Trends in the design and application of different capacitor typesNurudeen Ismail | October 20, 2022
In 1745, Ewald Georg Von Kleist discovered that electric charge could be stored by connecting an electrostatic generator by a wire into a glass jar containing water. This discovery sparked a series of activities that led to the discovery of capacitors with higher charge storage capacity. And by 1925, there were several types of capacitors made from different materials and with different capabilities.
It’s been over two centuries since capacitors were first discovered. Yet, newer (and better) capacitor designs have been emerging to solve engineering challenges. Today, four commonly used capacitors include electrolytic, ceramic, film, and supercapacitors.
Trends in electrolytic capacitors
An electrolytic capacitor is a capacitor in which the positive plate is made of an insulating metal (like aluminum and titanium) that forms an oxide layer. This oxide layer acts as the capacitor's dielectric, allowing it to store charges and achieve capacitance values ranging between 1 and 47 µF.
However, changes in the temperature around electrolytic capacitors usually affect the capacitance values. For instance, the electrolyte in an aluminum electrolytic capacitor typically evaporates at 85º C, causing leakage and deforming the capacitor’s body. Likewise, electrolytic capacitors don’t fare well under low temperatures as the electrolyte jelly freezes.
Hybrid electrolytic capacitors have been developed to solve this working temperature challenge of electrolytic capacitors. These hybrid devices can withstand temperatures of up to 125º C, making them ideal in applications with high thermal conditions.
Multilayer ceramic capacitors
Multilayer ceramic capacitors (MLCCs) are commonly used ceramic capacitors today. These capacitors are made of two (or more) alternating layers of ceramic and a metal layer, which acts as the electrode. They typically have a capacitance value ranging between 1 nF and 1 µF.
MLCCs offer several advantages over other types of capacitors. For instance, they are the capacitor of choice for applications where small capacitance values are needed. In addition, MLCCs offer small parasitic inductance, allowing them to provide better high-frequency performance than electrolytic capacitors. They are also more stable at high temperatures than electrolytic capacitors.
Some recent trends in the MLCC industry are highlighted below:
- Low-profile multilayer ceramic capacitors have been designed to have a small size and low equivalent series inductance (ESL). This is due to their external electrodes, which are placed lengthwise. In addition, they offer twice as much capacitance as conventional ceramic capacitors, and their small size makes them ideal to be mounted and used in IC packages.
- Conventional designs of ceramic capacitors are prone to high equivalent series resistance (ESR): which describes the extent to which capacitors act as a resistor and dissipate energy during charging and discharging. Soft termination MLCCs are helping to mitigate this issue as they offer low ESR value and are being used in high-reliability systems.
ESR = equivalent series resistance
f = frequency
D = total dissipation factor
C = capacitance
Film capacitors use thin plastics as their dielectric material. They offer stability, low self-inductance (ESL), low equivalent series resistance (ESR), and capacitance values ranging between 1 nF to 30 µF. In addition, these capacitors are not polarized, unlike electrolytic capacitors. This means there is no stringent requirement for the polarity of the voltage connected to the capacitor terminals, making them ideal in several AC applications.
Some recent trends in the film capacitor industry include:
- New metalized polypropylene AC film capacitors have been introduced for humid environments. These capacitors ensure stable capacitance and ESR values over a long shelf life in a harsh environment.
- Heat-resistant film capacitors have found use in converters and motor drives where there is a need for capacitors with high thermal resistance. For instance, these recent film capacitors can withstand temperatures of up to 125º C, whereas conventional film capacitors will fail under such thermal conditions.
Supercapacitors, also called ultracapacitors, are high-capacity capacitors with higher capacitance values than other types. In addition, these devices can deliver charges at a much higher power output than batteries.
These capacitors work by creating a very thin double layer of charge between two plates, which have a large surface area and are made from porous materials soaked in an electrolyte. This gives them the ability to store more charge.
There are several recent trends in the application of supercapacitors across different industries today. For instance, high-power supercapacitors are currently being tested and developed for use in space applications like geostationary Earth orbit subsystems and power bus voltage regulation. In addition, there is also a potential for the hybridization of supercapacitor banks with lithium-ion batteries to extend the lifetime of energy storage systems.
Supercapacitors, electrolytic, ceramic and film capacitor technologies have evolved with different capabilities and suitability for several applications. Therefore, engineers, technicians and facility managers are advised to reach out to capacitor manufacturers to discuss their application needs.