Solid-State RF Power
Solid-State RF Power is Coming to Industrial Systems. Slowly.
Because the power of RF energy to create heat is buried within industrial systems most people don’t even know exist.
However, if you’ve cursed those nasty, thick, cut-inflicting plastic enclosures protecting products like thumb drives, you’ve experienced the power of RF energy—in dielectric heating—to melt and merge two plastics together. That crunchy food that Fido loves so munch? It didn’t start out crunchy: It had to be dried, and chances are RF energy was the heat source. There are a lot more applications for dielectric heating, dozens in fact, as you can see in the following list:
Applications for dielectric heating span many industries.
- Increasing seed fertility
- Drying and backing carpet
- Drying agricultural products
- Drying textiles
- Accelerating concrete curing
- Heat setting nylon rope
- Drying sizing on glass fiber
- Printing carpet tiles
- Curing resin-bonded abrasive wheels
- Drying tobacco
- Drying pharmaceutical powders and pills
- Heating wool bales
- Drying gelatin
- Dye fixation
- Drying water-based adhesives
- RF transfer printing on textiles
- Drying synthetic fibers
- Drying leather
- Drying sand cores
- Bonding textiles
- Laminating flexible polycarbonate boards
- Drying timber and veneers
- Welding vehicle PVC interior trim
- Manufacturing fiberboard
- Welding camera cases
- Drying adhesives on cartons
- Inserting metal pieces into eyeglass frames
- Profiling of moisture on paper
- Drying potato chips
- Drying matchbox striking edges
- Pasteurizing hams and soft drinks
- Drying water-based printing inks
- Pasteurizing milk
- Preheating rubber
- Deactivating flour
- Curing and preheating PVC sheet
- Drying pasta
- Fabricating life jackets and life rafts
- Exterminating parasites
- Preheating thermoset plastic
- Post-baking of biscuits and cereals
- Welding and embossing PVC
- Drying soup powder
- Cracking concrete
- Mending asphalt roads
RF energy probably seems a lot more complicated than other methods like heating an electrode or burning fuel, but it’s typically less costly than the massive electrical power required to heat electrodes, is a lot more environmentally “friendly” than fossil fuels, and has unique benefits that the alternatives can’t deliver.
The RF power amplifiers used in RF heating have been powered for decades by vacuum tubes such as magnetrons. Even though solid-state devices (RF power transistors) might seem a more modern solution, they haven’t been tough enough to withstand high impedance mismatches and couldn’t produce enough RF power per transistor to make them viable.
That’s no longer true. Laterally Diffused Metal Oxide Semiconductor (LDMOS) RF transistors today can deliver more than 1.5 kW of RF power and do so into an impedance mismatch close to a direct short without performance degradation or failure. An amplifier using a half dozen of these devices can produce enough power to satisfy many industrial heating applications, and much higher power is achievable as well.
NXP MRF1K50H LDMOS RF Power Transistor
The MRF1K50GNR5 LDMOS RF power transistor, for example, is one of NXP’s latest devices for industrial and other high-power applications. It delivers RF output power of 1.5kW CW from 1.8 to 500MHz, and can withstand an impedance mismatch (VSWR) greater than 65:1 even when driven by twice its rated input power.
Unlike magnetrons that are either “on” or “off,” the output of transistors can be infinitely varied by controlling input power, gain, and drain voltages to deliver the correct amount of heat almost instantly. They also operate at 50VDC rather thousands of volts so they’re a lot safer, their operating life is millions rather than hundreds of hours, and their output doesn’t decline with time.
Why haven’t manufacturers of RF heating systems jumped at the opportunity to differentiate their products as “powered by solid-state devices?” First, RF technology is a means to an end in these machines, so manufacturers typically don’t have RF engineers who can design solid-state amplifiers. This has been frustrating for proponents of solid-state heating as they attempt to convince an industry steeped in vacuum tube technology to make the leap to solid-state. Second, it’s only recently that RF power transistors have been up to the task.
While it’s likely that in applications where hundreds of kilowatts of RF power are required, magnetrons will continue to be the power generation source of choice, systems requiring less power are fair game for solid-state devices. A few industrial heating system manufacturers have already taken the plunge and more are likely to follow, as the RF Energy Alliance spreads the word about how RF power transistors can be used in more industrial, medical, and cooking applications.
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