Metamaterial absorbers and reflectors for multiband and wideband applicationsa

Abstract

Metamaterials (MTMs) are materials artificially engineered by artificially arranging structural elements to achieve unusual properties that do not ordinarily exist in nature. It is no secret that electronic devices and communication devices such as mobile phones, pacemakers, infusion pumps, laptops and others, are becoming even more smaller, precise and sensitive. In addition to that, they tend to move towards higher frequency and are adopting the wireless technology which is susceptible to attenuation and interference. At lower frequencies, antennas are larger, therefore miniaturization is required to enable them fit into those tiny electronic devices. In general, electromagnetic waves propagation is characterized by multiple directions as well as many polarization angles, which contributes to the complexity of the signal at the receiver’s end. However, this complexity can be reduced by developing MTM absorbers to absorb any unwanted signals. It can be further reduced by developing MTM reflectors to guide the transmitted signal towards the intended destination. This thesis is aimed at taking advantages of the unusual properties offered by MTMs to develop X-band MTM absorbers and (artificial magnetic conductor) AMC/ MTM reflectors. The new MTM absorbers and MTM reflectors were designed using FR-4 substrate with thickness of 1.6 mm, loss tangent of 0.019 and dielectric constant of 4.6. The MTM absorber catered for the bulky size issues of conventional absorbers and narrow bandwidth issues associated with MTMs absorbers. Whereas the new MTM reflectors catered for the out of phase image current and surface current propagation supported by perfect electric conductor (PEC). Finally, copper wires were used as switches to demonstrate reconfigurability and compactness. The first proposed structure is based on circular ring (CR) structure. It resonated at 11.11 GHz and was modified to have four smaller extended circular rings to demonstrate the concept of size reduction by suppressing the resonance frequency. The second structure is based on the famous “H” pattern absorber, which was modified to have four copper wires as switches in order to manipulate the flow of the circulating charges. A dual-band absorption characteristic with reconfigurability between single band (7.20 GHz) and dual-band (7.20 GHz and 11.20 GHz) absorption was demonstrated. The third structure is made up of four-square patch separated by a vertical bar. The charges flow paths were manipulated by connecting the individual square patch to the vertical bar with copper wires. The concept of connecting multiple neighboring resonances to achieve a wideband absorption was demonstrated. Almost a 100% absorption across the entire X-band region (9.00 GHz to 13.00 GHz) was achieved and furthermore, switchability between total absorbance and total reflection at 11.20 GHz was demonstrated using copper wires. Reflection was more than 75%. The fourth structure is made up of two quad gapped square shaped split-ring resonators (QGSSSRR). This structure also achieved almost 100% absorption across the entire X-band region (9.00 GHz to 13.00 GHz), and it also demonstrated switchability between total absorbance and total reflection at 11.20 GHz. All the proposed designs were tested for incident wave angles (IWAs) in the range of 0o to 60o in which almost all of them performed excellently with a minimum absorption rate of close to 80% and reflection rate of close to 75%.