General > General Technical Chat
"Veritasium" (YT) - "The Big Misconception About Electricity" ?
adx:
While I am considering a reply to Huronking's post, I have to strongly disagree with this, on principle (of being right).
To the MRI thing - hell yes. Even I could work it out. You place stuff in a magnetic field - almost any field will do. You apply pulses - and notice there is an RF signal back from the stuff that is not a simple reflection. You notice that different materials produce different but very stable frequencies, which vary with DC field strength. You wonder if a gradient might allow a physical map of stuff's density to be ascertained simply from that radio reception. So you make an artifact and try it - MRI is born (except it stands for magnet radio imaging, because the concept of nuclear magnetic resonances are unknown). (I'm not talking about everything in tech that might have lead up to that discovery to make it seem so trivial, but the principle behind the discovery itself, and the fact that it would progress very rapidly without the known theoretical basis.)
The story behind the transistor is much more empirical and stumbley than you make out, and seems to owe a great debt to Julius Edgar Lilienfeld's patent on the FET in 1925, when physical theories were less advanced. The transistor was pretty much a poster child for advanced hacking and the physics following experiment.
Blue LED? You walked right into that one ... "discovered in 1907 by the English experimenter H. J. Round" (Wikipedia). I was so intrigued when I discovered that a few years back, that I tried it, with some 120 grit SiC sandpaper. It worked. Not very well, and a kind of pale greeny-blue, but definitely a blue LED.
I'm certainly not denying the great advances in physics or saying that all advances in engineering are disconnected from physics, just that there seems to be a current fashionable POV belief-in-science school of thought that misrepresents history and reality. Again I'm not saying I disagree completely, just with the false facts.
TimFox:
"Nuclear Magnetic Resonance" (NMR) was demonstrated by the physicists Felix Bloch and Edward Purcell, independently, in 1946.
At the fundamental level, it is a quantum effect, where the magnetic moment of the proton or other nucleus has only a finite number of states (2 for spin 1/2) and therefore has a resonant frequency for the energy transition between the two states in a constant external magnetic field. It is used in chemistry as a spectroscopic technique, showing the variations in local magnetic field due to the molecular structure. It is also useful for precise measurements of magnetic fields, such as making the main magnetic field for MRI as uniform as practicable.
"Magnetic Resonance Imaging" (MRI) is an application of NMR, and was developed for medical imaging by Paul Lauterbur (PhD in chemistry) in 1971, where he applied controlled gradients in the external magnetic field in order to encode position as a shift in the resonant frequency. In German, it is "Kernspintomografie", literally nuclear spin tomography. Other scientists contributed to the further development, along with tons of money and engineering improvements from the major companies in medical imaging.
Greatly oversimplified, if you apply a pulsed radio-frequency magnetic field (not a wave) to the sample full of appropriate nuclei (e.g., water), you can flip the nuclear spins if the frequency and field agree, and when the nuclei relax due to thermal interactions with the material and go back to the lower energy state, it induces an AC voltage in the receiving coil. Fourier analyzing the received voltage is used either for spectroscopy or to decode the nuclear density as a function of position (according to the field gradient). For hydrogen in nuclei (protons), a magnetic field of 1.5 Tesla (15 kgauss) corresponds to about 64 MHz.
bsfeechannel:
--- Quote from: adx on March 11, 2022, 02:30:55 am ---While I am considering a reply to Huronking's post, I have to strongly disagree with this, on principle (of being right).
To the MRI thing - hell yes. Even I could work it out. You place stuff in a magnetic field - almost any field will do. You apply pulses - and notice there is an RF signal back from the stuff that is not a simple reflection. You notice that different materials produce different but very stable frequencies, which vary with DC field strength. You wonder if a gradient might allow a physical map of stuff's density to be ascertained simply from that radio reception. So you make an artifact and try it - MRI is born (except it stands for magnet radio imaging, because the concept of nuclear magnetic resonances are unknown). (I'm not talking about everything in tech that might have lead up to that discovery to make it seem so trivial, but the principle behind the discovery itself, and the fact that it would progress very rapidly without the known theoretical basis.)
--- End quote ---
Oh, yeah! After the fact, anyone can say it would be easy to figure it out, no doubt. But it took a physicist to come up with that idea because he knew what to look for.
"Nuclear magnetic resonance was first described and measured in molecular beams by Isidor Rabi in 1938, by extending the Stern–Gerlach experiment, and in 1944, Rabi was awarded the Nobel Prize in Physics for this work."
"In collaboration with Gregory Breit, he developed the Breit–Rabi equation and predicted that the Stern–Gerlach experiment could be modified to confirm the properties of the atomic nucleus. His techniques for using nuclear magnetic resonance to discern the magnetic moment and nuclear spin of atoms earned him the Nobel Prize in Physics in 1944."
--- Quote ---The story behind the transistor is much more empirical and stumbley than you make out, and seems to owe a great debt to Julius Edgar Lilienfeld's patent on the FET in 1925, when physical theories were less advanced. The transistor was pretty much a poster child for advanced hacking and the physics following experiment.
--- End quote ---
Three misconceptions. The first one, that physics is theory, engineering is practice. Second, that the road to scientific breakthroughs is not bumpy. The third is that the transistor effect was discovered by accident. No, they knew exactly what they were looking for. Only that their initial prediction didn't work. So, they developed a new theory of physics to explain why so and conducted new experiments until they found what they were looking for. Pure physics.
And you know why these physicists were commissioned to invent the transistor? Because until then engineers could only produce boat anchors.
--- Quote ---Blue LED? You walked right into that one ... "discovered in 1907 by the English experimenter H. J. Round" (Wikipedia). I was so intrigued when I discovered that a few years back, that I tried it, with some 120 grit SiC sandpaper. It worked. Not very well, and a kind of pale greeny-blue, but definitely a blue LED.
--- End quote ---
And it is ironic that it took scientists to turn a mere curiosity into something so practical.
adx:
No, I'm saying that it wouldn't have taken another 84 years for me to discover NMR, or think of the potential applications, had it not been discovered by a physicist. It could have been anyone with a lab and a motivation, whether that be an engineer, physicist, or amateur. It would get easier and easier to discover by accident. Of course it would be easy to figure out, as I described.
Your noted misconceptions about the development of the transistor do not alter the fact that it was still advanced hacking. I'm not somehow against that. "So, they developed a new theory of physics to explain why so and conducted new experiments until they found what they were looking for. Pure physics." could be said of engineering too. All I am objecting to is the false dichotomy of deeming academic physics to be the basis of all engineered devices. There are many ways of achieving that, and it's not really practical to prevent that from being all (unless commercial secrecy precludes scientific study, thereby slowing down (but not stopping) advances).
Same with the blue LED. The first proper device was in 1972:
https://spectrum.ieee.org/rcas-forgotten-work-on-the-blue-led
It came from experiment (I don't care whether that was physics or engineering or whatever), it was a process issue. I also had the ‘holy shit! It’s actually a bright blue LED!’ moment in the 1990s, in almost exactly the same way - a rep had this LED in one of those LED testers and said look at this, of course all us guys peered into the thing thinking it would be nigh on impossible to see, and it almost burned our retinas out. I think he also said ‘yes, it is.’ and just disappeared down the hall. I digress, but 'I was there' not long after the birth of LED lighting. Also like Maruska, I don't begrudge the Nobel winners. I'm just against the 'physics is the source of all engineering' claptrap, as if it's an unavoidable 1-way street.
bsfeechannel:
--- Quote from: adx on March 11, 2022, 06:24:24 am ---Your noted misconceptions about the development of the transistor do not alter the fact that it was still advanced hacking.
--- End quote ---
What those guys did was what physicists do all the time. If you want to change its name to "advanced hacking", I have no problem with that.
A Nobel Prize in advanced hacking sounds way cooler than a Nobel Prize in physics, anyway.
--- Quote ---I'm just against the 'physics is the source of all engineering' claptrap, as if it's an unavoidable 1-way street.
--- End quote ---
OK. So name an engineering field that doesn't have its origin in--and/or whose current tenets weren't shaped by--science. Civil engineering, perhaps? Certainly not electronics. Electronics is drenched with physics and math.
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