The dielectric loss of a sample is negative at some frequency while it is possible at other frequencies. Can anyone please let me know whether it is right or not?
Dear Alam,
As far as I understand your question, I am trying to answer the query:
Dielectric loss (tangent) , mathematically expressed as ration of Im(permittivity) to Real (permittivity) i.e., and = e"/e', So basically it is the tangent angle on complex permittivity plot, where tand can be negative if these to the parameter are out of phase, either inductive effect is dominated in your system or circuit, Usually, this artefact generated with magnetic samples due to mismatch combination of sample holders inductive contribution or at or around some typical magnetic anomaly in the sample. Further, I like to clarify as resistance can not be zero due to scattering (either impurity or thermal or else), so the only possibility is with e' which can be negative. So at higher frequency(>1MHz), you can observe as at high-frequency inductive contribution is more than capacitive one.
Thanks
I don’t know how much my answer will help you, but nonetheless.
A medium with negative losses is called an active medium and amplifies the amplitude of the wave oscillations that propagate in it.
Such a situation is possible. This is a very specific situation, but it can even occur for isotropic dielectrics. If this medium is in certain external conditions (external force fields, applied stresses, body dynamics, etc.)
Are you sure this is not an artefact? Is it reproducible? Is it not noise? Does it appear only in certain frequency or temperature ranges?
Dear Dr. Alam
A capacitor is a device to store energy in the form of electrical field. When it is filled with a dielectric material, if dielectric loss does not occur, it acts as ideal capacitor. Due to lag of polarization with a. c. field, dielectric loss occurs in certain frequency range and then it does not work as ideal capacitor. Electrical energy is lost due to dielectric loss. If one says dielectric loss is negative, it means energy is being generated instead of loss which is an unlikely situation. In fact when measuring bridge is unavailable to respond in certain frequency range due to low impedance then digital impedance meter sometimes show spurious results and a negative sign appears which one interprets as negative dielectric loss. Please check your set up more carefully before you interpret your results.
Dr. A. Kumar