Wayv solid state MW thermos - Page 1
Forum section: electronics / projects

author: Bud
author_rank: Super Contributor
timestamp: June 10, 2016, 02:48:32 pm
content: I saw an article in Microwave & Rf magazine about this microwave coocking appliance product and my first thought was "BS", then i found a video showing the actual thing. There is a fairly good shot of the MW board section at the end of the video, perhaps is worth a discussion

author: N2IXK
author_rank: Frequent Contributor
timestamp: June 10, 2016, 03:33:52 pm
content: Completely real. NXP and Freescale Semiconductor have developed RF power FETs that are targeted at replacing magnetrons in microwave heating applications:http://www.nxp.com/pages/rf-and-microwave-power-solutions-for-heating:RF_HEATING_PGhttp://www.electronics-eetimes.com/news/domestic-microwave-oven-first-use-solid-state-rf-powerhttp://electronicdesign.com/blog/say-good-bye-last-vacuum-tube-productWhether they are as reliable as magnetrons is yet to be seen, however...

author: ConKbot
author_rank: Super Contributor
timestamp: June 10, 2016, 07:59:59 pm
content: Yep, real. I remember seeing the article in a journal we had laying around at work. Exclaimed to a co-worker. "Hey man, look, solid state microwaves". He replied "inverter microwaves aren't new" "No, solid state RF too, no magnetron" and that got his attention. Definitely had potential. By sweeping frequency, nodes and antinodes in the chamber can move, for more even heating. Smoother reduced power settings, (not 10 seconds on 10 seconds off for 50 percent power, though I suspect inverter microwaves should be able to do that) Less interference if the output isn't AM modulated at 100/120Hz like a magnetron is. Cheaper Kw range switching power supplies for scrapping and repurposing. (though MOTs are always handy for projects after bashing out the shunts.)And let's be real, gut the synthesizer and replace it with coax from a Wi-Fi access point and you could probably get WiFi to the ISS.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 10, 2016, 08:04:49 pm
content: When I was in SF I visited a place that made neutron generators - these need microwave powers similar to microwave ovens & they were looking at semiconductors from Freescale, from memory, a device about 20x10x5mm would do something like 130W at 2.4GHz with >70% efficiency.The main market for these is cellular basestations

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: June 10, 2016, 10:37:20 pm
content: Quote from: ConKbot on June 10, 2016, 07:59:59 pmIf you can hear the microwaves, take your head out of the oven first.

author: ConKbot
author_rank: Super Contributor
timestamp: June 11, 2016, 08:28:42 am
content: Quote from: Alex Eisenhut on June 10, 2016, 10:37:20 pmDefault keyboard on my LG (phone, not microwave!) is rather... aggressive. I need to change it back to swype.

author: coppice
author_rank: Super Contributor
timestamp: June 11, 2016, 10:56:11 am
content: Quote from: mikeselectricstuff on June 10, 2016, 08:04:49 pmThe size of RF power transistors is largely irrelevant. The space taken is all about the heatsinks and fans. You need to keep RF power transistors fairly cool. You can let a magnetron run really hot, requiring a lot less cooling effort.

author: Don Hills
author_rank: Regular Contributor
timestamp: June 12, 2016, 06:05:26 am
content: Quote from: coppice on June 11, 2016, 10:56:11 amThere is a limit. You need to keep the magnet below its Curie point.

author: Someone
author_rank: Super Contributor
timestamp: June 12, 2016, 09:40:20 am
content: Quote from: ConKbot on June 10, 2016, 07:59:59 pmThats not going to work given the narrow absorption band that microwaves use for heating (and are conveniently declared a license free ISM band).

author: SeanB
author_rank: Super Contributor
timestamp: June 12, 2016, 11:11:48 am
content: Quote from: Don Hills on June 12, 2016, 06:05:26 amYes, but is is going to be a lot easier to keep the magnet under 300C, as it is separated from the main heat generating anode, than it is to keep a silicon die under 150C which is the heat source. The actual diode valve itself will run happily at 400C using only the few pressed on vanes and forced air cooling to keep it running. They will run for at least 5 minutes without the fan running 9 think obstructed by dust or the fan has fallen off the shaft or seized because the bearings ran dry) before the thermal cutout will operate ( 130C) on the frame.Curie point for a lot of ferrites is around 450C.http://www.magnetsales.com/ferrite/ferrprops.htm

author: coppice
author_rank: Super Contributor
timestamp: June 12, 2016, 11:53:04 am
content: Quote from: Someone on June 12, 2016, 09:40:20 amWhat narrow absorption band? The first resonance of water is at 22.45GHz. If a microwave oven used that frequency the surface layer of the food would absorb so well the inner parts would only cook by conduction, as with conventional cooking.

author: CM800
author_rank: Frequent Contributor
timestamp: June 12, 2016, 12:36:42 pm
content: I bet you could do some really interesting chemistry / physics with these that is far out of my imagination.Anyone tried to get a price on them? Could be really quite interesting to see a home-made microwave.

author: Someone
author_rank: Super Contributor
timestamp: June 12, 2016, 01:06:56 pm
content: Quote from: coppice on June 12, 2016, 11:53:04 amISM band is 2.4GHz to 2.5GHz, you could stop transmitting and jump to the other bands but it still wouldn't be possible to sweep nodes through the cavity. Also there are lots of reasons why 2.45GHz is used for cooking purposes:http://www.emu.dk/sites/default/files/physics_of_microwave_oven.pdfhttp://www1.lsbu.ac.uk/water/microwave_water.htmlJust a few quick google hits away is a wealth of information on why the world is as it is.

author: Bud
author_rank: Super Contributor
timestamp: June 12, 2016, 01:12:15 pm
content: Quote from: TCWilliamson on June 12, 2016, 12:36:42 pmI think i saw a figure of $200.

author: coppice
author_rank: Super Contributor
timestamp: June 12, 2016, 01:37:35 pm
content: Quote from: Someone on June 12, 2016, 01:06:56 pmIts certainly hard to see how they could stir waves much by using the breadth of the 2.4GHz ISM band, but the use of multiple power transistors with multiple antennae offers the possibility of phase array approaches to the problem. The cost might be a problem, though. I suspect the use of only 200W output is not just because this is a small portable device. The solid state kitchen worktop model Midea have announced is also just 200W, probably because the price of an 800W one would be eyewatering when Galanz ship magnetron based microwave ovens for peanuts.

author: ConKbot
author_rank: Super Contributor
timestamp: June 13, 2016, 04:48:34 am
content: Quote from: Someone on June 12, 2016, 09:40:20 amI meant staying in band. Sweeping from 2.425G to 2.475 is only a 2mm change in wavelength, so it would depend on cavity design too, but if they can alter a stamping die and eliminate the need for a motor and the rolling ring, i suspect they would. Band hopping would certainly be interesting though, 5.8GHz has more loss in water, and 900MHz would have better penetration.https://en.m.wikipedia.org/wiki/Electromagnetic_absorption_by_water#/media/File%3ADielectric_loss_water.pngMaybe for once the different modes on the front of the microwave could do something useful.Then again how stable is a magnetron? I haven't exatly taken a spec-an or frequency counter and measured the output of a normal microwave. A cooking magnetron is going to be optimized for output power per $, so they very well could be sweeping all over the place as it is.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 13, 2016, 07:49:01 am
content: Quote from: coppice on June 12, 2016, 01:37:35 pmThat's surely a bit of a chicken/egg situation - if the market for these semiconductors gets big enough, through a combination of cellular and microwave ovens, they will get cheaper.It may also be the case that microwave ovens can use "seconds" from cellular production, as the requirements are a lot less stringent - at the very least I'm sure they don't need as much testing for MWO applications.

author: coppice
author_rank: Super Contributor
timestamp: June 13, 2016, 08:00:00 am
content: Quote from: mikeselectricstuff on June 13, 2016, 07:49:01 amGiven enough time most electronics becomes cheap. I was think more of the short term prospects. Transistors of the type needed for these ovens are made in millions for cellular applications, so there is already a reasonably high volume application which has been driving their price down for some time.I'm not sure what test cost reduction could be achieved. In lower power applications people use much cheaper packaging for less demanding applications, but that doesn't usually work out well for high power devices.

author: SeanB
author_rank: Super Contributor
timestamp: June 13, 2016, 07:02:56 pm
content: Quote from: ConKbot on June 13, 2016, 04:48:34 amNot stable at all, the frequency is being modulated at mains frequency and by the heating of the cavities as the magnetron heats up. Expect a minimum of 50MHz spread or more, so it is possible a magnetron will often be emitting power out of the allocated band some of the time. However as the power is contained mostly inside the casing this is not too much of a worry.

author: Bud
author_rank: Super Contributor
timestamp: June 13, 2016, 07:55:59 pm
content: Lets talk about practicality of this solution. A good thermal bottle will keep food warm for 24 hours (or cold/cool, which this product may not do), for much less cost. So you what, will store your food for 2-3 days in the container? How good the food will be after 2 days even if you warm it up. It may go bad left for that long in a small space, especially if the container is not insulated from ambient temperature. Not sure if i can see many use cases for this product.

author: coppice
author_rank: Super Contributor
timestamp: June 14, 2016, 01:40:57 am
content: Quote from: SeanB on June 13, 2016, 07:02:56 pmThe flimsy construction of the cavity in an oven magnetron also spreads the output spectrum, as the cavity vibrates. Magnetrons for radar use had a very solid, milled from a block, construction, and had far better spectral purity.