Margarita Chizh

Microwave imaging of moving subjects by combined use of video-tracker and multi-static radar

This paper presents preliminary experiments with a geometrically simple target and a new architecture of the microwave screening system capable of obtaining radar images of moving subjects. The system is based on the combined use of a video-tracker and a linear antenna array. Inverse synthetic aperture is formed by arbitrary motion of the target in the vicinity of the array. A video-based system tracks the target and allows coherent processing of synchronously registered radar data, and eventually obtaining detailed radar images of concealed objects.

Experimental simulation of multi-static radar with a pair of separated movable antennas

This paper describes a setup for experimental simulation of the signal obtained in electronically switched sparse antenna arrays by independently moving one transmit and one receive antennas. The concept of the system is given with detailed description of the current working realization and the methodology of conducting experiments. Examples of acquired radar signals are presented with corresponding radar images obtained after processing. Potential applications of the setup system in a variety of research projects are given. Further improvements of the system are suggested.

Experimental validation of sparse sensing technique in subsurface microwave holography

In this paper the implementation of the Sparse or Compressed Sensing (CS) technique to subsurface holography allowing data acquisition on a sparse grid is considered, which raises the scanning speed, reduces the amount of stored and transmitted data. To test various aspects of applying CS technique, a custom-built experimental setup acquiring data at several programmable sampling intervals was used. The setup consists of a vector network analyzer (VNA) with connected antenna and a two-coordinate mechanical scanner that moves the sample in the vicinity of the antenna. This technique allows simulating sparse sampling and testing various scanning and sounding parameters. As the test object a sample of cryogenic fuel tank thermal insulation was selected for the purpose of nondestructive testing (NDT). Upon acquisition, a complex data processing algorithm on the basis of windowing functions, interpolation, and filtering was applied. Then the Fourier-based back propagation algorithm was used for obtaining radar images by complex holograms reconstruction. Further development of the considered sensing technique is suggested, including the adaptive scanning on a non-equidistant grid.

Non-destructive testing at microwaves using a vector network analyzer and a two-coordinate mechanical scanner

This paper describes a system for non-destructive testing of radio transparent samples at microwaves. The main components of the system are a vector network analyzer (VNA), one or several stationary antennas connected to it, and a two-coordinate flat mechanical scanner that moves the sample in the antennas vicinity. The VNA and the scanner are controlled by a personal computer, which can acquire the parameters measured by the VNA in a set of pre-programmed positions over the sample. The technical description of the setup, software components, and sample radar images are provided. Possible research applications of the setup and its future improvements are suggested.

Experimental comparison of multi-static and mono-static antenna arrays for subsurface radar imaging

The performance of multi-static and mono-static radar systems is compared using experimental setup consisting of linear drives that move transmit and receive antennas in the programmable positions corresponding to multi-static or mono-static linear antenna arrays. The synthetic aperture in the direction perpendicular to the imitated linear arrays is formed by moving the target by an additional linear drive. Simulated and experimental radar images are obtained for various multi-static antenna configurations, and compared to their mono-static equivalents. The mono-static and multi-static signal processing technique is given. Possible applications of the described experimental technique are suggested.

Non-destructive testing of foam insulation by holographic subsurface radar

This paper describes a radar system intended for non-destructive testing of foam insulation used on cryogenic fuel tanks in space industry. The radar system consists of a radar and a two-coordinate mechanical scanner which moves the sample in the vicinity of radar antennas to form a synthetic aperture. The radar is build around an Infineon integral transceiver with nominal frequency range from 24 to 24.25 GHz. The radar has a compact size and can be used in combination with other robotic manipulators for data acquisition. The radar and the scanner are driven by a microcontroller with dedicated firmware, which is responsible for forming real-time signals for the stepper motors of the scanner and other peripheral units, such as DAC and ADC boards. The radar system is controlled by a personal computer with the user software written in Python. The component-view of the radar system is given and explained in details, sample radar images are presented and compared with the radar images of the same sample obtained with a previously created setup that featured a vector network analyzer instead of the custom radar.

On the use of augmented reality devices for subsurface radar imaging

The idea of using the emerging augmented reality (AR) devices with scanning contact sensors is considered in this paper. This concept is illustrated by the experimental setup which includes a holographic subsurface radar as a contact sensor, web-camera, and personal computer. The data acquisition is accomplished by tracking the radar antenna tagged by an AR-marker. The radar image is updated periodically in real time as more data samples become available, making the data acquisition adaptive. It is shown that the use of a video-based tracking system may increase the data acquisition speed by a factor of ten in comparison with the traditional scanning approach which requires collecting data along consecutive parallel lines over the whole area before calculating the radar image. The data visualization with AR removes the problem of radar data mapping from the computer screen to the probed scene. Further advantages of using AR-devices, which may influence the signal processing, including data from different sensors, are suggested.

Numerical comparison of mono-static and multi-static array performance in personnel screening systems

The comparison of the modern microwave screening systems is given in this paper in the aspect of employing mono-static or multi-static antenna configuration, with their numerical models described and applied in the presented numerical experiments. The phenomenological model of scattering from human body and foreign objects is used to obtain the radar signal, which is processed according to the given mono-static or multi-static signal processing algorithms. The model of scattering objects is based on point scatterer approximation of their surfaces. The numerical simulations are performed for human body and foreign objects to obtain detailed radar images for mono-static and two multi-static antenna configurations at a single and multiple frequencies. According to the results of numerical simulations, the same quality of radar images, visually assessed by achievable plan view resolution and the level of artifacts, can be obtained by significantly lesser number of antenna elements in the case of multi-static antenna configuration. It was shown that extending the frequency band from 10 to 16 GHz substantially increases the contrast of the foreign objects placed over the human body.

Microwave imaging of biological tissue phantom in different frequency ranges

In the present study the microwave images for the breast tissue phantom in different frequency ranges were obtained. The phantom was made of lard imitating fat breast tissue and dielectrically contrast inclusions. Experimental data were gathered by using the installation consisted of a vector network analyzer, two linear drives, a single transceiving antenna, flexible armored antenna feeders, a microcontroller board, and a computer. Recorded by the vector network analyzer scattered electromagnetic field parameters were further processed utilizing an algorithm written in Python Programming Language to reconstruct microwave image of the inner dielectric inhomogeneities of the phantom.

Experimental setup to simulate the performance of ISAR-based microwave personnel screening system

This paper presents experimental results to support the new architecture of the microwave personnel screening system, which can obtain radar images of concealed objects on moving subjects. The system uses natural motion of a subject to form the inverse synthetic aperture, which eliminates mechanical scanning from the system and reduces its microwave part to a linear antenna array. The coherent radar signal processing is achieved by using an RGB-D video sensor, which is responsible for tracking the subject as he or she moves in the vicinity of the linear antenna array. With the described experimental setup and imitation experiments with a moving mannequin it was shown that the joint processing of radar samples and video frames gives the detailed radar images of hidden objects.