A multi-channel high-speed magnetic field detection system based on FPGA for transcranial magnetic stimulation

Transcranial magnetic stimulation (TMS), a popular technology, acts on the brain by using a pulse magnetic field to cause a series of physiological and biochemical reactions. In order to detect the magnetic field generated by the TMS coil with high-speed and multi-channel performance, a novel magnetic field detection system based on a field programmable gate array (FPGA) is designed and implemented. The detection system includes an induction coil array, a data acquisition (DAQ) card, and upper computer monitor software. The DAQ card contains analog signal processing circuits, a multiplexer, an analog-to-digital converter, and a FPGA with a high-speed, parallel, and switching idea. The system can sample at a rate of 500 ksps, with 14-bit resolution and 12 channels. The three dimensional (3D) magnetic field can be monitored on the screen with a waveform display and 3D magnetic field vector display. The DAQ card has a good signal noise and distortion and cross talk of 88.35 dB and -79.69 dB, respectively. Compared with the NI DAQ card, the proposed system has a relative error smaller than 1.81% and a mean square error smaller than 2.89 × 10^-6, which verifies that the proposed detection system has a good performance. The multi-channel high-speed magnetic field detection system provides an important platform for the study of TMS in medical, engineering, and other fields.