RE-VOLT – Now is the time to join the Battery-Free IoT Revolution

By Masoud Zargari, Co-founder and Vice President of Engineering at Atmosic Technologies

It is believed that throughout the universe, more complex structures require denser flows of energy in order to maintain their complexity. This manifestation of the second law of thermodynamics — and its evil cousin entropy — applies to galaxies, stars and planets as well as the little civilization we’ve built in our neck of woods. While the second law of thermodynamics has sparked many philosophical debates throughout history, our focus here is on its simple yet daunting ramification: an exponentially increasing demand for energy to fuel our civilization.

Recent technological advances have not only intensified the need for energy, but also changed the forms in which we demand energy. The convenience offered by portable devices and wireless connectivity has increased the worldwide battery consumption to unsustainable levels. By some estimates, in just a few years there will be over 35 billion connected devices worldwide, most running on some form of battery. If we conservatively assume only 10% of those batteries need to be annually replaced, it will translate to over 3.5 billion disposed batteries every year… and the party is just beginning!

At Atmosic Technologies, we are fundamentally addressing this increasing demand for batteries by significantly reducing the power consumption of connected devices, so their batteries are drained less frequently and in turn last much longer. More importantly, once the power consumption of connected nodes is dramatically reduced, they can potentially run off harvested ambient energy from the environment. This means that a low power wireless node can run completely from sources such as radio frequency (RF) signals, in-door lighting, thermal gradient, or motion. Alternatively, the energy gathered from the environment can supply a regular trickle of current to the battery so that the device can operate longer between charges.

RF Energy Harvesting

The RF energy beamed from an RF transmitter can be picked up by a receiver at a faraway distance and, if this detected energy is large enough, it can be used to power up the receiver electronics. Although nowadays there are many sources of RF energy such as Wi-Fi routers and cellular devices around us, the overall ambient RF energy in a typical environment hardly gets large enough to be viewed as a reliable source to power today’s connected devices. However, if dedicated RF sources are strategically placed in the environment, they can beam RF power to a specific wireless node that is placed at a reasonable distance making the available RF energy at that node to be much higher than what is otherwise available in the ambient. This so called “controlled harvesting” can then be used as a reliable method of powering remote devices.

Controlled RF energy harvesting is especially useful in powering up electronics wirelessly in scenarios in which it is hard or impractical to replace batteries in a deployed wireless network. It is also useful when the network is deployed in difficult to access areas as in many industrial environments. RF Harvesting has the advantage that it can be available anytime when needed by simply turning on the RF source.  The frequency of the RF signal can be anywhere within the unlicensed frequency bands of several 100s of MHz to several GHz. The lower the frequency the longer the range of the RF power transmission. However, lower frequencies demand proportionally larger antenna sizes for the harvester which can become a limiting factor in applications where the size of the harvesting node is constrained.

Photovoltaic Harvesting

Since the development of the first silicon-based solar cell in the 1950s, the photovoltaic technology has been dramatically improved. Today’s advanced solar cells have better durability and efficiency and can produce larger output voltages for a given light intensity. The electric power generated by a solar cell is directly proportional to its size. However, the generated power can vary drastically depending on the intensity of ambient light. The same solar panel can produce up to a 1000 times higher power under direct sunlight vs. in a typical indoor office environment. Solar panels are not exactly color blind either meaning that they will behave differently under different indoor sources such as incandescent, florescent and LED lights.

Thermal Energy Harvesting

A thermoelectric generator (TEG) is a solid-state device that generates electricity by exploiting temperature gradient in the environment. The amount of generated power depends on the temperature difference as well as the amount of heat flux that can be successfully moved through the TEG device. The better the TEG construction is at moving heat from the hot side to the cold side and dissipating that heat once it arrives to the cold, the more power will be generated. Because of the need to maintain a temperature gradient, thermoelectric energy harvesting solutions can require larger form factors compared to other form of harvesters in order to generate useful amount of energy.

Motion-based Energy harvesting

There are two types of motion-based energy harvesters: (1) the more traditional ones using a coil and magnet and (2) the ones based on piezoelectric effect.  The coil and magnet-based harvesters can generate electric energy through the physical movement when a switch is flipped or when a door knob is turned.  These types of motion-based harvesters are usually bulkier due to the size of their required components: a coil, a magnet and frequently a spring. Piezoelectric energy harvesters generate electrical energy from mechanical strains, either in the form of continuous mechanical motion/vibration, or from intermittent strains such as clicking of a button. Because their small crystalline structure, piezoelectric harvesters are relatively small and light compared to other energy harvesting devices.  However, their generated power can vary significantly depending on how regular and frequent the motion is.

Atmosic M3 Bluetooth 5.0 SoC platform supports controlled RF energy harvesting as well as photovoltaic, thermal and motion-based harvesting. In particular, a fully integrated single IC with RF energy harvesting can provide small form factor battery-free operation up to a distance of several meters from the RF source.

While no one can defy the second law of thermodynamics, or any other law of physics for that matter, we can certainly create meaningful solutions that provide less pain to the IoT users and less harm to our environment. This is the first step in the journey. This is the time to RE-VOLT. This is the time to join the battery-free IoT revolution.

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