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Be it under the umbrella of Internet of Things (IoT), Smart Buildings or Smart Cities; Sensors and the data they produce are making our society more energy efficient. However, in a world full of sensors are we making sure the sensors themselves are energy efficient?

At present, 80% of the energy consumed by the sensors is used by the wireless connection. So the first logical step in making sensors more energy efficient, should be to reduce the amount of data they send. This can be done by processing and interpreting the data on the sensor itself, only sending the condensed results to the cloud. However, processing on the chip also consumes energy, so there is an optimal balance between on-chip processing and sending data to the cloud, in order to maximise energy efficiency.

RFID

Another element of additional edge processing is the extra computation power needed, thankfully recent advances in chip technology are ideal for integrating more powerful processing on the current small chips. On the other side of that coin, in the analogue world, we still need to add analogue interfaces to sensors, which don’t scale as well in the newest technology nodes.

Advanced micro-electromechanical systems (MEMS) were a key talking point of CES in 2016. MEMS sensors are already “the eyes and ears” of advanced technical systems and are used in tablets and smartphones. These sensors from major manufacturers like Bosch are getting smaller and smarter, and crucially, they are becoming more energy efficient.

Market reports suggest that 1.44 billion new smartphones were sold in 2015. About 76 million smartwatches and fitness armbands were launched into the market in 2015, and their sales are estimated to reach 173 million by 2019. All of the gadgets mentioned here use increasingly smaller and more efficient sensors capable of evaluating numerous types of data. The popularity of these devices is advancing the technology and driving down the price, with obvious implications for the Building Internet of Things (BIoT).

“For Bosch, this means huge potential business”, said Dr. Volkmar Denner, CEO of Bosch, earlier this year. Going forward, he said, Bosch is aiming to create systems, which can absorb energy from its environment via a technique known as energy harvesting. Such technology could change the whole sensor efficiency debate.

Meanwhile, Dutch researchers have created a tiny temperature sensor powered entirely by radio waves that could revolutionise smart building infrastructure. The sensor requires neither batteries nor wires, doing away with the major obstacles for more widespread adoption of Internet of Things technology in the built environment. All the sensor needs is a wireless network.

At merely two square millimetres in diameter and about as heavy as a grain of sand, the temperature sensor has been described as the world’s smallest. The team from Eindhoven University of Technology squeezed a tiny radio antenna into the device that receives radio waves from a tailor-made router to use as energy.

According to Peter Baltus, Professor of wireless technology at the Eindhoven University of Technology, the radio wave-powered sensors offer an ideal solution for smart buildings of the future that will have every aspect of their operations regulated by sophisticated systems capable of recognising the actual needs of their occupants.

Battery requirements are seen as a major obstacle in such buildings peppered with hundreds and thousands of such sensors. The researchers estimate that once mass-produced, the sensors wouldn’t cost more than 20 cents per piece.

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In the US, researchers at the Massachusetts Institute of Technology (MIT) have created a new circuit design that could lead to more power-efficient sensors. The new circuit design reduces transistor leakage by passing a negative charge through a set of capacitors and switches during idle time. The negative charge effectively banishes electrons from the electrical leads, reducing the conductivity of the silicon and also the opportunity for leakage.

The MIT team tested a chip based on the new design and found it used only 20 picowatts of power to save 10,000 picowatts that would otherwise have been lost to leakage. “A key challenge is designing these circuits with extremely low standby power, because most of these devices are just sitting idling, waiting for some event to trigger a communication”, explains Anantha Chandrakasan, Professor in Electrical Engineering at MIT. “When it’s on, you want to be as efficient as possible, and when it’s off, you want to really cut off the off-state power, the leakage power”.

In the sensor rich world we are racing towards, it is essential we keep the efficiency of the actual sensors in mind. While the energy use of a single sensor pales into insignificance next to the inefficiency issues they seek to solve, it would be counter productive to flood the world with billions of sensors that could themselves be much more efficient. And rather than the Internet of Everything, perhaps we should be striving for the Internet of Only What Is Actually Beneficial.