Wideband Measurements Research Articles

Polarization effects for subionospheric ELF/VLF signals penetrated into the seawater

Our study of electromagnetic wave penetration into the seawater was based on wide-band synchronous measurements of ELF/VLF atmospherics on the sea surface and underwater. Two crossed horizontal magnetic field components just above the sea surface and one horizontal electric component of underwater field have been examined to find the transfer function of a seawater layer of some 15 m in thickness. Using linearly-polarized antennae caused a number of polarization effects in the transfer function. The most prominent of the effects is that the water layer behaves as a spatial filter for modes in the Earth–ionosphere waveguide, making the transfer function irregular.

Wide-band low-noise tunnel current measurements in laser assisted experiments

A composite current-to-voltage converter that shows a superior bandwidth and signal-to-noise ratio (bandwidth ∼50 MHz at 410 kΩ transimpedance) was designed. Two options for the input stage were tested: a high input impedance wide-band operational amplifier (OP) OPA655 (Burr–Brown) and a differential cascade which is based on the junction field effect transistors SST440 (Siliconics). By using a wideband current feedback OPA658 in the second stage the achieved bandwidth gain product is ∼10 GHz. A method for testing the performance of the preamplifier by using laser induced electron emission is described. The technique’s possibility for measurements of laser induced acoustic waves with high sensitivity and nanometer local resolution is demonstrated. For further applications the design of a wide-bandwidth, low-noise, single tunneling electron counting capable preamplifier is discussed.

Wide-band complex magnetic susceptibility measurements of magnetic fluids as a function of temperature

Measurements of the complex magnetic susceptibility over the frequency and temperature ranges of 2MHz–6GHz and 20 to −100°C, respectively, are reported for the first time for a magnetic fluid. The fluid used was a colloidal suspension of magnetite particles of median diameter 9nm in a hydrocarbon oil (isopar m).Resonance was observed and found to increase from approx 1.5GHz to 3.3GHz in the temperature range 20 to −50°C. The increase in resonant frequency is attributed to a decrease in thermal fluctuations with decrease in temperature.At frequencies below approximately 19MHz, a significant drop in χ′(ω) with decrease in temperature over the temperature range 20 to −100°C, is observed and is attributed to the changes in the Néel and Brownian relaxation processes. Below −60°C, the temperature at which the suspension becomes solid, Brownian relaxation ceases to exist.

Impluse response of a fiber optic probe hydrophone determined with shock waves in water

The impluse response of a fiber optic probe hydrophone (FOPH) is determined through it’s step response obtained by using a self-focusing electromagnetic shock wave excitation. The experimental transfer function agrees well with the theoretical calculation of the transient response by diffraction of the acoustic wave at the fiber end face. A rise time of about 5 ns has been obtained for the shock front of the self-focusing shock wave generator by the deconvolution of the output signal of the hydrophone with it’s impulse response. The FOPH can be used as a standard hydrophone for the absolute wideband measurement of shock waves of lithotripters and of acoustic waves in liquids in general.

Novel characterization of PD signals by real-time measurement of pulse parameters

Measurements of partial discharge (PD) are used to examine the insulation characteristics of HV equipment. This test method is also suitable for low-cost components in mass production. To monitor the quality of prefabricated parts, products and production processes, short test cycles and automatic classification are indispensable. In addition, it is desirable to acquire more information about the PD signals for classification. This can be achieved with an ultra wide band (UWB) measurement system. In this paper a new test method, based on analog capture of PD parameters which describe the PD waveform, in addition to the usual parameters, is proposed. The analog values are further processed employing a digital signal processing hardware and a PC. Measurements of frequently encountered PD pulse shapes and their frequency spectra are used to discuss problems which arise from the integration in the frequency domain. These problems are avoided using integration in the time domain, which is employed to determine the apparent charge with the described measurement system. Using the PD pulse duration as an example, measurements on artificially created test samples are presented, which show the influence of the defect dimensions on the PD pulse parameters. This is feasible for test circuit dimensions not extending to a certain value, which depends on the used frequency range of the measurement system.

Transformer derating for harmonic currents: a wide-band measurement approach for energized transformers

Power system transformers must often be derated when supplying harmonic currents to nonlinear loads. IEEE Recommended Practice C57.110 extrapolates transformer loss for harmonic frequencies based on DC winding resistance and rated eddy-current loss. This paper describes an improved derating technique based on direct measurements performed at fundamental and harmonic frequencies. The measurements can be performed regardless of whether the transformer is energized and in service or deenergized and out of service. For energized transformers, the measurement can be performed regardless of whether the transformer is fully loaded or unloaded. Measurements of several distribution transformers show the improvement of this method over C57.110.

Simultaneous ultrawide and narrowband detection of PD pulses in dielectric liquids

Simultaneous narrow band (300 kHz) and wide band (500 MHz) measurements were carried out to obtain estimates of the apparent charge transfer associated with discrete isolated discharge pulses and discharge pulse bursts, which are observed to occur in dielectric liquids when wide band detection systems are utilized. The integrated apparent charge transfers determined with the narrow band system ranged from 12 to 95 pC, which represents typically the lower range of values normally encountered with PD activity in dielectric liquid-filled or impregnated equipment. While the discharge phenomena in perfluoro polyether liquids was found to be typified by sporadic appearances of single isolated pulses involving charge transfers between 33 and 38 pC, the discharge events in mineral oils assumed most frequently the form of pulse bursts, displaying the usual pulse sequences of quasi-ascending amplitudes; the overall integrated apparent charge transfer of the observed pulse bursts extended commonly from 12 to 16 pC. The charge release, occurring with the first (initiating) smallest discharge pulse within the pulse bursts, was estimated to be of the order of /spl sim/1 pC.

Wideband phase-noise measurement of mode-locked laser pulses by a demodulation technique

A new method is proposed and demonstrated for measuring the phase noise (pulse timing fluctuations) of mode-locked lasers. The instantaneous phases of the pulse intensity are extracted in a time domain, and the phase-noise power spectral density is calculated from the demodulated signals. Compared with the conventional method based on the single-sideband phase-noise measurement, the proposed method has a larger dynamic range and a wider frequency span. The phase noise of a mode-locked Cr:LiSAF laser is measured for 50-mHz-1-MHz Fourier frequencies.

Dynamical conductivity of an MBE-grown La 1.84Sr 0.16CuO 4 thin film at frequencies from 5 to 36 cm −1

We present the first wide-band (5–400 cm −1) measurements of the dynamical conductivity and the dielectric permittivity spectra of La 2− x Sr x CuO 4 ( x ≈ 0.16). A narrow Drude-like band is observed in the spectra, which is consistent with a d-wave pairing state. We determine the plasma frequency, scattering rate, and mean free path of the unpaired charge carriers responsible for this band. For the first time, “coherence peak”-like behavior is observed in the temperature dependence of the submillimeter conductivity of La 2− x Sr x CuO 4, associated with the temperature evolution of the band in the superconducting state.

Determination of Propagation Mechanisms Using Wideband Measurement Techniques - Abstract

In this paper we propose using wideband measurement techniques to determine propagation mechanisms. The factors that can affect the accuracy of the measurements are analyzed. The delay profiles can be obtained by applying inverse fast Fourier transforming (IFFT) on the measured frequency response. To avoid range ambiguity in the delay profile, the frequency response should be finely sampled. The peak values sampled in the delay profiles can be used to represent certain scattering mechanisms such as reflection coefficients or edge diffraction coefficients. To obtain accurate peak value, enough zeros will be padded to the frequency domain measurement data before applying IFFT. In this paper we also propose a calibration procedure so that the ordinate value in the delay profile can represent the propagation loss relative to that at the reference position. Wideband measurement techniques will be employed to determine wall reflection coefficients and edge diffraction coefficients. Consistency between the experimental and simulation results shows the effectiveness of the proposed methods.

Characterisation of propagation in 60 GHz radio channels

Narrowband as well as wideband measurements have been performed in various indoor and outdoor environments in order to enable the development of reliable prediction models for 60 GHz radio channels. In addition, results of deterministic modelling on the basis of geometric ray-tracing have been compared with measurement results, showing that simple ray-tracing can be used to estimate both the narrowband and wideband characteristics of a 60 GHz radio channel. This paper reviews the measurement and modelling activities performed by various research institutes.

Ultrasensitive laser measurements without tears

Several easily implemented devices for doing ultrasensitive optical measurements with noisy lasers are presented. They are all-electronic noise cancellation circuits that largely eliminate excess laser intensity noise as a source of measurement error and are widely applicable. Shot-noise-limited optical measurements can now easily be made at baseband with noisy lasers. These circuits are especially useful in situations where strong intermodulation effects exist, such as current-tuned diode laser spectroscopy. These inexpensive devices (parts cost approximately $10) can be optimized for particular applications such as wideband or differential measurements. Although they cannot eliminate phase noise effects, they can reduce amplitude noise by 55-70 dB or more, even in unattended operation, and usually achieve the shot-noise limit. With 1-Hz signal-to-noise ratios of 150-160 dB, they allow performance equal or superior to a complex heterodyne system in many cases, while using much simpler dual-beam or homodyne approaches. Although these devices are related to earlier differential and ratiometric techniques, their noise cancellation performance is much better. They work well at modulation frequencies from dc to several megahertz and should be extensible to approximately 100 MHz. The circuits work by subtracting photocurrents directly, with feedback applied outside the signal path to continuously adjust the subtraction for perfect balance; thus the excess noise and spurious modulation ideally cancel at all frequencies, leaving only the shot noise. The noise cancellation bandwidth is independent of the feedback bandwidth; it depends only on the speeds of the photodiodes and of the bipolar junction transistors used. Two noise-canceled outputs are available; one is a high-pass filtered voltage proportional to the signal photocurrent and the other is a low-pass filtered voltage related to the log ratio of the signal and comparison photocurrents. For reasonable current densities, the noise floors of the outputs depend only on the shot noise of the signal beam. Four variations on the basic circuit are presented: low noise floor, high cancellation, differential high power, and ratio-only. Emphasis is placed on the detailed operation and design considerations, especially performance extension by compensation of the nonideal character of system components. Experience has shown that some applications advice is required by most users, so that is provided as well.

A wide-band propagation model based on UTD for cellular mobile radio communications

The present wide-band propagation model based on uniform geometrical theory of diffraction (UTD) for cellular mobile radio communications includes two major contributions. First, a UTD-based narrow-band channel transfer function containing both the diffracted electric field and the reflection of diffracted electric fields is derived. Not only is it an important element of the wide-band modeling method, but it also leads to a total path-loss prediction model verified by comparisons with previously published theoretical and experimental results. In particular, the distance for horizontal placement on the street allows one to calculate the ray-path length difference (used in wide-band modeling) for the diffracted field and the reflection. Second, new refinements (including a number of explicit-form expressions to an existing method experimentally confirmed, simulating wide-band radiowave propagation for rural environments including terrain profiles) are added, making it applicable here. The method generates the time-domain path loss, wide-band path loss, and the relative power in the frequency domain. The time-domain path loss physically interprets and reasonably predicts the power delay profiles. The presence of this and similar power delay profiles, as well as the behavior of the relative power in the frequency domain, has been confirmed by existing wide-band propagation measurements. The value of the wide-band path loss is of the order of the total path loss at the carrier frequency.

Experimental Verifaction of Physical Conditions Restricting Chiral Material Parameters

The physical restrictions for the constitutive parameters of chiral media are looked for and tested against available measurement data. These restrictions include Kramers-Kronig relations for the constitutive parameters of isotropic chiral media and conditions developed from the wave propagation characteristics and the energy principle. The restrictions are applied to wideband measurement data of an isotropic chiral slab.

Linewidth of submillimeter wave flux-flow oscillators

A reliable technique for wide band measurements of the spectral linewidth of superconducting oscillators integrated on-chip with superconductor-insulator-superconductor (SIS) detectors has been developed. The spectral linewidth of flux-flow oscillators (FFO) based on the unidirectional and viscous flow of magnetic vortices in a long overdamped Josephson tunnel junction was measured in the frequency range 250–580 GHz, and a linewidth as low as 200 kHz was obtained at 450 GHz. Also stable frequency locking of a FFO to very high (≤60th) harmonics of an external microwave reference source has been demonstrated. The proposed technique may improve the sensitivity, frequency resolution, and stability of the fully superconducting integrated submillimeter wave receiver.

Optoelectronic techniques for ultrafast device network analysis to 700 GHz

Recent advances in state-of-the-art optoelectronic techniques are presented for small-signal electronic device network analysis. The impetus for optoelectronic approaches is given by the severely inadequate bandwidth coverage of existing measurement techniques. Based on a comparison of the trade-offs offered by various optoelectronic techniques, external electrooptic sampling was chosen. Then, the three basic building blocks of an electrooptic characterization system are discussed, which cover the areas of wide-band signal measurement, generation and transmission. The building blocks are subsequently integrated into a complete electrooptic network analyser system capable of active device characterization over a 100 GHz bandwidth. These capabilities are demonstrated on a heterojunction field-effect transistor with a directly-measured maximum frequency of oscillation of 94 GHz. Then, the performance of the electrooptic network analyser is optimized by minimizing transmission line losses, and by improving signal generation and measurement geometries. The resulting system exhibits an unprecedented single-measurement bandwidth of 700 GHz on passive structures. The system performance is verified by comparing measured results with simple models of the measured passive structures.

Characterization of highly dispersive materials using composite coaxial cells: electromagnetic analysis and wideband measurement

In this work, theoretical modeling and experimental characterization of composite coaxial-line cells are made for accurate dielectric measurement. The coaxial cells are designed such that highly dispersive materials can be characterized over a wide band of frequencies. In addition, a transmission line matrix (TLM) algorithm with a new type of node is proposed for electromagnetic analysis of the complex composite geometry of the measurement cells. Such a hybrid-mode simulation allows the electrical performance of the proposed cells to be determined for a variety of complex permittivity measurements. The proposed node in the cylindrical coordinate not only accommodates cylindrical coaxial discontinuities in the cell, but also describes the frequency-dependent properties of material. Experiments on a network analyzer were done with a number of APC-7 coaxial cells and various liquid samples to verify the wideband characteristics of the technique. It is found both theoretically and experimentally that the sample volume can be adjusted to ensure a wideband sensibility of the S-parameters. A sensitivity factor is also defined to characterize the frequency response of the coaxial cells. Such an electromagnetic analysis (direct problem) can be used in extracting unknown dielectric characteristics of a material (inverse problem) based on a recently proposed generic approach.

Simple derivation of the constitutive parameters of an isotropic chiral slab from wideband measurement data

Simple derivation of the complex constitutive parameters of an isotropic, lossy chiral slab from free-space measurement data is presented. The ambiguities in the solutions are commented upon. Uncertainties of the parameters are given in an analytic form as a function of the measurement uncertainties. The analytic equations are applied to wideband measurement data. © 1996 John Wiley & Sons, Inc.

Wide-band measurements of dc voltages using two-parametric amplitude adaptation

A method of analyzing the accuracy and speed of adaptive measuring instruments based on two-parametric iteration algorithms of amplitude adaptation in precision high-speed dc voltage measurements is discussed. The method makes it possible to estimate the real and maximum attainable accuracy of adaptive dc voltage measurements over a wide dynamic range.

Evaluation and verification of the VHF/UHF propagation channel based on a 3-D-wave propagation model

This paper is intended to increase and improve the knowledge concerning the characterization of digital VHF/UHF communication channels. This characterization of the propagation channel is based on the field strength-delay-spectrum (FDS) of the three-dimensional (3-D) multipath wave propagation. A statistical superposition of the predicted multipath signals yields the probability density function of the narrowband signal and the averaged channel impulse response of the wideband propagation channel. Thereof, the relevant parameters, e.g., standard deviations, mean values, delay spread, and correlation coefficients, are derived both in time and frequency domain. The angles-of-arrival of the multipath signals are used to calculate the Doppler spectra of moving receivers for the characterization the time-variant properties of the propagation channel. In total, a rather complete summary of derivations, algorithms and characteristics of the VHF/UHF propagation channel is presented. Narrowband and wideband measurements are included for verification.