Power Line Interference Cancelling in EEG Inspection

This paper presents a FIR adaptive filter to cancelling interference due to 50 Hz power line in human electroencephalographic (EEG) inspection. An overview of EEG techniques to study brain activity will be outlined. Then, the problem of spurious signal rejection, in this particular handset, shows the meaningfull application of adaptive filter structure. Poles of filter are driven to find an optimum bandwidth to eliminate noise. Least-Mean-Square (LMS) algorithm is used for adaptive process. Effect of finite filter length and non-zero response time, and their effect on time response will be also showed. I.Introduction Normal brain activity consist of a superposing of four types of “characteristic waves” denoted from greek alphabetical letter α, β, γ, δ. During an EEG exam, that shows these waves superposing, a very low amplitude periodic signal due to power line interference could be observed. So, an extraction signal method is necessary to preserve interesting biopotential. Figure 1: Characteristics brain waves Due to low levels of these signals, a fully numerical implementation of a detector and a filter is necessary, thus an adaptive FIR filter has been designed and simulated with typical EEG signals corrupted from this periodic interference. II. FIR system description This kind of system needs a couple of input signal: EEG observation, and a noisless reference signal input, that represents 50 Hz power line signals. Neverthless, noiseless signal is the goal, so the scheme in figure summarizes a choice for reference input obtained from primary input signal by a delay.