Pulse Duty Factor Research Articles

ワイヤ電解加工の加工速度に及ぼすパルス周期および衝撃係数の影響

The effect is investigated of pulsed current conditions, i. e. pulse period and duty factor, on feed rare of wire electrochemical machining.Dependence of feed rate on pulsed current conditions can be explained by assuming that the feed rate is restricted by instantaneous maximum value of reaction products concentration in the electrode gap. The feed rate can be improved by applying shorter pulse period than the residential time of the electrolyte; W/v (W; thickness of workpiece, v; electrolyte velocity), and by applying the larger duty factor, although using direct current is not necessarily favorable.Periodic disturbance is sometimes found in pulsed current form, when the feed rate is near its limit value. This disturbance is attributed to the periodic change of products concentration.

放電加工の自動化の研究 Ｉ 形彫り放電加工の最適制御

The method of optimum control has been investigated for the first step of a development of EDM automatic system. An aim of this optimum control is to obtain the maximum metal removal rate.The effective pulse efficiency was used as index performance of EDM process. A good correlation between the metal removal rate and effective pulse efficiency has been verified experimentally under the constant pulse duration and peak discharge current.The control parameters are (1) working voltage (servo referance voltage), (2) pulse duty factor, (3) electrode lifting cycle time, (4) dielectric pressure. An algorithm for controling four parameters was determined by experimental design method using the table of arthogonal arrays.The optimum control using established algorithm achieves more metal removal rate than manual operation by a skillfull operator.

Transient temperature behavior in pulsed double-drift IMPATT diodes

The temperatures in a pulsed double-drift IMPATT diode are calculated as a function of position and time by a finite difference calculation using the alternating direction algorithm. The results are given as a function of pulse length and duty factor for a typical double-drift diode designed to operate near X band. Techniques are described for choosing spatial meshes and time integrals which vary with position and time in a way that minimizes computation time. Numerical results are chosen to illustrate the distribution of temperature within the diode at different times during the pulse, the effect of a temperature-dependent breakdown voltage upon radial temperature distribution, and the interplay between the short thermal-diffusion times within the GaAs diode and the long times associated with the slow heating-up of the heat sink at great distances. An extended definition of thermal resistance for pulsed diodes is introduced and the implications upon reliability are discussed.

Recent Advances in High Voltage Electron Beam Injectors

A variety of electron gun systems in the 200 to 500 kV range have been placed into linac service during the past five years. These systems were specifically developed to improve the reliability and performance of high power linear accelerators by providing low emittance pulsed electron beams having highly stable flat-top characteristics. Lifetimes considerably in excesss of 5000 hours have been achieved through the use of low heater power dispenser cathodes, non-intercepting electrodes for control of beam emission and focusing, all-metal and ceramic high temperature brazed dc accelerating columns, and operational vacuum levels of 10-7 to 10-8 Torr. The design features and performance of several of these systems, including short beam pulse and high duty factor are discussed, and typical beam waveforms and equipment photographs are presented.

Ultrasonic Exposure Thresholds for Changes in Cells and Tissues

The first part of this paper reports an experimental investigation of some parameters that control the occurrence of biologically effective cavitation-type phenomena in the frequency region 0.25 4 MHz. The experimental criterion by which “cavitation” is recognized here is the simultaneous occurrence of degradation of DNA in aqueous solution, liberation of free I2 from KI solution, and generation of half-order subharmonic. The intensity threshold for cavitation rises with frequency from 0.14 to 17.5 W cm−2 (spatial peak) in the above frequency range. Pulse duration and duty factor are also found to be determining parameters, with cavitation activity reducing to zero when values of both parameters are sufficiently low. A strong positive correlation between ambient pressure and intensity threshold has also been determined. On the basis of observations of the levels of scattered half-order subharmonic signals from various media, no evidence could be found for cavitation activity in sonicated mammalian tissues, although such activity could be detected in a wide range of liquids. The second part of the paper consists of a review, conducted in the light of the above results, of published experimental data relating to the existence and values of exposure thresholds for possible nonthermal, noncavitational mechanisms of action of ultrasound in living cells and tissues.

Novel Technique for Real-Time Depth-Gated Acoustic Image Holography

An acoustic camera, which uses a scanning laser beam to detect an ultrasonic image, has been modified to incorporate the desirable depth-discrimination feature characteristic of pulse-echo techniques. The resultant system combines the virtues of acoustic holography with those of the pulse-echo method. It produces a real-time image hologram of a 2.268-MHz acoustic field with the transverse resolution characteristic of imaging (approximately three wavelengths or 2 mm), and the depth resolution of the pulse-echo technique (1–10 mm depending on the acoustic pulse length). The pulsing and gating action of the system prevents (1) image degradation due to too many out-of-focus cross sections, typical in imaging systems, and (2) most of the multiple reflection artifacts, typical in pulse-echo systems. Moreover, average acoustic power requirements for signal-to-noise considerations are lowered from the cw case by the pulse-duty factor.