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An impedance analyzer is a device that can measure how a particular substance or electrode surface responds to a a potential that is constantly increased and decreased within certain predefined limits (a potential wave).
Just like a potentiostat an impedance analyzer ensures that a potential is applied to a particular (liquid) substance, normally the applied signal of a potentiostat is stable, for impedance there is a small variation in the applied potential. This variation is a sinusoidal wave at an accurately controlled frequency and with a defined amplitude. For example, the PalmSens4 can apply sinusoidal waves with a frequency between 1 MHz and 10 μHz, the EmStat Pico can apply and measure sine waves up to 200 kHz.
Measurements with an impedance analyzer
The potential wave (Figure 1: blue) provides periodical potential differences between the electrode connected to the device and the object or (liquid) substance in contact with the electrode. This causes an electron current which also has sinusoidal waveform (Figure 1: green).
The impedance analyzer measures the difference between the maximum current and the minimum current (i.e. the height or amplitude of the waves), but also the time difference between the potential and the current wave-forms. This allows the calculation of the electrical resistance (or better impedance) of the liquid or object. If multiple frequencies are tested, single components and effects that are responsible for this resistance, can be identified.
Applications of an impedance analyzer
An impedance analyzer is mainly used for Electrochemical Impedance Spectroscopy (EIS) to investigate the electrical resistance (measured in Ohm) of substances and objects. A few examples:
- How resilient is a paint coating? In other words, how will a coating behave over time? Without an impedance analyzer a paint manufacturer could only reproduce the resilience of his coating in practice by long lasting exposure tests. However with an impedance analyzer it’s easy to predict the behavior for the next ten years with a short test. Read more about this on our Palmsens Corrosion website.
- How resilient is a concrete wall, does the steel in the wall not corrode too quickly? With an impedance analyzer you can predict in which type of concrete the steel corrodes faster.
- Measure the resistance of DNA of a particular cell. DNA always appears in double strands forming a helix. It is built up in such a way that the two strands of the pair match each other perfectly. If one strand is attached to an electrode, a coupling with the matching DNA strand is accompanied by a change in resistance. This can also be observed with an impedance analyzer.
Benefits of an impedance analyzer
The big advantage of an impedance analyzer is that it allows the user to perform tests without having to destroy the object. This allows a manufacturer to test any of his products before they actually leave the factory without actually using or damaging them.
A second advantage is the predictive value of tests that are made with the use of an impedance analyzer. An impedance analyzer test (a so called frequency scan) also does not take much time at all, while testing for corrosive properties by salt spray tests takes a very long time.
Sensors for an impedance analyzer
Many materials can be analyzed with an Impedance analyzer. In corrosion research the corroding materials are connected directly to the EIS analyzer. This is similar in fuel cell or battery research. In analytical chemistry, a number of sensors were developed that only change their resistance in contact with specific substances. Also modern biosensors are investigated using impedance spectroscopy.
Impedance analyzer software
An impedance analyzer is of no use without associated software. The PalmSens products all include their own easy-to-use software, which allows you to run experiments smoothly and then use the equivalent circuit fitting to get the all required information out of your data. If you prefer you can also use your own or third party spreadsheet software for creating charts.
Impedance analyzer prices
Impedance analyzers can be pretty expensive, with the PalmSens4 instrument and the Sensit Smart PalmSens managed to develop an impedance analyzer with outstanding specifications at a very competitive price.