RF Power Applications

RF (Radio Frequency) Induction Heating

Metals can be heated or melted rapidly by inducing a high current to flow through them. The heaters are used for many end purposes e.g.,

• heating metal car panels to enable them to be formed to shape.
• heating metal billets to allow them to be formed into tubes or rods
• induction welding of pipes
• fusion of metals for casting in the dental and jewellery industries
• iinduction hardening of metals.

RF Dielectric Heating

Rapid Drying of materials which usually contain water e.g. textiles, wood, wood glues, foodstuffs such as biscuits.

In this case the molecules of water in the material are made to vibrate by the application of a high RF field causing them to generate heat with the result that drying occurs.

RF Broadcast Transmitters

High power radio transmitters use these types of capacitors in the antenna circuit.

RF Power - Plasma Generators used in Semiconductor Manufacture.

(1 100MHz) RF Power used to ionise gas thus generating RF plasma used in various deposition 1 etching 1 cleaning processes.

High Power Matching Networks in Plasma Generators.

Matching network used to tune Plasma Chamber Impedance to a constant load.

Flat Panel Displays

Medical RF Generators

How and why these capacitors are used

The capacitors act as filters to block D and pass AC. They also form the capacitive part of the resonant circuit to drive the induction coil - please see the attached diagram for an explanation of where they are used in the circuit.

The ability to withstand high RF voltages.

They handle high RF power and current levels due to the low loss 1 high Q of the ceramic dielectrics employed.

The Doorknob range, in particular, exhibit low equivalent series inductance (ESL, due to their small size. The latter increases the self resonant frequency allowing their use at higher frequencies.

Tight tolerance grading can be offered, on certain parts, permitting precise tuning within the matching units thus minimising power loss within the load maximising efficiency.

The low temperature coefficients, particularly the NPO, of the dielectric materials used, result in minimal frequency drift with operating temperature again allowing precise tuning within matching units

RF Power Capacitor Applications

RF Induction Heating / Dielectric Heating

C1 = 1-5nF for induction heating
C1 = 50-200pF for dielectric heating

Capacitors
Coupling

• Passes ac
• Block dc

Blocking

• Blocks dc voltage
• Passed ac signal to RF resonant circuit

Decoupling

• FIlters out, to ground, ac noise generated in the cathode

Tank

• Tuned circuit comprising tank capacitor and inductance coil to provide high circulating current in the tuned resonant circuit

You may also find the following sections of particular interest if you are associated with high power RF applications:-

• Capacitors Tutorial and Guides
• RF Multilayer Capacitor Application