FID Frequency Extraction Engine

In the current market, magnetic brain imaging is extremely expensive, with MRI machines and magnetically shielded rooms costing upwards of millions of dollars. We are the Magnetocephalopods, the developers of the FID Frequency Extraction Engine designed for Fieldline Inc. Our product computes and displays in real time the frequency of an analog sinusoidal input to a high precision and with low noise. With the help of Fieldline’s Free Induction Decay Magnetometer, this could allow us to measure the magnetic field produced by the brain without a magnetically shielded room.

Our product, the FID Frequency Extraction Engine, receives an analog sinusoidal input from a source (e.g., signal generator, FieldLine’s FID Magnetometer, etc…) and outputs the calculated frequency of the input sinusoid. The intent of the product is to interpret the signal output of the FID Magnetometer made by our sponsor, FieldLine Inc. Since current brain imaging techniques are expensive due to the use of magnetically shielded rooms, Fieldline Inc. wishes to operate their product within the Earth’s magnetic field. FieldLine’s Magnetometer contains Rubidium-87, which produces an oscillating signal depending on the strength of the surrounding magnetic field. It is sensitive enough to detect the magnetic field generated by brain activity (10 fT). To properly measure the brain's field within the Earth’s magnetic field, the frequency of oscillation due to the Earth and the brain’s combined field must be calculated. 

The signal is first filtered with a 200-500 kHz bandpass filter to remove wide-band noise. It is then digitized with the LTC2209, 16-bit, 160 MHz ADC. The ADC output data bus connects to a CMOS buffer to improve performance. The output of the CMOS buffer is then sent to an Altera Cyclone V FPGA (5CEBA4F17C8), where it uses a zero crossing algorithm to determine the frequency. This algorithm works by counting the number of clock cycles between the zeros of the input signal, then finding the average of an integer number of periods of the input signal. This computer period is then transmitted to an external machine via a UART-USB bridge. The received UART data is then processed using a Python script and is displayed in near-real time with a live plotter.

 FieldLine Inc. – Magnetic sensing and imaging solutions

https://www.colorado.edu/ecee/fid-frequency-extraction-engine