Energy Harvesting:

Powering Up

The Battery-Free World

Oct 31, 2010 23:58 ideyoshi Kume

Sensors and Microcontrollers, Too!

Sensors are another type of peripheral components evolving rapidly. Sensors designed to acquire information such as temperature and humidity are shrinking and consuming less power. The brightness sensors used to control lighting, for example, are being mounted on mobile phones now, and over the past few years current consumption has droppedto one-fifth. A source at Avago Technologies, Inc. of Japan says “We’ve confirmed that we can maintain sensitivity while suppressing noise, even running on low voltage.”

The microcontrollers used to control energy harvesting circuits and sensor drive are also showing up in lower-power versions. One widely used design is the MSP430, from Texas Instruments Inc. (TI) of the US, which sells for as little as US$0.25 apiece.

Fig. 5 Standby Current a Key Point
In applications such as wireless sensor networks, standby time is significantly longer than actual operation time. (Diagram by Nikkei Electronics based on material courtesy Renesas Electronics)

The key points in microcontrollers are a low standby current consumption, and a very short wake-up time. Operation is intermittent in almost all wireless sensor networks, so standby current consumption is crucial. A comparison of this characteristic alone shows that 16-bit microcontrollers from Renesas Electronics Corp. of Japan have current consumption low enough to put them at the very top of the list for candidates (Fig. 5).

Thermoelectric Conversion Devices through Thinfilm Technology

In addition to merely improving the characteristics of peripheral components, however, other firms are working on the generating devices that are the heart of energy harvesting. For example, a thermoelectric conversion device with high electromotive force has appeared. Slated for volume production start in 2011, the device comes in a small, thin package, and can get 140mV from a temperature difference of about 1°C. Conventional devices measuring several cm on a wide can usually generate only about 50mV.

Fig. 6 Miniature High-Performance Thermoelectric Converters
Micropelt has begun supplying thermoelectric conversion devices, and modules using them (a). Made with thinfilm technology, they can provide satisfactory generating capacity even in small sizes (b). (Diagram by Nikkei Electronics based on material courtesy Micropelt)

The device was developed by Micropelt GbmH of Germany. Wladimir Punt, Vice President, Sales & Marketing at the firm, is confident in the technology: “We are constructing a plant now that will be able to manufacture 10 million modules annually.” Engineers applied thinfilm technology to create a device combining small size with high efficiency (Fig. 6) Note 5).

Note 5) In manufacturing, n-type and p-type devices are sputtered individually on separate wafers, which are then sandwiched together in alternation.

Sourced & published by Henry Sapiecha

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