Journal of Sensors http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2014 , Hindawi Publishing Corporation . All rights reserved. Nonnegative Matrix Factorization-Based Spatial-Temporal Clustering for Multiple Sensor Data Streams Thu, 17 Jul 2014 08:44:53 +0000 http://www.hindawi.com/journals/js/2014/824904/ Cyber physical systems have grown exponentially and have been attracting a lot of attention over the last few years. To retrieve and mine the useful information from massive amounts of sensor data streams with spatial, temporal, and other multidimensional information has become an active research area. Moreover, recent research has shown that clusters of streams change with a comprehensive spatial-temporal viewpoint in real applications. In this paper, we propose a spatial-temporal clustering algorithm (STClu) based on nonnegative matrix trifactorization by utilizing time-series observational data streams and geospatial relationship for clustering multiple sensor data streams. Instead of directly clustering multiple data streams periodically, STClu incorporates the spatial relationship between two sensors in proximity and integrates the historical information into consideration. Furthermore, we develop an iterative updating optimization algorithm STClu. The effectiveness and efficiency of the algorithm STClu are both demonstrated in experiments on real and synthetic data sets. The results show that the proposed STClu algorithm outperforms existing methods for clustering sensor data streams. Di-Hua Sun and Chun-Yan Sang Copyright © 2014 Di-Hua Sun and Chun-Yan Sang. All rights reserved. Data Fusion Based on Node Trust Evaluation in Wireless Sensor Networks Thu, 17 Jul 2014 08:08:34 +0000 http://www.hindawi.com/journals/js/2014/391401/ Abnormal behavior detection and trust evaluation mode of traditional sensor node have a single function without considering all the factors, and the trust value algorithm is relatively complicated. To avoid these above disadvantages, a trust evaluation model based on the autonomous behavior of sensor node is proposed in this paper. Each sensor node has the monitoring privilege and obligation. Neighboring sensor nodes can monitor each other. Their direct and indirect trust values can be achieved by using a relatively simple calculation method, the synthesis trust value of which could be got according to the composition rule of D-S evidence theory. Firstly, the cluster head assigns different weighted value for the data from each sensor node, then the weight vector is set according to the synthesis trust value, the data fusion processing is executed, and finally the cluster head sensor node transmits the fused result to the base station. Simulation experiment results demonstrate that the trust evaluation model can rapidly, exactly, and effectively recognize malicious sensor node and avoid malicious sensor node becoming cluster head sensor node. The proposed algorithm can greatly increase the safety and accuracy of data fusion, improve communication efficiency, save energy of sensor node, suit different application fields, and deploy environments. Zhou Jianming, Liu Fan, and Lu Qiuyuan Copyright © 2014 Zhou Jianming et al. All rights reserved. Acoustic Source Localization via Subspace Based Method Using Small Aperture MEMS Arrays Wed, 16 Jul 2014 00:00:00 +0000 http://www.hindawi.com/journals/js/2014/675726/ Small aperture microphone arrays provide many advantages for portable devices and hearing aid equipment. In this paper, a subspace based localization method is proposed for acoustic source using small aperture arrays. The effects of array aperture on localization are analyzed by using array response (array manifold). Besides array aperture, the frequency of acoustic source and the variance of signal power are simulated to demonstrate how to optimize localization performance, which is carried out by introducing frequency error with the proposed method. The proposed method for 5 mm array aperture is validated by simulations and experiments with MEMS microphone arrays. Different types of acoustic sources can be localized with the highest precision of 6 degrees even in the presence of wind noise and other noises. Furthermore, the proposed method reduces the computational complexity compared with other methods. Xin Zhang, Enliang Song, JingChang Huang, Huawei Liu, YuePeng Wang, Baoqing Li, and Xiaobing Yuan Copyright © 2014 Xin Zhang et al. All rights reserved. Two-Channel Metal Detector Using Two Perpendicular Antennas Thu, 10 Jul 2014 09:54:14 +0000 http://www.hindawi.com/journals/js/2014/412621/ Two-channel metal detector, having two sets of perpendicularly oriented sensor antennas, is proposed to expand detectable size, ranging from mm through cm scale, of metal sensor, while conventional metal sensor is dedicated for detection only in mm or cm scale. The characteristics of the two metal detection sensor channels were investigated, respectively, and the interference effect, while in simultaneous operation, between two sensor channels was discussed. Metal detection channel, having sensitivity in mm scale, showed detectable sensitivity to moving ferrous sphere, with diameter down to 0.7 mm, at 50 kHz exciting frequency and enhanced sensitivity distribution. And metal detection channel having sensitivity in cm scale showed more uniform sensitivity distribution with the flexibility for future modular construction. The effect of interference, while in simultaneous operation of two sensors, resulted in reduced output response, but still within usable detection range. Thus it was feasible to operate two sensors, having different sensitivity range, simultaneously and to extend detection range from mm to cm scale, within practically acceptable interference. Kyoo Nam Choi Copyright © 2014 Kyoo Nam Choi. All rights reserved. Key Updating Methods for Combinatorial Design Based Key Management Schemes Tue, 01 Jul 2014 06:29:35 +0000 http://www.hindawi.com/journals/js/2014/134357/ Wireless sensor network (WSN) has become one of the most promising network technologies for many useful applications. However, for the lack of resources, it is different but important to ensure the security of the WSNs. Key management is a corner stone on which to build secure WSNs for it has a fundamental role in confidentiality, authentication, and so on. Combinatorial design theory has been used to generate good-designed key rings for each sensor node in WSNs. A large number of combinatorial design based key management schemes have been proposed but none of them have taken key updating into consideration. In this paper, we point out the essence of key updating for the unital design based key management scheme and propose two key updating methods; then, we conduct performance analysis on the two methods from three aspects; at last, we generalize the two methods to other combinatorial design based key management schemes and enhance the second method. Chonghuan Xu and Weinan Liu Copyright © 2014 Chonghuan Xu and Weinan Liu. All rights reserved. Rain Sensor with Stacked Light Waveguide Having Tilted Air Gap Thu, 26 Jun 2014 11:25:39 +0000 http://www.hindawi.com/journals/js/2014/543530/ Vehicle sensor to detect rain drop on and above waveguide utilizing light deflection and scattering was realized, keeping wide sensing coverage and sensitivity to detect mist accumulation. Proposed sensor structure under stacked light wave guide consisted of light blocking fixture surrounding photodetector and adjacent light source. Tilted air gap between stacked light waveguide and light blocking fixture played major role to increase sensitivity and to enhance linearity. This sensor structure eliminated complex collimating optics, while keeping wide sensing coverage using simple geometry. Detection algorithm based on time-to-intensity transformation process was used to convert raining intensity into countable raining process. Experimental result inside simulated rain chamber showed distinct different response between light rain and normal rain. Application as automobile rain sensor is expected. Kyoo Nam Choi Copyright © 2014 Kyoo Nam Choi. All rights reserved. Shortest Paths Based Web Service Selection in Internet of Things Thu, 26 Jun 2014 07:22:33 +0000 http://www.hindawi.com/journals/js/2014/958350/ The connecting of things to the Internet makes it possible for smart things to access all kinds of Web services. However, smart things are energy-limited, and suitable selection of Web services will consume less resources. In this paper, we study the problem of selecting some Web service from the candidate set. We formulate this selection of Web services for smart things as single-source many-target shortest path problem. We design algorithms based on the Dijkstra and breadth-first search algorithms, propose an efficient pruning algorithm for breadth-first search, and analyze their performance of number of iterations and cost. Our empirical evaluation on real-life graphs shows that our pruning algorithm is more efficient than the breadth-first search algorithm. Xiangdong Yin and Jie Yang Copyright © 2014 Xiangdong Yin and Jie Yang. All rights reserved. A Novel Interdigital Capacitor Pressure Sensor Based on LTCC Technology Mon, 23 Jun 2014 08:02:02 +0000 http://www.hindawi.com/journals/js/2014/431503/ A novel passive wireless pressure sensor is proposed based on LTCC (low temperature cofired ceramic) technology. The sensor employs a passive LC circuit, which is composed of a variable interdigital capacitor and a constant inductor. The inductor and capacitor were fabricated by screen-printing. Pressure measurement is tested using a wireless mutual inductance coupling method. The experimental sensitivity of the sensor is about 273.95 kHz/bar below 2 bar. Experimental results show that the sensor can be read out wirelessly by external antenna at 600°C. The max readout distance is 3 cm at room temperature. The sensors described can be applied for monitoring of gas pressure in harsh environments, such as environment with high temperature and chemical corrosion. Qiulin Tan, Mingliang Yang, Tao Luo, Wei Liu, Chao Li, Chenyang Xue, Jun Liu, Wendong Zhang, and Jijun Xiong Copyright © 2014 Qiulin Tan et al. All rights reserved. A New Key Predistribution Scheme for Multiphase Sensor Networks Using a New Deployment Model Sun, 15 Jun 2014 08:53:35 +0000 http://www.hindawi.com/journals/js/2014/573913/ During the lifecycle of sensor networks, making use of the existing key predistribution schemes using deployment knowledge for pairwise key establishment and authentication between nodes, a new challenge is elevated. Either the resilience against node capture attacks or the global connectivity will significantly decrease with time. In this paper, a new deployment model is developed for multiphase deployment sensor networks, and then a new key management scheme is further proposed. Compared with the existing schemes using deployment knowledge, our scheme has better performance in global connectivity, resilience against node capture attacks throughout their lifecycle. Boqing Zhou, Jianxin Wang, Sujun Li, and Weiping Wang Copyright © 2014 Boqing Zhou et al. All rights reserved. Harvesting Ambient Environmental Energy for Wireless Sensor Networks: A Survey Thu, 12 Jun 2014 08:27:51 +0000 http://www.hindawi.com/journals/js/2014/815467/ In recent years, wireless sensor networks (WSNs) have grown dramatically and made a great progress in many applications. But having limited life, batteries, as the power sources of wireless sensor nodes, have restricted the development and application of WSNs which often requires a very long lifespan for better performance. In order to make the WSNs prevalent in our lives, an alternative energy source is required. Environmental energy is an attractive power source, and it provides an approach to make the sensor nodes self-powered with the possibility of an almost infinite lifetime. The goal of this survey is to present a comprehensive review of the recent literature on the various possible energy harvesting technologies from ambient environment for WSNs. Gongbo Zhou, Linghua Huang, Wei Li, and Zhencai Zhu Copyright © 2014 Gongbo Zhou et al. All rights reserved. Automatic Person Identification in Camera Video by Motion Correlation Tue, 03 Jun 2014 10:21:06 +0000 http://www.hindawi.com/journals/js/2014/838751/ Person identification plays an important role in semantic analysis of video content. This paper presents a novel method to automatically label persons in video sequence captured from fixed camera. Instead of leveraging traditional face recognition approaches, we deal with the task of person identification by fusing information from motion sensor platforms, like smart phones, carried on human bodies and extracted from camera video. More specifically, a sequence of motion features extracted from camera video are compared with each of those collected from accelerometers of smart phones. When strong correlation is detected, identity information transmitted from the corresponding smart phone is used to identify the phone wearer. To test the feasibility and efficiency of the proposed method, extensive experiments are conducted which achieved impressive performance. Dingbo Duan, Guangyu Gao, Chi Harold Liu, and Jian Ma Copyright © 2014 Dingbo Duan et al. All rights reserved. Data Fusion of Electronic Nose and Electronic Tongue for Detection of Mixed Edible-Oil Mon, 26 May 2014 13:32:01 +0000 http://www.hindawi.com/journals/js/2014/840685/ For the problem of the waste of the edible-oil in the food processing, on the premise of food security, they often need to add new edible-oil to the old frying oil which had been used in food processing to control the cost of the production. Due to the fact that the different additive proportion of the oil has different material and different volatile gases, we use fusion technology based on the electronic nose and electronic tongue to detect the blending ratio of the old frying oil and the new edible-oil in this paper. Principal component analysis (PCA) is used to distinguish the different proportion of the old frying oil and new edible-oil; on the other hand we use partial least squares (PLS) to predict the blending ratio of the old frying oil and new edible-oil. Two conclusions were proposed: data fusion of electronic nose and electronic tongue can be used to detect the blending ratio of the old frying oil and new edible-oil; in contrast to single used electronic nose or single used electronic tongue, the detection effect has increased by using data fusion of electronic nose and electronic tongue. Hong Men, Donglin Chen, Xiaoting Zhang, Jingjing Liu, and Ke Ning Copyright © 2014 Hong Men et al. All rights reserved. Photonic Material Selection of Scintillation Crystals Using Monte Carlo Method for X-Ray Detection in Industrial Computed Tomography Wed, 21 May 2014 07:22:58 +0000 http://www.hindawi.com/journals/js/2014/984716/ Currently industrial X-CT system is designed according to characteristics of test objects, and test objects determine industrial X-CT system structure, X-ray detector/sensor property, scanning mode, and so forth. So there are no uniform standards for the geometry size of scintillation crystals of detector. Moreover, scintillation crystals are usually mixed with some highly toxic impurity elements, such as Tl and Cd. Thus, it is indispensable for establishing guidelines of engineering practice to simulate X-ray detection performances of different scintillation crystals. This paper focuses on how to achieve high efficient X-ray detection in industrial X-CT system which used Monte Carlo (MC) method to study X-ray energy straggling characteristics, full energy peak efficiency, and conversion efficiency of some scintillation crystals (e.g., CsI(Tl), NaI(Tl), and CdWO4) after X-ray interacted with these scintillation crystals. Our experimental results demonstrate that CsI(Tl) scintillation crystal has the advantages of conversion efficiency, spectral matching, manufacturing process, and full energy peak efficiency; it is an ideal choice for high efficient X-ray detection in industrial X-CT system. Peng He, Biao Wei, Mi Zhou, Peng Feng, and Mianyi Chen Copyright © 2014 Peng He et al. All rights reserved. 1-Bit Compressive Data Gathering for Wireless Sensor Networks Thu, 15 May 2014 09:50:07 +0000 http://www.hindawi.com/journals/js/2014/805423/ Compressive sensing (CS) has been widely used in wireless sensor networks for the purpose of reducing the data gathering communication overhead in recent years. In this paper, we firstly apply 1-bit compressive sensing to wireless sensor networks to further reduce the communication overhead that each sensor needs to send. Furthermore, we propose a novel blind 1-bit CS reconstruction algorithm which outperforms other state-of-the-art blind 1-bit CS reconstruction algorithms under the settings of WSN. Experimental results on real sensor datasets demonstrate the efficiency of our method. Jiping Xiong and Qinghua Tang Copyright © 2014 Jiping Xiong and Qinghua Tang. All rights reserved. A Novel Blind Event Detection Method for Wireless Sensor Networks Wed, 07 May 2014 10:12:53 +0000 http://www.hindawi.com/journals/js/2014/531254/ Student's t-distribution is utilized to derive a novel method for event detection in wireless sensor networks. Numerical analysis is used to show that under the same conditions, the proposed event detection method is comparable to likelihood ratio-based detection method and that it significantly outperforms energy detection method in terms of detection performance. Moreover, the proposed method does not require perfect knowledge of noise variance to set up a decision threshold in terms of a false alarm probability as the likelihood ratio based detection and the energy detection do. Thuc Kieu-Xuan, Sungsoo Choi, and Insoo Koo Copyright © 2014 Thuc Kieu-Xuan et al. All rights reserved. Denoising Method Based on Sparse Representation for WFT Signal Thu, 13 Feb 2014 12:33:16 +0000 http://www.hindawi.com/journals/js/2014/145870/ Affected by external noise and various nature disturbances, Wheel Force Transducer (WFT) signal may be completely submerged, and the sensitivity and the reliability of measurement can be strongly decreased. In this paper, a new wavelet packet denoising method based on sparse representation is proposed to remove the noises from WFT signal. In this method, the problem of recovering the noiseless signal is converted into an optimization problem of recovering the sparsity of their wavelet package coefficients, and the wavelet package coefficients of the noiseless signals can be obtained by the augmented Lagrange optimization method. Then the denoised WFT signal can be reconstructed by wavelet packet reconstruction. The experiments on simulation signal and WFT signal show that the proposed denoising method based on sparse representation is more effective for denoising WFT signal than the soft and hard threshold denoising methods. Xu Chen, Guoyu Lin, and Yuxin Zhang Copyright © 2014 Xu Chen et al. All rights reserved. A Self-Oscillating System to Measure the Conductivity and the Permittivity of Liquids within a Single Triangular Signal Thu, 13 Feb 2014 08:34:38 +0000 http://www.hindawi.com/journals/js/2014/389764/ We present a methodology and a circuit to extract liquid resistance and capacitance simultaneously from the same output signal using interdigitated sensing electrodes. The principle consists in the generation of a current square wave and its application to the sensor to create a triangular output voltage which contains both the conductivity and permittivity parameters in a single periodic segment. This concept extends the Triangular Waveform Voltage (TWV) signal generation technique and is implemented by a system which consists in a closed-loop current-controlled oscillator and only requires DC power to operate. The system interface is portable and only a small number of electrical components are used to generate the expected signal. Conductivities of saline NaCl and KCl solutions, being first calibrated by commercial equipment, are characterized by a system prototype. The results show excellent linearity and prove the repeatability of the measurements. Experiments on water-glycerol mixtures validate the proposed sensing approach to measure the permittivity and the conductivity simultaneously. We discussed and identified the sources of measurement errors as circuit parasitic capacitances, switching clock feedthrough, charge injection, bandwidth, and control-current quality. Sylvain Druart, Denis Flandre, and Laurent A. Francis Copyright © 2014 Sylvain Druart et al. All rights reserved. Identification of Wheat Varieties with a Parallel-Plate Capacitance Sensor Using Fisher’s Linear Discriminant Analysis Thu, 06 Feb 2014 13:20:45 +0000 http://www.hindawi.com/journals/js/2014/691898/ Fisher’s linear discriminant (FLD) models for wheat variety classification were developed and validated. The inputs to the FLD models were the capacitance (), impedance (), and phase angle (), measured at two frequencies. Classification of wheat varieties was obtained as output of the FLD models. and of a parallel-plate capacitance system, holding the wheat samples, were measured using an impedance meter, and the value was computed. The best model developed classified the wheat varieties, with accuracy of 95.4%, over the six wheat varieties tested. This method is simple, rapid, and nondestructive and would be useful for the breeders and the peanut industry. C. V. K. Kandala, K. N. Govindarajan, N. Puppala, V. Settaluri, and R. S. Reddy Copyright © 2014 C. V. K. Kandala et al. All rights reserved. Energy Balance Routing Algorithm Based on Virtual MIMO Scheme for Wireless Sensor Networks Thu, 02 Jan 2014 13:19:43 +0000 http://www.hindawi.com/journals/js/2014/589249/ Wireless sensor networks are usually energy limited and therefore an energy-efficient routing algorithm is desired for prolonging the network lifetime. In this paper, we propose a new energy balance routing algorithm which has the following three improvements over the conventional LEACH algorithm. Firstly, we propose a new cluster head selection scheme by taking into consideration the remaining energy and the most recent energy consumption of the nodes and the entire network. In this way, the sensor nodes with smaller remaining energy or larger energy consumption will be much less likely to be chosen as cluster heads. Secondly, according to the ratio of remaining energy to distance, cooperative nodes are selected to form virtual MIMO structures. It mitigates the uneven distribution of clusters and the unbalanced energy consumption of the whole network. Thirdly, we construct a comprehensive energy consumption model, which can reflect more realistically the practical energy consumption. Numerical simulations analyze the influences of cooperative node numbers and cluster head node numbers on the network lifetime. It is shown that the energy consumption of the proposed routing algorithm is lower than the conventional LEACH algorithm and for the simulation example the network lifetime is prolonged about 25%. Jianpo Li, Xue Jiang, and I-Tai Lu Copyright © 2014 Jianpo Li et al. All rights reserved. Vapor Phase Sensing Using Metal Nanorod Thin Films Grown by Cryogenic Oblique Angle Deposition Mon, 23 Dec 2013 19:27:23 +0000 http://www.hindawi.com/journals/js/2013/823041/ We demonstrate the chemical sensing capability of silver nanostructured films grown by cryogenic oblique angle deposition (OAD). For comparison, the films are grown side by side at cryogenic (~100 K) and at room temperature (~300 K) by e-beam evaporation. Based on the observed structural differences, it was hypothesized that the cryogenic OAD silver films should show an increased surface enhanced Raman scattering (SERS) sensitivity. COMSOL simulation results are presented to validate this hypothesis. Experimental SERS results of 4-aminobenzenethiol (4-ABT) Raman test probe molecules in vapor phase show good agreement with the simulation and indicate promising SERS applications for these nanostructured thin films. Piyush Shah, Dongquan Ju, Xiaoxu Niu, and Andrew M. Sarangan Copyright © 2013 Piyush Shah et al. All rights reserved. Damage Detection of Closed Crack in a Metallic Plate Using Nonlinear Ultrasonic Time Reversal Method Wed, 11 Dec 2013 14:38:26 +0000 http://www.hindawi.com/journals/js/2013/652743/ Initial cracks in metallic structures incline to be closed at rest. Such incipient damage generally fails to be detected and located with traditional linear ultrasonic techniques because ultrasonic waves penetrate the contact area of the closed crack. In this paper, an imaging algorithm based on nonlinear ultrasonic time reversal method is proposed to detect closed cracks in aluminum plates. Two surface-bonded piezoelectric transducer arrays are used to generate, receive, and reemit ultrasonic wave signals. The closed crack is simulated by tightening a bolt on the aluminum plate. By applying large amplitude excitation voltage on the PZT transducers, the closed crack could be opened and closed. The transmitted waves recorded by PZT array contain nonlinear components, the signals are time reversed and emitted back, and the tone burst reconstructions are achieved. The linear reciprocity and the time reversibility break down due to the presence of the nonlinear components. The correlation coefficient between the original excitation signal and the reconstructed signal is calculated to define the damage index for individual sensing path and is used to develop an imaging algorithm to locate the closed crack on the plate. The experimental results demonstrate that incident wave signals and their reconstructed signals can be used to accurately detect and locate closed cracks. Wang Zhang, Weiliang Wu, Xiaoyi Sun, Li Xiao, and Wenzhong Qu Copyright © 2013 Wang Zhang et al. All rights reserved. Implicit Active Contours Driven by Local and Global Image Fitting Energy for Image Segmentation and Target Localization Wed, 27 Nov 2013 10:27:56 +0000 http://www.hindawi.com/journals/js/2013/713536/ We propose a novel active contour model in a variational level set formulation for image segmentation and target localization. We combine a local image fitting term and a global image fitting term to drive the contour evolution. Our model can efficiently segment the images with intensity inhomogeneity with the contour starting anywhere in the image. In its numerical implementation, an efficient numerical schema is used to ensure sufficient numerical accuracy. We validated its effectiveness in numerous synthetic images and real images, and the promising experimental results show its advantages in terms of accuracy, efficiency, and robustness. Xiaosheng Yu, Yuanchen Qi, Ziwei Lu, and Nan Hu Copyright © 2013 Xiaosheng Yu et al. All rights reserved. Sensors for Robotics Mon, 25 Nov 2013 09:16:14 +0000 http://www.hindawi.com/journals/js/2013/293656/ Aiguo Song, Guangming Song, Daniela Constantinescu, Lei Wang, and Quanjun Song Copyright © 2013 Aiguo Song et al. All rights reserved. Routing Protocols for Wireless Multimedia Sensor Network: A Survey Sun, 24 Nov 2013 15:40:34 +0000 http://www.hindawi.com/journals/js/2013/469824/ Multimedia applications have become an essential part of our daily lives, and their use is flourishing day by day. The area of wireless sensor network is not an exception where the multimedia sensors are attracting the attention of the researchers increasingly, and it has shifted the focus from traditional scalar sensors to sensors equipped with multimedia devices. The multimedia sensors have the ability to capture video, image, audio, and scalar sensor data and deliver the multimedia content through sensors network. Due to the resource constraints nature of WSN introducing multimedia will add more challenges, so the protocols designed for multimedia wireless sensor network should be aware of the resource constraints nature of WSN and multimedia transmission requirement. This paper discusses the design challenges of routing protocols proposed for WMSN. A survey and comprehensive discussion are given for proposed protocols of WMSN followed by their limitations and features. Mohammed Abazeed, Norshiela Faisal, Suleiman Zubair, and Adel Ali Copyright © 2013 Mohammed Abazeed et al. All rights reserved. Mobile Visual Recognition on Smartphones Tue, 19 Nov 2013 15:43:06 +0000 http://www.hindawi.com/journals/js/2013/843727/ This paper addresses the recognition of large-scale outdoor scenes on smartphones by fusing outputs of inertial sensors and computer vision techniques. The main contributions can be summarized as follows. Firstly, we propose an ORD (overlap region divide) method to plot image position area, which is fast enough to find the nearest visiting area and can also reduce the search range compared with the traditional approaches. Secondly, the vocabulary tree-based approach is improved by introducing GAGCC (gravity-aligned geometric consistency constraint). Our method involves no operation in the high-dimensional feature space and does not assume a global transform between a pair of images. Thus, it substantially reduces the computational complexity and memory usage, which makes the city scale image recognition feasible on the smartphone. Experiments on a collected database including 0.16 million images show that the proposed method demonstrates excellent recognition performance, while maintaining the average recognition time about 1 s. Zhenwen Gui, Yongtian Wang, Yue Liu, and Jing Chen Copyright © 2013 Zhenwen Gui et al. All rights reserved. System-Level Design Considerations for Carbon Nanotube Electromechanical Resonators Tue, 05 Nov 2013 10:37:11 +0000 http://www.hindawi.com/journals/js/2013/384643/ Despite an evermore complete plethora of complex domain-specific semiempirical models, no succinct recipe for large-scale carbon nanotube electromechanical systems design has been formulated. To combine the benefits of these highly sensitive miniaturized mechanical sensors with the vast functionalities available in electronics, we identify a reduced key parameter set of carbon nanotube properties, nanoelectromechanical system design, and operation that steers the sensor’s performance towards system applications, based on open- and closed-loop topologies. Suspended single-walled carbon nanotubes are reviewed in terms of their electromechanical properties with the objective of evaluating orders of magnitude of the electrical actuation and detection mechanisms. Open-loop time-averaging and 1ω or 2ω mixing methods are completed by a new 4ω actuation and detection technique. A discussion on their extension to closed-loop topologies and system applications concludes the analysis, covering signal-to-noise ratio, and the capability to spectrally isolate the motional information from parasitical feedthrough by contemporary electronic read-out techniques. Christian Kauth, Marc Pastre, Jean-Michel Sallese, and Maher Kayal Copyright © 2013 Christian Kauth et al. All rights reserved. Augmented Reality to Support On-Field Post-Impact Maintenance Operations on Thin Structures Thu, 31 Oct 2013 18:40:52 +0000 http://www.hindawi.com/journals/js/2013/619570/ This paper proposes an augmented reality (AR) strategy in which a Lamb waves based impact detection methodology dynamically interacts with a head portable visualization device allowing the inspector to see the estimated impact position (with its uncertainty) and impact energy directly on the plate-like structure. The impact detection methodology uses a network of piezosensors bonded on the structure to be monitored and a signal processing algorithm (the Warped Frequency Transform) able to compensate for dispersion the acquired waveforms. The compensated waveforms yield to a robust estimation of Lamb waves difference in distance of propagation (DDOP), used to feed hyperbolic algorithms for impact location determination, and allow an estimation of the uncertainty of the impact positioning as well as of the impact energy. The outputs of the impact methodology are passed to a visualization technology that yielding their representation in Augmented Reality (AR) is meant to support the inspector during the on-field inspection/diagnosis as well as the maintenance operations. The inspector, in fact, can see interactively in real time the impact data directly on the surface of the structure. To validate the proposed approach, tests on an aluminum plate are presented. Results confirm the feasibility of the method and its exploitability in maintenance practice. Luca De Marchi, Alessandro Ceruti, Alessandro Marzani, and Alfredo Liverani Copyright © 2013 Luca De Marchi et al. All rights reserved. Development and Application of the Single-Spiral Inductive-Capacitive Resonant Circuit Sensor for Wireless, Real-Time Characterization of Moisture in Sand Sat, 26 Oct 2013 13:52:47 +0000 http://www.hindawi.com/journals/js/2013/894512/ A wireless, passive embedded sensor was designed and fabricated for monitoring moisture in sand. The sensor, consisted of an inductive-capacitive (LC) resonant circuit, was made of a printed spiral inductor embedded inside sand. When exposed to an electromagnetic field, the sensor resonated at a specific frequency dependent on the inductance of the inductor and its parasitic capacitance. Since the permittivity of water was much higher than dry sand, moisture in sample increased the parasitic capacitance, thus decreasing the sensor’s resonant frequency. Therefore, the internal moisture level of the sample could be easily measured through tracking the resonant frequency using a detection coil. The fabrication process of this sensor is much simpler compared to LC sensors that contain both capacitive and inductive elements, giving it an economical advantage. A study was conducted to investigate the drying rate of sand samples of different grain sizes. The experimental data showed a strong correlation with the actual moisture content in the samples. The described sensor technology can be applied for long term monitoring of localized water content inside soils and sands to understand the environmental health in these media, or monitoring moisture levels within concrete supports and road pavement. Andrew J. DeRouin, Zhanping You, Morgan Hansen, Aboelkasim Diab, and Keat Ghee Ong Copyright © 2013 Andrew J. DeRouin et al. All rights reserved. Radio Context Awareness and Applications Sun, 22 Sep 2013 11:16:40 +0000 http://www.hindawi.com/journals/js/2013/491092/ The context refers to “any information that can be used to characterize the situation of an entity, where an entity can be a person, place, or physical object.” Radio context awareness is defined as the ability of detecting and estimating a system state or parameter, either globally or concerning one of its components, in a radio system for enhancing performance at the physical, network, or application layers. In this paper, we review the fundamentals of context awareness and the recent advances in the main radio techniques that increase the context awareness and smartness, posing challenges and renewed opportunities to added-value applications in the context of the next generation of wireless networks. Luca Reggiani, Jocelyn Fiorina, Sinan Gezici, Simone Morosi, and Montse Najar Copyright © 2013 Luca Reggiani et al. All rights reserved. Cooperative Spectrum Sensing and Localization in Cognitive Radio Systems Using Compressed Sensing Tue, 03 Sep 2013 11:22:13 +0000 http://www.hindawi.com/journals/js/2013/606413/ We propose to fuse two main enabling features in cognitive radio systems (CRS): spectrum sensing and location awareness in a single compressed sensing based formalism. In this way, we exploit sparse characteristics of primary units to be detected, both in terms of spectrum used and location occupied. The compressed sensing approach also allows to overcome hardware limitations, in terms of the incapacity to acquire measurements and signals at the Nyquist rate when the spectrum to be scanned is large. Simulation results for realistic network topologies and different compressed sensing reconstruction algorithms testify to the performance and the feasibility of the proposed technique to enable in a single formalism the two main features of cognitive sensor networks. Wael Guibène and Dirk Slock Copyright © 2013 Wael Guibène and Dirk Slock. All rights reserved.