Simple Waveform Research Articles

Aeroacoustic Control of Fan Tone Noise

Mathematical formulations of the unsteady three-dimensional flowfield induced by a rotating annular cascade interacting with an oncoming periodic gust and disturbances from an oscillating actuator surface composed as a part of the duct wall are presented on the basis of a linearized unsteady lifting surface theory. The problem of suppressing the tone noise due to interaction of the rotor with the gust by means of the actuator motion is studied. Theoretical analysis with numerical calculations is conducted for a simple harmonic sinusoidal gust, and a simple harmonic sinusoidal circumferential wave form of the actuator motion and optimum conditions of the actuator motion are investigated. There are substantial differences in the optimum phase and amplitude of the actuator motion between the conditions of suppressing the upstream and downstream acoustic powers. In the case of multiple cut-on duct modes, the actuator motions of the cut-off circumferential wave numbers are desirable to effectively suppress the total acoustic powers.

Low-frequency ionospheric sounding with Narrow Bipolar Event lightning radio emissions: regular variabilities and solar-X-ray responses

Abstract. We present refinements of a method of ionospheric D-region sounding that makes opportunistic use of powerful (109–1011 W) broadband lightning radio emissions in the low-frequency (LF; 30–300 kHz) band. Such emissions are from "Narrow Bipolar Event" (NBE) lightning, and they are characterized by a narrow (10-μs), simple emission waveform. These pulses can be used to perform time-delay reflectometry (or "sounding") of the D-region underside, at an effective LF radiated power exceeding by orders-of-magnitude that from man-made sounders. We use this opportunistic sounder to retrieve instantaneous LF ionospheric-reflection height whenever a suitable lightning radio pulse from a located NBE is recorded. We show how to correct for three sources of "regular" variability, namely solar zenith angle, radio-propagation range, and radio-propagation azimuth. The residual median magnitude of the noise in reflection height, after applying the regression corrections for the three regular variabilities, is on the order of 1 km. This noise level allows us to retrieve the D-region-reflector-height variation with solar X-ray flux density for intensity levels at and above an M-1 flare. The instantaneous time response is limited by the occurrence rate of NBEs, and the noise level in the height determination is typically in the range ±1 km.

Characterizing Multistage Nonlinear Drivers and Variability for Accurate Timing and Noise Analysis

Nanoscale device characteristics and noise coupling have rendered traditional waveform-based gate delay models increasingly difficult to adopt. While the widely adopted delay models are built upon the assumption of simple ramp-like signal waveforms, realistic signal shapes in nanoscale designs can be far more complex. The need for considering process-voltage-temperature (PVT) variations imposes further accuracy requirement on gate models. We present a parameterizable waveform independent gate model (PWiM) where no assumption is made upon the input waveforms. The PWiM model is constructed by encapsulating the driver's intrinsic nonlinear dc and dynamic characteristics, which are important to model for complex signal waveforms, via novel and yet easy-to-implement characterization steps. As such, PWiM can provide near-SPICE accuracy for input signals that significantly deviate from simple ramps. While recently developed current-based models can only be applied to single channel-connected component, PWiM can work for multistage cells leading to improved library compactness and analysis efficiency. Our experiments have indicated that the proposed driver model not only provides up to two orders of magnitude speedups over SPICE for delay and noise analysis, it also offers accurate assessment of performance variability introduced by process and environmental variations.

Simple Waveform Model of Inductive Interconnects by Delayed Quadratic Transfer Function with Application to Scaling Trend of Inductive Effects in VLSI's

A simple analytical model based on Delayed Quadratic (DQ) Transfer Function approximation is proposed for estimating waveforms of inductive single-line interconnects in VLSI's. An expression for overshoot voltage is derived by the model within 17% error for the line width less than 10 times the minimum line width and typical input signal. A delay expression is also proposed within 15% for the same condition. The strength of the inductive effect is shown to be expressed by a closed-form expression, A = 2(L(CT + 0.5C))1/2/(RT(CT + CJ) + RTC + RCT + 0.4RC). By using the criteria, a scaling trend of inductive effects in VLSI's is discussed. It is shown that the inductive effect of single-line, minimum-width VLSI interconnect peaks off at 90 nm based on the ITRS predicted para-meters.

Yielding oscillator subjected to simple pulse waveforms: numerical analysis & closed‐form solutions

AbstractNumerical and analytical solutions are presented for the elastic and inelastic response of single‐degree‐of‐freedom yielding oscillators to idealized ground acceleration pulses. These motions are typical of near‐fault earthquake recordings generated by forward rupture directivity and may inflict damage in the absence of substantial structural strength and ductility capacity. Four basic pulse waveforms are examined: (1) triangular; (2) sinusoidal; (3) exponential; and (4) rectangular. In the first part of the article, a numerical study is presented of the effect of oscillator period, strength, damping, post‐yielding stiffness and number of excitation cycles, on inelastic response. Results are presented in the form of dimensionless graphs and regression formulas that elucidate the salient features of the problem. It is shown that conventional R–µ relations may significantly underestimate ductility demand imposed by near‐fault motions.The second part of the article concentrates on elastic‐perfectly plastic oscillators. Closed‐form solutions are derived for post‐yielding response and associated ductility demand. It is shown that all three ground motion histories (i.e. acceleration, velocity, and displacement) control oscillator response—contrary to the widespread view that ground velocity alone is of leading importance. The derived solutions provide insight on the physics of inelastic response, which is often obscured by the complexity of numerical algorithms and actual earthquake motions. The model is evaluated against numerical results from near‐field recordings. A case study is presented. Copyright © 2006 John Wiley & Sons, Ltd.

S-Domain Analysis of Grounding Electrodes Impulse Response

Simple closed-form expressions are derived and presented to describe the transient performance of grounding electrodes. In contrary to the available time-domain solutions, which are applicable only to simple standard time waveforms, the resulting expressions can be applied to any current or voltage stimulus at the electrode input terminals, taking into account the input impedance of the source. In order to perform a comparison between the suggested and the currently available solutions, most of the results, however, will be presented for double-exponential sources. After validating the model, interesting parameter studies were conducted on the wave attenuation due to the series (electrode) and the shunt (soil) losses. Moreover, the effect of both damping components, as well as the electrode length, on the frequency response of the electrode input impedance will be investigated.

A corrected microwave multisine waveform generator

This paper proposes a solution for one of the major difficulties associated with arbitrary waveform generation at microwave frequencies: the nonideal RF circuits used for signal generation. It presents a practical implementation of a RF multisine signal generator that corrects for the linear and nonlinear impairments identified with its output RF circuitry. The integration of an adaptive predistortion algorithm with a previously presented methodology for multisine synthesis with prescribed higher-order statistics, proved the feasibility of a simple microwave arbitrary waveform generator that meets the aims of previously developed signal synthesis theory

Benefit of millisecond waveform durations for patients with high defibrillation thresholds

Patients with a high defibrillation threshold (DFT) present an atypical but vexing problem with regard to implantable cardioverter-defibrillator (ICD) therapy. Their implant procedures are lengthy and involve more risk of complications. These patients often sustain a reduced safety margin that may compromise their survival. The purpose of this study was to evaluate the use of fixed millisecond duration model-optimized biphasic waveforms compared with conventional tilt-based waveforms in patients having a high DFT. We compared a 65%/65% tilt biphasic waveform to a millisecond duration biphasic waveform based on the biphasic burping theory using a 90-microF shock capacitor. Fifty-four patients were evaluated. Mean DFT with tilt was reduced from 11.0 +/- 5.5 J to 8.8 +/- 4.1 J, for a mean reduction of 20% (P < .0001). For the 13 patients with tilt-based DFTs > or = 15 J, DFT was reduced from 18.7 +/- 4.1 J to 13.4 +/- 3.5 J, for a mean DFT reduction of 28% (P = .009). The population peak DFT was reduced from 29.0 J to 17.5 J, for a 41% reduction (P = .03). Use of simple millisecond biphasic waveforms instead of conventional tilt-based waveforms can lead to substantial reductions in DFT, especially in patients with high DFT.

An Analytical Method for Determining the Optimal Modulating Waveform for Dithered Clock Generation

A new method for determining the optimal modulating waveform for spread spectrum clock generation (SSCG) is proposed to minimize the peak amplitude of the harmonic spectra measured in electromagnetic interference (EMI) tests. The optimal waveform can be easily obtained as a solution of a first-order differential equation that includes the impulse response of the receiver filter used for the spectrum measurement. To verify the validity of the proposed method, modulating waveforms and the resultant harmonic spectra are calculated for various modulating frequencies and resolution bandwidths. Results show that the optimal modulating waveform becomes similar to a simple triangular waveform if the modulating frequency is much lower or much higher than the resolution bandwidth. It is also found that dithering is most effective when the modulating frequency is equal to or slightly higher than the resolution bandwidth. The proposed method is applicable to and especially effective for dithered clock systems with a programmable modulating waveform.

Concept and Results of New Operation Scheme with Improved Control System for Radio Frequency Heating in JT-60U

The control system of the RF heating system in JT-60U has been improved with the concept of dispersion processing and by featuring a real-time waveform shaping method. The new dispersion processing system has higher performance and reliability than the old single-processor system before modification. Moreover, improvement of operator role sharing, using the real time waveform shaping has enabled more efficient and smooth operation. In the typical role sharing, a simple rectangular waveform of the RF heating power is set by the experiment operator, and the waveform is reshaped with the parameter set by the RF operator who is familiar with the condition of the RF system at that time. The simple and flexible composition of the new control system will also enable further improvement of hardware to enhance plasma performance and facilitate fusion experiments.

A fretting fatigue crack detection feasibility study using shear wave non-destructive inspection

A study was conducted to assess the viability of using ultrasonic shear wave non-destructive inspection (NDI) methods to detect fatigue cracks nucleating in the vicinity of a contact regionin situ. Use of this method is hampered by the presence of electronic and acoustic noise in the laboratory environment and by the contact in the experimental configuration. A previously established fretting fatigue test fixture was selected, in which nominally flat pads are held in contact against a thin, flat specimen and gross sliding between the pad and specimen is eliminated. Experiments were performed with Ti-6Al-4V at 300 Hz andR=0.5 for average clamping stresses of 200 and 620 MPa, and applied fatigue stresses of 330 and 250 MPa. The shear wave response was monitored during each test, and the test was interrupted when changes in the waveform were thought to indicate a crack. Also, the effect of the contact load and the sensitivity of the technique under the contact conditions were assessed. For the lower clamping stress, a sizeable portion of life was spent nucleating cracks, and the propagation life was too short to allow interruption of the tests. At the higher clamping stress, cracks with surface lengths of ∼2.5 mm were detected on, 10 mm wide specimens in tests conducted using the shear wave NDI technique. While the presence of the contact produced changes in the ultrasonic waveform, additional changes occurred as the crack propagated that permitted crack detection. A simple waveform correlation was used post-test to quantify the waveform changes, and thereby validate the viability of this NDI method for use in contact regions. In the configuration used for this study, the shear wave NDI technique was insensitive to small cracks. Some refinements that could dramatically improve crack detection capability are discussed.

Pulsed Amperometric Detection of Histamine at Glassy Carbon Electrodes Modified with Gold Nanoparticles

AbstractGold nanocrystal‐modified glassy carbon electrodes (nAu‐GCE) were prepared and used for the determination of histamine by flow injection and high performance liquid chromatography using pulsed amperometric detection (PAD) as the detection mode. Experimental variables involved in the electrodeposition process of gold from a HAuCl4 solution were optimized. A catalytic enhancement of the histamine voltammetric response was observed at the nAu‐GCE when compared with that obtained at a conventional Au disk electrode, as a consequence of the microdispersion of gold nanocrystals on the GC substrate. The morphological and electrochemical characteristics of the nAu‐GCE were evaluated by SEM and cyclic voltammetry. PAD using a very simple potential waveform consisting of an anodic potential (+700 mV for 500 ms) and a cathodic potential (−300 mV for 30 ms), was used to avoid the electrode surface fouling when histamine was detected under flowing conditions. Flow injection amperometric responses showed much higher Ip values and signal‐to‐noise ratios at the nAu‐GCE than at a conventional gold disk electrode. A limit of detection of 6×10−7 mol L−1 histamine was obtained. HPLC‐PAD at the nAu‐GCE was used for the determination of histamine in the presence of other biogenic amines and indole. Histamine was determined in sardine samples spiked at a 50 μg g−1 concentration level, with good results. Furthermore, the chromatographic PAD method was also used for monitoring the formation of histamine during the decomposition process of sardine samples.

Development of Wireless Electronic Stethoscope System and Abnormal Cardiac Sound Analysis Method (Sound Characteristic Waveform Analysis)

This paper is concerned with the development of a wireless electric stethoscope system and cardiac sound analytical method for cardiovascular disease diagnosis. This system consists of an electronic stethoscope, data acquiring amplifier/filter circuits, wireless transmitter and receiver modules, and a notebook computer. The cardiac sound acquired by the electronic stethoscope and can be easily transmitted to the computer by wireless transmitter and receiver modules. The input-output characteristics of the electronic stethoscope and wireless modules are investigated in detail. Furthermore, one-DOF analytical model based on the consideration of the eardrum property is proposed for abnormal cardiac sound analysis. With the analytical model the original heart sound signal can be converted to a simple characteristic waveform which fits the behaviors of some cardiovascular diseases. Some case studies using the characteristic waveforms show that the normal sound can be distinguished visually from the abnormal cases such as the mitral regurgitation, aortic incompetence, allorhythmic pulse and so on.

THE USE OF SIMPLE PULSES TO ESTIMATE INELASTIC RESPONSE SPECTRA

Inelastic response spectra are estimated for elasto-plastic SDOF systems subjected to strong earthquake ground motions by applying the strength reduction factors determined for a simple pulse to the elastic response spectrum of the ground motion. This approach relies upon similarities in the strength reduction factors computed for earthquake ground motions and for short duration pulses. The accuracy of the estimated inelastic spectra obtained using 24 simple pulse waveforms is assessed in order to identify subsets of just several pulse waveforms that are suited for this purpose. Based upon the ground motions and pulses investigated, this approach appears to be equally applicable to short and long duration ground motions and those having near-fault forward directivity features.

Input current wave‐shaping technique using inductor voltage sensing for high‐power‐factor flyback rectifier

AbstractIn this paper, a simple input current waveform shaping method for a rectifier with a high power factor using the induced voltage of a flyback transformer is proposed. The duty ratio of the present shaping circuit is obtained by comparison of the integration signal of the rectified induced voltage and the ramp carrier waveform with a negative slope. By means of the proposed method, the input voltage sensor, current control loop, multiplier, and inductance current sensor can be eliminated, simplifying the control circuit. In order to confirm the proposed method, a flyback rectifier circuit for 100 W is fabricated for an experimental investigation. The results confirm that the input current waveform of the rectifier becomes closer to a sinusoidal shape and harmonic components become smaller by the use of the present shaping method. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(10): 26–35, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10188

A frequency-modulated-carrier digital communication technique for multipath underwater acoustic channels

Along with interferences, multipath propagation and, in particular, its instability in shallow sea is the main obstacle to increasing the digital data transfer rate in underwater acoustic communication systems. Given these conditions, the use of simple waveforms, for which the product of bandwidth by the length of the processing interval is close to unity, makes testing the quality of the communication channel much more difficult and strongly limits the possibilities of devices that compensate for current waveform distortions, such as, for example, equalizers. In multipath channels with random parameters, various complex waveforms with different spectrum spreading techniques had been used for years. Complex waveforms with a large base (time-bandwidth product) offer advantages in efficiently suppressing narrowband interferences and providing asynchronous multiple-access communications. This paper proposes a new complex waveform, which uses sequences of chirp pulses. On receiving, this waveform can be divided into individual responses through converting the delays of these individual responses to frequency offsets. After a special frequency conversion of the received signal, the multipath responses are separated in the frequency domain by conventional band-pass filtering.

Small‐scale ultralow‐velocity zone structure imaged by ScP

Short‐period, teleseismic ScP phases from events in the Tonga‐Fiji region recorded at the short‐period, small‐aperture Warramunga Array in Australia are used to study structure at the core‐mantle boundary (CMB). We examine the data for evidence of precursors and postcursors to ScP. Such additional arrivals are generated by the interaction of ScP with structure at the reflection and conversion point at or near the CMB. We show precursors and postcursors to ScP, indicating an ultralow‐velocity zone (ULVZ) at the CMB in the region between Tonga‐Fiji and Australia. One‐dimensional forward modeling of the short‐period data leads to models of the ULVZ with thickness varying between 5 and 20 km, velocity reductions of 0–10% and 10–30% for P velocity and S velocity, respectively, and 0–50% density increase. Many events, however, show simple waveforms, consistent with a locally simple CMB. Models for proximal events can vary greatly, indicating very complex, three‐dimensional structure with scale lengths of a few tens of kilometers. These results point to complex chemical and physical processes in the lowermost mantle.

Transient deformation of a poroelastic channel bed

AbstractThe coupled transient response of a poroelastic bed form due to stream flow and non‐linear water waves is investigated numerically. The theory of potential flow is applied to channel flow while Biot's theory of poroelasticity (J. Appl. Phys. 1962; 33(4):1482) is adopted to deal with the deformable porous bed. A boundary‐fitted co‐ordinate system is used to calculate the variation in the bed form. The result of a simple periodic wave form over a soft poroelastic bed agrees well with the analytical solution of Hsieh et al. (J. Eng. Mech., ASCE 2000; 126(10):1064). However, due to the rapidly damping second dilatational wave inside the soft poroelastic bed, the solution for transient bed form near the interface is not easy to compute accurately. In order to overcome this difficulty, a simplified numerical model based on the boundary layer correction concept proposed by Hsieh et al. (2000) is established, which neglects Darcy's terms. The transient deformation of an irregular poroelastic bed that includes a trench and a downward step at the channel bed is simulated successfully. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Solenoidal skin vibrator energized by complex electric waveforms

A new skin vibrator converts simple or complex electrical waveforms into simple or complex mechanical waveforms or vibrations that are applied to the skin and underlying tissues for therapy or pleasure. The complex waveforms may be completely random in response to the output of a random electrical noise generator, or non-random but complex in response to music or speech. In effect, random acoustic vibrations or speech or musical vibrations are induced in the skin and underlying tissues. The vibrator comprises an oblong hollow body having a solenoidal motor mounted inside. The solenoid is partially damped at both extremes of its stroke to buffer the impact within the vibrator and thereby soften the vibration. Wires extend from the vibrator for connection with a signal generator, audio amplifier or other source of the electrical waveforms.

Noise sources in a low-Reynolds-number turbulent jet at Mach 0.9

The mechanisms of sound generation in a Mach 0.9, Reynolds number 3600 turbulent jet are investigated by direct numerical simulation. Details of the numerical method are briefly outlined and results are validated against an experiment at the same flow conditions (Stromberg, McLaughlin &amp; Troutt 1980). Lighthill's theory is used to define a nominal acoustic source in the jet, and a numerical solution of Lighthill's equation is compared to the simulation to verify the computational procedures. The acoustic source is Fourier transformed in the axial coordinate and time and then filtered in order to identify and separate components capable of radiating to the far field. This procedure indicates that the peak radiating component of the source is coincident with neither the peak of the full unfiltered source nor that of the turbulent kinetic energy. The phase velocities of significant components range from approximately 5% to 50% of the ambient sound speed which calls into question the commonly made assumption that the noise sources convect at a single velocity. Space–time correlations demonstrate that the sources are not acoustically compact in the streamwise direction and that the portion of the source that radiates at angles greater than 45° is stationary. Filtering non-radiating wavenumber components of the source at single frequencies reveals that a simple modulated wave forms for the source, as might be predicted by linear stability analysis. At small angles from the jet axis the noise from these modes is highly directional, better described by an exponential than a standard Doppler factor.