Mart Min

Aspects of Using Chirp Excitation for Estimation of Bioimpedance Spectrum

Short frequency swept signals, known as chirps, are widely used as excitation or stimulus signals in various areas of engineering as radar and sonar techniques, acoustics and ultrasonics, optical and seismological studies, but also in biomedical investigations, including bioimpedance measurement and impedance spectroscopy (Muller & Massarani, 2001; Misaridis & Jensen, 2005; Barsoukov & Macdonald, 2005; Nahvi & Hoyle, 2009).

Simple Signals for System Identification

Event accessible for observation can be investigated by examining timeline of certain measureable values. Usually the process is referred to as time domain analysis of signals. Such a signal can be of many different origins. It could be comprised of values of electrical current or voltage, mechanical displacement or force, value of stock or popularity of politicians, reaction of the patient to medication, and essentially anything which is observable, measurable and quantifiable with reasonable accuracy. Observer will quite intuitively search for certain patterns and periods in signal if phenomena changes along the timeline. Some of them are easily detectable, such as periodic variation of the suns activity; some might appear as random fluctuations at the first glance, such as parameters of the seismic waves in Earths crust. Of course sources of noise and other disturbances are usually omnipresent and will make matters much more difficult to observe and explain.

Improved extraction of information in bioimpedance measurements

A wideband bioimpedance measurement method is proposed, which can enhance the interpretation of measurement results due to the improved resolution of monitoring. On the other hand, the corresponding measurement system uses a binary chirp waveform for excitation signal, which simplifies the signal processing hardware and does not require sophisticated software. It is shown that the binary chirp excitation has some essential advantages compared to its counterpart – the maximum length sequence (MLS) excitation.