Software-Defined Cooking (SDC) Goes Solid-State

The solid-state RF cooking chip is the large one in the middle [photo: TIRIAS Research]

Paul Teich, Principal Analyst

Freescale is stepping up their smart kitchen profile; they aim to reinvent cooking for a software-defined age. Software-defined technologies have become the norm for emerging smart home ecosystems, but cooking has proven a difficult challenge for two reasons:

  1. Heating is difficult to control with both thermal (heat) and temporal (time) precision. Heating elements take time to heat, are frequently not calibrated to a precisely measured numeric temperature scale, and then take time to cool to lower temperatures. All of these thermal and temporal settings then drift over time because there is no mechanism to recalibrate our cooking devices over their sometimes decades-long lifecycles.
  2. It is extremely difficult to track the “doneness” state of the inside of food with precision. We use the outside appearance of food while cooking as a proxy for the interior state, and we can probe specific interior points with a thermometer. Ideally, we prefer both the exterior surface and the interior volume of our food to be cooked correctly.

The feedback loop between sensing doneness and adjusting temperature (and then finally removing the food from the cooking environment) has been performed mostly by human observation, judgement and labor throughout recorded human history. I say “mostly” because we have invented timers that alert people when the food is probably cooked correctly, like pop-up poultry thermometers. But, these are not automated in the sense that they don’t turn ovens off, or even cool an oven to prevent over-cooking. Many modern high-end ovens do have the ability to connect a probe thermometer; however, I would like to see data on how many owners use them (I assume very few do use them).

Software-defined products continuously:
1. Gather and analyze sensor data.
2. Maintain peak performance and health based on sensor data analysis (feedback loop).
3. Communicate their analysis with other software-define products and cloud services for continuous improvement.

Change Starts With Innovation

Freescale’s key innovation to enable software-defined cooking is deceptively simple — solid-state, high-power output, high-operating temperature radio frequency (RF) transmitter technology.

Freescale Technology Forum 2015 RF Cooking Chips Display [photo: TIRIAS Research]

Freescale manufactures their cooking transmitters using N–channel enhancement–mode laterally diffused MOSFET (LDMOS), a type of asymmetric power MOSFET commonly used in wireless base station RF transmitters. Freescale has a wide range of RF chips listed on their site, from 10 to 350W power output.

Freescale’s RF transmitters work at the same electromagnetic (EM) frequencies as microwave ovens, 0.9 and 2.45 GHz. (For my view of the history of cooking and market implications for RF transmitters in the kitchen, including the marketing use of “RF” vs. “microwave,” keep reading here.)

Using the same frequencies as microwave ovens is where the similarities between Freescale’s RF and traditional microwave oven technologies end. A microwave oven magnetron is like a light bulb — it radiates in all directions — and so designers direct the energy into the cooking compartment with waveguides. Because magnetron and waveguide radiate indiscriminately into the cooking compartment, microwave ovens need only one heating element of sufficient power to flood the cooking compartment. Heating is often wildly uneven due to standing wave patterns in the EM shielded cooking compartment. Because EM radiation behaves like waves, reflections of those waves from the walls of a microwave oven sometimes reinforce each other and sometimes cancel each other. Areas where waves reinforce receive too much energy and heat faster, and the opposite happens where waves cancel — food heats slower. Most microwave ovens include a motorized turntable to rotate food through the standing waves to promote more even cooking. Like the fan used to circulate air in a convection oven, a rotating turntable is not a high tech solution.

RF transmitters use antennas placed inside the walls of an oven to steer EM beams with some precision. The small size of solid-state RF transmitters means that multiple transmitters can be used in an oven instead of only one. Multiple transmitters means that standing waves can be minimized for more even cooking. And, because steerable antennas can be used, RF can generate consistent temperatures throughout the cooking compartment, where a magnetron cannot.

Freescale talks about measuring the power reflected from the food in an RF oven, in real-time, to guide their steerable RF beams to further improve the cooking experience. Freescale plans to use a portion of their RF transmitter circuitry to measure the power absorbed by the food against the power reflected from the food, and will use that information to help guide the cooking process. This will not require an additional sensor — it will be built into the RF cooking circuit. Other sensors can also be added to an oven design to enhance the cooking process. These sensing capabilities will provide far better insight into the cooking process than microwave ovens can usefully employ.

Freescale has not yet provided details on types of sensors they are planning to deploy in the cooking compartment, nor the information they would receive from those sensors, but they believe the information will provide much more precise heating data than thermocouple based thermometers, plus that data would describe the entire cooking compartment in real-time.

Freescale’s RF web page tags RF cooking as a focus for their RF transmitters, and similarly cooking appliances are a major target for Freescale’s sensor products.

The Whole Package

RF transmitters and antennas used in cooking appliances must be capable of repeatedly cycling through a wide range of cooking temperatures — thousands of hot and cold cycles over many years. Water boils at 212°F (100°C) at sea level, however, avocado and refined safflower oils have smoke points above 500°F (260°C). Even with well-designed insulation, electronic components in heating appliances also get hot. RF transmitters and any sensors in the cooking compartment must be capable of operating as RF energy heats food to these temperatures and the food then radiates thermal energy into the cooking compartment in response.

For example, Freescale’s MHT1000HR5 part has a case operating temperature (TC) rating of 150°C, or just over 300°F. With insulation, this should survive quite well embedded in a heating appliance. It should survive, given that Freescale’s automotive engine compartment products have very similar temperature range and thermal cycling requirements.

Freescale RF Cooking Application Fixture, Side View [photo: TIRIAS Research]
Freescale RF Cooking Application Fixture, Top View [photo: TIRIAS Research]

The electrical efficiency of Freescale’s RF cooking modules is in line with modern microwave ovens — in the mid-60% efficiency ballpark — but microwave oven technology is very mature, while high-power output solid-state RF is beginning its learning curve and should get more efficient in the future. The copper block in the cooking application fixture (shown in the above photos) is a “thermal mass” designed to absorb and dissipate the third of the input power wasted as inefficient heat, more than 100W for a 350W device.

Because Freescale’s RF transmitters use the same frequencies as microwave ovens, similar shielding will be required to prevent radiation leakage while operating. However, because RF beams can be steered it may be possible to use many RF transmitters, each operating at slightly lower power, which could reduce the amount of shielding required or provide more safety headroom.

In the same spirit, using several comparatively lower power RF transmitters instead of a magnetron means appliance designers might be able to build slimmer walls build around cooking compartment, resulting in more visually appealing designs than boxy microwave ovens.

Freescale’s Sage RF Oven Concept Design [photo: TIRIAS Research]

RF technology might also be designed into conventional ovens to speed up cooking without reducing cooking compartment volume, similar to today’s convection fans. That would give food the correct finish and texture, but even faster than convection ovens.

Developing A Flavor For Software-Defined Cooking

The first and foremost attribute of SDC is precision, generated by a sensor-drive feedback loop. Continuous calibration for repeatable, precision cooking will result. With self-calibration comes self-diagnosis and performance tuning.

Connecting a smart oven to the Internet will then provide the ability to both diagnose problems as they occur and to improve their cooking performance by sharing data with cloud services. The result may be that ovens can better cook basic foods and then handle increasingly more complex recipes — and then customize recipes for changing cultural tastes. Smart ovens might even become a partner in cooking foods, guiding owners step-by-step through complex recipes (“now fold in two eggs and return the bowl to the oven…”)

High-power solid-state RF transistors will enable smart ovens and other smart cooking appliances to assist their owners in expertly preparing meals. However, it will take a decade or more for Freescale’s RF innovation to change cooking. We are in the early days of software-defined cooking, and like all kitchen technologies, the recipe for success is guaranteed to evolve as the technology matures.

Freescale gave me a complimentary media pass to Freescale Technology Forum 2015. I am not currently working on projects for any of the companies mentioned, nor have I invested in them.