The widely held belief that billions upon billions of interconnected devices will make up the Internet of Things within just a handful of years rests partly on a parallel assumption: That many of these devices will be tiny sensors often deployed in far-flung places.
Such devices may only "light up" a few times each month or year, sending messages back to core systems, but still need to be on standby. That means they require extremely efficient and flexible power supplies. Researchers at MIT have just made what appears to be a significant advancement in this area, as the university's news office reports:
A sensor might, for instance, wake up every so often, take a measurement, and perform a small calculation to see whether that measurement crosses some threshold. Those operations require relatively little current, but occasionally, the sensor might need to transmit an alert to a distant radio receiver. That requires much larger currents.
Generally, power converters, which take an input voltage and convert it to a steady output voltage, are efficient only within a narrow range of currents. But at the International Solid-State Circuits Conference last week, researchers from MIT’s Microsystems Technologies Laboratories (MTL) presented a new power converter that maintains its efficiency at currents ranging from 500 picoamps to 1 milliamp, a span that encompasses a 2,000,000-fold increase.
The control circuitry for the switches includes a circuit that measures the output voltage of the converter. If the output voltage is below some threshold — in this case, 0.9 volts — the controllers throw a switch and release a packet of energy. Then they perform another measurement and, if necessary, release another packet.
If no device is drawing current from the converter, or if the current is going only to a simple, local circuit, the controllers might release between 1 and a couple hundred packets per second. But if the converter is feeding power to a radio, it might need to release a million packets a second.
To accommodate that range of outputs, a typical converter — even a low-power one — will simply perform 1 million voltage measurements a second; on that basis, it will release anywhere from 1 to 1 million packets. Each measurement consumes energy, but for most existing applications, the power drain is negligible. For the internet of things, however, it’s intolerable.
There's much more detail on the converter's design in MIT's full report. Overall, the design achieves a 50 percent reduction in the use of "quiescent" power—energy consumed while a device is essentially at rest—than previous ones, according to the researchers.
Looking forward, there will be opportunities to apply the converters to applications involving new kinds of energy sources, including body-powered electronics, they added.
The research was funded by Shell and Texas Instruments. It's not clear when the work will surface in commercial products, but it's the type of research crucial to the future of IoT, says Constellation Research VP and principal analyst Andy Mulholland.
"Power and batteries have been at the heart of every part of the computer revolution, starting from chip design through to the latest tablets and smartphones," he says. "However, all these devices work on a comparatively well-defined and limited set of power parameters. IoT has introduced a huge range of devices, all of which may have radically different power requirements. Freeing current constraints and inefficiencies in power is a hugely important part of the digital economy and that's what makes this research very encouraging."
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