Dear Parveen kumar,

In general, as frequency increases, the material’s net polarisation drops as each polarisation mechanism ceases to contribute, and hence its dielectric constant drops. but in your material exhibit different way that may be only low temperature. Many materials, possess permanent dipoles, there is a significant variation of the dielectric constant with temperature. This is due to the effect of heat on orientational polarisation. However, this does not mean that the dielectric constant will increase continually as temperature is lowered. There are several discontinuities in the dielectric constant as temperature changes. First of all, the dielectric constant will change suddenly at phase boundaries. This is because the structure changes in a phase change and the dielectric constant is strongly dependent on the structure. Dielectric polarization in nonconductors has mostly two causes, namely electronic polarizability (electrons shifting within molecules) and orientational polarizability (dipolar molecules rotating or flipping, or ions changing places). The first effect has a rather weak temperature dependence, the second a rather pronounced one. In a polar medium, high temperature disturbs the alignment of dipoles in an outer field: the dielectric constant decreases with temperature. In a ferroelectric medium, the dipoles are already aligned and, unless the outer field is very strong, thus do not contribute to the orientational polarizability. High temperature disturbs the ferroelectric alignment and produces molecules that are free to reorient in an external field, and these contribute to the dielectric constant. Well, this is a kind of very simplistic explanation, but it may give you an idea which forces are at work.

Dear Parveen kumar,

In general, as frequency increases, the material’s net polarisation drops as each polarisation mechanism ceases to contribute, and hence its dielectric constant drops. but in your material exhibit different way that may be only low temperature. Many materials, possess permanent dipoles, there is a significant variation of the dielectric constant with temperature. This is due to the effect of heat on orientational polarisation. However, this does not mean that the dielectric constant will increase continually as temperature is lowered. There are several discontinuities in the dielectric constant as temperature changes. First of all, the dielectric constant will change suddenly at phase boundaries. This is because the structure changes in a phase change and the dielectric constant is strongly dependent on the structure. Dielectric polarization in nonconductors has mostly two causes, namely electronic polarizability (electrons shifting within molecules) and orientational polarizability (dipolar molecules rotating or flipping, or ions changing places). The first effect has a rather weak temperature dependence, the second a rather pronounced one. In a polar medium, high temperature disturbs the alignment of dipoles in an outer field: the dielectric constant decreases with temperature. In a ferroelectric medium, the dipoles are already aligned and, unless the outer field is very strong, thus do not contribute to the orientational polarizability. High temperature disturbs the ferroelectric alignment and produces molecules that are free to reorient in an external field, and these contribute to the dielectric constant. Well, this is a kind of very simplistic explanation, but it may give you an idea which forces are at work.

Dear Parveen Kumar,

Could you explain me what material you are working on? Assuming that you have done your measurements correctly, your observation answers your own question with yes. But it is not what you would expect indeed. Normally motions (also dipole motions) have a certain inertia and above a certain frequency the oscillatory motion is damped.

An increase in dielectric constant with frequency would mean that the friction against dipole motion drops with frequency. Let us speculate about this. Assume that the friction of the dipole motion is due to molecular rearrangements of the environment. In case that the timescale of these rearrangements is slower than the timescale of the dipole motion, the friction will indeed be less at higher frequencies. But to be honest, this is pure speculation and first more info about the material has to be given.

Dear Parveen Kumar,

You didn't mention which type of material is it. Further whether the increase in dielectric constant with frequency is with increase in temperature or decrease in temperature? What is the temperature range, etc. is not clear.

Dielectric permeability decreases with frequency increase. Opposite to that, conductants of dielectric increases with frequensy. See MAXWELL - WAGNER model of dielectric in

WIKIPEDIA.

No way you can explain increase of dilectric permittivity with frequency. There seems some problem with the measurement. If you provide complete dielctric spectrum, measuring instrument and cell configuration only then you may get proper feedback which may help to resolve the issue.

Here is a paper that may be useful to you.

Increase in the apparant value of the dielectric constant (permittivity) may be due to various parasitic effects. It must not be confused with real increase in the value of thedielectric constant of material. In the attached paper you can see one of the cause of increase in the dielectric constant due to parasitic effect with increase of frequency. Similar parasitic effects are observed in the low frequency region as well.

See another paper on low frequency parasitic effects.

Ms Kumar,

I like V. Jayaramakrishnan's general explanation (and the others' were helpful, too). At higher frequency, the electronic contribution to polarizability should stay high while heavy-ion and heavy-atom contributions should decrease. But this brings up Hongbo Liu's question: In what frequency range do you see permittivity increasing? You can sort of "calibrate" your mind's frequency meter by looking at the hypothetical spectrum from dielectric spectroscopy given on this web page:

http://en.wikipedia.org/wiki/Permitivity

(I think the spectrum will be the second figure.)

The dielectric constant decrease with increasing frequency

Dear Parveen kumar

The dielectric constant is about Molecule but frequency is about bond therefore there is not direct relation between of them

Typically, the frequency increases with decreasing dielectric constant. If a certain temperature range with increasing frequency permittivity increases, it may be due to structural changes (or transitions) in this area.

But structure can not change with frequency at a constant temperature. It will change only if temperature is being changed. If latter is the case then there are several other reasons as well.

Dear Parveen Kumar,

Could you detail the temperatura range and the frequency used?

That phenomenon is presented in state change of foods specially at low frequencies.

Dear Perveen,

First of all I will appreciate and regard your question and the useful views of good people. These views and explanations are really useful and represents the comprehensive understanding about the frequency dependence of the dielectric constant. In my opinion, many things are important in your case. Initially, the frequency range. whether the effect is seen in KHz, MHz or GHz range. Since, different electric dipoles have different relaxation frequencies. secondly, the conductivity of your sample. if the sample is dominated by localized charge carriers or itinerant conduction is dominant? Thirdly, if the frequency dependence is for wide frequency range i.e more than one order of magnitude or narrower?

regards

This may be a rather simplistic answer or comment, but as far as I know the value of static permittivity (the new name for the old dielectric constant) remains constant in a frequency range that depends on the size of the compounds molecules. This constancy stops when relaxation starts and there is a drop in value as the frequency increases. At least this is what is shown in the typical graph of permittivity vs log of frequency that appears in every textbook. The reason for this behavior is, of course,  among the many detailed comments listed above.   

Hello, Praveen Kumar. 

We know that dielectric material becomes polarized in an applied electric field. for the material to become polarized, some time span is needed to orient the dipoles according to the direction of applied field. this time span is called 'relaxation time'. (probably in the range of picoseconds), so if the direction of applied field changes nearer to 8GHz and above, the dipoles inside the material may not able to reorient themselves at this frequency, and hence at higher frequencies, the dielectric constant drops down. The dielectric constant also depends on the structure, as the phase changes the dielectric constant also changes (suddenly at phase boundaries). For your case, may be the temperature factor is affecting the phase at particular temperatures hence such effect may be observed.

In order to give a satisfactory answer to this question, one must know what is this material to find out which polarization mechanisms is effective. In case of ionic polarization, the dielectric constant increases with frequency before resonance, then it peaks at resonance and decreases again at frequencies above resonance. In case of orientation polarization the dielectric constant decreases with frequency. At extremely high frequency the electronic polarization is dominant where it behaves with frequency like the ionic polarization. Therefore, it is important to show the range of frequencies of your measurements. In addition one has to be sure for the correctness of the measure nets. also, one has to consider the effect may be due to specific structural change in the material as you change the temperature.

Best wishes

NO!

In my opinion, the permittivity increase with frequency has been considered as an unexpected or questionable behavior. This is because strongly polarization dependent and the total polarization arising from electronic, ionic, dipolar and space charge polarization show a decrease as the frequency increases. Such unexpected behavior could be obtained at very high frequencies of the measuring technique as an experimental errors.

regards

What material is under study? Normally, the permittivity decreases with the increase of frequency. The type of material may help to explain this particular explaination.

Correct your English??? There not their........ Then suggest your answer???

structure not change with frequency at a constant temperature. It will change only if temperature is changed.

Following.

Normally, dielectric constant should decrease with frequency at constant temperature; until there is structure change ( the chance is minor) or some resonance.