Bioelectrical impedance spectroscopy (BIS) is a well-established and non-invasive method to
determine and monitor body composition. Commercially available bioelectrical impedance
systems use coated hydrogel-aluminium electrodes, where the hydrogel acts as an adhesive
and as an electrolytic medium. The gel/adhesive is physiologically inert over short periods.
However, when used over longer periods, hydrogel-aluminium electrodes present limitations,
which capacitive electrodes may overcome. First measurements using capacitive electrodes
have shown that commercial devices are not designed to work with these kind of electrodes.
The presented high impedance, specially at low frequencies (e.g. 5kHz), presents a challenge
for the current injection and therefore for the design of the current source. Within this
project, a bioimpedance spectroscopy (BIS) system to perform measurements using capacitive
electrodes has been developed. The system has been tested in the critical frequency
range, namely in the lower frequency range (5 kHz - 43 kHz). Measurements have been performed
using dummy electrical models, which simulate di erent values of skin and electrode
impedance. The results obtained show the better performance of the device in comparison
to a commercial device (Xitron Hydra 4200, Xitron Technologies) for that frequency range.
An important item in this thesis has been the design of a multi-frequency current source able
to perform measurements using capacitive electrodes.
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