Thermoelectric energy harvesting systems generate electricity from the temperature difference between the human body and the environment. Wearable devices equipped with thermoelectric generators (TEGs) or thermoelectric modules (TEMs) can harness this temperature gradient to produce electrical power.
Here's a basic explanation of how thermoelectric energy harvesting works in wearable devices:
Thermoelectric Effect: Thermoelectric materials exhibit a phenomenon known as the "Seebeck effect." When there is a temperature difference across a thermoelectric material, it generates a voltage. This effect occurs because of the movement of charge carriers (electrons or holes) due to the temperature gradient.
Wearable Placement: The wearable device is strategically placed on the body to take advantage of the temperature difference between the body's skin and the surrounding environment. For example, the device may be placed on the wrist, where the skin temperature is slightly higher than the ambient temperature.
Thermoelectric Module: The heart of the thermoelectric energy harvesting system is the thermoelectric module. It contains multiple thermoelectric materials, usually in the form of p-type and n-type semiconductor elements. These elements are electrically connected in series, but thermally connected in parallel.
Temperature Gradient: One side of the thermoelectric module is in contact with the warm surface of the body (e.g., the skin), and the other side is exposed to the cooler ambient environment.
Voltage Generation: As the body heat is transferred through the thermoelectric module, a voltage is generated due to the Seebeck effect. The temperature difference between the two sides of the module amplifies this effect.
Power Conversion: The generated voltage is then converted into usable electrical power. Thermoelectric energy harvesting systems typically incorporate power management circuits and energy storage (e.g., batteries or capacitors) to store and regulate the generated electricity.
Power Usage: The harvested electrical power can be used to run the wearable device itself, charge a battery, or power low-power sensors and components in the device.
It's important to note that while thermoelectric energy harvesting can produce some electricity, the power output is generally relatively low, especially in wearable devices due to their compact size and limited surface area for heat exchange. As a result, thermoelectric energy harvesting is often used in combination with other power sources, such as batteries or solar panels, to create more efficient and sustainable wearable devices. Nevertheless, the technology holds promise for capturing wasted heat and converting it into usable electrical power in various applications, including wearables.