I am working on a methodology that allows the use of LIAs for broadband spectroscopy of materials. Initially, I was not expecting many issues assuming one has enough experience employing Impedance Analyzers for such kind of research. However, during my dissertation work it became clear that it was not the case. While the accuracy of the measurements were found to be very superior, the overall measurement procedure was complex and very time consuming.
I have been working on a way to simplify the process and it would be nice to find related work. However, for the papers that I have investigated, whenever LIA is used for dielectric spectroscopy, the related methodology is not explained in details. For instance, the process of system calibration at each frequency point. Also, the potential constraints for the dielectric cell design at this LIA context. I would like to compare my approach with existing ones, if available.
Dear Agnelo, When I started my career in 1980 my first boss was Dr. Peter Hedvig, who wrote a fairly popular book on Dielectric Spectrosopy. At that time he used lock-in amplifiers to detect the real and imgainary parts of the dielectric permittvitiy but only at a few selected frequencies and the scanned variable was temperature. Later, when the microprocessors became widespread this method seemed to decline. I do not exactly know whether the present day broadband dielectric analyzers use Fourier transform of decay functions only or they combine it with other technologies too. Fourier transform is the standard technique used at low frequencies.
Dear Gyorgy, than you for the comments. Indeed, modern FRAs typically employ signal processing techniques to achieve the results. Nonetheless, I still observe two main issues with this approach. First, the limited high-end frequency, in general smaller than 10MHz. Second, the "black box" effects: the researcher is usually limited to the excitation and sensitivity levels of those equipments.
On the other hand, if we employ LIA, almost all aspects of the experiment are under our control. For instance, I was able to perform dielectric measurements of dry soil between 1 to 25kHz with LIA when all other traditional methods failed due to the lack of sensitivity. In this case, I used LIA and an external sinewave with 70Vrms! Indeed, a dangerous experiment with thermal and dielectric breakdown aspects to be carefully considered. Nonetheless, the experiments were successfully performed. The drawback is the complexity of the setup that forced me to use just few selected frequency points, as you mentioned from Dr. Hedvig's experience.
Your comments reminded me the need to also investigate information from the manufacturers of FRAs and similar devices. Thanks!!
Yes, the possibility of using higher voltages is something to be considered. Most high-end equipment uses about 1 V voltage. There are power frequency generators up to kV voltages - but not for other frequencies. I am a poor chemist, not an electrical engineer - I presume this has to do with signal shape distortion at higher frequencies if you want to increase the voltage. Anway, in systems having space charges in th sample or at the electrode/dielectric surface it would be useful to see the nonlinear effects as a function of frequency too - ven if this frequency range is less than for up-to-date broadband dielectric spectroscopes. You have to find a market niche if you want to develop new, commercially attractive devices and this is a possible "gap" to fill in.
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