Electrical Impedance Principles Measurement and Applications by Luca Callegaro
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Electrical Impedance Principles Measurement and Applications by Luca Callegaro

Motivation The interest in the accurate measurement of electrical impedance is shared by scientists and engineers from different backgrounds. Impedance measurements can be performed on an impedance standard, to perform a calibration and issue a calibration certificate. Electromechanical appliances and electronic components can be characterized by impedance measurement to identify the parameters of their equivalent electrical model. Properties such as resistivity, permittivity, and permeability of material samples can be derived from impedance measurements conducted with proper electrical fixtures.

Biological quantities related to a tissue, or even to a living being, can be related to their impedance. Sensors of many physical quantities can have electrical impedance as their output. Impedance spectroscopy permits to follow the evolution of an ongoing electrochemical reaction; impedance tomography is an imaging technique. Despite such broad range of existing applications, and the potential for new ones, high school and university courses show a marginal interest to the subject of impedance measurement.

Often, impedance measurement techniques are described as minor variations of the corresponding dc resistance measurements; recent publications may cite obsolete measurement techniques. Difficulties When performing an impedance measurement, the experimenter faces conceptual and practical difficulties that are not encountered in resistance measurements. Voltages and currents become geometry-dependent quantities, and different parts of the measurement circuit can interact in unexpected ways because of mutual capacitances and inductances. Even commercial impedance meters ask for careful wiring techniques, which may involve a number of conductors.

The measurement result can be expressed in a variety of representations, related by non-trivial mathematical transformations, prone to be misinterpreted. Outline Chapter 1 recollects main definitions of the quantities related to impedance, some theorems of particular interest, and the issue of impedance representation. Chapter 2 introduces the problem of impedance definition, electromagnetic ways to distinguish the impedance to be measured from the environment. Chapter 3 gives a list of devices, appliances, circuits, and instruments employed as building blocks of impedance measurement setups.

Chapter 4 attempts a classification of main impedance measurement methods, and for the most important give details on their implementation when a specific impedance definition is chosen. The increasing use of mixed-signal electronics in impedance measurement setups is discussed in Chapter 5. Chapter 6 gives a list of applications and some details on the measurement of electromagnetic properties of materials. Chapters 7 to 9 are devoted to impedance metrology. After Chapter 7, an introduction, Chapter 8 is devoted to artifact impedance standards, the material basis of measurement traceability. Chapter 9 deals with primary metrology: the realization and reproduction of SI impedance units. Limitations

The science of impedance measurement spans over more than 150 years, and even a condensed recollection of all important theoretical results, measurement methods and implementations is beyond the scope of the book and, frankly, of the author’s capacity. A large part of circuits reported are principle schematics; equations expressing a measurement model are reported without an explicit derivation. No operative measurement procedures or troubleshooting techniques are reported. No hint about the expression of measurement uncertainty is given.

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