Tuesday, June 25, 2024

Let’s Warm Things Up

Parent Category: HFE Magazine

By Tom Perkins


Microwave cooking has been feasible for about 70 years, and commonly available to consumers since about 1970. It is estimated that as many as 90 percent of US households may now own at least one of these venerable devices. A large and diverse company called NXP®, with headquarters in the Netherlands, recently announced a variant on this wonderful invention – a Smart Defrost Solution. The idea is to use a microwave oven-like device to provide rapid high-quality defrosting in a convenient and safe manner. An innovative approach to this daily encountered culinary challenge was recently announced at the Consumer Electronics Show (CES) in Las Vegas, NV.


First, air and water methods for defrosting take hours and are results are inconsistent. Continuous “hovering” is required to monitor progress of the thaw which is inconvenient and costly. Bacterial growth risk becomes a problem when surface temperature of the food exceeds 40°F/4°C. Hot and cold spots often occur when using a conventional microwave oven. Also, moisture loss reduces nutritional content.

The modern technology introduced is somewhat like a microwave oven, but there are differences. Instead of using a magnetron as a source at about 2,450 MHz, the RF energy is generated by solid-state electronics at VHF. These low frequency electromagnetic waves pass completely through food. Like at microwave frequencies, molecule rotation and collisions create friction heat (see Figure 1).

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Figure 1 • Molecule rotation and collisions create friction heat.

Configuration of the Thawing Machine

Referring to Figure 2, first a power supply is required to convert 117 or 230-volt AC to required DC voltages. The VHF RF source creates the energy used to raise the food temperature. The source (oscillator) energy is then amplified using Laterally Diffused Metal Oxide Semiconductor (LDMOS) technology to a level of approximately 300 watts (54.8 dBm). A Smart Tuning Unit (STU) adjusts the operation of the unit to best match the properties of the selected food within the defrost chamber. The delivery of the energy into the cavity is provided by Electrodes analogous to, but not, typical antenna elements. The Electrodes protrude into the Cavity which is an enclosed space for defrosting frozen food. Finally, a Host Control, aka, main appliance control and user command interface make the unit complete.

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Figure 2 • Smart Defrost Solution Features and Functionality.


NXP claims the following benefits for this technology.

It is:

  • Automatic
    • Single button operation
    • Intelligent system ceases heating at target temperature


  • Fast
    • Requires minutes, not hours to defrost
    • High efficiency
    • Managed power levels

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Figure 3 •  Even defrost (left) and uneven thaw (right).

  • Even/Uniform (See Figure 3)
    • No hot spots
    • Complete food penetration
    • Retains moisture and quality


  • Economical
    • Keep food frozen until needed – prevents spoilage
    • Defrost on demand reduces risk of spoilage


  • Food Safe
    • Closed loop monitoring
    • Original equipment manufacturer optional added cool air flow limits bacteria growth by keeping temperature less than 4°C


During an early January briefing prior to the CES rollout which at the time was subject to embargo, it was learned that this technology has a focus on defrosting, not cooking, maybe better called thawing. During the briefing it occurred to this writer that there may be some other subtle benefits to this scheme. First, using very high frequencies (VHF) rather than microwaves, the oven cavity would be beyond waveguide cutoff and thus energy radiated to unintended directions would be rapidly attenuated. Also, shielding the door might be less difficult. Also, the voltages involved in the power supply for solid-state electronics are not as hazardous as those needed to run a magnetron. That power supply may also be more compatible with smart computing and “Internet of Things” or “Internet of Services” functionality that may come along for these devices, much like is happening with refrigerators.

These devices may come in various forms as suggested by NXP In Figure 4.

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Figure 4 • Possible Configurations.

Microwave Oven RevolutionSimultaneously Cooking an Entire Meal

The microwave oven may itself undergo significant upgrades. Microwave ovens generally never got beyond a supporting role in most kitchens because it couldn’t be configured to cook a complete meal from scratch. Bear in mind that most conventional ovens also cannot cook a complete meal in the oven. Most hot meal preparation requires simultaneous use of stovetop “burners” and oven(s). An extreme example tends to occur, say at Thanksgiving in Canada (October) or US (November), when every available cooker might be activated simultaneously.

As stated earlier, microwaves work from the outside in, so they can’t really cook food evenly, not good in raw meat preparation. Plus, they can remove much or all the moisture out of some foods, turning bread and other carbohydrates into inedible “bricks or clinkers”. Abundantly deployed microwave ovens are primarily used for reheating meals and popping popcorn.

The magnetron, requiring about 4 kilovolts at 300 mA and delivering about 1 kilowatt of microwave energy, sends out the waves that stimulate food molecules and create heat, but does so with a shotgun approach. Some areas get hot, while others remain tepid. And, while using the settings for different foods may help a bit, microwave cooking is still largely an imperfect process.

An Israeli company named Goji Food Solutions says it has a better idea. This could be called pseudo disruptive technology. Like the defroster described earlier, it is based on solid state radio frequency (RF) technology that provides much more precision and control over the radio wave energy being emitted. Not only does that enable food to be cooked faster, but it also makes it possible to treat different foods in separate ways, all at the same time.

An RF oven would allow cooking a whole meal at once, with amplifiers sending out one RF beam set to cook meat, another to cook vegetables and a third to bake a dinner roll. That works because Goji has added to the RF technology precise sensors that can read the makeup, thickness and moisture of the food and appropriately adapt the frequency, phase and amplitude of the radio waves. The process creates a feedback loop in which the amount of radio waves reflected from within the food is detected. Every few seconds, an algorithm recalculates the sensor data and the signal is adjusted as needed. Thinking about this it is not unlike an adaptive radar, except until now we always think that this would have prohibitive cost, not to mention considerable size and possibly weight impacts.

“In order to obtain optimal heating results for a dish, our system senses the food and adjusts the heating parameters using a unique algorithm in real time,” explains Goji Food Solutions President Yuval Ben-Haim. “This process also allows us to make adjustments when the food changes during the heating process; for example, a cake which rises during baking, frozen meat being defrosted, or apple chips being dried. Beyond cutting cooking time significantly for a wide range of dishes, this method results in tastier and healthier food by cooking it more evenly.”

RF-prepared food is healthier, according to Goji, because the rapid cooking makes it possible for the food to retain more nutrients and moisture.

To show just how precise RF cooking can be, Goji officials have demonstrated how they can effectively cook a salmon still frozen in a block of ice—without melting the ice.

Future Meals, Cost, and other Applications

Goji’s technology has its roots in organ transplants. They hold a number of U.S. patents for its methods and devices). Circa 2005, researchers looking for ways to preserve human transplant organs discovered that they could use radio waves to defrost frozen tissue evenly. It became evident that it could have much broader applications.

But refining the process so that it could work in a person’s kitchen brought a steep learning curve, Ben-Haim acknowledges. Knowing it could work was one thing; bringing together all the components was quite another.

“The greatest challenge was transferring our product out of the lab and into serial production,” he says. “While we are not the first to have manufactured high-power RF systems, we are, to our knowledge, the only ones to have done so at high scale.”

While Goji was expected to have the first generation of its RF oven on the market last year, it probably will be a few more years before there’s much consumer adoption. The first models are likely to cost in the range of high-end conventional ovens, perhaps US $5,000 or more. The first buyers are expected to be commercial operations, such as restaurants, hotels and schools. This appears to be much like the early years of the original microwave ovens. However, with the rapid pace of advanced and agile manufacturing technology, the reduction of costs may be in terms of months instead of years. Also, the basic RF cooking concept is already widely accepted.

The company is optimistic that it won’t be too long before it can start selling a less expensive countertop version. At the same time, it hopes to one day be able to get food manufacturers to include a special Goji bar code on their packaging. It could be read by a smartphone, which would then pass the info on to the oven, so the food would be cooked to the precise specifications.

Ben-Haim sees other possibilities, even beyond food preparation.

“RF technology could be used in restaurants, coffee shops, even vending machines to cook fresh and healthy food quickly. Imagine having your croissant freshly baked for you while you pay,” he says.

There are several other companies working on similar technology. For example, STMicroelectronics has a recent patent which refers to beamforming cells and feedback circuits. NXP claims that Solid State Cooking (SSC) will save 60% of energy over conventional ovens.

Goji also embraces another exciting application, clothes drying. By incorporating RF technology into tumble dryers, they managed to shorten drying cycles significantly, while providing other benefits such as low temperature drying, which results in less wear and creasing.

There may be industrial processes such as plastics and acrylics that could benefit from this as well. Kiln drying lumber, coal etc. is also within the realm of possibility.

Note: All Figures Compliments of NXP.

About the Author

Tom Perkins is HFE’s Senior Technical Editor.

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