International Journal of High Speed Electronics and Systems

Drinking water systems are vulnerable to attack. While homeland security initiatives commonly focus on aerial CW/BW attacks, they have tended to ignore the far more inexpensive and easy to orchestrate attacks on drinking water distribution networks. An approach that utilizes off-the-shelf broad-spectrum analytical instruments coupled with advanced interpretive algorithms to provide detection-response networks for water is described. This report summarizes the development of interpretive algorithms applied to drinking water instrumentation and the implications for immediately engineering and deploying distribution based detection-protection systems. Data obtained from in house testing along with testing at ECBC was used to produce fingerprint response data from traditional as well as non-military threat agents. Data obtained from a Battelle/EPA ETV study addresses issues such as long-term deployment and ability to detect and characterize contaminants. Loop testing at ECBC and Battelle demonstrates extrapolation of beaker testing fingerprints to flowing systems. Real world deployment data is used to demonstrate recognition and classification of actual events and heuristic capabilities of the system along with its potential role in enhancing water quality above and beyond its obvious security aspects. The system is shown to be a practical measure to detect and characterize backflow events involving both chemicals and bioagents.

The increasing value of safe, purified water in today's global environment presents many challenges for improving water purification processes while accelerating water quality monitoring technologies. These challenges include: escalating worldwide security threats, increasing demands by consumers and regulatory agencies for higher water quality standards, and proliferation of contamination events.

A major concern in protecting water purity is the detection and control of harmful microorganisms in water sources, treatment, and distribution. Due to the length of time for standard laboratory methods to yield results, typically 24-72 hours, current analytical techniques have not been able to reliably detect microorganisms in real time and provide an immediate warning of biological contamination.

Through years of research and development, an emerging technology called MALS (multi-angle light scattering) can now achieve on line, real time detection and classification of microorganisms in water. The method utilizes a laser beam focused into a slip-stream of water and the light scattered by microorganisms generates unique patterns. These “bio-optical signatures” are instantaneously captured by photodetectors, matched against catalogue profiles in an on-board data base, and subsequently classified within minutes of detection. The system can then immediately alert personnel to the contamination event while extracting a water sample for further confirmation.

Chip-size wavelength detectors are described that can resolve the spectrum of the incident light with high accuracy over a broad spectral range. The devices can be configured either as compact spectrometers or precise wavelength shift detectors. Applications that are anticipated to benefit from the spectrometers include reagentless optical identification of analytes in fluidic and aerosol samples. The wavelength shift detector is widely applicable as read-out instrument for optical sensors in which a stimulus (e.g., temperature, strain, PH-value, etc.) results in a wavelength shift of an optical output signal, examples include the interrogation system for Fiber Bragg Grating sensors, photonic crystal sensors, Fabry-Perot type sensors, and sensors in which an analyte influences a laser cavity and thereby its emission wavelength.

Laser-induced native fluorescence is measured on a set of bio-molecules from different classes (bacteria, proteins, fungi) for excitation at 266nm and 355nm. A method of preprocessing the spectra to obtain an inherently normalized set of data is described. Class identification on the normalized data set is demonstrated.

The Chesapeake Bay is a valued ecological, economic, recreational, cultural and scenic resource. The Bay watershed States and the District of Columbia, in conjunction with the EPA Chesapeake Bay Program, have worked and teamed together over the past 20 years to protect and restore the Bay ecosystem. A key component of this effort is water quality and habitat monitoring to assess the impact of management actions and natural processes, and evaluate habitat parameters on living resources such as submerged aquatic vegetation (SAV), oysters, and fisheries. Using aerial and satellite remote sensing imagery has become a practical and effective means of monitoring water quality in a timely manner. Of particular interest in evaluation of water clarity are several initiative measures. Specifically, Secchi-Disk Transparency (SDT) and Chlorophyll a (Chl-a) have been widely accepted as critical indicators of water quality and their reliable estimation using satellite imagery provides a cost effective and speedy means for water quality monitoring. Work done at Water Resources Center, University of Minnesota has demonstrated the feasibility of performing regional assessment of lake water quality using LANDSAT image data. This paper investigates an approach similar to their work but uses a different type of satellite imagery, EO-1 ALI imagery where the SDT and Chl-a are also used as indicators to estimate water quality for the Chesapeake Bay and DC area (Potomac River). In doing so, three major issues are investigated, which are (1) the study site that is an open Bay area, not a self-contained lake; (2) investigation of applicability of equations that are used to specify the SDT and Chl-a to our Bay area study; (3) the use of a different type of satellite imagery for water quality monitoring. This paper develops techniques to address these three issues and presents preliminary experiments which show encouraging results.

We have conducted studies of deep UV laser-induced fluorescence (LIF) for the reagentless detection of trace species and Dissolved Organic Compounds (DOC's) in water. Our LIF detection system had two interchangeable UV lasers, 266 nm and 355 nm, illuminating a flow cell containing a water sample. The fluorescence emitted at 90 degrees to the laser beam was collected by focusing optics, passed through cut-off and interference filters with 21 optical bandpass channels (240–680 nm), and detected by a photomultiplier tube (PMT). The samples analyzed by the system included bottled, tap and river water; we have also worked with biological and chemical species (Bacillus Globigii, malathion). In terms of the excitation wavelength, it was observed that the deep UV excitation resulted in spectra that contained more features, and had better separation of the LIF from the Raman peak, thus enhancing the detection of unique spectral features.

A detection approach based on the principles of Fourier Transform Infrared Spectroscopy (FTIR) is presented for the trace level detection of toxic compounds in water. The main advantages of this approach are that it operates in heterogeneous aqueous environments, provides fast detection (< 10 min), and exhibits high sensitivity/selectivity to nonvolatile toxic materials with minimal false alarms. The key enablers to using FTIR for aqueous-based detection is the development of a selective and robust sampling protocol coupled to a miniaturized portable FTIR unit. The sampling approaches involve synthesizing and tailoring microporous, mesoporous, and nonporous metal oxide powders/films that are amenable for in situ FTIR measurements. In this paper we provide an overview of the material synthesis and surface modification strategies, and present results obtained using these materials for the low level detection of the organophosphate pesticide phosmet. Phosmet is used as a surrogate for the nerve agent VX.

Many of the functionally relevant collective vibrations of proteins and other biopolymers are expected to occur at terahertz frequencies. Precise absorption measurements combined with careful titration of biopolymers in water have allowed us to directly measure the terahertz absorption spectra associated with these motions, despite the strong background absorption of the solvent. We have also explored the circular dichroism spectroscopy of biomolecules over this same frequency range. Since circular dichroism requires the presence of net chirality in a molecule and chirality is present in nearly all biomaterial, it has the potential to capture the background free spectral features in biopolymers. To undertake these studies we have developed a broad band terahertz spectrometer suitable for both direct absorption and circular dichroism measurements of proteins in water between 0.75 – 3.72 THz. Direct terahertz absorption spectra of prototypical proteins bovine serum albumin (BSA) and hen egg white lysozyme have been documented and are described here. We have also successfully demonstrated the magnetic circular dichroism in semiconductors, and placed an upper bound on the terahertz circular dichroism signature of solvated BSA. In the terahertz frequency range, it appears that circular dichroism signatures are exceedingly small and detection remains a challenge.

Protection of military personnel and civilians from water supplies poisoned by chemical warfare agents (CWAs) requires an analyzer that has sufficient sensitivity (μg/L, ppb), specificity (differentiate the CWA from its hydrolysis products), and speed (less than 10 minutes) to be of value. In an effort to meet these requirements, we have been investigating the ability of surface-enhanced Raman spectroscopy (SERS) to detect cyanide and sulfur mustard in water. In our work, we have developed a novel SERS-active material that consists of a porous glass with trapped metal particles. Previously, we coated the inside walls of glass vials and measured cyanide at 1 mg/L in water in as little as 1 minute. However, measurements of sulfur mustard have only been measured to 10 mg/L. Recently, we filled glass capillaries with the SERS-active material. Here we describe measurements of cyanide, sulfur mustard, and it's hydrolysis product, thiodiglycol, using these capillaries and a portable Raman analyzer suitable for point and continuous water monitoring.

Currently there exists a critical need within the military and homeland defense for highly sophisticated yet, small, lightweight portable sensors and detection systems for identifying and quantifying biological and biowarfare agents (BWA) in both liquid and aerosolized form. Our proposed BWA detection system is based upon Fourier Transform Infrared Spectroscopy (FTIR), where the main advantages of this approach are that it is reagentless, operates in heterogeneous aqueous environments, and provides fast detection and high sensitivity/selectivity to bacterial spores with minimal false alarms.

The key enabler to using FTIR for BWA detection is to develop selective and robust sampling protocols coupled to a miniaturized, portable FTIR unit. To that end, we have developed front-end liquid flow cells which incorporate electric field (E-Field) concentration methods for spores onto the surface of an Attenuated Total Reflection (ATR) IR crystal. IR spectra are presented which show collection and detection results with BG spores in water. The approaches we have developed take advantage of the fact that all spores are negatively charged in neutral pH solutions. Therefore, E-Field concentration of spores directly onto an ATR sampling element enables low level concentration measurements to be possible.

Concentration of 1-micron-size micro-organisms from about 100 ml of liquid, whether drawn from a bio-aerosol collector or from an environmental water source, into a volume of 1 to 2 ml. is achieved by a liquid flow system including a reversible filter through which filtered liquid can be recirculated or disposed of and from which a concentrated sample is recovered by opening a solenoid valve leading to a detector or to a collection container and reversing the pump for a short time. The reversing action flushes the collected particles off the filter and into the detector or container.

The effectiveness of this approach was demonstrated by measuring the cumulative fluorescence of 1-micron-size blue fluorescent microspheres versus cumulative volume withdrawn from our WEP collector after capture from an aerosol suspension of about 140 particles/ml drawn from a test chamber over a 5-minute period at a sampling rate of 500 liters/minute. As the liquid was being withdrawn from the WEP collector, it was filtered at a rate of 1 ml/second and the filter back-flushed with small portions of filtrate at 1-minute intervals. The relative cumulative concentration of captured particles in the first back-flushed 1-ml fraction was around 56 as compared with a value of 1.4 in the first 60-ml filtered fraction, which constitutes a liquid-to-liquid concentration enhancement by a factor of 40 and an air-to-liquid concentration factor of >1.25 × 10⁶.

An innovative passive standoff system for the detection of chemical/biological agents is described. The spectral, temporal and spatial resolution of the data collected are all adjustable in real time, making it possible to keep the tradeoff between the sensor operating parameters at optimum at all times. The instrument contains no macro-scale moving parts and is therefore an excellent candidate for the development of a robust, compact, lightweight and low-power-consumption sensor. The design can also serve as a basis for a wide variety of spectral instruments operating in the visible, NIR, MWIR, and LWIR to be used for surveillance, process control, and biomedical applications.

An In_1−xGa_xAs/GaSb_yAs_1−y hetero-system with staggered band-lineups as solid-state platform for design of an interband resonant double-barrier tunneling diode (I-RTD) based optically-pulsed (OT) hybrid device for generating THz oscillations is theoretically investigated. It is demonstrated that this optical I-RTD hybrid is compatible with the robust state-of-art 1.55 micron laser technology Multi-band wave equations in the framework of six-band Kane's model are applied for understanding the carrier dynamics when strain-induced effects are present. Simulation results for practical circuit implementations clearly show the superiority of this new oscillator concept.

A high mobility two-dimensional electron system exhibits large changes in the resistance, and zero-resistance states, under microwave and Terahertz excitation. We describe associated experimental results and the possibility of using this system as a radiation detector.

In this paper we explore the design of microwave-based structures that can enhance the interaction of electromagnetic fields with cold-atom ensembles, leading to novel sensing modalities based on the quantum-mechanical behavior of these systems. In particular, we discuss electromagnetically-induced transparency in a single uncondensed cold-atom cloud, and a two-cloud version of a SQUID, where the clouds are BEC's and take the place of the weakly coupled superconductors. These systems are both promising candidates for use in the high-precision detection of chemical contaminants.

Detection of gaseous effluent plumes from airborne platforms provides a unique challenge to the remote sensing community. The measured signatures are a complicated combination of phenomenology including effects of the atmosphere, spectral characteristics of the background material under the plume, temperature contrast between the gas and the surface, and the concentration of the gas. All of these quantities vary spatially further complicating the detection problem. In complex scenes simple estimation of a “residual” spectrum may not be possible due to the variability in the scene background. A common detection scheme uses a matched filter formalism to compare laboratory-measured gas absorption spectra with measured pixel radiances. This methodology can not account for the variable signature strengths due to concentration path length and temperature contrast, nor does it take into account measured signatures that are observed in both absorption and emission in the same scene. We have developed a physics-based, forward model to predict in-scene signatures covering a wide range in gas / surface properties. This target space is reduced to a set of basis vectors using a geometrical model of the space. Corresponding background basis vectors are derived to describe the non-plume pixels in the image. A Generalized Likelihood Ratio Test is then used to discriminate between plume and non-plume pixels. Several species can be tested for iteratively. The algorithm is applied to airborne LWIR hyperspectral imagery collected by the Airborne Hyperspectral Imager (AHI) over a chemical facility with some ground truth. When compared to results from a clutter matched filter the physics-based signature approach shows significantly improved performance for the data set considered here.

In this paper, we compare several detection algorithms that are based on spectral matched (subspace) filters. Nonlinear (kernel) versions of these spectral matched (subspace) detectors are also discussed and their performance is compared with the linear versions. These kernel-based detectors exploit the nonlinear correlations between the spectral bands that are ignored by the conventional detectors. Several well-known matched detectors, such as matched subspace detector, orthogonal subspace detector, spectral matched filter and adaptive subspace detector (adaptive cosine estimator) are extended to their corresponding kernel versions by using the idea of kernel-based learning theory. In kernel-based detection algorithms the data is implicitly mapped into a high dimensional kernel feature space by a nonlinear mapping which is associated with a kernel function. The detection algorithm is then derived in the feature space which is kernelized in terms of the kernel functions in order to avoid explicit computation in the high dimensional feature space. Experimental results based on simulated toy-examples and real hyperspectral imagery shows that the kernel versions of these detectors outperform the conventional linear detectors.

This paper focuses on the measurement of spectroscopic signatures of Chemical Warfare Agent Simulants (CWAS), degradation products of chemical agents and Toxic Industrial Compounds (TIC) using vibrational spectroscopy. Raman Microscopy, Fourier Transform Infrared Spectroscopy in liquid and gas phase and Fiber Optics Coupled-Grazing Angle Probe-FTIR were used to characterize the spectroscopic information of target threat agents. Ab initio chemical calculations of energy minimization and FTIR spectra of Chemical Warfare Agents were accompanied by Cluster Analysis to correlate spectral information of real agents and simulants.

We have developed a number of programmable hyperspectral imagers operating from the ultraviolet to the longwave infrared using an acousto-optic tunable filter (AOTF) in conjunction with a suitable camera. Each of these AOTFs is fabricated with a single transducer to operate over only one octave in wavelength. Recently, we have developed two separate tellurium dioxide (TeO₂) noncollinear AOTF cells that operate over two octave range. Each cell has an aperture of 1.5 × 1.5 cm² with a field-of-view of 4.2°, and two thin-plate lithium niobate transducers are bonded on it. The tuning range of the first cell is 0.43–2.1 μm, and 0.69–4.0 μm for the second cell. We have used each of these cells to carry out spectral imaging experiments with CCD, InGaAs, and InSb cameras to cover the spectral region from the visible to the midwave infrared. We image the two orthogonally polarized diffracted beams to get spectropolarimetric information from the scene, as well as a broadband image by using one of the undiffracted beams. In this paper, we discuss the two AOTF cells, the imaging experiments, and present the results obtained.

In this paper, recent progress made in the development of quartz and KDP crystal based acousto-optic tunable filters (AOTF) are presented. These AOTFs are developed for operation over deep-UV to near-UV wavelengths of 190 nm to 400 nm. Preliminary output performance measurements of quartz AOTF and design specifications of KDP AOTF are presented. At 355 nm, the quartz AOTF device offered ∼15% diffraction efficiency with a passband full-width-half-maximum (FWHM) of less than 0.0625 nm. Further characterization of quartz AOTF devices at deep-UV wavelengths is progressing. The hermetic packaging of KDP AOTF is nearing completion. The solid-state optical sources being used for excitation include nonlinear optics based high-energy tunable UV transmitters that operate around 320 nm and 308 nm wavelengths, and a tunable deep-UV laser operating over 193 nm to 210 nm. These AOTF devices have been developed as turn-key devices for primarily for space-based chemical and biological sensing applications using laser induced Fluorescence and resonance Raman techniques.

This paper describes a remotely operable miniature spectrometer for the detection of Toxic Industrial Chemicals (TIC) using Near Infra-Red (NIR) spectroscopy. The spectrometer discussed here is compact, rugged and capable of operating on either as a handheld unit or on robotic platforms. The packaged unit consists of two modules: an optical head unit and an electronics unit. The optical head contains an infra-red light source, an Acousto-Optical Tunable Filter (AOTF) spectrometer, and associated electronics. The other module is contains the associated electronics assembly and cables connecting it with the optical head. This unit has fiber optic and free space detection capabilities and can be operated using 24 V battery power packs. We have developed a method to detect unknown chemical threat using measured signatures of known chemicals and chemometric techniques. At this time the system can detect chemicals in solid and liquid forms. We are currently optimizing the system for detection of chemicals in gaseous/vapor forms.

Two terminal devices have traditionally provided band-structure based high frequency operation. Third terminal control often involves hybrid design approaches. The presence of diluted magnetic semiconductor layers in device fabrication should permit the magnetic field to function as a pseudothird terminal. This is discussed for single barrier, double barrier and superlattice structures, where control is demonstrated. The limits of high frequency operation are discussed in general terms with application to barrier devices and superlattices containing DMS layers.