Browsing by Subject "Sensors"

Now showing 1 - 20 of 77

Open Access
50 nm Hall Sensors for Room Temperature Scanning Hall Probe Microscopy
(Institute of Physics Publishing, 2004) Sandhu, A.; Kurosawa, K.; Dede, M.; Oral, A.
Bismuth nano-Hall sensors with dimensions ∼50nm × 50 nm were fabricated using a combination of optical lithography and focused ion beam milling. The Hall coefficient, series resistance and optimum magnetic field sensitivity of the sensors were 4 × 10-4 Ω/G, 9.1kΩ and 0.8G/√Hz, respectively. A 50nm nano-Bi Hall sensor was installed into a room temperature scanning Hall probe microscope and successfully used for directly imaging ferromagnetic domains of low coercivity garnet thin films.
Open Access
Adaptive decision fusion based cooperative spectrum sensing for cognitive radio systems
(IEEE, 2011) Töreyin, B. U.; Yarkan, S.; Qaraqe, K. A.; Çetin, A. Enis
In this paper, an online Adaptive Decision Fusion (ADF) framework is proposed for the central spectrum awareness engine of a spectrum sensor network in Cognitive Radio (CR) systems. Online learning approaches are powerful tools for problems where drifts in concepts take place. Cooperative spectrum sensing in cognitive radio networks is such a problem where channel characteristics and utilization patterns change frequently. The importance of this problem stems from the requirement that secondary users must adjust their frequency utilization strategies in such a way that the communication performance of the primary users would not be degraded by any means. In the proposed framework, sensing values from several sensor nodes are fused together by weighted linear combination at the central spectrum awareness engine. The weights are updated on-line according to an active fusion method based on performing orthogonal projections onto convex sets describing power reading values from each sensor. The proposed adaptive fusion strategy for cooperative spectrum sensing can operate independent from the channel type between the primary user and secondary users. Results of simulations and experiments for the proposed method conducted in laboratory are also presented. © 2011 IEEE.
Open Access
Bluetooth or 802.15.4 technologies to optimise lifetime of wireless sensor networks: Numerical comparison under a common framework
(IEEE, 2008-04) Buratti, C.; Körpeoğlu, İbrahim; Karasan, Ezhan; Verdone, R.
This paper aims at comparing through simulations the network lifetime of a wireless sensor network using Bluetooth-enabled or IEEE802.15.4 compliant devices. The evaluation is performed under a common reference framework, namely the EMORANS scenario for wireless sensor networks. Since the two enabling technologies rely on different MAC paradigms, suitable definition of the performance metrics is needed, in order to make the comparison meaningful. Thus, the paper has also a methodological objective. In particular, three different definitions of network lifetime are introduced, and a comparison of performance obtained by applying the different definitions is provided. Then, the comparison between the two standards is introduced: it is shown that there are no orders of magnitude of difference in network lifetime when the two technologies are used and the choice of the technology depends on the application requirements.
Open Access
Circular high-Q resonating isotropic strain sensors with large shift of resonance frequency under stress
(2009) Melik, R.; Unal, E.; Perkgoz, N.K.; Puttlitz, C.; Demir, Hilmi Volkan
We present circular architecture bioimplant strain sensors that facilitate a strong resonance frequency shift with mechanical deformation. The clinical application area of these sensors is for in vivo assessment of bone fractures. Using a rectangular geometry, we obtain a resonance shift of 330 MHz for a single device and 170 MHz for its triplet configuration (with three side-by-side resonators on chip) under an applied load of 3,920 N. Using the same device parameters with a circular isotropic architecture, we achieve a resonance frequency shift of 500 MHz for the single device and 260 MHz for its triplet configuration, demonstrating substantially increased sensitivity. © 2009 by the authors.
Open Access
Colloidal photoluminescent refractive index nanosensor using plasmonic effects
(De Gruyter, 2018) Guzatov, D. V.; Gaponenko, S. V.; Demir, Hilmi Volkan
Fluorescence enhancement by metal nanostructures which is sensitive to refractive index n of an ambient medium is suggested as an operation principle of a novel refractive index sensor for liquids. Calculations are made for spherical and spheroidal Ag particles, and potential feasibility of sensitivity of the order of Δn=10-4 is demonstrated. Sensors of this type can be made fully colloidal with metal bodies deposited on a substrate or comprising a metal layer covering colloidal assembly of dielectric particles to serve as a test strip as well as placed on a fiber tip end to get local probing of refractive index in the tip-enhanced refractometry mode. Colloidal core-shell semiconductor nanocrystals may become the best candidates for this type of sensors whereas molecular probes may be affected by chemical properties of tested liquids.
Open Access
Combined component swapping modularity for a VCT engine controller
(ASME, 2010) Çakmakcı, Melih; Ulsoy, A.G.
The use of bi-directional communication provides additional design freedom which can be used to maximize the swapping modularity of networked smart components. In this paper, application of a design method for combined swapping modularity of two or more system components is discussed. Development of measures for combined swapping modularity is important to be able to analyze more realistic engineering cases. The combined modularity problem is a more difficult problem compared to the individual component swapping modularity problem. First, two approaches (simultaneous and sequential) for combining component swapping modularity of two or more components are presented. Then these combined modularity approaches are used to design controllers which maximize the component-swapping modularity of the Variable Camshaft Timing (VCT) component (i.e. actuator and sensor) and the Exhaust Gas Oxygen (EGO) sensor for an internal combustion engine. Copyright © 2009 by ASME.
Open Access
A comparative study of map building techniques by processing sonar arc-maps
(2005) Kurt, Arda; Barshan, Billur
In this study, four signal processing schemes regarding sonar sensor based map-building applications were compared. The newly proposed method, Directional Maximum is found to be successful in terms of reducing the innate angular ambiguity of the sonar sensors. With respect to several works presented earlier in the same field and specifically map-building related studies, the new method is successful both in terms of mean absolute error and computational cost.
Open Access
Comparison of the CAF-DF and sage algorithms in multipath channel parameter estimation
(IEEE, 2008-07) Güldoğan, M. Burak; Arıkan, Orhan
In this paper, performance of the recently proposed Cross Ambiguity Function - Direction Finding (CAF-DF) technique is compared with the Space Alternating Generalized Expectation Maximization (SAGE) technique. The CAF-DF, iteratively estimates direction of arrival (DOA), time-delay, Doppler shift and amplitude corresponding to each impinging signal onto an antenna array by utilizing the cross ambiguity function. On synthetic signals, based on Monte Carlo trials, performances of the algoritms are tested in terms of root Mean Squared Error (rMSE) at different Signal-to-Noise Ratios (SNR). Cramer-Rao lower bound is included for statistical comparisons. Simulation results indicate the superior performance of the CAF-DF technique over SAGE technique for low and medium SNR values. © 2008 IEEE.
Open Access
A comparison of two methods for fusing information from a linear array of sonar sensors for obstacle localization
(IEEE, 1995) Arıkan, Orhan; Barshan, Billur
The performance of a commonly employed linear array of sonar sensors is assessed for point-obstacle localization intended for robotics applications. Two different methods of combining time-of-flight information from the sensors are described to estimate the range and azimuth of the obstacle: pairwise estimate method and the maximum likelihood estimator. The variances of the methods are compared to the Cramer-Rao Lower Bound, and their biases are investigated. Simulation studies indicate that in estimating range, both methods perform comparably; in estimating azimuth, maximum likelihood estimate is superior at a cost of extra computation. The results are useful for target localization in mobile robotics.
Open Access
Compressed sensing on ambiguity function domain for high resolution detection
(IEEE, 2010) Güldoǧan, Mehmet B.; Pilancı, Mert; Arıkan, Orhan
In this paper, by using compressed sensing techniques, a new approach to achieve robust high resolution detection in sparse multipath channels is presented. Currently used sparse reconstruction techniques are not immediately applicable in wireless channel modeling and radar signal processing. Here, we make use of the cross-ambiguity function (CAF) and transformed the reconstruction problem from time to delay-Doppler domain for efficient exploitation of the delay-Doppler diversity of the multipath components. Simulation results quantify the performance gain and robustness obtained by this new CAF based compressed sensing approach. ©2010 IEEE.
Open Access
Developing a transducer based on localized surface plasmon resonance (LSPR) of gold nanostructures for nanobiosensor applications
(Trans Tech Publications, 2013) Turhan, Adil Burak; Ataman, D.; Çakmakyapan, S.; Mutlu, M.; Özbay, Ekmel; Vlachos, D. S.; Hristoforou, E.
In this work, we report the nanofabrication, optical characterization, and electromagnetic modeling of various nanostructure arrays for localized surface plasmon resonance (LSPR) based biosensing studies. Comparison of the experimental results and simulation outputs of various nanostructure arrays was made and a good correspondence was achieved.
Open Access
Diferansiyel PIR algılayıcılarla dalgacık tabanlı alev tespiti
(IEEE, 2012-04) Erden, F.; Töreyin, B. U.; Soyer, E. B.; İnaç, İ.; Günay, O.; Köse, K.; Çetin, A. Enis
Bu makalede, diferansiyel kızılberisi algılayıcı (PIR) kullanılarak geliştirilen bir alev tespit sistemi önerilmektedir. Diferansiyel kızılberisi algılayıcılar, yalnızca görüş alanlarındaki ani sıcaklık değişikliklerine duyarlıdır ve zamanla değişen sinyaller üretir. Algılayıcı sinyaline ait dalgacık dönüşümü, öznitelik çıkarmak için kullanılır ve bu öznitelik vektörü hızlı titreşen kontrolsüz bir ateşin alevi ve bir kişinin yürümesi olaylarıyla eğitilmiş Markov modellerine sokulur. En yüksek olasılıkla sonuçlanan modele karar verilir. Karşılaştırmalı sonuçlar, sistemin geniş odalarda ateş tespiti için kullanılabileceğini düşündürmektedir.
Open Access
Direct magnetic imaging of ferromagnetic domain structures by room temperature scanning hall probe microscopy using a bismuth micro-Hall probe
(Japan Society of Applied Physics, 2001) Sandhu, A.; Masuda, H.; Oral, A.; Bending, S. J.
A bismuth micro-Hall probe sensor with an integrated scanning tunnelling microscope tip was incorporated into a room temperature scanning Hall probe microscope system and successfully used for the direct magnetic imaging of microscopic domains of low coercivity perpendicular garnet thin films and demagnetized strontium ferrite permanent magnets. At a driving current of 800 μA, the Hall coefficient, magnetic field sensitivity and spatial resolution of the Bi probe were 3.3 × 10-4 Ω/G, 0.38 G/√Hz and ∼ 2.8 μm, respectively. The room temperature magnetic field sensitivity of the Bi probe was comparable to that of a semiconducting 1.2μm GaAs/AlGaAs heterostructure micro-Hall probe, which exhibited a value of 0.41 G/√Hz at a maximum driving current of 2μA.
Open Access
Dual integrated actuators for extended range high speed atomic force microscopy
(A I P Publishing LLC, 1999-09-13) Sulchek, T.; Minne, S. C.; Adams, J. D.; Fletcher, D. A.; Atalar, Abdullah; Quate, C. F.; Adderton, D. M.
A flexible system for increasing the throughput of the atomic force microscope without sacrificing imaging range is presented. The system is based on a nested feedback loop which controls a micromachined cantilever that contains both an integrated piezoelectric actuator and an integrated thermal actuator. This combination enables high speed imaging (2 mm/s) over an extended range by utilizing the piezoelectric actuator’s high bandwidth (15 kHz) and thermal actuator’s large response (300 nm/V). A constant force image, where the sample topography exceeds the range of the piezoelectric actuator alone, is presented. It has also been demonstrated that the deflection response of the thermal actuator can be linearized and controlled with an integrated diode.
Open Access
Electrospinning combined with atomic layer deposition to generate applied nanomaterials: A review
(American Chemical Society, 2020) Vempati, S.; Ranjith, K. S.; Topuz, Fuat; Bıyıklı, Necmi; Uyar, Tamer
Combining different material processing techniques is one of the keys to obtain materials that depict synergistic properties. In this review, we have reviewed a combination of two highly potential techniques, namely, electrospinning and atomic layer deposition (ALD), in the view of various applications. Over the past 10 years, our research groups are involved in the exploration of employing this combination for a range of applications. We also include some basic information on both the processes and diversity of nanostructures as a result of their combination. Nonwoven nanofiber membranes are excellent candidates for a wide range of applications. Also, they can act as templates to produce various other kinds of nanostructures when combined with ALD in small/large scale production. These nanostructures could be used as such or further subjected to other processing techniques yielding hierarchical structures. In this review, we exclusively survey and highlight the unique capabilities of combined electrospinning and ALD for applications in catalysis, photocatalysis, solar cells, batteries and gas sensors.
Open Access
An energy efficient scatternet formation algorithm for Bluetooth-based sensor networks
(IEEE, 2005-02) Saginbekov, Sain; Körpeoğlu, İbrahim
In this paper, we propose an energy-efficient scatternet formation algorithm for Bluetooth based sensor networks. The algorithm is based on first computing a shortest path tree from the base station to all sensor nodes and then solving the degree constraint problem so that the degree of each node in the network is not greater than seven, which is a Bluetooth constaint. In this way, less amount of energy is spent in each round of communication in the sensor network. The algorithm also tries to balance the load evenly on the high-energy consuming nodes which are the nodes that are close to the base station. In this way, the lifetime of the first dying node is also prolonged. We obtained promising results in the simulations. © 2005 IEEE.
Open Access
Escaping local optima in a class of multi-agent distributed optimization problems: a boosting function approach
(IEEE, 2014) Sun, X.; Cassandras, C. G.; Gökbayrak, Kaan
We address the problem of multiple local optima commonly arising in optimization problems for multi-agent systems, where objective functions are nonlinear and nonconvex. For the class of coverage control problems, we propose a systematic approach for escaping a local optimum, rather than randomly perturbing controllable variables away from it. We show that the objective function for these problems can be decomposed to facilitate the evaluation of the local partial derivative of each node in the system and to provide insights into its structure. This structure is exploited by defining 'boosting functions' applied to the aforementioned local partial derivative at an equilibrium point where its value is zero so as to transform it in a way that induces nodes to explore poorly covered areas of the mission space until a new equilibrium point is reached. The proposed boosting process ensures that, at its conclusion, the objective function is no worse than its pre-boosting value. However, the global optima cannot be guaranteed. We define three families of boosting functions with different properties and provide simulation results illustrating how this approach improves the solutions obtained for this class of distributed optimization problems.
Open Access
An experimental setup for performance analysis of an online adaptive cooperative spectrum sensing scheme for both in-phase and quadrature branches
(IEEE, 2011) Yarkan, S.; Qaraqe, K.A.; Töreyin, B.U.; Çetin, A. Enis
Spectrum sensing is one of the most essential characteristics of cognitive radios (CRs). Robustness and adaptation to varying wireless propagation scenarios without compromising the sensing accuracy are desirable features of any spectrum sensing method to be deployed in CR systems. In this study, an online adaptive cooperation technique for spectrum sensing is proposed in order to maintain the level of reliability and performance. Cooperation is achieved by sensors which employ energy detection. These sensors send their output to a center where data fusion operation is carried out in an online and adaptive manner. Adaptation is realized by the use of orthogonal projections onto convex sets (POCS). In conjunction with the proposed method, an end-to-end methodology for a flexible experimental setup is also proposed in this study. This setup is arranged to emulate the proposed adaptive cooperation scheme for spectrum sensing and validate its practical use in cognitive radio systems. Comparative performance results for both inphase and quadrature branches are presented. © 2011 IEEE.
Open Access
Fall detection using single-tree complex wavelet transform
(Elsevier, 2013) Yazar, A.; Keskin, F.; Töreyin, B. U.; Çetin, A. Enis
The goal of Ambient Assisted Living (AAL) research is to improve the quality of life of the elderly and handicapped people and help them maintain an independent lifestyle with the use of sensors, signal processing and telecommunications infrastructure. Unusual human activity detection such as fall detection has important applications. In this paper, a fall detection algorithm for a low cost AAL system using vibration and passive infrared (PIR) sensors is proposed. The single-tree complex wavelet transform (ST-CWT) is used for feature extraction from vibration sensor signal. The proposed feature extraction scheme is compared to discrete Fourier transform and mel-frequency cepstrum coefficients based feature extraction methods. Vibration signal features are classified into "fall" and "ordinary activity" classes using Euclidean distance, Mahalanobis distance, and support vector machine (SVM) classifiers, and they are compared to each other. The PIR sensor is used for the detection of a moving person in a region of interest. The proposed system works in real-time on a standard personal computer.
Open Access
Fizik tedavi egzersizlerinin giyilebilir hareket algılayıcıları işaretlerinden dinamik zaman bükmesiyle sezimi ve değerlendirilmesi
(IEEE, 2014-04) Yurtman, Aras; Barshan, Billur
Giyilebilir hareket algılayıcılarından kaydedilen sinyalleri işleyerek fizik tedavi egzersizlerini algılamak ve değerlendirmek için özerk bir sistem geliştirilmiştir. Bir fizik tedavi seansındaki bir ya da birden fazla egzersiz tipini algılamak için, temeli dinamik zaman bükmesi (DZB) benzeşmezlik ölçütüne dayanan bir algoritma geliştirilmiştir. Algoritma, egzersizlerin doğru ya da yanlış yapıldığını değerlendirmekte ve varsa hata türünü saptamaktadır. Algoritmanın başarımını degerlendirmek için, beş katılımcı tarafından yapılan sekiz egzersiz hareketinin üç yürütüm türü için birer şablon ve 10’ar sınama yürütümünden oluşan bir veri kümesi kaydedilmiştir. Dolayısıyla, eğitim ve sınama kümelerinde sırasıyla 120 ve 1,200 egzersiz yürütümü bulunmaktadır. Sınama kümesi, boş zaman dilimleri de içermektedir. Öne sürülen algoritma, sınama kümesindeki 1,200 yürütümün % 8.58’ini kaçırmakta ve boş zaman dilimlerinin % 4.91’ini yanlış sezim olarak değerlendirerek toplam 1,125 yürütüm algılamaktadır. Doğruluk, sadece egzersiz sınıflandırması ele alındığında ˘ % 93.46, hem egzersiz hem de yürütüm türü sınıflandırması içinse % 88.65’tir. Sistemin bilinmeyen egzersizlere karşı davranışını sınamak için, algoritma, her egzersiz için, o egzersizin şablonları dışarıda bırakılarak çalıştırılmış ve 1,200 egzersizin sadece 10’u yanlış sezilmiştir. Bu sonuç, sistemin bilinmeyen hareketlere karşı gürbüz olduğunu göstermektedir. Öne sürülen sistem, hem bir fizik tedavi seansının yoğunluğunu kestirmek, hem de hastaya ve fizik tedavi uzmanına geribildirim vermek amacıyla egzersiz hareketlerini değerlendirmek için kullanılabilir.