NXP Semiconductors NV : "How to build a better microwave oven using solid-state RF"

Microwave ovens have used the same basic design for decades, but, as described in our new white paper , upgrading to solid-state electronics promises to change how we cook food.

Today's ovens are powered by a magnetron, which is a device originally developed for World War II radar systems. Magnetrons use old-fashioned vacuum tubes (valves) to generate the necessary short-wavelength radio waves for cooking, and this leads to certain drawbacks.

Magnetrons don't always heat evenly, so food can be overcooked in some places and raw in others, and they deliver less power when they're warm, which means the same dish can require more time to cook if the oven has been in heavy use.

Magnetrons also have a relatively short lifespan - about 500 hours in the average household oven, and about a year of continuous use in commercial environments - and they get weaker as they age, so food takes longer to cook before the oven stops working entirely.

The goods new, though, is that magnetrons can finally be retired. Recent developments in wireless communication have yielded radio frequency (RF) components - including the high-power transistors needed for microwave generation - that deliver higher efficiency, greater power density, and improved voltage capability, at prices that are competitive enough for consumer appliances like microwave ovens.

Replacing magnetrons with solid-state electronics promises to transform microwave cooking, with appliances that cook more evenly, more consistently, more efficiently, and with more predictable results. Here are some of the benefits:

• Fewer hot spots - Using solid-state RF for precise phase control makes it possible to redirect hot spots, for more uniform heating and greater efficiency. Multi-source phase locking, a concept used in mobile phones to improve signal delivery, adds another level of control and efficiency.
• Higher accuracy and stability - With solid-state components, power control is more linear, so there's less variation in temperature within a cooking cycle. Also, the latest modulation and digital signal-processing (DSP) techniques make the microwave signal more accurate and more stable.
• Higher efficiency - Solid-state RF supports frequency tuning (used in Bluetooth accessories), which makes better use of the frequency spectrum to increase efficiency. It also makes it easier to modify the oven's operation based on what's being cooked, since a bag of popcorn is different from a raw potato or a frozen turkey.
• Better cooking algorithms - Sensor technology, used to measure the reflection of RF power, lets the oven become a measurement system, and supports the development of new, closed-loop algorithms that can monitor, modify, and optimize cooking in real time.
• Longevity - Solid-state RF components, which are used in rugged applications like cellular base stations, have to operate without interruption for as long as fifteen years, so they're designed for reliability.

Our in-depth white paper on cooking with solid-state RF looks at these benefits in more detail, and provides a number of recommendations, including how to test performance and choose frequency bands, plus considerations for algorithm development and integration with conventional ovens.