Implantable sensors that telemeter bioelectrical events have been developed based on a passive RF backscatter modulation technology. These devices operate at 915 MHz and 2.45 GHz and consist of only two active diode components. They are small enough to be injected into body tissue through syringe needles and depend on a dipolar microelectrodes that double as an antenna system for both receiving and transmitting.
The design strategy of these devices is to reduce the implant circuitry to only a few active components, power them directly with microwave or ultrasound energy, and then place the greater demands on external circuitry for amplification and control of the implanted device.
Schwert, H., Xu, W., Shekhar, S., Abbaspour-Tamijami, A., Towe, B., Miranda Chae, J.,. A Fully Passive Wireless Microsystem for Recording of Neuropotentials Using RF Backscatter Methods”,. Journal of Microelectromechanical Systems, vol. 20 no. 5, 1119 – 1130, (2011).