Tuesday, May 31, 2016

Portable, battery-powered microwaves?

It looks like the microwave oven as we've always known it is about to become obsolete.

The Adventurer is a portable battery-powered microwave the size of a Thermos. Campers, hikers, and anyone else away from the grid can make a hot meal in minutes without a fire. Camp cooking could get a whole lot easier.

The three-pound Adventurer is more than a handy piece of kit, though. This is one of the first fruits of a new technology that could not only nuke your lunch on the go, but also make an impact in areas as diverse as crop protection and oil extraction.

. . .

Portable gadgets like the Adventurer are just the start—solid-state microwave sources are driving a new generation of kitchen appliances ... "The 'more controllable' feature cannot be overestimated," says Klaus Werner, executive director of the RF Energy Alliance, an organiation dedicated to realizing the potential of this technology. "It gives you perfect process control via fast control loops. The Magnetron is very slow at best. Sensitive processes such as food pasteurization, blood thawing, sous vide cooking or pharmaceutical reactions all benefit greatly from this technology."

Looking further afield, Werner says that solid state has myriad other possibilities. "The technology allows a number of hitherto impossible radio-frequency applications—automotive ignition, radio-frequency ablation, hypothermia treatment, plasma lighting, novel industrial heating systems..."

At the extreme end of the microwave revolution is a novel alternative to fracking. Rather than injecting the ground with chemicals at high pressure to force hydrocarbons out of shale, Peter Kearl and colleagues at Qmast LLC use microwaves ... The highly efficient heating provided by microwaves also makes them appealing for crop protection. Vines in particular are vulnerable to frost after new leaves break out. The traditional protection is to set out thousands of frost candles to warm the air, which are spectacular but inefficient. Some wine growers are now experimenting with microwave-based heating ... in which a series of emitters bathe the vines in gentle warmth when frost threatens. Someday, maybe solid-state microwaves will take our wines to a better state.

There's more at the link.

All this sounds fascinating, but what will exposure to such radiation do to humans in the area?  Current microwaves employ heavy shielding to protect those around them.  Even though the new technology emits much less radiation than traditional magnetron microwave ovens, won't even that lower radiation put people at risk?  After all, it's just been alleged by a very authoritative source that cellphone radiation - which is a tiny fraction of that from microwave emitters - is potentially hazardous to our health.  Who will guarantee - can anyone guarantee - that we don't face any risk from the new microwave appliances?



bmq215 said...

Conflating electromagnetic radiation (such as microwaves) with ionizing radiation is a common mistake. The general public hears "radiation" and immediately begins thinking about lead shielding, meltdowns, and horrible cancer cases. In fact, there are many types of radiated energy and comparing two forms is often an "apples and oranges" situation.

I could start a whole rant here about the sad state of science education, but I won't...

Current microwaves do not "employ heavy shielding". Since microwave energy is similar to radio waves (right between that in infrared in size) all you need is a Faraday cage, which is pretty light. That's actually what the stippled pattern on the window is part of. So the shielding for a portable unit isn't a problem. The cellphone radiation link is interesting but I'll note that A) it's a tiny sample, B) the effect was small and only limited to male rats (which raises a big "why?"), and C) this is the first study that's detected such a link. So in summary it's plausible and certainly worth looking into more but far from definite.

I'm much more interested in how the battery life will pan out. Residential microwaves tend to use 600-1200W. Using a 900W microwave for 5 minutes works out to about 75W. That's not a huge amount by household standards but it is when it comes to batteries. For reference, a standard laptop battery has about 40-60W in it and is designed for a much slower discharge (it would have less capacity at a high rate, if it survived).

In conclusion this sounds cool but I'm not holding my breath.

bmq215 said...
This comment has been removed by the author.
bmq215 said...

Couple of things to add (because my comment wasn't already long enough):

In the interest of completeness should note that electromagnetic radiation and ionizing radiation are not mutually exclusive categories. However, the ionizing electromagnetic radiation is on the high end of the spectrum (ultraviolet and beyond). Microwaves and radio-waves, being on the other side of the visible spectrum, are nowhere near that.

The difference between microwaves and cellphones is that microwaves can be shielded because the only need to affect what's inside the shielding (the food). Cell phones, on the other hand, can't be shielded because that ruins the whole purpose of the emitted radiation (data transmission). So microwaves are inherently much safer despite being much more powerful emitters.

Mogrith said...

Just as an aside there have been a couple of new studies showing rats exposed to cellphone radiation get fewer cancers. (but don't live any longer just die of something else)

SiGraybeard said...

I don't think there's anything we're around that has been studied as much as radio frequency (RF) energy safety. Before I retired, as the most senior RF designer in the radar section, I had to end up being the RF safety guy. I read everything I could get my hands on like I was cramming for a final.

As a first rough clue, if something is studied once and a weak association shows up (let's say cellphones causing cancer or something), do the study again with a bigger sample. RF safety was there decades ago.

There have been literally thousands of studies of RF safety in general, and hundreds of studies of cellphones causing cancer in particular. The fact that no strong, final answer has emerged is really all the answer we need. If there was a strong link, it would have shown up. In this case, you can say if there is a link it's very weak. With world usage of cellphones and WiFi (within a factor of 2 in frequency) as high as they are, if there was a strong health issue, links wouldn't be elusive and hard to find.

The only thing that has consistently shown up in studies as health effect is heating. Certain tissues with low blood flow (corneas, for instance) are more easily injured than tissues with generous blood flow (like hands). Heating is very well understood, and the vast majority of the world uses the same limits for power density (in milliwatts per square centimeter). One or two countries use lower limits, but there's no real evidence they're being any safer. As it is, the limits in the US and other countries have a large safety factor built in (at least 10x - maybe 100x).

Today's microwave ovens are built with a light, sheet metal, Faraday cage to keep the fields outside the cooking area low enough to meet the heating safety numbers. They could use metal screen, but sheet metal gives some structural strength, too.

As BMQ215 said, the weak spot here is likely to be the battery. His numbers sound about right to me.

Marc Berte said...

The power level is listed on the site, 200W, and so is the battery life, ~30min.
Assuming a reasonable 60-70% battery to RF efficiency for the SSPA's, this equates to ~300W and 150Whr, or ~1kg battery, discharging at 2C...all in all, completely reasonable.
That's also ~200W for 1800s, or 360kJ, enough to bring to boiling temp ~1 liter of water...which sucks, but if you think about it, enough to cook 4+ person-meals, and do so in <10min each time.

Is it mass effective compared to a portable stove...no, but for a quick bite or a take-a-long for a day excursion, it could be quite useful, especially due to faster setup/use and no exposed flame (and 2C discharge is well below. Where anyone would be concerned with the battery cooking off.

Anonymous said...

The devices they're talking about use LDMOS transistors to generate RF for heating, not a magnetron like you'd find in a conventional microwave oven. These are quite a bit more energy efficient, which combined with the most recent set of advances in battery technology explains some of the optimism expressed in the article.

The specific thermos product Peter linked to runs at 200 W for 30+ minutes. That implies that when it's fully charged it holds about 360 kilojoules. Modern Li-Ion batteries have an energy density of about 460 kilojoules/kilogram, so the battery pack probably masses a little over 3/4 of a kilo (~1.7 lbs).

For BMQ's example, if a microwave runs at 900 W for 5 minutes, then it has used 270 kilojoules, requiring only 0.58 kg of Li-Ion battery.

Marc Berte said...

Follow up. Since most camp food can be cooked with hot water, a far more effective use would be to skip the microwave part and resistance heat. There is a utility to the battery as stored energy cooking, namely, solar recharging--a small 20-30W (backpack size) solar panel would recharge 100Whr in a days hiking, and the battery would allow one to use that stored energy much faster when it's dinner time.
So in addition to the day-at rip kind of aspect, there is an "ultra-extended" utility to even the microwave style. If the reliability is right, you could use this plus a ~1kg solar panel and cook a meal every night for years with a total mass of ~2.5kg...which can't be beat really.

Anonymous said...

I see you beat me to the punch, Marc :p

I assumed that their listed power output was for the battery/power-system, not the RF produced.

Inconsiderate Bastard said...

Or, is all this armchair analysis perhaps an example of "missing the market"?

Outfit called Zodi makes a bunch of different propane-powered camping stuff; one of their single-burner showers got us through the week without electricity after hurricane Charlie in 2004, and it was used prior, and since, on camping trips. On each of those camping trips we arrived by vehicle in which were sleeping bags, a small camp stove, a medium cooler of food and beverages, a tent, etc. and, usually, a Zodi water heater (Coleman makes one, too).

The vehicle, oddly enough, had a good sized 12 volt battery under the hood, and a 500 watt inverter, plus enough gasoline in the tank to run the engine at fast idle for hours and hours to make the alternator put out electricity if the unfolded Goal Zero panels on the roof aren't enough.

I've done this kind of camping for many years, quite a bit of motorcycle camping decades ago, and more than a few backpacking and canoe trips. I've seen a number of Zodi water heaters but always adjacent to a vehicle, never in a canoe or backpack. Could "vehicle adjacent camping" be the market this new microwave technology is headed for? There's stuff one takes car camping that never is considered for backpacking. This seems like one of those things. I know I'm never humping a battery larger than a AA up Mt. Washington....

m4 said...

IB has probably nailed it there. Nutnfancy is my authority on this and if he ever does a video on this then ignore me entirely, but I suspect he'll say it's not something he'd ever take out hiking. His hiking is several days worth, and size and weight constraints factor heavily into his loadout. Might be useful for short hikes or places where fire isn't an option, but much more useful for anything done with a vehicle on-hand.

In particular it's unlikely to be good for long-term hiking. If you want to cook with fire in a forest, you can do so more or less indefinitely if you bring a knife and a firesteel. You want to cook for several days with a portable microwave? You're going to need either a battery for every day you want to use it (and it doesn't seem to have replaceable batteries!) or a solar array. How heavy is all that gonna be? Use for dinner and breakfast? Nope. Extended use in poor sun conditions? Nope. Use for more people or more stuff at a time? Nope. Certainly won't be able to use it for warmth, drying clothes, and anything else where a fire really is your best option out there.

In short: Yes there's downsides. You should temper your analysis based on the foreseen Philosophy Of Use, and in this case long hikes are just not it. POU is somewhat limited, but I imagine there's a market for it nonetheless.

Bruce said...

Y'all are missing the mark on this. Solid state generation of microwaves. Gee, what else could we generate with solid state? In a few years time as we progress technology down this path? It wasn't that long ago that we could only do powerful lasers with expensive and very large chemical lasers that had a very limited number of uses (shots) - yes, I'm talking about the AABML. Now solid state lasers have advanced to the point that we're starting to deploy them - still under development, but the testing is going on aboard naval vessels. What's next?

Billll said...

High tech as all get-out. You'll know the farmer is using microwaves if as you walk by his orchard/vineyard/whatever, you seem to get a warm, fuzzy feeling....