RFID Transponder

Early Project Design Goal:

The main goal I had when joining HOPE was to undertake a project on a topic I knew very little about. With absolutely NO prior experience with high frequency circuit systems and antennas, pursuing wireless communication was a daunting task, but one I was excited to take on.

The Design Journey:

Fortunately, the actual circuit design isn't too complicated to understand and the function of each component is easy to identify:

Antenna: Facilitate Near Field Communication (NFC) by enabling magnetic coupling between transponder and transceiver

Varactor (tunable capacitor): Fail-safe to ensure impedance matching regardless of imperfections and error

Writeable NFC Chip: Process incoming waveform under magnetic coupling and harvest magnetic energy

De-coupling Capacitor: Ensure no energy is lost during contact

The Design Challenge:

I quickly realized how delicate this project would be, there are many factors that have to be taken into considering when dealing with wireless communication. By far the greatest challenge I faced was developing an antenna that would actually enable RF communication. The physical parameters of the coil affect the impedance of the antenna and have to be designed and calculated precisely.

Impedance Matching:

After tediously creating the antenna layout which followed the physical parameters I calculated, I had to ensure that the overall output impedance would be able to reach resonance at 13.56 MHz (NFC Frequency). In order to increase the chances that I would be able to achieve this, I added a variable capacitor to be able to tune the output impedance of my circuit and adjust the resonance frequency if needed.

The Final Product:

The project was an overall success! The board is able to interact with NFC readers as a write-able NFC transponder. This means this device can interact wirelessly with the majority of modern phones!