Slashdot Mirror
Using Microwaves to Drill Through Glass
Linux_ho writes "UPI is reporting that Israeli researchers have developed a drill that can melt a small hole in glass, ceramics, or concrete with no dust or noise. Nature.com reports that it doesn't work very well with good heat conductors or materials with very high melting points, but the researchers envision a wide variety of manufacturing applications, and possibly some medical uses as well."
According to the nature article- cost.
And that drives everything
Except that the leatest, greatest armour is ceramic, not steel. But, according to the article, it limited to the 1/4 wave of the microwaves - an inch or so. And it only makes tiny holes. Somehow I doubt that making pinholes in the armour of a tank is going to slow it down much.
Consciousness is an illusion caused by an excess of self consciousness.
Don't play with microwaves.
I've heard stories of people removing the magnetron and transformer arrangement from old microwaves, and firing it up. The reason it's a stupid idea is that it cooks you from the inside out. You don't feel it - no-one has heat sensing nerves on the inside of their bodies. By the time you realize something's wrong too much damage has been done.
It also leads to blindness. Don't fsck with microwaves unless you know what you're doing.
From the article: "The device is limited to a penetration depth of a quarter of the wavelength of the microwaves used -- in this case, about an inch. If the drill bit is any longer, the microwaves are no longer beamed forward but instead radiate in every direction like an antenna."
If I understand correctly the drill works as a highly directive antenna - beaming microwaves towards the material to be melted. The drill needs to be short to achieve good directivity.
Different frequenciens have different penetration depths - that is, how deep the electric field or radiation energy can penetrate into the material which is being "drilled". The penetration depth also depends on the conductivity of the material, so different materials can have very different penetration depths for the same frequency.
I think the depth of "a quarter of its wavelength" is just a very approximate rule given to journalists. It is more of a comparison rule: the penetration depth is comparable to a quarter of the wavelength. (Although I'm not sure why, the penetration depth is proportional to the square root of the wavelength, if I remember correctly.)
After they have reached the penetration depth, they need to move the antenna/drill forward. So of course they can drill deeper holes than that, but not at a time.
What kind of an "antenna" are they using? To achieve good directivity, they would need to use "traveling wave antennas" (or whatever they are called in english), I'd imagine. Does anybody know any details of this?
If I'm understanding correctly, the microwave beam has a very limited range. This would make it much harder to accidentally hurt someone with it. You can hurt someone on the other side of a large room, or possibly in the next room over, with an industrial laser.
CAUTION: Product may be hot after heating
Common mis-understanding about microwaves. Cooking "from the inside out" is misleading. They only penetrate 3-4 cms (Might want to check exact). This is why cooking large items in a microwave is problematic.
You risk burning the outside of the food while the inside is still under cooked. For things like roasts, etc it is still better to use the slow and steady approach as the temperature has more of a chance to distribute evenly throughout the food, ensuring an even consistency. But I digress.
Your warning is a good one, but generally you do feel "warm" if you step in front of an active feed horn, before any damage is done.
You are very correct about the blindness though, looking directly into a hot horn can blind you before you knew what happened. Your eyes resonate right around the microwave range and absorbe them readily.
I've had enough abrasive sigs. Kittens are cute and fuzzy.
I thought microwave ovens and the like work because the microwaves are the same frequency range as the rotational bands in water (of which we're what, 70%?). Thus, they make the water's spin which makes them hot - boiling the humour in the eyeball doesn't strike me as a fun thing to have done...
I thought microwave ovens and the like work because the microwaves are the same frequency range as the rotational bands in water
Well, sorta, but there is nothing magical about 2.4Ghz. It's not the "frequency that water resonates at", as I've even seen printed in semi-credible places.
google cache of message
This message on the wireless list sums it up pretty well, although it doesn't exist anymore, google cache has it.
The bottom line is that lower frequencies penetrate better in general, 2.4Ghz is just a pretty good compromise between penetration and reflection/absorbtion.
Of course things are different when you aren't inside a metal box like a microwave oven. In the oven, all reflected energy is going to eventually absorb into the object in the oven, or reflect back into the magnetotron. In free space, reflected waves are just going to fly off into space.
In free space, objects that are about the right size to resonate at a frequency don't reflect much of the energy, they absorb most of the energy, but most of it stays near the surface, this is called the skin effect. High voltages are induced on the surface of the object that is resonating, causing resistive heating. This skin effect is also what is responsible for sparks when you have small metal objects in the microwave. Larger objects like spoons and forks are actually less likely to arc than things like metal twist-ties, the twist-ties are closer to resonant, and also have tiny ends which concentrate the voltage. (blunt objects are less likely to arc, arcing happens when the volts/surface area reach a critical value)
The FCC has done lots of research on exposure to EM fields, and has come up with SAR (specific absorption rate) in humans, for many frequencies. It mostly boils down to this, your entire body most readily absorbs VHF energy around 400 Mhz, your head gets it worst around 900Mhz, and your eyes absorb the most in the microwave ranges. This is compounded by the fact that your corneas don't have much way to dissipate heat, and are pretty sensitive organs.
Anyway, the original poster is right, don't play around with this stuff unless you understand it. Although, more likely to kill you taking a microwave oven apart is the 1000 volts at several amps that the power supply puts out. Nasty stuff. Much more dangerous than taking apart something like a monitor.
I've had enough abrasive sigs. Kittens are cute and fuzzy.