|
|
Application of impedance spectroscopy for fish detection: Technical report project "Monitoring of aquatic life using a capacitive sensor array technique" Authors: M. Penkowski and B. Truyen Publication Date: Apr. 2006
Abstract: Electrical impedance spectroscopy is an important branch of biological impedance measurements. Biological cells are enclosed in biological membranes. The basic component of biological membranes is a lipid bilayer. Lipids are molecules with low conductivity. In the membrane, these molecules form a molecular bilayer with a hydrophobic inner part. The cell membrane, therefore, behaves as a dielectric interface. When an electrical field is applied, ions move and accumulate on both sides of the membrane. When the field is alternating above a certain frequency, ions have no longer time enough to accumulate. A polarisation relaxation occurs for frequencies on the order of several kHz. At lower frequencies polarisation of the whole cell can be observed.
The most reliable detection of living fish in water will be at a frequency range which is just over the relaxation frequency of the cell polarisation. Considering this fact, it is important to remember that penetration depth of the electrical field in a conducting medium is a reciprocal function of the frequency. Conduction of river water in estuaries can vary as the result of accidental pile up of sea water during storms. Hence, the detection range can be restricted by this factor, and sea water must be used for all estimations. Another problem is the polarisation of metallic electrodes, caused by the flow of electric current. Especially in the low frequency range, impedance of the double layer of ions can dominate the overall impedance.
|
|
