Semiconductor microwave ovens improve cooking

Robin Wesson
Advanced Application Architect
ampleon-semiconductor-microwave-cooking-plain
Microwave ovens have used magnetrons that date back to the Second World War - now semiconductor technology promises a brighter future for cooking.

Microwave ovens have been using the same basic cooking technology for decades. Now, with the availability of solid state cooking techniques promises to significantly change how we cook our food.

Today’s ovens are powered by a magnetron, a device originally developed for World War II radar systems. Magnetrons use an old-fashioned vacuum tube (valves) approach to generate the necessary short-wavelength radio waves for cooking. But what are the challenges with this approach? Why should we change?

The first observation is that magnetrons don’t actually cook food very well. They 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 already been in heavy use.

Magnetrons also have a relatively short lifespan – typically 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 good news, 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. The overall cooking experience will be greatly enhanced with this approach.

As I’m sure we’ve all experienced from time to time, microwaves do produce hot and cold spots in the food. 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. Controlling frequency and power output depending on the food being cooked will also improve this aspect of microwave cooking.

The use of solid-state components results in a more accurate and stable cooking cycle. Power control is more linear with this approach so there is less temperature variation within a cooking cycle. Also, the latest modulation and digital signal-processing (DSP) techniques make the microwave signal more accurate and more stable. Being able to support frequency tuning ensures that the oven can make full use of the frequency spectrum in order to increase cooking efficiency and thereby improve overall power efficiency. In this way it makes it easier to modify the oven’s operation based on what’s being cooked, since a bag of popcorn is very different from a raw potato or a frozen turkey.

Another major benefit is that by using modern sensor technology it is possible to constantly monitor, adapt and optimize the cooking process in real-time. By means of sensors and closed-loop algorithms the oven incorporates a far more sophisticated measurement system that can take account of reflected power and the absorption characteristics of the food being cooked. This is of course a long way from the extremely simple on/off cycle that most microwaves employ today.

The final observation is that of reliability. Already used in high reliability rugged applications such as cellular base stations, solid-state RF components are designed to operate without interruption for a long as fifteen years. Manufacturers will greatly value the positive influence that having a reliable microwave oven will add to their brand. For consumers a more reliable, effective and power efficient cooking device will open up the microwave oven to becoming a more trusted and flexible kitchen appliance that can be used for a lot more than just warming up last night’s takeaway!

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