Designing a bio-implantable antenna in CST to obtain MHz resonance frequency involves several steps, including:

Here's a more detailed explanation of each step:

1. Defining the Antenna Specifications:

• Resonant Frequency: The target frequency range for bio-implantable antennas typically lies within the MHz range to minimize power consumption and tissue penetration.
• Operating Band: The antenna should operate within the allocated frequency bands for medical applications, such as the Medical Implant Communication Service (MICS) band or the Industrial, Scientific, and Medical (ISM) band.
• Radiation Pattern: The radiation pattern should be tailored to the specific application, such as omnidirectional for general communication or focused for specific tissue interrogation.

2. Modeling the Antenna Geometry:

• Accuracy: The antenna model should accurately represent the actual dimensions, material properties, and any internal structures to achieve reliable simulation results.
• Material Properties: Material properties of biological tissues, such as permittivity and conductivity, should be incorporated into the model to account for the interaction with the implant environment.

3. Setting the Simulation Parameters:

• Frequency Range: The frequency range of the simulation should encompass the desired resonant frequency and extend sufficiently to observe the antenna's behavior across a broader range.
• Excitation Type: The excitation type should be appropriate for the antenna configuration, such as a port for traditional antennas or a lumped port for electrically small antennas.
• Boundary Conditions: Boundary conditions should accurately represent the surrounding environment, such as perfect electric conductor (PEC) for external testing or a tissue model for in-body simulations.

4. Running the Simulation:

• Frequency Domain Simulation: Perform a frequency domain simulation to calculate the antenna's scattering parameters (S-parameters) over the specified frequency range.
• S-parameter Analysis: Analyze the S-parameters to identify the resonant frequency, which corresponds to the frequency at which the antenna exhibits maximum reflection or minimum transmission.

5. Refining the Design:

• Parameter Optimization: Based on the simulation results, adjust the antenna's dimensions, material properties, or excitation parameters to optimize the resonant frequency and radiation characteristics.
• Iteration: Repeat the simulation and optimization process until the desired performance is achieved.

6. Validation and Testing:

• Fabrication: Fabricate a physical prototype of the optimized antenna design using appropriate materials and fabrication techniques.
• Real-world Measurements: Perform real-world measurements of the antenna's performance, such as resonant frequency, radiation pattern, and impedance, to validate the simulation results.
• Refinement: If necessary, refine the antenna design based on the discrepancies between simulation and measurement results.

You have said this is a "magnetic induction communication-based antenna".

You need a coil, or other suitable magnetic antenna, not a patch. A patch matched for 25 MHz will be huge, even inside the body, or very inefficient.

Look up RFID at 13.56 MHz. It is magnetic induction communication-based. You should be able to use and adapt all that technology for your system, which is close in frequency. There are lots of application notes from various suppliers giving all the antenna parameters, how to design them and the power budget for the system.

See https://ww1.microchip.com/downloads/en/devicedoc/21299e.pdf for an example.

@Malcolm:I agree the way to do this is a magnetic dipole resonant.....do you really need a true antenna or just some sport of wireless coupler in the near field?

Fritz Caspers

You may already know this!

rfid in this band uses a very weakly coupled resonant air-cored magnetic transformer. Read the application notes - they are interesting and fun. It isn't an antenna. It is in the inductive near field, where the coupling is 1/r3. The tag is the secondary and receives enough power to turn on, and modulate its own impedance, which is detected as a very small impedance change in the primary. The system doesn't radiate (much), so it is like a toothbrush charger, but much more weakly coupled. Power goes into the tag, and is wasted only to losses in the primary, and to eddy currents in any surrounding metalwork.

@Malcolm: Yes I know this (since 50 years) but often some people call a device antenna which is not really one; thanks for you comment anyway.. good for student to better understand the context.