This paper presents a new method for imaging, localizing, and tracking motion behind walls in real time. The method takes advantage of the motion-induced variance of received signal strength measurements made in a wireless peer-to-peer network. Using a multipath channel model, we show that the signal strength on a wireless link is largely dependent on the power contained in multipath components that travel through space containing moving objects. A statistical model relating variance to spatial locations of movement is presented and used as a framework for the estimation of a motion image. From the motion image, the Kalman filter is applied to recursively track the coordinates of a moving target. Experimental results for a 34-node through-wall imaging and tracking system over a 780 square foot area are presented.

See-Through Walls: Motion Tracking Using Variance-Based Radio Tomography Networks

[신간안내] Computational Electrodynamics (the finite difference time - domain method)

Through-wall imaging approaches are highly desirable for a range of applications including police, fire and rescue, first responder, and military applications. The ultimate desire of such systems is to provide detailed information in areas that cannot be seen through conventional measures. Borrowing from successes in geological and medical imaging environments, researchers have attempted to apply radio frequency (RF) and other sensing modes to penetrate wall materials and optimally estimate the content and structure of rooms and buildings. There are many propagation differences that provide unique challenges that must be addressed to make through-wall penetration sensors operationally viable. This paper outlines the historical context of early research and provides new directions for future research in the exciting interplay between electromagnetic propagation, signal processing, and knowledge-based reasoning algorithms.

Through-wall imaging: Historical perspective and future directions

Through wall imaging is highly desirable for police, fire and rescue, first responder, and military applications. The ultimate desire of such system is to provide detailed information in areas that cannot be seen using conventional measures. Borrowing from successes in geological and medical imaging environments, researchers are applying radio frequency (RF) and other sensing modes to penetrate wall materials and make intelligent decisions about the contents of rooms and buildings. For this application, they are many propagation differences that provide unique challenges that must be addressed to make through wall penetration sensors operationally viable. This paper outlines the historical context of early research as well as providing new directions for future research in this exciting interplay between electromagnetic propagation, signal processing, and knowledge-based reasoning algorithms.

Through wall imaging: Historical perspective and future directions

This paper presents the development of a low-cost real-time ultrawideband (UWB) see-through-wall (STW) imaging radar system. The designs of the microwave front end, the UWB data acquisition, and the system integration are discussed in detail. As for the most challenging task, the UWB data acquisition, we introduce a custom low-cost module based on commercial field-programmable gate array (FPGA) boards and low-speed analog-to-digital converters. The introduced module does not require a custom implementation of high-speed wideband mixed-signal circuitry but only depends on the FPGA firmware design, which favors a rapid system prototyping. The data acquisition module accomplishes a 100-ps equivalent-time sampling resolution at 100-Msamples/s real-time rate, while the developed STW system provides a 2-D real-time view of motion with a 1.5-ms speed behind walls. The system allows for an easy reconfiguration to support multiple operating frequency ranges, pulse sampling resolutions, and array deployments, thus providing a tremendous experimental flexibility. Our studies indicate that utilizing available technologies and off-the-shelf components could produce a practical stand-alone STW system at reasonable design effort and cost, which will lead to a better understanding of the challenging problems associated with STW technology.

Development and Implementation of a Real-Time See-Through-Wall Radar System Based on FPGA

In this paper, millimeter-wave imaging of foreign object debris (FOD)-type objects on the ground is studied with the help of ground-based synthetic aperture radar (GB-SAR) technique To test the feasibility of detecting runway FODs with this technique, some preliminary experiments are conducted within short antenna-to-target ranges of small imaging patches An automated stripmap GB-SAR system with stepped-frequency transmission is constructed together with a quasi-monostatic data collection operation The imaging experiments for various braces and screws are then carried out by using 32–36 GHz and 90–95 GHz frequency bands of the millimeter-wave Images reconstructed by a matched-filter based algorithm are analyzed to determine the proper system parameters for an efficient imaging and to comprehend the factors against a successful detection Results demonstrate the capability of GB-SAR imaging in accurately locating these FOD-like targets under near-range operating conditions

Millimeter-wave Ground-based Synthetic Aperture Radar Imaging for Foreign Object Debris Detection: Experimental Studies at Short Ranges

The radiation properties of a novel wire antenna are investigated. The main part of this antenna is a sinusoidal wire undulator, which radiates by coupling electromagnetic energy from a Goubau line located near the antenna. Far-field patterns and S-parameters composed of three sets of antenna are measured. The measured patterns are compared with the calculated ones and the phase and attenuation constants of all the antennas are calculated. Frequency behavior and the dependency on the antenna dimensions of those wave parameters are investigated. Measured and calculated field patterns are also compared with the MoM patterns and some properties of the wave propagating along structure are explained by using MoM current distributions. It is shown that a broadside transversal radiation occurs in a narrow frequency band. The radiation intensity strongly depends on the coupling distance between the Goubau line and the sinusoidal undulator. This antenna is used as the basic element of the security fence radar antenna array working at 1.25 GHz in the L-band, which detects intruders approaching the fence. The performance of the antenna in the array is investigated and the near field distribution of the array is measured. The received signals caused by an intruder are given. The effects of rain and wind are also considered. The results suggests that the security fence radar introduced in this study can be used for the perimeter control of closed areas such as airports, malls, etc.

The Radiation Properties of a Novel Wire Antenna for the Security Fence Radar

Tomographic methods of image reconstruction of two-dimensional cross-sections of volumetric objects in millimeter wavelengths band are suggested and considered.

Modeling of microwave images of buried cylindrical objects

In the present work new results of experimental investigation on TWWI with using the microwave tomography technique are submitted. A tomographic algorithm is employed for the cross-section imaging of dielectric and metal objects on the other side of a concrete wall and within a concrete block. The cross-section restoration of studied objects is based on the tomography integral equation. The scattered field of the object is measured on a direct line parallel to the wall investigated. The solution of this integral equation gives the possibility to find the function representing the normalized polarization current distribution in the probing cross-section which is normal to the wall surface and in which the scan line lies (vertical cross-section). The normalized polarization current distribution depends on frequency and can be calculated for a set of frequencies. The image function is defined as modulus of the sum of the normalized polarization current distributions. If the wall material in vertical cross-section is not homogeneous because of the presence of defects or quests within the wall or on the other side of the wall, one can see these inhomogeneities. A set of images in different vertical cross-sections allows us to reconstruct a 3D image of the object. It is shown that advanced through-wall and wall images can be obtained by application of an indemnification procedure to the field caused by final sizes of the scanning line and also by using an algorithm allowing us to allocate from the complete field the scattering component.

Through-wall and wall microwave tomography imaging

The sub-terahertz passive radiometric imaging systems based on the single channel design are developed for disclosure of dangerous objects concealed under persons' clothing in short distances and for passive visualization of remote targets. Antenna systems, such as based on aspheric lens and on parabolic reflector, were adopted and refined for passive imaging application. Low-noise, compact receiver (noise factor 4.5dB for 90–100GHz) involving four stages was developed. The radiometric imaging peculiarities of the different reflecting and absorbing targets were investigated against the brightness temperature of sky. The system was demonstrated to successfully detect and recognize the metallic weapon hidden under outer clothing in the distance about 10 m. The scanning process (80×80 pixels in an area about 32×32 cm) approximately takes 40 seconds.

Alexey A. Vertiy

Papers

Millimeter-wave Ground-based Synthetic Aperture Radar Imaging for Foreign Object Debris Detection: Experimental Studies at Short Ranges

The Radiation Properties of a Novel Wire Antenna for the Security Fence Radar

Modeling of microwave images of buried cylindrical objects

Through-wall and wall microwave tomography imaging

Passive radiometric imaging systems in millimeter wavelength range