Multichannel Synchronous Real-Time Transcranial Magnetic Stimulation Magnetic Field Detection System Based on FPGA

In order to actually detect the spatial magnetic field generated by the transcranial magnetic stimulation (TMS) coil and to solve the problems of insufficient resolution, channel synchronization, and real-time performance of the detection results of the existing equipment, a multichannel synchronous real-time magnetic field detection system is proposed. According to the magnetic field, a three-dimensional sensor array of the human brain model is established, and the circuit structure of the multichannel data acquisition card (DAQ card) is designed. With the addition of signal triggering, up to 320 channels of synchronous acquisition can be achieved to ensure the detection of space magnetic fields. The design of sampling window is added to realize real-time transmission of data acquisition. The static error of the analog-to-digital converter (ADC) is calibrated by polynomial fitting, and the dynamic performance of the ADC is analyzed in the frequency domain. Finally, the performance of the acquisition card is verified by comparison experiments, and the actual magnetic field distribution is measured. The interchannel delay is less than 35 ns, the application of the sampling window reduces the data volume by
$600\times $
, and the data transmission time is controlled within 10 ms, which verifies the channel synchronization and real-time performance. Compared with the COMSOL Multiphysics (COMSOL) simulation test, the relative error (RE) is 1.22%, and the effective number of bits of the DAQ card can reach 11.5, which verifies the acquisition resolution and the accuracy of the acquisition results. The spurious-free dynamic range (SFDR) is 76.3 dB, the signal-to-noise ratio (SNR) is 70.0 dB, and the crosstalk is −81.9 dB, verifying its dynamic stability. The magnetic field detection system has strong practical application value in space multichannel synchronization, real-time acquisition, and acquisition accuracy. This system is of great significance for TMS magnetic field detection and related biological applications.