Electromagnetic Waves

Wave propagation in a double negative (DNG) medium, i.e., a medium having negative permittivity and negative permeability, is studied both analytically and numerically. The choices of the square root that leads to the index of refraction and the wave impedance in a DNG medium are determined by imposing analyticity in the complex frequency domain, and the corresponding wave properties associated with each choice are presented. These monochromatic concepts are then tested critically via a one-dimensional finite difference time domain (FDTD) simulation of the propagation of a causal, pulsed plane wave in a matched, lossy Drude model DNG medium. The causal responses of different spectral regimes of the medium with positive or negative refractive indices are studied by varying the carrier frequency of narrowband pulse excitations. The smooth transition of the phenomena associated with a DNG medium from its early-time nondispersive behavior to its late-time monochromatic response is explo...

An Internet of Things (IoT) application that employs wireless transmission data such as Wireless Sensor Node need to be designed well enough, So its data doesn't loss in its transmission between the node. Therefore to build an IoT application such as Wireless Sensor Node path loss propagation model is a must. In this paper, we proposed a new path loss model to be used on a near ground 2.4 GHz Wireless Sensor Node network in forest environment application. Our methods are using one of IoT node such as Microcontroller Wemos to do walk test and then capture statistical data the RSSI level every 5 meters and compare it to the simulation. Our new proposed model has a better result for forest environment at about 2.01 dB forest with High grass more than 30cm, 0.69 dB low grasses less than 10cm, and 0.26 dB without grass compare with other model and compare to the measurement at 65 meters.

Volume or statistical averaging of the microscopic Maxwell equations (MEs), i.e. transition from microscopic MEs to their macroscopic counterparts, is one of the main steps in electrodynamics of materials. In spite of the fundamental importance of the averaging procedure, it is quite rarely properly discussed in university courses and respective books; up to now there is no established consensus about how the averaging procedure has to be performed. In this paper we show that there are some basic principles for the averaging procedure (irrespective to what type of material is studied) which have to be satisfied. Any homogenization model has to be consistent with the basic principles. In case of absence of this correlation of a particular model with the basic principles the model could not be accepted as a credible one. Another goal of this paper is to establish the averaging procedure for metamaterials, which is rather close to the case of compound materials but should include magne...

Abstract. The microwave thermal thruster heats propellant via a heat-exchanger then expands it through a rocket nozzle to produce thrust. The heat-exchanger is simply a microwave-absorbent structure through which propellant flows in small channels. Nuclear thermal thrusters are based on an analogous principle, using neutrons rather than microwaves, and have experimentally demonstrated specific impulses exceeding 850 seconds. A microwave equivalent will likely have a similar specific impulse, since both nuclear and microwave thermal thrusters are ultimately constrained by material thermal limits, rather than the energy-density limits of chemical propellants. We present the microwave thermal thruster concept by characterizing a novel variation for beamed-energy launch. In reducing the thruster concept to practice, the enabling physical process is microwave absorption by refractory materials, and we examine semiconductor and susceptor-based approaches to achieving this absorption withi...

In this paper, the characteristics of layered structures (photonic or electromagnetic bandgaps), including chiral media, are studied by means of two different numerical methods, one in the time domain (finite differences in the time domain, FDTD) and the other in the frequency domain (coupled-mode method, CMM). The results (reflection and transmission coefficients for a plane wave normally incident over a layered structure) obtained by means of both well different techniques are practically identical. Copyright © 2009 John Wiley & Sons, Ltd.

Estimation of groundwater table by hydrogeologists in
Ghana over the past decades has proven to be difficult due to the
dearth of data on piezometric heads from the very few boreholes
present to access this data. The importance of this information in
infrastructure planning therefore calls for the need to establish a
precise geophysical method that can predict the depth to the
water table at a relatively lower cost and higher efficiency as
compared with prevailing conventional methods. This paper
demonstrates how the ground based ground penetrating radar
(GPR) has been successfully used to delineate water table depths
and possible ground water flow directions. The MALA GPR
equipment with unshielded rough terrain antenna of  25 MHz
central frequency in the common offset mode was employed for
the data collection. Data was taken along 21 profiles with interprofile separation of 50 m over the study site of areal extent 1
km
2
. Water table depths were estimated at an average depth of 21
m in an environment permeated by vertical structures which
possibly served as pathways for groundwater infiltration. The
general groundwater flow pattern was north-east in the northern
and southern parts, and south-west at the central, eastern and
western parts of the study area. The contact between the duricrust
and the weathered saprolite was found at an average depth of 8
m. GPR-derived groundwater table depths were validated by
drilled boreholes which intercepted the groundwater table at an
average depth of 20 m within a lithology  comprised of sandy
clay and granite with varying degrees of weathering.  This paper
demonstrates the use of GPR as an efficient method for the
estimation of groundwater table depth, groundwater flow
direction as well as mapping of near surface lithological units;
hence, it can serve as a baseline study for future applications.

... Citation Akhlesh Lakhtakia, Vasundara V. Varadan, and Vijay K. Varadan, "Field equations, Huygens's principle, integral equations, and theorems for radiation and ... wave propagation and scattering in isotropic chiral media (D =εE + βεΔ × E, B = νH + βνΔ × H) are explored here. ...

The wire medium is a type of complex artificial material we conceptually envision as many identical finite-length, parallel, thin wire inclusions embedded within a host medium. It is representative of a class of novel artificial materials characterized by long thin inclusions. Unlike some ...

Metamaterials (MTM) have become a major electromagnetic research topic. Initial studies have focused on understanding their electromagnetic properties and interactions. This paper presents a novel virtual tool, MTM-FDTD, for the visualization of electromagnetic wave interacting with different metamaterials. Snapshots from characteristic examples during these interactions are presented. Scenarios with normal and oblique incidences, demonstrating focusing beams in planar metamaterials and

LiDAR, typically used as an acronym for "'light detection and ranging'", is essentially a sonar that uses pulsed laser waves to map the distance to surrounding objects. It is used by a large number of autonomous vehicles to navigate environments in real time. Its advantages include impressively accurate depth perception, which allows LiDAR to know the distance to an object to within a few centimetres, up to 60 metres away. It's also highly suitable for 3D mapping, which means returning vehicles can then navigate the environment predictably-a significant benefit for most self-driving technologies. One of the key strengths of LiDAR is the number of areas that show potential for improvement. These include solid-state sensors, which could reduce its cost tenfold, sensor range increases of up to 200m, and 4-dimensional LiDAR, which senses the velocity of an object as well as its position in 3-D space. However, despite these exciting advances, LiDAR is still hindered by a key factor; its significant cost. LiDAR is not the only self-driving detection technology, with cameras as the major rival, championed by Tesla as the best way forward. Elon Musk has described LiDAR as "a fool's errand" and "unnecessary". The argument runs that humans drive based only on ambient visible light, so robots should equally be able to. A camera is significantly smaller and cheaper than LiDAR (although more of them are needed), and has the advantage of seeing in better resolution and in colour, meaning it can read traffic lights and signs. However, cameras have a wide host of characteristics that make them tricky to use in common driving conditions. Whereas LiDAR uses near infra-red light, cameras use visible light, and are thus more susceptible to issues when faced with rain, fog, or even some textures. In addition, LiDARs do not depend on ambient light, generating their own light pulses, whereas cameras are more sensitive to sudden light changes, direct sunlight and even raindrops.