Impedance Meters & Impedance Spectroscopy

Electrical impedance spectroscopy enables the characterization of the electrical or dielectric properties of a device under test (DUT). In contrast to a pure DC or common mode measurement of resistance, electrical impedance spectroscopy captures the complex impedance - represented by magnitude and phase or real and imaginary components as a function of frequency. Depending on the field of application, one speaks of impedance spectroscopy, complex impedance analysis, AC resistance measurement or dielectric spectroscopy - but ultimately always the same is meant: the measurement of frequency-dependent complex impedances. The underlying electrical material properties include: Dielectric properties. They are a significant component of characteristic material parameters. This applies to all types of materials - technically used as well as biological, solid as well as liquid or gaseous. In many cases, the electrical properties allow drawing conclusions about the structural and functional properties of materials, components, but also biological tissues or even more complex entities such as organs. In addition to the analysis of existing structures or objects, electrical impedance is also frequently used as a mediating variable for sensors. While the target parameter to be detected is, for example, a gas concentration, a mass or the presence of certain pathogens, an electrical impedance is first measured at the sensor. In such cases, this is often not the impedance of the target object to be detected (e.g. the gas), but that of a "mediator" (also known as a "transducer"). This can be, for example, a functional layer on the sensor, which changes its electrical properties depending on the target substance. In this way, even elusive parameters become measurable with the easily manageable electrical measurement. The use of electrical impedance spectroscopy thus extends over a very wide field, from materials science and environmental sensing to the testing of technical components, bioanalytics and clinical diagnostics.

Examples of application areas

Bioanalysis - cell biological assays

From the smallest biosensor and point-of-care solutions to multi-channel biochip systems and massive multi-channel solutions for automated process control or pharmacological testing applications - scalability is in our genes. Bioanalytics have always represented the largest share of our use cases. The most typical representative are applications based on cell cultures - so-called cell-based assays. The cell cultures can either grow on substrates with electrode structures or be in flow-through (e.g. in microfluidic channels). Three-dimensional arrangements of cell clusters and electrodes are also becoming increasingly common, as is particularly relevant in so-called organ-on-chip applications. The electrical impedance of cell clusters or, in some cases, individual cells is measured. The electrical properties allow conclusions to be drawn about the structure or the physiological state. Dynamic physiological activity such as the "beating" of heart muscle cells (cardiomyocytes) or the typing of cell types in flow channels are also typical application scenarios for impedance spectroscopy. Specific derived parameters are often extracted from the impedance data - for example the TEER (trans epitelial electrical resistance) or growth parameters such as tissue density. The potential applications of such cell biological assays are far-reaching. Particularly exciting representatives are efficacy and tolerability testing of pharmaceutical agents and clinical diagnostics, e.g. phenotyping of risk groups for certain neurodegenerative or cardiovascular diseases. Sciospec has always worked intensively with specialized partners in bioanalytics and has developed numerous OEM products for this purpose over the years.

Medical technology - clinical diagnostics

Not only cell cultures and removed tissue have electrical properties that can be used diagnostically. Complex biological entities ranging from artificial organs to patients can also be examined with impedance spectroscopy. A particularly illustrative example is impedance tomography for monitoring lung and heart activity. Electrical impedance (typically viewed here as complex conductivity) is used to perform imaging analyses. This can be used to derive parameters important for artificial ventilation, for example, or indicators of impending traumatic events for lung and heart functionality.

Component testing

The testing of passive and active electrical components such as resistors, capacitors and miniature energy storage devices poses increasing challenges for their manufacturers. On the one hand, these components must be specified more and more extensively in data sheets, and on the other hand, it must be possible to verify these specifications in production. This results from the rapidly increasing requirements of electronic products for the mass market. Whereas a few years ago it was only necessary to install very precise components in the development of price-intensive products, now articles in the consumer sector with high quality requirements are also in demand. Whereas until a few years ago RLC test equipment with a single frequency measurement on a few samples per production batch was typically sufficient, today more and more components with complex frequency-resolved impedance characteristics have to be tested. In addition, test quotas have risen sharply: In the example of miniature energy storage devices, which are increasingly needed in the current IoT trend, test rates of 100% are required due to the electrical conditioning and susceptibility to interference. The combination of application-specific high-precision impedance spectroscopy and high channel count is an excellent fit for Sciospec's product portfolio.

Materials science

In the development and testing of materials, the electrical properties factually always play at least a secondary role, in many cases they are even the primary focus. Very typical examples are functional surface coatings, materials for the construction of technical systems or substrates for energy storage. Since the electrical properties are a decisive factor in determining how suitable a material is for a particular application, impedance spectroscopy plays an essential role during the development and production of the materials.