Mihai Dimian

Analysis of earth effects on transmitting and receiving antennas characteristics with applications in subsurface object detection systems

This article provides an analysis of the earth effects on the transmitter and receiver antenna radiation patterns and their main characteristics. The soil moisture, soil structure and soil electrical properties are taking into account in this study. The results can be used for improving the design of the subsurface object detection system as well as for developing smart control adapted to the environmental conditions.

Analysis of the radiation patterns and transmission for a subsurface object detection system

This paper explores the transmission between a horn and a microstrip patch antenna with the existence of a single layer or a dual layer infinite planar earth model. At different distances between the transmitter and the receiver, the results are compared to free space transmission. The purpose is to understand the wave propagation process with application in landmine detection.

Noise Spectral Density of Hysteretic Systems

This chapter presents the analysis of output spectral density for hysteretic systems driven by noisy inputs. Closed form analytical solutions for output spectra are derived for bistable hysteretic systems, as well as for complex hysteretic systems that can be described through Preisach model as weighted superposition of symmetric rectangular operators. The mathematical machinery of diffusion processes on graphs is used to circumvent the difficulties related to the non-Markovian property of the output of hysteretic systems. The calculations are appreciably simplified by the introduction of the “effective” distribution function. The implementation of the method for the case of Ornstein-Uhlenbeck process is presented in details and general qualitative features of these spectral densities are examined. Due to the universality of the Preisach model, this approach can be used to describe hysteresis nonlinearities of various physical origins. In the last part of this chapter, the spectral density analysis is extended to other models of hysteresis, such as the energetic model, the Jiles-Atherton model, the Coleman-Hodgdon model, the Bouc-Wen and model, and the Preisach model. The statistical technique to compute the output spectra is based on Monte-Carlo simulations and Fast Fourier Transforms. The intrinsic differences between the algebraic, differential, and integral modeling of hysteresis are well exposed when the systems are driven by noisy inputs and their stochastic behaviors are compared against each other.

Noise and Stochastic Processes

This chapter presents an overview of the noise models that will be used throughout the book. In the area of magnetic hysteresis, most of the research employed Gaussian white noise as noise model, which is mathematically described by independent and identically distributed random variables following a Gaussian distribution. Once the interest in hysteresis was extended beyond the traditional area of magnetism, various noise models appeared naturally in the hysteresis analysis. For example, pink noise is ubiquitous in multi-stable electronic systems, Brown noise is very common in physical and chemical diffusion processes, and even white noise is often encountered in its impulsive form in economics and biological hysteretic systems, so Cauchy or Laplace probability distributions emerge as better model choices in these systems than Gaussian white noise. Various noise models and the numerical methods used in this study to simulate them are discussed in the first part of this chapter. The second part is devoted to introducing the theory of stochastic processes defined on graphs recently developed by Freidlin and Wentzell, which proved to be naturally suited to the stochastic analysis of hysteretic systems. First, several definitions and general properties of stochastic processes are discussed, stressing the link between transition probability of Markov processes and the semigroups of contractions. This relationship provides the characterization tool for the diffusion processes that can be defined on a graph, subject that is elaborated in the final sections of this chapter.

Mathematical Models of Hysteresis

This chapter offers an overview of the hysteresis models that will be used throughout the book. After a short general classification of hysteresis models and parameter identification methods, the rectangular hysteresis operator is introduced. Then, the chapter focuses on summarizing the main equations, properties, and characteristics of the Preisach, energetic, Jiles-Atherton, Coleman-Hodgdon, and Bouc-Wen models. Particular attention is given to the analytical description of the general properties of hysteresis curves such as differential susceptibilities, remanence, coercivity, saturation, anhysteretic curve, energy lost, stability, accommodation, and limit cycle for each model. The second part of the chapter presents two techniques for the modeling of rate-dependent hysteresis, one based on the feedback (effective field) theory and the other one on the relaxation time approximation. Finally, a unified theory of vector models is presented; this theory can be applied to generalize any scalar model of hysteresis to vector systems.

Noise Driven Relaxation Phenomena in Hysteretic Systems

This chapter analyzes noise driven relaxation phenomena in scalar and vector hysteretic systems. The analysis is performed only in the time domain without making any reference to the frequency domain. Analytical and numerical results are presented for most hysteretic models introduced in the first chapter. It is shown that the effect of thermal relaxation is to erase the history of the system by bringing it to a new, nondeterministic state. Special consideration is given to the degradation of the Preisach distribution and the separation line between the positive and negative hysterons in the Preisach model. The chapter also introduces scalar and vector viscosity coefficients and discusses the data collapse phenomenon.

Radar Cross Section of subsurface objects under tapered wave illumination

In this paper we investigate the Radar Cross Section (RCS) of subsurface objects under tapered electromagnetic wave illumination. A layered soil model is incorporated into full-wave simulation. The tapered wave is approximated by superposition of a set of plane waves whose magnitude and polarization are carefully chosen to form an incident beam with finite spatial width. The proposed strategy of modeling incident waves and subsurface objects has potential applications in landmine detection systems with directional transmitters (TX) and receivers (RX). Specifically, the radiation patterns of TX/RX can be synthesized with this method. Metallic objects with cylindrical shape have been used as typical landmine model to extract their RCS features.

Radar cross section calculation for subsurface objects

In this paper we establish a layered soil model with full wave electromagnetic simulation software package FEKO to characterize subsurface objects, in particular landmines and improvised explosive devices (IEDs). We perform a parametric study of the landmine Radar Cross Section (RCS) by varying the material properties (permittivity and conductivity) of the landmine, the depth of the landmine, as well as the incident wave direction. The simulation provides insight into the relationship between the physical parameters of the landmine and its radar signatures. The results are helpful in developing landmine detection systems with forward looking capability. The methodology is advantageous for accumulating landmine RCS information in a cost-effective manner.

Analysis of polarization and frequency effects on radio wave transmission characteristics over layered soil

This paper investigates the characteristics of radio wave transmission between two specific antennas: a horn and a microstrip patch antenna, with the existence of layered infinite planar soil. The distance between the transmitter (TX) and the receiver (RX), as well as the operating frequency and polarization status of the TX/RX pair results are taken into account. The TX/RX radiation patterns and the transmission coefficients are characterized. The soil is modeled using its complex dielectric constant. The results provide guidance for improving the design of a variety of wireless systems for them to adapt to environmental conditions. Examples include subsurface object detection systems as well as wide band mobile radio communication systems.

Layered soil effects on Vivaldi antenna as wide-band radar receiver

This paper characterizes the Vivaldi antenna as the receiver in a synchronous impulse reconstruction (SIRE) radar system. In particular, the effects of layered soil which typically exists in a battle field environment are taken into account. Using the full-wave simulation package FEKO, the Vivaldi antenna model along with an infinite planar layered soil structure is analyzed. The general difference between the radiation patterns of the Vivaldi antenna under the influence of soil and those in free space is summarized. The observations may serve at the radar system design stage as the base for the development of smart control capability adapted to the environment.