Energy harvesters generate electrical energy by various methods. To power an IoT device, an energy harvester is connected to a battery management module of the device and provide energy to the electronic components on the device circuit board including microprocessors and the radio modules. There are some common methods that an energy harvester can use to generate energy.
Solar Energy Harvesters
First, energy harvesters can generate electric energy from ambient lights such as solar and indoor lights.
Piezoelectric Effect Bases Energy Harvesters
Energy harvesters can also generate electrical power from motions or mechanical strains such as linear movements and vibrations. For example, this method can be used on some end devices that require a linear motion action to trip the radio transmission events such as the light switches and the door handles.
Energy harvesting can simply be explained as the process in which energy extracted from external sources is captured, stored, and used for multiple different uses. Some of these uses include wearable electronics and wireless sensor networks. Harvesting energy from outside sources has been and will be a large topic of interest over the next decade(s) as new and improved technologies emerge. Some current popular techniques are the use of light such as solar panels and water such as hydroelectric dams. In addition, the use of wind turbines has been over interest and use for years. On the different side of the spectrum, vibrational energy is beginning to spike increased interest.
One major sources of these comes from mechanical vibrations, in which these vibrations are converted into electricity. Current ways of doing this include the use of electromagnetic induction, piezoelectricity, and electrostatics. Piezoelectrics can be described as a subclass of asymmetric crystals, which create a small potential difference (voltage) when deformation occurs due a vibration(s).
Also, energy harvesting-based modules can power the end device mounted on a vibratory object such as a working electrical motor or an engine which usually has vibratory motions.
Thermoelectric Energy Harvesters
Next, thermoelectric energy harvesters can generate electrical power based on thermoelectric effects such as thermogradient formed between two different conductors. This can be used on the end devices installed on an object having two-sided surface with different temperatures or in other words, a double-sided surface with a cold surface and a hot surface.
Lastly, the ambient radio frequency signals can also be scavenged to provide electric energy to end devices. One typical example is the RFID tags on our credit cards where the tags harvest energy from the radio frequency signals sent by the card readers. The power is generated by the temperature difference on the hot surface of your coffee cup and the cold surface on the other side of the board.
There are many energy harvesters on the market and some can harvest energy from additional methods such as kinetic sea wave energy and they can be used in many applications.
In summary, energy harvesters are used in application-specific scenarios. So, the system design and network performance need to be carefully considered.