arXiv subjects

Ankit Vora

Publications and source records attributed to Ankit Vora.

26 records · Page 2Linked to original sources

arXiv2020

Localization in Autonomous Vehicles Using a Generalized Inner Product

Fine localization in autonomous driving platforms is a task of broad interest, receiving much attention in recent years. Some localization algorithms use the Euclidean distance as a similarity measure between the local image acquired by a camera and a global map, which acts as side information. The global map is typically expressed in terms of the coordinate system of the road plane. Yet, a road image captured by a camera is subject to distortion in that nearby features on the road have much larger footprints on the focal plane of the camera compared with those of equally-sized features that lie farther ahead of the vehicle. Using commodity computational tools, it is straightforward to execute a transformation and, thereby, bring the distorted image into the frame of reference of the global map. However, this nonlinear transformation results in unequal noise amplification. The noise profile induced by this transformation should be accounted for when trying to match an acquired image to a global map, with more reliable regions being given more weight in the process. This physical reality presents an algorithmic opportunity to improve existing localization algorithms, especially in harsh conditions. This article reviews the physics of road feature acquisition through a camera, and it proposes an improved matching method rooted in statistical analysis. Findings are supported by numerical simulations.

eess.SP↗

arXiv2019

Localization Requirements for Autonomous Vehicles

Autonomous vehicles require precise knowledge of their position and orientation in all weather and traffic conditions for path planning, perception, control, and general safe operation. Here we derive these requirements for autonomous vehicles based on first principles. We begin with the safety integrity level, defining the allowable probability of failure per hour of operation based on desired improvements on road safety today. This draws comparisons with the localization integrity levels required in aviation and rail where similar numbers are derived at 10^-8 probability of failure per hour of operation. We then define the geometry of the problem, where the aim is to maintain knowledge that the vehicle is within its lane and to determine what road level it is on. Longitudinal, lateral, and vertical localization error bounds (alert limits) and 95% accuracy requirements are derived based on US road geometry standards (lane width, curvature, and vertical clearance) and allowable vehicle dimensions. For passenger vehicles operating on freeway roads, the result is a required lateral error bound of 0.57 m (0.20 m, 95%), a longitudinal bound of 1.40 m (0.48 m, 95%), a vertical bound of 1.30 m (0.43 m, 95%), and an attitude bound in each direction of 1.50 deg (0.51 deg, 95%). On local streets, the road geometry makes requirements more stringent where lateral and longitudinal error bounds of 0.29 m (0.10 m, 95%) are needed with an orientation requirement of 0.50 deg (0.17 deg, 95%).

cs.RO↗

arXiv2018

Optimal Design of Thin-film Plasmonic Solar Cells using Differential Evolution Optimization Algorithms

An approach using a differential evolution (DE) optimization algorithm is proposed to optimize design parameters for improving the optical absorption efficiency of plasmonic solar cells (PSC). This approach is based on formulating the parameters extraction as a search and optimization process in order to maximize the optical absorption in the PSC. Determining the physical parameters of three-dimensional (3-D) PSC is critical for designing and estimating their performance, however, due to the complex design of the PSC, parameters extraction is time and calculation intensive. In this paper, this technique is demonstrated for the case of commercial thin-film hydrogenated amorphous silicon (a-Si:H) solar photovoltaic cells enhanced through patterned silver nano-disk plasmonic structures. The DE optimization of PSC structures was performed to execute a real-time parameter search and optimization. The predicted optical enhancement (OE) in optical absorption in the active layer of the PSC for AM-1.5 solar spectrum was found to be over 19.45% higher compared to the reference cells. The proposed technique offers higher accuracy and automates the tuning of control parameters of PSC in a time-efficient manner.

physics.app-ph↗

arXiv2018

Ultra-Broadband Terahertz Perfect Absorber based on Doped Silicon

The requirement for metamaterial perfect absorbers (MPA) based on doped semiconductors is steadily increasing due to the available matured fabrication and simulation technology. There is a particular interest in developing terahertz (THz) perfect absorbers using doped semiconductors for achieving characteristics such as polarization-independence, wide-angle, and broadband absorption. We report MPA based on patterned arrays of tapered micro-cylindrical structures of doped silicon to enable them with broadband, wide-angle, and polarization-independent response. In this work, we modeled the MPA structures using COMSOL Multiphysics to evaluate its electromagnetic wave response using the software's RF Module running in parallel on a Beowulf cluster. We evaluated the doped silicon MPA structures for its response in the frequency spectrum of 0.1 to 5.0 THz for transverse magnetic and transverse electric polarizations at the normal and oblique incidence up to 75 degrees. This proposed doped silicon MPA was found to support a perfect absorption for a wide frequency spectrum from 1.7 to 3.9 THz along with insensitivity towards polarization and incident angles up to 60 deg. The execution of MPA on simplified Beowulf cluster significantly reduced the simulations time by the orders of magnitude compared to the sequential simulations.

physics.app-ph↗

arXiv2017

Copper-oxide Nanowires based Humidity Sensor

This paper presents investigated results of copper-oxide nanowires used as a humidity sensor. Copper-oxide nanowires films were grown over cross-comb type gold electrodes on a SiO2 substrate using thermal annealing technique, and its humidity sensitive characteristics were investigated through resistance across the gold electrodes. These copper-oxide nanowires films revealed high sensitivity and long-term stability with fast response time. It was found that resistance across gold electrodes of the fabricated sensor decreases with increase in humidity almost linearly on a logarithmic scale. It appears that copper-oxide nanowires can be used as low-cost humidity sensor with high output reliability and reproduction rate. The observations were carried out at room temperature (RT) and relative humidity (RH) in the range of 6% to 97%.

physics.app-ph↗

arXiv2017

New approach for SCR selection and optimization for Septum magnet power supply with high reliability

A new approach for selection of Silicon-Controlled Rectifier (SCR) for switching high pulsed currents in the septum magnet power supply is described. In this approach, an attempt is made to select the SCR from its I2t rating given in data sheet. For this, a factor which we have called I2t derating factor is defined as the ratio of I2t rating of SCR to the I2t value of current pulse to be switched. Thus, the SCR to be used in power supply is selected from its I2t derating factor. Three different experiments were performed using SCR of different manufacturers, to estimate the value of I2t derating factors. In these experiments, the SCR was subjected to maximum thermal stress till SCR started showing degradation. The forward blocking voltage and the leakage current are the parameters used for characterizing the SCR before and after the stress. The results of these experiments are presented and discussed. This approach will be of great help when pulse rating of SCR, like, transient thermal impedance is not available. Finally, a method is presented which can contribute to design low-cost and high-reliability septum magnet power supply.

physics.ins-det↗

arXiv2014

Multi-resonant silver nano-disk patterned thin film hydrogenated amorphous silicon solar cells for Staebler-Wronski effect compensation

We study polarization independent improved light trapping in commercial thin film hydrogenated amorphous silicon (a-Si:H) solar photovoltaic cells using a three-dimensional silver array of multi-resonant nano-disk structures embedded in a silicon nitride anti-reflection coating (ARC) to enhance optical absorption in the intrinsic layer (i-a-Si:H) for the visible spectrum for any polarization angle. Predicted total optical enhancement (OE) in absorption in the i-a-Si:H for AM-1.5 solar spectrum is 18.51% as compared to the reference, and producing a 19.65% improvement in short-circuit current density (JSC) over 11.7 mA/cm2 for a reference cell. The JSC in the nano-disk patterned solar cell (NDPSC) was found to be higher than the commercial reference structure for any incident angle. The NDPSC has a multi-resonant optical response for the visible spectrum and the associated mechanism for OE in i-a-Si:H layer is excitation of Fabry-Perot resonance facilitated by surface plasmon resonances. The detrimental Staebler-Wronski effect (SWE) in a-Si:H solar cell can be minimized by the additional OE in the NDPSC and self-annealing of defect states by additional heat generation, thus likely improving the overall stabilized characteristics of a-Si:H solar cells.

physics.optics↗

arXiv2014

Exchanging Ohmic Losses in Metamaterial Absorbers with Useful Optical Absorption for Photovoltaics

Using metamaterial absorbers, we have shown that metallic layers in the absorbers do not necessarily constitute undesired resistive heating problem for photovoltaics. Tailoring the geometric skin depth of metals and employing the natural bulk absorbance characteristics of the semiconductors in those absorbers can enable the exchange of undesired resistive losses with the useful optical absorbance in the active semiconductors. Thus, Ohmic loss dominated metamaterial absorbers can be converted into photovoltaic near-perfect absorbers with the advantage of harvesting the full potential of light management offered by the metamaterial absorbers. Based on experimental permittivity data for indium gallium nitride, we have shown that between 75%-95% absorbance can be achieved in the semiconductor layers of the converted metamaterial absorbers. Besides other metamaterial and plasmonic devices, our results may also apply to photodectors and other metal or semiconductor based optical devices where resistive losses and power consumption are important pertaining to the device performance.

physics.optics↗