How to calculate real and imaginary parts of dielectric constant from impedance measurement?
The dielectric constant signifies the efficiency of dielectric material to store the electrical energy and the dielectric loss indicates to loss of electrical energy in the form of heat energy. In ac fields permittivity becomes complex quantity and has real and imaginary parts. The imaginary part (εi) is associated with dielectric losses and the real part (Ɛr) an indication of the degree of polarization. The greater the degree of polarization, the greater the value of Ɛr. The dielectric constant is a function of frequency. As frequency increases, the value decreases due to polarization mechanisms no longer being able to follow the rapidly changing field. Imaginary part is always positive and represents loss factor or energy absorbed. The measurement of the real part of relative permittivity, εr is generally done by measuring the charge in capacitance of a capacitor by the introduction of the dielectric between its electrodes. The imaginary part or the complex dielectric constant εi is found from the measurement of tan δ, which is the loss factor of the dielectric. [tan δ = εi/Ɛr ].
I will agree with Jiban,
I would suggest you to read some old research articles which are published in ferroelectrics, American ceramic society, ....
Wish you good luck.
There's an Oxford University undergraduate practical on this:
http://ptcl.chem.ox.ac.uk/~hmc/tlab/experiments/210.pdf
which physical process quantifies the real and imaginary part of the dielectric constant?
The real part of the dielectric constant of the material arises due to polarization under electric filed. The phase angle between I and V of an ideal capacitor should be 90o . However, a part of energy gets dissipated due to heating and as a result the angle will be slightly less than 90o. The tangent of that angle is known as dielectric loss represented by tan delta. tan delta = Imaginary part of the dielectric constant /real part of dielectric constant. Hence, Imaginary part of the dielectric constant = real part of dielectric constant x tan delta. Which actually represents the loss of energy.
@ Chandra Bhal Singh Sir, If you have good quality of alpha analyser, you can easily calculate real and imaginary part of dielectric constant. An image of NOVOCONTROL Alpha Analyser is attached with this answer. Kindly take a look at it. You may find many parameters using this instrument. Also the graph can be generated with respect to frequency and temperature as well.
Can anyone tell me how much does the NOVOCONTROL Alpha Anayzer costs?
Saravanakumar Arumugam
'From $11.2K'... Google is your friend - search on 'novocontrol alpha analyzer price'
While calculating Resistivity from impudence using the formula, Resistivity = Z(area/thickness), what we have to take either |Z| or Z'(real part) ?
Dear Chandra Bhal Singh ,
I think you have to elaborate your question. It is the complex impedance measurements of a capacitor filled with the intended dielectric that can be used to determine the real and imaginary part of the dielectric constant. One has to measure also the so called vacuum capacitance Cv of the capacitor.
It is so that C/Cv = epsilon r = epsilon r real - j epsilon r imaginary
By measuring the admittance of the capacitor, one gets
y= jwC= jw Cv epsilon r =jwCv (epsilon r real + j epsilon r imaginary)
y= jwCv epsilon r real + wCv epsilon r imaginary
As you see by measuring the real admittance and the imaginary admittance and knowing Cv and the frequency one can determine the real and imaginary parts of the dielectric constant of a dielectric materials.
Best wishes
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