Giz Explains: Why Everything Wireless is 2.4GHz

You live your life at 2.4GHz. Your router, your cordless phone, your Bluetooth earpiece, your baby monitor and your garage opener all love and live on this radio frequency, and no others. Why? The answer is in your kitchen.
What We're Talking About

Before we charge too far ahead here, let's run over the basics. Your house or apartment, or the coffee shop you're sitting in now, is saturated with radio waves. Inconceivable numbers of them, in fact, vibrating forth from radio stations, TV stations, cellular towers, and the universe itself, into the space you inhabit. You're being bombarded, constantly, with electromagnetic waves of all kind of frequencies, many of which have been encoded with specific information, whether it be a voice, a tone, or digital data. Hell, maybe even these very words.
On top of that, you're surrounded by waves of your own creation. Inside your home are a dozen tiny little radio stations: your router, your cordless phone, your garage door opener. Anything you own that's wireless, more or less. Friggin' radio waves: they're everywhere.

Really, it's odd that your cordless phone even has that 2.4GHz sticker. To your average, not-so-technically-inclined shopper, it's a number that means A) nothing, or B) something, but the wrong thing. ("2.4GHz? That's faster than my computer!")


What that number actually signifies is broadcast frequency, or the frequency of the waves that the phone's base station sends to its handset. That's it. In fact, the hertz itself just a unit for frequency in any context: it's the number of times that something happens over the course of a second. In wireless communications, it refers to wave oscillation. In computers, it refers to processor clock rates. For TVs, the rate at which the screen refreshes; for me, clapping in front of my computer right now, it's the rate at which I'm doing so. One hertz, slow clap.
The question, then, is why so many of your gadgets operate at 2.4GHz, instead of the ~2,399,999,999 whole number frequencies below it, or any number above it. It seems almost controlled, or guided. It seems, maybe, a bit arbitrary. It seems, well, regulated.
A glance at FCC regulations confirms any suspicions. A band of frequencies clustered around 2.4GHz has been designated, along with a handful of others, as the Industrial, Scientific, and Medical radio bands. "A lot of the unlicensed stuff—for example Wi-Fi—is on the 2.4GHz or the 900Mhz frequencies—the ISM bands. You don't need a license to operate on them." That's Ira Kelpz, Deputy Chief, Office of Engineering and Technology at the Federal Communications Commission, explaining precisely why these ISM bands are attractive to gadget makers: They're free to use. If routers and cordless phones and whatever else are relegated to a small band 2.4GHz, then their radio waves won't interfere with, say, cellphones operating at 1.9GHz, or AM radio, which broadcasts between 535 kHz and 1.7 MHz. The ISM is, in effect, a ghetto for unlicensed wireless transmission, recommended first by a quiet little agency in a Swiss office of the UN, called the ITU, then formalized, modified and codified for practical use by the governments of the world, including, of course, our own FCC.
The current ISM standards were established in 1985, and just in time. Our phones were one the cusp of losing their cords, and in the near future, broadband internet connections would come into existence and become magically wireless. All these gadgets needed frequencies that didn't require licenses, but which were nestled between the ones that did. Frequencies that weren't so high that they sacrificed broadcast penetration (through walls, for example), but weren't so low that they required foot-long antennae. In short, they needed the ISM bands. So they took them.

ThermOweld

The ThermOweld connection process is a simple, efficient method of welding copper to copper or copper to steel. One advantage is that NO outside power is required when using the thermOweld exothermic process. The thermOweld process uses high temperature reaction of powdered copper oxide and aluminum. The reaction takes place in a semi-permanent graphite mold. These molds should last for approximately fifty or more welds if proper care is given. The reaction takes place very rapidly; therefore the total amount of heat applied to the conductors or surfaces is considerably less than that of brazing or soldering. This is important to remember when welding to insulated cable or thin wall pipe.


This system is very field friendly, since it is light and portable and requires no outside power source. It requires very little time or skill to obtain an efficient, maintenance free connection when using the thermOweld process.

The system was used in ensuring a ground protection for all electrical instruments used in the field.

http://www.thermoweld.com/ 

Superconductors - Meissner effect

When a material makes the transition from the normal to superconducting state, it actively excludes magnetic fields from its interior; this is called the Meissner effect.

This constraint to zero magnetic field inside a superconductor is distinct from the perfect diamagnetism which would arise from its zero electrical resistance. Zero resistance would imply that if you tried to magnetize a superconductor, current loops would be generated to exactly cancel the imposed field (Lenz's law). But if the material already had a steady magnetic field through it when it was cooled trough the superconducting transition, the magnetic field would be expected to remain. If there were no change in the applied magnetic field, there would be no generated voltage (Faraday's law) to drive currents, even in a perfect conductor. Hence the active exclusion of magnetic field must be considered to be an effect distinct from just zero resistance. A mixed state Meissner effect occurs with Type II materials.

One of the theoretical explanations of the Meissner effect comes from the London equation. It shows that the magnetic field decays exponentially inside the superconductor over a distance of 20-40 nm. It is described in terms of a parameter called the London penetration depth.

A superconductor is fundamentally different from our imaginary 'perfect' conductor. Contrary to popular belief, Faraday's Law of induction alone does not explain magnetic repulsion by a superconductor. At a temperature below its Critical Temperature, Tc, a superconductor will not allow any magnetic field to freely enter it. This is because microscopic magnetic dipoles are induced in the superconductor that oppose the applied field. This induced field then repels the source of the applied field, and will consequently repel the magnet associated with that field. This implies that if a magnet was placed on top of the superconductor when the superconductor was above its Critical Temperature, and then it was cooled down to below Tc, the superconductor would then exclude the magnetic field of the magnet. This can be seen quite clearly since magnet itself is repelled, and thus is levitated above the superconductor. For this experiment to be successful, the force of repulsion must exceed the magnet's weight. This is indeed the case for the powerful rare earth magnets supplied with our kits. One must keep in mind that this phenomena will occur only if the strength of the applied magnetic field does not exceed the value of the Critical Magnetic Field, Hc for that superconductor material. This magnetic repulsion phenomena is called the Meissner Effect and is named after the person who first discovered it in 1933. It remains today as the most unique and dramatic demonstration of the phenomena of superconductivity.

On account of the polycrystalline nature of a typical ceramic superconductor, the Meissner Effect appears to be a bulk phenomena. This can be demonstrated by stacking two or more superconductor disks. With the addition of each disk, the magnet will be levitated higher. This result is particularly advantageous if the Meissner Effect is being demonstrated to an audience with the help of an overhead projector.

Another interesting observation is that the levitated magnet does not slide off the superconductor. This seemingly stable equilibrium is actually a manifestation of Flux Pinning, a phenomena uniquely associated with Type II superconductors, of which our high temperature ceramic superconductors are examples. Here lines of magnetic flux associated with a magnet can penetrate the bulk of the superconductor in the form of magnetic flux tubes. These flux tubes are then pinned to imperfections or impurities in the crystalline matrix of the superconductor thereby pinning the magnet.

In other words, what is happening is that you are initially forcing the magnetic field to exist in these non superconducting regions, by "squeezing" it though the cracks between the superconducting crystals. These regions of the material are surrounded by superconducting material. Think of a gallon jug, filled with water, that has a small pin hole in the bottom. The jug is the superconductor, the water is the magnetic field. This superconducting material will not allow a magnetic field to pass though it, in much the same way the jug will not allow the water to pass though it. However, the tiny non superconducting regions will allow the magnetic field to pass though, in the same way the pin hole in the jug allows the water to pass though. When you lift the magnet up, the force of gravity acting on the pellet (F=ma first semester physics stuff), is not great enough to force the trapped magnetic field to pass though the superconducting material, hence, like a weight on a string, you can lift the pellet. The string in this case is the magnetic field, and the weight is the superconductor.

Doppler effect

In astronomy, the Doppler effect was originally studied in the visible part of the electromagnetic spectrum. Today, the Doppler shift, as it is also known, applies to electromagnetic waves in all portions of the spectrum. Also, because of the inverse relationship between frequency and wavelength, we can describe the Doppler shift in terms of wavelength. Radiation is redshifted when its wavelength increases, and is blueshifted when its wavelength decreases.

Astronomers use Doppler shifts to calculate precisely how fast stars and other astronomical objects move toward or away from Earth. For example the spectral lines emitted by hydrogen gas in distant galaxies is often observed to be considerably redshifted. The spectral line emission, normally found at a wavelength of 21 centimeters on Earth, might be observed at 21.1 centimeters instead. This 0.1 centimeter redshift would indicate that the gas is moving away from Earth at over 1,400 kilometers per second (over 880 miles per second).

Shifts in frequency result not only from relative motion. Two other phenomena can substantially the frequency of electromagnetic radiation, as observed. One is associated with very strong gravitational fields and is therefore known as Gravitational Redshift . The other, called the Cosmological Redshift, results not from motion through space, but rather from the expansion of space following the Big Bang, the fireball of creation in which most scientists believe the universe was born.