Antenna design and communication module architecture for fully implantable micro ECoG Device

This is my part of the group final project for the Implantable Medical Devices (IMD) class that I took in Fall 2022 (EE 597) with Dr. Mehdi Kiani.

The objective is to design and simulate the core components for a design of a fully implantable wireless micro Electrocorticography (ECoG) device. The device aims to solve common ECoG disadvantages such as bulkiness, high invasiveness and a need for cables and meet clinical constraints such as ease of implantation, longevity, safety and small size

Structure

We designed and simulated the main elements of an IC for ECoG recording using a 3-coils power transfer module, a telescopic cascode amplifier, a clock generator for independent control over multiple amplifiers and a set of antennas for wireless communication with minimal occupied area and specific absorption rate (SAR).


My focus and efforts were mostly regarding the wireless communication system between the implanted chip and the outside chip.

Antenna design

The antenna is a crucial component for having efficient data transmission without loss and use of cables and permitting the full implantability of the device.
When designing an antenna it is important to consider several aspects:
Because of these reasons we decided to use silver since it is a highly conductive and biocompatible material.


Simulink Antenna Toolbox was used to design the three antennas shown in figure 5.1: one implanted 1 cm deep, between the skull and the dura, one applied at skin level to act as a middle coil and a third applied at 1 cm from the skin to deliver energy to the other two coils and connected to an external IC.

Electric Field

To simulate the propagation of the electric field through the brain, I used MATLAB to recreate a human head modelled as planar layers with different densities and conductivities. The antenna shape was chosen to be spiral shaped with one or two arms depending on the size and s11 parameter optimization to resonate at 406 MHz.

SAR analysis

To simulate the Specific Absorption Rate of the transmitter antenna I wrote a MATLAB code that given a set of 3 antenna designs realized with the Antenna Toolbox extracts the gain, power and electric field of the antenna and simulates the intensity of the electric field through the different tissue layers of the head and the absorption rate in W/Kg to make sure that the tissue heating follows FCC regulations (<1.6 W/Kg).

Wireless module architecture

The wireless module was designed with the idea of using backscattering to send information to the external system continuously. In this way less power would be consumed to communicate between the devices and there wouldn’t be the need to use packaged data as well as big on chip storage for the data.


When the data is received from the ADC converter it is first encoded through a Miller Encoder to separate correctly each value in an efficient way that is quick, easy and doesn’t occupy excessive bandwidth compared to other encoding methods such as Manchester. The encoded information is then sent to the ASK (Amplitude Shift Keying) modulator which converts the bits into variations of amplitude in the signal which is then sent out through the implanted antenna.
On the receiver side, the signal is received by the external antenna and separated from the sent-out power from a directional coupler. The data received is then amplified, passed to the mixer and filtered to remove frequencies above and below the frequency range of interest (considering a bandwidth of 10 MHz, 401 MHz – 411 MHz). Finally, the signal is decoded and sent to an ADC which converts it to digital signal.

Team members

The project was performed with:

• Mitch Tang
  
• Fan Yang
  
• Zhiyu Zhang