Hi Melanie,

Thanks for your question on battery-less RFID (Radio Frequency Identification) sensors. What you described is more commonly known as an "Energy Harvesting" or "Energy Scavenging" sensors. There are numerous ways that these sensors can harvest ambient energy in order to not require a battery.

The First Law of Thermodynamics states that energy cannot be created nor destroyed, but can simply be transformed from one state to another. This is a simple law of conservation of energy. Photovolatic (Light), Piezoelectric (motion and vibrations), Electromagnetic (EM) and Thermoelectric (heat) energy can all be transformed into electric energy, and vice-versa.

So the RFID sensor you describe would have some sort of thermoelectric transducer to convert the energy from the thermal gradient in the ambient air to electric energy to power itself. Since these sensors typically don't require a lot of electric power to work, a small temperature difference would likely be enough to power it.

There are a few limitations with this type of device. First, what happens when there is no temperature differential to draw energy from? In order to provide reliable energy, the sensor should have some sort of energy storage system and the ability to condition the power to the proper voltage.

Cymbet makes a device called the "EnerChip" which takes these limitations into consideration. Tellurex also makes thermoelectric sensors, which according to their website are debuting this month. Also, there is a company called Perpetua that has also been developing this type of sensor.

Hope this helps! Good Luck.

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