Its almost magical… You put your food inside a small metal box, press a switch, and one minute later its cooked, yet, the box remains cold… In a Timesï¿½ magazine survey a couple of years ago, the majority of people asked what the most brilliant invention of the century was, answered “The Microwave Oven”. Indeed, this device now finds itself in almost every kitchen and household in the world, cooking food faster, more efficiently, and safer than any of its predecessors…
But the concept of Radio Frequency heating lends itself for a lot more than just heating foods and drying industrial items… In laboratories it is used for plasma research, particle accelerators, and even nuclear fusion research.
Without getting too much into the workings of an oven (check my links page for that), PowerLabs here presents what *NOT* to do with your Microwave oven!I was the microwave expert on MTV’s “Big Urban Myth Show”, which aired in February 2003. In the show my friend Slava and I talk about how microwave ovens work, and what happens when you put metals inside them. We even got to blow an oven up for the show intro. Click the picture or this link to watch the 14.8MB movie. Plasma Production
Microwaving strange items
What you see here is a 10cm (4″) glass globe filled with low pressure neon gas. Those are sold in some shops under the name of “Love Lamp” or something along those lines. When you plug it into 220V the metal sphere in the middle flickers with an eerie orange glow… I use those for making plasma globes (just attach it to a suitable high voltage generator and hundreds of thin plasma streams dance around the glass).
In this picture the globe is inside a microwave oven and a standing wave pattern can be seen from the ionized gas as microwaves travel through it, creating nodes of constructive and destructive interference. It very interesting to watch the globe inside a rotating dish oven; the standing wave pattern moves around and the brightness of the globe varies as it passes through different areas of higher and lower field density in the oven.
As with most plasma pictures, it is difficult to capture the true beauty of the display. It is actually bright enough to light up a room! It also becomes very hot, very fast, and will explode if microwaved for more than a few seconds… This has happened to me before with light bulbs, and it is not fun to clean up afterwards!
Ball lightning has been known for centuries, and yet no one can explain those mysterious balls of plasma that seem to appear during thunderstorms (more specifically when there are lightning strikes) and move around, sometimes fading away, other times exploding. This effect can be re-created in the microwave oven. Although there is no agreed upon theory as to why that happens, this is what my knowledge and experiments lead me to speculate:
Microwaves will bounce off any conductive material. That can be anything from metal to carbon or even molten glass. Upon doing so, it will induce a current flow on the metal at their frequency (2.45GHz for microwave ovens). It is actually that current flow going through the metal that re-transmits the microwaves.
As electrons concentrate at the extremities of the conductive surface (electrostatic field theory, faraday’s law), they easily reach field potentials above 16kv/cm and leave the surface, causing sparking and localized heating. They will also flow between two conductors placed in a microwave field. When the metal reaches a high enough temperature, it begins to vaporize (placing burning matter into the cooking cavity greatly increases this effect, which is why burning candles, toothpicks, and even cigarettes work so well), and this metal vapor will then absorb the microwaves and it too will experience a current flow, which will effectively ionize it and make it glow.
Instead of dissipating, however, this mass of ionized metal vapor will suffer the effects of the current flow that is ionizing it in such a way that it will pull itself together. It also glows because it is very hot (due to the current flow), and its color changes are attributed to its temperature and to the ions present inside it. When the microwave energy being inputted equals the heat being dissipated, the BL will reach an energy equilibrium and stop growing. Consequentially, more power would equal larger plasma balls. My record is a 10cm diameter sphere that lasted little over 3 minutes, which brings me to the phenomena of disappearing BL: It disappears when it reaches a “dead spot”: a place where the microwaves are at their lowest energy. That happens because microwave ovens radiate irregularly, so some regions receive less energy than others. If you keep it from moving around, it won’t disappear, but it will melt whatever confinement you have…
Ball Lightning buzzes inside microwave ovens because the half-wave voltage doubler causes the magnetron to pulse 50 times a second (or 60 if the input is 60Hz). During power off, the BL is giving out heat and light so it cools and reduces in size. During power on it increases in size. Those oscillations cause the 50Hz humming you hear. If you get a MW oven to operate in continuous mode, you should have twice as big BL that doesn’t hum… It will also be more stable.
Oven’s will not last long if you do this. The microwaves are not fully absorbed and they come back to the magnetron, causing the anode to overheat decreasing useful life.
Some Contained “Ball Lightning” created by PowerLabs:
Microwaving Strange Items:
The POWERLABS Microwave Gun!
Despite its name, the microwave gun is not actually meant to be used as a weapon (much like a CRTs “Electron Gun”). It was actually the byproduct of my microwave plasma research, and the idea here was to be able to produce the plasma outside a cooking cavity where wires would not be affected so much by the field. Here is what came out of it. Run the cursor over the pictures for a small description.
As is shown, this device will spread microwaves in a 180 degree range all around the magnetron probe. In order to obtain a progressively expanding pattern, which would maximize the field strength, a microwave horn is necessary (parabolas don’t work in here because of the long wavelength). Check back later for a picture of my horn and some pictures of objects being fried at a distance.
WARNING: Attempting to operate a magnetron outside its designed cavity is VERY dangerous and will not only decrease its useful life, but will also pose a serious threat to the operator of the device. Microwaves can cause cataracts and deep thermal burns. Any electronic equipment within range of the magnetron will be instantly destroyed.