1,721,083 research outputs found
Effects of etch holes in microelectromechanical resonators
No full textMicromachining processes such as surface machining of polysilicon microstructures or SOI-based processes often require etch holes to be created in the structural layer for purposes of releasing the mechanical structures. The present work examines the effect of the nature and density of etch holes on the resonant frequency of micromechanical resonators. Micromechanical resonators find applications as electronic filters or as timing references in oscillators and any process-induced offset in resonant frequency can significantly affect system performance. A general analytical formulation based on the Rayleigh-Ritz principle is used as a starting point to model the resonant frequencies for microstructures of a given topology. The analytical approach is compared to finite element simulation results for a multitude of resonator topologies for varying etch hole size and location. This analytical model enables the formulation of design rules that allow minimization of resonant frequency offsets in MEMS resonators due to the presence of etch holes
Method for optimising the performance of PML in anchor-loss limited model via COMSOL
No full textPerfectly matched layer has been used for solving anchor-loss limited quality factor in the Micro electromechanical systems. However, setting up a well-behaved perfectly matched layer requires users to change the parameters of a perfectly matched layer to give correct results, while the current existing methods for choosing the right parameters are vague and lack theoretical support. Based on the mathematical theory of perfectly matched layer and simulation results of a beam structure's quality factor, this paper proposes a method for choosing the parameter to optimise the performance of perfectly matched layer in COMSOL. The accuracy of the proposed method is proved by matching the effect of substrate height on beam's quality factor with theory prediction. The author also studies the effect of beam height and beam width on the quality factor of the beam. The results demonstrate that simulated quality factors are in agreement with analytical values when the ratio of height over length is small but will show great divergence when height equals the length. This trend can be observed for the beam width as well. Especially for larger ratio of beam width over beam length, instead of decreasing monotonously as analytical equitation would expect, the simulated quality factor will converge into a stable value of 1700, which matches the result of two-dimensional model for the same beam structure. This means that a three-dimensional model has to be used for estimating the quality factor of a beam structure
Voltage programmable dual-band bandpass/bandstop filter response in a single micro-electro-mechanical device
No full textThis paper reports on a switchable multi-band filter response achieved within a single micro-electro-mechanical device. A prototype device fabricated in a SOI process demonstrates a voltage programmable and tunable, dual-band, band-pass/band-stop response. Both analytical and finite element models are introduced in this paper to elucidate the operating principle of the filter and to guide filter design. Voltage programmability of the filter characteristic is demonstrated with the ability to independently tune the centre frequency and bandwidth for each band. A representative measurement shows that the minimum 3 dB-bandwidth (BW) is 155 Hz, 140Hz, and 20 dB-BW is 216 Hz, 203Hz for the upper-band and lower-band center frequencies located at 131.5 kHz and 130.7 kHz, respectively
User behaviour monitoring using mobile phones to improve 5G services and performance
No full textAbstract
4G has been widely commercialised, and 5G is currently under development. The expected data bandwidth for 5G is 100 times faster than 4G and 500 times faster than 3G; however, the evolution of telecommunication technologies involves both a boost in speed and the enhancement of user experience. The key word used to describe 5G is ‘user-centric’, rather than ‘service-centric’ for 4G, and thus user behaviours of mobile data usage should be further investigated. On the other hand, the testing equipment currently being used for base stations is limited to hardware devices, such as spectrum analysers and power meters. These testing methods do not include the considerable potential variations in data demands due to changes in user behaviours, which could be resolved by presuming that all data resources could be dynamically allocated by real-time events.
A complete system has been designed and implemented in this study to investigate current user behaviours regarding mobile data usage. The system consists of three individual parts, including a user iOS application, a web server and an administrative iOS application. Ten devices were tested within the two-month data collection period. Although the sample size was too small to produce any statistical results, it was found that data usage behaviours differ from user to user, with the exception of using more than 10 times the Wi-Fi over WWAN data at all times. The data also proved that some of the usage case families, which are described in the NGMN 5G white paper, do have strong demands, which could not be fulfilled using current telecommunication technologies due to technological gaps.
This paper shows that the system proposed is a feasible method to investigate user behaviours of mobile data usage. If the sample size of users involved could be increased in the future, it would be possible to develop a model for real-time simulations of mobile users in specific areas so that limited connection resources could be dynamically allocated. Moreover, the basic communication infra-structures, such as base stations, should be well-planned and developed in advance to fulfill the potential 5G demand.</jats:p
A hybrid method to calculate optical torque: application to a nano-dumbbell trapped by a metalens
No full textThe hyper-fast rotation frequency realized in an optical levitation system provides an essential platform for various applications. Benefiting from the development of integrated photonics, optically trapping and manipulating a micro-particle via a metalens has been a significant development trend. The metalens' powerful and flexible controlling ability of the optical field opens the door to tailoring optical trapping potential. However, the existing methods are difficult to compute optical forces and torques on a non-spherical particle trapped by a metalens-based trapping system, especially when the trapping potential is tailored by a delicately designed metalens. Therefore, a hybrid method by combining the finite difference in time-domain and discrete dipole approximation method is proposed in this paper to realize this goal. The relative error of this method is verified to be below 10%. Based on this hybrid method, the fractional vortex field is found in a metalens-based trapping system for the first time. Then, the optical torque's dependency on a nano-dumbbell's geometrical parameters and spatial orientation angles are studied. It is found that there is a torque driving the nano-dumbbell to rotate about the optical axis, and the long axis of the nano-dumbbell tends to be aligned to the polarization plane because of the transverse optical torques if the long axis of the nano-dumbbell is not aligned to the optical axis.</p
Monolithically integrated polarization rotator and splitter with designed power ratio
No full textInverse designs are widely used for creating ultra-compact photonic devices, but suffer from high computation power due to the optimization complexity. General Stoke’s theorem proves that the overall change present at the outer boundary is equal to the integral of the change over the inner intervals, providing the possibility to divide one sophisticated device into several simple building blocks. Thus, we integrate this theorem with the inverse designs as a novel design methodology for optical devices. Compared with conventional inverse designs, the separated regional-optimisations can reduce the computational complexity significantly. The overall computational time is around five times shorter than optimizing the whole device region. To validate the proposed methodology, a monolithically integrated polarization rotator and splitter is designed and fabricated to demonstrate the performance experimentally. The device achieves polarization rotation (TE
00 to TE
00 and TM
00 modes) and power splitting with the designed power ratio. The exhibited average insertion loss is <1 dB and the crosstalk is <-9.5 dB. These findings confirm the advantages of the new design methodology, as well as its feasibility for achieving multiple functions on one monolithic device.
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Anchor limited Q in flexural mode resonators
No full textThis paper reports a preliminary examination of the effect of anchor geometry design on the quality factor of flexural mode resonators operating in vacuum using both FE simulation and measurements of resonator frequency response. Three types of structures have been considered in this study: an elliptical mode ring, a double ended tuning fork, and a doubly-clamped beam. We consider the relative distribution of strain energies in both the resonant structure and the connecting stem, which is indicative of the measured quality factor. The measured quality factors of the different structures are compared against each other, based on which suggestions are proposed for optimizing the anchor limited quality factor (Q) in flexural mode micromechanical resonators
Digital-coding metamaterials for on-chip beamsteering and reconfigurable millimeter-wave interconnects
No full textOn-chip millimeter-wave interconnects are becoming crucial for advancing on-chip and inter-chip transmission technologies, improving transmission efficiency and system scalability, especially in Wireless Network-on-Chip (WiNoC) and chip-scale 2.5D and 3D integration. However, due to the inherent limitations of on-chip integration related to antenna size and microfabrication compatibility. On-chip wireless channels often necessitate the use of compact, planar antennas. These antennas typically suffer from limited transmission gain, lack of beam control, and poor interference immunity, posing challenges to the reliability and versatility of millimeter-wave interconnects. This paper presents a 1-bit digital-coding metamaterial to address these challenges. The metamaterial features a 3x5 tunable unit-cell array, with each cell switchable between the ’0’ or ’1’ state with a distinct refractive index. The refractive index distribution within the unit cell array can be controlled through different binary coding sequences to manipulate the electromagnetic waves and achieve different transmission functions. When integrated with an on-chip dipole antenna, the metamaterial can achieve adjustable beamsteering in the range of ± 40°, 3.3 dB transmission gain enhancement, 90° beam splitting, and efficient energy attenuation. The proposed digital-coding metamaterial allows precise control and reconfiguration of the wireless signal distribution on silicon, significantly enhancing the flexibility, efficiency, and scalability of on-chip millimeter-wave communications
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