Power Attenuator Research Articles

Flow ripple reduction in hydrostatic transmission by means of fluid power attenuators

Noise from fluid power systems is still a severe problem in many applications. During the last decade we have been dealing with fluid power attenuators mainly in systems terminated by different types of valves. However, there have, with varying success, also been a number of attempts with attenuators in hydrostatic transmissions. In order to clarify this noise problem a further look is taken into the phenomena related to the use of attenuators in hydrostatic transmissions.Previous studies have shown different methods to measure flow ripple. One of the methods, the anechoic termination method, has been the main method for our experimental research, both of fluid power attenuators and of pumps as sources of flow ripple. This method is characterized by the fact that no standing waves will occur in the measurement pipe. To verify the accuracy of this method it is compared with measurements carried out by means of the so-called 2-microphone method. The agreement has turned out to be very good.

Liquid helium cooled sample stage for the investigation of microwave irradiated samples by scanning electron microscopy

A liquid helium cryostat is described for use with the scanning electron microscope (SEM) CamScan 4-DV. The back of the sample is in direct contact with the liquid helium while its front can be irradiated with microwaves and with the electron beam of the SEM. The microwave source, e.g. a klystron, and the other microwave components such as power meters and attenuators are arranged outside the cryostat and can easily be changed during operation of the system. The microwave is then guided by a waveguide (E-band, i.e. 60–90 GHz) to the vicinity of the sample. The system is well suited for spatially resolved imaging of low temperature properties of microwave irradiated samples such as the distribution of critical current density at microwave induced constant-voltage steps of superconducting tunnel junctions.

FLUID POWER ATTENUATORS ANALYSIS, MEASUREMENTS AND PERFORMANCE OPTIMIZATION

Fluid power systems and components become more complex and sophisticated. Although great efforts have been made to make hydraulic components quieter, noise and vibration problems are major and growing drawbacks of fluid power systems.A variety of methods to measure the oscillary flow from a fluid power pump have been proposed during the last decades. This paper is concerned with the “anechoic termination” method. A mathematical model is proposed in order to control the errors introduced by the actual device used to achieve anechoic conditions. Results from measurements on pump flow ripple using this method are presented.The noise and vibration problems can be considerably reduced by means of a fluid power attenuator. A very simple one, the one-chamber expansion chamber attenuator, is studied in this paper.Standing wave phenomena due to the chamber itself are carefully penetrated. It is also shown how to improve the attenuation by means of a mode cancellation pipe. In both cases simulations and measurements are carried out and the agreement is generally fairly good.

A Miniature Spark Counter for Public Communication and Education

The fabrication of a miniature spark counter for public communication and education using naturally occurring radon as a radioactive source without involving any man-made radioactivity is described. The battery-powered miniature spark counter weighs 2.07 kg with a volume of 4.844 x 10/sup -4/ m/sup 3/. The circuitry consists of seven major components: timer, high-voltage power supply, attenuator, noninverting amplifier, low-pass filter, one-shot generator, and counter. Cellulose nitrate films irradiated with alpha particles from radon emanating from soil were etched and counted. The visible sparks during counting are rather heuristic, which can be used to demonstrate naturally occurring radioactivity in classrooms or showplaces.

Terminal Invariant Parameter Determinations from Complex Signal Ratio Measurements

Engen of the National Bureau of Standards (NBS) has pointed out significant advantages in calibrating power sensors and attenuators in terms of efficiencies rather than scattering parameters. For example, efficiency measurements require the use of repeatable low-loss connectors, but do not demand carefully specified impedances. This offers hope of more accurate calibration of field-type components fitted with nonprecision connectors. Existing efficiency measuring procedures usually require tuned measuring networks to realize necessary conditions. This paper presents procedures that utilize complex signal ratio data (obtained, for example, from a network analyzer) taken from untuned microwave networks. Such procedures offer advantages in speed and convenience.

Generalized Theory of Waveguide Differential Phase Sections and Application to Novel Ferrite Devices

Since Fox introduced the concept of differential phase shift(DPS) sections in TE/sub 11/ mode cylindrical waveguide, most interest has been concentrated on devices having fixed DPS of 90/spl deg/ or 180/spl deg/. This paper gives exact solutions for the magnitude, phase, and polarization of the wave output from three sections having variable DPS and orientations. The RF field is, successively resolved into components along the birefringence axes. Experimental results of tests carried out at X band, using a transversely magnetized ferrite tube, closely support the theory. It is shown how the latter can be applied, not only to familiar devices such as the rotary phase shifter or single sideband modulator, but also to new devices using ferrite sections of variable DPS or of switchable birefringence axes. A three-section power divider and attenuator is explained, together with a new two-section polarizer, with possible applications to satellites and search RADAR. It is also shown how one section can be used as a phase shifter. Some experimental results are given. Thus complete characterization of DPS section devices is offered by the theory, together with the quantitative effect of any of their parameters.

A high power attenuator for microwaves.

A high power variable attenuator has been developed for use in 10-cm wave guide transmission lines. The attenuating material is a liquid which serves also to transfer the absorbed energy. The attenuator can handle power levels up to 100 watts, has a power standing wave ratio less than 1.1 to 1, and an attenuation which is variable from 1.5 db to 40 db.