Effect Of Excitation Frequency Research Articles

Eddy current detection of subsurface defects for additive/subtractive hybrid manufacturing

In this study, an eddy current (EC) detector is integrated in an additive/subtractive hybrid manufacturing (ASHM) process. The detector facilitates in-process inspection and repair operations through material deposition, defect detection, and removal processes layer by layer. A feasibility test is carried out on eddy current detection of subsurface defects in additively manufactured parts by using an EC detector. The study compares the results obtained from the EC detection with those by the X-ray computed tomography and the destructive methods. Experiments and simulations are conducted to investigate the effect of excitation frequency on intensity of the eddy current signal. The effects of residual heat of an additively manufactured specimen and lift-off distance of an EC probe on impedance changes are also investigated. In addition, the effect of defect width on EC signal is analyzed. The study shows that the EC method is capable of detecting subsurface defects in the ASHM parts. It is promising to integrate the EC detection and subtractive manufacturing into additive manufacturing to produce parts with improved quality and better performances.

In-House fabrication and Electrical characterization of planner si-nanogap

Nanogap is increasingly known to be beneficial, dependable and higher sensing technology. Another possible purpose is to examine a bioactivity and study the reaction of single molecule. It is important to carefully recognize the differences between the sensor surface and electrode in order to incorporate the biological system with nanogap. Also, it crucial to examine the dielectric properties between the planar nanogap with and without a sample. Electrical concentration between the electrodes could be increased due to integrating of microfluidic channel when the sample is being used. This paper is a report on an electrical point of view of planar nanogap capacitor device with comparison of different excitation frequency with and without microfluidic channel. By using 40 nm Si nanogap devices, the sensitivity of nanogap was compared by dropping deionized water and pH 7 onto the target. Experiments were carried out in wide range of frequencies from 1 Hz to 1 MHz at room temperature with 30 mV input signal (0 V, DC, Offset). Both effects of excitation frequency on capacitance sampling with 10 µm microfluidic integration were analyzed.

Dynamic analysis of a planetary gear system with multiple nonlinear parameters

Considering time-varying meshing stiffness, comprehensive gear error and piece-wise backlash nonlinearities, a torsional nonlinear dynamic model of multistage gear of planetary gear system is established. By using Runge–Kutta numerical integration method, the dynamic responses are solved, analyzed and illustrated with the bifurcation parameters variation including excitation frequency, gear backlash and damping. The motions of the planetary gear system and diverse nonlinear dynamics characteristics are identified through global bifurcation diagram, FFT spectra, Poincaré map, the phase diagram and the largest Lyapunov exponent (LLE). The numerical results expose that system experiences a diverse transformation range of the periodic motion, non-periodic states systematically and quantitatively when the parameters are changed. Analysis results show that the variation of meshing frequency as the external excitation could transit the states of the system. Additionally, the motions and the routes of entering chaos at low excitation frequency and at high excitation frequency are different. Under the bifurcation parameter of dimensionless backlash and damping coefficient, the system motion is observed. The higher damping coefficient and suitable backlash could suppress the region of chaos. Correspondingly, parameters of the system should be designed properly and controlled timely for the better operation and enhancing life of the system. • A dynamic model of a system is established, considering multi nonlinear parameters. • The simulation focuses on the effects of excitation frequency and gear error. • The different parameters have different influences on the motion of the gear system. • The suitable coefficients should be specified so that chaotic behavior can be avoided.

Dynamic Analysis of a Novel Moving Magnet Linear Actuator

A novel moving magnet linear actuator is proposed for linear oscillations in the linear resonant compressors for household refrigerators. This paper provides stator and armature design including CAD model and geometric parameters. Furthermore, the working principle of the proposed actuator is explained. The stator assembly is composed of two reversely wound coils, which are electrically excited with single phase ac power and oscillates the radially magnetized armature. With the help of the electromechanical analytical model, the dynamic parameters such as stroke, velocity, and acceleration of the armature are derived. Additionally, the time-dependent current model of the stator winding is proposed. An experimental setup is used to validate these responses at the resonance excitation frequency with the help of sensors. The system kinetics are discussed to estimate the spring, damping, inertial, and magnetic forces. A simulation is executed to estimate the time-domain responses of these dynamic parameters and the effects of excitation frequency are discussed. The force models are experimentally validated at the resonance frequency excitation. In order to evaluate the performance of the proposed actuator, a comparison of the performance parameters, such as efficiency, stroke, current, and mass flow rate is demonstrated with the conventional rotary as well as the linear motors for linear compressor application.

Piezoelectric energy harvester for low engine vibrations

Piezoelectric materials are well known for their use as sensors and actuators in flexible structures. Researchers have also focused on harvesting energy from the waste vibrations generated by different sources using piezoelectric materials. In its running condition, an engine generates vibrations. These vibrations can be converted into electric energy by using a suitable energy harvester. The minute energy generated from these waste vibrations can be used as an additional source to batteries or a resource to run sensors and actuators in automotive vehicles. This paper focuses on harvesting energy from engine vibrations using a piezoelectric cantilever beam. The power from these vibrations has been enhanced even at low vibrations. A mathematical equation for the estimation of voltage and power using a piezoelectric cantilever beam has been derived. The effect of excitation frequency, amplitude, and material properties on power output has been considered. Based on the simulation results, a piezoelectric cantilever beam is designed and fabricated, and experiments are conducted. Analytical results are validated with the experimental results, and a close match has been observed between the experimental and analytical results.

Energy harvesting using porous piezoelectric beam with impacts

An analytical model of impact energy harvester consisting of a cantilever beam with integrated piezoelectric patches and a ball is developed in this paper. The material chosen to extract the energy is porous PZT, a composite material made of two phases: air and PZT. This material offers good control of the capacitance and the stiffness of the resultant composite material and expands the design space for the harvester. The cantilever beam is modelled using a single degree-of-freedom approximation, and a load resistor is used to represent the external circuit. The response of the energy harvester and the power output is obtained for harmonic base excitation, and the effect of excitation frequency, boundary distance, load resistance and porosity of the PZT material. The results highlight the potential for the impact harvester and motivate further studies to optimize the harvester.

Effect of excitation frequency on characteristics of mixture discharge in fast-axial-flow radio frequency-excited carbon dioxide laser

A one-dimensional fluid model has been used to describe the effect of radio frequency (RF) on the characteristics of carbon dioxide (CO2), nitrogen (N2) and helium (He) mixture discharge at 120 mbar in fast-axial-flow RF-excited CO2 laser. A finite difference method was applied to solve the one-dimensional fluid model. The simulation results show that the spatial distributions of electron density and current density rely strongly on the modulating driven frequency. When the excitation frequency changes from 5 to 45 MHz, the plasma discharge is always in α mode. Moreover, as the excitation frequency increasing, the higher densities of CO2V001 and N2*Vib can be obtained, which is important to get higher excitation efficiency for the upper laser level.

Analysis of solenoid based linear compressor for household refrigerator

This article presents the analytical modeling of an oil-free solenoid actuator based linear compressor used in household refrigerators. The stator coil was excited with the pulse width modulated signal which caused linear oscillations in the armature using helical spring. Dynamic characteristics of the linear compressor were studied analytically considering the nonlinearity of the gas and electromagnetic force. The system dynamic models were validated with the finite element simulation as well as a specially designed experimental setup. Frequency response functions of stroke to current as well as pressure to current ratios were generated to evaluate the effect of excitation frequency on the compressor performance. The higher efficiency of the solenoid actuator was achieved when excited at the natural frequency. The results show that the natural frequency of the designed system is around 19 Hz and the work done in a cycle is approximately 1.3 J. Additionally, 47% isentropic and 87% electrical efficiency were achieved.

Three-dimensional span effects of high-aspect ratio synthetic jet forcing for separation control on a low Reynolds number airfoil

The three-dimensional structure of the reattached flow caused by synthetic jet actuation on an airfoil was investigated using surface flow visualization. Without active control, the flow was stalled with laminar boundary layer separation occurring near the leading edge. Tuft and oil visualization showed the shape and spanwise extent of the attached flow due to a finite span synthetic jet where the effect of excitation frequency and blowing ratio was the focus. For all excitation frequencies tested, a similar contraction of the spanwise extent of the attached flow towards the trailing edge was observed due to edge effects of the finite span jet. Increasing the blowing ratio was found to decrease the amount by which the attached flow contracted.

Re-configurable multi-level temperature sensing by ultrasonic “spring-like” helical waveguide

This paper introduces a novel technique for multi-level temperature measurement using a single reconfigurable ultrasonic wire waveguide that is configured in the form of a helical spring. In this embodiment, the multiple sensing levels located along the length of the helical waveguide wire can be repositioned by stretching or collapsing the spring to provide measurements at different desired spacing in a given area/volume. This method can measure over a wide range of temperatures. The transduction is performed using Piezo-electric crystals that are attached to one end of the waveguide which act as transmitter as well as receiver. The wire will have multiple reflector embodiments (notches was used here) that allow reflections of input L(0,1) mode guided ultrasonic wave, in pulse echo mode, back to the crystal. Using the time of fight measurement at multiple predefined reflector locations, the local average temperatures are measured and compared with co-located thermocouples. The finite element modeling simulation was used to study the effect of excitation frequency and the mean coil diameter of the “spring-like” waveguide. This technique improves on the limitations of a straight waveguide technique earlier reported.

Delayed-feedback vibration absorbers to enhance energy harvesting

Recovering energy from ambient vibrations has recently been a popular research topic. This article is conceived as a concept study that explores new directions to enhance the performance of such energy harvesting devices from base excitation. The main idea revolves around the introduction of delayed feedback sensitization (or tuning) of an active vibration absorber setup. To clarify the concept, the Delayed Resonator theory is reviewed and its suitability for energy harvesting purposes is studied. It is recognized that an actively tuned and purely resonant absorber is infeasible for such applications. The focus is then shifted to alternative tuning schemes that deviate from resonance conditions. Also called Delayed Feedback Vibration Absorbers, these devices may indeed provide significant enhancements in energy harvesting capacity. Analytical developments are presented to study energy generation and consumption characteristics. Effects of excitation frequency and absorber damping are investigated. The influences of time-delayed feedback on the stability and the transient performance of the system are also treated. The analysis starts from a stand-alone absorber, emulating seismic mass type harvesters. The work is then extended to vibration control applications, where an absorber/harvester is coupled with a primary structure. The results are demonstrated with numerical simulations on a case study.

Effects of base excitation frequency on the stability of a freestanding rigid block

The behavior of a freestanding block subjected to base excitation is a nonlinear problem. In the past, many researchers have analyzed freestanding blocks subjected to base excitation and reported their findings. However, still more understanding is required to understand excitation frequency effects on the stability of a freestanding block. Detailed experiments and numerical analysis were performed on a parallelepiped block having an aspect ratio of four, for different values of coefficient of friction and base amplitudes. It was observed that base excitation frequency has a predominant role on the motion and hence the stability of a freestanding block. Contrary to the present understanding of the subject, it was observed that initiation of any mode of motion (like sliding, rocking) from rest depends not only on the parameters like amplitude of base excitation, coefficient of friction and aspect ratio, but also on the base excitation frequency. A freestanding system initially at rest shall remain in rest until excited by a base excitation frequency below a particular value.We numerically determined the value of this frequency (termed as cutoff frequency) for different values of coefficient of friction (0.1–1) and base amplitude (0.1–1 g) for a constant aspect ratio of four of a parallelepiped block with square base. Using data generated from numerical analysis, a three-dimensional diagram named as initiation criteria diagram was developed that identifies various regions corresponding to sliding, rocking, slide–rock and rest (no motion) phase for a freestanding block subjected to base excitation. A novel finding was the presence of a region of no motion above a frequency value for any given combination of parameters. The ratio of the amplitude of acceleration obtained at the top of the block to the amplitude of applied base acceleration (amplification factor) was calculated for different experimental cases. The dependence of the amplification factor on the base excitation frequency was also studied. Hence, it was concluded that the base excitation frequency plays an important role in determining the stability of a freestanding rigid block.

Effect of frequency on microplasmas driven by microwave excitation

The effect of excitation frequency on the breakdown voltage of a microwave (mw) microdischarge and its steady-state plasma parameters is studied by the self-consistent one-dimensional Particle-in-Cell Monte Carlo collisions model. It is found that for microdischarges in which the electron wall losses are significant, an increase in the mw frequency results in a decrease in the breakdown voltage. For conditions in which the electron wall losses become negligible, an increase in the frequency does not influence significantly the breakdown voltage. At the same time, for both regimes, the increase in the frequency results in an increase in the steady-state plasma density. The analysis of the steady-state plasma parameters have shown that the dominant electron heating mechanism is the Joule heating while the stochastic heating is negligible. Also, it is found that the electron energy distribution function consists of two electron groups, namely, slow and fast electrons. The presence of fast electrons in the plasma bulk indicates the non-local nature of microwave excited microdischarges.

Experimental Study of the Unsteady Actuation Effect on Induced Flow Characteristics in DBD Plasma Actuators

The main aim of this paper is to investigate unsteady actuation effects on the operation of dielectric barrier discharge (DBD) plasma actuators and to study induced flow characteristics of steady and unsteady actuators in quiescent air. The parameters affecting the operation of unsteady plasma actuators were experimentally measured and compared with the ones for steady actuators. The effects of excitation frequency and duty cycle on the induced flow pattern properties were studied by means of hot-wire anemometers, and the smoke visualization method was also used. It was observed that the current and the mean induced velocity linearly increase with increasing duty cycle while they are not sensitive to excitation frequency. Furthermore, with increasing excitation frequency, the magnitude of vortices shedding from the actuator decreases while their frequency increases. Nevertheless, when the excitation frequency grows beyond a certain level, the induced flow downstream of the actuator behaves as a steady flow. However, the results for steady actuators show that by increasing the applied voltage and carrier frequency, the velocity of the induced flow first increases and then decreases with actuator saturation and the onset of the emission of streaky glow discharge.

Effect of driven frequency on flow and heat transfer of an impinging synthetic air jet

In this study, impingement heat transfer from a synthetic air jet on a heated surface was experimentally studied. A synthetic jet provides a high heat transfer coefficient and a compact design, which is suitable for the thermal management of electronic devices. The synthetic jet is produced by the high frequency oscillating motion (200–800 Hz) of a piezoelectric actuator, and a jet Reynolds number ranging from 500 to 1300. The instantaneous and time-averaged velocity profiles of the synthetic jet issuing from the jet hole were measured using a hot wire anemometer. The jet hole diameter was 3 mm and the jet-to-surface spacing (Z/d) ranged from 0 to 25. The excitation frequency effect, jet-to-surface spacing, and jet Reynolds number were tested. The heat transfer enhancement of the synthetic jet was at least double the natural convective heat transfer. At a small jet-to-surface spacing, the warm air circulates inside small spaces, jeopardizing heat transfer. An optimal driven frequency of 600 Hz in this study provided the highest jet flow rates and heat transfer enhancement.

Finite Element Modal Analysis of a Semi-Trailer Frame

The paper carries out the finite modal analysis of a Semi-trailer frame and obtains the modal parameters such as frame natural frequency and vibration mode. It also compares the modal analysis results with the excitation frequency effect caused by the road on the frame, the conclusion supports a reference to improve the frame design.

Experimental and numerical study on long-span reticulate structure with multidimensional high-damping earthquake isolation devices

Abstract Multidimensional high-damping earthquake isolation device (MHEID) for long-span reticulate structure is an innovative passive vibration control device. In this paper, the results of horizontal and vertical property tests are presented first and then effects of excitation frequency, displacement on MHEID are studied. In order to consider the effects of excitation frequency, displacement amplitude and temperature on MHEID, a new mathematical model, i.e., fractional-derivative equivalent standard solid model, is put forward to describe the dynamic properties of MHEID precisely in both horizontal and vertical directions. Then, horizontal and vertical pseudo-dynamic tests on structures with and without MHEID are conducted. It can be seen from the experimental results that MHEID can obviously reduce the displacement responses, acceleration responses and input forces of the long-span reticulate structure. In order to analyze the earthquake isolation effect of MHEID on long-span reticulate structures, the dynamic responses are simulated by using a new dynamic response analysis method. The numerical results fit well with the experimental results and it is indicated that the proposed method can simulate the dynamic responses of the long-span reticulate structure.

Prediction of Dynamic Characteristics of a Bump-Type Foil Bearing Structure with Consideration of Dynamic Friction

Friction forces within the foil structure, which provide most of the damping characteristics of gas foil bearings (GFBs), depend not only on surface topology and normal force but also on foil materials, displacement, and relative velocity of contact surfaces; therefore, describing the dynamic behavior of GFBs through Coulomb friction yields insufficient results. This article presents a numerical model of a bump-type foil bearing structure, for which the dynamic friction forces within the foil structure are considered. Each bump is simulated as a horizontally spaced spring and two rigid links. The contact surfaces between the bump strip and the top foil, as well as those between the bumps and the housing, are considered interfaces through elastic bristles. A dynamic friction model, the LuGre model (C. Canudas de Wit, et al., 1995, IEEE Transactions on Automatic Control, Vol. 40), is used to calculate the variations in friction forces from the deformation of the foil structure. An important feature of the proposed model is that it can simulate the effect of excitation frequency on dynamic friction force. The predictions of a six-bump strip show that both dynamic friction force and energy dissipation vary with excitation frequency. The calculated hysteresis loop shows good agreement with published experimental data. Results of a full GFB structure show that the dynamic characteristics are largely affected by excitation amplitude and frequency, friction coefficient, and bearing assembly preload. To a certain extent, the calculation results match well with published test data, which shows that the proposed model is reasonable for predicting the dynamic characteristics of foil structures.

Modeling of Magnetic Properties of GO Electrical Steel Based on Epstein Combination and Loss Data Weighted Processing

The extended modeling of the magnetic properties of grain oriented electrical steel is presented in this paper which is based on a set of standard and scaled-down Epstein frames and a proposed two-level weighted processing of Epstein data, including the mean magnetic path length, specific magnetization loss and exciting power. The effects of excitation frequency, strip angle, and ambient temperature on the results obtained from the Epstein frames are investigated. It is shown that using the proposed Epstein combination and the two-level weighted processing method is an efficient way of building a model for determining magnetic losses more realistically, hence, improving the value of Epstein strip measurement data.

Effects of excitation frequency on high-order terahertz sideband generation in semiconductors

We theoretically investigate the effects of the excitation frequency on the plateau of high-order terahertz sideband generation (HSG) in semiconductors driven by intense terahertz (THz) fields. We find that the plateau of the sideband spectrum strongly depends on the detuning between the near-infrared laser field and the band gap. We use the quantum trajectory theory (three-step model) to understand the HSG. In the three-step model, an electron–hole pair is first excited by a weak laser, then driven by the strong THz field, and finally recombined to emit a photon with energy gain. When the laser is tuned below the band gap (negative detuning), the electron–hole generation is a virtual process that requires quantum tunneling to occur. When the energy gained by the electron–hole pair from the THz field is less than 3.17 times the ponderomotive energy (Up), the electron and the hole can be driven to the same position and recombined without quantum tunneling, so that the HSG will have large probability amplitude. This leads to a plateau feature of the HSG spectrum with a high-frequency cutoff at about 3.17Up above the band gap. Such a plateau feature is similar to the case of high-order harmonics generation in atoms where electrons have to overcome the binding energy to escape the atomic core. A particularly interesting excitation condition in HSG is that the laser can be tuned above the band gap (positive detuning), corresponding to the unphysical ‘negative’ binding energy in atoms for high-order harmonic generation. Now the electron–hole pair is generated by real excitation, but the recombination process can be real or virtual depending on the energy gained from the THz field, which determines the plateau feature in HSG. Both the numerical calculation and the quantum trajectory analysis reveal that for positive detuning, the HSG plateau cutoff depends on the frequency of the excitation laser. In particular, when the laser is tuned more than 3.17Up above the band gap, the HSG spectrum presents no plateau feature but instead sharp peaks near the band edge and near the excitation frequency.