When people refer to the emerging Internet of Things (IoT) phenomenon, they usually refer to the increasing amount of information being generated by sensors and controllers interfacing with a "thing" and being sent to the Internet somewhere. For example, a thermostat (the thing) continuously sending temperature readings to a server (the internet). Another example would be a motion sensor that continuously analyzes the vibration of industrial machinery (thing) and sends a notification to a server (internet) when the vibration seems abnormal.
Sometimes, these things need to be wireless and are basically inaccessible (inside a sealed casing or deep inside a machine), where it would be impractical to charge them by USB. This means you either need a large enough battery that will last for the product's entire expected lifetime. However, placing a large battery in a limited space to be able to make a single sensor last for years is not always possible or practical.
This means you need to harvest your energy from the ambient environment to power your device. How does one do that?
Electric energy can be converted from kinetic energy using what is called the piezoelectric effect. Using piezo elements, which are materials that generate electricity when vibrated or tapped, energy can be harvested from the surrounding movement in a device's environment.
If the product or device in which the electronics is embedded vibrates, moves, or gets pressured with enough force and speed, it can be produce enough power to feed most of today's low-power radio microprocessors and sensors. Even if there is not quite enough movement to provide constant power to a system, there are methods to store the energy in a large capacitor or battery for later use.
Photovoltaics is another important method of ambient energy harvesting. Photovoltaics is the conversion of light into electricity using semiconducting materials. Although solar panels are mostly used to produce electricity to power homes and factories, there are small and cheap photovoltaic panels that exist that made to power electronics.
A bright sunny day is more than enough to power some of the most (relatively) active electronics. This means that if you have a device that resides outdoors and only needs to poll a sensor every second, it is entirely possible to feed it with a few photovoltaic cells. The only downside is that you will need to account for cloudy, rainy days as well as nighttime. This is where you will need a small battery or a large cap to balance out the off-hours when there is little sunlight or none at all.
Wireless Inductive Charging
Wireless inductive charging works by generating an AC signal in a coil so that it induces a similar electrical signal in another closely placed coil, effectively creating inductive coupling between two coils. Wireless charging is usually meant for situations where you need to charge a device's battery but don't want to necessarily plug it into a device (putting your phone on a wireless charger platform, for example). The same applies to a wide range of low-power electronics where it can charge itself if you drop it in the right spot on your living room table. In an energy harvesting context, wireless charging becomes interesting when you want to power a device that would otherwise be solely powered by other means such as light or vibrations but are simply not available at that moment.
This post was written by our former employee Alexander Courtemanche.
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