Electrical bioimpedance spectroscopy in time-variant systems : Is undersampling always a problem?

摘要: During the last decades, Electrical Bioimpedance Spectroscopy (EBIS) has been applied mainly by using frequency-sweep technique, across a range of many different applications. Traditionally, tissue under study is considered to be time-invariant and dynamic changes activity are ignored treating as noise source. A new trend in EBIS simultaneous electrical stimulation with several frequencies, through application multi-sine, rectangular or other waveform. This method can provide measurements fast enough sample tissues, such cardiac muscle. high sampling rate comes at price reduction SNR increase complexity devices. Although technique often inadequate for monitoring variant system, it used successfully applications focused on slowly-variant part system. However, order use time-variant systems, paramount consider effects aliasing especially folding higher desired frequency e.g. DC level. paper discusses sub-Nyquist thoracic its case pulmonary oedema. It concluded that considering aliasing, proper implementation smoothing filters, well random sampling, assessing properties biological even presence aliasing. In general, undersampling not always problem, but does require consideration.