Measurement techniques and results of an intercomparison for RFpower in a 3.5 mm coaxial line up to 26 GHz

The methods and results of an international comparison are presented for measurements of RF power in a 3.5 mm coaxial line at seven frequencies up to 26 GHz. Three national laboratories of metrology having different measurement techniques participated in the comparison. The agreement between the mean values of the calibration factor of the traveling standard reported by the participants is well within their reported uncertainties (k=2), which are between 0.5% and 3.1%     

Calculable coaxial resistors for precision measurements

Coaxial straight-wire resistors have been constructed with the purpose of improving comparisons between resistors, capacitors, and inductors in the audio-frequency range. The design is based on the principle that a coaxial line with a cylindrical shield can be described by relatively simple equations for the real and imaginary parts of the impedance. The resistors, with values at and above 100 Ω will be used as transfer standards for characterization of the frequency dependence of standard resistors and of the quantum Hall resistance in the audio frequency range     

Calibration of a coaxial antenna-probe for microwave dielectric measurements

It is proposed calibrating an antenna-probe in the form of an open section of coaxial line against standard samples in the centimeter-wave band. __________ Translated from Izmeritel’naya Tekhnika, No. 4, pp. 52–53, April, 2007.     

A new method for high-sensitivity noise measurements

A new method for high-sensitivity noise measurement, based on the elaboration in the time domain of the signals coming from two identical amplifiers, is presented in this paper. The most important advantage of this method, which in most cases allows obtaining an equivalent background noise 30 dB below that of the amplifiers which are used in the measurement chain, lies in its simplicity and in the fact that it does not depend on the method used for the estimation of the noise spectra.     

A new power standard for audio-frequency measurements

A thermal power comparator for audio-frequency measurements is presented. It is essentially a double-bridge-type multiplier that consists of two multijunction thermal converters that contain two heaters. Together with a precision inductive voltage divider and current transformer for extending the voltage and current range, the comparator ensured a high-precision power standard with an AC/DC transfer error of less than 15 p.p.m. in the audio-frequency range     

A new nanofiber fabrication technique based on coaxial electrospinning

In tissue engineering, nanofibrous scaffolds can achieve better biological responses than microfibrous scaffolds and electrospinning is a common method for producing fibrous scaffolds. However, not all biopolymers can be made into nanofibers through conventional electrospinning. The current investigation developed an innovative nanofiber fabrication technique based on coaxial electrospinning and used poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) as an example for achieving nanofibers. For obtaining PHBV nanofibers, core-shell structured fibers were fabricated first via coaxial electrospinning, with PHBV being the core and chitosan being the shell. The chitosan shell was then removed by washing electrospun scaffolds with water, leading to the formation of nanofibrous PHBV scaffolds. The PHBV nanofiber diameter was affected by the inner polymer (i.e., PHBV) solution concentration during coaxial electrospinning, which can be explained in terms of the coaxial electrospinning process and polymer solution viscosity. Compared to the approach of using a conductivity-enhancing salt in polymer solution to produce polymer nanofibers, the new technique not only eliminates the biocompatibility concerns but also provides a more effective way of reducing fiber diameters to the nano-size range.     

A method to determine the calorimetric equivalence correction for acoaxial microwave microcalorimeter

A way is presented to obtain the microcalorimeter correction factor by direct measurement rather than by an indirect estimate or modeling. The microcalorimeter is used to measure the effective efficiency of a reference standard thermistor mount. The correction factor accounts for the different thermal paths and losses in the microcalorimeter reference standard combination. The uncertainty in the measurement depends primarily on an accurate determination of the correction factor. This has been an especially difficult problem in the coaxial case because of the center conductor. The method requires the fabrication of components that duplicate the thermal and RF loss in the microcalorimeter and reference standard. Using the technique with the new National Institute of Standards and Technology (NIST) type N coaxial microcalorimeter has substantially reduced the systematic uncertainty. The total uncertainty is about one-half the uncertainty of the prior NIST standard at frequencies above 1 GHz     

A new method for power measurements in digital wireless communication systems

Repeatability problems, usually accompanied by low accuracy, are often experienced in power measurements, especially in those concerning spread spectrum signals, peculiar to digital wireless communication systems, and involving a specified frequency range. For this concern, a new method for power measurements is presented. The method applies original and straightforward digital signal-processing algorithms to the input signal power spectrum, preliminarily provided by optimized versions of well-known estimators, such as those based on weighted overlapped segment averaging and multitaper approaches. The outcomes of many experiments, conducted on spread spectrum signals of third-generation telecommunication systems, confirm the efficacy of the proposed method in assuring reliable and accurate results in various types of power measurement.     

Influence of direct current on performance of niobium conductor for miniature coaxial line

We have investigated the characteristics at 4.2 K and from 100 MHz to 2.3 GHz of a coaxial line containing a niobium wire which carries a direct current in addition to the high frequency current. The results can be understood in terms of flux penetration and are compared with published data relating to cold worked niobium in the mixed state.     

A new bridge technique for neutron tomography and diffraction measurements

An attractive feature of neutron techniques is the ability to identify hidden materials and structures inside engineering components and objects of art and archaeology. Bearing this in mind we are investigating a new technique, “Tomography Driven Diffraction” (TDD), that exploits tomography data to guide diffraction experiments on samples with complex structures and shapes. The technique can be used utilising combinations of individual tomography and diffraction instruments, such as NEUTRA (PSI, CH) and ENGIN-X (ISIS, UK), but is also suitable for new combined imaging and diffraction instruments such as the JEEP synchrotron engineering instrument (DIAMOND, UK) and the proposed IMAT neutron imaging and diffraction instrument (ISIS, UK).     

New VNIIM comparator for measurements of line scales for length

An interference comparator is described for measuring line scales and gratings in which total conformity is provided for the sections being compared, the effect of water vapor in the refractometer chamber is overcome, and a laser confocal microscope and digital processing of signals are used. In comparisons, the length-dependent divergence is 1·10⁻⁸L, and independent of length the standard divergence is 2 nm. __________ Translated from Izmeritel’naya Tekhnika, No. 5, pp. 31–35, May, 2007.     

A new method of absolute temperature measurements

Summary Preliminary experimental data shows the possibility of measuring temperature by the number of voltage noise pulses. In theory, this method provides absolute and comparative temperature measurements over a wide range: the upper limit being that at which the resistor is destroyed; the lower boundary, in theory, is limited by the superconductivity temperature of the resistor material. The sensitivity of the method rises with decreasing temperatures.There are reasons to believe that by counting pulses over a longer period of time with highly stable temperature fields and amplifier gain with an adjustable threshold of discrimination, it will be possible to raise the absolute accuracy of temperature measurements as compared with other existing methods.     

Acceleration of transients in a microcalorimeter for microwave power converters

It is shown that additional heating accelerates the calibration of a microwave power converter in a microcalorimeter. __________ Translated from Izmeritel’naya Tekhnika, No. 9, pp. 55–57, September, 2007.     

A stress analysis model for composite coaxial cylinders

An analytical model describing the elastic response of a system of coaxial thick-walled cylinders in contact is presented. The materials from which the cylinders are constructed must exhibit orthotropic elasticity. The loading can be uniaxial tension, torsion or internal pressure. The model allows inter- and intralaminar stresses to be determined. Examples of applications include pipes and light weight drive shafts reinforced with a helical winding, composite pressure vessels and single cells from fibrous plants such as flax and hemp. This revised version was published online in November 2006 with corrections to the Cover Date.     

A new data reduction method for pulse diffusivity measurements on coated samples

A new method, based on numerical solutions of the heat conduction equation, is presented for reducing flash diffusivity data to determine the diffusivity of a coating on a substrate of known thermal properties. Measurements are performed with a conventional thermal flash apparatus and the calculated curve from the numerical simulations is fitted to the measured temperature–time curve, the “thermogram”. The current work is a natural extension of previous work on single layer, homogeneous samples [1]. The main advantage of this new data reduction method, which incorporates nonlinear least-squares regression, is that both the thermal diffusivity of the coating and the thermal contact resistance can be determined. When the thermal contact resistance is small, the solution automatically converges to the perfect thermal contact case. To demonstrate its efficacy, the method is first implemented by analyzing a group of simulated data and then applied to a set of experimental data obtained from three different bilayer samples.