Wireless power and data transfer was achieved for an implanted medical device to directly stimulate injured nerves in a rat model. A small receiver coil implanted in rats was able to receive 27 volts of power wirelessly from an external transmitter coil. Circuitry including a voltage cap and low pass filter processed the received power and transmitted voltage data readings to an external receiver using an XBee chip. Stimulating the rats' sciatic nerves at different frequencies using the implanted receiver coil allowed determination of the voltage needed for stimulation and observation of the rats' recovery progress over time. This simple wireless power and data transmission design could enable various implantable medical devices to be powered and monitored clinically in a minimally invasive manner.

1. Introduction: In medicine there is a need for wireless data and power transfer from implanted medical
devices. One useful application in particular could be direct nerve stimulation. In patients with peripheral
nerve injury, monitoring their recovery is important. By stimulating an injured nerve directly, it is possible
to more easily quantify functional nerve recovery. Doing so wirelessly with an implant could be less
invasive and lower the risk of infection. Inductive coupling was the method used for power transfer with
the thin film wireless power receivers. Models for nerve stimulation to possibly aid in nerve recovery
were examined in rats.
Materials and Methods: Wireless power transmission was achieved using Red Rock Laboratories WiRe
product. It is a small implantable wireless power receiver coil that was equipped with tuning capacitors
and a diode. A class E oscillator controlled the transmitter coil, and a signal frequency was established by
either a function generator or a 555 timer circuit. The transmitter and receiver coils must be within a few
centimeters of each other and in the proper orientation to transfer a significant amount of energy.
Determining voltages based on rats’ position was found using a receiver coil attached to a small PCB with
an XBee for data transfer. A receiver XBee was attached to an arduino microcontroller to process data.
The PCB also contained components to make up a low pass filter and a voltage cap. Receiver coils were
incased in silicone and implanted in rats. Medwire platinum-iridium lead wires were attached to the rats’
sciatic nerves. Sciatic nerves were crushed or cut to simulate injury. The rat’s nerves were stimulated at
various frequencies (up to about 80 Hz when tetanus occurs). Rats’ reaction to nerve stimulation was
observed at several intervals post operatively.
Results and Discussion: The 14 mm receiver coils are able to receive about 27 volts while under no load.
This is too large for the XBee chip so a voltage cap was implemented before the signal was sent to the
XBee. There is also a low pass filter to eliminate noise from the circuit and the carrier frequency from
being transferred. The XBee system gives data about how much voltage is being induced on the receiver
coil. When the rats’ sciatic nerves are stimulated from an implanted receiver coil and XBee circuit it is
possible to determine the exact voltage at which they are being stimulated with the proper implanted
circuit.
Conclusions: Given the simplicity of the receiver coil’s design, they could also be applied to powering
and charging other implantable medical devices. Using the XBee chips as a model, wireless data transfer
out of implants is also possible in a clinical setting.
Figure 1. Schematic diagram of
the backpack and implant circuit
containing an XBee for data
transfer.
Figure 2. Rat walked
under a transmitter coil
with backpack containing
XBee circuit.
Figure 3. 14 mm receiver coil
compared to penny.