Narrow Results

Nonlinear coupling of a piezoelectric cantilever to an external magnetic force increases the power harvested from a broadband vibration source for relatively large acceleration vibrations. A threshold exists in the minimum acceleration needed for enhancement of the cantilever response. Below this threshold the nonlinear coupling damps the cantilever motion, and the power output is reduced compared to the noncoupled cantilever. By reducing the size of the coupling magnet, the acceleration required to scavenge usable power can be greatly reduced. The smaller diameter magnet decreases the spatial extent of the magnetic force, reducing the acceleration required to surmount the local potential barrier. The experiments result in a six-fold decrease in the acceleration threshold, to levels comparable to those observed in ambient environmental vibrations. The results are in good agreement with numerical calculations.

Models of acoustic scattering that predict the echo time history of targets are essential tools for the development of signal processing algorithms in underwater active detection systems. Realistic simulation of echoes requires a multi-frequency evaluation of acoustic scattering. This can be achieved by numerically modeling the surface of the object of interest as a collection of facets and calculating the scattered field using the Helmholtz-Kirchhoff approximation. Time and frequency domain analysis of a simple object (e.g. a sphere) and a complex structure using this technique in monostatic and bistatic configurations are given as examples.

TiO₂@MWCNT heterostructure containing single one carbon nanotube has been successfully prepared via solvothermal method. X-ray diffration (XRD) analysis shows that TiO₂ nanocrystals only contain highly crystallized tetragonal anatase phase. Interestingly, scanning electron microscope (SEM) and transmission electron microscope (TEM) results show that most of the TiO₂ nanocrystals are perpendicular to the surface of multi-walled carbon nanotube (MWCNT) and only single one carbon nanotube is coated by TiO₂ crystals. The electromagnetic (EM) characteristics are investigated at 0.5–18.0 GHz range. The EM properties show that both the permittivity and the permeability present a typical resonance behavior at 11.0 GHz and 12.0 GHz, respectively. Besides, the TiO₂@MWCNT heterostructures exhibit a broadband absorption throughout the whole Ku wave bands (12.0–18.0 GHz). Interestingly, the reflection loss (RL) of the TiO₂@MWCNT heterostructures change slightly as the thickness of the heterostructures increase from 3.0 mm to 5.0 mm in the 8.0–13.0 GHz range.

The current topic of clean air and water is often left incomplete. When we discuss cleaner cars or more regulations, we forget that none of this can genuinely be sustainable without improving our infrastructure, an objective we are mostly avoidant. With this sprouting age of technology, we have companies interject that their model is “the newest in sustainability.” Still, the systems that support production have fallen rapidly behind due to a lack of funding and push from the public. In this paper, I hope to begin a discussion on the importance of improving our energy infrastructure over the course of my lifetime. Eventually, a sprout of real change might happen to improve the lives of those around me.

The Fast Multipole Boundary Element Method (FMBEM) reduces the $O(N^2)$ computational and memory complexity of the conventional BEM discretized with $N$ boundary unknowns, to $O(NlogN)$ and $O(N)$, respectively. A number of massively parallel FMBEM models have been developed in the last decade or so for CPU, GPU and heterogeneous architectures, which are capable of utilizing hundreds of thousands of CPU cores to treat problems with billions of degrees of freedom (dof). On the opposite end of this spectrum, small-scale parallelization of the FMBEM to run on the typical workstation computers available to many researchers allows for a number of simplifications in the parallelization strategy. In this paper, a novel parallel broadband Helmholtz FMBEM model is presented, which utilizes a simple columnwise distribution scheme, element reordering and rowwise compression of data, to parallelize all stages of the fast multipole method (FMM) algorithm with a minimal communication overhead. The sparse BEM near-field and sparse approximate inverse preconditioner are also constructed and executed in parallel, while the flexible generalized minimum residual (fGMRES) solver has been modified to apply the FMBEM matrix-vector products and corresponding minimum residual convergence within the parallel environment. The algorithmic and memory complexities of the resulting parallel FMBEM model are shown to reaffirm the above estimates for both the serial and parallel configurations. The parallel efficiency (PE) of the FMBEM matrix-vector products and fGMRES solution for the present model is shown to be satisfactory; achieving PEs up to $92.3\%$ and $74.1\%$ in the fGMRES solution using 3 and 6 CPU cores respectively, when applied to models having $>10^4$ dof per CPU core. The PE of the precalculation stages of the FMBEM — in particular the FMM precomputation stage which is largely unparallelized — reduces the overall PE of the FMBEM model; resulting in average efficiencies of $68.3\%$ and $47\%$ for the 3-core and 6-core models when treating problems with $>10^4$ dof per CPU core. The present model is able to treat large-scale acoustic scattering problems involving up to $10^7$ dof on a workstation computer equipped with 128GB of RAM, while acoustic target strength (TS) results calculated up to 3kHz for the BeTSSi II submarine model demonstrate its capabilities for large-scale TS modeling.

Models of acoustic scattering that predict the echo time history of targets are essential tools for the development of signal processing algorithms in underwater active detection systems. Realistic simulation of echoes requires a multi-frequency evaluation of acoustic scattering. This can be achieved by numerically modelling the surface of the object of interest as a collection of facets and calculating the scattered field using the Helmholtz-Kirchhoff approximation. Time and frequency domain analysis of a simple object (e.g. a sphere) and a complex structure using this technique in monostatic and bistatic configurations are given as examples.

Serial IOs are widely used to expand the system bandwidth in communication systems. This paper provides an overview of serial IO design trade-offs with regard to power, cost, and performance. Circuit techniques are discussed to achieve low jitter and high bandwidth.

Quantum well infrared photodetectors (QWIPs) have been widely investigated for the 3–5 μm mid-wavelength infrared (MWIR) and 8–12 μm long-wavelength infrared (LWIR) atmospheric spectral windows as well as very long wavelength infrared (VLWIR: λ_c > 14μm) imaging array applications in the past decade. The mature III-V compound semiconductor growth technology and the design flexibility of device structures have led to the rapid development of various QWIP structures for infrared focal plane arrays (FPAs) applications. In addition to the single-color QWIP with narrow bandwidth, multi-color or broadband QWIPs required for advanced IR sensing and imaging applications have also emerged in recent years. Using band gap engineering approach, the multi-color (2, 3, and 4-color) QWIPs with multi-stack quantum wells and voltage-tunable asymmetrical coupled quantum well structures for detection in the MWIR, LWIR, and VLWIR bands have been demonstrated recently. The triple-coupled (TC-) QWIP employs the quantum confined Stark effect to tune the peak detection wavelength by the applied bias voltage. A typical single-color QWIP exhibits a rather narrow spectral bandwidth of 1 to 2 μm. For certain applications, such as spectroscopy, sensing of a broader range of infrared radiation is highly desirable. Using the stacked quantum wells with different well width and depth, the digital-graded superlattice barrier (DGSLB) or the linear-graded barrier (LGB) structures, broadband (BB-) QWIPs covering the 8–14 μm atmospheric spectral window have been reported recently.

In this chapter, the basic operation principles of a QWIP, and the design, fabrication, and characterization of multi-color and broadband QWIPs based on the GaAs/AlGaAs and InGaAs/AlGaAs material systems for the MW/LW/VLWIR applications are depicted.

A new-type high frequency broadband acoustic transducer was put forward in this article. Two methods which are composite materials and multi-mode coupled vibration have been used to expand the bandwidth of a high frequency acoustic transducer. With the help of ANSYS software, we get the vibration characteristic of the piezoelectric vibrator by building and analyzing the mode of piezoelectric vibrator. Then, we confirm the optimal design scheme of the piezoelectric sensitive element according to the simulation results. The simulation results show that the -3 db bandwidth of this transducer can reach 340KHz to 420KHz and its maximal transmitting sound level can reach 147.8 dB. It can expand the bandwidth of the transducer effectively.

In order to research the problem of broadband vibration energy harvesting of cantilever beam piezoelectric generator, frequency characteristic analysis of multi-degree-of-freedom (MDOF) cantilever beam piezoelectric generator based on ANSYS was carried out, and compared the single-degree-of-freedom (SDOF) cantilever beam piezoelectric generator, the two-degree-of-freedom (2-DOF) cantilever beam piezoelectric generator with the three-degree-of-freedom (3-DOF) cantilever beam piezoelectric generator. The simulation results show that 2-DOF cantilever beam piezoelectric generator not only has larger bandwidth at the first order natural frequency, but also can reduce the gap between the first order natural frequency and the third order natural frequency. As a result, the 2-DOF cantilever beam piezoelectric generator has certain advantages in broadband vibration energy harvesting.