Solid-state RF energy set to improve cooking, lighting...

December 15, 2016 // By Martin Rowe
A certain person in my household has been known to burn microwave popcorn — fortunately, without starting a fire. What's really needed here is a microwave oven that detects the changes taking place in food as it cooks and makes the appropriate adjustments. Such an oven is now possible, though it might be a few years before it's practical and affordable.

RF energy is on the cusp of bringing changes to cooking, lighting, industrial heating, automotive spark plugs, and a host of other applications. It's made possible through the development of RF transistors that can provide sufficient power at the right frequencies, namely the 2.45 GHz ISM band. Yes, the same band used by Wi-Fi and Bluetooth.

As with any new technology, RF energy applications come with engineering challenges such as thermal dissipation, cost, size, and measurement. At EDICON 2016 in Boston, I met with Klaus Werner, Executive Director of the RF Energy Alliance, who also gave a presentation that day. After the conference, I spoke with Mark Murphy, Senior Director Marketing and Business Development for RF Power at MACOM and with Robin Wesson, Advanced Applications Architect at Ampleon.

"RF energy could change the way we cook food," said Werner, "but it's being used in other applications." He explained that RF energy, generated by RF transistors in power amplifiers, could replace the magnetrons in microwave ovens. By generating energy with semiconductors and more than one antenna (Figure 1), microwave ovens could produce energy sufficient for cooking and adapt to changing conditions as food cooks. That can result in more even cooking than we currently get from our microwave ovens, which essentially operate as on/off, open-loop systems. Instead, the next generation of microwave ovens will have complete closed-loop control. Some of today's ovens have mode-stirrers or turntables to attempt to produce a uniform field inside the cavity while others use humidity sensors that provide some feedback, but not enough, for the kind of control needed.

Figure 1: Power transistors such as these from MACOM and Ampleon can produce 300 W or power at 2.45 GHz. (The Ampleon device is rated at 250 W, but a 300-W version is available.) MACOM uses a GaN-on-silicon process while Ampleon uses laterally diffused metal-oxide-silicon (LDMOS).


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