Sensors

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Open AccessCorrection

Correction: Yoshie, T. et al. Optical Microcavity: Sensing downto Single Molecules and Atoms. Sensors 2011, 11, 1972-1991

by Tomoyuki Yoshie, Lingling Tang and Shu-Yu Su

Sensors 2011, 11(6), 6493; https://doi.org/10.3390/s110606493 - 22 Jun 2011

Cited by 1 | Viewed by 6815

Abstract

The coefficient of the expression of Equation (6) was not properly written. [...] Full article

(This article belongs to the Special Issue Optical Resonant Microsensors)

719 KiB

Open AccessArticle

An Image Segmentation Based on a Genetic Algorithm for Determining Soil Coverage by Crop Residues

by Angela Ribeiro, Juan Ranz, Xavier P. Burgos-Artizzu, Gonzalo Pajares, Maria J. Sanchez del Arco and Luis Navarrete

Sensors 2011, 11(6), 6480-6492; https://doi.org/10.3390/s110606480 - 17 Jun 2011

Cited by 17 | Viewed by 12164

Abstract

Determination of the soil coverage by crop residues after ploughing is a fundamental element of Conservation Agriculture. This paper presents the application of genetic algorithms employed during the fine tuning of the segmentation process of a digital image with the aim of automatically [...] Read more.

Determination of the soil coverage by crop residues after ploughing is a fundamental element of Conservation Agriculture. This paper presents the application of genetic algorithms employed during the fine tuning of the segmentation process of a digital image with the aim of automatically quantifying the residue coverage. In other words, the objective is to achieve a segmentation that would permit the discrimination of the texture of the residue so that the output of the segmentation process is a binary image in which residue zones are isolated from the rest. The RGB images used come from a sample of images in which sections of terrain were photographed with a conventional camera positioned in zenith orientation atop a tripod. The images were taken outdoors under uncontrolled lighting conditions. Up to 92% similarity was achieved between the images obtained by the segmentation process proposed in this paper and the templates made by an elaborate manual tracing process. In addition to the proposed segmentation procedure and the fine tuning procedure that was developed, a global quantification of the soil coverage by residues for the sampled area was achieved that differed by only 0.85% from the quantification obtained using template images. Moreover, the proposed method does not depend on the type of residue present in the image. The study was conducted at the experimental farm “El Encín” in Alcalá de Henares (Madrid, Spain). Full article

(This article belongs to the Special Issue Sensors in Agriculture and Forestry)

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1711 KiB

Open AccessArticle

Enviro-Net: From Networks of Ground-Based Sensor Systems to a Web Platform for Sensor Data Management

by Gilberto Z. Pastorello, G. Arturo Sanchez-Azofeifa and Mario A. Nascimento

Sensors 2011, 11(6), 6454-6479; https://doi.org/10.3390/s110606454 - 17 Jun 2011

Cited by 16 | Viewed by 12009

Abstract

Ecosystems monitoring is essential to properly understand their development and the effects of events, both climatological and anthropological in nature. The amount of data used in these assessments is increasing at very high rates. This is due to increasing availability of sensing systems [...] Read more.

Ecosystems monitoring is essential to properly understand their development and the effects of events, both climatological and anthropological in nature. The amount of data used in these assessments is increasing at very high rates. This is due to increasing availability of sensing systems and the development of new techniques to analyze sensor data. The Enviro-Net Project encompasses several of such sensor system deployments across five countries in the Americas. These deployments use a few different ground-based sensor systems, installed at different heights monitoring the conditions in tropical dry forests over long periods of time. This paper presents our experience in deploying and maintaining these systems, retrieving and pre-processing the data, and describes the Web portal developed to help with data management, visualization and analysis. Full article

(This article belongs to the Special Issue Sensors in Agriculture and Forestry)

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Open AccessArticle

An Electronic Nose for Reliable Measurement and Correct Classification of Beverages

by Mazlina Mamat, Salina Abdul Samad and Mahammad A. Hannan

Sensors 2011, 11(6), 6435-6453; https://doi.org/10.3390/s110606435 - 17 Jun 2011

Cited by 49 | Viewed by 12795

Abstract

This paper reports the design of an electronic nose (E-nose) prototype for reliable measurement and correct classification of beverages. The prototype was developed and fabricated in the laboratory using commercially available metal oxide gas sensors and a temperature sensor. The repeatability, reproducibility and [...] Read more.

This paper reports the design of an electronic nose (E-nose) prototype for reliable measurement and correct classification of beverages. The prototype was developed and fabricated in the laboratory using commercially available metal oxide gas sensors and a temperature sensor. The repeatability, reproducibility and discriminative ability of the developed E-nose prototype were tested on odors emanating from different beverages such as blackcurrant juice, mango juice and orange juice, respectively. Repeated measurements of three beverages showed very high correlation (r > 0.97) between the same beverages to verify the repeatability. The prototype also produced highly correlated patterns (r > 0.97) in the measurement of beverages using different sensor batches to verify its reproducibility. The E-nose prototype also possessed good discriminative ability whereby it was able to produce different patterns for different beverages, different milk heat treatments (ultra high temperature, pasteurization) and fresh and spoiled milks. The discriminative ability of the E-nose was evaluated using Principal Component Analysis and a Multi Layer Perception Neural Network, with both methods showing good classification results. Full article

(This article belongs to the Special Issue Bioinspired Sensor Systems)

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Open AccessArticle

Low-Cost Gas Sensors Produced by the Graphite Line-Patterning Technique Applied to Monitoring Banana Ripeness

by Alexandra Manzoli, Clarice Steffens, Rafaella T. Paschoalin, Alessandra A. Correa, William F. Alves, Fábio L. Leite and Paulo S. P. Herrmann

Sensors 2011, 11(6), 6425-6434; https://doi.org/10.3390/s110606425 - 17 Jun 2011

Cited by 55 | Viewed by 10860

Abstract

A low-cost sensor array system for banana ripeness monitoring is presented. The sensors are constructed by employing a graphite line-patterning technique (LPT) to print interdigitated graphite electrodes on tracing paper and then coating the printed area with a thin film of polyaniline (PANI) [...] Read more.

A low-cost sensor array system for banana ripeness monitoring is presented. The sensors are constructed by employing a graphite line-patterning technique (LPT) to print interdigitated graphite electrodes on tracing paper and then coating the printed area with a thin film of polyaniline (PANI) by in-situ polymerization as the gas-sensitive layer. The PANI layers were used for the detection of volatile organic compounds (VOCs), including ethylene, emitted during ripening. The influence of the various acid dopants, hydrochloric acid (HCl), methanesulfonic acid (MSA), p-toluenesulfonic acid (TSA) and camphorsulfonic acid (CSA), on the electrical properties of the thin film of PANI adsorbed on the electrodes was also studied. The extent of doping of the films was investigated by UV-Vis absorption spectroscopy and tests showed that the type of dopant plays an important role in the performance of these low-cost sensors. The array of three sensors, without the PANI-HCl sensor, was able to produce a distinct pattern of signals, taken as a signature (fingerprint) that can be used to characterize bananas ripeness. Full article

(This article belongs to the Section Chemical Sensors)

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Open AccessArticle

Nitrogen Concentration Estimation in Tomato Leaves by VIS-NIR Non-Destructive Spectroscopy

by Valentina Ulissi, Francesca Antonucci, Paolo Benincasa, Michela Farneselli, Giacomo Tosti, Marcello Guiducci, Francesco Tei, Corrado Costa, Federico Pallottino, Luigi Pari and Paolo Menesatti

Sensors 2011, 11(6), 6411-6424; https://doi.org/10.3390/s110606411 - 16 Jun 2011

Cited by 79 | Viewed by 11790

Abstract

Nitrogen concentration in plants is normally determined by expensive and time consuming chemical analyses. As an alternative, chlorophyll meter readings and N-NO₃ concentration determination in petiole sap were proposed, but these assays are not always satisfactory. Spectral reflectance values of tomato leaves [...] Read more.

Nitrogen concentration in plants is normally determined by expensive and time consuming chemical analyses. As an alternative, chlorophyll meter readings and N-NO₃ concentration determination in petiole sap were proposed, but these assays are not always satisfactory. Spectral reflectance values of tomato leaves obtained by visible-near infrared spectrophotometry are reported to be a powerful tool for the diagnosis of plant nutritional status. The aim of the study was to evaluate the possibility and the accuracy of the estimation of tomato leaf nitrogen concentration performed through a rapid, portable and non-destructive system, in comparison with chemical standard analyses, chlorophyll meter readings and N-NO₃ concentration in petiole sap. Mean reflectance leaf values were compared to each reference chemical value by partial least squares chemometric multivariate methods. The correlation between predicted values from spectral reflectance analysis and the observed chemical values showed in the independent test highly significant correlation coefficient (r = 0.94). The utilization of the proposed system, increasing efficiency, allows better knowledge of nutritional status of tomato plants, with more detailed and sharp information and on wider areas. More detailed information both in space and time is an essential tool to increase and stabilize crop quality levels and to optimize the nutrient use efficiency. Full article

(This article belongs to the Special Issue Sensing of Toxic and Hazardous Metals in Various Environmental Media)

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472 KiB

Open AccessArticle

FRET-Based Quantum Dot Immunoassay for Rapid and Sensitive Detection of Aspergillus amstelodami

by Michele D. Kattke, Elizabeth J. Gao, Kim E. Sapsford, Larry D. Stephenson and Ashok Kumar

Sensors 2011, 11(6), 6396-6410; https://doi.org/10.3390/s110606396 - 16 Jun 2011

Cited by 58 | Viewed by 14005

Abstract

In this study, a fluorescence resonance energy transfer (FRET)-based quantum dot (QD) immunoassay for detection and identification of Aspergillus amstelodami was developed. Biosensors were formed by conjugating QDs to IgG antibodies and incubating with quencher-labeled analytes; QD energy was transferred to the quencher [...] Read more.

In this study, a fluorescence resonance energy transfer (FRET)-based quantum dot (QD) immunoassay for detection and identification of Aspergillus amstelodami was developed. Biosensors were formed by conjugating QDs to IgG antibodies and incubating with quencher-labeled analytes; QD energy was transferred to the quencher species through FRET, resulting in diminished fluorescence from the QD donor. During a detection event, quencher-labeled analytes are displaced by higher affinity target analytes, creating a detectable fluorescence signal increase from the QD donor. Conjugation and the resulting antibody:QD ratios were characterized with UV-Vis spectroscopy and QuantiT protein assay. The sensitivity of initial fluorescence experiments was compromised by inherent autofluorescence of mold spores, which produced low signal-to-noise and inconsistent readings. Therefore, excitation wavelength, QD, and quencher were adjusted to provide optimal signal-to-noise over spore background. Affinities of anti-Aspergillus antibody for different mold species were estimated with sandwich immunoassays, which identified A. fumigatus and A. amstelodami for use as quencher-labeled- and target-analytes, respectively. The optimized displacement immunoassay detected A. amstelodami concentrations as low as 10³ spores/mL in five minutes or less. Additionally, baseline fluorescence was produced in the presence of 10⁵ CFU/mL heat-killed E. coli O157:H7, demonstrating high specificity. This sensing modality may be useful for identification and detection of other biological threat agents, pending identification of suitable antibodies. Overall, these FRET-based QD-antibody biosensors represent a significant advancement in detection capabilities, offering sensitive and reliable detection of targets with applications in areas from biological terrorism defense to clinical analysis. Full article

(This article belongs to the Special Issue Sensing with Quantum Dots)

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Open AccessArticle

Reduction of Radiometric Miscalibration—Applications to Pushbroom Sensors

by Christian Rogaß, Daniel Spengler, Mathias Bochow, Karl Segl, Angela Lausch, Daniel Doktor, Sigrid Roessner, Robert Behling, Hans-Ulrich Wetzel and Hermann Kaufmann

Sensors 2011, 11(6), 6370-6395; https://doi.org/10.3390/s110606370 - 16 Jun 2011

Cited by 29 | Viewed by 11483

Abstract

The analysis of hyperspectral images is an important task in Remote Sensing. Foregoing radiometric calibration results in the assignment of incident electromagnetic radiation to digital numbers and reduces the striping caused by slightly different responses of the pixel detectors. However, due to uncertainties [...] Read more.

The analysis of hyperspectral images is an important task in Remote Sensing. Foregoing radiometric calibration results in the assignment of incident electromagnetic radiation to digital numbers and reduces the striping caused by slightly different responses of the pixel detectors. However, due to uncertainties in the calibration some striping remains. This publication presents a new reduction framework that efficiently reduces linear and nonlinear miscalibrations by an image-driven, radiometric recalibration and rescaling. The proposed framework—Reduction Of Miscalibration Effects (ROME)—considering spectral and spatial probability distributions, is constrained by specific minimisation and maximisation principles and incorporates image processing techniques such as Minkowski metrics and convolution. To objectively evaluate the performance of the new approach, the technique was applied to a variety of commonly used image examples and to one simulated and miscalibrated EnMAP (Environmental Mapping and Analysis Program) scene. Other examples consist of miscalibrated AISA/Eagle VNIR (Visible and Near Infrared) and Hawk SWIR (Short Wave Infrared) scenes of rural areas of the region Fichtwald in Germany and Hyperion scenes of the Jalal-Abad district in Southern Kyrgyzstan. Recovery rates of approximately 97% for linear and approximately 94% for nonlinear miscalibrated data were achieved, clearly demonstrating the benefits of the new approach and its potential for broad applicability to miscalibrated pushbroom sensor data. Full article

(This article belongs to the Section Remote Sensors)

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358 KiB

Open AccessArticle

Field Calibrations of Soil Moisture Sensors in a Forested Watershed

by Farhat Abbas, Ali Fares and Samira Fares

Sensors 2011, 11(6), 6354-6369; https://doi.org/10.3390/s110606354 - 16 Jun 2011

Cited by 26 | Viewed by 11341

Abstract

Spatially variable soil properties influence the performance of soil water content monitoring sensors. The objectives of this research were to: (i) study the spatial variability of bulk density (ρ_b), total porosity (θ_t), clay content (CC), electrical conductivity [...] Read more.

Spatially variable soil properties influence the performance of soil water content monitoring sensors. The objectives of this research were to: (i) study the spatial variability of bulk density (ρ_b), total porosity (θ_t), clay content (CC), electrical conductivity (EC), and pH in the upper Mākaha Valley watershed soils; (ii) explore the effect of variations in ρ_b and θ_t on soil water content dynamics, and (iii) establish field calibration equations for EC-20 (Decagon Devices, Inc), ML2x (Delta-T-Devices), and SM200 (Delta-T-Devices) sensors to mitigate the effect of soil spatial variability on their performance. The studied soil properties except pH varied significantly (P < 0.05) across the soil water content monitoring depths (20 and 80 cm) and six locations. There was a linear positive and a linear inverse correlation between the soil water content at sampling and ρ_b, and between the soil water content at sampling and θ_t, respectively. Values of laboratory measured actual θ_t correlated (r = 0.75) with those estimated from the relationship θ_t = 1 − ρ_b/ρ_s, where ρ_s is the particle density. Variations in the studied soil properties affected the performance of the default equations of the three tested sensors; they showed substantial under-estimations of the actual water content. The individual and the watershed-scale field calibrations were more accurate than their corresponding default calibrations. In conclusion, the sensors used in this study need site-specific calibrations in order to mitigate the effects of varying properties of the highly weathered tropical soils. Full article

(This article belongs to the Special Issue Sensors in Agriculture and Forestry)

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Open AccessArticle

Automatic Forest-Fire Measuring Using Ground Stations and Unmanned Aerial Systems

by José Ramiro Martínez-de Dios, Luis Merino, Fernando Caballero and Anibal Ollero

Sensors 2011, 11(6), 6328-6353; https://doi.org/10.3390/s110606328 - 16 Jun 2011

Cited by 82 | Viewed by 16592

Abstract

This paper presents a novel system for automatic forest-fire measurement using cameras distributed at ground stations and mounted on Unmanned Aerial Systems (UAS). It can obtain geometrical measurements of forest fires in real-time such as the location and shape of the fire front, [...] Read more.

This paper presents a novel system for automatic forest-fire measurement using cameras distributed at ground stations and mounted on Unmanned Aerial Systems (UAS). It can obtain geometrical measurements of forest fires in real-time such as the location and shape of the fire front, flame height and rate of spread, among others. Measurement of forest fires is a challenging problem that is affected by numerous potential sources of error. The proposed system addresses them by exploiting the complementarities between infrared and visual cameras located at different ground locations together with others onboard Unmanned Aerial Systems (UAS). The system applies image processing and geo-location techniques to obtain forest-fire measurements individually from each camera and then integrates the results from all the cameras using statistical data fusion techniques. The proposed system has been extensively tested and validated in close-to-operational conditions in field fire experiments with controlled safety conditions carried out in Portugal and Spain from 2001 to 2006. Full article

(This article belongs to the Special Issue Sensors in Agriculture and Forestry)

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Open AccessArticle

Relation of Biospeckle Activity with Quality Attributes of Apples

by Artur Zdunek and Justyna Cybulska

Sensors 2011, 11(6), 6317-6327; https://doi.org/10.3390/s110606317 - 14 Jun 2011

Cited by 54 | Viewed by 9746

Abstract

Biospeckle is nondestructive optical technique based on the analysis of variations of laser light scattered from biological samples. Biospeckle activity reflects the state of the investigated object. In this study the relation of biospeckle activity (BA) with firmness, soluble solids content (SSC), titratable [...] Read more.

Biospeckle is nondestructive optical technique based on the analysis of variations of laser light scattered from biological samples. Biospeckle activity reflects the state of the investigated object. In this study the relation of biospeckle activity (BA) with firmness, soluble solids content (SSC), titratable acidity (TA) and starch content (SC) during the shelf life of seven apple cultivars was studied. The results showed that the quality attributes change significantly during storage. Significant and pronounced positive correlation between BA and SC was found. This result shows that degradation of starch granules, which could be stimulated to vibration by intracellular cyclosis, causes a lesser number of laser light scattering centers and results in smaller apparent biospeckle activity. Full article

(This article belongs to the Special Issue Sensors in Agriculture and Forestry)

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504 KiB

Open AccessArticle

Diffusion-Based EM Algorithm for Distributed Estimation of Gaussian Mixtures in Wireless Sensor Networks

by Yang Weng, Wendong Xiao and Lihua Xie

Sensors 2011, 11(6), 6297-6316; https://doi.org/10.3390/s110606297 - 14 Jun 2011

Cited by 33 | Viewed by 8837

Abstract

Distributed estimation of Gaussian mixtures has many applications in wireless sensor network (WSN), and its energy-efficient solution is still challenging. This paper presents a novel diffusion-based EM algorithm for this problem. A diffusion strategy is introduced for acquiring the global statistics in EM [...] Read more.

Distributed estimation of Gaussian mixtures has many applications in wireless sensor network (WSN), and its energy-efficient solution is still challenging. This paper presents a novel diffusion-based EM algorithm for this problem. A diffusion strategy is introduced for acquiring the global statistics in EM algorithm in which each sensor node only needs to communicate its local statistics to its neighboring nodes at each iteration. This improves the existing consensus-based distributed EM algorithm which may need much more communication overhead for consensus, especially in large scale networks. The robustness and scalability of the proposed approach can be achieved by distributed processing in the networks. In addition, we show that the proposed approach can be considered as a stochastic approximation method to find the maximum likelihood estimation for Gaussian mixtures. Simulation results show the efficiency of this approach. Full article

(This article belongs to the Special Issue Collaborative Sensors)

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Open AccessArticle

An Improved Equivalent Simulation Model for CMOS Integrated Hall Plates

by Yue Xu and Hong-Bin Pan

Sensors 2011, 11(6), 6284-6296; https://doi.org/10.3390/s110606284 - 10 Jun 2011

Cited by 36 | Viewed by 8596

Abstract

An improved equivalent simulation model for a CMOS-integrated Hall plate is described in this paper. Compared with existing models, this model covers voltage dependent non-linear effects, geometrical effects, temperature effects and packaging stress influences, and only includes a small number of physical and [...] Read more.

An improved equivalent simulation model for a CMOS-integrated Hall plate is described in this paper. Compared with existing models, this model covers voltage dependent non-linear effects, geometrical effects, temperature effects and packaging stress influences, and only includes a small number of physical and technological parameters. In addition, the structure of this model is relatively simple, consisting of a passive network with eight non-linear resistances, four current-controlled voltage sources and four parasitic capacitances. The model has been written in Verilog-A hardware description language and it performed successfully in a Cadence Spectre simulator. The model’s simulation results are in good agreement with the classic experimental results reported in the literature. Full article

(This article belongs to the Section Physical Sensors)

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Open AccessArticle

Robust Crop and Weed Segmentation under Uncontrolled Outdoor Illumination

by Hong Y. Jeon, Lei F. Tian and Heping Zhu

Sensors 2011, 11(6), 6270-6283; https://doi.org/10.3390/s110606270 - 10 Jun 2011

Cited by 124 | Viewed by 13077

Abstract

An image processing algorithm for detecting individual weeds was developed and evaluated. Weed detection processes included were normalized excessive green conversion, statistical threshold value estimation, adaptive image segmentation, median filter, morphological feature calculation and Artificial Neural Network (ANN). The developed algorithm was validated [...] Read more.

An image processing algorithm for detecting individual weeds was developed and evaluated. Weed detection processes included were normalized excessive green conversion, statistical threshold value estimation, adaptive image segmentation, median filter, morphological feature calculation and Artificial Neural Network (ANN). The developed algorithm was validated for its ability to identify and detect weeds and crop plants under uncontrolled outdoor illuminations. A machine vision implementing field robot captured field images under outdoor illuminations and the image processing algorithm automatically processed them without manual adjustment. The errors of the algorithm, when processing 666 field images, ranged from 2.1 to 2.9%. The ANN correctly detected 72.6% of crop plants from the identified plants, and considered the rest as weeds. However, the ANN identification rates for crop plants were improved up to 95.1% by addressing the error sources in the algorithm. The developed weed detection and image processing algorithm provides a novel method to identify plants against soil background under the uncontrolled outdoor illuminations, and to differentiate weeds from crop plants. Thus, the proposed new machine vision and processing algorithm may be useful for outdoor applications including plant specific direct applications (PSDA). Full article

(This article belongs to the Special Issue Sensors in Agriculture and Forestry)

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Open AccessArticle

Implementation of the CMOS MEMS Condenser Microphone with Corrugated Metal Diaphragm and Silicon Back-Plate

by Chien-Hsin Huang, Chien-Hsing Lee, Tsung-Min Hsieh, Li-Chi Tsao, Shaoyi Wu, Jhyy-Cheng Liou, Ming-Yi Wang, Li-Che Chen, Ming-Chuen Yip and Weileun Fang

Sensors 2011, 11(6), 6257-6269; https://doi.org/10.3390/s110606257 - 10 Jun 2011

Cited by 37 | Viewed by 12150

Abstract

This study reports a CMOS-MEMS condenser microphone implemented using the standard thin film stacking of 0.35 μm UMC CMOS 3.3/5.0 V logic process, and followed by post-CMOS micromachining steps without introducing any special materials. The corrugated diaphragm for the microphone is designed and [...] Read more.

This study reports a CMOS-MEMS condenser microphone implemented using the standard thin film stacking of 0.35 μm UMC CMOS 3.3/5.0 V logic process, and followed by post-CMOS micromachining steps without introducing any special materials. The corrugated diaphragm for the microphone is designed and implemented using the metal layer to reduce the influence of thin film residual stresses. Moreover, a silicon substrate is employed to increase the stiffness of the back-plate. Measurements show the sensitivity of microphone is −42 ± 3 dBV/Pa at 1 kHz (the reference sound-level is 94 dB) under 6 V pumping voltage, the frequency response is 100 Hz–10 kHz, and the S/N ratio >55 dB. It also has low power consumption of less than 200 μA, and low distortion of less than 1% (referred to 100 dB). Full article

(This article belongs to the Section Physical Sensors)

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1968 KiB

Open AccessArticle

Georeferenced LiDAR 3D Vine Plantation Map Generation

by Jordi Llorens, Emilio Gil, Jordi Llop and Meritxell Queraltó

Sensors 2011, 11(6), 6237-6256; https://doi.org/10.3390/s110606237 - 9 Jun 2011

Cited by 53 | Viewed by 14214

Abstract

The use of electronic devices for canopy characterization has recently been widely discussed. Among such devices, LiDAR sensors appear to be the most accurate and precise. Information obtained with LiDAR sensors during reading while driving a tractor along a crop row can be [...] Read more.

The use of electronic devices for canopy characterization has recently been widely discussed. Among such devices, LiDAR sensors appear to be the most accurate and precise. Information obtained with LiDAR sensors during reading while driving a tractor along a crop row can be managed and transformed into canopy density maps by evaluating the frequency of LiDAR returns. This paper describes a proposed methodology to obtain a georeferenced canopy map by combining the information obtained with LiDAR with that generated using a GPS receiver installed on top of a tractor. Data regarding the velocity of LiDAR measurements and UTM coordinates of each measured point on the canopy were obtained by applying the proposed transformation process. The process allows overlap of the canopy density map generated with the image of the intended measured area using Google Earth^®, providing accurate information about the canopy distribution and/or location of damage along the rows. This methodology was applied and tested on different vine varieties and crop stages in two important vine production areas in Spain. The results indicate that the georeferenced information obtained with LiDAR sensors appears to be an interesting tool with the potential to improve crop management processes. Full article

(This article belongs to the Special Issue Sensors in Agriculture and Forestry)

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602 KiB

Open AccessArticle

Interfacial Chemistry and the Design of Solid-Phase Nucleic Acid Hybridization Assays Using Immobilized Quantum Dots as Donors in Fluorescence Resonance Energy Transfer

by W. Russ Algar and Ulrich J. Krull

Sensors 2011, 11(6), 6214-6236; https://doi.org/10.3390/s110606214 - 9 Jun 2011

Cited by 34 | Viewed by 9220

Abstract

The use of quantum dots (QDs) as donors in fluorescence resonance energy transfer (FRET) offer several advantages for the development of multiplexed solid-phase QD-FRET nucleic acid hybridization assays. Designs for multiplexing have been demonstrated, but important challenges remain in the optimization of these [...] Read more.

The use of quantum dots (QDs) as donors in fluorescence resonance energy transfer (FRET) offer several advantages for the development of multiplexed solid-phase QD-FRET nucleic acid hybridization assays. Designs for multiplexing have been demonstrated, but important challenges remain in the optimization of these systems. In this work, we identify several strategies based on the design of interfacial chemistry for improving sensitivity, obtaining lower limits of detection (LOD) and enabling the regeneration and reuse of solid-phase QD-FRET hybridization assays. FRET-sensitized emission from acceptor dyes associated with hybridization events at immobilized QD donors provides the analytical signal in these assays. The minimization of active sensing area reduces background from QD donor PL and allows the resolution of smaller amounts of acceptor emission, thus lowering the LOD. The association of multiple acceptor dyes with each hybridization event can enhance FRET efficiency, thereby improving sensitivity. Many previous studies have used interfacial protein layers to generate selectivity; however, transient destabilization of these layers is shown to prevent efficient regeneration. To this end, we report a protein-free interfacial chemistry and demonstrate the specific detection of as little as 2 pmol of target, as well as an improved capacity for regeneration. Full article

(This article belongs to the Special Issue Sensing with Quantum Dots)

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347 KiB

Open AccessArticle

Energy-Efficient Algorithm for Sensor Networks with Non-Uniform Maximum Transmission Range

by Yimin Yu, Chao Song, Ming Liu and Haigang Gong

Sensors 2011, 11(6), 6203-6213; https://doi.org/10.3390/s110606203 - 8 Jun 2011

Cited by 8 | Viewed by 6823

Abstract

In wireless sensor networks (WSNs), the energy hole problem is a key factor affecting the network lifetime. In a circular multi-hop sensor network (modeled as concentric coronas), the optimal transmission ranges of all coronas can effectively improve network lifetime. In this paper, we [...] Read more.

In wireless sensor networks (WSNs), the energy hole problem is a key factor affecting the network lifetime. In a circular multi-hop sensor network (modeled as concentric coronas), the optimal transmission ranges of all coronas can effectively improve network lifetime. In this paper, we investigate WSNs with non-uniform maximum transmission ranges, where sensor nodes deployed in different regions may differ in their maximum transmission range. Then, we propose an Energy-efficient algorithm for Non-uniform Maximum Transmission range (ENMT), which can search approximate optimal transmission ranges of all coronas in order to prolong network lifetime. Furthermore, the simulation results indicate that ENMT performs better than other algorithms. Full article

(This article belongs to the Section Physical Sensors)

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Open AccessArticle

A Standard CMOS Humidity Sensor without Post-Processing

by Oleg Nizhnik, Kohei Higuchi and Kazusuke Maenaka

Sensors 2011, 11(6), 6197-6202; https://doi.org/10.3390/s110606197 - 8 Jun 2011

Cited by 8 | Viewed by 7153

Abstract

A 2 µW power dissipation, voltage-output, humidity sensor accurate to 5% relative humidity was developed using the LFoundry 0.15 µm CMOS technology without post-processing. The sensor consists of a woven lateral array of electrodes implemented in CMOS top metal, a Intervia Photodielectric 8023-10 [...] Read more.

A 2 µW power dissipation, voltage-output, humidity sensor accurate to 5% relative humidity was developed using the LFoundry 0.15 µm CMOS technology without post-processing. The sensor consists of a woven lateral array of electrodes implemented in CMOS top metal, a Intervia Photodielectric 8023-10 humidity-sensitive layer, and a CMOS capacitance to voltage converter. Full article

(This article belongs to the Section Physical Sensors)

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Open AccessArticle

A Wireless Sensor Network for Vineyard Monitoring That Uses Image Processing

by Jaime Lloret, Ignacio Bosch, Sandra Sendra and Arturo Serrano

Sensors 2011, 11(6), 6165-6196; https://doi.org/10.3390/s110606165 - 7 Jun 2011

Cited by 138 | Viewed by 14999

Abstract

The first step to detect when a vineyard has any type of deficiency, pest or disease is to observe its stems, its grapes and/or its leaves. To place a sensor in each leaf of every vineyard is obviously not feasible in terms of [...] Read more.

The first step to detect when a vineyard has any type of deficiency, pest or disease is to observe its stems, its grapes and/or its leaves. To place a sensor in each leaf of every vineyard is obviously not feasible in terms of cost and deployment. We should thus look for new methods to detect these symptoms precisely and economically. In this paper, we present a wireless sensor network where each sensor node takes images from the field and internally uses image processing techniques to detect any unusual status in the leaves. This symptom could be caused by a deficiency, pest, disease or other harmful agent. When it is detected, the sensor node sends a message to a sink node through the wireless sensor network in order to notify the problem to the farmer. The wireless sensor uses the IEEE 802.11 a/b/g/n standard, which allows connections from large distances in open air. This paper describes the wireless sensor network design, the wireless sensor deployment, how the node processes the images in order to monitor the vineyard, and the sensor network traffic obtained from a test bed performed in a flat vineyard in Spain. Although the system is not able to distinguish between deficiency, pest, disease or other harmful agents, a symptoms image database and a neuronal network could be added in order learn from the experience and provide an accurate problem diagnosis. Full article

(This article belongs to the Special Issue Sensors in Agriculture and Forestry)

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Open AccessArticle

The Multi-Chamber Electronic Nose—An Improved Olfaction Sensor for Mobile Robotics

by Javier Gonzalez-Jimenez, Javier G. Monroy and Jose Luis Blanco

Sensors 2011, 11(6), 6145-6164; https://doi.org/10.3390/s110606145 - 7 Jun 2011

Cited by 85 | Viewed by 11988

Abstract

One of the major disadvantages of the use of Metal Oxide Semiconductor (MOS) technology as a transducer for electronic gas sensing devices (e-noses) is the long recovery period needed after each gas exposure. This severely restricts its usage in applications where the gas [...] Read more.

One of the major disadvantages of the use of Metal Oxide Semiconductor (MOS) technology as a transducer for electronic gas sensing devices (e-noses) is the long recovery period needed after each gas exposure. This severely restricts its usage in applications where the gas concentrations may change rapidly, as in mobile robotic olfaction, where allowing for sensor recovery forces the robot to move at a very low speed, almost incompatible with any practical robot operation. This paper describes the design of a new e-nose which overcomes, to a great extent, such a limitation. The proposed e-nose, called Multi-Chamber Electronic Nose (MCE-nose), comprises several identical sets of MOS sensors accommodated in separate chambers (four in our current prototype), which alternate between sensing and recovery states, providing, as a whole, a device capable of sensing changes in chemical concentrations faster. The utility and performance of the MCE-nose in mobile robotic olfaction is shown through several experiments involving rapid sensing of gas concentration and mobile robot gas mapping. Full article

(This article belongs to the Section Chemical Sensors)

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364 KiB

Open AccessArticle

Mitigation Technique for Receiver Performance Variation of Multi-Color Channels in Visible Light Communication

by Muhammad Shahin Uddin, Jae Sang Cha, Jin Young Kim and Yeong Min Jang

Sensors 2011, 11(6), 6131-6144; https://doi.org/10.3390/s110606131 - 7 Jun 2011

Cited by 28 | Viewed by 10204

Abstract

“Green” and energy-efficient wireless communication schemes have recently experienced rapid development and garnered much interest. One such scheme is visible light communication (VLC) which is being touted as one of the next generation wireless communication systems. VLC allows communication using multi-color channels that [...] Read more.

“Green” and energy-efficient wireless communication schemes have recently experienced rapid development and garnered much interest. One such scheme is visible light communication (VLC) which is being touted as one of the next generation wireless communication systems. VLC allows communication using multi-color channels that provide high data rates and illumination simultaneously. Even though VLC has many advantageous features compared with RF technologies, including visibility, ubiquitousness, high speed, high security, harmlessness for the human body and freedom of RF interference, it suffers from some problems on the receiver side, one of them being photo sensitivity dissimilarity of the receiver. The photo sensitivity characteristics of a VLC receiver such as Si photo-detector depend on the wavelength variation. The performance of the VLC receiver is not uniform towards all channel colors, but it is desirable for receivers to have the same performance on each color channel. In this paper, we propose a mitigation technique for reducing the performance variation of the receiver on multi-color channels. We show received power, SNR, BER, output current, and outage probability in our simulation for different color channels. Simulation results show that, the proposed scheme can reduce the performance variation of the VLC receiver on multi-color channels. Full article

(This article belongs to the Section Physical Sensors)

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383 KiB

Open AccessArticle

Simultaneous Second Harmonic Generation of Multiple Wavelength Laser Outputs for Medical Sensing

by Seung Nam Son, Jae-Jin Song, Jin U. Kang and Chang-Seok Kim

Sensors 2011, 11(6), 6125-6130; https://doi.org/10.3390/s110606125 - 7 Jun 2011

Cited by 68 | Viewed by 8206

Abstract

Multiple wavelength light sources in the medical spectral window region are useful for various medical sensing applications in tissue by distinguishing the absorption and scattering coefficients optically. We propose a simultaneous second harmonic generation of multiple wavelength fiber laser output using parallel channels [...] Read more.

Multiple wavelength light sources in the medical spectral window region are useful for various medical sensing applications in tissue by distinguishing the absorption and scattering coefficients optically. We propose a simultaneous second harmonic generation of multiple wavelength fiber laser output using parallel channels of periodically-poled lithium niobate (PPLN) waveguides. High intensity dual wavelength lasing output is experimentally realized with two tunable fiber Bragg gratings of 1,547.20 nm and 1,554.48 nm for the efficient conversion to the half wavelengths, 773.60 nm and 777.24 nm, by using two parallel PPLN channels. Compared with a conventional dual second harmonic generation (SHG) configuration based on two different input wavelengths from each independent light source, this method has a relatively higher efficiency to align the input light beam into the adjacent parallel PPLN channels simultaneously. The use of fiber lasers offers several advantages since they are relatively inexpensive, provide high power in excess of tens of watts, are widely tunable, and can produce pulses from milliseconds to femtoseconds. Full article

(This article belongs to the Section Physical Sensors)

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192 KiB

Open AccessArticle

Optimization of NIR Spectral Data Management for Quality Control of Grape Bunches during On-Vine Ripening

by Virginia González-Caballero, Dolores Pérez-Marín, María-Isabel López and María-Teresa Sánchez

Sensors 2011, 11(6), 6109-6124; https://doi.org/10.3390/s110606109 - 7 Jun 2011

Cited by 47 | Viewed by 10634

Abstract

NIR spectroscopy was used as a non-destructive technique for the assessment of chemical changes in the main internal quality properties of wine grapes (Vitis vinifera L.) during on-vine ripening and at harvest. A total of 363 samples from 25 white and red [...] Read more.

NIR spectroscopy was used as a non-destructive technique for the assessment of chemical changes in the main internal quality properties of wine grapes (Vitis vinifera L.) during on-vine ripening and at harvest. A total of 363 samples from 25 white and red grape varieties were used to construct quality-prediction models based on reference data and on NIR spectral data obtained using a commercially-available diode-array spectrophotometer (380–1,700 nm). The feasibility of testing bunches of intact grapes was investigated and compared with the more traditional must-based method. Two regression approaches (MPLS and LOCAL algorithms) were tested for the quantification of changes in soluble solid content (SSC), reducing sugar content, pH-value, titratable acidity, tartaric acid, malic acid and potassium content. Cross-validation results indicated that NIRS technology provided excellent precision for sugar-related parameters (r² = 0.94 for SSC and reducing sugar content) and good precision for acidity-related parameters (r² ranging between 0.73 and 0.87) for the bunch-analysis mode assayed using MPLS regression. At validation level, comparison of LOCAL and MPLS algorithms showed that the non-linear strategy improved the predictive capacity of the models for all study parameters, with particularly good results for acidity-related parameters and potassium content. Full article

(This article belongs to the Section Chemical Sensors)

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1246 KiB

Open AccessArticle

An Air-Ground Wireless Sensor Network for Crop Monitoring

by João Valente, David Sanz, Antonio Barrientos, Jaime del Cerro, Ángela Ribeiro and Claudio Rossi

Sensors 2011, 11(6), 6088-6108; https://doi.org/10.3390/s110606088 - 7 Jun 2011

Cited by 146 | Viewed by 18415

Abstract

This paper presents a collaborative system made up of a Wireless Sensor Network (WSN) and an aerial robot, which is applied to real-time frost monitoring in vineyards. The core feature of our system is a dynamic mobile node carried by an aerial robot, [...] Read more.

This paper presents a collaborative system made up of a Wireless Sensor Network (WSN) and an aerial robot, which is applied to real-time frost monitoring in vineyards. The core feature of our system is a dynamic mobile node carried by an aerial robot, which ensures communication between sparse clusters located at fragmented parcels and a base station. This system overcomes some limitations of the wireless networks in areas with such characteristics. The use of a dedicated communication channel enables data routing to/from unlimited distances. Full article

(This article belongs to the Special Issue Sensors in Agriculture and Forestry)

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502 KiB

Open AccessArticle

A General Analysis of the Impact of Digitization in Microwave Correlation Radiometers

by Xavier Bosch-Lluis, Isaac Ramos-Perez, Adriano Camps, Nereida Rodriguez-Alvarez, Enric Valencia and Hyuk Park

Sensors 2011, 11(6), 6066-6087; https://doi.org/10.3390/s110606066 - 3 Jun 2011

Cited by 15 | Viewed by 7664

Abstract

This study provides a general framework to analyze the effects on correlation radiometers of a generic quantization scheme and sampling process. It reviews, unifies and expands several previous works that focused on these effects separately. In addition, it provides a general theoretical background [...] Read more.

This study provides a general framework to analyze the effects on correlation radiometers of a generic quantization scheme and sampling process. It reviews, unifies and expands several previous works that focused on these effects separately. In addition, it provides a general theoretical background that allows analyzing any digitization scheme including any number of quantization levels, irregular quantization steps, gain compression, clipping, jitter and skew effects of the sampling period. Full article

(This article belongs to the Section Remote Sensors)

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418 KiB

Open AccessArticle

Probabilistic Dynamic Deployment of Wireless Sensor Networks by Artificial Bee Colony Algorithm

by Celal Ozturk, Dervis Karaboga and Beyza Gorkemli

Sensors 2011, 11(6), 6056-6065; https://doi.org/10.3390/s110606056 - 3 Jun 2011

Cited by 163 | Viewed by 10388

Abstract

As the usage and development of wireless sensor networks are increasing, the problems related to these networks are being realized. Dynamic deployment is one of the main topics that directly affect the performance of the wireless sensor networks. In this paper, the artificial [...] Read more.

As the usage and development of wireless sensor networks are increasing, the problems related to these networks are being realized. Dynamic deployment is one of the main topics that directly affect the performance of the wireless sensor networks. In this paper, the artificial bee colony algorithm is applied to the dynamic deployment of stationary and mobile sensor networks to achieve better performance by trying to increase the coverage area of the network. A probabilistic detection model is considered to obtain more realistic results while computing the effectively covered area. Performance of the algorithm is compared with that of the particle swarm optimization algorithm, which is also a swarm based optimization technique and formerly used in wireless sensor network deployment. Results show artificial bee colony algorithm can be preferable in the dynamic deployment of wireless sensor networks. Full article

(This article belongs to the Section Physical Sensors)

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696 KiB

Open AccessArticle

Use of Mobile Phones as Intelligent Sensors for Sound Input Analysis and Sleep State Detection

by Ondrej Krejcar, Jakub Jirka and Dalibor Janckulik

Sensors 2011, 11(6), 6037-6055; https://doi.org/10.3390/s110606037 - 3 Jun 2011

Cited by 69 | Viewed by 13583

Abstract

Sleep is not just a passive process, but rather a highly dynamic process that is terminated by waking up. Throughout the night a specific number of sleep stages that are repeatedly changing in various periods of time take place. These specific time intervals [...] Read more.

Sleep is not just a passive process, but rather a highly dynamic process that is terminated by waking up. Throughout the night a specific number of sleep stages that are repeatedly changing in various periods of time take place. These specific time intervals and specific sleep stages are very important for the wake up event. It is far more difficult to wake up during the deep NREM (2–4) stage of sleep because the rest of the body is still sleeping. On the other hand if we wake up during the mild (REM, NREM1) sleep stage it is a much more pleasant experience for us and for our bodies. This problem led the authors to undertake this study and develop a Windows Mobile-based device application called wakeNsmile. The wakeNsmile application records and monitors the sleep stages for specific amounts of time before a desired alarm time set by users. It uses a built-in microphone and determines the optimal time to wake the user up. Hence, if the user sets an alarm in wakeNsmile to 7:00 and wakeNsmile detects that a more appropriate time to wake up (REM stage) is at 6:50, the alarm will start at 6:50. The current availability and low price of mobile devices is yet another reason to use and develop such an application that will hopefully help someone to wakeNsmile in the morning. So far, the wakeNsmile application has been tested on four individuals introduced in the final section. Full article

(This article belongs to the Section Physical Sensors)

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987 KiB

Open AccessArticle

Digital Image Sensor-Based Assessment of the Status of Oat (Avena sativa L.) Crops after Frost Damage

by Antonia Macedo-Cruz, Gonzalo Pajares, Matilde Santos and Isidro Villegas-Romero

Sensors 2011, 11(6), 6015-6036; https://doi.org/10.3390/s110606015 - 3 Jun 2011

Cited by 47 | Viewed by 11496

Abstract

The aim of this paper is to classify the land covered with oat crops, and the quantification of frost damage on oats, while plants are still in the flowering stage. The images are taken by a digital colour camera CCD-based sensor. Unsupervised classification [...] Read more.

The aim of this paper is to classify the land covered with oat crops, and the quantification of frost damage on oats, while plants are still in the flowering stage. The images are taken by a digital colour camera CCD-based sensor. Unsupervised classification methods are applied because the plants present different spectral signatures, depending on two main factors: illumination and the affected state. The colour space used in this application is CIELab, based on the decomposition of the colour in three channels, because it is the closest to human colour perception. The histogram of each channel is successively split into regions by thresholding. The best threshold to be applied is automatically obtained as a combination of three thresholding strategies: (a) Otsu’s method, (b) Isodata algorithm, and (c) Fuzzy thresholding. The fusion of these automatic thresholding techniques and the design of the classification strategy are some of the main findings of the paper, which allows an estimation of the damages and a prediction of the oat production. Full article

(This article belongs to the Special Issue Sensors in Agriculture and Forestry)

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2974 KiB

Open AccessArticle

Terahertz Active Photonic Crystals for Condensed Gas Sensing

by Alexander Benz, Christoph Deutsch, Martin Brandstetter, Aaron M. Andrews, Pavel Klang, Hermann Detz, Werner Schrenk, Gottfried Strasser and Karl Unterrainer

Sensors 2011, 11(6), 6003-6014; https://doi.org/10.3390/s110606003 - 3 Jun 2011

Cited by 37 | Viewed by 10039

Abstract

The terahertz (THz) spectral region, covering frequencies from 1 to 10 THz, is highly interesting for chemical sensing. The energy of rotational and vibrational transitions of molecules lies within this frequency range. Therefore, chemical fingerprints can be derived, allowing for a simple detection [...] Read more.

The terahertz (THz) spectral region, covering frequencies from 1 to 10 THz, is highly interesting for chemical sensing. The energy of rotational and vibrational transitions of molecules lies within this frequency range. Therefore, chemical fingerprints can be derived, allowing for a simple detection scheme. Here, we present an optical sensor based on active photonic crystals (PhCs), i.e., the pillars are fabricated directly from an active THz quantum-cascade laser medium. The individual pillars are pumped electrically leading to laser emission at cryogenic temperatures. There is no need to couple light into the resonant structure because the PhC itself is used as the light source. An injected gas changes the resonance condition of the PhC and thereby the laser emission frequency. We achieve an experimental frequency shift of 10⁻³ times the center lasing frequency. The minimum detectable refractive index change is 1.6 × 10⁻⁵ RIU. Full article

(This article belongs to the Section Physical Sensors)

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Sensors, Volume 11, Issue 6 (June 2011) – 57 articles , Pages 5529-6493

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