BECAUSE

LINEARITY MATTERS

Bio-Logic’s range of quality indicators are valuable tools that help researchers validate their experiments and ensure a long-term approach to quality as well as help them make the right research decisions.

Dr. Aymeric Pellissier, EC-Lab Product Manager, describes the benefits and the origins of this suite of validation functionality software, a range of tools unique to Bio-Logic’s EC-Lab control software.

Accurate measurements are often dependent on a number of factors dependent on their objectives, including a need to guarantee steady-state conditions, linearity and a noise-free environment, so when it comes to EIS, the measurement recorded by your Potentiostat/Galvanostat may not necessarily be the right one, and the data has to be validated before any important decisions are made.

Bio-Logic’s range of quality indicators was born out of this research need and we now have three quality indicators in place, the first of which was THD.

THD: A project born from customer needs & Bio-Logic know-how

The starting point for this quality indicator functionality began when Dr. Bogdan Petrescu, Senior Scientist at Bio-Logic, attended a major international EIS conference. During one of the breakouts, Dr. Petrescu gained some interesting feedback from a group of researchers who were unanimous in their need for a reliable EIS validation tool.  At the time, the tools that existed to test impedance results had serious limitations and offered no real strength-in-depth (Kramers Kronig, or Lissajous, for example, will tell you when a measurement is incorrect, but will not necessarily detect any linearity issues or give any quantitative data). Similarly, such was the need that a number of clients had even reported to us that they had tried to develop their own, in-house validation tools, but these projects had met with limited success.

Thus, a seed was sown for the development of Bio-Logic’s first quality indicator, THD.

The efficacy of THD is widely recognized in academic circles and the technique has the added advantage over Lissajous of being simpler to execute (the technique requires inspection of a Lissajous figure at each frequency, as opposed to just one point for THD).

Energy, materials and corrosion: the benefits of THD

THD can add value to a wide range of applications, but energy is one where it has special relevance because of low cell impedance (even the slightest variation in voltage will induce a large current response -U=RI).

Researchers can therefore find themselves walking a scientific tightrope, where tiny deviations in voltage can send impedance values away from the linearity response. Corrosion and materials are similar such applications where THD can add significant value, green lighting values when they are correct, and alerting researchers to problems when the experiment is going off-track.

Linearity Matters…but so does non-stationary distortion, noise and transient regime…

Whilst Bio-Logic’s THD quality indicator had solved the problem of linearity, Dr. Petrescu realized that the EIS puzzle would not be complete without similar tools, which would work in parallel with the THD indicator for non-stationary distortion and noise.

In addition, while the answer to the problem of linearity had been solved with an existing technique (Bio-Logic had automated, but not invented the technique for Total Harmonic Distortion), he knew that he would have to invent a new solution for non-stationary and noise issues. This led to the creation of two additional quality indicators, unique to Bio-Logic software:

  • NSD: (Non-stationary distortion) indicates the effect of time variance of cell parameters and transient regime
  • NSR (Noise to signal ratio) ensures that the signal is large enough in relation to measurement noise.

The combination of these tools now enables users to quickly, and efficiently validate EIS data make the right research decisions. The scientific community has responded very positively to this triumvirate of quality indicators. With researchers commenting not only on the tools’ efficiency, but also of their ease of use.

Bio-Logic is currently investigating new ways of opening up their use to the market. Watch this space for more information.

For more information

Applications notes:

AN#65 – THD: parameters affecting its value and comparison with other methods of linearity assessment.

AN#64 – Introducing EC-Lab® EIS quality indicators: THD, NSD and NSR

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