Half-power Bandwidth Research Articles

Numerical evaluation of acoustic characteristics of a thrust chamber with quarter-wave resonators

Acoustic characteristics of a thrust chamber with quarter-wave resonators are numerically studied based on the unsteady Reynolds-averaged Navier-Stokes (URANS) method. Organized pressure disturbance model and constant-volume bomb model are applied as artificial disturbances to excite pressure oscillations in the chamber. Eigenfrequencies and amplitudes of acoustic modes of the chamber are obtained by fast fourier transform (FFT) analysis, while damping characteristics are evaluated by the half-power bandwidth method. Predicted damping capacities of the chamber with and without quarter-wave resonators agree well with experimental results. Pressure oscillations can be controlled by a quarter-wave resonator mainly through reducing the amplitude of target acoustic mode, rather than increasing damping capacity of the chamber. Major damping mechanism of the resonator is cutting down pressure peak of target acoustic mode and raising up its pressure trough (CPRT); therefore the amplitude of target acoustic mode is reduced significantly. Moreover, acoustic energy can be dissipated by vortex at the orifice and by viscosity on the surface of a resonator, which increase damping capacity of the chamber slightly. Under the condition with multi-modes pressure oscillations, a resonator can still suppress pressure oscillations of target acoustic mode through CPRT. However, it may enhance pressure oscillations of other modes due to redistribution of oscillation energy among all acoustic modes.

Multi-factors analysis on the energy harvesting performance of PEH under multiple-frequency excitation

The piezoelectric energy harvesters (PEHs) undergoing coupled bending-torsional vibrations were designed by crossbeam-offset and asymmetric mass, and the maximum output peak voltage at the first mode (Up-max1) and the minimum resonance frequency difference between the first and second modes (Δf0) were 81.5 V and 16.0 Hz chosen as the optimization objectives in the multi-factors analysis based on the orthogonal test method. The geometrical parameters including the crossbeam length, mass ratio, substrate thickness and primary beam length are correspondingly determined, before the PEHs were fabricated to investigate the optimum resistance and energy harvesting efficiency. The PEHs were constructed as the series connection structure, and the mechanical vibration experiments were performed to measure output peak voltage vs frequency curve. When the load resistance is applied from 47 to 1000 kΩ, all of the optimum resistances are about 470 kΩ for the PEHs with the offset ratio 1.23 and mass ratio 4. The errors are at the ranges of 5.0%–16.4% for Up-max and 1.1%–6.5% for f0, and the measurement reliability is acceptable. The sums of half-power bandwidths are regarded as the energy harvesting characteristic to evaluate the efficiency, and they are broaden by 133% and 180% for the PEHs with crossbeam-offset and asymmetric mass under multiple-frequency excitation. PEH undergoing coupled bending-torsion vibrations could harvest more electrical power at multiple resonance frequencies in nature environment.

Effects of Using Various Methods for Car Shock Absorbers Diagnostic Tests

The work concerns the diagnostic assessment of the technical condition of the car suspension. The paper discusses practical problems that usually appear during testing of car shock absorbers mounted in a vehicle. The results of experimental tests for passenger car, carried out according to the EUSAMA standard test, were compared with the results obtained using newer methods (phase angle method and half power bandwidth method – HPBM). The article also deals with the issue of incompatibility of typical excitation at diagnostic devices for testing suspension with the one that often occurs in road conditions (by simulation method). The main purpose of the work was to assess the usefulness and reliability of various diagnostic methods intended for the testing of vehicle shock absorbers without disassembly them from the vehicle. The analyses carried out indicated the advantages and disadvantages of these methods in practice. It is also shown that the conditions of diagnostic tests correspond poorly to the operating conditions of the shock absorbers under normal vehicle operating conditions. An important factor in this case is the sliding friction in the suspension.

Analysis, Design, and Implementation of a New Extremely Ultrathin 2-D-Isotropic Flexible Energy Harvester Using Symmetric Patch FSS

Electromagnetic (EM) energy exists far and wide in the environment and can be harnessed and transferred to the desired load(s). The researchers mostly designed and implemented the planar metasurface energy harvester (MEH) offering a restricted look-angle. In this article, we propose an extremely ultrathin 2-D-isotropic flexible MEH using multipolarized patch frequency selective surface. This MEH, which has a curved shape, enjoys a relatively constant performance over a huge range of oblique incident waves. The final structure can be prepared by a small slice of a cylinder. A classic model inspired from the dipole antenna concept is used for impedance matching. Theoretical analyses, design, and fabrication of the structure are presented using a deep subwavelength PCB substrate having a thickness of $\sim 0.004~\lambda _{0}$ . EM energy harvesting is analyzed with an equivalent circuit model. The experimental results are acceptably in agreement with the simulation results. The design can be scaled to different RF bands; however, to provide the required energy for Internet-of-Things (IoT) instruments, we have used WiFi as a crowded frequency band. The simulation efficiency of the flat style extremely ultrathin MEH (EMEH) for normal incidence (at 5.81 GHz) and 60° oblique angle incidence with transverse magnetic (TM) and transverse electric (TE) polarizations are 87.35%, 93.26%, and 64.42%, respectively. In addition, half power bandwidth (HPBW) for these situations is 6.97%, 8.86%, and 5.61%, respectively.

Estimation of damping in riveted short cantilever beams

In layered and riveted structures, vibration damping happens because of a micro slip that occurs because of a relative motion at the common interfaces of the respective jointed layers. Other parameters that influence the damping mechanism in layered and riveted beams are the amplitude of initial excitation, overall length of the beam, rivet diameter, overall beam thickness, and many layers. In this investigation, using the analytical models such as the Euler–Bernoulli beam theory and Timoshenko beam theory and half-power bandwidth method, the free transverse vibration analysis of layered and riveted short cantilever beams is carried out for observing the damping mechanism by estimating the damping ratio, and the obtained results from the Euler–Bernoulli beam theory and Timoshenko beam theory analytical models are validated by the half-power bandwidth method. Although the Euler–Bernoulli beam model overestimates the damping ratio value by a very less fraction, both the models can be used to evaluate damping for short riveted cantilever beams along with the half-power bandwidth method.

A three-dimensional ultra-broadband and polarization insensitive metamaterial absorber and application for electromagnetic energy harvesting

ABSTRACT In this paper, a three-dimensional (3D), ultra-broadband and polarization insensitive metamaterial absorber (MA) base on the metal loading resistive films structure was introduced. Numerical results show that ultra-wideband absorption more than 90% can be achieved from 4.8 to 14.67 THz, the relative bandwidth up to 101%. The reason of the highly efficient absorption is contributed to the metal Ohm loss and load absorption of the resistive film in the gap of metallic SRRs (split-ring resonators) mainly. Importantly, we found loading resistive film in the gap of the metal-film can significantly promote absorption. Circle currents are formed on twelve SRRS and the electromagnetic energy is collected on the resistive films. The surface currents are researched to explain the physics mechanism of the MA. Moreover, the harvesting efficiencies for energy on the normal and oblique incidences are investigated. Finally, we calculated the HPBW (Half Power Band Width) of harvesting efficiency, a characteristic with dual-band half power absorption is obtained.

Seismic inversion of soil damping and stiffness using multichannel analysis of surface wave measurements in the marine environment

SUMMARY Determination of soil material damping is known to be difficult and uncertain, especially in the offshore environment. Using an advanced inversion methodology based on multichannel spectral analysis, Scholte and Love wave measurements are used to characterize subsea soil from a North Sea site. After normalization, a determinant-based objective function is used in a genetic algorithm optimization to estimate the soil shear modulus. The inverted shear-modulus profile is comparable to previously published results for the same data, although a higher degree of certainty is achieved in the near-surface layers. The half-power bandwidth method is used for extracting the attenuation curve from the measurements and efficient reference data points are chosen based on wavelet compression. The material-damping ratio inversion is performed using a modified stochastic optimization algorithm. Accounting for measurement errors, the material-damping ratio profile is retrieved from the fundamental-mode Scholte wave with a high degree of certainty. Furthermore, a method is proposed for identifying the frequency dependence of the material-damping ratio from in situ measurements. No evidence for frequency dependence is found and the small-strain soil material-damping ratio at this site can be said to be frequency independent for the measured conditions.

Contribution of carbon nanotubes to vibration damping behavior of epoxy and its carbon fiber composites

The main objective of this study was to investigate contribution of the non-functionalized multi-walled carbon nanotubes on the vibration damping behavior of first neat epoxy resin and then unidirectional and bidirectional continuous carbon fiber reinforced epoxy matrix composites. Epoxy/carbon nanotubes nanocomposites were produced by ultrasonic solution mixing method, while the continuous carbon fiber reinforced composite laminates were obtained via resin-infusion technique. Vibration analysis data of the specimens were evaluated by half-power bandwidth method; and the mechanical properties of the specimens were determined with three-point bending flexural tests, including morphological analyses under scanning electron microscopy. It was generally concluded that when even only 0.1 wt% carbon nanotubes were incorporated into neat epoxy resin, they have contributed not only to the mechanical properties (flexural strength and modulus), but also to the vibration behavior (damping ratio) of the epoxy. When 0.1 or 0.5 wt% carbon nanotubes were incorporated into continuous carbon fiber reinforced epoxy matrix composites, although they have no additional contribution to the mechanical properties, their contribution in terms of damping ratio of the composites were significant.

Four-Layer Tunable Wideband Electromagnetic Shield Based on Cold Plasma

In this paper, we present a four-layer tunable wideband electromagnetic shield based on cold plasma. It consists of two dielectric matched layers, one backside housing dielectric layer and one vacuum chamber in between where cold plasma can be produced through a glow discharge. No plasma is produced within the vacuum chamber when low-power communication signal impinges on the shield and it can easily propagate through with very low return and absorption loss. When a high-power microwave pulse impinges on the shield, cold plasma can be timely produced within the chamber to reflect and absorb the high-intensity microwave energy. Input impedance, standing wave ratio, transmission and reflection coefficients and shielding effectiveness for proposed four-layer structure electromagnetic shield are deduced and formulated. Transparent mode of the electromagnetic shield for communication frequency at 3.5GHz is developed based on transmission line and plane wave theory. Simulation results show that the transmission coefficient is close to unity, and the reflection coefficient is near to zero. The half-power transmission bandwidth is 16% for proposed structure with central communication frequency of 3.5GHz. The impact of plasma frequency and plasma collision frequency on the absorption, reflection, shielding effectiveness for interference frequency between 0-6GHz are investigated. Simulation results show that higher the plasma frequency, better the shielding effectiveness is in the investigated frequency band when plasma collision frequency is fixed. It was also demonstrated that the shielding effectiveness of proposed structure can be tuned by changing plasma collision frequency.

Mechanical and Dynamic Properties of Basalt Fiber-Reinforced Composites with Nanoclay Particles

Mechanical and dynamic characteristics of basalt fiber-reinforced polymer (BFRP) composites were experimentally investigated in terms of natural frequency and damping properties. Epoxy resin of BFRP composites was modified by nanoclay (NC) particles at different weight contents (0, 0.5, 1, 1.5, 2, and 3 wt%). Mechanical tests were performed with tensile, flexural, and impact measurements in accordance with ASTM standards. Impact properties of the samples were evaluated by using Charpy impact tests in accordance with ISO 179/92 standards for both of edgewise and flatwise impact directions. After the mechanical and impact tests, damage mechanisms of the fractured samples were analyzed over the damaged regions, and their morphologies were analyzed by using scanning electron microscopy. In vibration tests, dynamic properties such as loss and storage modulus were evaluated only for fundamental natural frequency, and their corresponding damping properties were measured by using the half-power bandwidth method from frequency response curves. Results showed that the small amount of NC particle incorporations into BFRP composites was found the most effective for damping and natural frequency of the produced NC modified basalt/epoxy nanocomposites, and incorporation of NC particles into the epoxy resin improves the flexural strength up to the 29%, tensile strength up to the 7.61%, and impact resistance (edgewise impact) up to the 16.8%, at NC contents of 1.5, 2, and 0.5 wt%, respectively.

Estimation of the Dynamic Characteristics of the Foam Concrete

Dynamic properties of the building materials are not often under investigation because of complexity and difficulty of the dynamic problems, which need to be solved. Foam concrete (FC) is a material that has wide application and utilization in the civil engineering structures. FC is a mixture of cement, water, additives and technical foam and principle of fabrication is well known for more than 30 years. Currently, it is mainly used in the floor structures of the buildings, thus static parameters are investigated. Its usability can be much wider thanks to its specific properties. A research aimed at the application of the foam concrete in the pavement structures takes place at our workplace. FC could be utilized as a sub-base layer at the road reconstructions, excavations or as a structure layer of the new pavements. This paper presents the preliminary outputs of the experimental and numerical analyses of the selected dynamic properties of the FC. Results were obtained from the dynamic hammer testing and the Finite Element (FEM) simulation as a background for the design procedure of the pavement structures. Relevant dynamic parameters such as dynamic modulus of elasticity at low strain or damping parameters were determined in this article. This paper is also aimed at the estimation of the Rayleigh damping coefficients. For the Rayleigh damping coefficients, a half-power bandwidth method was selected. Conclusions indicate some dispersion of the observed quantities and further testing and analysis to increase the reliability of the determined characteristics is required. Obtained dynamic parameters will be a background for the pavement design using the FC.

A Critical Step to Using a Parametric Array Loudspeaker in Mobile Devices.

A parametric array (PA) loudspeaker is a highly directional audio source that might grant one's convenience if it is used with mobile devices. However, conventional PA loudspeakers is almost impossible to apply in mobile devices using a battery because of the large power consumption and large device size. In this study, a PA loudspeaker system (PALS) was fabricated and evaluated to show that those difficulties could be overcome to apply it to mobile devices. In order to construct a PALS for demonstration, a power amplifier and signal-processing unit should also be properly designed and built. The PA source transducer should also be designed and built for a mobile device application. These components were integrated into a single PALS. The PALS generated a 125-dB primary wave and 62 dB of a different frequency wave (DFW) through the PA at 0.45 m in a 3 m × 3 m × 2 m semi-anechoic chamber. We confirmed that the half-power bandwidth (HPBW) formed a 6° beam at 83 kHz of DFW and 90 kHz of the primary wave (PW), and the HPBW formed a 7.3° beam at 5 kHz of DFW and a 7.1° beam at 10 kHz of DFW, respectively. Lastly, the power required was 6.65 W without a matching circuit, and 3.25 W with such a circuit.

Differentially driven wideband Fabry–Perot cavity antenna

A wideband differential Fabry–Perot cavity antenna (FPCA) is presented. Unlike the mostly used patch antennas, a rectangular dielectric resonator antenna (DRA) has been investigated as primary radiation source. A compact partially reflective surface (PRS) is proposed and used as superstrate layer over the DRA for wideband gain enhancement. Measurements show that the antenna exhibits a wide impedance bandwidth (for |S 11 |<−10 dB) as well as half-power gain bandwidth of 30% ranging from 2.27 to 3.05 GHz with a maximum boresight gain of 9.95 dBi. However, the gain of FPCA is improved all over the band; it is 4.5 dB higher than the DRA's gain at 2.7 GHz. The differential operation provides higher noise immunity than the single-ended high gain antennas. Furthermore, the presence of DRA and imperfect phase of PRS have been considered for estimation of optimum height of the cavity. Characteristics of a rectangular DRA in a Fabry-Perot cavity are studied through a detailed parametric study and presented here.

High power density spring-assisted nonlinear electromagnetic vibration energy harvester for low base-accelerations

This work explores an enhanced magnetic spring based energy harvester design that uses a dual-mass and a geometrically nonlinear mechanical planar spring as a route to significantly improve power metrics of traditional magnetic spring based energy harvesters. Prototypes of the enhanced harvester are constructed and characterized experimentally. Nonlinear dynamical models of the harvester are developed and validated against experimental data. Additionally, prototypes of the commonly studied magnetic spring based energy harvesters are constructed, characterized, and modeled. Results show excellent agreement between model simulations and experimental data. Results show that the enhanced harvester significantly outperforms the commonly studied magnetic spring based vibration energy harvesters, especially at low acceleration levels. The enhanced harvester generates 1.97 [mW/cm3 g2] at 0.4 g [m/s2] which is approximately 400% the amount of power generated by the traditional magnetic spring based harvester, i.e. 0.5 [mW/cm3 g2]. Additionally, the half-power frequency bandwidth of the enhanced harvester is 90% wider compared to the traditional harvester. At lower acceleration, i.e. 0.1 g [m/s2], the enhanced harvester exhibits 4000% increase in power metrics compared to the traditional harvester. This makes the presented enhanced harvester design exceptionally suitable for applications where low acceleration oscillations are abundant including harvesting vibrations from highway bridges and human body motion.

Radio Frequency Angular Momentum Biased Quasi-LTI Nonreciprocal Acoustic Filters.

We report on the design and operation of a novel class of nonreciprocal acoustic filters operating in the radio frequency (RF) range. These devices use the spectral characteristics of commercial acoustic filters placed in angular momentum biased networks to achieve large nonreciprocity, low insertion loss (I.L.), and wideband operation. Owing to the high rejection exhibited by acoustic filters, these novel devices can achieve an unprecedented suppression of undesired intermodulation products, thus approaching the spectral purity attained by conventional linear-time-invariant (LTI) filtering components. In addition, a new analytical model suitable to capture the behavior of any angular-momentum-biased nonreciprocal device is presented. This model allows us to identify the main characteristics of the transfer function (poles and zeroes) relative to this new class of nonreciprocal filters, thus enabling new synthesis capabilities through standard numerical methods. Ultimately, the performance of a built 1.1-GHz nonreciprocal acoustic filter prototype is reported. This device relies on a modulation implemented through switched capacitors and shows I.L., isolation, and half-power bandwidth values of 4.5 dB, 28 dB, and 20 MHz, respectively, achieved through the use of a 40-MHz modulation frequency. Moreover, by showing an intermodulation distortion lower than -34 dBc, it approaches the operation of LTI circuits.

Bidirectional to unidirectional emission of fluorescence controlled by optical traveling wave antennas

Abstract Tailoring the fluorescence emission of quantum emitters to a desired direction is a crucial issue to achieve high efficient photodetection and realize unique optoelectronic devices. In this study, the directional emission of quantum dots controlled by optical traveling wave antennas based on 1D silver nanowires (NWs) was investigated. Both leaky waves and surface waves on a single NW are utilized for fluorescence emission control, and we show that the coupled fluorescence transforms from bidirectional to unidirectional emission when the surrounding medium changes from air to water. Moreover, in the unidirectional case, we obtain an ultra-narrow half-power bandwidth about 20°. Finite-difference time-domain simulations and Green’s function method in a stratified medium are used to calculate the far-field emission patterns of the hybrid structures, which agree well with the experiments. Further analyses based on typical modes and the dipole-chain model also reveal the mechanism behind the bidirectional and unidirectional fluorescence emission. These results show that the structures have great potential in integrated on-chip, sensing and photon-collection devices.

Damping characteristics of full-scale grouped helical piles in dense sands subjected to small and large shaking events

A full-scale pile testing program was implemented using the large outdoor shake table at the University of California – San Diego. Nine steel helical piles with varying geometry were embedded in dense sand and tested individually and in 2×2 groups, comparing fixed and pinned pile head connections. The test piles were subjected to shake motions ranging from pulses and white noise to replicated earthquakes. Strain gauges attached to the exterior pile walls and accelerometers placed on the pile caps and within the soil provided data for analyzing the behavior of these piles. Foundation damping (herein soil–pile system) is a substantial parameter in seismic design of the foundation–structure. Therefore, the damping characteristics of the soil bed along with the combined soil–pile system consisting of single and grouped helical piles are discussed based on the experimental pulse, white noise, and shake excitations. Several methods, including logarithmic decrement, half-power bandwidth, and energy (equivalent) methods, were implemented to estimate the damping ratio over a range of strains. Based on the experimental data gathered from this study, the suitability and accuracy of different computational methods to determine damping ratio as well as the effect of type and location of instrumentation on the calculated damping ratio were evaluated.

A packaged piezoelectric vibration energy harvester with high power and broadband characteristics

This paper presents the new design and fabricating process of a packaged micro piezoelectric vibration energy harvester (PVEH). Structures are designed and parameters are optimized through finite element modelling and analysis. The double L-shaped tungsten proof mass block and thick copper-based PZT bimorph are proposed to ensure the harvester with high electrical power. Polymethyl methacrylate (PMMA) packaging and epoxy resin bonding supply the flexible clamping of piezoelectric cantilever, which decreases the resonant frequency, increase average PZT stress, reduces the maximum PZT stress and broadens the effective frequency range. Bulk PZT bonding is used in PVEH prototype fabrication. Experimental results show that the packaged PVEH resonates under the excitation of 1 g (9.8 m s−2) at 160 Hz. It has an optimum resistance load of 47 kΩ. More importantly, its maximum output power is 2.49 mW in experiments, and the half-power bandwidth is 22 Hz. After package, it has a high volume power density of 0.64 mW/cm3 g2 with the volume of 3.9 cm3 (2 cm × 1.5 cm × 1.3 cm). Connected with energy harvesting circuit, PVEH can light up a light emitting diode (LED) under broadband vibration frequency. The proposed PVEH with broadband output power in mW level is promised to power up some microelectronic devices for application.

A music-box-like extended rotational plucking energy harvester with multiple piezoelectric cantilevers

Vibrational interference has been found to incur inefficient system responses and suboptimal energy harvesting performance as the rotational frequency increases in the conventional rotational plucking energy harvester. As a result, this letter proposes a music-box-like structure of a rotational plucking energy harvester to overcome the problem by extending the rotary cylinder out of plane. A model is proposed and experimentally validated by characterizing its dynamic and energetic characteristics. Numerical analyses show that the proposed rotational plucking structure can reduce the vibrational interference and be capable of harvesting more energy at high rotational frequencies as well as extending the operating frequency range and broadening the half-power bandwidth.

A Bond Wire Connection Implementation at mm-Wave Active Microstrip Antenna

A bond wire to microstrip line transition, featuring two impedance transformers, is presented for a mm-wave microstrip antenna and power amplifier (PA) integration using conventional bond wires. Simulated return loss bandwidth for the transition is 4 GHz with a minimum insertion loss of 1 dB. Measurement results for the designed active antenna are compared with measurements for a passive antenna and a standalone PA. The maximum gain is 29 dBi, compared with 16.7-dBi passive antenna maximum gain. The half-power gain bandwidth is 7%. The measured active antenna radiation pattern is in good agreement with simulations. The maximum deembedded PA output power is close to 9 dBm.