Current Affairs in IoT

While estimates vary, it is generally accepted that around 15 billion Internet of Things (IoT) devices have been deployed worldwide. Many of these devices are mobile, or are widely distributed geographically in remote regions, as in the case of a vast network of sensors. In these cases in particular, powering the IoT devices can be a big challenge. Without being able to connect to the electrical grid, batteries are the most frequently used source of energy.

But batteries need to be recharged, and as they lose efficiency over time, they need to be replaced. When the number of devices under management is in the thousands, or even millions, that quickly becomes a logistical nightmare — not to mention the expense. These considerations have led developers of IoT solutions to look more closely at energy harvesting technologies in recent years.

Energy harvesting is the process of capturing and converting ambient sources of energy, such as sunlight, vibrations, or heat, into usable electrical power. Electrostatic generators in particular have captured a lot of interest for their noted ability to convert a wide variety of energy sources — like wind, waves, vibration, and human movements — into electricity. But while these generators have proven to be highly efficient, versatile, and inexpensive, they also have a critical flaw. They exhibit a high output impedance, which causes an impedance mismatch when paired with the electronics in a conventional IoT device. This, in turn, results in a very low efficiency level when powering these devices.

That may no longer be the case in the future, however, thanks to the efforts of a research team at Tsinghua University. They have developed an energy management unit (EMU) that substantially enhances the efficiency of electrostatic generators when powering electronics like IoT devices. When paired with one specific type of electrostatic generator, a rotary electret generator, 1.2 times greater power output was achieved. Tests with a triboelectric nanogenerator were even more impressive, with power output being increased by 1.5 times.

The EMUs key components include a buck converter, responsible for converting the high voltage, low current output from the electrostatic generator to a lower voltage, higher current output suitable for electronic devices. A spark switch, which is both highly efficient and reliable, controls the flow of current through the buck converter. Additionally, an input capacitor is integrated to enhance available charge, and an RF inductor facilitates high-speed energy transfer within the EMU.

To test the EMU, a self-powered wireless temperature sensor node was developed. Leveraging an electrostatic generator powered by wind, it was demonstrated that this node could wirelessly transmit sensor measurements every few seconds, even under light winds traveling at 0.5 meters per second. By efficiently using the harvested energy, the EMU could allow for large networks of sensors like this one to operate with little to no maintenance.

This advancement has the potential to make vast networks of distributed IoT nodes more practical than they have ever been. And by harvesting energy from ambient sources, it could also be a boon to environmental protection efforts.