Danilo Erricolo

Radio Frequency Tomography for Tunnel Detection

Radio frequency (RF) tomography is proposed to detect underground voids, such as tunnels or caches, over relatively wide areas of regard. The RF tomography approach requires a set of low-cost transmitters and receivers arbitrarily deployed on the surface of the ground or slightly buried. Using the principles of inverse scattering and diffraction tomography, a simplified theory for below-ground imaging is developed. In this paper, the principles and motivations in support of RF tomography are introduced. Furthermore, several inversion schemes based on arbitrarily deployed sensors are devised. Then, limitations to performance and system considerations are discussed. Finally, the effectiveness of RF tomography is demonstrated by presenting images reconstructed via the processing of synthetic data.

Superhydrophobic and conductive carbon nanofiber/PTFE composite coatings for EMI shielding

This paper presents a solvent-based, mild method to prepare superhydrophobic, carbon nanofiber/PTFE-filled polymer composite coatings with high electrical conductivity and reports the first data on the effectiveness of such coatings as electromagnetic interference (EMI) shielding materials. The coatings are fabricated by spraying dispersions of carbon nanofibers and sub-micron PTFE particles in a polymer blend solution of poly(vinyledene fluoride) and poly(methyl methacrylate) on cellulosic substrates. Upon drying, coatings display static water contact angles as high as 158° (superhydrophobic) and droplet roll-off angles of 10° indicating self-cleaning ability along with high electrical conductivities (up to 309 S/m). 100 μm-thick coatings are characterized in terms of their EMI shielding effectiveness in the X-band (8.2-12.4 GHz). Results show up to 25 dB of shielding effectiveness, which changed little with frequency at a fixed composition, thus indicating the potential of these coatings for EMI shielding applications and other technologies requiring both extreme liquid repellency and high electrical conductivity.

Measurements on scaled models of urban environments and comparisons with ray-tracing propagation simulation

Scaled models of simple two-dimensional (2-D) urban environments are considered in order to investigate propagation along a vertical plane. Specifically, path loss measurements are taken for different positions of the transmitting and receiving antennas at 25 GHz. Then measurement results are compared with theoretical predictions computed by a ray-tracing polygonal line simulator. The measurements indicate a very good agreement between the ray-tracing model and the experiments.

Two-dimensional simulator for propagation in urban environments

A new two-dimensional (2-D) ray-tracing simulator for electromagnetic (EM) propagation prediction in an urban environment is described. The new features are that no practical restrictions are imposed on the profile of the cross section connecting the transmitter to the receiver and that each surface is characterized by its own value for the surface impedance; also, second-order diffraction coefficients for impedance wedges are used to allow for arbitrary values of the heights of both antennas. Comparisons with other methods and numerical results are presented.

Acceleration of the convergence of series containing Mathieu functions using Shanks transformation

A modification of the standard application of Shanks transformation is shown to improve the convergence rate in certain cases where the straightforward application of Shanks transformation fails. Here, the straightforward application of Shanks transformation to a well known series expansion containing Mathieu functions failed to improve the convergence rate. However, convergence was achieved by a new method of applying Shanks transformation. This new method requires analysis of the behavior of the series terms to determine the cause of the slow or failing convergence. Then, the Shanks transformation was applied only to the slowly convergent part of the series. This work is important because, with this new method, convergence may be achieved in cases where the standard application of Shanks transformation fails to improve the convergence rate. The paper takes as a case study the electromagnetic problem of the expansion of a cylindrical wave in a series of Mathieu functions.

RF Tomography for Below-Ground Imaging of Extended Areas and Close-in Sensing

Three extensions to radio-frequency (RF) tomography for imaging of voids under wide areas of regard are presented. These extensions are motivated by three challenges. One challenge is the lateral wave, which propagates in proximity of the air-earth interface and represents the predominant radiation mechanism for wide-area surveillance, sensing of denied terrain, or close-in sensing. A second challenge is the direct-path coupling between transmitters (Txs) and receivers (Rxs), that affects the measurements. A third challenge is the generation of clutter by the unknown distribution of anomalies embedded in the ground. These challenges are addressed and solved using the following strategies: 1) A forward model for RF tomography that accounts for lateral waves expressed in closed form (for fast computation); 2) a strategy that reduces the direct-path coupling between any Tx-Rx pair; and 3) an improved inversion scheme that is robust with respect to noise, clutter, and high attenuation. A finite-difference time domain simulation of a scenario representing close-in sensing of a denied area is performed, and reconstructed images obtained using the improved and the classical models of RF tomography are compared.

Exact radiation and scattering for an elliptic metal cylinder at the interface between isorefractive half-spaces

An elliptic metal cylinder located at the interface between two isorefractive half-spaces, with its cross-sectional major axis either parallel or perpendicular to the interface is considered. The problems of scattering of an incident plane wave with arbitrary polarization and direction of incidence, and of radiation from an electric or magnetic line source parallel to the cylinder axis are solved exactly. The particular case of a metal strip either parallel or perpendicular to the interface is examined in detail. Several numerical results for far fields and surface currents are presented.

Algorithm 861: Fortran 90 subroutines for computing the expansion coefficients of Mathieu functions using Blanch's algorithm

A translation to Fortran 90 of Gertrude Blanchs algorithm for computing the expansion coefficients of the series that represent Mathieu functions is presented. Its advantages are portability, higher precision, practicality of use, and extended documentation. In addition, numerical validations and comparisons with other existing methods are presented.

Time-domain analysis of measurements on scaled urban models with comparisons to ray-tracing propagation simulation

This work deals with propagation prediction for wireless communications in urban environments. Its purpose is to clearly distinguish the different field contributions collected by the receiving antenna through a series of wide-band frequency measurements and a time-domain (TD) analysis of the obtained results. The experimental data are then compared to the field predictions given by a ray-tracing electromagnetic wave propagation simulator. The application of this research lies in the modeling of the urban channel for wireless communication systems of the third generation such as UMTS and beyond.

An Approach to Rapid Calculation of Temperature Change in Tissue Using Spatial Filters to Approximate Effects of Thermal Conduction

We present an approach to performing rapid calculations of temperature within tissue by interleaving, at regular time intervals, 1) an analytical solution to the Pennes (or other desired) bioheat equation excluding the term for thermal conduction and 2) application of a spatial filter to approximate the effects of thermal conduction. Here, the basic approach is presented with attention to filter design. The method is applied to a few different cases relevant to magnetic resonance imaging, and results are compared to those from a full finite-difference (FD) implementation of the Pennes bioheat equation. It is seen that results of the proposed method are in reasonable agreement with those of the FD approach, with about 15% difference in the calculated maximum temperature increase, but are calculated in a fraction of the time, requiring less than 2% of the calculation time for the FD approach in the cases evaluated.