The antenne *is* the drill bit - and the quarter wave rule is to stop it acting as a real antenna and broadcasting microwaves all round the room. Below 1/4 wavelength, some undecribed mechanism creates intense heating just below the drill bit, which is where you want to drill.
That's what I said: the drill is a highly directional antenna. The undescribed mechanism is the radiation energy absorbed by the material which is being drilled. (Energy equals heat, among some other things.)
They can't move the drill forward without moving the (presumably non-conducting) chuck, or all their micropwave energy will radiate sideways, gently heating that which they do not want to heat and failing to heat that which they want to drill.
Yes, you're right about that. I first thought that the mechanism of drilling is as follows: heat the material with microwaves and when the material is sufficiently hot/soft, push the drill/antenna as deep as you can and repeat. The problem is that the "hole" made is just wide enough for the antenna, so they can't push the drill/antenna any further. So they can't make holes any deeper than the given a quarter of wavelength rule.
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?
Actually, Fortran still is quite popular in the field of scientific computing. Fortran90/95 and High Performance Fortran that is, definitely NOT Fortran77. F90/95 is actually a rather easy language to program in, it is very similar to Matlab (the leading choise of many scientists for numerical analysis) in many ways, which makes porting from Matlab to Fortran easy. (Many projects start with a rough "first draft" code in Matlab and then move on to more powerful languages as the project advances and computational requirement increase.) Memory management, vector and matrix manipulation is also definitely a lot easier in Fortran than in C.
It still doesn't mean that Fortran is making a comeback. It just fills a particular niche.
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The antenne *is* the drill bit - and the quarter wave rule is to stop it acting as a real antenna and broadcasting microwaves all round the room. Below 1/4 wavelength, some undecribed mechanism creates intense heating just below the drill bit, which is where you want to drill.
That's what I said: the drill is a highly directional antenna. The undescribed mechanism is the radiation energy absorbed by the material which is being drilled. (Energy equals heat, among some other things.)
They can't move the drill forward without moving the (presumably non-conducting) chuck, or all their micropwave energy will radiate sideways, gently heating that which they do not want to heat and failing to heat that which they want to drill.
Yes, you're right about that. I first thought that the mechanism of drilling is as follows: heat the material with microwaves and when the material is sufficiently hot/soft, push the drill/antenna as deep as you can and repeat. The problem is that the "hole" made is just wide enough for the antenna, so they can't push the drill/antenna any further. So they can't make holes any deeper than the given a quarter of wavelength rule.
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?
Actually, Fortran still is quite popular in the field of scientific computing. Fortran90/95 and High Performance Fortran that is, definitely NOT Fortran77. F90/95 is actually a rather easy language to program in, it is very similar to Matlab (the leading choise of many scientists for numerical analysis) in many ways, which makes porting from Matlab to Fortran easy. (Many projects start with a rough "first draft" code in Matlab and then move on to more powerful languages as the project advances and computational requirement increase.) Memory management, vector and matrix manipulation is also definitely a lot easier in Fortran than in C.
It still doesn't mean that Fortran is making a comeback. It just fills a particular niche.
You might want to read The Straight Dope about speed reading...