In my former posts, I discussed conditions for an Internet of Things (IoT) to become reality. Some of the aspects are still on a wish list. We will see the results only in several years. Nevertheless, there are already concrete developments that take the fast lane in the direction to a real IoT, for instance in the field of energy-harvesting wireless technology.
The specific characteristics of this technology enable sensors and actuators to work with an unlimited source of energy harvested from the surrounding environment, making them suitable for many IoT applications where flexibility and maintenance-free operation is highly requested.
Strong power sources are temperature differences, for instance. A difference of just 1 degree C (1 K) is sufficient to power a wireless sensor. A temperature difference of more than 10 degree C allows the operation of more elaborate wireless sensors to monitor and report conditions. The secret behind is an optimized combination of a Peltier element and a DC/DC converter. Standalone Peltier elements only produce very small voltages of about 10 mV per degree Kelvin.
Electronic circuitry connected to this, a sensor module for example, needs a typical supply voltage of 3 V. Therefore, a DC/DC converter is needed to complement the system. An optimized oscillator already starts to resonate upwards of 10 mV input voltage. On 20 mV or more (i.e. about 2K), a useful output voltage of more than 3 V is generated. For a temperature difference of only 7K, approximately 100 microwatts of energy is generated.
This kind of energy-harvesting principle is particularly interesting for predictive maintenance applications in the industrial sector. In production plants, virtually every unit of industrial machinery generates waste heat. Here, we find perfect conditions for the use of thermal-powered sensors. Typically, the temperature difference between the machine's heat and the cooler environment provides enough energy to realize a complete autonomous wireless sensor that measures and sends data twice a day. Some might now ask: only twice a day? Yes, this is sufficient for analyzing oscillation of bearings and for monitoring deviations from the normal status and irregularities of measured values. Such sensor systems achieve highly attractive scaling effects.