Dielectric losses are an important aspect in electrical engineering and materials science, especially in the development of capacitors, insulators and other components operated in electric fields. These losses affect the efficiency of components and must be considered in the development and selection of materials. This article explains the fundamentals of dielectric loss, including the mechanisms of polarisation, the calculation of the loss factor and the effects on capacitors and other electronic components.
GOBA supplies low-loss polyester films and insulation materials with a low dielectric loss factor for high-frequency and high-voltage applications.
What is dielectric loss and how does it arise in the electric field?
Dielectric loss refers to the energy loss that occurs when a material is exposed to an electric field. It results from the conversion of part of the electrical energy stored in the material into heat. The main cause of these losses is the polarisation of the molecules in the material, which is caused by the applied electric field. Polarisation means that the positive and negative charges within the material shift when it is exposed to an electric field.
In an ideal dielectric (insulator), the molecules would align perfectly and generate no energy losses. In practice, however, the interaction between the molecules and the electric field causes friction that leads to heat. These dielectric losses are essentially a form of energy lossand influence the efficiency of many electronic components.
Definition of dielectric loss and energy loss in the dielectric
Dielectric loss therefore describes the energy loss in a dielectric that arises during polarisation and depolarisation. It can be described mathematically by the dielectric loss factor, which quantifies the inefficiency of a material when storing energy in an electric field.
Dielectric loss is directly related to dielectric absorption, since both concepts concern the ability of a material to store electrical energy while losing energy in the process. Dielectric absorption describes the phenomenon that a dielectric absorbs energy when it is charged and releases this energy again when the electric field is removed.
Mechanisms of polarisation and their influence on dielectric losses
Polarisation is the key mechanism that causes dielectric loss. There are several types of polarisation, each with different effects on dielectric losses. The most important are:
- Orientation polarisation: here, the dipoles of a material align along the applied electric field. This occurs in materials with strong dipoles, such as water. This type of polarisation can cause significant losses because the dipoles do not swing immediately into the new direction when the electric field changes, leading to phase shift and heat losses.
- Electronic polarisation: this occurs when the electron shell of an atom is displaced in an electric field. This type of polarisation usually causes low losses because the electrons respond very quickly to changes in the field.
- Ionic polarisation: here, the ions in the material shift in the direction of the applied electric field. This type of polarisation occurs mainly in electrolytes and is associated with higher losses, particularly with alternating current.
Behaviour of dipoles in an alternating field and resulting heating
When a dielectric material is operated in an alternating-current field, the dipoles constantly move in step with the changes in the electric field. Due to the inertia of the molecules and the interaction between the dipoles, a delay occurs in the alignment of the dipoles with the alternating current. This leads to a phase shift between the applied electric field and the polarisation, which in turn leads to losses in the form of heat. This type of loss is often observed in capacitors and other components operated with alternating current.
How is the dielectric loss factor calculated and measured?
The dielectric loss factor, also known as tan delta, is a figure that indicates how much energy is lost as heat in the dielectric in relation to the energy stored as electrical energy. The loss factor is usually calculated with the formula tan delta = Im(epsilon) / Re(epsilon), where Im(epsilon) is the imaginary part and Re(epsilon) is the real part of the dielectric constant.
The loss factor is frequency-dependent and generally increases with increasing frequency. This means that materials tend to exhibit higher losses at high frequencies. This must be taken into account when selecting materials for applications such as high-frequency capacitors.
There are various measurement methods for determining the loss factor. A common method is dielectric spectroscopy, in which the behaviour of a material is studied over a broad frequency range. This method provides detailed information about dielectric relaxation and the losses in a material.
What role does dielectric absorption play in capacitors?
In capacitors, dielectric absorption is of central importance. It describes the behaviour of capacitors during charging and discharging. When a capacitor is charged, the stored energy is insulated by the dielectric and the electric field polarises the material. However, during discharge there is a delay in depolarisation, leading to energy losses. This loss is known as dielectric absorption.
In modern capacitors, minimising these losses is decisive. Excessive dielectric absorption can reduce the performance and efficiencyof the capacitor and can be problematic in some applications, for example in energy transmission or in high-frequency circuits.
How does polarisation influence the behaviour of a dielectric?
Polarisation plays a central role in the dielectric behaviour of a material. It affects not only the dielectric loss but also the capacitance and performance of a dielectric. Materials with higher polarisation store more energy but also tend to have higher losses because polarisation is often accompanied by a delay in the alignment of the dipoles.
Dielectric relaxation describes the process by which a dielectric adjusts its polarisation to the applied field over time. This process has a direct effect on the losses caused by dielectric heating. Polarisation thus influences the behaviour of a material in an alternating-current field and contributes significantly to the losses.
What is the significance of relative permittivity for dielectric losses?
Relative permittivity (epsilon), also known as the dielectric constant, is a measure of a material's ability to store electrical energy. A higher relative permittivity means that the material can store more energy. However, it is also an important factor in dielectric losses, because materials with higher permittivity usually exhibit higher losses.
Relative permittivity and the dielectric loss factorare linked, since a higher permittivity is often associated with higher polarisation and correspondingly higher losses.
How do dielectric losses affect practical applications?
In practical applications such as capacitors or insulators, it is decisive to minimise dielectric losses in order to maximise energy efficiency and performance. When selecting materials, the dielectric properties must be carefully considered to ensure they meet the requirements of the respective application area.
Dielectric heating is a phenomenon that leads to lossesin many electronic circuits. Materials that exhibit high thermal stability and low dielectric losses are therefore particularly sought after to improve the efficiency of components.
GOBA Takeaway
Dielectric losses are an important factor in materials science and electrical engineering, since they can impair the efficiency of capacitors, insulators and other components. By understanding the mechanisms of polarisation and dielectric absorption, engineers can optimise materials to meet the requirements of modern electronic circuits. By selecting the right dielectric materials and minimising the loss factor, the performance and efficiency in many industrial applications can be significantly increased.