Using novel fluorescent polymers as sensory materials forabove-ground sensing of chemical signature compounds emanating fromburied landmines

Chemical vapors originating from the explosive charge within landmines and unexploded ordnance (UXO) form a chemical “signature” unique to these devices. The fact that canines can detect this signature was a primary motivation for the Defense Advanced Research Projects Agency's (DARPA) Dog's Nose Program. One goal of this program was to develop electronic chemical sensors that mimic the canine's ability to detect landmines. The sensor described here, developed under this program, utilizes novel fluorescent polymers to detect landmine signature vapors in air at ultratrace concentration levels (parts-per-trillion or less). Thin films of the polymers are highly emissive but undergo a dramatic reduction in emission intensity when molecules of target analytes bind to the polymer. Binding of a single explosive molecule can quench the fluorescence from hundreds of polymer repeat units, resulting in an amplification of the quenching response. The polymer structure contains receptor sites designed to interact specifically with nitroaromatic explosives, enhancing the selectivity of the polymers for target analytes. A man-portable sensor prototype, similar in size and configuration to metal detectors currently used for mine detection, has demonstrated performance comparable to that of canines during field tests monitored by DARPA at Fort Leonard Wood, MO     

Dual frequency scintillation measurement for remote sensing

A scheme is proposed for utilising measurements of radiowave amplitude scintillation at two frequencies for remote sensing of wind speed and atmospheric turbulence parameters. The main advantage of the method is that all quantities are estimated solely from measured scintillation parameters without the need for secondary measurements. It is shown that the method yields results which compare well with other measurements     

A C-band scatterometer for remote sensing the air-sea interface

An airborne C-band scatterometer system (C-Scat) has been developed to remotely sense ocean surface winds and improve upon the present understanding of the relationship between normalized radar cross section (NRCS) and ocean surface roughness influences such as wind speed and direction, wave height and slope, and the air-sea temperature difference. The scatterometer utilizes a unique frequency-steered microstrip array antenna that is installed beneath the fuselage of an airplane. The antenna is electronically scanned in elevation, from 20° to 50° off-nadir, and mechanically spins in azimuth. The system is capable of measuring ocean surface NRCS from altitudes as high as 25000 ft. The system is divided into four subsystems: the transmitter and receiver, the spinning antenna, the computer control and data acquisition subsystem, and the digital and analog interface electronics     

Current conveyor-based differential capacitance analog interface for displacement sensing application

A current conveyor-based analog electronic interface for differential capacitive sensors is here shown. The read-out circuit that utilizes second generation Current Conveyors (CCIIs) as active blocks is able to evaluate differential capacitive variations performing a capacitance-to-voltage conversion. This solution has been implemented both in a discrete element board and as integrated version in a standard 350  nm CMOS technology. Simulations and experimental results have shown a linear input/output characteristic and a good agreement with theoretical expectations, being the former performed for both the designed solutions, whereas the latter only for a discrete prototype board (employing a low cost commercial component (AD844). Sensitivity and resolution data on a practical case-study of a displacement sensor are constant and their values are satisfactory. Both simulated and measured results make the proposed architecture a good candidate as first stage of analog front-ends to be employed in differential capacitive instrumentation.     

A novel relay-aided centralized cooperative spectrum sensing scheme using radio frequency energy harvesting

In a cooperative spectrum sensing (CSS) network, the primary signal can be used as a radio frequency (RF) source in order to power the energy-constrained sensor nodes of the secondary network. This work presents a novel hybrid model combining an optimal relay selection scheme to incorporate RF energy harvesting in a centralized CSS network. The secondary users, which are equipped with RF energy harvesting capabilities, act as relays in order to forward the sensing information to a fusion center. Here, we have derived an enhanced multi-relay selection strategy to maximize the end-to-end signal-to-noise ratio of the links. Furthermore, a new voting rule is proposed based on the generalized K-out-of-M rule, such that it minimizes our objective error function. The performance analysis of our proposed model is presented with respect to the flexible relay positions. We have used complementary receiver operating characteristic curves for analyzing the detection performance of the CSS model with our derived voting rule. Simulation results using MATLAB show that the proposed model gives a better detection probability and a smaller error rate than some related existing works.     

Microfluidic integration of porous photonic crystal nanolasers for chemical sensing

We have recently developed planar photonic crystal nanolasers based on porous cavity designs. High-quality factor cavities confine light within the pores of the photonic crystal and, thus, our lasers are ideally suited for the investigation of nanoscale interactions between light and matter. We have demonstrated the operation of photonic crystal lasers within different chemical solutions, embedded them into silicone microfluidic flow channels, and were able to detect refractive index changes as small as /spl Delta/n=0.005. We predict that our porous nanolasers can detect refractive index changes as small as /spl Delta/n=8.23/spl middot/10/sup -4/.     

Target signature using nonsinusoidal radar signals

A target recognition method that utilizes both target length determined from target signature duration for target classification and target shape determined from target signature amplitude variation for target identification is presented. The transformation of the target axes coordinate system into a rotated coordinate system enables target recognition at any aspect angle. The information obtained about target shape and size, in addition to the velocity information supplied by the Doppler effect, can be used to generalize Woodward's ambiguity function to a range-velocity-shape resolution function. Thumbtack range-velocity-shape resolution functions are easily obtained by increasing the number of pulses in the transmitted radar signal     

Research of compressed sensing for predistortion with relatively low sampling frequency

In order to improve the TWTA digital predistortion linearizer with relatively low sampling frequency, the LUT and indirect learning architecture were used, which was cumbersome. A digital predistortion linearizer with compressed sensing technology was presented, which can provide good linearity improvement with simple and stable way.     

A noninvasive technique for detecting hypernasal speech using anonlinear operator

Speakers with a defective velopharyngeal mechanism produce speech with inappropriate nasal resonance (hypernasal speech). It is of clinical interest to detect hypernasality as it is indicative of an anatomical, neurological or peripheral nervous system problem. There are various clinical techniques used to determine hypernasality. The current techniques are physically invasive or intrusive to some extent. A preferred approach for detecting hypernasality, would be noninvasive to maximize patient comfort and naturalness of speaking. In this study, a noninvasive technique based on the Teager Energy operator is proposed. Utilizing a property of the Teager Energy operator and a model for normal and nasalized speech, a significant difference between the Teager Energy profile for lowpass and bandpass filtered nasalized speech is shown. This difference is shown to be nonexistent for normal speech. A classification algorithm is formulated that detects the presence of hypernasality using a measure of the difference in the Teager Energy profiles. The classification algorithm was evaluated using a native English speaker population producing front (/i/) and mid (/A/) vowels. Results show that the presence of hypernasality in speech can be reliably detected using the proposed classification algorithm     

Digital signature for Diffie-Hellman public keys without using aone-way function

The author proposes digital signature schemes without using a one-way function to sign Diffie-Hellman public keys. The advantage of this approach is, instead of relying overall security on either the security of the signature scheme or the security of the one-way function, the security of this proposed scheme is based on the discrete logarithm problem     

Joint spectrum sensing and resource allocation optimization using genetic algorithm for frequency hopping–based cognitive radio networks

In cognitive radio (CR) networks, secondary users should effectively use unused licensed spectrums, unless they cause any harmful interference to the primary users. Therefore, spectrum sensing and channel resource allocation are the 2 main functionalities of CR networks, which play important roles in the performance of a CR system. To maximize the CR system utility, we propose a joint out‐of‐band spectrum sensing and operating channel allocation scheme based on genetic algorithm for frequency hopping–based CR networks. In this paper, to effectively sense the primary signal on hopping channels at each hopping slot time, a set of member nodes sense the next hopping channel, which is called out‐of‐band sensing. To achieve collision‐free cooperative sensing reporting, the next channel detection notification mechanism is presented. Using genetic algorithm, the optimum sensing and data transmission schedules are derived. It selects a sensing node set that participate the spectrum sensing for the next expected hopping channel during the current channel hopping time and another set of nodes that take opportunity for transmitting data on the current hopping channel. The optimum channel allocation is performed in accordance with each node's individual traffic demand. Simulation results show that the proposed scheme can achieve reliable spectrum sensing and efficient channel allocation.     

Fast chemical sensing with metal-insulator silicon carbidestructures

It is demonstrated that the current-voltage characteristics of platinum-thin insulator silicon carbide diodes react rapidly to changes of the concentration of oxygen and hydrocarbons in the ambient already at temperatures around 500°C-600°C. In this letter, we use moving gas outlets to, for the first time, estimate time constants of the response in the order of a few milliseconds. The short time constants of these sensors make them suitable for applications in combustion monitoring. The new method to modulate gas concentrations rapidly at surfaces has the potential to be a valuable tool for evaluation of device structures for fast chemical sensing     

随机混沌感知矩阵及其在成像雷达中的应用

根据压缩感知理论提出了一种适用于成像雷达的新算法,在成像目标分布满足稀疏性前提下,利用发射的随机混沌序列( SCS )形成卷积矩阵,然后通过随机行抽取构造随机感知矩阵( SC-SM)。给出了完整的算法实现框架,从理论上证明了SCS的随机性和统计独立性以及SCSM的有限等距性( Restricted Isometry Property,RIP)。仿真结果验证了算法的有效性,同时分析了影响算法性能的主要因素。与匹配滤波法相比,所提算法重构误差小,输出旁瓣低。 SCSM与其他随机矩阵具有相同的性能,然而,SCSM容易在硬件上实现,且更适用于要求保密性高和抗干扰能力强的场合。     

一种可用于化学传感的对角对称光子晶体光纤设计

本文提出了一种可用于化学传感的具有高双折射、低损耗的光子晶体光纤,并系统地分析了空气孔参数对光纤光学特性的影响.研究表明,最优结构的光纤在典型波长1.55μm时对水、乙醇和苯的相对灵敏度分别可达56.3％、59.9％和62.5％,相比现有光子晶体光纤分别提高1.05～6.25倍、1.05～4.99倍和1.03～4.63...     

红外化学遥感数字信号处理算法的研究进展

介绍了几种为远距离红外蒸汽信号监测开发的分类器设计，频域数字滤波，时域数字滤波等数字信号处理技术。对线性分类器，分段线性分类器和神经网络分类器等在红外化学遥感系统中的应用做了初步的探讨。对背景扣除技术，频域数字滤波技术，数字滤波的切趾方法等做了简要的描述。阐述了时域滤波技术的基本原理及实际应用。展望了红外化学遥感数字信号处理算法的研究前景。     

Feedback-testing by using multiple input signature registers

In this article, the use of Multiple Input Signature Registers (MISRs) as random pattern generators is investigated. This additional function helps to reduce hardware overhead and testing time, when BIST (Built-In Self-Test) structures are integrated on the chip, because the MISR can at the same time generate test patterns and collect test responses. A formula is presented, which determines the number of clock cycles needed to generate a given number of random patterns. Finally we suggest a method for how the number of test patterns can be reduced when the MISR acts as test pattern generator and compressor in a feedback loop.     

Multilayered coated infra-red surface plasmon resonance fibre sensors for aqueous chemical sensing

A series of surface plasmonic fibre devices were fabricated by depositing multiple thin coatings on a lapped section of a standard single mode telecoms fibre forming a D-shaped section and then inscribing a grating-type structure using UV light. The coatings consisted of base coatings of semi-conductor (germanium) and dielectric (silicon dioxide) materials, followed by different metals. These fibre devices showed high spectral refractive index sensitivity with high coupling efficiency in excess of 40 dB for indices in the aqueous regime and below, with estimated index sensitivities of Δλ/Δn = 90–800 nm from 1 to 1.15 index range and Δλ/Δn = 1200–4000 nm for refractive indices from 1.33 to 1.39.     

Temperature and frequency characterization of InAs nanowire and HfO2 interface using capacitance-voltage method

InAs/HfO₂ nanowire capacitors using capacitance-voltage (CV) measurements are investigated in the range of 10 kHz to 10 MHz. The capacitors are based on vertical nanowire arrays that are coated with an 8 nm-thick HfO₂ layer by atomic layer deposition. CV characteristics are measured at temperatures in the range between −140 and 40 °C and the CV characteristics for nanowires with different Sn and Se n-type doping levels are compared. The comparison of the data at various doping levels points towards large number of traps for highly doped samples, caused by the preferential dopant precursor incorporation at the nanowire surface. We also evaluate the frequency dispersion of the accumulation capacitance and determine values below 2% with weak temperature dependence, indicating the existence of border traps in these nanowire capacitors.     

A CMOS-integrated `ISFET-operational amplifier' chemical sensoremploying differential sensing

The ISFET (ion-sensitive field-effect transistor) pH sensor is first matched with a MOSFET at the differential input stage of a CMOS operational amplifier (called the ISFET-operational amplifier) to cancel out the temperature sensitivity. Then, the output of an ISFET-operational amplifier with a Ta₂O₅/SiO₂ gate (58-59 mV/pH) ISFET is differentially amplified against the output of another on-chip ISFET-operational amplifier with a SiO_x N_y/Si₃N₄/SiO₂ gate ISFET (18-20-mV/pH). An on-chip noble metal counterelectrode serves as the electrical contact to define the electric potential of the electrolyte. No external reference electrode is required. The difference measurement technique achieves (1) common-mode rejection of the solution potential, and (2) relaxation of the requirement that the on-chip reference electrode be ideal. The CMOS-compatible ISFET process is modified from a standard self-aligned polysilicon gate CMOS process with minimal process redesign. The standard CMOS sequence is unaltered until the contact windows are opened. The complete sensor has 40-43-mV/pH pH sensitivity and demonstrates common-mode rejection to ambient light and noise from the electrolyte