728 research outputs found

    Penetrating 3-D Imaging at 4- and 25-m Range Using a Submillimeter-Wave Radar

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    We show experimentally that a high-resolution imaging radar operating at 576–605 GHz is capable of detecting weapons concealed by clothing at standoff ranges of 4–25 m. We also demonstrate the critical advantage of 3-D image reconstruction for visualizing hidden objects using active-illumination coherent terahertz imaging. The present system can image a torso with <1 cm resolution at 4 m standoff in about five minutes. Greater standoff distances and much higher frame rates should be achievable by capitalizing on the bandwidth, output power, and compactness of solid state Schottky-diode based terahertz mixers and multiplied sources

    3D Holographic Millimeter-Wave Imaging for Concealed Metallic Forging Objects Detection

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    This chapter investigates the feasibility of using 3D holographic millimeter-wave (HMMW) imaging for diagnosis of concealed metallic forging objects (MFOs) in inhomogeneous medium. A 3D numerical system, including radio frequency (RF) transmitters and detectors, various realistic MFOs models and signal and imaging processing, is developed to analyze the measured data and reconstruct images of target MFOs. Simulation and experimental validations are performed to evaluate the HMMW approach for diagnosis of concealed MFOs. Results show that various concealed objects can be clearly represented in the reconstructed images with accurate sizes, locations and shapes. The proposed system has the potential for further investigation of concealed MFOs under clothing in the future, which has the potential applications in on body concealed weapon detection at security sites or MFOs detection in children

    Millimetre wave imaging for concealed target detection

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    PhDConcealed weapon detection (CWD) has been a hot topic as the concern about pub- lic safety increases. A variety of approaches for the detection of concealed objects on the human body based on earth magnetic ¯eld distortion, inductive magnetic ¯eld, acoustic and ultrasonic, electromagnetic resonance, MMW (millimetre wave), THz, Infrared, x-ray technologies have been suggested and developed. Among all of them, MMW holographic imaging is considered as a promising approach due to the relatively high penetration and high resolution that it can o®er. Typical concealed target detection methods are classi¯ed into 2 categories, the ¯rst one is a resonance based target identi¯cation technique, and the second one is an imaging based system. For the former, the complex natural resonance (CNR) frequencies associated with a certain target are extracted and used for identi¯cation, but this technique has an issue of high false alarm rate. The microwave/millimetre wave imaging systems can be categorized into two types: passive systems and active sys- tems. For the active microwave/millimetre wave imaging systems, the microwave holographic imaging approach was adopted in this thesis. Such a system can oper- ate at either a single frequency or multiple frequencies (wide band). An active, coherent, single frequency operation millimetre wave imaging system based on the theory of microwave holography was developed. Based on literature surveys and ¯rst hand experimental results, this thesis aims to provide system level parame- ter determination to aid the development of a target detection imager. The goal is approached step by step in 7 chapters, with topics and issues addressed rang- ing from reviewing the past work, ¯nding out the best candidate technology, i.e. the MMW holographic imaging combined with the resonance based target recog- i nition technique, the construction of the 94 GHz MMW holographic prototype imager, experimental trade-o® investigation of system parameters, imager per- formance evaluation, low pro¯le components and image enhancement techniques, feasibility investigation of resonance based technique, to system implementation based on the parameters and results achieved. The task set forth in the beginning is completed by coming up with an entire system design in the end.

    Concealed Object Detection for Passive Millimeter-Wave Security Imaging Based on Task-Aligned Detection Transformer

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    Passive millimeter-wave (PMMW) is a significant potential technique for human security screening. Several popular object detection networks have been used for PMMW images. However, restricted by the low resolution and high noise of PMMW images, PMMW hidden object detection based on deep learning usually suffers from low accuracy and low classification confidence. To tackle the above problems, this paper proposes a Task-Aligned Detection Transformer network, named PMMW-DETR. In the first stage, a Denoising Coarse-to-Fine Transformer (DCFT) backbone is designed to extract long- and short-range features in the different scales. In the second stage, we propose the Query Selection module to introduce learned spatial features into the network as prior knowledge, which enhances the semantic perception capability of the network. In the third stage, aiming to improve the classification performance, we perform a Task-Aligned Dual-Head block to decouple the classification and regression tasks. Based on our self-developed PMMW security screening dataset, experimental results including comparison with State-Of-The-Art (SOTA) methods and ablation study demonstrate that the PMMW-DETR obtains higher accuracy and classification confidence than previous works, and exhibits robustness to the PMMW images of low quality

    94 GHz Radiometer for Benchmarking its Operational Parameters for the Remote Detecton of Concealed Threat

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    Standoff detection of concealed threat, using millimeter wave radiometer, is being experimented worldwide for enhancing the frame rate and detection probability, as an alternative to personnel frisking, for enhancing passenger service rate and avoiding exposure to harmful radiations. The development of 94 GHz Dicke radiometer and experimentation to bench mark its operational parameters like spatial sampling rate, scan rate and dwell time for the detection of concealed threat, under the fabrics of a human is described. The experimentation provided operational methodology and imaging phenomenology in a given background for the detection of metallic threats. The experimental results have established that radiometer can be considered as an alternate to frisking of personnel and celebrities at public places for security reasons

    Submillimetre wave 3D imaging radar for security applications

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    There is ongoing worldwide interest in finding solutions to enhance the security of civilians at airports, borders and high risk public areas in ways which are safe, ethical and streamlined. One promising approach is to use submillimetre wave 3D imaging radar to detect concealed threats as it offers the advantages of high volumetric resolution (~1 cm3) with practically sized antennas (<0.5 m) such that even quite small objects can be resolved through clothing. The Millimetre Wave Group at the University of St Andrews has been developing submillimetre wave 3D imaging radars for security applications since 2007. A significant goal is to achieve near real-time frame rates of at least 10 Hz, to cope with dynamic scenes, over wide fields of view at short range with high pixel counts. We review the radar systems we have developed at 340 and 220 GHz and the underpinning technologies which we have employed to realise these goals.PostprintNon peer reviewe

    Millimeter-Wave Imaging Sensor

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    Computational polarimetric microwave imaging

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    We propose a polarimetric microwave imaging technique that exploits recent advances in computational imaging. We utilize a frequency-diverse cavity-backed metasurface, allowing us to demonstrate high-resolution polarimetric imaging using a single transceiver and frequency sweep over the operational microwave bandwidth. The frequency-diverse metasurface imager greatly simplifies the system architecture compared with active arrays and other conventional microwave imaging approaches. We further develop the theoretical framework for computational polarimetric imaging and validate the approach experimentally using a multi-modal leaky cavity. The scalar approximation for the interaction between the radiated waves and the target---often applied in microwave computational imaging schemes---is thus extended to retrieve the susceptibility tensors, and hence providing additional information about the targets. Computational polarimetry has relevance for existing systems in the field that extract polarimetric imagery, and particular for ground observation. A growing number of short-range microwave imaging applications can also notably benefit from computational polarimetry, particularly for imaging objects that are difficult to reconstruct when assuming scalar estimations.Comment: 17 pages, 15 figure

    Indoor Full-Body Security Screening: Radiometric Microwave Imaging Phenomenology and Polarimetric Scene Simulation

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    The paper discusses the scene simulation of radiometric imagers and its use to illustrate the phenomenology of full-body screening of people for weapons and threats concealed under clothing. The aperture synthesis technique is introduced as this offers benefits of wide field-of-views and large depths-of-fields in a system that is potentially conformally deployable in the confined spaces of building entrances and at airport departure lounges. The technique offers a non-invasive, non-cooperative screening capability to scrutinize all human body surfaces for illegal items. However, for indoor operation, the realization of this capability is challenging due to the low radiation temperature contrasts in imagery. The contrast is quantified using a polarimetric radiometric layer model of the clothed human subject concealing threats. A radiation frequency of 20 GHz was chosen for the simulation as system component costs here are relatively low and the attainable half-wavelength spatial resolution of 7.5 mm is sufficient for screening. The contrasts against the human body of the threat materials of metal, zirconia ceramic, carbon fiber, nitrogen-based energetic materials, yellow beeswax, and water were calculated to be ≤7 K. Furthermore, the model indicates how some threats frequency modulate the radiation temperatures by ~ ±1 K. These results are confirmed by experiments using a radiometer measuring left-hand circularly polarized radiation. It is also shown using scene simulation how circularly polarized radiation has benefits for reducing false alarms and how threat objects appear in canyon regions of the body, such as between the legs and in the armpits

    Investigation of resolution limits for indirect microwave holographic imaging

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    This work describes how indirect holography which has previously been applied to the determination of antenna radiation patterns can be adapted for the imaging of passive objects. It provides details of how complex scattered field values can be obtained in a simple and inexpensive manner from sampled scalar intensity measurements taken over a single scanning aperture. This work uses indirect holographic techniques to image a number of simple objects including a rectangular metallic plate, a small metal plate covered by a dielectric sheet and a small metallic circular annulus. This work demonstrates that good quality images can be reconstructed from simple scalar intensity patterns. It demonstrates that clear outlines can be obtained in particular from reconstructed phase patterns and that good images can be obtained from objects with dimensions of the order of a half wavelength
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