Feature: Military
Figure 1: High-voltage capacitors and assemblies
more compact. Te ability to handle higher temperatures simplifies thermal designs, too.
Mica capacitors Mica paper capacitors (Figure 2) are commonly used for high- voltage, high-temperature applications and are widely used in space-age radar, missile, satellite, ignition, detonation, cryogenic, transmission, laser, medical and oil-and-gas exploration systems. “Grade A” mica paper in capacitors is an excellent dielectric – a material that does not conduct electricity, but can sustain an electric field. Te mica paper consists of flexible, continuous and uniform
layers of mica that are reconstituted or reformed into paper-like electrical insulating material composed of small, thin, overlapping platelets. Mica capacitors offer several benefits when used in high- power electronic systems: • High-voltage handling: Tey can withstand high voltages, making them suitable for applications where voltage ratings are critical. Tey are oſten used in high-voltage power supplies, pulse power systems and applications where voltage spikes are common.
• High-temperature stability: Mica capacitors exhibit excellent temperature stability, maintaining their capacitance and other electrical properties across a wide temperature range. Tis characteristic is essential in aerospace and defence applications where components can experience extreme temperature variations.
• Low dielectric losses: Mica capacitors have low dielectric losses, which means they dissipate minimal energy as heat during operation. Tis makes them suitable for high-frequency and high-power applications where efficiency is crucial.
• Low leakage current: Mica capacitors typically have low leakage currents, which is important for maintaining the integrity of circuits, especially in high voltage or high impedance
applications. Low leakage ensures that the capacitor retains its charge and does not significantly affect circuit performance.
• High insulation resistance: Mica capacitors offer high insulation resistance, which helps prevent electrical leakage and ensures reliable operation in demanding environments. Tis property is particularly advantageous in aerospace and defence systems where reliability is paramount.
• Mechanical stability: Mica capacitors are mechanically robust and resistant to vibration, shock and mechanical stress. Tis makes them suitable for use in harsh environments encountered in aerospace and defence applications, where reliability under extreme conditions is essential.
• Low ageing rate: Mica capacitors low ageing rate helps them maintain their electrical characteristics over time with minimal degradation. Tis property contributes to the long-term reliability and stability of electronic systems in aerospace and defence applications.
• High quality factor: Mica capacitors typically have a high quality factor, indicating low losses and high efficiency in resonant circuits. Tis makes them suitable for applications requiring precise tuning and high performance, such as RF filters and oscillators. Overall, mica capacitors offer a combination of high voltage
handling, temperature stability, low losses and high reliability, making them well-suited for use in high-power electronic systems in many applications for harsh environments, like in aerospace and defence.
Encapsulation, insulation and shielding Te reliability of power electronic systems extends beyond component assembly. Encapsulation, a critical process, shields delicate electronic components from environmental factors, mechanical stresses and electromagnetic interference (EMI), ensuring sustained operation under harsh conditions. Potting
www.electronicsworld.co.uk May 2024 39
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