Twisted Radio Waves

For over 30 years we have been know that we can "twist" light. This was first detected inside some optical  cavities. It's called a "screw dislocation or phase singularity". (I will refrain from using that phrase ever again.) It was first documented in a paper by John F. Nye and Michael V. Berry, in 1974. If you think you can imagine a "dislocations in wave train" please try to read their work here. I'll admit most of it's over my head.  But the general idea is that light can be twisted around its axis of travel, like the thread of a screw. Interestingly, through this twisting, the light waves at the axis itself cancel each other out and leave a null. It actually reminds me of the way twisted pair reduce noise.

So even if you don't fully understand all that,  you do already know that light and radio waves are both just different forms of electromagnetic energy. So what is possible with one segment of the spectrum is usually applicable to another. Astrophysicist Fabrizio Tamburini made that leap. In March of this year he published a paper Encoding many channels on the same frequency through radio vorticity: first experimental test. I'll quote the abstract here:

"We have shown experimentally, in a real-world setting, that it is possible to use two beams of incoherent radio waves, transmitted on the same frequency but encoded in two different orbital angular momentum states, to simultaneously transmit two independent radio channels. This novel radio technique allows the implementation of, in principle, an infinite number of channels in a given, fixed bandwidth, even without using polarization, multiport or dense coding techniques. This paves the way for innovative techniques in radio science and entirely new paradigms in radio communication protocols that might offer a solution to the problem of radio-band congestion."

You can read it all here. Being Italian, he goes on to falsely credit Marconi in the introductory paragraphs. Let's skip all that and get to the exciting stuff. In a test within the 2.4 GHz WiFi band, they broadcast on 15 and 27 MHz. This is difficult to visualize as most people visualize radio waves like ripples on the surface of water. This is not inaccurate, (were you under the water yourself) but is poorly expressed without the math.

The unfamiliar variable here is the orbital angular momentum (OAM) [More here.] It expresses a fundamental physical quantity each with a set of of eigenstates. This is important because linear momentum and polarization are two-dimensional concepts. OAM by comparison is orthogonal, and can be used to describe three-dimensional vectors. These concepts can be used to mathematically describe and thus quantify the "twist" of the wave. If that can be done consistently it can be used to add additional layers of multiplexing to radio waves and embed them with even more data.  If Mr. Tamburini is correct this could be done not only in broadcast but also in wired networks. His tests succeeded at a distance of 442 meters (1,414 feet) that is from lighthouse of San Giorgio Island to the balcony of Palazzo Ducale in Venice (Italy). While open ocean is an absolutely ideal test ground in terms of propagation, the point of reception is in a major city with all the local sources of interference you might expect. It appears that this is an effective way to increase transmission capacity without increasing bandwidth. It may have some limitations but so does FM.

At the Speed of Radio

It is usually said that radio waves travel at the speed of light. This is not exactly true, the speed of radio waves is actually variable. [Wikipedia has this wrong] In 1865 James Clerk Maxwell first made the first observations on the similar properties of light and radio waves. He proposed equations that described light waves and radio waves as "waves." This critical early observation was correct. Light and radio waves are both electromagnetic radiation and they propagate the same way. (Even if we aren't exactly sure how that is.)

The speed of light is usually represented as "C" because the speed of light is a very long number.  It is 299,792,458 m/s (meters per second) or 983,571,056 ft/s (feet per second) or about 300,000 kilometers per second. Radio waves certainly are able to travel at this speed, but can only do so in a vacuum. When propagating through any medium they are slowed down according to the permeability and permittivity of the substance.  We calculate this as C = 1÷  √(Permeability * Permittivity). The permittivity ε and permeability of a medium determine the phase velocity C of electromagnetic radiation through that medium. These are important enough to define here and not send you off to links you're probably not going to read.

• Permeability: This is is ability of a material to support the formation of a magnetic field within itself. All matter is thus divided into four categories, depending on their level of permeability. Diamagnetic, Non-magnetic, Paramagnetic and Ferromagnetic. Air for example falls into the category of Nonmagnetic, copper would obviously be paramagnetic but so are many metals. Aluminum is an exception, it is Paramagnetic, only carrying a magnetic field when one is externally applied. Iron is also an exception as it is Ferromagnetic. In other words it can be permanently magnetized. It's not alone in that category, lithium gas is ferromagnetic at about 1 degrees kelvin.

• Permittivity: This is the measure of the resistance encountered when forming an electric field in a medium. It is determined by the ability of a material to polarize in response to the field. It's expressed as the ratio of its electric displacement to the applied field strength. In some application is is also called the dielectric constant.

NOTE: In a circuit, permittivity is defined as a measure of the capacitance and dimensions of a capacitor, and permittivity is reduced to the a constant as defined by amperes law. 

Photons travel at the speed of light until they hit an atom. Then they are interact with the electromagnetic fields created by the arrangements structure of those atoms. It is in an excited state while interacting with these fields. it returns to the speed of light on the other side. These infinitesimal pauses accumulate and are what produces the variance between any medium and it's travel through a vacuum. Empedocles, a Greek philosopher born in 430 BCE, was the first to claim that the light has a finite speed. [image above] He maintained that light was something in motion, and therefore must take some time to travel. Around 1270 Erazmus Witelo a Polish mathematician, first suggested that light traveled at an infinite speed in vacuum, but slowed down in denser matter. The first decent estimate of the speed of light was made in 1676 by Ole Rømer and he was still off by over than 25%. In 1729, James Bradley estimated C to within 5 seconds and that's close enough for me. You can read about that here.

Water, air, and copper all transmit radio waves at below the speed of light. Actually they travel through copper at around 10% the speed of light. It's something we rarely think about because even at that speed you can connect to anywhere in the world in a few seconds. But the exact speed it travels is directly proportional to the capacity of the mass of copper. The longer the wire, the more electricity is needed to "fill it." This is a situation that John Steele Gordon once compared to filling a garden hose with water. Attenuation does not slow down the signal, it merely reduces the amplitude. Even as the wave is being attenuated to nothing it is still traveling at a fraction of C as determined by permeability and permittivity. What speeds it up is much more complicated.

Radio Waves = POWER

Yes, media can quickly disseminate information, and that makes radio powerful.. But in this context I mean actual power. As in the electricity that powers everything. Video here.

In Erie Pensylvania a cancer researcher named John Kanzius found a way to burn salt water. He was actually trying to desalinate the seawater with a RF generator. What happened is that the radio frequencies made the seawater flammable. H2O is very stable normally. It's been discussed as a source of hydrogen fuel, but that H is strongly bonded to those two Os. It turns out that the application of radio waves frees the hydrogen. This of course raises the possibility that salt water.. one of the most abundant things on Earth as a fuel.


Kanzius' work was verified by Rustum Roy, a Penn State University chemistto confirm the observations. They are out hunting funding as we speak. test are still needed to determine how much power is consumed vs. produced. the reaction is 4(Na+) + (O2) => 2Na2O or (Na+) + (O^2-) => Na2O (hence the yellow flame) the 2nd law of thermodynamics tells us this should not have a net gain, but that dosent mean it's useless either.