In general, radio wave absorbers are mainly used in a stealth technology to make it difficult to detect by radar and a technology to detect effectively a weak radio wave signal for the purpose of communications or broadcasting using the same. The stealth technology may refer to that it is closest to materials engineering of using the absorbing material. In the case of using a radio wave absorber for a communication or broadcasting, a technique using ferrite materials or ferromagnetic materials is mainly utilized for the purpose of trying to enhance the strength of the radio waves.
These techniques have to use the expensive materials having an absorption property of absorbing the radio waves. Further, these techniques have a difficulty of putting to practical use since chemical components and the molecular structure of the material are concealed as a security technique mainly and also have a very narrow field of usage.
On the other hand, meta-materials collectively refer to substances that are artificially synthesized to exhibit special electromagnetic properties that are not common in nature.
The radio waves in most materials are propagated in compliance with the right-hand rule of the vector fields E, H, and β, where E is an electric field, H is a magnetic field and β is a wave vector. The direction of the phase velocity is the same as the direction of energy signal propagation (group velocity), and the refractive index is a positive number. The material having the above properties refers to as a Right Handed (RH) material. Most natural materials are RH materials. Artifacts are also the RH materials.
The meta-material has an artificial structure. When the meta-material is designed a structural average unit cell size ‘p’ much smaller than the wavelength of electromagnetic energy that is guided by the meta-material, the meta-material can behavior like as a homogeneous medium with respect to the electromagnetic energy being guided. Unlike the RH material, the meta-material may represent a negative refractive index in which the relative direction of the vector fields (E, H, β) becomes opposite to the direction of the energy propagation and phase velocity of signals that comply with the left-hand rule. The meta-material that supports only the negative refractive index is a Left Handed (LH) meta-material.
Many of the meta-materials are a mixture of the LH meta-materials and RH meta-materials and, therefore, are a Composite Right and Left Handed (CRLH) meta-materials. A CRLH meta-material may exhibit a property of an RH meta-material at a high frequency and a property of an LH meta-material at the low-frequency. The design and attribute for the CRLH meta-materials are disclosed by Christophe Caloz and Tatsuo Itoh, “Electromagnetic Metamaterial: Transmission Line Theory and microwave applications” John Wiley & Sons, 2006. The CRLH meta-materials and their applications in antennas are disclosed by Tatsuo Itoh, “invited paper: Prospects for Metamaterials”, E-Journal, Volume 40, No. 16, August 2004. Both of which are hereby incorporated by reference as if fully set forth herein.
The CRLH meta-materials may be organized and processed to represent the electromagnetic attributes that are produced for special purposes to use in applications where it is difficult or impractical or impossible to use other materials. Further, the CRLH meta-materials may also be used to develop new applications and organize new elements that are not possible with the RH meta-materials.
Conventionally, the CRLH meta-materials remain at the technical level of shielding or blocking the electromagnetic wave radiated from the terminal device.
USPTO Backgrounds
USPTO Backgrounds