High Frequency Excitation Research Articles

Nonlinear low frequency water waves in a cylindrical shell subjected to high frequency excitations – Part I: Experimental study

This paper presents an experimental investigation on nonlinear low frequency gravity water waves in a partially filled cylindrical shell subjected to high frequency horizontal excitations. The characteristics of natural frequencies and mode shapes of the water–shell coupled system are discussed. The boundaries for onset of gravity waves are measured and plotted by curves of critical excitation force magnitude with respect to excitation frequency. For nonlinear water waves, the time history signals and their spectrums of motion on both water surface and shell are recorded. The shapes of water surface are also measured using scanning laser vibrometer. In particular, the phenomenon of transitions between different gravity wave patterns is observed and expressed by the waterfall graphs. These results exhibit pronounced nonlinear properties of shell–fluid coupled system.

Design Strategies for Eddy-Current Displacement Sensor Systems: Review and Recommendations

This paper presents a comprehensive study of the design aspects of eddy-current displacement sensor (ECS) systems. In accordance with the sensor analysis presented in this paper, design strategies to compensate for important sensor imperfections are recommended. To this end, the challenges that are associated with ECS interfaces are identified, with focus on advanced industrial applications. This paper also provides a technical overview of the design advances of ECS interfaces proposed in the last decade and evaluates their pros and cons. Recently reported interface solutions for demanding industrial applications with respect to high resolution, stability, bandwidth, and low power consumption, at a sufficiently high excitation frequency, are addressed in more detail.

Theoretical Research on New Laminated Structure Flux Switching Permanent Magnet Machine for Novel Topologic Plug-In Hybrid Electrical Vehicle

In this paper, a novel configuration for University of Technology Sydney (UTS) plug-in hybrid electric vehicle (PHEV) is introduced which has only one electric machine functioning as either a motor or generator at a time. For continuous working, more strict requests are made to the drive machine, mainly including good thermal dissipation capability, high torque density, great flux weakening ability, etc. One new laminated structure flux switching permanent magnet machine (LSFSPMM) is proposed in this paper, which stator and rotor are laminated in parallel to the axis. It can make full use of PM flux linkage and reduce the core loss particularly in the high excitation frequency. Based on the 2D model prediction by finite element algorithm (FEA), LSFSPMM has lower cogging torque, higher torque density, greater flux weakening ability, higher efficiency, etc., and hence it can be regarded as one ideal candidate for the UTS PHEV drive system.

Investigation of energy relaxation in 1-D nonlinear lattices by wavelets

The movement and relaxation of the localized energy on FPU lattices have been studied by using Wavelet transforms methods. The energy relaxation mechanism for nonlinear chains involves the degradation of higher frequency excitations into lower frequencies. It is shown that low frequency modes decay more slowly in nonlinear chains. The wavelet spectrum exhibits a behavior involving the interplay of phonon modes and breather modes.

Quantum Capacitance in Topological Insulators

Topological insulators show unique properties resulting from massless, Dirac-like surface states that are protected by time-reversal symmetry. Theory predicts that the surface states exhibit a quantum spin Hall effect with counter-propagating electrons carrying opposite spins in the absence of an external magnetic field. However, to date, the revelation of these states through conventional transport measurements remains a significant challenge owing to the predominance of bulk carriers. Here, we report on an experimental observation of Shubnikov-de Haas oscillations in quantum capacitance measurements, which originate from topological helical states. Unlike the traditional transport approach, the quantum capacitance measurements are remarkably alleviated from bulk interference at high excitation frequencies, thus enabling a distinction between the surface and bulk. We also demonstrate easy access to the surface states at relatively high temperatures up to 60 K. Our approach may eventually facilitate an exciting exploration of exotic topological properties at room temperature.

Investigating the fidelity of a pseudo-analytical solution of a rib-stiffened, layered plate structure subjected to high frequency acoustic loading

There is a need for a fast and reliable tool to assist in the analysis, design, and optimization of submarine and UUV coatings due to high frequency incident acoustic pressure loading. An existing pseudo-analytical, frequency domain solution for wave propagation in coated, ribbed, three-dimensional elastic layered plates excited by acoustic plane waves provides fast solutions for high frequency excitations. Weidlinger Associates, Inc. (WAI) is developing an analysis software tool which integrates this solution methodology while adding some technical improvements to the formulation. The solution methodology, which is found to be numerically unstable under certain conditions, contains a fundamental ansatz regarding the set of excited wave forms expressed through a particular wave number expansion in the direction of periodicity. Evidence is presented to show that the numerical instability is due to the specific choice of the wave number basis used in the solution. In order to provide a remedy while retaining the positive aspects of the solution methodology, WAI is implementing a pre-processing step to determine the optimal wave number basis: the set of admissible propagating (and attenuating) waves are predetermined via an eigenvalue analysis and then substituted into the wave number basis in computing the pseudo-analytical solution.

RADIO FREQUENCY MAGNETIZATION NONVOLATILITY

Long time magnetization thermal switching under small amplitude high frequency excitation is analyzed. Approaches based upon conventional time-dependent energy barrier are not sufficient to describe magnetization nonvolatility under GHz excitations. Methods based upon large angle nonlinear magnetization dynamics are developed for both coherent and noncoherent magnetization switching. This dynamic approach is not only important for fundamental understanding of magnetization dynamics under combined radio frequency excitations and thermal fluctuations, but also critical for practical design of emerging spintronic devices. When applied to spin torque random access memory read operations, as sensing current duration reaches nanosecond, dynamic approach gives a switching probability estimation orders of magnitude different from that obtained from conventional time-dependent energy barrier approach.

Gas heating mechanisms in capacitively coupled plasmas

Capacitively coupled plasma (CCP) tools utilized for plasma etching of dielectric features utilize large amounts of power for processing. As a result, neutral gas heats up significantly during processing. The resulting gas density variations across the reactor can affect reaction rates, radical densities, plasma characteristics and uniformity within the reactor. In this paper, results from a two-dimensional computational investigation of an Ar/CF4 CCP discharge incorporating an energy equation solution for all ions and neutrals are discussed. The dominant neutral gas heating process is identified to be elastic collisions with ions while conduction is found to be the major mechanism of heat transport. Some species such as F and CF3 demonstrate higher temperatures than the feedstock gases owing to additional heating via charge-exchange reactions and/or Franck–Condon heating. Typical process parameters such as pressure, frequency of excitation, power and gas composition are varied to investigate their impact on gas temperature. At higher excitation frequency and/or pressure, increased elastic collisions with ions lead to greater heat generation. The heat generated per molecule of the radicals, however, decreases with increase in pressure leading to a decrease in gas temperature. The increase in neutral collision frequencies with pressure also results in the decrease in temperature difference between species in the plasma. As CF4 fraction increases, both the elastic collision cross-section and Franck–Condon heating sources increase, leading to higher gas temperatures.

Office-Based Elastographic Technique for Quantifying Mechanical Properties of Skeletal Muscle

Our objectives were to develop a new, efficient, and easy-to-administer approach to ultrasound elastography and assess its ability to provide quantitative characterization of viscoelastic properties of skeletal muscle in an outpatient clinical environment. We sought to show its validity and clinical utility in assessing myofascial trigger points, which are associated with myofascial pain syndrome. Ultrasound imaging was performed while the muscle was externally vibrated at frequencies in the range of 60 to 200 Hz using a handheld vibrator. The spatial gradient of the vibration phase yielded the shear wave speed, which is related to the viscoelastic properties of tissue. The method was validated using a calibrated experimental phantom, the biceps brachii muscle in healthy volunteers (n = 6), and the upper trapezius muscle in symptomatic patients with axial neck pain (n = 13) and asymptomatic (pain-free) control participants (n = 9). Using the experimental phantom, our method was able to quantitatively measure the shear moduli with error rates of less than 20%. The mean shear modulus ± SD in the normal biceps brachii measured 12.5 ± 3.4 kPa, within the range of published values using more sophisticated methods. Shear wave speeds in active myofascial trigger points and the surrounding muscle tissue were significantly higher than those in normal tissue at high frequency excitations (>100 Hz; P < .05). Off-the-shelf office-based equipment can be used to quantitatively characterize skeletal muscle viscoelastic properties with estimates comparable to those using more sophisticated methods. Our preliminary results using this method indicate that patients with spontaneous neck pain and symptomatic myofascial trigger points have increased tissue heterogeneity at the trigger point site and the surrounding muscle tissue.

Control of Cavity Flow Oscillations by High Frequency Forcing

Time resolved two-dimensional particle image velocimetry (2DPIV) experiments have been conducted to contribute to the understanding of the physics governing the suppression mechanism of cavity flow self-sustained oscillations by means of high frequency excitation of the cavity shear layer. High frequency excitation was introduced by the spanwise coherent vortex shedding in the wake of a cylindrical rod positioned just upstream the cavity entrance, at the edge of the incoming boundary layer. The effectiveness of this suppression was demonstrated for a cavity having the length-to-depth ratio equal to three, in incompressible flow. The spatial and time resolved PIV measurements of the whole flow field in the plane normal to the cavity floor, linear stability analysis of the measured shear layer mean velocity profiles, and preliminary PIV measurements in a plane parallel to the cavity allowed us to offer a better insight into the involved physical mechanisms in suppressing cavity self-sustained oscillations.

Effects of Duty Cycles of the Plasma Actuators on Improvement of Pressure Distribution Above a NLF0414 Airfoil

This paper investigates the effects of duty cycle on improvement of pressure distribution above a NLF0414 airfoil using the plasma actuators. Three dielectric barrier discharges as the plasma actuators are flush mounted on airfoil surface in different positions in order to improve pressure at post-stall angle of attacks. The experiments were performed at ReC = 7.5 × 105 and the post-stall angles of attacks. The main aim of the related experiments in this paper is to better understand how duty cycles must be applied in order to have the most effective conditions for different excitation frequencies and different angles of attack. Results show that the plasma actuators in unsteady excitations are more effective in lower duty cycles on low excitation frequencies, but the lower duty cycles loss their effectiveness on higher excitation frequencies.

Dual compensation strategy for real‐time hybrid testing

SUMMARYReal‐time hybrid testing is an experimental technique for evaluating the dynamic responses of structural systems under seismic loading. Servo‐hydraulic actuators, by nature, induce inevitable time delay between the command and the achieved displacements. This delay would lead to incorrect test results and even cause instability of the system; therefore, delay compensation is critical for stability and accuracy of hybrid simulations of structural dynamic response. In this paper, a dual delay compensation strategy is proposed by a combination of a phase lead compensator and a restoring force compensator. An outer‐loop feed‐forward phase lead compensator is derived by introducing the inverse model in the z domain. The adaptive law based on the gradient algorithm is used to estimate the system delay in the format of parametric model during the test. It is shown mathematically that the parameter in the delay estimator is guaranteed to converge. The restoring force compensator is adopted to improve the accuracy of experimental results especially when the structure is subjected to high frequency excitations. Finally, analytical simulations of an inelastic SDOF structure are conducted to investigate the feasibility of the proposed strategy. The accuracy of the dual compensation strategy is demonstrated through several shaking table tests. Copyright © 2012 John Wiley &amp; Sons, Ltd.

A Probabilistic Approach for Human Safety Evaluation of Grounding Grids in the Transient Regime

A statistical description of safety aspects of grounding grids based on a new definition for risks of shock for human safety in the transient regime is presented in this paper. The procedure is based on a mathematical approach to evaluate the statistical distribution of lightning current followed by the Monte Carlo simulation of the grounding grid response to the probabilistic distribution of the injected current. The frequency-domain method of moments solution of the governing electric-field integral equation is used to simulate the grounding grid performance. The mapping of frequency-domain data to the corresponding transient data and vice-versa are achieved through appropriate use of the fast Fourier transform (FFT) and inverse FFT techniques, respectively. The proposed simulation methodology is used to obtain the probability by which the safety limits of a given grounding grid are violated. The safety limits are defined by comparing a severity parameter that is calculated by integration of an appropriate function of the current passing through human body over the time span of lighting current. Simulation results demonstrate the compatibility of the low-frequency safety index with that recommended in this paper for transient (high frequency) excitation of a grounding grid.

Smart Processing of Micro Photonic Crystals for Terahertz Wave Control - Freeform Fabrication by Stereolithographic Technique -

Photonic crystals with periodically arranged structures of ceramics can reflect light or electromagnetic waves through Bragg diffraction and exhibit forbidden gaps in transmission spectra. We have successfully fabricated micro diamond crystals including twined lattices with plane defects to realize wavelength selections in terahertz frequency ranges. Novel smart processing composed of computer aided design, manufacturing and evaluation was established. The terahertz waves are expected to detect micro cracks in material surfaces and structural defects in electric circuits by fine wave interferences, and to analyze cancer cells in human skins and toxic bacteria in natural foods through high frequency excitations. In the fabrication processes using micro patterning stereo-lithography, the photo sensitive resin paste including alumina fine particles were spread on a glass substrate with 10 µm in layer thickness by moving a knife edge, and cross sectional images of ultra violet ray were exposed by using a digital micro mirror device with 2 µm in part accuracy. Through the layer stacking process, micrometer order structures were formed exactly. Dense ceramic components could be obtained through dewaxing and sintering heat treatments. The electromagnetic wave transmission spectra were measured by terahertz wave spectroscopy. The micro diamond lattices could form perfect photonic band gaps opining for all crystal directions. The introduced plane defects realized the wave select resonations. This resonation behavior was visualized and analyzed by finite difference time domain simulations.

Stabilization of Buckled Beam with Coulomb Friction by High-Frequency Excitation

The paper deals with the effect of high-frequency excitation on the buckling of a hinged-hinged beam. The hinged supporting points suffer the bending moment due to Coulomb friction. Even if it is very small, in the neighborhood of the critical point of the buckling, it has been known that the stable equilibrium region appears around the branches in the case without Coulomb friction. In this paper, it is theoretically clarified that the equilibrium region is shifted by high-frequency excitation.

Effective Dynamometer for Measuring High Dynamic Process Force Signals in Micro Machining Operations

The authors present an innovative piezoelectric dynamometer (MicroDyn) providing the base for measuring high frequency signals in micro machining operations. Cutting tools with one or more cutting edges used in micro machining processes are mostly running with rotational speeds of more than 100’000rpm, resulting in high excitation frequency. Thus, the interference of the excitation frequency of those processes with the natural frequency of commercially available dynamometers makes it impossible to measure process forces within a wide frequency range. This paper presents the dynamometer design, results of various laboratory tests and first cutting force measurements taken from high dynamic cutting processes as single grain cutting.

Magnetoplasmon spectrum of two-dimensional helical metals

We investigate theoretically the magnetoplasmon spectrum of two-dimensional helical metals. The effects of the Zeeman energy and Coulomb interaction on the collective excitation modes are examined through the charge-density excitation (CDE) and spin-density excitation (SDE) intensities. At low excitation frequencies, the CDE is always accompanied by an SDE and is almost unaffected by the change in the Zeeman energy or Coulomb interaction intensity. However, at some higher excitation frequencies, the CDE and SDE can be decoupled and a strong SDE with a weak CDE can be realized by tuning either the Zeeman energy or the Coulomb interaction intensity.

Experimental Study of High-Frequency Vibration Assisted Micro/Mesoscale Forming of Metallic Materials

Micro/mesoscale forming is a promising technology for mass production of miniature metallic parts. However, fabrication of micro/mesoscale features leads to challenges due to the friction increase at the interface and tool wear from highly localized stress. In this study, the use of high-frequency vibration for potential application in micro/mesoscale forming has been investigated. A versatile experimental setup based on a magnetostrictive (Terfenol-D) actuator was built. Vibration assisted micro/mesoscale upsetting, pin extrusion and cup extrusion were conducted to understand the effects of workpiece size, excitation frequency, and the contact condition. Results showed a change in load reduction behavior that was dependent on the excitation frequency and the contact condition. The load reduction exhibited in this study can be explained by a combination of stress superposition and friction reduction. It was found that a higher excitation frequency and a less complicated die-specimen interface were more likely to result in a friction reduction by high-frequency vibration.

Robust Piezo Impedance Magnitude Measurement Method

Piezo impedance spectroscopy is widely used in structural health monitoring (SHM) applications. Purpose of the research was tofind most robust and cheap method for impedance magnitude measurement. Proposed system consists of analog front end (AFE), signalsynthesizer and microcontroller unit. AFE enables to use low sampling rate, while using high frequency excitation signal. Proposedsystem uses chirp excitation signal in 20kHz- 600kHz frequency range. Results were compared against measurements made withcommercial impedance analyzer. Results show great potential for this method in SHM applications. Ill. 6, bibl. 10 (in English; abstractsin English and Lithuanian). http://dx.doi.org/10.5755/j01.eee.113.7.623

Eddy-Current Sensor Interface for Advanced Industrial Applications

In this paper, a novel integrated eddy-current sensor interface is presented. The main targeted application is displacement measurement in an industrial environment, with resolution in the submicrometer range. A high excitation frequency of about 22 MHz is applied to minimize the skin effect of the generated eddy currents, when thin targets are used. The price to be paid is to process high-frequency signals. This is very challenging when high performance has to be achieved with respect to resolution and stability at minimum power consumption. To ensure high immunity of the interface to electromagnetic interferences, a second-order oscillator with a steep bandpass resonator is utilized as a front-end stage. The noise performance of the front-end stage is analyzed. To reduce the effect of this noise source on the resolution, a ratiometric measurement principle is proposed. In order to extract the displacement information, a novel amplitude-demodulation approach, including an offset cancellation technique, is introduced. The proposed circuit has been designed and implemented in a 0.35-μm BiCMOS process. In this design, the full-scale displacement range is 1.5 mm. The noise level allows a dynamic range of 75 dB with a measurement signal bandwidth of 1 kHz and only 9.5-mW power dissipation. A comparison with state-of-the-art eddy-current sensor interfaces shows an improved figure of merit, which confirms the high performance of the proposed interface.