Usable Frequency Bandwidth Research Articles

Development of a universal, machine tool independent dynamometer for accurate cutting force estimation in milling

When integrating a dynamometer into a machining system, it is necessary to identify the dynamic relationship between the effective input forces and the measured output signals (i.e., its transmissibility) through dedicated experimental modal analysis. Subsequently, a filter can be derived and applied to reconstruct the effective input forces from the measured signals. Unfortunately this identification phase can be complex, posing challenges to the device’s applicability in both laboratory and industrial conditions. Here this challenge is addressed by introducing a novel dynamometer concept based on both load cells and accelerometers, along with a Universal Inverse Filter. Notably, this filter is independent of the dynamic behavior of the mechanical system where the device is installed. A single calibration suffices, ideally conducted by the device manufacturer or by an expert, allowing the dynamometer’s integration by a non-expert user into any machining system without the need for repeating the identification phase and the filter generation. Furthermore, this new concept offers another significant advantage: it attenuates all inertial disturbances affecting the measured signals, including those arising from the cutting process and those originating from exogenous sources such as spindle rotation, linear axes’ movements, and other vibrations propagating through the machine tool structure. To illustrate, a simplified model is introduced initially, followed by an overview of the novel dynamometer design, innovative identification phase, and filter construction algorithm. The outstanding performance of the novel (non-parametric) Universal Inverse Filter – about 5 kHz of usable frequency bandwidth along direct directions and 4.5 kHz along cross dir. – was experimentally assessed through modal analysis and actual cutting tests, compared against state of the art filters. The efficacy of the new filter, which is even simpler than its predecessors, was successfully demonstrated for both commercial and taylor-made dynamometers, thus showing its great versatility.

Realistic weather conditions and removal of time-varying sea-surface effects: Application on ocean-bottom-cable data

In marine seismic acquisition, seismic reflections at the sea surface, such as sea-surface ghosts and multiples, affect the accuracy of the retrieved subsurface reflections and reduce the usable frequency bandwidth. These sea-surface effects tend to increase with the increasing roughness of the weather conditions. Consequently, processing techniques that neglect the roughness and time variation of the sea surface induce errors in the data that could compromise the validity of the final images and interpretations. We study the impact of time-varying rough sea surfaces using a modeling method derived from the Rayleigh reciprocity theorem for time-varying surfaces, and we analyze errors in the source-deghosting operation. We show that the source-deghosting limitations are weather dependent for data including sea-surface multiples: For calm sea states (wave heights below 1.25 m), the error made by the source-deghosting process is negligible; however, for rough seas (wave heights above 1.5 m), it becomes significant and blurs the deghosted image at the sea-surface multiple signals. To accurately remove all sea-surface effects from the seismic data, we simultaneously apply source-deghosting and multiple-removal operations to the same up-going wavefield. This procedure is shown to be weather independent based on our theoretical derivation and the synthetic results. Finally, this is tested on a 2D OBC data set. Comparing the proposed inversion to up-down deconvolution, we observe similar features in both wavefields: Source ghosts and sea-surface multiples seem to have been correctly removed from the data, and the inverted result indicates a slightly better resolution for deeper reflections.

Reinforcement learning-based dynamic band and channel selection in cognitive radio ad-hoc networks

In cognitive radio (CR) ad-hoc network, the characteristics of the frequency resources that vary with the time and geographical location need to be considered in order to efficiently use them. Environmental statistics, such as an available transmission opportunity and data rate for each channel, and the system requirements, specifically the desired data rate, can also change with the time and location. In multi-band operation, the primary time activity characteristics and the usable frequency bandwidth are different for each band. In this paper, we propose a Q-learning-based dynamic optimal band and channel selection by considering the surrounding wireless environments and system demands in order to maximize the available transmission time and capacity at the given time and geographic area. Through experiments, we can confirm that the system dynamically chooses a band and channel suitable for the required data rate and operates properly according to the desired system performance.

Uncertainty quantification and spatial variability of velocity- and attenuation-frequency dependence along a 14-km seabed survey on the Malta Plateau

We study compressional-wave frequency dependence of sound velocity and attenuation in the seabed by inverting reflectivity data recorded by an autonomous underwater vehicle (AUV) on the Malta Plateau along a 14-km survey track. The AUV towed a 32-hydrophone array and a source emitting signals at ~4-m intervals in two frequency bands (900–1300 and 1900–3600 Hz). The reflection data are processed in terms of reflection coefficients which results in ~1500 data sets, each with a seabed footprint of <20 m. For efficient Bayesian uncertainty quantification, a trans-dimensional particle filter is applied. The dataset provides a usable frequency bandwidth of 1000–3400 Hz to study velocity- and attenuation-frequency dependence which is modelled with viscous grain shearing theory. The trans-dimensional model allows frequency-dependence inferences as a function of depth while fully accounting for the unknown seabed stratification which substantially affects the estimates. Finally, the AUV acquisition provides the means to study the frequency-dependent seabed variability at mesoscales of several meters which are poorly understood. [Data are from CLUTTER JRP, a collaboration of ARL-PSU, DRDC, CMRE, and NRL. Research supported by the Natural Sciences and Engineering Research Council of Canada.]We study compressional-wave frequency dependence of sound velocity and attenuation in the seabed by inverting reflectivity data recorded by an autonomous underwater vehicle (AUV) on the Malta Plateau along a 14-km survey track. The AUV towed a 32-hydrophone array and a source emitting signals at ~4-m intervals in two frequency bands (900–1300 and 1900–3600 Hz). The reflection data are processed in terms of reflection coefficients which results in ~1500 data sets, each with a seabed footprint of <20 m. For efficient Bayesian uncertainty quantification, a trans-dimensional particle filter is applied. The dataset provides a usable frequency bandwidth of 1000–3400 Hz to study velocity- and attenuation-frequency dependence which is modelled with viscous grain shearing theory. The trans-dimensional model allows frequency-dependence inferences as a function of depth while fully accounting for the unknown seabed stratification which substantially affects the estimates. Finally, the AUV acquisition provides the me...

Nonlinear Dynamic Characteristics of Variable Inclination Magnetically Coupled Piezoelectric Energy Harvesters

This paper investigates the nonlinear dynamic characteristics of a magnetically coupled piezoelectric energy harvester under low frequency excitation where the angle of the external magnetic field is adjustable. The nonlinear dynamic equation with the identified nonlinear magnetic force is derived to describe the electromechanical interaction of variable inclination angle harvesters. The effect of excitation amplitude and frequency on dynamic behavior is proposed by using the phase trajectory, power spectrum, and bifurcation diagram. The numerical analysis shows that a rotating magnetically coupled energy harvesting system exhibits rich nonlinear characteristics with the change of external magnet inclination angle. The nonlinear route to and from large amplitude high-energy motion can be clearly observed. It is demonstrated numerically and experimentally that lumped parameters equations with an identified polynomials for magnetic force could adequately describe the characteristics of nonlinear energy harvester. The rotating magnetically coupled energy harvester possesses the usable frequency bandwidth over a wide range of low frequency excitation by adjusting the angular orientation.

Chaos in the fractionally damped broadband piezoelectric energy generator

Piezoelectric materials play a significant role in harvesting ambient vibration energy. Due to their inherent characteristics and electromechanical interaction, the system damping for piezoelectric energy harvesting can be adequately characterized by fractional calculus. This paper introduces the fractional model for magnetically coupling broadband energy harvesters under low-frequency excitation and investigates their nonlinear dynamic characteristics. The effects of fractional-order damping, excitation amplitude, and frequency on dynamic behaviors are proposed using the phase trajectory, power spectrum, Poincare map, and bifurcation diagram. The numerical analysis shows that the fractionally damped energy harvesting system exhibits chaos, periodic motion, chaos and periodic motion in turn when the fractional order changes from 0.2 to 1.5. The period doubling route to chaos and the inverse period doubling route from chaos to periodic motion can be clearly observed. It is also demonstrated numerically and experimentally that the magnetically coupling piezoelectric energy harvester possesses the usable frequency bandwidth over a wide range of low-frequency excitation. Both high-energy chaotic attractors and large-amplitude periodic response with inter-well oscillators dominate these broadband energy harvesting.

Estimating quality factor from surface seismic data: A comparison of current approaches

Abstract The performances of the spectral ratio (SR), frequency centroid shift (FCS), and frequency peak shift (FPS) methods to estimate the effective quality factor Q are compared. These methods do not demand true amplitude data and their implementations were done following an “as simple as possible” approach to highlight their intrinsic potentials and limitations. We use synthetic zero-offset seismic data generated with a simple layer-cake isotropic model. The methods can be ranked from simple to complex in terms of automation as: FPS, FCS and SR. This is a consequence of: (i) peak identification consists basically of a sorting procedure, (ii) centroid estimation involves basically the evaluation of two well-behaved integrals, and (iii) implementation of the SR method involves at least choosing a usable frequency bandwidth and fitting a gradient. The methods can be ranked from robust to sensitive in the presence of noise content in the sequence SR, FCS, and FPS. This is consequence of: (i) the gradient estimate associated to the SR method averages out the noise content in the entire usable frequency bandwidth, (ii) in the presence of moderate-to-high noise level, the centroid estimation is biassed towards overestimating Q due to noise contribution in the tail of the amplitude spectrum, and (iii) peak identification is unstable due to local noise fluctuation in the amplitude spectrum around the peak frequency. Regarding the stability of the estimates relative to the attenuation amount, SR and FCS methods show similar behaviours, whereas FPS method presents an inferior performance. This fact is an indirect consequence of the sensitivity of FPS method to the noise content because the higher is the attenuation the lower is the signal-to-noise ratio. Finally, regarding the robustness of the methods to the presence of dipping layers, only SR and FCS methods provide good estimates, at least to typical dips in non-faulted sedimentary layers, with the estimates obtained with SR method being more accurate that those obtained with FCS method. Except in relation to the automation complexity, which is less important than the performances of the methods, SR method was superior or showed similar performance to FCS method in all scenarios we tried.

Grating lobe reduction in transducer arrays through structural filtering of supercritical plates

The effect of placing a structural acoustic filter between water and the transducer elements of an array to help reduce undesirable grating lobes is investigated. A supercritical plate is mounted to transducer elements with a thin decoupling polyurethane layer between the transducers and the plate. The plate acts as a radiation/incidence angle filter to pass energy at angles near normal incidence, but suppress energy at large incidence angles. Grating lobe reduction is achieved at the expense of limiting the available steering of the main lobe. Within this steer angle limitation, the main lobe can be steered as normal while the grating lobe level is reduced by the plate's angular filtering. The insertion of a plate structural filter provides, in principal, an inexpensive and easily implemented approach to extend usable frequency bandwidth with reduced level grating lobes, without increasing the number of array elements. Even though the data match theory well, a practical material has yet to be found that possesses optimal material properties to make the proposed idea practical. This work represents the first attempt to advantageously utilize a plate above its critical frequency to provide angular dependent sound transmission filtering.

WPAN용 디지털 음향기기 및 통신기기간 스펙트럼 상호운용을 위한 채널 할당기술에 관한 연구

This paper presents the calculation of the required bandwidth of common frequency bandwidth applying queueing theory for maximizing the efficiency of frequency resource of WPAN(Wireless Personal Area Network) based Digital acoustic and communication devices. It assumed that LBT device(ZigBee) and FH devices (DCP, RFID and Bluetooth) coexist in the common frequency band for WPAN based Digital acoustic and communication devices. Frequency hopping (FH) and listen before talk (LBT) have been used for interference avoidance in the short range device (SRD). The LBT system transmits data after searching for usable frequency bandwidth in the radio wave environment. However, the FH system transmits data without searching for usable frequency bandwidth. The queuing theory is employed to model the FH and LBT system, respectively. As a result, the throughput for each channel was analyzed by processing the usage frequency and the interval of service time for each channel statistically. When common frequency bandwidth is shared with SRD using 250mW, it was known that about 35 channels were required at the condition of throughput 84%, which was determined with the input condition of Gaussian distribution implying safety communication. Therefore, the common frequency bandwidth is estimated with multiplying the number of channel by the bandwidth per channel. These methodology will be useful for the efficient usage of frequency bandwidth.

Grating Lobe Reduction in Transducer Arrays Through Structural Filtering of Supercritical Plates

The effect of placing a structural acoustic filter between water and the transducer elements of an array is investigated to help reduce undesirable grating lobes. A plate is mounted to transducer elements with a thin decoupling polyurethane layer between the transducer and the plate. The plate acts as a radiation/incidence angle filter to pass energy at angles near normal incidence, but suppress energy at large incidence angles. Grating lobe reduction is achieved at the expense of limiting the available steering of the main lobe. Within this steer angle limitation, the main lobe can be steered as normal while the grating lobe level is reduced by the plate’s angular filtering. The insertion of a plate structural filter provides an inexpensive and easily implemented approach to extend usable frequency bandwidth with reduced level grating lobes, without increasing the number of array elements. Even though some data matches theory well, a practical material has yet to be found that possesses optimal material properties. To the author’s knowledge, this work represents the first attempt to advantageously utilize a plate to provide angular dependent sound transmission filtering above the plate’s critical frequency (the supercritical frequency region). [Work sponsored by ONR Code 333, Dr. David Drumheller.]

A hybrid boundary integral equation method for the computation of source time functions for 3-D rupture propagation

A hybrid space and spatial transform convolution method is developed for computing source time functions based on numerically solving an integral equation formulation of the mixed boundary value problem for fault displacements and tractions. The space domain method is an adaptation of the method of Das (1980) in which the displacements on the broken region of the crack and the tractions on the unbroken region of the crack are computed by convolving the Green's function for a point source with the tractions from all times back to the onset of faulting. The spatial transform domain method performs the convolutions by obtaining the 2-D Fourier transform of the stresses and Green's functions; multiplying them in the transform domain; and then inverse transforming back to the space domain. The space domain method is more accurate and rapid for small grid sizes; it is used for convolving over the tip of the Green's function cone. The spatial transform method is more rapid, and reproduces the old spatial domain method it replaces within 1 per cent; it is used for convolving over the higher times of the Green's function cone. As a check of the accuracy of the overall method the results are compared against the analytic results of Kostrov (1964) for a circular crack which grows without stopping at a fixed rupture velocity of 0.5α. Good agreement is found for the slip displacements. We also test the grid size dependence of the numerical fracture criterion, and show that it decreases somewhat more rapidly than Δx−1/2 for average rupture velocities above about 0.4α but is not well resolved for lower rupture velocities due to the coarse grid sizes involved. The usable frequency bandwidth of both the slip velocities on the fault and the synthetic seismograms is determined by the granularity of the discretization of the rupture process. The usable spectral bodywaves radiated from this model extend in a band 1.0 decades above the corner frequency.