The Internet of Things (IoT) is a system of integrated computing devices or sensors that transmit data over a network. These devices can be controlled and monitored remotely. But how is this intricate network powered and sustained?
In January 2018, Perry Lea wrote Internet of Things for Architects on the best practices for designing and implementing IoT devices and sensors. This book outlines many of the problems associated with IoT technology and how various energy sources can mitigate those challenges.
Energy harvesting and power management constraints often dictate the most appropriate energy source to utilize when designing an IoT. Energy harvesting is a method of generating electrical energy from normally unused energy sources available in the surrounding environment. It is crucial that designers map out how power will be distributed throughout the device for tasks such as data collections and communications. They should also harvest and store excess energy for later use when energy inputs are low, or demand is high.
Solar harvesting, an increasingly common energy source, generates electricity by harnessing natural or artificial light. This process is environmentally friendly and best applicable to IoT devices and sensors located in consistently warm, well lit areas. However, indoor solar generation remains an inefficient process and direct sunlight can be unreliable as it is dependent on weather conditions and light exposure.
Piezoelectric energy is an alternative power source for IoT devices and sensors that utilizes motion, sound, and vibrations to generate electricity. This source applies Faraday’s law, which states that a changing magnetic flux across a wire coil will create an electric current. MEMS piezo-mechanical devices, electrostatic and electromagnetic systems are the most common forms of this power source. While it does not typically generate a sufficient voltage, piezoelectric energy is a scalable and cost effective solution when micro-machining and semiconductor fabrication is incorporated.
The biggest challenge associated with piezoelectric energy is that the energy must be conditioned before it can be used or stored. This process is usually performed by a passive rectifier with filtering capacitor.
RF Energy Harvesting
A widespread growth of wireless communication and electronics has prompted a significant increase in radio-frequency (RF) energy harvesting. Radio-frequency identification (RFID) tagging is often used for near-field communication while far-field applications require broadcast transmissions with radio, cell, and television frequencies. The biggest challenge associated with this energy source is that far-field RF signals have a relatively small energy density.
Thermoelectric modules (TEM) do not have any moving parts, operate 24/7 irrespective of bad weather, and do not require battery backup. This makes them an extremely reliable energy source. TEMs are also a cost effective solution for a wide variety of technology challenges.
IoT devices and sensors typically use batteries or supercapacitors to store energy. When constructing a device, it is important to consider the following:
- Available volume allowance
- Energy capacity of battery
- Weight constraints
- Required maintenance
- Storage needs
The most commonly used batteries are lithium-ion (Li-ion) because they have an efficient energy density and a lifespan of 10 years. Comparatively, alkaline batteries last approximately 5 years. The lifespan of batteries are dependent on the amount of degradation they experience. This process may be expedited if it is exposed to high-temperature environments.
Supercapacitors can store high volumes of energy quickly without the risk of overcharging. One additional advantage to this energy storage method is that it can report how much longer power will be available. However, supercapacitors require expensive materials such as graphene and can experience leakage current. They are often paired with regular batteries to reap the benefits of both technologies.
II-VI Marlow specializes in manufacturing cutting-edge thermoelectric energy sources for remote IoT devices and sensors. For more information, check out our products page.
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