Showing papers in "IEEE Transactions on Instrumentation and Measurement in 1999"
TL;DR: A new monitoring method using passive radio requestable SAW sensors is presented and the friction coefficient can be measured by evaluating the mechanical strain in the tire surface contacting the road-utilizing the deformation of the tread elements.
Abstract: The term "intelligent tire" describes tires equipped with sensor systems to monitor thermal and mechanical parameters while driving. Information about temperature, tire pressure, tread wear, etc., is collected and used for car operation and maintenance support. The contact between tire and road surface is a key parameter when characterizing the ability to accelerate, decelerate and steer a vehicle, therefore making contact monitoring important for modern car control systems. Following numerous previous theoretical works, the friction coefficient can be measured by evaluating the mechanical strain in the tire surface contacting the road-utilizing the deformation of the tread elements. A new monitoring method using passive radio requestable SAW sensors is presented. The principle, measurement setup and experimental results are shown.
216 citations
TL;DR: The design for testability (DFT) of active analog filters based on oscillation-test methodology is described and the DFT techniques investigated are very suitable for automatic testable filter synthesis and can be easily integrated in the tools dedicated to automatic filter design.
Abstract: The oscillation-test strategy is a low cost and robust test method for mixed-signal integrated circuits. Being a vectorless test method, it allows one to eliminate the analog test vector generator. Furthermore, as the oscillation frequency is considered to be digital, it can be precisely analyzed using pure digital circuitry and can be easily interfaced to test techniques dedicated to the digital part of the circuit under test (CUT). This paper describes the design for testability (DFT) of active analog filters based on oscillation-test methodology. Active filters are transformed to oscillators using very simple techniques. The tolerance band of the oscillation frequency is determined by a Monte Carlo analysis taking into account the nominal tolerance of all circuit under test components. Discrete practical realizations and extensive simulations based on CMOS 1.2 /spl mu/m technology parameters affirm that the test technique presented for active analog filters ensures high fault coverage and requires a negligible area overhead. Finally, the DFT techniques investigated are very suitable for automatic testable filter synthesis and can be easily integrated in the tools dedicated to automatic filter design.
141 citations
TL;DR: The proposed digital signal processing technique for measuring the operating frequency of a power system provides correct and noise-free estimates for near-nominal, nominal, and off- Nominal frequencies in about 25 ms, and it requires modest computations.
Abstract: This paper describes the design, computational aspects, and implementation of a digital signal processing technique for measuring the operating frequency of a power system. The technique provides correct and noise-free estimates for near-nominal, nominal, and off-nominal frequencies in about 25 ms, and it requires modest computations. The proposed technique is implemented using a DSP-based board and has been extensively tested using voltage signals obtained from a dynamic frequency source and from a power system. Some test results are presented in the paper.
141 citations
TL;DR: Field tests and comparisons of the DAS against the standard Eppley precision spectral pyranometer (PSP) have shown a slightly nonlinear correlation and that the accuracy of this measurement system as applied to solar radiation monitoring is fairly good.
Abstract: The hardware design and operation of a battery-powered microcontroller-based data acquisition system (DAS) for unattended remote measurements are presented. The system was designed around the ST62E20 8-bit microcontroller and applied for solar radiation monitoring. The measurement system uses the SolData silicon-cell pyranometer as the solar radiation sensor. The data from the sensor is collected by means of on-chip A/D converter and stored in a serial EEPROM until uploaded to a portable computer. Keeping the DAS in a low-power mode, which is only interrupted when measurements are to be taken or when a computer is connected to retrieve the stored data, minimizes power consumption. An on-chip timer provides an interrupt to awaken the system from its low-power wait mode at 10-min intervals to sample and store the data. At the end of each data collection period, the acquired data will be transmitted to the computer through the RS232 serial port for subsequent analysis. Only unprocessed data is stored in EEPROM. Quality control and data analysis is done off-line in the laboratory to minimize system cost, complexity and system downtime. Field tests and comparisons of this measurement system against the standard Eppley precision spectral pyranometer (PSP) have shown a slightly nonlinear correlation and that the accuracy of this measurement system as applied to solar radiation monitoring is fairly good, typically /spl plusmn/13 W/m/sup 2/.
140 citations
TL;DR: The CVC proposed is based on a symmetrical structure containing two half ac bridges, is intrinsically immune to parasitic capacitances and resistances, is capable of detecting capacitance changes from dc up to at least 10 kHz, is able to handle both single and differential capacitance, and can easily be realized with discrete components.
Abstract: There is a need for capacitance to voltage converters (CVC's) for differential capacitive sensors like pressure sensors and accelerometers which can measure both statically and dynamically. A suitable CVC is described in this paper. The CVC proposed is based on a symmetrical structure containing two half ac bridges, is intrinsically immune to parasitic capacitances and resistances, is capable of detecting capacitance changes from dc up to at least 10 kHz, is able to handle both single and differential capacitances, and can easily be realized with discrete components. Its sensitivity is very high: detectable capacitance changes of the order of 2 ppm of the nominal value (24 aF with respect to a nominal capacitance of 12 pF) result in a measured output voltage of 1.5 mV. However, due to drift the absolute accuracy and resolution of the CVC is limited to 3.5 ppm. A differential accelerometer for biomedical purposes was connected to the CVC and showed a sensitivity of 4 V/g. The measured rms output voltage noise in the frequency range of 2-50 Hz is 750 /spl mu/V, resulting in a signal to noise ratio of 75 dB at an acceleration of 1 g in the frequency range of 2-50 Hz.
126 citations
TL;DR: In this paper, the authors report the measurement of hyperfine splittings of the P(54)32-0 and R(57) 32-0 transitions near 532 nm.
Abstract: With the aid of two iodine spectrometers, we report for the first time the measurement of the hyperfine splittings of the P(54)32-0 and R(57)32-0 transitions near 532 nm. Within the tuning range of the frequency-doubled Nd:YAG laser, modulation transfer spectroscopy recovers nine relatively strong ro-vibrational transitions of /sup 127/I/sub 2/ molecules with excellent SNR. These transitions are now linked together with their absolute frequencies determined by measuring directly the frequency gaps between each line and the R(56)32-0:/spl alpha//sub 10/ component. This provides an attractive frequency reference network in this wavelength region.
125 citations
TL;DR: In this article, a modification to this measurement technique utilizing two dielectric plugs which are used to house the granular or liquid materials was described, where no approximation to the measurement apparatus is made while the presence of the plugs are fully accounted for in the derivations.
Abstract: There are numerous dielectric property characterization techniques available in the microwave regime each with its own uniqueness, advantages and disadvantages. The two-port completely-filled waveguide (transmission line) technique is a robust measurement approach which is well suited for solid dielectric materials. In this case, the dielectric material can be relatively easily machined to fit inside the waveguide and the subsequent measurement of the scattering parameters of this two-port device renders the dielectric properties of the material filling the waveguide. However, this technique is not well suited for measuring the dielectric properties of granular and liquid materials. These materials are used in the production of various composites which are increasingly replacing the use of metals in many environments. If this technique is directly applied to these types of materials, several approximations either in the measurement apparatus or the formulation must be made. To overcome this problem, this paper describes a modification to this measurement technique utilizing two dielectric plugs which are used to house the granular or the liquid dielectric material. In this approach no approximation to the measurement apparatus is made while the presence of the plugs are fully accounted for in the derivations. Using this technique, the dielectric properties of cement powder, corn oil, antifreeze solution and tap water, constituting low- and high-loss dielectric materials (granular and liquid) were measured. In addition, the important issue of measurement uncertainty associated with this technique is also fully addressed. The issue of optimal choice of various measurement parameters is also discussed as it relates to the measurement uncertainty.
122 citations
TL;DR: This paper describes the wideband radio channel sounding techniques for mobile radio channel measurements and implementation of the cross-correlation method using both a sliding correlator and a matched filter detector is presented.
Abstract: This paper describes the wideband radio channel sounding techniques for mobile radio channel measurements. Implementation of the cross-correlation method using both a sliding correlator and a matched filter detector is presented. Limitations and accuracy of radio channel measurements are discussed. Typically, delay resolution of about 20 ns is achieved with 100 MHz bandwidth. With a sliding correlator, a dynamic range of 25 dB was obtained with maximum Doppler bandwidth of 25 Hz and maximum excess delay of 19 /spl mu/s. Digital matched filtering with a maximum sampling rate of 125 MHz can be used in real-time measurements with Doppler shifts of several kilohertz and 30 dB dynamic range. Using matched filter deconvolution as a resolution enhancement technique is discussed. Examples of the time-variant complex impulse response measurements are given.
116 citations
TL;DR: Limitations in time and frequency resolution inherent in the STFT lead to the development and investigation of the Wigner-Ville Distribution for use in the measurement of nonsinusoidal waveforms.
Abstract: This paper is concerned with the measurement of nonsinusoidal waveforms, in particular the use of waveform transforms in the calibration of power frequency harmonic analyzer instruments designed to make harmonic measurements under nonstationary conditions. The suitability of the Fourier transform (FT) for the analysis of nonstationary waveforms is discussed. A method involving windowing of the waveform data known as the short-time Fourier transform (STFT) and its application to harmonic amplitude measurements is considered. Limitations in time and frequency resolution inherent in the STFT lead to the development and investigation of the Wigner-Ville Distribution for use in this application. The performance of the various transforms are compared by simulation. Results using a test signal, typical of a practical signal encountered by harmonic analyzers, are presented for each transform.
104 citations
TL;DR: Experiments show that the accuracy of resonant perturbation method has been greatly increased after the amendment, especially for extremely low-loss dielectric samples.
Abstract: The quality factor of a resonant cavity may increase after introducing an extremely low-loss dielectric, so the conventional cavity perturbation method, widely used in dielectric permittivity measurement, may be invalid for extremely low-loss dielectric samples. After a brief review of the conventional cavity perturbation theory, this paper discusses the change of quality factor of a resonant cavity due to the introduction of a dielectric sample. A new concept, expected quality factor Q/sub 0/ is introduced in this paper to denote the quality factor of a resonant cavity loaded with a strictly no-loss sample, and a calibration procedure is proposed to find the frequency dependence of Q/sub 0/. The conventional resonant perturbation formulas are then amended by substituting the quality factor before the perturbation with the expected quality factor Q/sub 0/ corresponding to the frequency after the perturbation. Experiments show that the accuracy of resonant perturbation method has been greatly increased after the amendment, especially for extremely low-loss dielectric samples.
95 citations
TL;DR: In vitro calibrations of a glucose sensor obtained with the subminiature potentiostat/telemetry unit and a traditional potentiOSTat correlated extremely well (R/sup 2/=0.9994).
Abstract: A subminiature implantable potentiostat and telemetry electronics package was developed to provide remote monitoring of implantable amperometric glucose sensors. Included are a new potentiostat for sensor biasing, a transimpedance amplifier to produce the sensor-current proportional voltage, and an optically coupled interface to the commercially available telemetry unit which transmits glucose concentration data to a corresponding receiver and computer. Potentiostat components were individually tested in vitro for accuracy and stability, and as a system utilizing telemetry for end-to-end remote data monitoring. In vitro calibrations of a glucose sensor obtained with our subminiature potentiostat/telemetry unit and a traditional potentiostat correlated extremely well (R/sup 2/=0.9994). Instrumentation developed in this paper will allow other researchers to easily develop implantable units for their own applications.
TL;DR: This novel method involves the use of an evanescent microwave probe (EMP) and it is capable of imaging a variety of nonuniformities in biological materials including conductivity, permittivity, and density variations.
Abstract: Scanning tunneling microscopes (STM) and atomic force microscopes (AFM) are used to study biological materials. These methods, often capable of achieving atomic resolutions, reveal fascinating information regarding the inner workings of these materials. However, both STM and AFM require physical contact to the specimen. In the case of STM the specimen needs to be conducting as well. Here we introduce a new method for imaging biological materials through air or a suitable liquid using decaying or evanescent fields at the tip of a properly designed microwave resonator. This novel method involves the use of an evanescent microwave probe (EMP) and it is capable of imaging a variety of nonuniformities in biological materials including conductivity, permittivity, and density variations. EMP is a noncontact and nondestructive sensor and it does not require conducting specimens. Its spatial resolution is currently around 0.4 /spl mu/m at 1 GHz. We have used this probe to map nonuniformities in a variety of materials including metals, semiconductors, insulators, and biological and botanical samples. Here we discuss applications of EMP imaging in bone, teeth, botanical, and agricultural specimens.
TL;DR: This paper gives a rigorous and exact formulation in which the dominant mode and the evanescent higher-order modes are used as basis functions to obtain the solution for the reflection coefficient at the waveguide aperture.
Abstract: Open-ended rectangular waveguides are extensively used in nondestructive dielectric material evaluation. The dielectric properties of an infinite-half space of a material are calculated from the measured reflection properties referenced to the waveguide aperture. This calculation relies on a theoretical and numerical derivation of the reflection coefficient likewise referenced to the waveguide aperture. Most of these derivations assume the dominant mode field distribution across the waveguide aperture. However, when dealing with low permittivity and low loss dielectric materials, there may exist significant errors when calculating the dielectric properties from the measured reflection coefficient. These errors have also shown to be more significant in the upper frequency portion of a waveguide band. More accurate results are obtained when higher order modes are considered in addition to the dominant waveguide mode. However, most studies incorporating higher-order modes have used various approximations when calculating the reflection properties and have not provided a full discussion on the influences of dielectric properties of the infinite-half space and the frequency of operation. This paper gives a rigorous and exact formulation in which the dominant mode and the evanescent higher-order modes are used as basis functions to obtain the solution for the reflection coefficient at the waveguide aperture. The analytic formulation uses Fourier analysis in addition to the forcing of the necessary boundary conditions at the waveguide aperture. The solution also readily accounts for the complex contributions of both TE and TM higher-order modes. Finally, the influences of the dielectric properties of the infinite-half space and the frequency of operation are investigated.
TL;DR: For the first time, optimized current/voltage waveforms for maximum PAE of microwave field effect transistors (FET's) have been measured and confirm the theory on high efficiency microwave power amplifiers.
Abstract: One of the most important requirements that RF and microwave power amplifiers designed for radiocommunication systems must meet is an optimum power added efficiency (PAE) or an optimal combination of PAE and linearity. A harmonic active load-pull system which allows the control of the first three harmonic frequencies of the signal coming out of the transistor under test is a very useful tool to aid in designing optimized power amplifiers. In this paper, we present an active load-pull system coupled to a vectorial "nonlinear network" analyzer. For the first time, optimized current/voltage waveforms for maximum PAE of microwave field effect transistors (FET's) have been measured. They confirm the theory on high efficiency microwave power amplifiers. The proposed load-pull setup is based on the use of three separated active loops to synthesize load impedances at harmonics. The measurement of absolute complex power waves is performed with a broadband data acquisition unit. A specific phase calibration of the set-up allows the determination of the phase relationships between harmonic components. Therefore, voltage and current waveforms can be extracted. The measurement results of a 600 gate periphery GaAs FET (Thomson Foundry) exhibiting a PAE of 84% at 1.8 GHz are given. Such results were obtained by optimizing the load impedances at the first three harmonic components of the signal coming out of the transistor. Optimum conditions correspond to a class F operation mode of the FET (i.e., square wave output voltage and pulse shaped output current). A comparison between measured and simulated current/voltage waveforms is also presented.
TL;DR: The effects of main error sources are analyzed in terms of integral and differential nonlinearity with the aim of setting up a unified error model, useful both to economically generate a look-up table for error correction and to quickly produce diagnosis models for fault detection and isolation.
Abstract: The influence of the architecture on analog-to-digital converter modeling is investigated for the three most widespread architectures: integrating, successive approximations, and flash. The effects of main error sources are analyzed in terms of integral and differential nonlinearity with the aim of setting up a unified error model. Such a model is useful both to economically generate a look-up table for error correction and to quickly produce diagnosis models for fault detection and isolation. Numerical simulations aimed to show the model effectiveness and experimental tests carried out to validate the model are discussed.
TL;DR: This paper focuses on the theoretical description of the self-mixing effect by presenting a survey of the existing literature as it applies to the specific implementation of this 3-D laser range imaging system, followed by some experimental results.
Abstract: In this work, we implemented a three-dimensional (3-D) laser range imaging system using the well-known self-mixing effect in a frequency-modulated semiconductor laser diode. The system generates 3-D point sets of a scene, using a single semiconductor laser diode serving both as the light source and as the detector. The experimental imaging accuracy was measured to be 0.87 mm at a distance of 0.55 m after some filtering. This paper focuses on the theoretical description of the self-mixing effect by presenting a survey of the existing literature as it applies to our specific implementation, followed by some experimental results.
TL;DR: The experimental results show the effectiveness of the improved, simple and cost effective experimental procedure and an equally simple post-experimental data processing to obtain the flux-linkage-current curves at varying rotor positions of the SRM.
Abstract: Experimental determination of magnetization characteristics of switched reluctance motors (SRMs) is quite important in their accurate performance prediction. Over the last decade, various experimental procedures have been used to obtain these characteristics. Every evolved new method has its own limitations and constraints. This paper describes an improved, simple and cost effective experimental procedure and an equally simple post-experimental data processing to obtain the flux-linkage-current curves at varying rotor positions of the SRM. The experimental results on a 4 kW, four-phase, 8/6 pole SRMs show the effectiveness of the method and the results compare well with the previously results compare well with the previously published results of similar and higher rating SRM's.
TL;DR: An accurate bipolar voltage source for AC and DC metrology, based on the quantized pulses of Josephson junctions, is developed by generating bipolar waveforms where arrays of junctions are driven with both a broadband two-level digital code and a sinusoidal frequency.
Abstract: We have developed an accurate bipolar voltage source for AC and DC metrology, based on the quantized pulses of Josephson junctions. The output voltage is a factor of 4-6 higher than the amplitude of previous unipolar waveforms; this is achieved by generating bipolar waveforms where arrays of junctions are driven with both a broadband two-level digital code and a sinusoidal frequency. We experimentally demonstrate two bipolar waveforms: a 5 kHz sine wave with /spl plusmn/18 mV peak amplitude and quantization noise power eight orders of magnitude below the power in the fundamental frequency, and a 3.5 kHz square wave with /spl plusmn/13 mV peak amplitude and even harmonics at -100 dB (carrier).
TL;DR: This paper gives accurate error estimates for a selection of typical input signals, shows how well the rules perform for these signals and concludes that, although the rules provide good upper bounds for the error, they can not be reliably used for error correction.
Abstract: The dynamic behavior of an oscilloscope is usually described by its bandwidth, which is not sufficient for well-founded error estimation for rise time measurement. Two rules of thumb have become most common that describe (a) a relation between bandwidth and rise time of an oscilloscope and (b) an estimation of the error resulting from the rise time limitation of the oscilloscope. Although it is well understood that these rules are approximations, no information on their accuracy and extent of validity appears in the literature. In this paper, we analyze these rules of thumb with their underlying assumptions and respect a more realistic model for oscilloscope behavior. We give accurate error estimates for a selection of typical input signals, show how well the rules perform for these signals and that, although the rules provide good upper bounds for the error, they can not be reliably used for error correction.
TL;DR: A new robust method for finding the parameters of Engen's six-ports-to-four-port reduction algorithm for six-port reflectometer calibration has been developed and has been used successfully to calibrate a newly developed six- port reflectometer in GaAs MMIC technology working between 1.3 GHz and 3.0 GHz.
Abstract: A new robust method for finding the parameters of Engen's six-port-to-four-port reduction algorithm for six-port reflectometer calibration has been developed. Like other previously published methods, it uses a minimum of five loads with an unknown but constant absolute value of the reflection coefficient and unknown but well-distributed phases. However, the quality of the parameter estimates is improved, especially in noisy environments, by efficiently eliminating cases in which these earlier methods may become ill-conditioned. The new method has been used successfully to calibrate a newly developed six-port reflectometer in GaAs MMIC technology working between 1.3 GHz and 3.0 GHz.
TL;DR: Experimental results on narrow line cooling of strontium atoms are presented and Frequency chirp cooling is successfully demonstrated as a means of expanding the cooling range.
Abstract: Experimental results on narrow line cooling of strontium atoms are presented. Doppler cooling is performed on the /sup 1/S/sub 0/-/sup 3/P/sub 1/ intercombination transition at 689 nm resulting in temperatures near the recoil limit in a one-dimensional (1-D) optical molasses. Frequency chirp cooling is successfully demonstrated as a means of expanding the cooling range.
TL;DR: An efficient least-squares algorithm for estimating the time-base distortion of sampling oscilloscopes and can accurately estimate the order of the harmonic model that is used to account for the amplitude nonlinearity of the sampling channel.
Abstract: We present an efficient least-squares algorithm for estimating the time-base distortion of sampling oscilloscopes. The method requires measurements of signals at multiple phases and frequencies. The method can accurately estimate the order of the harmonic model that is used to account for the amplitude nonlinearity of the sampling channel. We study several practical problems related to the time-base distortion estimation, such as the effect of averaging and sample size requirements. We also compare the relative performance of various methods for estimating time-base distortion using simulated and measured data.
TL;DR: The introduction of this new virtual instrument for time-frequency analysis may be of help to the scientists and practitioners in signal analysis.
Abstract: A virtual instrument for time-frequency analysis is presented. Its realization is based on an order recursive approach to the time-frequency signal analysis. Starting from the short time Fourier transform and using the S-method, a distribution having the auto-terms concentrated as high as in the Wigner distribution, without cross-terms, may be obtained. The same relation is used in a recursive manner to produce higher order time-frequency representations without cross-terms. Thus, the introduction of this new virtual instrument for time-frequency analysis may be of help to the scientists and practitioners in signal analysis. Application of the instrument is demonstrated on several simulated and real data examples.
TL;DR: This work presents a discrete-time TDE suitable for measuring the delay between two periodic signals with a resolution of a fraction of the sampling period, based upon a separate reference, external to the two measured signals, which is allowed to vary with subsample increments of delay.
Abstract: Time delay estimation (TDE) techniques based upon the identification of the extremum of the cross-correlation function, or some other statistic of two signals, typically use some form of interpolation between points to obtain a resolution finer than the sample period. Often these techniques introduce some bias because of mismatch between the interpolating function and the actual discrete-time correlation function. We present a discrete-time TDE suitable for measuring the delay between two periodic signals with a resolution of a fraction of the sampling period. The technique is based upon a separate reference, external to the two measured signals, which is allowed to vary with subsample increments of delay. Simulations show that the incremental reference technique does not exhibit any significant bias and is superior to parabolic interpolation at both high and low SNR. The technique is suited to the measurement of group-delay or range of an object.
TL;DR: The result shows that the reliable density-independent moisture measurement can be made for timbers, and the mean value of the measurement error is 1.4%, and the maximum error is 4.4%.
Abstract: A new method for density-independent moisture measurement using the microwave free-space technique is proposed. The method is based on the measurement of two microwave phase shifts at two different frequencies. The principle is demonstrated experimentally in the moisture measurement of three wood species, Douglas fir, spruce and cedar. The result shows that the reliable density-independent moisture measurement can be made for timbers. In the moisture range from 2% to 30% on a dry basis, the mean value of the measurement error is 1.4%, and the maximum error is 4.4%.
TL;DR: A novel voltage-to-current (V/I) converter circuit is proposed, which is based on an operational transconductance amplifier (OTA) integrated circuit, and new circuits for the temperature-insensitive general-grounded resistance converter, instrumentation amplifier, electronically tunable gyrator, and analog multiplier are presented.
Abstract: A novel voltage-to-current (V/I) converter circuit is proposed, which is based on an operational transconductance amplifier (OTA) integrated circuit. The V/I transconductance gain is insensitive to temperature and the input differential voltage swing limitation of the OTA integrated circuit is alleviated. New circuits for the temperature-insensitive general-grounded resistance converter, instrumentation amplifier, electronically tunable gyrator, and analog multiplier are presented. Experimental and simulation results that demonstrate the performances of the V/I convertor and its applications are also included.
TL;DR: A coupled thermal and electromechanical model for squirrel-cage induction motor simulation and analyses is presented and an original thermal observer based on the direct stator temperature measurement under normal running condition with no additional sensors is proposed.
Abstract: In this paper, the authors present a coupled thermal and electromechanical model for squirrel-cage induction motor simulation and analyses. The effect of iron saturation, rotor parameter variation due to current displacement (skin-effect) and temperature variations of both stator and rotor resistances are taking into account simultaneously. A new device for the temperature measurement in the stationary as well as rotating parts of electric machines is built. The unique construction of the device for continuous rotor temperature monitoring is briefly described. This device is a part of a complete acquisition system, which is used for precise testing and investigating of a coupled thermal and electromechanical phenomena. An original thermal observer based on the direct stator temperature measurement under normal running condition with no additional sensors is proposed.
TL;DR: Experimental results show that the present technique is accurate and reliable for the measurement of the permittivity tensor of uniaxial media.
Abstract: Based on microwave resonant perturbation theory, a bimodal TE/sub 112/ cylindrical cavity is developed for the measurement of permittivity tensor of uniaxially anisotropic dielectrics. The two perpendicular TE/sub 112/ degenerate modes in the cavity are used to measure the two complex components in the permittivity tensor of a uniaxial sample, respectively. In the measurement of each component, only the corresponding mode resonates in the bimodal cavity, and the real and imaginary parts of the complex component are deduced from the changes of the resonant frequency and the quality factor of the cavity due to sample insertion. In the present technique, the quality factors of the cavity before and after sample insertion are measured at the same frequency, so the uncertainties caused by the variation of the total stored energy in the cavity due to sample insertion are eliminated. Experimental results show that the present technique is accurate and reliable for the measurement of the permittivity tensor of uniaxial media. As an example, the dielectric properties of /spl alpha/-SiO/sub 2/ samples with different crystal orientations are characterized using the present technique.
TL;DR: Test results and design details for the first short-term frequency standard to achieve ultrahigh stability without the use of liquid helium are presented and the capability of the 10 K CSO to eliminate local oscillator degradation for atomic frequency standards is shown.
Abstract: We present test results and design details for the first short-term frequency standard to achieve ultrahigh stability without the use of liquid helium. With refrigeration provided by a commercial cryocooler, the compensated sapphire oscillator (10 K CSO) makes available the superior short-term stability and phase noise performance of cryogenic oscillators without periodic interruptions for cryogen replacement. Technical features of the 10 K CSO include use of a two-stage cryocooler with vibration isolation by helium gas at atmospheric pressure, and a new sapphire/ruby resonator design giving compensated operation at 8 K to 10 K with Q=(1-2)/spl times/10/sup 9/. Stability of the first unit shows an Allan deviation of /spl sigma//sub y//spl les/2.5/spl times/10/sup -15/ for measuring times of 200 s/spl les//spl tau//spl les/600 s. We also present results showing the capability of the 10 K CSO to eliminate local oscillator degradation for atomic frequency standards. Configured as local oscillator (L.O.) for the LITS-7 trapped mercury ion frequency standard, the CSO/LITS combination demonstrated a limiting performance of 3.0/spl times/10/sup -14///spl tau//sup 1/2/, the lowest value measured to date for a passive atomic frequency standard, and virtually identical to the value calculated from photon statistics.
TL;DR: Improved transfer standards have been developed to support National Institute of Standards and Technology (NIST) calibration services over the range 10 M/spl Omega/ to 1 T/ spl Omega/ and to support extension of the calibration service to 10 T/spl omega/ and 100 T/Spl Omega/.
Abstract: An improved design for a guarded transfer standard in the resistance range 1 M/spl Omega/ to 100 G/spl Omega/ is described. Existing transfer standards and their limitations are reviewed along with a description of guard circuit theory. Measurements made to evaluate the effectiveness of guard networks are described and results are reported that verify the guard circuit behaviour. Guarded transfer standards have been tested with internal and external guard networks showing the benefits of guarding transfer standards for high-resistance measurements. Interchangeable guard networks are used in the improved transfer standards to ensure complete guarding during all phases of the measurement process thus reducing errors caused by leakages to ground. These improved transfer standards have been developed to support National Institute of Standards and Technology (NIST) calibration services over the range 10 M/spl Omega/ to 1 T/spl Omega/ and to support extension of the calibration service to 10 T/spl Omega/ and 100 T/spl Omega/.