Dielectric absorption, also known as dielectric relaxation or soakage, is a phenomenon observed in certain types of capacitors that can impact their charge storage capabilities. To understand its significance, let's first look at the basic components of a capacitor.
A capacitor is an electronic component designed to store and release electrical energy. It consists of two conductive plates separated by an insulating material called a dielectric. When a voltage is applied across the plates, an electric field is created in the dielectric, which leads to the buildup of opposite charges on the plates. This accumulation of charges allows the capacitor to store electrical energy.
Dielectric materials are chosen for their ability to withstand high electric fields and reduce energy losses due to leakage currents. However, no dielectric material is perfect, and they exhibit some level of imperfections and limitations. One significant phenomenon related to dielectric materials is dielectric absorption.
Dielectric absorption occurs when a capacitor is charged and then discharged, but it does not return to its original state immediately. Instead, some charge remains trapped within the dielectric material temporarily. This effect is due to the polarization of the dielectric, where the electric dipoles in the material align with the applied electric field during charging. When the external voltage is removed, these dipoles take some time to realign and release the trapped charge back into the capacitor plates. This delayed release of charge can affect the capacitor's overall performance.
The impact of dielectric absorption can be summarized as follows:
Voltage Recovery Time: Dielectric absorption leads to a slow discharge of the capacitor after it has been disconnected from the charging circuit. The time required for the capacitor to return to its original voltage level is longer compared to what would be expected from an ideal capacitor with no dielectric absorption.
Effective Capacitance: The effective capacitance of the capacitor is temporarily reduced due to the trapped charge in the dielectric. During discharge, the released charge combines with the charge stored on the capacitor plates, effectively increasing the total capacitance for a short duration.
Circuit Behavior: In some circuits, especially those with high impedance, the presence of dielectric absorption can cause unexpected behavior. It can lead to voltage fluctuations and affect the accuracy and stability of circuits that rely on precise timing or charge storage characteristics.
Manufacturers often provide a specification called the "dielectric absorption ratio" or "soakage ratio" to quantify this effect. This ratio is defined as the ratio of the voltage remaining on the capacitor after a specified period (usually a few minutes) to the initial voltage before discharge.
It's worth noting that not all capacitors exhibit significant dielectric absorption. Capacitor technologies like ceramic and tantalum capacitors have relatively low dielectric absorption, while electrolytic capacitors, especially those with solid electrolytes, can have more noticeable dielectric absorption characteristics.
In most applications, dielectric absorption is not a critical concern, but in situations where precise charge storage and discharge characteristics are essential, designers may need to consider this phenomenon and select capacitors with lower dielectric absorption ratios.