Impulse ground-penetrating radar antenna design and optimization for homogeneous and low-loss dielectric multilayer media

• Autor(a) principal: Maria Victoria Africano Contreras
• Data de Publicação: 2021
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Repositório Institucional da UFMG
• Texto Completo: http://hdl.handle.net/1843/37517; https://orcid.org/0000-0001-5097-3781
• topic: Ground penetrating radar; Multilayer problem; Pavement materials; Ricker wavelet; UWB antenna optimization; Engenharia elétrica; Antenas (Eletrônica); Otimização

Non-destructive assessment of multilayer media represents an inverse electromagnetic problem that can be solved with methods in the time- or frequency-domain. Solution techniques in the time-domain are more widely used and popular because they allow the use of simple equations to obtain the layers' properties from the Ground Penetrating Radar (GPR) measurements. For this, it is assumed that the dielectrics are low-loss, non-magnetic, and that the layers are linear, isotropic and homogeneous. However, the quality of the results depends directly on the adequate detection of the reflection peaks measured by the GPR. This can turn the technique unfeasible when there is an overlap between some of the signal components received by the GPR. In this context, this thesis proposed a new practical methodology to obtain the antenna design requirements (operating frequency and temporal response) that avoid overlapping reflected pulses. The methodology is based on the analysis of the inquiring signal and the evaluated multi-layer structure. The main contribution is that the proposed methodology enables the production of specific antennas for the analyzed multilayer problem, serving as a practical guide for GPR antenna design. A typical flexible pavement composed of three overlapping layers (asphalt, base, and subgrade) was the multilayer structure selected to show how the methodology can be applied to obtain the antenna requirements. Once the antenna requirements were obtained, the candidate antenna topologies were selected and two optimization approaches were proposed and evaluated: the first one consists of the frequency-domain optimization of a multi-objective problem based on traditional objective functions (impedance matching and gain), and the second optimization approach uses a time-domain electromagnetic solver to assess a new proposal of objective function directly in the time-domain (the received pulse amplitude). As a result of the frequency-domain optimization, an ultra-wideband (UWB) directive microstrip monopole antenna with admissible dispersion was obtained according to the design specifications extracted from the test problem. The antenna simulation was compared and validated with antenna measurements carried out in a non-anechoic environment. In turn, the optimization of the new single-objective function applied to two different antenna topologies (microstrip monopole and Vivaldi) allowed obtaining compact solutions that met the time-domain antenna requirement. Also, simulations of this optimization problem showed that the new objective function represents an alternative to the traditional multi-objective optimization approach. Besides, the definition of one single-objective function facilitates the antenna design process avoiding convergence problems and any posterior decision-making process.