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1
Mir, Fariha, Debdyuti Mandal e Sourav Banerjee. "Metamaterials for Acoustic Noise Filtering and Energy Harvesting". Sensors 23, n. 9 (23 aprile 2023): 4227. http://dx.doi.org/10.3390/s23094227.
Testo completoAbstract (sommario):
Artificial methods for noise filtering are required for the twenty-first century’s Factory vision 4.0. From various perspectives of physics, noise filtering capabilities could be addressed in multiple ways. In this article, the physics of noise control is first dissected into active and passive control mechanisms and then further different physics are categorized to visualize their respective physics, mechanism, and target of their respective applications. Beyond traditional passive approaches, the comparatively modern concept for sound isolation and acoustic noise filtering is based on artificial metamaterials. These new materials demonstrate unique interaction with acoustic wave propagation exploiting different physics, which is emphasized in this article. A few multi-functional metamaterials were reported to harvest energy while filtering the ambient noise simultaneously. It was found to be extremely useful for next-generation noise applications where simultaneously, green energy could be generated from the energy which is otherwise lost. In this article, both these concepts are brought under one umbrella to evaluate the applicability of the respective methods. An attempt has been made to create groundbreaking transformative and collaborative possibilities. Controlling of acoustic sources and active damping mechanisms are reported under an active mechanism. Whereas Helmholtz resonator, sound absorbing, spring-mass damping, and vibration absorbing approaches together with metamaterial approaches are reported under a passive mechanism. The possible application of metamaterials with ventilation while performing noise filtering is reported to be implemented for future Smart Cities.
2
Asiri, S., A. Baz e D. Pines. "Periodic Struts for Gearbox Support System". Journal of Vibration and Control 11, n. 6 (giugno 2005): 709–21. http://dx.doi.org/10.1177/1077546305052784.
Testo completoAbstract (sommario):
Passive periodic structures exhibit unique dynamic characteristics that make them act as mechanical filters for wave propagation. As a result, waves can propagate along the periodic structures only within specific frequency bands called “pass bands” and wave propagation is completely blocked within other frequency bands called “stop bands”. In this paper, the emphasis is placed on developing a new class of these periodic structures called passive periodic struts, which can be used to support gearbox systems on the airframes of helicopters. When designed properly, the passive periodic strut can stop the propagation of vibration from the gearbox to the airframe within critical frequency bands, consequently minimizing the effects of transmission of undesirable vibration and sound radiation to the helicopter cabin. The theory governing the operation of this class of passive periodic struts is introduced and their filtering characteristics are demonstrated experimentally as a function of their design parameters. The presented concept of the passive periodic strut can be easily used in many applications to control the wave propagation and the force transmission in both the spectral and spatial domains in an attempt to stop/confine the propagation of undesirable disturbances.
3
Guan, Haofei, e K. C. Wong. "Spring-Damped Underactuated Swashplateless Rotor on a Bicopter Unmanned Aerial Vehicle". Machines 12, n. 5 (28 aprile 2024): 296. http://dx.doi.org/10.3390/machines12050296.
Testo completoAbstract (sommario):
The stabilisation capabilities of unmanned aerial vehicles (UAVs) with bicopter underactuated swashplateless rotors are highly sensitive to motor-induced vibration. Due to the requirement of the active control of underactuated swashplateless rotors, conventional designs are limited in reducing vibration through control optimisation. A solution with customized passive spring-damping structures on a unique underactuated swashplateless rotor of a tiltrotor bicopter platform is presented. The implementation of this structure effectively reduces the self-coherent vibration in flights. As a result, a higher level of control authority has been achieved without setting excessive low-pass filtering for vibration. Experimentally obtained inertial measurement unit (IMU) data, rotor speed, rotor tilt angle, and the cyclic stator response are presented for comparison with Simulink model predictions.
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Baz, A. "Active Control of Periodic Structures". Journal of Vibration and Acoustics 123, n. 4 (1 giugno 2001): 472–79. http://dx.doi.org/10.1115/1.1399052.
Testo completoAbstract (sommario):
Conventional passive periodic structures exhibit unique dynamic characteristics that make them act as mechanical filters for wave propagation. As a result, waves can propagate along the periodic structures only within specific frequency bands called the “Pass Bands” and wave propagation is completely blocked within other frequency bands called the “Stop Bands.” In this paper, the emphasis is placed on providing the passive structures with active control capabilities in order to tune the spectral width and location of the pass and stop bands in response to the structural vibration. Apart from their unique filtering characteristics, the ability of periodic structures to transmit waves, from one location to another, within the pass bands can be greatly reduced when the ideal periodicity is disrupted resulting in the well-known phenomenon of “Localization.” In the case of passive structures, the aperiodicity (or the disorder) can result from unintentional material, geometric and manufacturing variability. However, in the case of active periodic structures the aperiodicity is intentionally introduced by proper tuning of the controllers of the individual substructure or cell. The theory governing the operation of this class of Active Periodic structures is introduced and numerical examples are presented to illustrate their tunable filtering and localization characteristics. The examples considered include periodic/aperiodic spring-mass systems controlled by piezoelectric actuators. The presented results emphasize the unique potential of the active periodic structures in controlling the wave propagation both in the spectral and spatial domains in an attempt to stop/confine the propagation of undesirable disturbances.
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Alajlouni, Sa’ed, e Pablo Tarazaga. "A passive energy-based method for footstep impact localization, using an underfloor accelerometer sensor network with Kalman filtering". Journal of Vibration and Control 26, n. 11-12 (21 gennaio 2020): 941–51. http://dx.doi.org/10.1177/1077546319890520.
Testo completoAbstract (sommario):
An underfloor accelerometer sensor network can be used to track occupants in an indoor environment using measurements of floor vibration induced by occupant footsteps. To achieve occupant tracking, each footstep impact location must first be estimated. This paper proposes a new energy-based algorithm for footstep impact localization. Compared to existing energy-based algorithms, the new algorithm achieves higher localization accuracy and removes a previously required calibration step (removal of the need to estimate floor-dependent parameters). Furthermore, the algorithm uses a much smaller data sampling rate compared to time of flight/arrival localization methods, which greatly reduces data and data-processing time. The new algorithm is a two-step location estimator: the first step is a coarse location estimate, with the second step as a fine location search through a nonlinear minimization problem. The performance of the proposed algorithm is evaluated using a single occupant walking experiment on an instrumented floor inside an operational smart building. This paper also demonstrates that higher localization accuracy is obtained using an additional Kalman filtering scheme.
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Li, Jianying, Yunchang Xiao, Minsheng Yang, Jianqi Li e Jingying Wan. "The Research on Harmonic Transfer Characteristics of Integrated Multi-Winding Inductive Filtering Converter Transformer and Its Filter System". Electronics 11, n. 13 (3 luglio 2022): 2088. http://dx.doi.org/10.3390/electronics11132088.
Testo completoAbstract (sommario):
A novel integrated multi-winding inductive filter converter and its filter system used in HVDC conversion station are proposed. Specifically, the schemes include two paralleled-connected delta filter windings with zero impedance, and the 11th and 13th tuned filtering branches are installed at the taps. On this basis, the 5th and 7th harmonic filters are eliminated and the 5th, 7th, 11th, and 13th harmonics of the valve-side are suppressed. Moreover, the cost of the filter is reduced, and the negative impact on the converter transformer body caused by the transfer of harmonic current is avoided, such as vibration, noise, and harmonic loss. In this paper, first, the mathematical models of integrated multi-winding inductive filter converter and its filter system are established. Accordingly, the current relationships between the primary winding side and two secondary winding sides are derived. Then, the transfer path of each characteristic harmonic current in the new system is analyzed and discussed. Moreover, a simulation model is established to study the operation characteristics of the system. Finally, through the designed experimental prototype, a new DC transferring system platform is constructed to testify the operation characteristics of an integrated multi-winding inductive filter converter and its filter system. The experimental results show that the total harmonic distortion rate of the grid-winding current can be reduced to 4.68% only by installing the 11th and 13th tuned filters, so the effect of active filtering is approximated realized by the passive filtering method.
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Jafari, Hamid, e Ramin Sedaghati. "Analysis of an Adaptive Periodic Low-Frequency Wave Filter Featuring Magnetorheological Elastomers". Polymers 15, n. 3 (31 gennaio 2023): 735. http://dx.doi.org/10.3390/polym15030735.
Testo completoAbstract (sommario):
This study aims to enhance and tune wave-propagation properties (Bandgaps) of periodic structures featuring magnetorheological elastomers (MREs). For this purpose, first, a basic model of periodic structures (square unit cell with cross-shaped arms), which does not possess noise filtering properties in the conventional configuration, is considered. A passive attenuation zone is then proposed by adding a cylindrical core mass to the center of the conventional geometry and changing arm angles, which permitted new bandgap areas. It was shown that better wave-filtering performance may be achieved by introducing a large radius of the cylindrical core as well as low negative cross-arm angles. The modified configuration of the unit cell was subsequently utilized as the basic model for the development of magnetoactive metamaterial using a MRE capable of varying the bandgaps areas upon application of an external magnetic field. The finite element model of the proposed MRE-based periodic unit cell was developed, and the Bloch theorem was employed to systematically investigate the ability of the proposed adaptive periotic structure to attenuate low-frequency noise and vibration. Results show that the proposed MRE-based periodic wave filter can provide wide bandgap areas which can be adaptively changed and tuned using the applied magnetic field. The findings in this study can provide an essential guide for the development of novel adaptive periodic structures to filter low-frequency noises in the wide frequency band.
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Kulskyi, Oleksander L., S. V. Lysochenko, Volodymyr Vasylovych Ilchenko, Vasyl S. Mostovyi, Mykola M. Nikiforov, Anatolii Tymofiiovych Orlov e Volodymyr A. Zelinskyi. "Piezoelectric Sensor of Mechanical Vibrations". Microsystems, Electronics and Acoustics 27, n. 2 (29 agosto 2022): 265031–1. http://dx.doi.org/10.20535/2523-4455.mea.265031.
Testo completoAbstract (sommario):
Creation of high-sensitive sensor of mechanical vibrations, capable of non-distorted transformation of the vibrations source energy into electric signal within a wide dynamic range, is necessary for determination of characteristics of the source as well as for obtaining the information on parameters of medium in which the vibrations propagate. Fast and successful usage of obtained data can be achieved with employment of programming algorithms of identification of type of a source of vibrations and finding their fundamental Eigen frequencies and quality factors of the structures at these frequencies. Calculations of the schematic-and-technical decisions, selection of elements, making of mock-ups, and working-out of variants of the sensor. Mathematical modeling, analysis and identification of dynamical parameters of the structures in which there are used the fundamental eigenfrequencies and the structures’ quality factors at these frequencies. The Fourier and wavelet analyses of the spectra. Algorythms of digital filtering (moving average of measured data). Sensors of mechanical vibrations and a system for collection, analysis, and digital processing of the output data arrays are created. New effective method for analysis of conditions of natural and artificial objects is suggested. Algorythm for identification of type of mechanical vibrations source is developed. Transducers of mechanical vibrations are developed using film-based piezoelectric sensors of new generation. System for storing and processing of the sensors’ output data arrays is developed and a technique for transferring and saving the information is formulated. Structural parameters such as fundamental eigenfrequencies and the structures’ quality factors at corresponding frequencies are applied for identification of conditions of natural and engineering objects. Methodology for expertise of both the natural-based (wind) and the test-pulses-assisted dynamical loading is developed. Sets of single-type sub-models suitable for modeling, by their superposition, of the whole process are considered, and optimal sets of the model’s free parameters are determined. Degree of the model’s closeness to data obtained within a selected metrics serves as a criterion of optimality. Algorithm for identification of type of a mechanical vibrations’ source is developed basing on the signals representation as wavelets. The sensor-measured total signal includes wavelets from multiple sources and, because of this, the task of separation of the aggregated signal into constituents is accomplished. To achieve this, regularities within the signal should be found which might be interpreted as wavelet. Enumeration of the wavelets is determined with excess; the algorithm employs rules in accordance with which the enumeration and wavelets parameters are selected with more accuracy, and connection of wavelets with certain vibration sources is specified. Performance of the proposed sensor is fully confirmed by experimental data. Successful tests targeted at determination of technical characteristics of the sensor of mechanical vibrations are conducted within a passive survey system of stationary security installation. Seismograms of an approaching pedestrian are obtained for the distance of 30 m. Characteristics of the piezoelectric sensor of mechanical vibrations make it possible a plenty of applications of technical decisions, laid into its basis, in various spheres of science and technology.
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Yoon, Sang-Hee, e Ki Lyug Kim. "Passive low pass filtering effect of mechanical vibrations by a granular bed composed of microglass beads". Applied Physics Letters 89, n. 2 (10 luglio 2006): 021906. http://dx.doi.org/10.1063/1.2220012.
Testo completo
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Jang, Hoon-Seok, Mannan Saeed Muhammad, Guhnoo Yun e Dong Hwan Kim. "Sampling Based on Kalman Filter for Shape from Focus in the Presence of Noise". Applied Sciences 9, n. 16 (9 agosto 2019): 3276. http://dx.doi.org/10.3390/app9163276.
Testo completoAbstract (sommario):
Recovering three-dimensional (3D) shape of an object from two-dimensional (2D) information is one of the major domains of computer vision applications. Shape from Focus (SFF) is a passive optical technique that reconstructs 3D shape of an object using 2D images with different focus settings. When a 2D image sequence is obtained with constant step size in SFF, mechanical vibrations, referred as jitter noise, occur in each step. Since the jitter noise changes the focus values of 2D images, it causes erroneous recovery of 3D shape. In this paper, a new filtering method for estimating optimal image positions is proposed. First, jitter noise is modeled as Gaussian or speckle function, secondly, the focus curves acquired by one of the focus measure operators are modeled as a quadratic function for application of the filter. Finally, Kalman filter as the proposed method is designed and applied for removing jitter noise. The proposed method is experimented by using image sequences of synthetic and real objects. The performance is evaluated through various metrics to show the effectiveness of the proposed method in terms of reconstruction accuracy and computational complexity. Root Mean Square Error (RMSE), correlation, Peak Signal-to-Noise Ratio (PSNR), and computational time of the proposed method are improved on average by about 48%, 11%, 15%, and 5691%, respectively, compared with conventional filtering methods.
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Hajjaj, Amal Z., e Nizar Jaber. "Controlling Resonator Nonlinearities and Modes through Geometry Optimization". Micromachines 12, n. 11 (10 novembre 2021): 1381. http://dx.doi.org/10.3390/mi12111381.
Testo completoAbstract (sommario):
Controlling the nonlinearities of MEMS resonators is critical for their successful implementation in a wide range of sensing, signal conditioning, and filtering applications. Here, we utilize a passive technique based on geometry optimization to control the nonlinearities and the dynamical response of MEMS resonators. Also, we explored active technique i.e., tuning the axial stress of the resonator. To achieve this, we propose a new hybrid shape combining a straight and initially curved microbeam. The Galerkin method is employed to solve the beam equation and study the effect of the different design parameters on the ratios of the frequencies and the nonlinearities of the structure. We show by adequately selecting the parameters of the structure; we can realize systems with strong quadratic or cubic effective nonlinearities. Also, we investigate the resonator shape effect on symmetry breaking and study different linear coupling phenomena: crossing, veering, and mode hybridization. We demonstrate the possibility of tuning the frequencies of the different modes of vibrations to achieve commensurate ratios necessary for activating internal resonance. The proposed method is simple in principle, easy to fabricate, and offers a wide range of controllability on the sensor nonlinearities and response.
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Tsaliev, T. A., e A. O. Vakarchuk. "CHARACTERISTICS OF VIBRATOR ARRAYS DIRECTIVITY ON HARMONICS OF MAIN FREQUENCY". Proceedings of the O.S. Popov ОNAT 1, n. 2 (31 dicembre 2020): 40–49. http://dx.doi.org/10.33243/2518-7139-2020-1-2-40-49.
Testo completoAbstract (sommario):
Antenna patterns representing dependences of the directivity factor (DF) on angular coordinates for arrays formed from Yagi-Uda aerials are considered and discussed. The results of computer modelling are based on the decision of integral equations by the method of moments. Patterns that represent dependences of the coefficient of the directivity factor (DF) for an array and her elements from angular coordinates are counted on fundamental frequency and four harmonics. The data obtained confirmed the validity of the assumptions that the directivity properties of vibrator antenna arrays can significantly affect the EMC conditions for harmonics of the fundamental frequency. At these frequencies, several main maxima appear in the radiation patterns, the level of directivity in which may even exceed the maximum directivity in the main lobe at the fundamental frequency. The DF patterns shown in the article refer to the case of in-phase excitation of the active elements of the array (without supply lines). However, in the presence of such lines with sequential or mixed power supply circuits, the dependence of the directivity on the angular coordinates can change significantly. The presence of bandpass filters in the input and output stages of the radar will make it possible to largely suppress the levels of harmonic interference, however, if these filters are made on the basis of transmission line segments, their parameters at harmonic frequencies may be insufficient. Further research can be aimed at studying the spatial characteristics and directivity of vibrator antenna arrays based on wave channel antennas with an increased number of passive vibrators, as well as with various power supply and filtering schemes.
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Oladejo, Olagoke Peter, Theophilus Aanuoluwa Adagunodo, Lukman Ayobami Sunmonu, Moruffdeen Adedapo Adabanija, Charity Adaeze Enemuwe e Patrick Omoregie Isibor. "Aeromagnetic mapping of fault architecture along Lagos–Ore axis, southwestern Nigeria". Open Geosciences 12, n. 1 (13 luglio 2020): 376–89. http://dx.doi.org/10.1515/geo-2020-0100.
Testo completoAbstract (sommario):
AbstractA seismic wave is released when there is sudden displacement on a fault plane. The passage of this wave along the fault plane or within the lithosphere could result in ground shaking or vibration at the surface of the Earth. To provide a geophysical explanation to this phenomenon, the high-resolution aeromagnetic data of the sedimentary terrain and part of the Basement Complex of Southwestern Nigeria were processed and interpreted to provide fault architecture of the area, which could serve as conduit for the passage of seismic energy in the study area. High-resolution aeromagnetic data along the Lagos–Ore axis are processed for fault mapping in the study area. The reduced-to-equator (RTE) residual aeromagnetic data used were enhanced using the total horizontal derivative (THD) and upward continuation (UC) filtering techniques on Oasis Montaj 6.4.2 (HJ) software. The resultant maps were overlaid and compared with the plotted RTE residual maps for relevant interpretations. Varying signatures of magnetic anomalies are grouped into high (57.9–89.1 nT), intermediate (38.2–57.9 nT), and low (4.0–38.2 nT) magnetic intensities, which are associated with contracting basement rocks features. The obtained lineaments from the THD reveal areas of various deformations such as brittle, which is associated with faults/fractures, and ductile deformation, which is associated with folds of geological features. The faults, as depict by the UC map, reveal different depth ranges of 500–2250 m at the western side and 1,500–1,250 m at the northwestern area of the study. Since it has been on record that September 11, 2009, earth tremor of magnitude 4.4, with the epicenter at Allada, Bennin Republic, 128 km west of Lagos, Nigeria occurred within the study area, it can be inferred that the established geologic fault architecture could be responsible for the hazard and be part or synthetic to the Ifewara-Zungeru fault in Nigeria.
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Alsaffar, Yaser, Sadok Sassi e Amr Baz. "Band Gap Characteristics of Nonrotating Passive Periodic Drill String". Journal of Vibration and Acoustics 140, n. 2 (4 ottobre 2017). http://dx.doi.org/10.1115/1.4037851.
Testo completoAbstract (sommario):
A new class of drill strings is investigated whereby strategically designed and placed periodic inserts are utilized to filter out the vibration transmission along the drill strings. Such mechanical filtering capabilities allow the vibrations to propagate along the periodic drill string only within specific frequency bands called the “pass bands” and completely block it within other frequency bands called the “stop bands.” The design and the location of the inserts are selected to confine the dominant modes of vibration of the drill string within the stop bands generated by the periodic arrangement of the inserts in order to completely block the propagation of the vibrations. A finite element model (FEM) that simulates the operation of this new class of drill strings is developed to describe the complex nature of the vibration encountered during drilling operations. Experimental prototype of the passive periodic drill string was built and tested to demonstrate the feasibility and effectiveness of the concept of periodic drill string in mitigating undesirable vibrations. The experimental results are used to validate the developed theoretical model and to develop a scalable design tool that can be used to predict the dynamical behavior of this new class of drill strings.
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Zhang, Dajun, Akhil Polamarasetty, Muhammad Osama Shahid, Bhuvana Krishnaswamy e Chu Ma. "Metamaterial-based passive analog processor for wireless vibration sensing". Communications Engineering 3, n. 1 (8 marzo 2024). http://dx.doi.org/10.1038/s44172-024-00190-8.
Testo completoAbstract (sommario):
AbstractReal-time, low-cost, and wireless mechanical vibration monitoring is necessary for industrial applications to track the operation status of equipment, environmental applications to proactively predict natural disasters, as well as day-to-day applications such as vital sign monitoring. Despite this urgent need, existing solutions, such as laser vibrometers, commercial Wi-Fi devices, and cameras, lack wide practical deployment due to their limited sensitivity and functionality. Here we proposed a fully passive, metamaterial-based vibration processing device, fabricated prototypes working at different frequencies ranging from 5 Hz to 285 Hz, and verified that the device can improve the sensitivity of wireless vibration measurement methods by more than ten times when attached to vibrating surfaces. Additionally, the device realizes an analog real-time vibration filtering/labeling effect, and the device also provides a platform for surface editing, which adds more functionalities to the current non-contact sensing systems. Finally, the working frequency of the device is widely adjustable over orders of magnitudes, broadening its applicability to different applications, such as structural health diagnosis, disaster warning, and vital signal monitoring.
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Liu, Jie, Zezheng Liu, Wanqian Chen, Jing Lv, Zixuan Jiang, Jiahao Pang e Libin Du. "Response spectrum-based analysis of airborne radar random vibration and multi-point control improvement". Scientific Reports 14, n. 1 (30 marzo 2024). http://dx.doi.org/10.1038/s41598-024-56783-y.
Testo completoAbstract (sommario):
AbstractDuring the flight of a UAV (unmanned aerial vehicle), the LiDAR device undergoes random vibrations due to the changing flight attitude and wind speed conditions of the UAV. It is important to control the frequency and amplitude of the vibrations within a reasonable range by means of a damping structure. As the vibrations caused by various factors during flight are random and non-linear, this paper innovates the analysis principle and damping control means for the random vibrations of airborne optoelectronic devices. The response spectrum analysis theory is used to establish the shock response spectrum, and an optimised and improved recursive digital filtering method is used to fit the frequencies of random vibration to the synthetic shock response. Considering the uncertainty of the vibration excitation signal, a virtual excitation method is used for the first time to simulate the random vibration to which the radar may be subjected in the air, and to simplify the calculation steps. The shock plate structure is designed using a multi-point control method to innovate a passive response to the random excitation. Finally, a modal analysis of the synthesised impact response was carried out. It is verified that the first six modal frequencies are controlled within 220 Hz, realising the frequency reduction. The amplitude of the three x, y, and z directions is controlled to within 0.5 mm, thus achieving vibration damping.
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Robin, Guillaume, Thomas Huchard, Marc Ponçot e El Mostafa Daya. "Identification method on the vibration properties of a periodic core sandwich: Thermal impact on the band gap". Journal of Vibration and Control, 10 maggio 2024. http://dx.doi.org/10.1177/10775463241249576.
Testo completoAbstract (sommario):
This paper focuses on the thermal impact of filtering properties on sandwich structures with periodic core. The evolution of the bandgap is carefully studied as a function of temperature. Sandwich structure allows to shear the viscoelastic core layer and increases passive damping. Two polymers are selected for their viscoelastic properties and their adhesion properties with metal surfaces. The mechanical properties, shear modulus G(ω) and loss factor η(ω) of these polymers, are determined at temperature by an inverse method. The periodicity of the sandwich structure is achieved by alternating two materials with specific viscoelastic properties in the core, allowing resonant frequencies to be located in beams creating frequency ranges without resonant peaks. Temperature has a strong influence on the mechanical properties of polymer materials. This is why we felt it was important to be able to carry out a temperature investigation. Numerical finite element modelling is developed considering periodicity and temperature. Periodic sandwich fabricated in our laboratory are tested under thermal conditioned. The results show the importance of considering the effect of temperature. It has a direct impact on the filtering properties obtained by periodic structures.
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Fuchs, G., N. Berg, L. M. Broman e L. Prahl Wittberg. "P2791Method for detection of blood clots in ventricular assist devices". European Heart Journal 40, Supplement_1 (1 ottobre 2019). http://dx.doi.org/10.1093/eurheartj/ehz748.1106.
Testo completoAbstract (sommario):
Abstract Background The technical development of modern ventricular assist devices (VAD) shows continued improvement in patient outcome. VADs continue to gain increased use not only as bridge to transplant but also as a destination therapy. However, VAD therapy is associated with complications, among which thromboembolic complications are common. Better management for early detection is paramount to improve patient outcome. Purpose The aims of this study were to determine if the VADs under consideration may retain clots, and to assess the feasibility of early clot detection using a non-invasive technique. Methods Two different VADs, the HeartMate II (HMII) and HeartMate 3 (HM3) were tested in a mock loop. Clot analogs (2 cm yarn fragments) were introduced into the loop upstream to the pump. Sound and vibration of the pump was measured using two hydrophones and at the inflow and outflow of the VAD (frequency range: 0.1Hz to 180kHz). The acoustic/vibration data was analyzed concerning the spectral content. Results The flow at the outflow section contained a low frequency swirling component. This appeared to be the basic flow feature. However, in the presence of clot analogs, the frequency signal was amplified. For the HMII this occurred below 10Hz. Concerning the HM3 this signal was more difficult to analyze due to HM3's non-constant rotational speed. However, by using wavelet filtering, it was possible to detect the low frequency signal in the presence of clot analogs. It was also observed that clot analogs tended to accumulate at certain regions in the respective VAD. In the HM3, clot fragments remained in a stagnation region at the bottom pump. This experimental finding contradicts published washout results based on a passive scalar model. Conclusions These mock loop results indicated the feasibility of early detection of blood clots in VADs by analysis of the sound/vibration induced by the clot. The signal “finger-print” needed for detection may also be possible to recover under non-continuous operational rotational speed as in the HM 3.
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Loiko, Yu, V. Ahufinger, R. Corbalán, G. Birkl e J. Mompart. "Filtering of matter-wave vibrational states via spatial adiabatic passage". Physical Review A 83, n. 3 (30 marzo 2011). http://dx.doi.org/10.1103/physreva.83.033629.
Testo completo
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Mutahira, Husna, Vladimir Shin, Unsang Park e Mannan Saeed Muhammad. "Jitter noise modeling and its removal using recursive least squares in shape from focus systems". Scientific Reports 12, n. 1 (18 agosto 2022). http://dx.doi.org/10.1038/s41598-022-18150-7.
Testo completoAbstract (sommario):
AbstractThree-dimensional shape recovery from the set of 2D images has many applications in computer vision and related fields. Passive techniques of 3D shape recovery utilize a single view point and one of these techniques is Shape from Focus or SFF. In SFF systems, a stack of images is taken with a single camera by manipulating its focus settings. During the image acquisition, the inter-frame distance or the sampling step size is predetermined and assumed constant. However, in a practical situation, this step size cannot remain constant due to mechanical vibrations of the translational stage, causing jitter. This jitter produces Jitter noise in the resulting focus curves. Jitter noise is invisible in every image, because all images in the stack are exposed to the same error in focus; thus, limiting the use of traditional noise removal techniques. This manuscript formulates a model of Jitter noise based on Quadratic function and the Taylor series. The proposed method, then, solves the jittering problem for SFF systems through recursive least squares (RLS) filtering. Different noise levels were considered during experiments performed on both real as well as simulated objects. A new metric measure is also proposed, referred to as depth distortion (DD), which calculates the number of pixels contributing to the RMSE in percentage. The proposed measure is used along with the RMSE and correlation, to compute and test the reconstructed shape quality. The results confirm the effectiveness of the proposed scheme.