What happened to RF cooking? - Page 1
Forum section: electronics / general

author: jmw
author_rank: Frequent Contributor
timestamp: June 13, 2023, 11:40:10 pm
content: I remember about five years ago there was a big splash about improving microwave ovens and RF cooking: replace magnetrons with adjustable output solid-state RF power amps, with some ideas about specialty defrosters using HF & low-VHF frequencies. There was a prototype oven from Miele for an insane price, NXP made a line of transistors that are now unobtainium, although one part seems to live on in the MRF300. Then the buzz died and nothing was brought to market. Anyone know why things stopped?

author: Marco
author_rank: Super Contributor
timestamp: June 14, 2023, 12:07:11 am
content: Miele is still selling them, at around 10k$ just not many are buying.Having say 10 kV 13.56 MHz at kW range between the top and bottom of the oven interior is just hard. The oscillator is hard, meeting EMI limits is hard, making it safe is hard.

author: KaneTW
author_rank: Frequent Contributor
timestamp: June 14, 2023, 01:27:56 am
content: I just found Goji from some googling. Apart from that, I've only seen inverter microwaves around which also allow for adjustment.

author: Marco
author_rank: Super Contributor
timestamp: June 14, 2023, 01:45:20 am
content: Quote from: KaneTW on June 14, 2023, 01:27:56 amThey say "Dielectric RF heating typically operates within a band of 13 MHz – 6 GHz. Our latest RF module operates in the 2400 – 2500 MHz band."It seems to me that it's not dielectric heating, but they are using an array of patch antennas rather than a magnetron tube.'PS. also seem to be varying the frequency to move standing wave nodes around.

author: coppercone2
author_rank: Super Contributor
timestamp: June 14, 2023, 02:16:18 am
content: lol they probobly taste tested it and figured out that it still tastes better from a $40 toaster ovenI have a inverter microwave, its good for defrosting left overs, if you have the time, they are less dry. If you vacuum freeze a big holiday dinner it really wins for reheatin that food.'And its like hard to compete with ranges IMO. If you ever put pizza on a cast iron pan to reheat... the microwave one seems only good if you are strapped for time.

author: Marco
author_rank: Super Contributor
timestamp: June 14, 2023, 02:30:34 am
content: You could use the dielectric oven for faster reverse sear, it penetrates deeper than microwaves and faster than convection at low temperature.Other than that it can do the gimmick of heating food in a block of demineralised ice.

author: IanB
author_rank: Super Contributor
timestamp: June 14, 2023, 02:57:45 am
content: Quote from: jmw on June 13, 2023, 11:40:10 pmEngineering is why things stopped. Engineers figured out how the reduce the manufacturing cost of microwave ovens to the absolute minimum, because the only thing that sells consumer products these days is "Cheap! Cheap! Cheaper!"Put two competing products on the retail shelf, one costing $50 and the other costing $75, and the $50 product will outsell it 10:1. Try making a product costing $150 and it will sit on the shelf forever gathering dust, no matter how much better the quality or performance.I've stood next to people in shops and watched them buy the crap product instead of the good product, because the crap product was cheaper. It's depressing, and is the reason why it becomes increasingly difficult to buy quality products these days.

author: Marco
author_rank: Super Contributor
timestamp: June 14, 2023, 03:03:05 am
content: Just need to wait for Apple ovens.They'll pretend they've invented it and suddenly it will sell.

author: EPAIII
author_rank: Super Contributor
timestamp: June 14, 2023, 09:01:30 am
content: "Cheap! Cheap! Cheaper!" I am too poor to afford that.After going through four or five, I have lost count, microwave ovens in my kitchen, I went expensive this last time. Six months and counting. Only time will tell.

author: Miyuki
author_rank: Frequent Contributor
timestamp: June 14, 2023, 09:45:17 am
content: Hundreds of watts GHz transmitters will be pretty expensive stuff compared to a simple magnetron with probably a single-digit cost.And those cheap magnetrons with plain transformer works just right for 95% of people.Some people will invest in inverter-fed magnetron ovens to get better regulation.But I cannot imagine spending high hundreds or thousands $/€ on a microwave oven for heating leftovers.And for cooking, common convection ovens are more practical and have wider use. They are also easier to scale. Can offer cooking in steam and various other modes.

author: Marco
author_rank: Super Contributor
timestamp: June 14, 2023, 10:30:22 am
content: Inverter is cheaper than a transformer.For European kitchens I think one 45cm height combi and one 60cm oven is the most natural setup. Why waste space on a microwave when you can combine it with a convection oven with grill?

author: tom66
author_rank: Super Contributor
timestamp: June 14, 2023, 10:40:18 am
content: Magnetrons are dirt cheap 2.45GHz RF sources. Unstable, poorly regulated, but dirt cheap.You can improve them to some degree with power control, which is what inverter microwaves do. These can vary the power between about 40% and 100%, at less than 40% I guess the magnetron isn't stable so they cycle the power instead (maybe there's another reason but my Panasonic inverter microwave does this.)RF power electronics would need to fall towards the $25 or so a microwave oven transformer, magnetron and capacitor achieve to go truly mass market, and at least be within the $100-$200 cost region to be at least in the premium market (say for a $500 oven.) It's a big ask, it may well happen eventually but it will take some time if it does.

author: Marco
author_rank: Super Contributor
timestamp: June 14, 2023, 10:49:19 am
content: The Ampleon amplifiers are at the same time remarkably cheap and at the same time still way to expensive to compete with magnetron tubes. The more even space filling possible with multiple emitters and some frequency modulation is nice, but not that nice.

author: tom66
author_rank: Super Contributor
timestamp: June 14, 2023, 11:22:15 am
content: Quote from: IanB on June 14, 2023, 02:57:45 amThere are still premium products out there. But really to make this work we need manufacturers to have enforced warranties. The EU originally had 2 years minimum on products but that should be 5 years. This would mean that there's little incentive to produce crap appliances.One kitchen appliance we have is an ice maker. I bought it second hand from a charity shop. It's about 3.5 years old now. Since then I've replaced: the tray motor (died), cooling fan (bearing went), microswitches to detect the tray position (plastic case on one just cracked and switch fell apart), and the piping for the water pump (as the pipe began to disintegrate and leak), and most recently the IR detection barrier - the LED/photodiode combination failed as the leads rusted so I replaced those. Really, about the only thing that hasn't broken is the compressor and refrigeration circuit. I imagine most people would have thrown the product in the bin by now, and it was probably sold with a 1 year warranty. Such badly built products shouldn't be allowed to be marketed.

author: BradC
author_rank: Super Contributor
timestamp: June 14, 2023, 12:11:09 pm
content: Quote from: IanB on June 14, 2023, 02:57:45 amI've met plenty of people who've saved for months just to be able to afford to buy the base level crap product (oh lets let's say it's an aluminium electric kettle with a steel element that will rapidly succumb to dissimilar metal corrosion). When it fails 35 milliseconds outside of the warranty period they then get screwed again. Damned if you do, and damned if you don't.On the flip side, we have my great grandmothers treadle singer sewing machine. When she died and we inherited it we gave it a "birthday" and found the payment book in the bottom drawer. She paid it off over 2 years starting in the late 1920's, used it to provide for the family for 30 years as a seamstress and it's still serviceable.There's a message in those two paragraphs, but buggered if I can figure out what it is. I've always been taught "A poor man pays twice".

author: tom66
author_rank: Super Contributor
timestamp: June 14, 2023, 12:19:21 pm
content: Quote from: BradC on June 14, 2023, 12:11:09 pmhttps://en.wikipedia.org/wiki/Boots_theoryfrom the late Pratchett's novels.Quote

author: BradC
author_rank: Super Contributor
timestamp: June 14, 2023, 12:38:49 pm
content: We recently replaced our NZ built Dishwasher. In 22 years it had 1 new hose and 4 new capacitors. The reason it had to be replaced was my son decided to use the drawer handles as steps and bent the chassis in several places. We replaced it with another brand because the new ones are no longer made in NZ, and whilst the price is relatively similar (from an income perspective) to when I bought it, the longevity of the new ones isn't (even the guy selling them warned us off, even if it meant buying from another chain).Sometimes you can't buy the device you want with the quality you want at any price. We've had to settle for a totally different machine from a different manufacturer, with a completely different operational philosophy just to ensure continued spare parts availability and serviceability. Anyway, I'm rambling now.

author: BrokenYugo
author_rank: Super Contributor
timestamp: June 14, 2023, 03:49:04 pm
content: I didn't live through it, but this whole thread reminds me of when home microwave ovens first got popular/affordable and there was (based on literature that survived) a great deal of interest in this new "microwave cooking" until it was realized the only cooking you can easily/practically do well in one is reheating and steaming things. There's a lot of goodness going on in that whole browning/frying process that any RF oven just won't do without more trouble than it's worth.

author: tom66
author_rank: Super Contributor
timestamp: June 14, 2023, 05:41:16 pm
content: Quote from: BrokenYugo on June 14, 2023, 03:49:04 pmI guess it's a bit like those old ads for microwave ovens, which showed people cooking whole chickens or turkeys inside one;https://www.ebay.com/itm/185790969368I don't think I know of anyone who actually does that. If they do, I hope I'm not invited over for dinner.

author: BrokenYugo
author_rank: Super Contributor
timestamp: June 14, 2023, 06:01:57 pm
content: Quote from: tom66 on June 14, 2023, 05:41:16 pmMy parents actually had one of those old timey top of the line "cook everything" models until it got replaced by an inverter. "Quasar" brand, solid floor, came with a temperature probe and 1/4 inch headphone socket for it in the oven wall. The only thing I remember my mom making in it with that feature was meatloaf, and even that came out better in a real oven, the manual had instructions for whole birds and whatnot, even detailed strategic aluminum foil application for reasons I forget.But yeah, feels very reinventing the wheel trying to improve a microwave oven, advances in driving the cheap magnetron aside they're very mature tech, the market long ago shook out the desired feature set and I don't think much has changed in the meantime.

author: SeanB
author_rank: Super Contributor
timestamp: June 14, 2023, 06:24:50 pm
content: Hey, did an entire warthog in one of those ovens, it was delicious. When programming the oven we just told it that it was doing a 2kg chicken. that little piggy was delicious, soft, tender and very tasty, nothing was left at all. At least it was easier to handle than that 250kg waterbuck.https://en.wikipedia.org/wiki/Common_warthogWhat the dinner looked like.https://upload.wikimedia.org/wikipedia/commons/thumb/0/05/Female_warthog_with_young.jpg/292px-Female_warthog_with_young.jpghttps://en.wikipedia.org/wiki/Waterbuck

author: Miyuki
author_rank: Frequent Contributor
timestamp: June 15, 2023, 11:12:21 am
content: Quote from: BrokenYugo on June 14, 2023, 06:01:57 pmMost of those were/are combined with grill and convection cooking

author: Marco
author_rank: Super Contributor
timestamp: June 16, 2023, 08:11:11 pm
content: I wonder if a toaster oven sized dielectric heater could succeed where the Dialog fails. No separate functions complicating design, just big enough to put a couple steaks in and get them up to a relatively even temperature, far faster than sous vide or low temperature convection can. Throw your steaks in the dielecric heater for a couple minutes, scorch it with cast iron/carbon steel/torch and done.Market it as waterless hyperspeed sous vide or some such bullshit. Might do well on Kickstarter.

author: jmw
author_rank: Frequent Contributor
timestamp: June 16, 2023, 08:41:19 pm
content: I'd buy one! But as you said the R&D to make it safe is hard, and probably not at a Kickstarter-friendly price.

author: Bud
author_rank: Super Contributor
timestamp: June 16, 2023, 09:42:28 pm
content: Have you people become that stupid that you can't cook a whole chicken in the oven? Why do you need a zeebeoues technology appliance to do this? All you need is a beer bottle half filled with water and a knife. I cant believe what I am reading.

author: Marco
author_rank: Super Contributor
timestamp: June 17, 2023, 12:23:22 am
content: I wonder if I overestimate how high the voltages have to be, meat is salty water as far as the signal is concerned, which has a very high dielectric constant. So it will pull all the potential towards itself. A single kV might be enough.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 17, 2023, 01:29:06 am
content: Quote from: Marco on June 17, 2023, 12:23:22 amBig Clive had great success with a mere 240V applied using electrodes. A bit too intense, actually.If you use capacitive coupling instead, you'll just have to calculate the reactance the capacitance would add.

author: Marco
author_rank: Super Contributor
timestamp: June 17, 2023, 11:48:12 am
content: Oops, I turned it around ... the high k dielectric will cause a large capacitance, which will have the least voltage across. So back to 10s of kV to put a couple 100 Watt into a steak.The sidewalls in an oven are a bit of a bother as well. Industrial heaters can just have a giant air cavity and tell people to stay away, the cavity in an oven is shielded. You'd make the inner chamber slotted obviously, but all the capacitance to ground (the shield) will bunch the voltage in the middle, without adding yet more capacitance to even it out. All that capacitance is going to draw circulating current, annoying for both efficiency and the driver.

author: KaneTW
author_rank: Frequent Contributor
timestamp: June 17, 2023, 11:38:22 pm
content: I'd gladly spend ~2-3k on an oven that can actually uniformly (i.e. not just the surface, and not the spots that regular microwave cause) heat food.

author: tom66
author_rank: Super Contributor
timestamp: June 18, 2023, 10:50:55 am
content: Quote from: KaneTW on June 17, 2023, 11:38:22 pmFor microwaves, you want one with an RF stirrer. Panasonic make a number of "inexpensive" consumer ovens with this function, e.g.https://www.panasonic.com/uk/consumer/home-appliances/microwaves/combination-microwaves/nn-df386bpq.htmlWe have a similar one at work. It's weird not having a turntable to put things on. But you can put something in it at any position and it's even throughout.I was looking at this one for our kitchen but unfortunately the oven function requires a lot of space behind the oven to be kept clear, so wouldn't work where we wanted it.