[Physics Class Notes] on Dielectric Loss Pdf for Exam

Dielectric is considered to be a material that has poor electrical conductivity and gets the ability to store electrical charge due to the phenomenon of Dielectric polarisation. 

What is Dielectric Loss?

The Loss of energy involved in heating a Dielectric material in an assorted electric domain is called Dielectric Loss. For instance, a capacitor assimilated in an alternating-current circuit is barely charged and discharged each half cycle. Most importantly, Dielectric Losses generally are based on the frequency and the Dielectric material. 

Dielectric Loss is measured utilising what is referred to as the Loss tangent or tan delta (tan δ). In layman’s language, tan delta is the tangent of the angle between the alternating field vector and the material’s Loss component. So, the higher the value of tan δ the significant the Dielectric Loss should be.

Heating through Dielectric Losses is considerably used in industries for drying lumber and various other fibrous materials, heating thermosetting glues, fast jelling and drying foam rubber, and preheating plastics prior to moulding. Dielectric constant and Loss tangent are numerical values that help define the permittivity of a Dielectric material. The permittivity of Dielectric material is indicated by ‘ε’.

The Dielectric constant formula is [K = frac{E_{0}}{E}] , or the ratio of the electric field in a vacuum to that in the Dielectric material, and is considerably connected to the polarizability of the material.

Dielectric Loss refers to the Loss of energy that goes into heating a Dielectric material in a varying, electric field. It tends to depend mainly on the Dielectric material and the frequency.

Dielectric Loss is measured using the Loss of tangent which is also commonly referred to as tan delta (tan δ). The higher the value of tan delta is, the more the Dielectric Loss is likely to be. 

What is a Loss Tangent? 

Loss Tangent or tan δ is a dimensionless quantity. It tends to calculate the estimated Loss of signal because of the fundamental dissipation of electromagnetic energy that takes place in the substrate of the printed circuit board. 

Formula: 

[ D = tan delta = cot theta = frac {1}{2pi R_{p}C_{p}} ]

Here, 

[tan delta] – the Loss angle 

[theta] – the phase angle

[f] – the frequency 

[R_{p}] – equivalent parallel resistance

[C_{p}] – equivalent parallel capacitance 

The Loss Tangent tends to play a key role in frequencies that are extremely high, i.e., above 1 GHz, and also tends to analogue signals so as to decide the signal attenuation.

Loss Tangent (tan (δ)) estimates signal Loss because of the fundamental dissipation of electromagnetic energy in the substrate of the printed circuit board. Moreover, it is a dimensionless quantity and mostly considered as; Loss Factor, Tan δ, Dissipation factor and Loss angle. The Loss Tangent definition is then referred to as the ratio or angle in a complex plane of the Lossy reaction to the electric field in the curl equation to Lossless reaction. 

The Formula for Loss Tangent is:

[ D = tan delta = cot theta = frac {1}{2pi R_{p}C_{p}} ]

Where; δ is the Loss angle, θ is the phase angle, f is the frequency, R_p is equivalent parallel resistance, and C_p is equivalent parallel capacitance. Loss Tangent has a vital part in extremely high frequencies above 1 GHz and analog signals to decide the signal attenuation.

Causes of Dielectric Loss

A coherent Dielectric supports a varied charge with the least possible dissipation of energy in the form of heat. There are normally two major forms of Loss that may dissipate energy inside a Dielectric. During conduction Loss, a flow of charge through material results in energy dissipation. The Dielectric Loss tangent is the dissipation of energy through the movement charges in a substituting electromagnetic field as polarisation switches direction. 

Moreover, Dielectric Losses are particularly high around the relaxation or resonance frequencies of polarisation mechanisms. The polarisation delays the applied field, resulting in an interaction between the field and the Dielectric’s polarisation, leading to heating. 

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A Dielectric Loss is prone to be higher in materials with higher Dielectric constants. It is the prominent drawback of employing these materials in practical applications. 

For example, Dielectric Loss is used to heat food in a microwave oven. The frequency of a microwave utilised is nearly the same as the relaxation frequency of the orientational polarisation mechanism in the water. It means that any water present soaks up extensive energy that is then dissipated in the form of heat. Moreover, the exact frequency utilised is a little away from the frequency at which maximum Dielectric Loss happens in water to ensure that the microwave is not all engrossed by the first layer of water they confront; thus letting proper heating of the food.

A Dielectric that is efficient, tends to support varying charges with the dissipation of energy in the form of heat to the minimum. 

There are 2 primary types of Losses that are likely to dissipate energy within a Dielectric. 

• One is conduction Loss wherein dissipation of energy is caused when the charge flows through the material.

• The other is Dielectric Loss wherein the dissipation of energy is caused through the movement of charges in an alternating magnetic field because polarisation switches its direction. 

The second type of Loss tends to be especially high around the resonance or relaxation frequencies of the polarisation mechanisms. This is mainly because the lagging of the polarisation behind the applied field leads to an interaction between the field and the Dielectric’s polarisation, which in turn results in heating. 

The one drawback of utilising Dielectric materials in practical applications is that materials that have higher Dielectric constants face higher Dielectric Loss. 

Factors Affecting Dielectric Loss

The Dielectric Losses and d.c conductivity of insulating oils reduce with time after the oil is added to the test cell, excluding the electric stress and room temperature. When the cell is heated instantly after filling, the Loss tangent and d.c conductivity upsurge to a maximum, but then reduces to a much lower value with time at persistent temperature. The maximum value, the rate of increase to that value and the subsequent reduction with time are basic functions of the thermal capacity and shape of the cell. It is the method employed to clean the cell, the temperature and the oxygen element of the oil. 

The following drop-in Dielectric Loss is considered because of the catalytic oxidation of most elements in the oil at the metal-electrode surface, even though it’s attainable that ions may simply be confined at this surface. The effects are detected with a low-viscosity cable infusion, both unused and widely contaminated, transformer oil and a synthetic hydrocarbon. 

Moreover, the imputations of the effect are examined in reference to regular testing of oils, to an analysis of the contamination effects
in oils and to work on oil-infused paper. It’s possible that the utilisation of plastic-coated electrodes may partially or entirely remove the effect.

The d.c conductivity as well as the Dielectric Loss of insulating oils tends to reduce with time when the oil is added to the test cell. This situation, however, excludes the room temperature and the electric stress. The tan δ and d.c conductivity tend to upsurge to a maximum when the cell is heated immediately after filling. But at a persistent temperature, with time, they reduce to a much lower value. The basic functions of the shape of the cell along with its thermal capacity include the maximum value, the rate of increase to that value, the subsequent reduction that happens with time. That method is used to clean the cell, the temperature, as well as the oxygen element of the oil. 

Due to the catalytic oxidation of most of the elements at the metal-electrode surface in the oil, the following drop-in Dielectric Loss is considered, even though ions may simply confine the metal-electrode surface. 

Moreover, in reference to the regular testing of oils, the imputations of the said effect are carefully examined to an analysis of the effects of contamination in oils, and to work on paper that has been infused in the oil itself. 

It is possible that using electrodes that have been coated with plastic may or may not remove the effect partially or in its entirety. 

A material with a poor electrical conductivity that receives the ability to store an electrical charge because of Dielectric polarisation is referred to as Dielectric. Hence, showing only displacement current makes it perfect for constructing a capacitor; to store and return electrical energy. To understand the topic better, you must know the Dielectric Loss definition and other related concepts.