How MACOM Will Revolutionize Ovens, Cars and Medical Technology

Markus Schäfer, Director Sales EMEA at MACOM: Magnetrons are quite large and require a voltage of several kilovolts (kV). By contrast, semiconductor systems are content with 28V. They are smaller, consume less energy and can be easily adjusted to the energy required for each use. The energy can be exactly directed to where it is needed. You can put a steak next to a scoop of ice cream on the plate in a microwave oven and prepare the steak according to your taste – without the scoop of ice cream next to it melting. The plate no longer has to rotate, as in traditional microwave ovens, in order that the food to be cooked gets on average the correct amount of energy of the preset electromagnetic radiation. In addition, semiconductor systems achieve a much longer lifetime and are more robust than magnetrons.

The RF energy market is predicted to grow to as much as USD 1 billion over the next five years. However, at the moment there are still limitations. The RF energy system does not only consist of transistors and amplifiers, it also includes a lot of other components, through to passive devices and connectors. Everything must be compatible so that users can build the systems into their equipment as simply as possible. After all, they do want to have to become experts in the areas of RF energy transistors and RF electronics. An ecosystem relating to RF energy must, therefore, be created.

This can be done in a number of ways. The RF Energy Alliance (RFEA), in which a whole range of different companies are represented, has already been established. The companies represented here range from manufacturers of transistors and amplifiers to integrated circuit manufacturers, through to manufacturers of other necessary components such as RF connectors. In addition, OEMs from various sectors, such as household appliances, lighting, automotive technology, medical technology and industrial drying equipment are also present. The aim of the RF Energy Alliance is to develop standards and enable manufacturers to jointly implement RF energy systems that are reliable, meet the specifications of the target markets, and which OEMs purchase at reasonable costs and can easily integrate into their equipment. MACOM is a founding member of the RF Energy Alliance.

With the “RF Energy Toolkit”, MACOM has launched a development kit targeted to help OEMs adapt their product designs to incorporate solid-state RF energy systems for a wide range of applications spanning microwave ovens, plasma lighting, industrial heating/drying, medical/pharmaceutical, automotive ignition systems and beyond.

Until recently only LDMOS transistors, which were driven by developments for basestations and can now be cost effectively manufactured, could be considered. Conventional gallium nitride (GaN) transistors achieve higher efficiency by more than 10 percent, and are more rugged due to their lower breakdown voltage and lower operating temperature, and achieve a higher power density by a factor of 5 to 6. However, up to now they were also 5 to 10 times more expensive than transistors based on established technologies.

MACOM is focusing on gallium nitride on silicon (GaN-on-Si) transistors. This technology enables transistors with the necessary characteristics to be manufactured far more cost-effectively.

The goal set by the RF Energy Alliance is 5 US cents per Watt. MACOM recently presented a GaN-on-Si transistor that achieves 300W and over 70% efficiency. It sells at around USD 15. This level of price to performance has simply not been attainable until now. It also delivers high gains at 900 MHz and 2.45 GHz frequencies. These are the unlicensed frequency bands that are important in many sectors.

The RF Energy Alliance is recommending an overall system efficiency of 60% measured from the power outlet to the food to be cooked. It is widely accepted among experts that the use of GaN technology is the only way of achieving such a target. China is currently considering adopting this as a standard. This would be a very clear signal because not less than 80% of the world’s microwave ovens are manufactured in China!

Over 70 million microwave ovens are currently manufactured annually. However, this not only includes low-cost consumer grade ovens, but also high-end professional ovens that can easily cost USD 25,000. It is evident that a few extra dollars spent at the beginning on RF energy sources compared with magnetrons become more or less negligible. By contrast, particularly in the professional market, its advantages are very important: The long lifetime becomes very quickly apparent in catering applications where ovens run 24 hours a day, 7 days a week, especially in view of the fact that the performance of magnetrons declines before the end of their lifetime. Service technicians often replace magnetrons on a weekly basis. This is where RF energy sources can provide significant cost savings.

Varying the phase between multiple antennae can enable the field distribution inside the oven to be controlled. When equipped with the appropriate intelligence, very homogeneous cooking results can be achieved. By modifying the frequency and phase, the energy delivery efficiency can be set very precisely. We can attain an efficiency of above 90%, even for small loads. As previously mentioned, the overall efficiency of our gallium nitride on silicon (GaN-on-Si) transistors is 10 percent above that of LDMOS.

The manufacturing costs for our gallium nitride on silicon (GaN-on-Si) transistors are substantially lower than those for silicon carbide (SiC). This will not change significantly in the future.

Today’s microwave ovens lack effective control of the power, which results in hot spots and sometime overheating. By contrast, with RF energy sources the frequency, amplitude, phase, pulse width and modulation can all be accurately controlled. With closed-loop control between the RF power amplifier and the RF synthesizer, the forward and reflected power levels can be continuously optimized for the respective application. Three or four transistors and the appropriate antennae make it possible to direct the energy exactly to where it is required; the reflection and absorption can be accurately measured. This control loop enables an oven to accurately determine how well the food is cooked.

The particular subtleties of a recipe can be reproduced over and over again. You no longer need to sense whether the eggs are cooked just right; they will be cooked successfully just the way you want them. Without having to manually enter lots of parameters, the cooking result is far more predictable than in the past, and the interface to the oven becomes much more user-friendly.

The power supply can be very much simpler, no flyback transformer is required, and there is also no longer a need for a motor to rotate the turntable. In addition, there are the advantages resulting from longer lifetime and greater robustness.

It consists of a small-signal generator plus controller, high-power amplifier plus heat sink and a power supply. From the amplifier, the radiation then reaches the actual oven where the food is contained – or in the case of other applications, in an otherwise confined environment, which has the required level of EMC shielding.

Extremely promising: RF energy sources have the potential to replace automotive spark plugs. This would enable no less than 10 percent fuel saving and, in addition, significantly reduce harmful emissions. This is because RF energy can ignite the gas mixture anywhere at the same time, whereas in conventional systems the combustion process progresses wavelike from the ignition spark.

RF energy is used in medical technology to be able to accurately remove tissue layers from tumors. Because the output power can be precisely adjusted, RF energy-based devices will open up entirely new fields of application in medicine which are not at all possible with the old magnetron technology. RF energy sources also have the advantage here that they are extremely compact, robust and efficient.

The same applies to plasma lightings, which are very close to the spectrum of sunlight and can be used for a wide range of applications. Many possibilities will also arise in drying processes in industry, such as for wood. RF energy will find its place in manufacturing, food processing, agriculture and waste management.

I expect that the first microwave ovens based on RF energy will be available in a year, initially in equipment for the professional market. The first appliances for private households will follow one to two years later.