Zero phase filtering for active compensation of periodic physiological motion

Abstract

Periodic physiological motions have been a source of disturbance to many medical interventions and diagnostics that require high precision. This paper presents a new method that performs zero phase filtering to extract a periodic signal within a predetermined frequency band. The basic concept of the proposed adaptive zero phase bandpass filter is to design a pair of cascaded lowpass and highpass IIR filters, such that the phase lag caused by the lowpass filter is balanced by the phase lead introduced by the highpass filter. Since phase angle of a IIR filter is frequency dependent, we adopt the weighted-frequency Fourier linear combiner (WFLC) algorithm as an adaptive frequency estimator to provide the instantaneous dominant frequency of the signal of interest to the system to adjust the filter coefficients to yield the required performance. The proposed filter is implemented in an experiment to perform active stablization of video images captured by a camcorder subjected to an oscillatory disturbance with varying frequency.