The Internet of Things (IoT) is gradually gaining importance in our everyday lives and it is set to become a real revolution. The technological barriers and limitations to its implementation are increasingly being overcome. One of these barriers is the use of sensors and their power supply. Let’s look at this in more detail here.
Importance and problems of IoT sensors
Kevin Ashton, creator of the concept of the Internet of Things, explained in one of his articles the need for computers to be able to collect data by themselves, to really give people control of their environment. Without this autonomous data-collection capability, the amount of information that people are able to feed into computers themselves is limited.
That is the mission of sensors in IoT: to measure a magnitude and, depending on its value, to act accordingly. The level of monitoring that can be achieved, as well as the type of variables to be measured, is growing day by day and is one of the essential components of any IoT system.
One of the problems faced by IoT sensor designers is power supply, especially in remote and isolated systems. Having sensors that use their own battery is an operational solution, but it has two major drawbacks: it makes the sensor more expensive and it reduces its lifetime, as the batteries live for a shorter time than the sensor itself. This leaves two options: either shorten the life of the sensor or design the battery to be replaceable.
Even for sensors located in places with access to mains power, using the mains power itself may not be the best option. For example, a sensor that monitors the opening of a door or window in a house as part of a security system. If such a sensor were powered by the house’s own power supply, it would present a strong vulnerability as it would be very easy to de-energise the house, and therefore the sensor, which would then be useless in terms of a security system.
There is a solution to all this problem: energy harvesting.
What is energy harvesting?
Energy harvesting is the process by which energy is absorbed from environmental sources (solar, wind, kinetic, etc.), captured and stored in small autonomous devices, such as IoT sensors or wearable objects.
The amount of energy that can be obtained by these means is very low in absolute terms, but for application in small devices that need very little consumption, it has potential. This energy exists in the environment around the devices, which would mean that they could be powered autonomously by drawing energy from their own environment.
The power consumption of many devices used as IoT sensors is between 0.1 μW and 1 W (remote sensors, Bluetooth transceivers, GPS systems, etc.), so it is achievable with energy harvesting technologies.
This is something that is already being used, for example in watches that are powered by the kinetic energy of a person’s movement. We also see it, albeit on a different scale, in the weather-measuring devices throughout the world, which use a small photovoltaic system to power their batteries.
The sources of energy from which it is possible to obtain power through energy harvesting are very varied, ranging from more common sources such as solar or piezoelectric to others that are less well-knows, such as vibrations, electromagnetic radiation, electrostatic, etc.
Energy harvesting in IoT sensors.
Returning to the aforementioned problem regarding the power supply of these sensors, an energy harvesting system could supply the batteries of these devices in situ, allowing them to operate uninterruptedly for the necessary time period.
These systems basically consist of 3 components: a dedicated transducer, an interface circuit with or without storage capacity and a receiver. The transducer is responsible for ‘harvesting’ energy from the environment and converting it into an electrical signal that the interface unit regulates and adapts to the receiver. If the device has a storage unit, the installation and initial power supply is simpler and the storage unit also provides a power safety net, however this is not strictly necessary.
Energy harvesting is therefore a technological solution that allows IoT sensors to be powered even in remote and inaccessible locations, eliminating the need for a fixed-charge battery as a power source. These devices could function properly with only a small storage capacity and by harnessing energy from the environment.
When designing such devices, we need to understand what kind of energy sources are available and which of them can provide enough energy to ensure the optimal operation of the device.
In this way, the life of the device would not be limited to the life of the fixed-charge battery, but until the device itself fails or is refurbished. To achieve this, in addition to the energy harvesting solution, other optimisations from the point of view of the device’s energy efficiency would also have to be considered.
For example, the energy demand of the sensor could be reduced by using communication systems that require less energy and allow information to be sent efficiently. Implementing sleep systems so that the sensor goes into a standby state as long as it is not needed and is only activated when it needs to carry out its function would also be another option. In this way, energy demand is reduced so that the harvesting systems are sufficient to power the device throughout its lifetime.
Which sectors can benefit from energy harvesting?
There are many sectors that can benefit from this type of technology. For example, in military defence devices, it allows the replacement of heavy batteries with autonomous or rechargeable devices, something that is highly applicable in drones, for example. In transport systems, vibrations can be harnessed to generate energy. In homes and businesses, energy harvesting will enable the further development of automation and smart homes. And, of course, the industry base will be needed to develop all these devices, which is a great market opportunity.
