thin-film batteries. One example is the growing demand for green lighting and temperature control systems where governments and private companies looking to lower energy costs are imposing regulations.
Other examples include factory automation, process control, machine health, and structural monitoring. Companies seeking to increase energy efficiency by retrofitting existing homes, buildings, factories, or equipment with wired networked solutions face significant and sometimes prohibitive installation cost challenges.
CHALLENGES AND A SOLUTION
Although wireless networks avoid the high installation costs of wired networks, they often come with a maintenance cost penalty. Lifespan limitations around existing, conventional battery technologies necessitate manual replacement of the batteries at each sensor node, typically within three to five years. The solution to this dilemma appears simple—develop an affordable micro power source that embeds into each sensor node and never requires replacement.
Overcoming the related technical challenges of such an ideal micro power source isn’t so simple. In fact, it requires three distinct technologies working together: ambient energy harvesters such as solar cells, thermal electric generators, and piezos; ultra-efficient power-management electronics; and a new type of long-lasting energy storage. The greatest development challenge of the three is creating an ideal battery technology that meets the long cycle life, low self-discharge rates, and power capability requirements of a wireless sensor node.
Depicting such a solution required some intelligent guesswork a few years ago. However, some changes are on the horizon. For example, the Infinergy micro power module (MPM) product family integrates three functional elements in a miniaturized footprint: near lossless energy storage, highly efficient power-management electronics, and regulated output voltage (Fig. 1).
For the energy storage element, the MPMs rely on solid-state, rechargeable, Thinergy micro-energy cell (MEC) components (Fig. 2). These devices provide energy storage with high continuous discharge currents (high when compared to coin cells), ultra-low self-discharge rates in the realm of less than 1% charge loss per year, and a cycle life beyond 10,000 cycles at 100% depth of discharge.
Further up the line, a passive power management unit (PPMU) serves as the arrangement’s power-management element. The ultra-efficient PPMU provides a simplified electronic interface between the ambient energy harvester and the Thinergy MEC. While charging the MEC, the PPMU circuit consumes less than 3 nA, allowing for charge efficiencies well in excess of 98%.
In addition to providing the raw battery output, the MPMs feature an integrated voltage regulator tailored to the requirements of the microprocessor and radio ICs deployed in a wireless sensor node. All together, the elements of an Infinergy MPM leverage energy harvesting to enable autonomous, perpetually powered wireless sensor networks.
EARLY ADOPTERS
Although the market is finally overcoming the technical challenges to perpetual micro energy, another obstacle remains in the energy-efficiency wireless sensor market: mass producing the new power technology at a suitable price point. This may result in early adoption by higher-value applications in end markets such as industrial, military, and aerospace.
For example, MECs and MPMs offer compelling advantages for a variety of applications requiring autonomy. Potential defense uses include unmanned aerial vehicles, smart weapons, self-destruct fuzes, communication devices, and structural monitoring. Other early adopters may include advanced medical devices, active radio-frequency identification and real-time location system (RFID/RTLS) tags, smart cards, and security systems.
As with other technologies, growing volume manufacturing, a further declining price point, and technology enhancements are certain to open up new applications, many of them unforeseen. With perpetual micro energy, there is the potential to realize ubiquitous sensing and computing.
Theoretically, designers can connect anything to anything else through intelligent tags and wireless networks, which means that almost every market imaginable from agriculture and toys to fashion is likely to feel the impact eventually. There were many years of development between the introduction of the personal computer and the arrival of the Internet, and the same will be the case with micro energy cells.
The year 2010 will see the achievement of important milestones for this new technology as volume shipments continue to ramp and more designers recognize the unique capabilities and benefits of technologies like MECs and MPMs over time. As challenges are overcome and commercial adoption proceeds, new standards, products, and applications will follow in first a trickle and eventually a flood.