Orthogonal Probes Research Articles

A model for obtaining the velocity vectors of spherical droplets in multiphaseflows from measurements using an orthogonal four-sensor probe

This paper presents a mathematical model which enables the velocity vectors anddiameters of spherical droplets (or bubbles) in bubbly two-phase flows to bedetermined from the outputs of a local four-sensor intrusive probe. Each of thefour sensors functions by measuring the fluid conductivity at its tip andso use of the probe is relevant to flows where there is a contrast in theelectrical conductivity of the continuous and dispersed phases. The motionof a non-conducting spherical droplet has been simulated as it movesacross a four-sensor probe, which has a leading sensor and three rearsensors in an orthogonal arrangement. The technique described in thispaper relies upon measuring the time intervals between the droplet surfacefirst contacting the leading sensor and then coming into contact witheach of the three rear sensors. Assuming that the surface of the dropletcomes into contact twice with each of the rear sensors, as the dropletmoves across the probe, there will be six such time intervals. It has beenshown that in order to obtain the droplet velocity components in thex,y andz directions with anaccuracy of ±2%, the six time delays must all be measured with an accuracy of ±10 µs. Ithas been shown that the probe dimensions are critical to the measurementtechnique and that the separation of the four sensors should be of theorder of 1 mm. It has also been shown that if the droplets are oblatespheroids rather than spheres then, provided their aspect ratio is greater than0.75, the magnitude of the additional error in the estimates of the dropletvelocity components is less than 10.5%. No account has been taken of theinfluence of the probe on either the shape or the motion of the droplet.

Wideband linear and circularly polarized patch antenna using a printed stepped T-feed

The inherent disadvantage of the narrow bandwidth of microstrip antennas is overcome by a wideband feed mechanism. A square patch excited by a stepped T-feed probe achieved an octave bandwidth (0.98 to 2.1 GHz) with a voltage standing wave ratio of <2. A similar return loss over an octave bandwidth (1.05 to 2.4 GHz) was measured when two orthogonal stepped T-feed probes fed by a log-periodic balun were used to generate circular polarization (CP). For CP, pattern symmetry is shown to occur over 50% of the band, and the CP 3 dB axial-ratio bandwidth is of the order of 30%.

Imaging of acoustic charge transport in semiconductor heterostructures by surface acoustic waves

We demonstrate room-temperature acoustic charge transport of electrons and holes in an InGaAs/GaAs heterostructure. The carriers are optically generated by interband absorption and then separated, stored, and transported in the piezoelectric potential superlattice of a surface acoustic wave. The charge distribution is detected with a spatial resolution of a few acoustic wavelengths by a second orthogonal probe beam, genererated by so-called tapered transducers. The image information is given as a phase shift signal in frequency space and allows for the direct comparison of the number of generated and transported carriers. Regions of mere carrier drag and full carrier capture and transport are observed simultaneously.

Examination of a Correction Procedure for the Flow Attenuation in Orthogonal Sonic Anemometers

In this study we examine the calibration of wind speed measured by a sonic anemometer, with an orthogonal probe configuration, with regard to the approximation of the flow angle, and the wind-speed dependence of the flow attenuation attributed to the transducer shadow. The flow angle θ should be calculated by the iterative method when the attenuation is relatively high. For a probe manufactured by Kaijo Co. TR-61C, the wind-speed dependence of the transducer shadow effect is formulated from the results of the wind-tunnel experiment. Assuming the equation is applicable to field observations, significant errors possibly remain especially when the wind speed is low, and /or the angle between the flow vector and the sonic path is small, if the wind-speed dependence in measurement errors is neglected.

Three-component turbulence measurements using a four-wire probe

A probe, consisting of two orthogonal X-wire probes, allows all three velocity fluctuation components to be measured simultaneously. Attractive features of the probe include its ease of construction, the use of a standard yaw–pitch calibration and the potential to correct for spatial resolution. The reliability of this probe was assessed using measurements in the near-field of a plane jet and in the self-preserving region of a cylinder wake. Statistics of all three components compare favourably with those obtained, though not simultaneously, using standard X-wires.

A miniature triple hot-wire probe for wall bounded flows

Four orthogonal and one non-orthogonal miniature triple hot-wire probes have been developed and tested in a two-dimensional turbulent boundary layer. The influence of the different wire configurations on measurements of the Reynolds stresses has been studied. A directional calibration with an analytical solution for the wire response equations was used for the measurements of the non-orthogonal probe and was tested for the orthogonal probes in order to correct their possible geometrical imperfections. It is shown that a directional calibration does not significantly improve the quality of the measurements for precisely manufactured orthogonal probes and that measuring errors are related rather to the measuring volume, the size of the domain of unique solutions for the instantaneous velocity vector and interference effects, i.e. the wire configuration itself.

Observation of induced modulational polarization instabilities and pulse-train generation in the normal-dispersion regime of a birefringent optical fiber

Four-photon mixing in a low-birefringence fiber is strongly influenced by the orientation of the pump and signal waves with respect to the fiber axes. We experimentally investigated the dependence of the modulational gain spectra on pump power and polarization by mixing orthogonal pump and probe light beams in a birefringent optical fiber. With a pump on the fast fiber axis, a cascade of sidebands was generated in the regime of normal fiber dispersion. These sidebands are shown to correspond to 0.2–0.3-THz trains of pulses with complex polarization profiles. The analysis reveals that, at particular values of the input pump and probe powers and signal frequency detuning, trains of dark-solitonlike pulses can be generated on the axis orthogonal to the pump.

Current density distribution measurement of negative point-to-plane corona discharge

The current density distribution on the plate electrode of a point-to-plane corona discharge is measured with a computer-controlled measuring system. The measurements are taken by rotating the plate which consist of built-in arrays of orthogonal probes. The current-density distribution can be measured for different separation distances between the point electrode and the plane electrode while the applied high voltage can be varied from the voltage required for the onset of corona discharge to 30 kV. The current-density distribution of a single needle is symmetric around its center point within the accuracy of the measurement system. However, the current-density distribution is radially nonuniform. The computer-controlled measuring system is capable of measuring the current distribution of single point and multipoint electrodes.

Spatial Characteristics of Motion Integration

We asked how the characteristics of a surround could affect the perception of a central component undergoing translational motion. Two adjacent patches of moving dots (100 dots per patch; diameter 2.5 deg) were presented on a VDU screen. A central ‘target’ patch consisted of a combination of signal dots, undergoing left - right translational motion, and noise dots, which moved in random directions at the same speed as the signal dots. To the right of this a ‘probe’ patch contained dots undergoing translational motion. A simple 2IFC task was used to detect the presence of left - right translational motion in the target patch. An adaptive staircase varied the ratio of translating (signal) to noise dots to measure the 79.4% correct point. Preliminary findings indicate that both the directional characteristics of the probe and the degree of separation between the two patches influence sensitivity to the target motion. At large separations, probe characteristics do not influence target sensitivity. As the two patches become closer together, probe motion parallel to the target patch increases sensitivity, whereas orthogonal probe motion decreases target sensitivity. Surprisingly, as the separation between the patches becomes even smaller, sensitivity to the target motion is reduced by a parallel probe and increased by an orthogonal probe. This suggests that spatial motion integration involves facilitation and inhibition between different motion directions, and that these two effects have different spatial characteristics.

Application of a dual color detection scheme in the screening of a random combinatorial peptide library

Selectide Technology is a random synthetic combinatorial library method in which millions of random compounds are screened in parallel for their ability to bind to a tagged macromolecular target. The library consists of millions of beads and each individual bead expresses a unique chemical compound such as a peptide. In the standard enzyme-linked colorimetric detection scheme, the positive bead which turns color is isolated for microsequencing. In this paper, a dual color detection scheme using two sequential orthogonal probes is described. This dual color system enables one to rapidly differentiate false positive beads from true positive beads, resulting in a much more efficient use of the microsequencer.

Interpreting Orthogonal Triple-Wire Data From Very High Turbulence Flows

For turbulence intensities of up to 30 percent, an orthogonal triple-wire probe can be used to make accurate measurements of the instantaneous velocity vector. Above this limit difficulties arise in the interpretation of the data due to the problem described as rectification. This paper presents a means by which data from an orthogonal triple-wire probe may be interpreted for single point measurements in Gaussian turbulence with intensity up to 50 percent resulting in unbiased estimates of the velocity mean vector, Reynolds stress tensor, and time correlation coefficients.

Measurement of velocity vectors with orthogonal and non-orthogonal triple-sensor probes

A new method of interpreting the signals from triple-sensor thermal anemometer probes has been developed based on fast solution for all the roots of the non-linear Jorgensen (1971) equations describing the directional response of each cylindrical sensor. The sensors can be oriented at arbitrary angles to each other, but always within a range of probe geometries that keep prong interference and thermal wake interference below acceptable levels. The properties of a class of non-orthogonal symmetric tetrahedral probe geometries are studied in relation to the range of flow vector angles that can be measured, the sensitivity of the probe with respect to changes in flow angle, and the sensitivity of the computed velocity components due to angular errors associated with the construction of the probe. The solutions of Jorgensen's equations are inherently multiple-valued, but if the velocity vector is restricted to be within a cone of angles, they are unique. It is shown that measurements with non-orthogonal triple sensor signals are sensitive to angular deviations of a few degrees of the sensor angles from the nominally orthogonal probe geometry, indicating the need of a non-orthogonal algorithm. The mean, rms, Reynolds stress, and power spectrum of the velocity in fully developed turbulent pipe flow were measured using a specially designed triple sensor probe and the proposed algorithm.

Orthogonal triplet probes: an efficient method for unbiased estimation of length and surface of objects with unknown orientation in space.

If the axis of anisotropy of oriented, tubular or lamellar objects is unknown, the unbiased stereological estimation of length density and surface density (Lv and Sv) requires counts on sections with isotropic uniform random (IUR) orientation. It is shown theoretically that in homogeneous, anisotropic specimens the precision of Lv and Sv estimation is considerably augmented if IUR-oriented sets of three mutually perpendicular sections (orthogonal triplet probes = ortrips) are used instead of three directionally independent IUR sections. The mechanism of variance reduction results from a negative covariance between sections within 'ortrips' and corresponds to the antithetic variate principle of Monte Carlo work. Heterogeneity decreases the efficiency of the ortrip method, but this effect can often be counteracted by systematic sampling of ortrips within specimens. Practical estimation of length and surface area of the highly anisotropic, tubular myocardial capillaries per tissue volume in the left ventricles of eight normal, adult, male perfusion-fixed Wistar rats provided estimates of excellent precision with CEs of 3.3% (Lv) and 2.1% (Sv) of the group mean. The method will hopefully allow stereologists dealing with arbitrary anisotropic structures to apply the same simple, efficient, and unbiased sampling designs that have long been used in the study of liver, lung, and kidney tissue.

ELF wave production by an electron beam emitting rocket system and its suppression on auroral field lines: Evidence for Alfven and drift waves

ELF electric disturbances in the frequency range from DC to 1 kHz produced in the auroral ionosphere by the injection of powerful electron beams have been studied by orthogonal probes on a free‐flying plasma diagnostics payload. Frequency spectrograms have been produced for various pitch angles, pulsing characteristics and other properties of the injected beams. The large‐scale DC ionospheric convection electric field has also been measured, as well as the auroral particle precipitation, the visual auroral forms and the ionospheric parameters. The convection field was strongly attenuated as the experiment system moved northward across discrete arcs but recovered to a higher value north of the arcs where the particle precipitation ceased. The production of ELF waves by beam injection was also strongly reduced in the arcs, and like the DC field, recovered to an even greater intensity north of the arcs. This behavior did not extend into the lower hybrid or whistler mode region. The DC field decrease has been explained by the high Pederson conductivity caused by auroral electron precipitation in the E‐region below the vehicle. It is postulated that the observed ELF waves are in the Alfven and drift modes and are generated by the positive vehicle potential during beam injection. More effective vehicle neutralization in the auroral arcs lowers the vehicle potential and, therefore, reduces wave production. Most features of the experimental observations can be qualitatively explained by this mechanism.

Responses of Electric-Field Probes Near a Cylindrical Model of the Human Body

A theoretical and experimental study on the response of an E-field probe near a cylindrical model of the human body has been conducted. The body is simulated with a long cylindrical dielectric shell filled with saline water, and a single E-field probe oriented in various directions, or an orthogonal probe is heated near its surface. The model with the probe is illuminated by a TE or TM plane EM wave. The response of the probe was found to be strongly dependent on the probe location with respect to the direction of the incident EM wave, the probe separation from the model surface, the probe orientation and the polarization of the incident EM wave. The effect due to the dielectric shell on the probe response, with and without the presence of saline water, was carefully investigated. In all cases, the agreement between theory and experiment was found to be very good.

Ion resonances and ELF wave production by an electron beam injected into the ionosphere: Echo 6

The interaction with the ionospheric plasma of two separately controllable electron beams injected from the Echo 6 sounding rocket in the auroral zone has been studied using orthogonal electric double probes and other instruments on a separate plasma diagnostics payload. The gun pulses produced a myriad of large electric probe signals covering the entire ion gyro range between dc and 1250 Hz. In particular a signal driven at the 1‐kHz gun frequency and a naturally occurring resonance at 840 Hz near the 799‐Hz proton gyrofrequency were studied. The 1‐kHz signal decreased by a factor of 100 between 45 and 90 m from the beam field line but was detectable in the 1‐mV/m range at 120 m, confirming previous findings that pulsed electron beams may serve as ELF wave sources in space. The 840‐Hz resonance was excited by a beam injected parallel to the magnetic field but could be quenched by the addition of a transverse beam in what appears to be a case of controlled damping. The 840‐Hz and 1‐kHz signals were superposed on large‐amplitude fluctuations and were extracted using power spectral analysis. The data contain a large variety of ion gyro range frequencies which are under study. The paper discusses the interpretation of the electric probe responses and large turbulent payload floating potential effects produced by the hot plasma generated by the beams.

High latitude stratospheric electrical measurements in fair and foul weather under various solar conditions

Stratospheric electric field and conductivity measurements during a wide variety of weather and solar conditions are presented. These data are all from high latitude sites (> 50°N GG) in the months of either April or August. The vector electric field is determined by orthogonal double probes connected through high impedance inputs to differential electrometers. The direct conductivity measurement involves determining the relaxation time constant of the medium after refloating a shorted pair of separated probes. Vertical electric field data from several balloon flights with average duration of 18 h at ceiling in fair weather are shown to be well modeled by a simple exponential altitude dependent equation. Examples of solar flare and magnetospheric effects on stratospheric electric fields are shown. Data collected over electrified clouds and thunderstorms are presented along with a discussion of the thunderstorm related electric currents. Lightning stroke signatures in the stratosphere during a large thunderstorm are identified in the electric field data. Current surges through the stratosphere due to DC currents as well as the sferic are calculated. In nearly 1000 h of balloon data no direct solar influence is identified in these data except during major flares. However, variations in all three components of the electric field during magnetically active conditions are discussed.

A Circularly Polarized Feed for an Automatic Tracking Telemetry Antenna

Characteristics of a feed that utilizes a unique method to produce a conically scanning main beam are discussed. Model and full scale test data are included to make the feed operation more clearly understood. Certain criteria such as gain, side lobe level, and polarization must be considered when designing a primary feed for a paraboloid reflector. Also, the automatic tracking requirement calls for some means of producing an error signal for given off-target angles. The feed discussed is a circular waveguide excited by orthogonal probes fed 90° out of phase to produce circular polarization. The electrical phase center of the feed is shifted around the focal point of the 60-foot diameter paraboloid reflector by rotating a hemispherical tapered-dielectric prism at the aperture of the waveguide. A ground plane around the waveguide mouth controls the illumination taper across the paraboloid aperture to yield equal E and H plane secondary beamwidths.