The Advent of Solid State Microwave Generation

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The Advent of Solid State Microwave Generation

 

We’re extremely excited and proud to be the creators of the PrecisePower™ family, our industry’s first fully solid state microwave power sources.  This family of system covers both the 900 MHz and 2400 Mhz bands with power levels up to 75 kilowatts.

Until now, the heart of every microwave heating device, including your home microwave oven, is the magnetron tube.  This specialized radio tube was invented in 1940 and has not fundamentally changed much since then, except for getting bigger and more powerful.  While magnetrons are very efficient in converting electric power to microwave energy, they have many limitations.  First is their limited lifetime, about 6000-8000 hours for 900 MHz tubes, and about 2000 hours for 2400 MHz tubes.  The transistors used in our new solid state systems have a lifetime in excess of 30 years – over 250,000 hours!  This long life also results in much higher reliability and less downtime.

Another crucial feature of solid state microwave generators is frequency agility.  Magnetrons operate on a single fixed frequency, either 915 MHz or 2450 MHz.  Solid state units can cover the entire government allocated ISM bands at 902-915 MHz and 2400-2500 MHz.   This has two big benefits.  First, most microwave applicators have hot and cold spots due to wave interaction.  That’s why home microwave ovens have turntables and industrial systems have rotating antenna to ensure even heating.  It turns out that when the microwave frequency is varied the hot and cold spots move around without mechanical assistance; simpler and more effective.  Second, for maximum power transfer from the generator to the load proper matching is important.  Mismatched systems will result in energy being reflected back to the generator which is lost as heat.  Very often, adjusting the generator frequency to a “sweet spot” will provide an excellent match without using a hardware tuner.

Power control with magnetrons can be slow (for 915 MHz systems) and/or limited (for 2450 MHz systems).   As reflected in their name, PrecisePower™ generators offer nearly instantaneous and extremely accurate (<0.1%) power control.

An interesting new PrecisePower™ capability is high speed pulsed mode operation.   This means the microwave can be switched at a frequency of up to 10 KHz with a variable duty cycle.  Some prior research suggests that pulsed modes may have significant benefits in certain drying, plasma generation, and other applications.  This field is largely unexplored because it’s nearly impossible to do with magnetrons.  We expect that some of our users will make some interesting and important discoveries in this area.

These features and many others are highly accessible and easy to use using a powerful interactive software suite.  The system can be controlled by a Windows app running on a PC via a USB connection.  The generators can also be controlled as a LabView device or using a PLC-type hardware interface.

 

 

 

07/27/2017 2:45 PM

Blog Contributors

Michael A. Mittman
Walter Wohlford-Wessels
Ken Kaplan
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