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The electrical impedance (Z) represents the opposition of an electrical circuit to alternating current as a complex number consisting of the amplitude change and phase shift. It is one of the most important parameters used to characterize electronic circuits and components, and also provides useful information in the study of electrode processes and complex interfaces in electrochemical systems. By applying a periodic small amplitude AC signal over a chosen frequency range and measuring the system response, the impedance spectrum together with a variety of related parameters is examined. These measurements can be performed either at room temperature or in bio-incubators over a wide temperature range (263 K – 363 K) using either a HP4194 Impedance/Gain-Phase Analyzer (100 Hz – 40 MHz), a HP4284 Precision LCR Meter (20 Hz – 1 MHz) or an IviumStat Electrochemical Interface and Impedance Analyzer (10 µHz – 2 MHz), depending on sample and measurement requirements.

The resulting Nyquist and Bode plots are for example employed in modeling the equivalent circuit parameters of complex electrical and electrochemical systems, the mapping of resonance characteristics in QCMs and MEMS, the study of DNA hybridization and denaturation and the read-out of protein- or MIP-based biosensors.