Electrical Path Length Research Articles

Multi‐Frequency SuperDARN Interferometer Calibration

AbstractThe ground‐based, high‐frequency radars of the Super Dual Auroral Radar Network (SuperDARN) observe backscatter from ionospheric field‐aligned plasma irregularities and features on the Earth's surface out to ranges of several thousand kilometers via over‐the‐horizon propagation of transmitted radio waves. Interferometric techniques can be applied to the received signals at the primary and secondary antenna arrays to measure the vertical angle of arrival, or elevation angle, for more accurate geolocation of SuperDARN observations. However, the calibration of SuperDARN interferometer measurements remains challenging for several reasons, including a 2π phase ambiguity when solving for the time delay correction factor needed to account for differences in the electrical path lengths between signals received at the two antenna arrays. We present a new technique using multi‐frequency ionospheric and ground backscatter observations for the calibration of SuperDARN interferometer data, and demonstrate its application to both historical and recent data.

A Study of the Efficacy of Flame Electrical Resistance for Standoff Measurements During the Oxyfuel Cutting Process

Abstract This is a study of the suitability of preheat flame electrical resistance as a potential method for measuring the standoff distance an oxyfuel cutting torch and a work piece. Careful scrutiny of forty-seven individual experiments demonstrate that when cut quality is good, there is a linear repeatable relationship between the two with uncertainty about ±0.3 mm (0.015 in.). As the cut quality degrades, the formation of top-edge dross reduces the electrical path length in the flame, and momentary reduction in the reaction rate in the kerf reduces the free electrons in the flame, causing increases in flame resistance. In these conditions, measurement uncertainty reduces to ±1 mm (0.040 in.) or worse.

A Novel Architecture for Frequency Doubler Featuring Compact 3-D Stacked Packaging and Four Multiplying Structures

This letter reports on a compact 110-GHz Schottky diode-based frequency doubler based on 3-D stacked packaging which allows combining four discrete multiplying circuits. The proposed architecture could increase the power handling capabilities by a factor of 4 compared with the traditional balanced doubler with drastically reduced electrical path length. Meanwhile, the whole circuit is composed of two critical submodules which can be evaluated separately to minimize the manually assembly and fabrication imbalances. The doubler is designed to operate in the 100-115-GHz band, which can deliver a peak power of 407 mW at 112 GHz when pumped with powers over 1.3 W. Besides, the measured conversion efficiency is roughly 82.6% of that of the single doubler, which directly proves the low combination losses of this architecture.

Resolution of electric field distribution and conductivity in a non-uniform electric field: A teaching proposal

This work offers an alternative teaching proposal for the instruction of challenging concepts of electric field distribution and specific conductivity in a non-uniform electric field. Specifically, electric field lines are initially plotted and later on the relation between the electric potential difference and electric field strength is validated. Additionally, on a selected electric field line, electric field strength versus path length and also conductivity versus path length are plotted to comprehend and teach exceedingly difficult concepts of uniform and non-uniform electric fields. In order to accomplish those tasks, a basic conducting sheet, that is simply a wet cardboard, is designed as a part of the apparatus together with a dc power supply, a multi meter and connecting cables. The established method is interesting in the sense that designed the conducting wet cardboard is novel, very practical, beneficial and minimal costing, hence the approach offers physics educators fresh teaching routes and opportunities to clarify the puzzling concepts of electrical field and conductivity.

Comparison of interferometer calibration techniques for improved SuperDARN elevation angles

The high frequency radars in the Super Dual Auroral Radar Network (SuperDARN) estimate the elevation angles of returned backscatter using interferometric techniques. These elevation angles allow the ground range to the scattering point to be estimated, which is crucial for the accurate geolocation of ionospheric measurements. For elevation angles to be accurately estimated, it is important to calibrate the interferometer measurements by determining the difference in the signal time delays caused by the difference in the electrical path lengths from the main array and the interferometer array to the point at which the signals are correlated. This time delay is known as tdiff. Several methods have been proposed to estimate tdiff using historical observations; these methods are summarised in this paper. Comparisons of the tdiff estimates from the different calibration methods are presented and sources of uncertainty discussed. The effect of errors in the estimated tdiff value on the accuracy of geolocation is evaluated and discussed. The paper concludes with a series of recommendations for both scientific SuperDARN data users and SuperDARN radar operators.

Qualitative Inverse Scattering for Sparse-Aperture Data Collections Using a Phase-Delay Frequency Variation Constraint

We present a formulation of the linear sampling method (LSM) for reconstructing target shape from spatially sparse data sets. The technique compensates for a lack of spatial data by incorporating $a$ priori propagation information into the LSM inversion. A constraint is placed on the LSM solution that enforces a phase relationship across frequency that is determined by the electrical path length between the array transmitters and the imaging scene pixels. The effect of the constraint is that image artifacts that do not evince the expected phase relationship according to their position relative to the array are suppressed. We apply the proposed technique to simulated and experimental sparse-aperture data sets and show that the resulting imagery is significantly more faithful to the true target shape as compared to the imagery created with the standard LSM.

CALCULATION OF POLYNOMIAL RATIO APPROXIMATED SURFACES OF BIFOCAL LENS

General imperfection of existent synthesis methods of bifocal lens surface is use complexity emerging over lack of analytical solution. Method of successive approximations is relatively simple, its main problem is determination of power polynomial coefficient approximating illuminated and shadow surface of being synthesized lens. To solve this problem it is suggest analytical determination method of polynomial coefficient approximating illuminated and shadow surface of bifocal lens. This method based on equality condition of electric path length of edge beam and beam passing through lens center. It is obtained analytical equation which permit to determine interdependence polynomials coefficients approximating illuminated and shadow surface of bifocal lens. Moreover, been finded equation allow to calculate bifocal lens thickness, that impossible using known methods of synthesis methods of bifocal lens surface. Cross-section of bifocal lens was be calculated with being suggested analytical method.

Phase calibration of interferometer arrays at high‐frequency radars

AbstractElevation angles of backscattered signals are calculated at the Super Dual Auroral Radar Network (SuperDARN) high‐frequency radars using interferometric techniques. These elevation angles make it possible to estimate the geographic location of the scattering point, an essential piece of information for many ionospheric studies. One of the most difficult parameters to measure is the effective time delay caused by the difference in the electrical path length that connects the main array and the interferometer arrays to the correlator (δtc). This time delay causes a bias in the measured difference in the signal phase, also known as a phase bias. Phase calibration is difficult due to unknown physical attributes of the hardware and the remote location of many radars. This leads to the possibility of sudden external changes, slow temporal drift, and a dependence on transmission frequency. However, it is possible to estimate δtc using the radar observations themselves. This article presents a method for estimating δtc using backscatter with a known location, such as backscatter from artificially generated irregularities, meteor echoes, or distinct groundscatter, which incorporates the uncertainty in the observations and may be used autonomously. Applying the estimated δtc is shown to improve elevation angle uncertainties at one of the SuperDARN radars from their current potential tens of degrees to less than a degree.

Cloud radar with hybrid mode towards estimation of shape and orientation of ice crystals

Abstract. This paper is devoted to the experimental quantitative characterization of the shape and orientation distribution of ice particles in clouds. The characterization is based on measured and modeled elevation dependencies of the polarimetric parameters differential reflectivity and correlation coefficient. The polarimetric data are obtained using a newly developed 35 GHz cloud radar MIRA-35 with hybrid polarimetric configuration and scanning capabilities. The full procedure chain of the technical implementation and the realization of the setup of the hybrid-mode cloud radar for the shape determination are presented. This includes the description of phase adjustments in the transmitting paths, the introduction of the general data processing scheme, correction of the data for the differences of amplifications and electrical path lengths in the transmitting and receiving channels, the rotation of the polarization basis by 45°, the correction of antenna effects on polarimetric measurements, the determination of spectral polarimetric variables, and the formulation of a scheme to increase the signal-to-noise ratio. Modeling of the polarimetric variables is based on existing back-scattering models assuming the spheroidal representation of cloud scatterers. The parameters retrieved from the model are polarizability ratio and degree of orientation, which can be assigned to certain particle orientations and shapes. The developed algorithm is applied to a measurement of the hybrid-mode cloud radar taken on 20 October 2014 in Cabauw, the Netherlands, in the framework of the ACCEPT (Analysis of the Composition of Clouds with Extended Polarization Techniques) campaign. The case study shows the retrieved polarizability ratio and degree of orientation of ice particles for a cloud system of three cloud layers at different heights. Retrieved polarizability ratios are 0.43, 0.85, and 1.5 which correspond to oblate, quasi-spherical, and columnar ice particles, respectively. It is shown that the polarizability ratio is useful for the detection of aggregation/riming processes. The orientation of oblate and prolate particles is estimated to be close to horizontal while quasi-spherical particles were found to be more randomly oriented.

Bi-functional Fresnel zone plate from transformation optics

Instead of reshaping the standard parabolic reflector or the hyperbolic lens to propose their planar counterparts, here we choose to flatten the primary spherical wave front based on the quasi-conformal transformation optics. Ray traces, travelling from the source to the transformed planar surface, can thus be maintained of the equal electrical path length in terms of the transformation-optics Fresnel zone plate. Due to the symmetrical feature of our transformation setup, the proposed device would readily possess dual functionalities in the light focusing and collimation that can either be applied to a reflector when incorporated with a plane mirror or directly employed as a standalone lens according to the principle of the image theory.

Direct current breakdown in gases for complex geometries from high vacuum to atmospheric pressure

The demand for improved performances of power transmission devices requires ever smaller dimensions and higher working voltages which lead to increased risk of breakdown, for example, in satellite slip rings. Previous works are mostly limited to breakdown in simple geometries such as parallel plates or pin to plate. Here we discuss the effect of more complex geometries for dc breakdown in gases over a large pressure range (2 × 10−5 to 103 mbar). Experimental measurements of dc gas discharge breakdown in a ring assembly geometry are compared with a numerical simulation model for gas breakdown using a fluid model. Starting with parallel plates (1 and 100 mm gap width representing approximately the shortest and longest electric field path lengths in the ring assembly geometry) and extending to double gap and multi-gap geometries, an understanding of the overall shape of the breakdown voltage versus pressure curve is established. The high (low) pressure thresholds of gas discharge are determined by the shortest (longest) electric field path length in a complex geometry. Moreover, the availability of multiple path lengths leads to a breakdown voltage minimum over a wide range of intermediate pressure because breakdown can occur in the most favourable gap. Finally, the numerical simulation in the ring assembly shows the importance of parameters such as the secondary electron emission coefficient which play a major role in determining the breakdown voltage value.

A compact UHV package for microfabricated ion-trap arrays with direct electronic air-side access

We have demonstrated a new apparatus for operating microfabricated ion-trap arrays in a compact ultra-high-vacuum setup with excellent optical and electrical access. The approach uses conventional components, materials and techniques in a unique fashion. The microtrap chip is mounted on a modified ceramic leadless chip carrier, the conductors of which serve as the vacuum feedthrough. The chip carrier is indium-sealed to stainless-steel components to form vacuum seals, resulting in short electrical path lengths of ≤20 mm from the trap electrodes under vacuum to air side. The feedthrough contains conductors for the radio-frequency trap drive, as well as 42 conductors for DC electrodes. Vacuum pressures of ∼1 × 10−11 mbar are achieved, and ions have been confined and laser cooled in a microtrap chip. The apparatus enables accurate measurements of radio-frequency voltage amplitudes on the trap electrodes, yielding an excellent agreement between measured and modelled trap efficiencies. This feature is of significant use in establishing initial operation of new devices. The principle of the connectivity scheme presented here is applicable to larger ceramic chip carriers containing many more conductors.

700 MHz 대역 LTE용 광대역 PIFA 설계

본 논문은 휴대폰용 700 MHz 대역 LTE용 안테나의 광대역 설계 기법을 제안한 것이다. 제안한 안테나는 역 F(Planar Inverted - F) 구조를 기본으로 설계되었다. 광대역을 실현하기 위해 전기적 길이를 제어하는 방법으로 라운드 구조와 이중 공진 특성을 얻을 수 있는 지선 소자가 설계에 도입되었다. 그 결과, 복소비 유전율이 4.4인 FR-4 기판에서 <TEX>$30{\times}34mm$</TEX>의 협소한 공간임에도 불구하고, 약 95 MHz의 대역폭을 실현했다. 측정된 반사손실, 대역폭과 이득 방사 패턴은 계산 값과 잘 일치하였다. This paper proposes a design technique of wide-band antenna for handy phone with 700 MHz LTE(Long Term Evolution) low frequency bandwidth. The proposed antenna based on the PIFA(Planar Inverted-F type Antenna) structure was designed and considered. In order to realize the wide bandwidth, a round structure which is able to control the electric path length of current and a branch line element which can be obtain the dual resonance characteristics were introduced in this design. As a result, It was realized about 95 MHz bandwidth in spite of very small space of <TEX>$30{\times}34mm$</TEX> used for FR-4 substrate with relative permitivity of 4.4 at 700 MHz band. Measurement results of return loss, bandwidth and gain radiation pattern were agreed well with their calculation results.

3D integration review

3-D integration delivers value by increasing the volumetric transistor density with the potential benefit of shorter electrical path lengths through use of the shorter third dimension. Several researchers have studied various aspect of 3Di such as bonding level, through silicon via processes and integration, thermomechanical reliability of the vias, and the impact of the vias on devices. In this paper, we review some of the literature with a view to understanding the key options and challenges in 3Di. We also discuss some important applications of this technology, and the constraints that have to be overcome to make it work.

Design and air–water calibration of a waveguide connector for TDR measurements of soil electric permittivity in stony soils

Time Domain Reflectometry (TDR) is one of the most widely used methods for measuring soil water content. TDR determines water content by measuring the apparent relative electric permittivity of the soil or relative permittivity ( ɛ ra ), which is directly related to soil water. For TDR waveguides used in stony soils, the connection between the Trase TDR probe head (Model Trase System 6051X1, Soilmoisture Equipment Co., USA) and the waveguides can be difficult because of the lack of parallelism between the waveguides. Such a lack of parallelism is caused by the occurrence of a large amount of rock fragments in the soil profile, which produces air gaps and compression zones around the waveguides causing errors in the estimation of ɛ ra when the Trase TDR probe head is connected to the waveguides. For this reason, a new type of flexible connector that minimises the existing problems has been designed. The signal travel time correction factor t 0 , which accounts for signal travel in the designed flexible waveguide connector, and the electrical path length of the waveguide L e have been calibrated. In addition, a software for analysing the waveform obtained using the Trase TDR system has been developed. The calibration results were considered to be good and the sensitivity of soil water content values to the estimates of t 0 was low. Higher values of soil apparent electric permittivity were found when the waveform was measured with the flexible connector than when the Trase connector was used; mainly with the waveguides 150 mm long and when the soil water content in the superficial layer was high.

Ultrathin Silicon Micropackaging for RF MEMS Devices

In this paper we report a technology for lightweight, small radio-frequency (rf) microelectromechanical system packaging with a short electrical path length. We used an ultrathin silicon substrate as the packaging substrate. Via holes for vertical feed-through were fabricated on the thin silicon wafer. Then, bottom-up gold electroplating was applied to fill via holes. For hermetic sealing, gold-gold direct metal bonding was used in the sealing line. The packaged rf device has a reflection loss below -22 dB and an insertion loss of -0.05 to -0.08 dB. Therefore, with the ultrathin silicon wafer, a lightweight, small device package can be constructed.

Ultra Thin 실리콘 웨이퍼를 이용한 RF-MEMS 소자의 웨이퍼 레벨 패키징

In this paper, we report a novel RF-MEMS packaging technology with lightweight, small size, and short electric path length. To achieve this goal, we used the ultra thin silicon substrate as a packaging substrate. The via holes lot vortical feed-through were fabricated on the thin silicon wafer by wet chemical processing. Then, via holes were filled and micro-bumps were fabricated by electroplating. The packaged RF device has a reflection loss under 22 〔㏈〕 and a insertion loss of -0.04∼-0.08 〔㏈〕. These measurements show that we could package the RF device without loss and interference by using the vertical feed-through. Specially, with the ultra thin silicon wafer we can realize of a device package that has low-cost, lightweight and small size. Also, we can extend a 3-D packaging structure by stacking assembled thin packages.

Phase distortions in an anisotropic Luneberg lens

The field phase distribution over the aperture of a Luneberg lens composed of radial dielectric rods is approximately calculated, and the influence of this distribution on the directivity pattern of this antenna is estimated. The results of calculations of the difference of electrical pathlengths for the angles ϕ=0 and 90° for Δe=0.2 are presented.

RF MEMS and their applications in NASA's space communication systems

Radio frequency (RF) and microwave communication systems rely on frequency, amplitude, and phase control circuits to efficiently use the available spectrum. Phase control circuits are required for electronically scanning phase array antennas that enable radiation pattern shaping, scanning, and hopping. Two types of phase shifters, which are the phase control circuits, are most often used. The first is comprised of two circuits with different phase characteristics such as two transmission lines of different lengths or a high pass and low pass filter and a switch that directs the RF power through one of the two circuits. Alternatively, a variable capacitor, or varactor, is used to change the effective electrical path length of a transmission line, which changes the phase characteristics. Filter banks are required for the diplexer at the front end of wide band communication satellites. These filters greatly increase the size and mass of the RF/microwave systems, but smaller diplexers may be made with a low loss varactor or a group of capacitors, a switch and an inductor.

Observations of precipitable water vapor fluctuations in convective boundary layer via microwave interferometry

At microwave frequencies, each centimeter of precipitable water vapor (PWV) causes about 6.45 cm of extra electrical path length relative to the “dry” air. The fluctuations of the water vapor dominate the changes of the effective path length through the atmosphere in a relatively short time period of a few hours. In this paper we describe a microwave interferometer developed for water vapor investigations and present the observation results. The interferometer consists of 10 antennas along two orthogonal 400‐m arms that form many baselines (antenna pairs) ranging from 100 to 400 m. All the antennas receive a common CW signal (11.7 GHz) from a geostationary television satellite, and phase differences between pairs of antennas are measured. The phase differences reflect the column‐integrated water vapor differences from the top of the atmosphere to the spatially separated antennas at the ground. The interferometric, baseline‐differential measurements allow us to study the statistical properties of the PWV fluctuations, as well as the turbulent activity of the convective boundary layer (CBL). Structure function analysis of the interferometer measurements shows good agreement with results obtained from the Very Large Array (VLA) and with a theoretical model developed for radio astronomical very long baseline interferometry (VLBI), reported previously by other investigators. The diurnally varying structure constant correlates remarkably well with the combination of the latent and sensible heat fluxes measured simultaneously from a 10‐m meteorological tower. The average drift velocity of the PWV over the interferometer was also derived from the measurements. The derived velocity agrees well during the morning hours with the wind measured by an anemometer at the center of the interferometer.