The benefits of RF Energy Harvesting

The Internet of Things burst onto the global tech scene a few years ago with a world of expectation attached to it - tall claims were being made about how it was going to change the world and connect practically every object in the world to the internet. Many wild predictions were made on how huge IoT was going to be. For instance, when Cisco predicted an astronomical 25 billion connected devices by 2015 and twice that by 2020, there were quite a few skeptics. And as if to validate the skepticism, actual numbers of connected devices fell considerably short of these numbers.

Of the biggest implicating factors was the power bottleneck that plagued the Internet of Things and prevented it from unleashing its full potential. Powering billions of IoT devices using traditional means was simply unimaginable. The key selling points of IoT networks - economy, convenience, and reach - were being undermined by the prospect of having to power billions of nodes using batteries. It just didn’t make any sense. 

It was obvious that the IoT revolution needed a more elegant power solution and fast! Granted there are green power solutions that were already well established, but they didn’t quite fit the bill for powering tiny microcontrollers and sensors. The need was for a green energy source that would accommodate the very specific needs of IoT edge devices. 

It is in this context that energy harvesting technologies offer so much promise. They make it possible for us to conceive of IoT solutions that are not limited by the constraints of using batteries, of which there are many - problems of maintenance, recharging/replacing, the size and weight of batteries, and most importantly, the grave environmental cost of relying on batteries. 

Energy harvesting to the rescue

It has now started becoming increasingly clear that IoT solutions of the future can’t rely on batteries. Globally, there is an ever-mounting pressure to find more ecologically sustainable power sources. In the search for the elusive power solution that is green, limitless, and sustainable, we’ve happened upon quite a few solutions that never lived up to the mark. The search to find a large-scale power solution that is cheap, reliable, and eco-friendly, is still on and is likely going to take a while. After all, powering the enormous industrial-economic engine of the modern world is no mean task. When it comes to powering IoT devices though, we seem to have found the holy grail - energy harvesting technology. 

The premise is quite simple actually - There is a colossal amount of energy in the environment around us, most of which is going unused - Why not find a way to harvest some of this energy and use it to power small devices? 

Energy harvesting is essentially predicated on this simple yet powerful idea. Energy harvesting has become hugely popular in recent years and as such, there are a variety of viable, commercially scalable energy harvesting options such as piezoelectric harvesting, RF energy harvesting, etc. available in the market today. 

In addition to the relatively more established forms of energy harvesting, there have been a host of new energy harvesting modalities that have emerged in recent times, which have not yet been brought to market in a commercially viable form. However, this just goes to show how much interest energy harvesting is generating globally and the magnitude of expectation being placed on it as the holy grail of IoT power solutions. 

RF energy harvesting - the basics

Radio Frequency Energy Harvesting (RFEH) is an exciting technology that has sparked tons of interest in recent years, especially in the IoT world. Even in comparison to other energy harvesting technologies, RF energy has some key attributes that make it particularly suitable for use in wearables, ultra-low-power electronics, IoT edge devices, microcontrollers, and wireless sensor networks (WSNs). 

RF energy harvesting essentially means converting ambient electromagnetic energy into usable electrical power. This ambient energy could be any kind of radio wave such as those emitted by TV/FM stations, WI-Fi routers, phone towers, or radar. 

Just this basic understanding of what RF energy harvesting is should give you a fair idea of why it’s attracting such huge bets as a green power solution - radio waves are ubiquitous in today’s world and there’s simply no getting away from them. Moreover, radiofrequency harvesting is particularly suited for the unique demands of IoT devices - they tend to be small (even nano-sized) and are often designed to operate in extremely harsh, remote locations. In many cases, sensors are part of embedded systems such as health monitors or other industrial solutions, which makes them inaccessible for maintenance or battery replacements. 

This makes RF energy harvesting a near ideal power solution for IoT devices. One other factor that makes them score heavily over battery based power solutions is that RF energy is essentially free energy! Using batteries, no matter how cheap or long lasting they are translates to a prohibitively high lifetime cost. Servicing, recharging, or replacing batteries over an entire IoT operation, containing hundreds or even thousands of sensors doesn’t make much economic sense. 

RF energy harvesting applications, on the other hand, are designed to be self-sustaining cost effective. They tend to require little to no maintenance over many years and often throughout the entire lifetime of the application. 

How does RF energy harvesting work?

Depending on the intended functionality and specifics of the particular application, RF energy harvesting systems can vary in their design. There are several methodologies for constructing RF energy harvesters - fundamentally though, all energy harvesting systems are based on a few general components and working principles. 

All energy harvesters contain a transducer or a harvester which collects and converts the energy from the source into electricity. The next indispensable component of energy harvesting systems is the energy storage unit, which could be a capacitor. 
The third component of an energy harvesting system is the one that deals with the management of the power that is generated. This part of the harvester conditions the electrical energy into a form that is ideal for the specific purpose that the device is intended for. Typically, conditioners may include regulators and complex control circuits which can intelligently manage and distribute power based on real-time power demand and the availability of power. 

The basic structure of an RF energy harvesting system is organised along similar lines - An RF energy generator typically consists of a receiving antenna, matching circuit, peak detector and voltage elevator. The antenna plays the role of a transducer and captures electromagnetic waves. The matching circuit amplifies the voltage of these waves as required and then, the signal is converted to a pre-determined voltage value by the peak detector. Finally, the voltage output is calibrated using the voltage elevator. This system is usually linked to a power storage device and a power management system which is responsible for managing the power use.
Energy harvesting circuits are meant to work with relatively small amounts of power, i.e. small voltages and currents. Therefore, it is imperative that these systems use modern technology to achieve very high energy efficiency. There is no room for transmission losses in energy harvesting systems, where the entire operation usually generates only a few microwatts of energy. 

Another key feature that RF energy harvesters need to have is tolerability. They need to be able to operate with a wide variety of voltages and currents due to the irregular nature of their operating conditions. Because there is a lot of variability involved in their power source, (i.e. ambient electromagnetic waves) it is essential that they are resilient enough to handle inconsistent operating conditions. 

Advantages of RF energy harvesting

1. Near universal supply

This one’s a no-brainer. There’s electromagnetic waves all around us, thanks to how ubiquitous computing devices and mobile/internet networks have become - this means that RF energy is essentially free energy that is waiting to be tapped into at any given moment. It is difficult to overstate the relevance of this fact - as we’d mentioned earlier in the post, the single most important reason that curtailed the growth of IoT to its predicted full potential, was the fact that there was seemingly no economically and ecologically sensible way to power them. RF energy harvesting essentially solves the problem of power availability.

2. Control 

To be fair, this one follows as a result of the previous factor but is nevertheless a major plus that RF energy has over other modalities. Because of the free and widespread supply of RF waves, it is possible to have a high degree of control over the energy input.

RF energy harvesting allows for precise calibration of the reception according to specific needs of the application. 

3. Cheaper

One can’t stress this point hard enough - RF energy harvesting is orders of magnitude more economical, in the long term, compared to battery based solutions. You don’t need to be a rocket scientist to figure out why - firstly, there’s the cost of manufacturing batteries and a higher BOM (Bill of Material). Then, there’s the inevitable maintenance cost of batteries every few years. Even the longest lasting battery eventually needs to replaced or recharged, 

RF energy harvesting eliminates all these costs in one fell swoop. Over the lifetime of an IoT operation, which may include thousands of sensors placed in several inaccessible and harsh locations, there’s simply no contest between an energy harvesting based solution and batteries. 

4. Can be used to augment battery life

Where power demands are high or of a nature that demands the use of batteries, RF based technology can be incorporated into the solution in order to support and recharge batteries. 

They can significantly extend the life of the battery by providing an alternative to manpower-intensive methods of maintenance and recharging. Naturally, this would make economic sense across an industrial scale operation and would add up to large cumulative benefits over a period of time. 

5. Versatile 

RF energy harvesting scores heavily over batteries in yet another way - batteries don’t just make for a more expensive and tedious solution by necessitating replacements and maintenance - thanks to the size and weight involved in batteries, they limit the number of applications into which an IoT device can be integrated. 

With wearable technology booming and many other IoT sectors quickly catching up, the need of the hour for IoT devices is complete versatility - RF energy harvesting makes it possible for IoT devices to have this flexibility. Because there are no bulky batteries involved and no need for battery slots and recharging. RF energy based IoT devices can easily be integrated into extremely small and unique devices, which are designed to operate in extremely inaccessible locations.

Let’s take the example of an implant or a healthcare-focused IoT device that’s designed to operate in the bloodstream or in some other location within the body - it wouldn’t make a lot of sense for this device to require battery replacements or even periodic maintenance, no matter how long the service interval is.

RF energy harvesting allows IoT to truly do justice to the breadth of its scope by making a potentially huge range of IoT enabled products possible.

5. Eco friendly

Batteries are a huge contributor to the ongoing environmental crisis. Lithium-ion batteries are considered hazardous and disposing of them safely poses a huge challenge. The worst part is that it’s not just the disposal - mining for minerals like cobalt and lithium leaves a disastrous imprint on the land and can have spine-chilling health effects on the local populace. 

RF energy harvesting offers a viable alternative that circumvents all these environmental shortcomings that batteries come with.