Design Of Cortical Potential Acquisition System

In brain function research,electrocorticography(ECoG)has been widely used because of its unique advantages,such as high spatial resolution,low noise,and large signal amplitude.At present,there are few domestic commercial instruments in the field of cortical potential signal acquisition.In order to investigate the performance characteristics of flexible microelectrodes array in acquiring cortical potential signals,a multi-channel cortical potential acquisition system applied to flexible electrodes array has been designed.At present,the advanced instruments for cortical potential acquisition on the market are mostly from foreign companies,which are relatively bulky and expensive.Most small domestic acquisition devices mainly used for acquiring Electroencephalography(EEG)which have lower frequency and smaller amplitude.The difference of these two signals is due to the different acquisition mode and position.However,cortical potential signals have higher frequencies,and higher spatial resolution than EEG,and it contain more disease information.Now the common-mode rejection ratio(CMRR)of an EEG acquisition device in the market is about 110 dB with 2 μVpp noise,and the bandwidth is generally 0.5 Hz 100 Hz.Therefore,the main purpose of this thesis is to design a high-performance multi-channel acquisition system applied for cortical potential acquisition.This system mainly includes hardware circuit design and software design.The analog circuit extracts weak physiological signals submerged in the common-mode signal and passes through the next stage of amplification and filtering.Digital circuits are responsible for high-speed processing and transmission.The most difficulty in circuit design is to increase the CMRR and reduce noise.Software design includes embedded software design,PC software design,and data processing program design.A real-time filtering algorithm was designed on the embedded software and PC software to filter 50 Hz power-line interference.Refer to the JJG1043-2008 "Verification Regulation of Electroencephalograph" to test the system performance.The CMRR is about 120 dB,and the band-width is about 0.5 Hz 300 Hz.The total system noise is less than 1 μVpp.Subsequently,ECoG experiments were carried out.The Local Field Potential(LFP)and Steady-State Visual Evoked Potentials(SSVEP)signals were collected simultaneously by this system and commercial instruments to evaluate the system performance.Then,by acquiring cortical potential signals with different types of flexible array electrodes,this system can obtain ECoG with higher Signal-to-noise ratio(SNR)utilizing flexible capacitive electrode.Due to the insulating properties of the capacitive electrode,it can ensure a higher safety and avoid the stimulation of rat cerebral cortex.The above results prove that the cortical potential acquisition system in this thesis can effectively acquire high-quality cortical potential signals.This device can be used for more brain scientific research applications.