Abstract
Electrical bioimpedance entails the measurement of the electrical properties of tissues as a function of frequency. It is thus a spectroscopic technique. It has been applied in a plethora of biomedical applications for diagnostic and monitoring purposes. In this tutorial, the basics of electrical bioimpedance sensor design will be discussed. The electrode/electrolyte interface is thoroughly described, as well as methods for its modelling with equivalent circuits and computational tools. The design optimization and modelling of bipolar and tetrapolar bioimpedance sensors is presented in detail, based on the sensitivity theorem. Analytical and numerical modelling approaches for electric field simulations based on conformal mapping, point electrode approximations and the finite element method (FEM) are also elaborated. Finally, current trends on bioimpedance sensors are discussed followed by an overview of instrumentation methods for bioimpedance measurements, covering aspects of voltage signal excitations, current sources, voltage measurement front-end topologies and methods for computing the electrical impedance.
Highlights
ELECTRICAL bioimpedance is a technique that has been applied in a wide range of biomedical applications for detection of pathologies and adverse physiological events and for the monitoring of physiological processes and tissue dynamics
In [73] the electrode impedance at 0.2 Hz became ~2.7 times smaller following electrophoretic deposition of multi-walled CNT (MWCNT) on stainless steel electrodes. It was reported in [74] that higher concentration suspensions and larger voltages lead to more homogeneous films, with uniform film thickness and higher film quality achieved with 10 μm final film thicknesses
This can be done without considering the sensitivity theorem and by varying the electrode geometry or arrangement and investigating the effect of frequency and conductivity/permittivity changes to the total simulated measured impedance [6], [13], [14], [107]
Summary
ELECTRICAL bioimpedance is a technique that has been applied in a wide range of biomedical applications for detection of pathologies and adverse physiological events and for the monitoring of physiological processes and tissue dynamics. As it will be discussed in more detail in subsequent sections, bioimpedance involves the measurement of the electrical properties of tissues and cell populations from a few Hz to a few MHz. One or more frequencies may be of interest depending on the application. The instrumentation required is somewhat more complicated as a signal needs to be generated to excite the biosample to obtain its required electrical properties as a function of applied signal frequency This signal needs to be known and, in most cases, it is kept constant, such that there is only one measurand needed to calculate the impedance using Ohm’s law. Can be deposited on the electrode surface to improve its interfacial impedance properties This tutorial paper provides holistic discussions on all matters necessary for the design of bioimpedance sensors and an overview of bioimpedance instrumentation.
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