Patrick Lj Valdez

Active wideband 350GHz imaging system for concealed-weapon detection

A prototype active wideband 350 GHz imaging system has been developed to address the urgent need for standoff concealed-weapon detection. This system is based on a wideband, heterodyne, frequency-multiplier-based transceiver system coupled to a quasi-optical focusing system and high-speed conical scanner. This system is able to quickly scan personnel for concealed weapons. Additionally, due to the wideband operation, this system provides accurate ranging information, and the images obtained are fully three-dimensional. Waves in the microwave, millimeter-wave, and terahertz (3 GHz to 1 THz) frequency bands are able to penetrate many optical obscurants, and can be used to form the basis of high-resolution imaging systems. Waves in the sub-millimeter-wave band (300 GHz to 1 THz) are particularly interesting for standoff concealed-weapon detection at ranges of 5 - 20+ meters, due to their unique combination of high resolution and clothing penetration. The Pacific Northwest National Laboratory (PNNL) has previously developed portal screening systems that operate at the lower end of the millimeter-wave frequency range around 30 GHz. These systems are well suited for screening within portals; however, increasing the range of these systems would dramatically reduce the resolution due to diffraction at their relatively long wavelength. In this paper, the standoff 350 GHz imaging system is described in detail and numerous imaging results are presented.

Standoff concealed weapon detection using a 350-GHz radar imaging system

The sub-millimeter (sub-mm) wave frequency band from 300 - 1000 GHz is currently being developed for standoff concealed weapon detection imaging applications. This frequency band is of interest due to the unique combination of high resolution and clothing penetration. The Pacific Northwest National Laboratory (PNNL) is currently developing a 350 GHz, active, wideband, three-dimensional, radar imaging system to evaluate the feasibility of active sub-mm imaging for standoff detection. Standoff concealed weapon and explosive detection is a pressing national and international need for both civilian and military security, as it may allow screening at safer distances than portal screening techniques. PNNL has developed a prototype active wideband 350 GHz radar imaging system based on a wideband, heterodyne, frequency-multiplier-based transceiver system coupled to a quasi-optical focusing system and high-speed rotating conical scanner. This prototype system operates at ranges up to 10+ meters, and can acquire an image in 10 - 20 seconds, which is fast enough to scan cooperative personnel for concealed weapons. The wideband operation of this system provides accurate ranging information, and the images obtained are fully three-dimensional. During the past year, several improvements to the system have been designed and implemented, including increased imaging speed using improved balancing techniques, wider bandwidth, and improved image processing techniques. In this paper, the imaging system is described in detail and numerous imaging results are presented.

A Flow-Through Ultrasonic Lysis Module for the Disruption of Bacterial Spores

An automated, flow-through ultrasonic lysis module that is capable of disrupting bacterial spores to increase the DNA available for biodetection is described. The system uses a flow-through chamber that allows for direct injection of the sample without the need for a chemical or enzymatic pretreatment step to disrupt the spore coat before lysis. Lysis of Bacillus subtilis spores, a benign simulant of Bacillus anthracis, is achieved by flowing the sample through a tube whose axis is parallel to the faces of two transducers that deliver 10 W cm−2 to the surface of the tube at 1.4-MHz frequency. Increases in amplifiable DNA were assessed by real-time PCR analysis that showed at least a 25-fold increase in amplifiable DNA after ultrasonic treatment with glass beads, compared with controls with no ultrasonic power applied. The ultrasonic system and integrated fluidics are designed as a module that could be incorporated into multistep, automated sample treatment and detection systems for pathogens.

Fully polarimetric differential intensity W-band imager

We present a novel architecture based upon a Dicke-switched heterodyne radiometer architecture employing two identical input sections consisting of horn and orthomode transducer to detect the difference between the horizontal (H) and vertical (V) polarization states of two separate object patches imaged by the radiometer. We have constructed and described previously a fully polarimetric W-band passive millimeter wave imager constructed to study the phenomenology of anomaly detection using polarimetric image exploitation of the Stokes images. The heterodyne radiometer used a PIN diode switch between the input millimeter wave energy and that of a reference load in order to eliminate the effects of component drifts and to reduce the effects of 1/f noise. The differential approach differs from our previous work by comparing H and V polarization states detected by each of two input horns instead of a reference load to form signals ΔH and ΔV from adjacent paired object patches. This novel imaging approach reduces common mode noise and enhances detection of small changes between the H and V polarization states of two object patches, now given as difference terms of the fully polarimetric radiometer. We present the theory of operation, initial proof of concept experimental results, and extension of the differential radiometer to a system with a binocular fore optics that allow adjustment of the convergence or shear of the object patches as viewed by the differential polarimetric imager.

Passive fully polarimetric W-band millimeter-wave imaging

We present the theory, design, and experimental results obtained from a scanning passive W-band fully polarimetric imager. Passive millimeter-wave imaging offers persistent day/nighttime imaging and the ability to penetrate dust, clouds and other obscurants, including clothing and dry soil. The single-pixel scanning imager includes both far-field and near-field fore-optics for investigation of polarization phenomena. Using both fore-optics, a variety of scenes including natural and man-made objects was imaged and these results are presented showing the utility of polarimetric imaging for anomaly detection. Analysis includes conventional Stokes-parameter based approaches as well as multivariate image analysis methods.

Progress in development of a 6LiF/ZnS-based neutron multiplicity counter

Neutron multiplicity counters are used in safeguards to provide rapid assay of samples which contain an unknown amount of plutonium in a potentially unknown configuration. Alternatives to the use of 3He for the detection of thermal neutrons are being investigated. With appropriate detector design, the neutron single, double, and triple coincidence events can be used to extract information of three unknown parameters such as the 240Pu-effective mass, the sample self-multiplication, and the (α,n) rate. A project at PNNL has investigated replacing 3He-based tubes with LiF/ZnS neutron-scintillator sheets and wavelength shifting plastic for light pipes. A demonstrator system was constructed and is being used to test potential data acquisition system options and neutron/gamma-ray discrimination algorithms for a larger-scale system. A full-scale system has been extensively modeled to better understand the impact of all the various components. The results of the current testing and modeling effort will inform the final design of a full scale system which is expected to match the performance of existing 3He-based neutron multiplicity counters. A review of the current effort and the most recent findings will be presented.

Wide-field-of-view millimeter-wave telescope design with ultra-low cross-polarization

As millimeter-wave arrays become available, off-axis imaging performance of the fore optics increases in importance due to the relatively large physical extent of the arrays. Typically, simple optical telescope designs are adapted to millimeter-wave imaging but single-mirror spherical or classic conic designs cannot deliver adequate image quality except near the optical axis. Since millimeter-wave designs are quasi-optical, optical ray tracing and commercial design software can be used to optimize designs to improve off-axis imaging as well as minimize cross-polarization. Methods that obey the Dragone-Mizuguchi condition for the design of reflective millimeter-wave telescopes with low cross-polarization also provide additional degrees of freedom that offer larger fields of view than possible with single-reflector designs. Dragones graphical design method does not lend itself readily to computer-based optical design approaches, but subsequent authors expanded on Dragones geometric design approach with analytic expressions that describe the location, shape, off-axis height and tilt of the telescope elements that satisfy Dragones design rules and can be used as a first-order design for subsequent computer-based design and optimization. We investigate two design variants that obey the Dragone-Mizuguchi conditions that exhibit ultra-low cross-polarization and a large diffraction-limited field of view well suited to millimeter-wave imaging arrays.

Phenomenology studies using a scanning fully polarimetric passive W-band millimeter-wave imager

We present experimental results obtained from a scanning passive W-band fully polarimetric imager. Passive millimeter wave imaging offers persistent day/nighttime imaging and the ability to penetrate dust, clouds and other obscurants, as well as thin layers of clothing and even dry soil. The selection of the W-band atmospheric window at 94 GHz offers a compromise as there is sufficient angular resolution for imaging applications using modestly-sized reflectors appropriate for mobile as well as fixed location applications. The imager is based upon an F/2.1 off-axis parabolic reflector that exhibits -34 dB of cross polarization suppression. The heterodyne radiometer produces a 6 GHz IF with 4 GHz of bandwidth resulting in an NEDT of < 200 mK. Polarimetric imaging reveals the presence of man-made objects due to their typically anisotropic nature and the interaction of these objects with incident millimeter wave radiation. The phenomenology studies were undertaken to determine the richest polarimetric signals to use for exploitation. In addition to a conventional approach to polarimetric image analysis in which the Stokes I, Q, U, and V images were formed and displayed, we present an alternative method for polarimetric image exploitation based upon multivariate image analysis (MIA). MIA uses principal component analysis (PCA) and 2D scatter or score plots to identify various pixel classes in the image compared with the more conventional scene-based image analysis approaches. Multivariate image decomposition provides a window into the complementary interplay between spatial and statistical correlations contained in the data.

A Novel Passive Millimeter Imager for Broad-Area Search - Final Report on Project PL09-NPMI-PD07 (PNNL-55180)

This report describes research and development efforts toward a novel passive millimeter-wave (mm-wave) electromagnetic imaging device for broad-area search. It addresses the technical challenge of detecting anomalies that occupy a small fraction of a pixel. The purpose of the imager is to pinpoint suspicious locations for cuing subsequent higher-resolution imaging. The technical basis for the approach is to exploit thermal and polarization anomalies that distinguish man-made features from natural features.