I get excited when I read about how scientists are able to create experimental conditions that do not occur normally in nature. Recently I was digesting an article on the PhysicsWorld website about how physicists have developed a method using a new class of materials called metamaterial to bring light to a complete stop. How is that even possible? Even with my limited expertise I started to comprehend the meaning of this, resulting in my imagination immediately going into total overdrive. Just think, we can now save the “Federation” because we have the technology to create devices just like the Klingon’s cloak. OK, I apologize, but the analogy was too good to pass up. Technology does actually exists that will cloak objects at microwave frequencies and it will just be a matter of time before it can be practically applied to the visible electro-magnetic (EM) spectrum.
Another example that is thankfully not based on my prolific imagination and related to the IT industry is how metamaterial-based devices are able to manipulate photons in the same manner that electrons are now controlled. This ability is a huge benefit in the world of fiber optic networks. To explain, if photons are used throughout the data transmission link, it avoids the need to convert the “zeros and ones” from one medium to another, thus eliminating bothersome timing issues typically associated with conversion buffers.
I suspect by now most of you are wondering what the heck this has to do with wireless radio technology and RF propagation. Technology using composites made from metamaterial is applicable across the entire EM spectrum and that includes every wireless device we all use on a daily basis. Before getting to specific examples, it is important to understand what a metamaterial actually is, so let’s start there.Metamaterials defined
According to Wikipedia, metamaterial is a term first used by Rodger M. Walser of the University of Texas at Austin in 1999. He defined metamaterials as:
Macroscopic composites having a manmade, three-dimensional, periodic cellular architecture designed to produce an optimized combination, not available in nature, of two or more responses to specific excitation.
Alrighty then, let’s see if I can break that down a bit. Metamaterials are composite materials engineered to alter electro-magnetic wave behavior in very specific ways that up until now were non-existent in the natural world. This abnormal behavior is only possible because the structure of the composite is physically smaller than the actual wavelength of the EM signal that is propagating through the metamaterial composite. So what is this abnormal behavior that has researchers all excited?Is Negative Index of Refraction that abnormal?
Scientists can now create a structure that exhibits a property called negative refractive index. This article by Duke University researchers explains negative refraction with reference to light, but once again this property applies to the entire EM spectrum. It is one of the best sources that I have found for explaining the difference between positive—naturally occurring—and negative refraction. As someone very interested in wave physics, I was sheepishly surprised to learn that EM waves only refracted in one direction and that negative refraction is understood to be abnormal.Significance to RF propagation
Leaving elementary wave physics behind, let’s look at what this means with regards to RF propagation and why it is so significant. I once again take a back seat to the experts, letting Rayspan—one of the leading developers of metamaterial communications technology—explain what this all means:
What essential communications components and subsystems are enabled by metamaterials? Metamaterials technology brings three powerful enabling capabilities: (1) the ability to strongly manipulate the propagation of electromagnetic waves in the confines of small structures, (2) simultaneous support of multiple RF functions, and (3) the freedom to precisely determine a broad set of parameters which include operating frequency and bandwidth; positive, negative and zero phase offsets; constant phase propagation; and matching conditions and number and positioning of ports.
These capabilities make possible a broad range of metamaterial components and subsystems:
- Physically small, but electrically large components such as compact antennas sized on the order of a signal's wavelength/10 while providing performance equal to or better than conventional antennas sized wavelength/2 - a five times size reduction.
- Broadband matching circuits, phase-shifting components and transmission lines which preserve phase linearity over frequency ranges five to ten times greater than those provided by conventional counterparts.
- Multi-band components whose frequencies of operation can be tailored to specific applications and are not limited to harmonic frequency multiples.
The last three points mentioned by Rayspan are especially significant. Each one has the potential to radically change our concept of RF propagation, almost to the point where there is a certain perceived intelligence involved with antennas. For example, Rayspan has developed metamaterial-based MIMO antenna arrays exhibiting performance characteristics equivalent to conventional MIMO antenna arrays, yet take up less space. The data sheet pertaining to the MIMO array is notably useful by furnishing actual azimuth and elevation radiation patterns.
Equipment developers are also starting to realize the potential of using components based on metamaterials. In fact Netgear introduced two new routers that use metamaterial antenna systems—WNR3500 and WNDR3300—at CES 2008. The routers and technology were reviewed by the very capable Tim Higgins at the SmallNetBuilder website.What’s in store?
It is important to realize that this technology is not specific to 8o2.11 equipment. The use of metamaterial components will revolutionize all wireless and mobile technologies. In future posts, I would like to dig a little deeper into some of the specific device uses of metamaterial composites and other cutting edge antenna technology. One such example is “isolated mode" antenna technology which uses multiple feed points and a single antenna to achieve MIMO characteristics.
As a slight sidebar, I would sincerely appreciate hearing if topics like this are of interest. If not, what topics would be better suited and of interest to you the members?