Video display terminal fringing magnetic field measurements

Possible occupational health or public health risks due to video display terminals (VDTs) are addressed. The authors note the errors of current jargon and correctly define the terms needed to describe the fringing magnetic flux density near any magnetically deflected, raster scan, cathode ray tube display. Theory and preliminary measurements have shown that the ELF AC electric field related to VDT display electronics is small, and the electromagnetic field strength at any frequency is truly negligible as an occupational health risk near any cathode ray tube display. Application of Maxwell's equations shows that the commonly used pickup coil responds to the derivative of magnetic flux density. The transducer needs an integrator to respond properly to the sawtooth waveforms of deflection fields. Correct measurements of VDT fringing magnetic fields are presented. A Swedish test method is briefly discussed. The conclusion from this work is strong. Theory and these measurements show there is not a verifiable occupational health risk from the fringing ELF electric or magnetic fields or any frequency electromagnetic fields near VDTs     

Magnetic penetration depth measurements in cuprate superconductors

We examine recent results on measurements of the magnetic penetration depth in cuprate superconductors, with particular emphasis on our results obtained with the microstrip and parallel-plate resonator techniques. The results show that the magnetic penetration depth temperature dependence in YBa₂Cu₃O_7– is not consistent with a simple scaled weak-coupled BCS temperature dependence. We present three classes of interpretations of these measurements, and how they relate to other experimental studies of the cuprates. Finally, these interpretations are discussed in terms of some theories of cuprate superconductivity.     

Magnetic penetration depth measurements with the microstrip resonator technique

The microstrip resonator technique is a convenient way to sensitively measure the temperature dependence of the magnetic penetration depth (T) in superconducting thin films. Because the method relies on measuring the resonant frequency of a high-Q transmission line resonator at microwave frequencies, one can very precisely measure small changes in (T). This technique is applied to studying the low-temperature dependence of (T), since that is in principle a measure of the low-lying pair-breaking excitations of the superconductor. We find that the penetration depth in niobium films is consistent with the predictions of weak coupled BCS theory. The low-temperature dependence of (T) inc-axis YBa₂Cu₃O_7– films can be interpreted as either a weak exponential or as a power law. In addition, the measured value of (0) is found to be strongly dependent on the form of the temperature dependence for (T) used in fitting the data. Best fits over the entire temperature range are obtained with a BCS temperature dependence having values for 2(0)/k _BT_c strictly less than 3.5, consistent with our measurements of the temperature dependence of (T) at low temperatures in YBa₂Cu₃O_7– .     

The penetration of an electric field into pure superconductors

The penetration of an electric field into superconductors with an arbitrary content of nonmagnetic impurities has been investigated. The result for the penetration depth of the electric field into impure superconductors, when the metal conductivity is determined by the electron scattering on the impurities, coincides with previous results. In the extremely pure superconductors the penetration depth is defined only by the electron-phonon interaction.     

Fluctuating collective oscillations and electric field penetration into superconductors

The spectrum of collective oscillations and the penetration of a constant longitudinal electric field into a superconductor are investigated based on microscopic Gor'kov equations integrated over the energy variable of one-particle excitations. The influence of the anharmonicity of collective oscillations upon the attenuation of these oscillations and upon the penetration of the longitudinal electric field into the superconductor has been studied as well. We investigate the problem of the self-attenuation of fluctuating collective oscillations in the vicinity of the critical temperature.     

Probe characterization in ac field measurements of surface crack depth

In the ac field method of crack depth measurement by the Crack Microgauge, the area of the loop formed in the probe gives rise to an induced voltage, which can introduce errors into the depth measurement. In this paper, a method for measuring the probe area is given, and the quality of the probe is thereby characterized. The underlying theory was given previously, and it is applied here to the probe characterization problem. The probe area is determined by two voltage measurements taken on an artificial rectangular flaw machined in an arbitrary metal. By measurements on several such specimens with the same probe, it is confirmed that the area so obtained is a characteristic of the probe and is independent of the specimen material. Thereafter, measurements on various rectangular flaws with probes of different characteristic area were taken, and very good agreement between predicted and real depths was achieved. Both theory and experiments show that probe characterization is of particular importance when this method is used to measure surface crack depths in metals of low permeability such as aluminum.     

Miniaturized magneto-optic sensor for pulsed magnetic field measurements

The design and performance of a miniaturized magneto-optic probe using a terbium doped paramagnetic glass are described. The compactness and simplicity of the device are achieved by using the polarizer sheets obtained from a commonly available liquid crystal display. Plastic optical fibers are used to transport the light. A pulsed magnetic field up to 48 T has been generated and measured using high-voltage capacitor discharge in single-turn coils. A rise time and magnetic field-dependent anomalous behavior is observed in the terbium glass characteristics at room temperature.     

Optimization of a variable electric field marine transformer sensor

Relations for the structural parameters of the coil of a sensor for which the highest value of the conversion factor can be achieved are obtained. __________ Translated from Izmeritel’naya Tekhnika No. 4, pp. 50–51, April, 2007.     

电场法土壤水分传感器研究

合适的土壤水分是作物良好生长和获得高产的条件之一,同时合理灌溉也是节约水资源的有效途径。基于电场法原理研制了测试土壤水分含量的传感器,并利用单片机实现自动控制。通过与烘干法对比研究,该传感器在土壤水分含量小于25%时实验误差小于5%,完全能满足农业生产需要。该传感器使用稳定安全,便于携带,能定点实时监测,精度较高,具有实用价值。     

Investigation of electric field penetration into superconducting tantalum near a normal-superconducting interface

The temperature dependence of the excess resistance of Ta-Cu-Ta sandwiches was investigated. The samples were prepared by the mutual rolling of the bulk materials, with the thickness of the superconducting plates (0.1 cm) much greater than the penetration length of the electric field into the superconductorl _E up to temperatures very close toT _c. The penetration of the electric field through the clean NS interface into a superconductor with a relatively long electronic mean path (1 ₀) was studied. We used an rf SQUID voltmeter to measure the resistance, 10^–9 , at currents not exceeding 1 mA. The experimental data were compared with the Artemenko-Volkov and Hsiang-Clarke theories. The electron-phonon relaxation time for our tantalum sample was estimated to be 1×10^–10 sec.     

Optical fiber sensor for electric field and electric charge using low-coherence, Fabry-Perot interferometry

An optical fiber sensor for electric field and electric charge, based on the deflection of a small cantilever, has been developed. When the sensor head is placed in an electric field, induced charging produces deflection of the cantilever, which is measured using low-coherence, Fabry-Perot interferometry. The sensor has been used to measure the electric field in the vicinity of a Van de Graaff generator, in the range 135-650 V/cm. The measured deflections are in good agreement with the predictions of a simple model equating the electrostatic and mechanical forces acting on the cantilever.     

Monte Carlo simulations and laser Doppler flow measurements with high penetration depth in biological tissuelike head phantoms

Laser Doppler flow measurements on biological tissuelike phantoms have shown that penetration depths of 30 mm could be obtained, thus exceeding the penetration depth of commercial instruments for the measurement of skin perfusion by more than an order of magnitude. Monte Carlo simulations were performed and compared with measurement results obtained on a headlike tissue model to quantify the influence of perfusion of the scalp on the cortex perfusion results. We found Doppler frequency spectra to be independent of the mean scattering angle and could be fitted with a sum of Gaussian functions, using a simple analytical model.     

A novel sensor array for field based ocular ultraviolet radiation measurements

The intensification of terrestrial solar ultraviolet radiation (UVR) due to the diminution of the ozone layer has promoted a variety of research into establishing the impact of this elevated potential dose of UVR on biological tissues. Certain anterior ocular tissues have been found to be susceptible to damage by incident UVR and potentially blinding diseases such as pterygium are thought to be a direct result of absorbed UVR at the nasal limbus. There is a need for more accurate quantification and localisation of incident UVR at the anterior ocular surface. A novel solar blind photodiode sensor array system has been designed, constructed and tested for this purpose. Initial measurements to quantify the irradiance across the anterior ocular surface within the latitudes known as the 'pterygium belt' provide us with a set of core data for different head orientations and tilt angles and indicate the accuracy and stability of the system.     

The limit sensitivity of a transformer variable electric field sensor in the sea

An analytical expression for the limit sensitivity of a transformer sensor is obtained. It is shown that at frequencies higher than a certain limit the sensitivity is determined solely by the geometrical dimensions of the sensor and is independent of the number of turns in its coil and the magnetic permeability of the core. __________ Translated from Izmeritel’naya Tekhnika, No. 7, pp. 51–53, July, 2008.     

Liquid crystal infiltrated photonic crystal fibers for electric field intensity measurements

The application of nematic liquid crystal infiltrated photonic crystal fiber as a sensor for electric field intensity measurement is demonstrated. The device is based on an intrinsic sensing mechanism for electric fields. The sensor probe, which consists of a 1 cm infiltrated section of photonic crystal fiber with a lateral size of ～125 μm, is very compact with small size and weight. A simple all-fiber design for the sensor is employed in an intensity based measurement scheme. The transmitted and reflected power of the infiltrated photonic crystal fiber is shown to have a linear response with the applied electric field. The sensor is operated in the telecommunication window at 1550 nm. The temperature dependence of the device at this operating wavelength is also experimentally studied and discussed. These structures can be used to accurately measure electric field intensity and can be used for the fabrication of all-fiber sensors for high electric field environments as both an in-line and reflective type point sensor.     

Moisture content estimation in paper pulp using fringing field impedance spectroscopy

Currently used methods for estimation of moisture content in paper pulp are restricted to levels of moisture concentration below 90%. Some of the existing methods require less practical double-sided contact measurements. A few other methods make restrictive assumptions, such as the constituents of the pulp that determine its conductance. This paper presents a technique that uses fringing field interdigital sensors to measure moisture concentration in paper pulp at levels as high as 96%. The method proposed in this paper uses single-sided measurements, offers high sensitivity, and does not require special operating conditions. The accuracy of the proposed method is also demonstrated. The repeatability and reproducibility of the sensor measurements are also shown.     

Determination of the depth resolution in Auger depth profiling measurements

The depth resolution Δz of the Auger depth profiling method was studied in multilayer thin films comprising alternate layers of nickel and molybdenum or of cobalt and molybdenum. The composition-depth profiles of several interfaces located at different depths within the same film were compared. Thus changes which depended on the sputtering depth z could be distinguished from effects which were independent of z. According to a statistical theory the profiles of the interfaces can be described by a gaussian error function. An empirical formula $\text{Δz = αz}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{+ β}$ was determined from the width of the profiles. The first term agrees with the statistical theory and the constant term is explained by the roughness of the interface. The order of magnitude of β (≈ 3 nm) suggests that the depth resolution in the films is not limited by the escape depth of the Auger electrons (? 1.5 nm). The relative depth resolution $\text{Δz}\text{z}$ improves with increasing sputtering depth.     

Uncertainty in relative energy resolution measurements

We suggest a new method for the determination of the detector relative energy resolution and its uncertainty based on spline approximation of experimental spectra and a statistical bootstrapping procedure. The proposed method is applied to the spectra obtained with NaI(Tl) scintillating detectors and ¹³⁷Cs sources.

The spectrum histogram with background subtracted channel-by-channel is modeled by cubic spline approximation. The relative energy resolution (which is also known as pulse height resolution and energy resolution), defined as the full-width at half-maximum (FWHM) divided by the value of peak centroid, is calculated using the intercepts of the spline curve with the line of the half peak height. The value of the peak height is determined as the point where the value of the derivative goes to zero. The residuals, which are normalized over the square root of counts in a given bin (y-coordinate), obey the standard Gaussian distribution. The values of these residuals are randomly re-assigned to a different set of y-coordinates where a new “pseudo-experimental” data set is obtained after “de-normalization” of the old values. For this new data set a new spline approximation is found and the whole procedure is repeated several hundred times, until the standard deviation of relative energy resolution becomes stabilized. The standard deviation of relative energy resolutions calculated for each “pseudo-experimental” data set (bootstrap uncertainty) is considered to be an estimate for relative energy resolution uncertainty.

It is also shown that the relative bootstrap uncertainty is proportional to, and generally only two to three times bigger than, , which is the relative statistical count uncertainty (N_tot is the total number of counts under the peak).

The newly suggested method is also applicable to other radiation and particle detectors, not only for relative energy resolution, but also for any of the other parameters in a measured spectrum, like peak position, shape parameters, etc.     

Key comparisons CCEM.RF-K-20 in the area of electric field strength measurements

The method of calibration of a portable standard on equipment of the state standard GéT 45-94 for electric field strength is presented. Analysis of the results of key comparisons CCEM.RF-K-20 is provided. __________ Translated from Izmeritel’naya Tekhnika, No. 9. pp. 69–72, September, 2007.     

Traceability of electric field intensity measurements at frequencies from 0 TO 1000 MHz

The present state of the traceability of electric field intensity measurements at frequencies from 0 to 1000 MHz is considered. Calibration schemes of electric field measuring instruments at 0 to 20 kHz and 0.0003 to 1000 MHz are proposed.Translated from Izmerital'naya Tekhnika, No. 8, pp. 51–53, August, 1995.