RF Power Electric Feedthroughs - Introduction
RF Power Feedthroughs are specifically designed for the transmission of Radio Frequency power into the vacuum environment. Differences between the ISI™ conventional DC Power Feedthroughs and ISI<™ RF Power Feedthroughs are found in the construction materials used at ceramic to metal interfaces. ISI™ RF-Power feedthroughs are state of the art ceramic to metal seal components. They are constructed entirely of non-magnetic materials, i.e. copper and stainless steel, which enhance their performance in RF induction fields. These feedthroughs are used primarily in high power and high frequency induction load applications.
A common application of ISI™ RF Power Feedthroughs is in-vacuum induction heating. Designs having power ratings as high as 35kW and frequencies up to 13.56MHz are available.
ISI™ RF Power Feedthroughs are constructed using copper alloys, which have low susceptibility to RF coupling. The nickel-iron alloys used in standard DC Power Feedthroughs are ideal for joining to alumina ceramics because of their low coefficient of thermal expansion. However, the magnetism and higher resistance of nickel-iron alloys make them highly susceptible to RF coupling. When standard power feedthroughs are used with radio frequencies, the induced heating effect can cause failure at power levels as low as a few kilowatts.
To further minimize heating effects, RF Power Feedthroughs are water cooled. At high frequencies, current is conducted along the outer surface or “skin” of a conductor. The “skin effect” reduces the effective cross-sectional area of the conductor, increasing resistive heating. Additional heat dissipation provided by water cooling helps offset this effect and allow high power loads. RF Power Feedthroughs must be installed with properly grounded cooling systems. In a test of the 35kW feedthrough, the minimum allowable coolant flow rate was determined to be 4 gallons/hour.
When installing two 35kW/13.56MHz RF power feedthroughs side by side, their center-to-center spacing must be greater than 2.00 inches. RF Power Feedthrough users must allow adequate clearance between the feedthrough and any surrounding hardware in order to avoid RF coupling.
Intended Operating Conditions
Electrical ratings are safe operating limits. These ratings are determined by various factors, including dielectric strength, geometry and system operating pressure. Please note that all ISI™ catalog products are electrically rated for operation with one side in dry atmospheric conditions and the other side in a vacuum environment with a maximum system pressure of 1 x 10-4 Torr. We advise that users make allowances for deviations from stated operating parameters and take adequate safety precautions when feedthroughs are operated at high voltages or high currents.
Insulator Seal (ISI) brand catalog and custom engineered ceramic to metal seal products are manufactured to ISO 9001:2008 standard utilizing our qualified hermetic brazing and joining processes.