Stand-Off Through-the-Wall W-Band Millimeter-Wave Imaging Using Compressive Sensing

Through-the-wall radar imaging is a research area which has gathered renewed interest with the development of powerful millimeter-wave sources and detectors. Imaging techniques that require some sort of reconstruction can suffer from slow speeds and lack of complexity in the data acquisition phase of the measurements. These reconstruction methods can be greatly improved using compressive sensing (CS)-based tools that increase speed during these processes. Here, a %V-band single-pixel imaging system based on CS, which utilizes a mechanically controlled spatial light modulator to rapidly acquire the image, is demonstrated for metallic targets placed behind drywall. The system uses a frequency-modulated continuous wave W-band transmitter to illuminate the wall and the target. The image reflected off the target's field of view is spatially modulated by 10 x 10 array patterned masks and the signals are collected through a heterodyne receiver. The system can differentiate and locate a behind-the-wall object through the frequency swept Michelson interferometry analysis, since the strong reflections from the surface of the wall and the object induce an interference effect, which is observed at the receiver. The overall design of the optical system is optimized with respect to the geometry of the modulation pattern in the image plane resulting in successfully reconstructed images of objects using CS-based algorithms. Using larger optics and uniquely patterned masks such techniques can provide the solutions toward cast-effective, rapid analysis of structural changes in or behind visibly opaque media

Stand-Off Through-the-Wall W-Band Millimeter-Wave Imaging Using Compressive Sensing

Through-the-wall radar imaging is a research area which has gathered renewed interest with the development of powerful millimeter-wave sources and detectors. Imaging techniques that require some sort of reconstruction can suffer from slow speeds and lack of complexity in the data acquisition phase of the measurements. These reconstruction methods can be greatly improved using compressive sensing (CS)-based tools that increase speed during these processes. Here, a %V-band single-pixel imaging system based on CS, which utilizes a mechanically controlled spatial light modulator to rapidly acquire the image, is demonstrated for metallic targets placed behind drywall. The system uses a frequency-modulated continuous wave W-band transmitter to illuminate the wall and the target. The image reflected off the target's field of view is spatially modulated by 10 x 10 array patterned masks and the signals are collected through a heterodyne receiver. The system can differentiate and locate a behind-the-wall object through the frequency swept Michelson interferometry analysis, since the strong reflections from the surface of the wall and the object induce an interference effect, which is observed at the receiver. The overall design of the optical system is optimized with respect to the geometry of the modulation pattern in the image plane resulting in successfully reconstructed images of objects using CS-based algorithms. Using larger optics and uniquely patterned masks such techniques can provide the solutions toward cast-effective, rapid analysis of structural changes in or behind visibly opaque media

Super-Resolution Image Reconstruction Applied to an Active Millimeter Wave Imaging System based on Compressive Sensing

The development of passive and active millimeter wave imaging systems is progressing rapidly fueled by the need for many applications in the area of security and defense. Imaging schemes that may either utilize array detectors or single detectors in scan architectures offer suffer from poor resolution due to the longer wavelengths used and the limits of the optical system in terms of lens and mirror dimensions. In order to overcome this limit, super-resolution techniques can be employed to enhance the resolution of the imaging system. Here, a form of this technique based on oversampling is applied to reconstruct the image of a target which is acquired using compressive sensing based on scanning the image plane using randomly patterned masks with fixed pixel sizes. The mm-wave stand-off imaging system uses a 93 GHz center frequency source and heterodyne sub-harmonic receiver place in a bi-static configuration to image a target in reflection mode. The image of the target is projected onto a mechanically scanned spatial light modulator (SLM), which is a patterned two-dimensional mask that is translated along one axis. In order to improve the resolution of the image, the masks are shifted by half the pixel size (2.5mm). To enhance the resolution of the image, the patterns are shifted by smaller steps, thereby each pixel is oversampled and the resulting new pattern and detected intensity is fed into the CS algorithm to reconstruct the image of the target. After the image reconstruction process, sharper edges are observed for a circular object of 12mm diameter compared to the image acquired by whole pixel step scanning

Enhancing the image resolution in a single-pixel sub-THz imaging system based on compressed sensing

Compressed sensing (CS) techniques allow for faster imaging when combined with scan architectures, which typically suffer from speed. This technique when implemented with a subterahertz (sub-THz) single detector scan imaging system provides images whose resolution is only limited by the pixel size of the pattern used to scan the image plane. To overcome this limitation, the image of the target can be oversampled; however, this results in slower imaging rates especially if this is done in two-dimensional across the image plane. We show that by implementing a one-dimensional (1 -D) scan of the image plane, a modified approach to CS theory applied with an appropriate reconstruction algorithm allows for successful reconstruction of the reflected oversampled image of a target placed in standoff configuration from the source. The experiments are done in reflection mode configuration where the operating frequency is 93 GHz and the corresponding wavelength is lambda = 3.2 mm. To reconstruct the image with fewer samples, CS theory is applied using masks where the pixel size is 5 mm x 5 mm, and each mask covers an image area of 5 cm x 5 cm, meaning that the basic image is resolved as 10 x 10 pixels. To enhance the resolution, the information between two consecutive pixels is used, and over-sampling along 1-D coupled with a modification of the masks in CS theory allowed for oversampled images to be reconstructed rapidly in 20 x 20 and 40 x 40 pixel formats. These are then compared using two different reconstruction algorithms, TVAL3 and l(1)-MAGIC. The performance of these methods is compared for both simulated signals and real signals. It is found that the modified CS theory approach coupled with the TVAL3 reconstruction process, even when scanning along only 1-D, allows for rapid precise reconstruction of the oversampled target. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE