3.3 Artificial Magnetic Conductor (AMC) and Electromagnetic Band Gap (EBG) Structures
AMC and EBG structures are periodic assemblies of unit cells that are composed of a geometrical arrangement of readily available materials (such as dielectrics, conductors, etc.). Due to the periodicity and electromagnetic interactions among the unit cells, these structures can exhibit unique properties that cannot be found in any of their bulk individual constituents. For example, at particular frequency ranges, EBG structures prevent the propagation of electromagnetic waves in certain directions. Due to this property, 2-D EBG structures (see Figure 14) are often employed to enhance the radiation performances of the patch antennas by suppressing the surface wave propagation. Likewise, AMC surfaces can reflect incident electromagnetic waves without any phase shift at particular frequency regions [2].
Figure (14) A 2-D EBG structure (this mushroom-like unit cell introduced by Sievenpiper [2])
A 2D EBG structure can also act as an AMC surface when being operated at their band-gap frequencies. On the other hand, an AMC surface configuration does not necessarily display a band-gap property. To design the EBG/AMC structures, two different models are generally utilized by different research groups. These models are named as [23]:
Lumped element, and full wave computational.
In the following subsection, we well briefly explain these models:
3.3.1 Models for Designing EBG/AMC Unit Cells
3.3.1.1 The Lumped Element Model
This model is the simplest among all others. The unit cell is modeled as a lumped circuit consisting of capacitors and inductors. For the mushroom type unit cell introduced by ...
... middle of paper ...
...n [A]
Multiband AMC surfaces can be designed using multi-layered AMCs surfaces resonating at different frequencies. For example in [31], zero reflection phases were achieved at two frequency bands (850MHz and 1900MHz) by using dual AMC surfaces. Another approach is to use an optimization algorithm to design the unit cell layout to cover multiple bands. In [32], an increase in the bandwidth from 31% to 81% was achieved in a tri-band AMC surface using genetic algorithm. Tunable multiband AMC surfaces were also investigated by integrating diodes among the metallic patches. For instance in [33], the AMC was designed to operate at two particular frequencies by using the on/off state of the diode. Another multiband design operating at 2.4, 4.5, 5.2, and 5.8GHz were designed using multilayer substrates [34].
The advent of neural net with the seminal work of Hopfield , popularized the use of machine intelligence techniques in the pattern recognition. However, the dense and inherent structure of neural networks is not suitable for VLSI implementation. So, researchers in the neural network domain tried to simplify the structure of the neural network by pruning unnecessary connections. Simultaneously, the CA research community explored the advantages of the sparse network structure of cellular automata for relevant applications. The hybridization of cellularity and neural network has given rise to the popular concept of cellular neural networks.
Esterberg’s discussion of the connection between theory and data says that in order to carry out qualitative research you need to use inductive reason. Deductive reasoning is the opposite approach inductive reasoning which correlates with quantitative research. When looking at deductive research you begin with creating a theory that you want to test by creating a hypothesis and picking a sample to study. Looking at inductive reasoning you begin with analyzing the world around you and strategize different characteristics to form a theory. To me theory means reasoning’s to test something to find answers. I believe it helps us understand the world around us better but making correlations between two different things.
Current collectors are made of graphitic materials due to its good conduction. GDL gas diffusion layers are made of carbon paper, which has low electronic resistance in order to provide maximum electronic contact and prevent water flooding. Bipolar plates are made of either graphite sot thermosets materials. [Lister & McLean ]
I therefore predict that the higher the intensity, the greater the emf across the cell, the greater the power output of the
The class GEB3213 has allow me to have a peek of the work load will encounter if I become a Health Care Administer. The following is an outline of what I have learn in this course and how I will use it in the Health Care Administration field.
ASDA's Hierarchial Structure A hierarchical structure has many levels. Each level is controlled by one person. A hierarchical company tends to be a very big company just like ASDA is. In a hierarchical company, instructions are generally passed down from one person to another until it gets to the bottom.
Their performance can be modelled, predicted and analyzed using equivalent circuits, and this experiment examines one of these circuits. MEASUREMENTS ------------ Short-circuit test: Primary voltage (Vsc) = 26V Primary current (I1) =
In fabrication micro-sensors and devices micro-electro-mechanical systems (MEMS) provides significant opportunities, which are borrowed it fabrication abilities from semiconductor technology.
The purpose of the antenna is to capture the radio signal from the air waves and into the tuner. An AM antenna is simply a wire or a metal stick.
One of the most commonly used dielectric materials used to construct dielectric EAPs is VHB 4910 tape by 3M as shown in figure~
* Microwaves are reflected by metal surfaces, much as a ball would bounce off a wall. The metal walls of the cooking space actually form a cavity resonator. In other words, the enclosure is designed to resonate the microwaves as they are radiated from the magnetron tube. The principle of resonance may be illustrated using sound waves. When a piano key is struck, it produces sound vibrations or sound waves. Sometimes a note is played on a piano, and an object across the room, perhaps a wineglass, can be heard vibrating and producing the same sound.
Analog communication employs continuous transmission of an electromagnetic wave form that varies in frequency and amplitude.
When Kleinfeld's efforts at Siemens he has an idea in his mind to get the company restructured in a new and appropriate way. He planned to restructure the company by aligning the lines of responsibilities as it was done previous at Jack Welch at General Electric. Kleinfeld has tried a lot to make the structure as simple as possible and to make it less bureaucratic. He wanted it because of the fact that the decisions can be made more quickly and smartly. He wanted to turnaround the business units which are underperforming and giving no chance to earn revenues and incomes. Finally he thought to make simplified the structure of the company in order to reduce complexity and to gain competitive advantage (Armstrong,2006).
In 2010 two Russian-born scientists pioneered and synthesized a form of “wonder material” that generates heat and electricity at faster speeds, copes with high temperatures, and is almost transparent. Graphene is arranged in a flat hexagon lattice (like microscopic chicken wire) and is one atom thick two-dimensional 〖sp〗^2 bonded carbon. It is the world’s thinnest and strongest material, which can be manufactured into a plethora of provisions that can be used for next generation technology, such as planes, satellites, cars, and computers. However, uses of the material can be expensive and difficult to manufacture for mass production, which is why many of us today do not have access to graphene or use it for various applications in technology in day-to-day life. Graphene is a newly developing material, which is under scrutiny and scientific study in order to integrate it simply and effectively into everyday life.
The waves can be absorbed and reflected by surrounding objects before they reach the nearest cell tower. For example when you put your phone next to your head, during a...