Sound focusing by gradient index sonic lenses

Gradient index sonic lenses based on two-dimensional sonic crystals are here designed, fabricated and characterized. The index-gradient is achieved in these type of flat lenses by a gradual modification of the sonic crystal filling fraction along the direction perpendicular to the lens axis. The focusing performance is well described by an analytical model based on ray theory as well as by numerical simulations based on the multiple-scattering theory.Comment: 4 pages, 4 figure

Refractive devices for acoustical and flexural waves

The aim of this work has been the design and demonstration of refractive devices, not only for acoustic waves, but also for flexural waves in thin plates. Mathematically these problems have been treated by means of the multiple scattering theory, because the geometries of the problems were mainly circular and such theory is the best one in these cases. The multiple scattering theory, previously stated, is here explained. Additionally, a multilayer scattering theory for flexural waves is here introduced and successfully used to numerically simulate their behavior. Therefore, this PhD thesis is divided in two parts. The first part is devoted to describe two acoustic refractive devices: a gradient index lens and an omnidirectional broadband acoustic absorber, or “acoustic black hole”. Both are based on sonic crystals consisting of of rigid cylinders immersed in a fluid background. As the homogenization method states, the desired refractive index can be obtained by tailoring the radii of the cylinders. Thereafter, numerical simulations and measurements were conducted to test the behavior of each device. For this purpose, two specific measuring systems were developed: the two-dimensional chamber and the impedance chamber. Both are here explained in detail. The second part describes the design of refractive devices for flexural waves. Instead of using “platonic crystals”, we made use of the peculiar dispersion relationship of flexural waves. As the equation states, the wave speed is modified not only by the elastic properties of the plate, but also from its thickness. Using the latest approach a set of numerical simulations of known circularly symmetrical gradient index lenses have been performed. Additionally, an omnidirectional broadband insulating device for flexural waves has been designed. It consist of a well-like thickness profile in an annular region of the plate, that mimics the combination of an attractive and repulsive potentials. The waves are focused at its bottom and dissipated by means of an absorptive layer placed on top. Numerical simulations are here presented and discussed. Finally, we present an in-plane flexural resonator, consisting of a hole in a thin plate traversed by a beam. Here, a closed form of the transfer matrix is obtained by coupling the Kirchhoff-Love and the Euler-Bernoulli motion equations. Numerical simulations, tested against a commercial finite element simulator, prove its efficiencyClimente Alarcón, A. (2015). Refractive devices for acoustical and flexural waves [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/48536TESI

Analysis of flexural wave cloaks

This work presents a comprehensive study of the cloak for bending waves theoretically proposed by Farhat et al. [see Phys. Rev. Lett. 103, 024301 (2009)] and later on experimentally realized by Stenger et al. [see Phys. Rev. Lett. 108, 014301 (2012)]. This study uses a semi-analytical approach, the multilayer scattering method, which is based in the Kirchoff-Love wave equation for flexural waves in thin plates. Our approach was unable to reproduce the predicted behavior of the theoretically proposed cloak. This disagreement is here explained in terms of the simplified wave equation employed in the cloak design, which employed unusual boundary conditions for the cloaking shell. However, our approach reproduces fairly well the measured displacement maps for the fabricated cloak, indicating the validity of our approach. Also, the cloak quality has been here analyzed using the so called averaged visibility and the scattering cross section. The results obtained from both analysis let us to conclude that there is room for further improvements of this type of flexural wave cloak by using better design procedures. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).This work has been supported by the Spanish Ministerio de Economia y Competitividad and the European Union Fondo Europeo para el Desarrollo Regional (FEDER) under Grant with Ref. TEC2014-53088-C3-1-R. We gratefully acknowledge Nicolas Stenger for providing us the parameters listed in Table I.Climente Alarcón, A.; Torrent Martí, D.; Sánchez-Dehesa Moreno-Cid, J. (2016). Analysis of flexural wave cloaks. AIP Advances. 6(12):121704-1-121705-16. https://doi.org/10.1063/1.4968611S121704-1121705-1661

Single-phase metamaterial plates for broadband vibration suppression at low frequencies

[EN] By studying platonic crystals based on lattices of cavities containing N-beam resonators, we conclude that crystals made of 1-beam resonators easily produce low-frequency omnidirectional bandgaps. Based on this favorable property, hardly obtained for resonant cavities containing a higher number of beams N >= 2, we have designed single-phase metamaterial plates for the suppression of low frequency flexural waves in a broad range of frequencies. These metamaterials are obtained by using resonant cavities containing a multiple number M of identical 1-beam resonators uniformly distributed in the cavity. Square lattices of this type of resonators have been studied by using the impedance matrix approach and the multiple scattering method. This semi-analytical method has been employed to show the existence of complete bandgaps whose width can be optimized by increasing M. For the case M = 4, the largest number of resonators studied here, three complete bandgaps separated by two narrow passbands appear in the band structure. The formation of these complete bandgaps originates from the dynamic interaction between different local resonators as well as their interaction with the propagating waves in the host plate. By using composite structures consisting of platonic crystal slabs with complementary bandgaps, these separated bandgaps easily merge into a broadband wave attenuation region. The normalized width, defined as the percentage of the bandwidth to its central frequency, reaches 95.3%, representing an enhancement of about one order of magnitude compared with the absolute bandwidth obtained for the case of a single 1-beam resonator in the cavity. It is shown that the gaps can be easily tuned to lower frequencies by changing the geometrical parameters, such as the length of the beam, the radius and thickness of the smaller circular plate. Since the metamaterial is made of a single-phase material without attaching heavy masses, the work reported here provides a simple approach to construct low-cost structures with potential applications in aeronautic and astronautic industries for broadband vibration suppression at low frequencies. (C) 2018 Published by Elsevier Ltd.This work was supported by the Ministerio de Economia y Competitividad of the Spanish government and the European Union Fondo Europeo de Desarrollo Regional (FEDER) [Grant No. TEC2014-53088-C3-1-R], and the National Natural Science Foundation of China [Grant Nos. 11432004 and 11421091]. Penglin Gao acknowledges a scholarship provided by China Scholarship Council [Grant No. 201606120070].Gao, P.; Climente Alarcón, A.; Sánchez-Dehesa Moreno-Cid, J.; Wu, L. (2019). Single-phase metamaterial plates for broadband vibration suppression at low frequencies. Journal of Sound and Vibration. 444:108-126. https://doi.org/10.1016/j.jsv.2018.12.022S10812644

Theoretical study of platonic crystals with periodically structured N-beam resonators

[EN] A multiple scattering theory is applied to study the properties of flexural waves propagating in a plate with periodically structured N-beam resonators. Each resonator consists of a circular hole containing an inner disk connected to background plate with N rectangular beams. The Bloch theorem is employed to obtain the band structure of a two-dimensional lattice containing a single resonator per unit cell. Also, a numerical algorithm has been developed to get the transmittance through resonator slabs infinitely long in the direction perpendicular to the incident wave. For the numerical validation, a square lattice of 2-beam resonators has been comprehensively analyzed. Its band structure exhibits several flat bands, indicating the existence of local resonances embedded in the structure. Particularly, the one featured as the fundamental mode of the inner disk opens a bandgap at low frequencies. This mode has been fully described in terms of a simple spring-mass model. As a practical application of the results obtained, a homogenization approach has been employed to design a focusing lens for flexural waves, where the index gradient is obtained by adjusting the orientation of the resonators beams. Numerical experiments performed within the framework of a three-dimensional finite element method have been employed to discuss the accuracy of the models described here. Published by AIP Publishing.This work was supported by the Ministerio de Economia y Competitividad of the Spanish government and the European Union Fondo Europeo de Desarrollo Regional (FEDER) through Project No. TEC2014-53088-C3-1-R, and the National Science Foundation of China under Grant No. 11432004. Penglin Gao acknowledges a scholarship with No. 201606120070 provided by China Scholarship Council.Gao, P.; Climente Alarcón, A.; Sánchez-Dehesa Moreno-Cid, J.; Wu, L. (2018). Theoretical study of platonic crystals with periodically structured N-beam resonators. Journal of Applied Physics. 123(9). https://doi.org/10.1063/1.5009170S123

Recent Educational Experiences in Electric Machine Maintenance Teaching

[EN] Maintenance of electric machines and installations is a particularly important area; eventual faults in these devices may lead to significant losses in terms of time and money. The investment and concern in developing proper maintenance protocols have been gradually increasing over recent decades. As a consequence, there is a need to instruct future engineers in the electric machines and installations maintenance area. The subject ¿Maintenance of Electric Machines and Installations¿ has been designed under this idea. It is taught within an official master degree in Maintenance Engineering. This work describes the educational experiences reached during the initial years of the teaching of the subject. Aspects such as student profiles, subject approaches, design of the syllabus, methodology and structure of the laboratory sessions are remarked in the work. In addition, the paper discusses other educational strategies which are being introduced to increase the interest in the subject, such as integration of Information and Communication Technologies (ICT), promotion of the collaborative work, inclusion of the possibility of remote learning or development of new assessment systems.This work was supported by the Conselleria d’Educació, Formació i Ocupació of the Generalitat Valenciana, in the framework of the ‘‘Ayudas para la Realización de Proyectos de I+D para Grupos de Investigación Emergentes’’, project reference GV/2012/020.Antonino Daviu, JA.; Pons Llinares, J.; Climente Alarcón, V. (2013). Recent Educational Experiences in Electric Machine Maintenance Teaching. International Journal of Engineering Pedagogy. 3(3):21-26. https://doi.org/10.3991/ijep.v3iS3.2742S21263

Gradient index lenses for flexural waves based on thickness variations

Copyright (2014) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics along with the following message: The following article appeared in Applied Physics Letters 105, (6) and may be found at http://dx.doi.org/10.1063/1.4893153. Authors own version of final article on e-print serversThis work presents a method for the realization of gradient index devices for flexural waves in thin plates. Unlike recent approaches based on phononic crystals, the present approach is based on the thickness-dependence of the dispersion relation of flexural waves, which is used to create gradient index devices by means of local variations of the plate's thickness. Numerical simulations of known circularly symmetrical gradient index lenses have been performed. These simulations have been done using the multilayer multiple scattering method and the results prove their broadband efficiency and omnidirectional properties. Finally, finite element simulations employing the full three-dimensional elasticity equations also support the validity of the designed approach. (c) 2014 AIP Publishing LLC.This work has been supported by the U.S. Office of Naval Research under Grant No. N000140910554.Climente Alarcón, A.; Torrent Martí, D.; Sánchez-Dehesa Moreno-Cid, J. (2014). Gradient index lenses for flexural waves based on thickness variations. Applied Physics Letters. 105(6). https://doi.org/10.1063/1.4893153S1056Norris, A. N., & Vemula, C. (1995). Scattering of flexural waves on thin plates. Journal of Sound and Vibration, 181(1), 115-125. doi:10.1006/jsvi.1995.0129SQUIRE, V. A., & DIXON, T. W. (2000). SCATTERING OF FLEXURAL WAVES FROM A COATED CYLINDRICAL ANOMALY IN A THIN PLATE. Journal of Sound and Vibration, 236(2), 367-373. doi:10.1006/jsvi.2000.2953Movchan, A. ., Movchan, N. ., & McPhedran, R. . (2007). Bloch–Floquet bending waves in perforated thin plates. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 463(2086), 2505-2518. doi:10.1098/rspa.2007.1886Lee, W.-M., & Chen, J.-T. (2010). Scattering of flexural wave in a thin plate with multiple circular holes by using the multipole Trefftz method. International Journal of Solids and Structures, 47(9), 1118-1129. doi:10.1016/j.ijsolstr.2009.12.002Parnell, W. J., & Martin, P. A. (2011). Multiple scattering of flexural waves by random configurations of inclusions in thin plates. Wave Motion, 48(2), 161-175. doi:10.1016/j.wavemoti.2010.10.004McPhedran, R. C., Movchan, A. B., & Movchan, N. V. (2009). Platonic crystals: Bloch bands, neutrality and defects. Mechanics of Materials, 41(4), 356-363. doi:10.1016/j.mechmat.2009.01.005Hsu, J.-C., & Wu, T.-T. (2006). Efficient formulation for band-structure calculations of two-dimensional phononic-crystal plates. Physical Review B, 74(14). doi:10.1103/physrevb.74.144303Huang, C.-Y., Sun, J.-H., & Wu, T.-T. (2010). A two-port ZnO/silicon Lamb wave resonator using phononic crystals. Applied Physics Letters, 97(3), 031913. doi:10.1063/1.3467145Farhat, M., Guenneau, S., & Enoch, S. (2010). High directivity and confinement of flexural waves through ultra-refraction in thin perforated plates. EPL (Europhysics Letters), 91(5), 54003. doi:10.1209/0295-5075/91/54003Wu, T.-T., Chen, Y.-T., Sun, J.-H., Lin, S.-C. S., & Huang, T. J. (2011). Focusing of the lowest antisymmetric Lamb wave in a gradient-index phononic crystal plate. Applied Physics Letters, 98(17), 171911. doi:10.1063/1.3583660Pierre, J., Boyko, O., Belliard, L., Vasseur, J. O., & Bonello, B. (2010). Negative refraction of zero order flexural Lamb waves through a two-dimensional phononic crystal. Applied Physics Letters, 97(12), 121919. doi:10.1063/1.3491290Farhat, M., Guenneau, S., Enoch, S., Movchan, A. B., & Petursson, G. G. (2010). Focussing bending waves via negative refraction in perforated thin plates. Applied Physics Letters, 96(8), 081909. doi:10.1063/1.3327813Bramhavar, S., Prada, C., Maznev, A. A., Every, A. G., Norris, T. B., & Murray, T. W. (2011). Negative refraction and focusing of elastic Lamb waves at an interface. Physical Review B, 83(1). doi:10.1103/physrevb.83.014106Wang, C. H. (2003). Plate-Wave Diffraction Tomography for Structural Health Monitoring. AIP Conference Proceedings. doi:10.1063/1.1570323Fromme, P., Wilcox, P. D., Lowe, M. J. S., & Cawley, P. (2006). On the development and testing of a guided ultrasonic wave array for structural integrity monitoring. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 53(4), 777-785. doi:10.1109/tuffc.2006.1621505Berryman, J. G. (1980). Long‐wavelength propagation in composite elastic media I. Spherical inclusions. The Journal of the Acoustical Society of America, 68(6), 1809-1819. doi:10.1121/1.385171Krokhin, A. A., Arriaga, J., & Gumen, L. N. (2003). Speed of Sound in Periodic Elastic Composites. Physical Review Letters, 91(26). doi:10.1103/physrevlett.91.264302Torrent, D., Håkansson, A., Cervera, F., & Sánchez-Dehesa, J. (2006). Homogenization of Two-Dimensional Clusters of Rigid Rods in Air. Physical Review Letters, 96(20). doi:10.1103/physrevlett.96.204302Stenger, N., Wilhelm, M., & Wegener, M. (2012). Experiments on Elastic Cloaking in Thin Plates. Physical Review Letters, 108(1). doi:10.1103/physrevlett.108.014301Krylov, V. V., & Tilman, F. J. B. S. (2004). Acoustic ‘black holes’ for flexural waves as effective vibration dampers. Journal of Sound and Vibration, 274(3-5), 605-619. doi:10.1016/j.jsv.2003.05.010O’Boy, D. J., Krylov, V. V., & Kralovic, V. (2010). Damping of flexural vibrations in rectangular plates using the acoustic black hole effect. Journal of Sound and Vibration, 329(22), 4672-4688. doi:10.1016/j.jsv.2010.05.019Krylov, V. V., & Winward, R. E. T. B. (2007). Experimental investigation of the acoustic black hole effect for flexural waves in tapered plates. Journal of Sound and Vibration, 300(1-2), 43-49. doi:10.1016/j.jsv.2006.07.035Georgiev, V. B., Cuenca, J., Gautier, F., Simon, L., & Krylov, V. V. (2011). Damping of structural vibrations in beams and elliptical plates using the acoustic black hole effect. Journal of Sound and Vibration, 330(11), 2497-2508. doi:10.1016/j.jsv.2010.12.001Climente, A., Torrent, D., & Sánchez-Dehesa, J. (2013). Omnidirectional broadband insulating device for flexural waves in thin plates. Journal of Applied Physics, 114(21), 214903. doi:10.1063/1.4839375Šarbort, M., & Tyc, T. (2012). Spherical media and geodesic lenses in geometrical optics. 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A Novel Low Processing Time System for Criminal Activities Detection Applied to Command and Control Citizen Security Centers

[EN] This paper shows a Novel Low Processing Time System focused on criminal activities detection based on real-time video analysis applied to Command and Control Citizen Security Centers. This system was applied to the detection and classification of criminal events in a real-time video surveillance subsystem in the Command and Control Citizen Security Center of the Colombian National Police. It was developed using a novel application of Deep Learning, specifically a Faster Region-Based Convolutional Network (R-CNN) for the detection of criminal activities treated as "objects" to be detected in real-time video. In order to maximize the system efficiency and reduce the processing time of each video frame, the pretrained CNN (Convolutional Neural Network) model AlexNet was used and the fine training was carried out with a dataset built for this project, formed by objects commonly used in criminal activities such as short firearms and bladed weapons. In addition, the system was trained for street theft detection. The system can generate alarms when detecting street theft, short firearms and bladed weapons, improving situational awareness and facilitating strategic decision making in the Command and Control Citizen Security Center of the Colombian National Police.This work was co-funded by the European Commission as part of H2020 call SEC-12-FCT-2016-Subtopic3 under the project VICTORIA (No. 740754). This publication reflects the views only of the authors and the Commission cannot be held responsible for any use which may be made of the information contained therein.Suarez-Paez, J.; Salcedo-Gonzalez, M.; Climente, A.; Esteve Domingo, M.; Gomez, J.; Palau Salvador, CE.; Pérez Llopis, I. (2019). A Novel Low Processing Time System for Criminal Activities Detection Applied to Command and Control Citizen Security Centers. Information. 10(12):1-19. https://doi.org/10.3390/info10120365S1191012Wang, L., Rodriguez, R. M., & Wang, Y.-M. (2018). A dynamic multi-attribute group emergency decision making method considering expertsr hesitation. International Journal of Computational Intelligence Systems, 11(1), 163. doi:10.2991/ijcis.11.1.13Esteve, M., Perez-Llopis, I., & Palau, C. E. (2013). Friendly Force Tracking COTS solution. IEEE Aerospace and Electronic Systems Magazine, 28(1), 14-21. doi:10.1109/maes.2013.6470440Senst, T., Eiselein, V., Kuhn, A., & Sikora, T. (2017). Crowd Violence Detection Using Global Motion-Compensated Lagrangian Features and Scale-Sensitive Video-Level Representation. IEEE Transactions on Information Forensics and Security, 12(12), 2945-2956. doi:10.1109/tifs.2017.2725820Shi, Y., Tian, Y., Wang, Y., & Huang, T. (2017). Sequential Deep Trajectory Descriptor for Action Recognition With Three-Stream CNN. IEEE Transactions on Multimedia, 19(7), 1510-1520. doi:10.1109/tmm.2017.2666540Arunnehru, J., Chamundeeswari, G., & Bharathi, S. P. (2018). Human Action Recognition using 3D Convolutional Neural Networks with 3D Motion Cuboids in Surveillance Videos. Procedia Computer Science, 133, 471-477. doi:10.1016/j.procs.2018.07.059Kamel, A., Sheng, B., Yang, P., Li, P., Shen, R., & Feng, D. D. (2019). Deep Convolutional Neural Networks for Human Action Recognition Using Depth Maps and Postures. IEEE Transactions on Systems, Man, and Cybernetics: Systems, 49(9), 1806-1819. doi:10.1109/tsmc.2018.2850149Zhang, B., Wang, L., Wang, Z., Qiao, Y., & Wang, H. (2018). Real-Time Action Recognition With Deeply Transferred Motion Vector CNNs. IEEE Transactions on Image Processing, 27(5), 2326-2339. doi:10.1109/tip.2018.2791180Girshick, R., Donahue, J., Darrell, T., & Malik, J. (2016). Region-Based Convolutional Networks for Accurate Object Detection and Segmentation. IEEE Transactions on Pattern Analysis and Machine Intelligence, 38(1), 142-158. doi:10.1109/tpami.2015.2437384Suarez-Paez, J., Salcedo-Gonzalez, M., Esteve, M., Gómez, J. A., Palau, C., & Pérez-Llopis, I. (2018). Reduced computational cost prototype for street theft detection based on depth decrement in Convolutional Neural Network. Application to Command and Control Information Systems (C2IS) in the National Police of Colombia. International Journal of Computational Intelligence Systems, 12(1), 123. doi:10.2991/ijcis.2018.25905186Ren, S., He, K., Girshick, R., & Sun, J. (2017). Faster R-CNN: Towards Real-Time Object Detection with Region Proposal Networks. IEEE Transactions on Pattern Analysis and Machine Intelligence, 39(6), 1137-1149. doi:10.1109/tpami.2016.2577031Hao, S., Wang, P., & Hu, Y. (2019). Haze Image Recognition Based on Brightness Optimization Feedback and Color Correction. Information, 10(2), 81. doi:10.3390/info10020081Peng, M., Wang, C., Chen, T., & Liu, G. (2016). NIRFaceNet: A Convolutional Neural Network for Near-Infrared Face Identification. Information, 7(4), 61. doi:10.3390/info7040061NVIDIA CUDA® Deep Neural Network library (cuDNN)https://developer.nvidia.com/cuda-downloadsWu, X., Lu, X., & Leung, H. (2018). A Video Based Fire Smoke Detection Using Robust AdaBoost. Sensors, 18(11), 3780. doi:10.3390/s18113780Park, J. H., Lee, S., Yun, S., Kim, H., & Kim, W.-T. (2019). Dependable Fire Detection System with Multifunctional Artificial Intelligence Framework. Sensors, 19(9), 2025. doi:10.3390/s19092025García-Retuerta, D., Bartolomé, Á., Chamoso, P., & Corchado, J. M. (2019). Counter-Terrorism Video Analysis Using Hash-Based Algorithms. Algorithms, 12(5), 110. doi:10.3390/a12050110Zhao, B., Zhao, B., Tang, L., Han, Y., & Wang, W. (2018). Deep Spatial-Temporal Joint Feature Representation for Video Object Detection. Sensors, 18(3), 774. doi:10.3390/s18030774He, Z., & He, H. (2018). Unsupervised Multi-Object Detection for Video Surveillance Using Memory-Based Recurrent Attention Networks. Symmetry, 10(9), 375. doi:10.3390/sym10090375Muhammad, K., Hamza, R., Ahmad, J., Lloret, J., Wang, H., & Baik, S. W. (2018). Secure Surveillance Framework for IoT Systems Using Probabilistic Image Encryption. IEEE Transactions on Industrial Informatics, 14(8), 3679-3689. doi:10.1109/tii.2018.2791944Barthélemy, J., Verstaevel, N., Forehead, H., & Perez, P. (2019). Edge-Computing Video Analytics for Real-Time Traffic Monitoring in a Smart City. Sensors, 19(9), 2048. doi:10.3390/s19092048Aqib, M., Mehmood, R., Alzahrani, A., Katib, I., Albeshri, A., & Altowaijri, S. M. (2019). Smarter Traffic Prediction Using Big Data, In-Memory Computing, Deep Learning and GPUs. Sensors, 19(9), 2206. doi:10.3390/s19092206Xu, S., Zou, S., Han, Y., & Qu, Y. (2018). Study on the Availability of 4T-APS as a Video Monitor and Radiation Detector in Nuclear Accidents. Sustainability, 10(7), 2172. doi:10.3390/su10072172Plageras, A. P., Psannis, K. E., Stergiou, C., Wang, H., & Gupta, B. B. (2018). Efficient IoT-based sensor BIG Data collection–processing and analysis in smart buildings. Future Generation Computer Systems, 82, 349-357. doi:10.1016/j.future.2017.09.082Jha, S., Dey, A., Kumar, R., & Kumar-Solanki, V. (2019). A Novel Approach on Visual Question Answering by Parameter Prediction using Faster Region Based Convolutional Neural Network. International Journal of Interactive Multimedia and Artificial Intelligence, 5(5), 30. doi:10.9781/ijimai.2018.08.004Cho, S., Baek, N., Kim, M., Koo, J., Kim, J., & Park, K. (2018). Face Detection in Nighttime Images Using Visible-Light Camera Sensors with Two-Step Faster Region-Based Convolutional Neural Network. Sensors, 18(9), 2995. doi:10.3390/s18092995Zhang, J., Xing, W., Xing, M., & Sun, G. (2018). Terahertz Image Detection with the Improved Faster Region-Based Convolutional Neural Network. Sensors, 18(7), 2327. doi:10.3390/s18072327Bakheet, S., & Al-Hamadi, A. (2016). 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Sensors, 18(11), 3779. doi:10.3390/s18113779AMD Embedded RadeonTMhttps://www.amd.com/en/products/embedded-graphic

Omnidirectional broadband insulating device for flexural waves in thin plates

This work presents a gradient index device for insulating from vibrations a circular area of a thin plate. The gradient of the refractive index is achieved exploiting the thickness-dependence of the dispersion relation of flexural waves in thin plates. A well-like thickness profile in an annular region of the plate is used to mimic the combination of an attractive and repulsive potentials, focusing waves at its bottom and dissipating them by means of an absorptive layer placed on top. The central area is therefore isolated from vibrations, while they are dissipated at the bottom of the well. Simulations have been done using the multilayer multiple scattering method and the results prove their broadband efficiency and omnidirectional properties.This work has been supported by the U.S. Office of Naval Research under Grant No. N000140910554.Climente Alarcón, A.; Torrent Martí, D.; Sánchez-Dehesa Moreno-Cid, J. (2013). Omnidirectional broadband insulating device for flexural waves in thin plates. Journal of Applied Physics. 114(21):214903-214912. https://doi.org/10.1063/1.4839375S21490321491211421Hsu, J.-C., & Wu, T.-T. (2006). Efficient formulation for band-structure calculations of two-dimensional phononic-crystal plates. Physical Review B, 74(14). doi:10.1103/physrevb.74.144303McPhedran, R. C., Movchan, A. B., & Movchan, N. V. (2009). Platonic crystals: Bloch bands, neutrality and defects. Mechanics of Materials, 41(4), 356-363. doi:10.1016/j.mechmat.2009.01.005Farhat, M., Guenneau, S., Enoch, S., Movchan, A. B., & Petursson, G. G. (2010). Focussing bending waves via negative refraction in perforated thin plates. Applied Physics Letters, 96(8), 081909. doi:10.1063/1.3327813Pierre, J., Boyko, O., Belliard, L., Vasseur, J. O., & Bonello, B. (2010). Negative refraction of zero order flexural Lamb waves through a two-dimensional phononic crystal. 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