In the last 30 days

• Open/close Determination of the thickness and optical constants of amorphous silicon

  R Swanepoel 1983 J. Phys. E: Sci. Instrum. 16 1214 Tag this article

  Article References Full text PDF (669 KB)

  The rigorous expression for the transmission of a thin absorbing film on a transparent substrate is manipulated to yield formulae in closed form for the refractive index and absorption coefficient. A procedure is presented to calculate the thickness to an accuracy of better than 1% with similar accuracies in the values of n. A method to correct for errors due to slit width is also given. Various formulae to calculate the absorption coefficient accurately over almost three orders of magnitude are discussed. Only data from the transmission spectrum are used and the procedure is simple, fast and very accurate. All formulae are in closed form and can be used on a programmable pocket calculator.

• Open/close The fluxgate magnetometer

  F Primdahl 1979 J. Phys. E: Sci. Instrum. 12 241 Tag this article

  Article References Full text PDF (1.34 MB)

  Presents a review of fluxgate magnetometry based on a survey of the literature and on the work of the author and colleagues. The theory is outlined and an evaluation of the merit of the different types of sensors is made based on the sensor geometry. The design of a second-harmonic feedback magnetometer is discussed with respect to sensor configuration, frequency response, noise, offset, temperature dependence and long-term stability. Examples of the parameters are compiled from the literature and some new results on the long-term stability are presented.

• Open/close A simple method for the determination of the optical constants n, k and the thickness of a weakly absorbing thin film

  J C Manifacier et al 1976 J. Phys. E: Sci. Instrum. 9 1002 Tag this article

  Article References Full text PDF (271 KB)

  A new calculation following traditional methods is proposed for deducing optical constants and thickness from the fringe pattern of the transmission spectrum of a thin transparent dielectric film surrounded by non-absorbing media. The particular interest of this method, apart from its easiness, is that it makes a directly programmable calculation possible; the accuracy is of the same order as for the iteration method.

• Open/close Determination of surface roughness and optical constants of inhomogeneous amorphous silicon films

  R Swanepoel 1984 J. Phys. E: Sci. Instrum. 17 896 Tag this article

  Article References Full text PDF (728 KB)

  Inhomogeneities in thin films have a large influence on the optical transmission spectrum. If not corrected for, this may lead to too large calculated values for the absorption coefficient or the apparent presence of an absorption band tail as well as serious errors in the values of refractive index and thickness. The effects of thickness variation, surface roughness and variation in refractive index on the transmission spectrum are analysed. Analytical expressions are derived from which all the optical constants of an inhomogeneous film can be calculated from the transmission spectrum.

• Open/close Simple apparatus for electropolishing metal single crystals

  Zhang Ji-kang et al 1986 J. Phys. E: Sci. Instrum. 19 314 Tag this article

  Article References Full text PDF (98 KB)

  An electrolytic tank in which the electrolyte is subjected to continuous and controlled agitation is described. The equipment has been used successfully to electropolish single crystals of silver and copper.

• Open/close An AC potential drop system for monitoring crack length

  T V Venkatsubramanian and B A Unvala 1984 J. Phys. E: Sci. Instrum. 17 765 Tag this article

  Article References Full text PDF (600 KB)

  The design of an AC potential drop (ACPD) system for monitoring crack length in fracture specimens is outlined. The amplified voltage across a cracked specimen is compared with that across a reference specimen by employing a dual-slope analogue to digital convertor in the radiometric mode. The resultant digital output provides an accurate measure of the crack length. Because of the strong skin effect in steel even at relatively low frequencies, the output varies linearly with crack length. Although the output is insensitive to variations in specimen current and temperature, it is affected by the position of the sensing and current leads and by the presence of ferromagnetic materials in the vicinity of the specimen. In the case of steel, whilst the ACPD output is increased by crack growth it is decreased by tensile stress and plasticity in the specimen. The competition between the two opposing effects enables the ACPD to detect initiation of crack extension even when crack growth is accompanied by large scale plasticity.

• Open/close Resonator sensors-a review

  R M Langdon 1985 J. Phys. E: Sci. Instrum. 18 103 Tag this article

  Article References Full text PDF (1.45 MB)

  Control systems are becoming increasingly dependent on digital processing and so require sensors able to provide direct digital inputs. Resonator sensors, configured to have a mechanical resonance frequency or relative phase of oscillation dependent on the measured parameter, are a subject of considerable practical interest. The author reviews the wide range of devices which have been proposed and developed, including sensors for liquid or gas density and viscosity, liquid level, mass and mechanical force, and fluid flow rates. Techniques cover the frequency range from audio, for sensors based on vibrating vanes or tubes, to 100 MHz or more for surface acoustic wave devices. Resonator sensors based on single crystal materials such as quartz and silicon are of particular interest because they combine high accuracy and repeatability and low cost of manufacture and potentially very low power consumption.

• Open/close Piezoelectric ceramics and ultrasonic transducers

  J A Gallego-Juarez 1989 J. Phys. E: Sci. Instrum. 22 804 Tag this article

  Article References Full text PDF (1.34 MB)

  The author reviews the basic characteristics and progress in transducer properties of the different types of piezoelectric ceramics. The application of these materials in practical ultrasonic transducers is also reported.

• Open/close Passive screening of switched magnetic field gradients

  R Turner and R M Bowley 1986 J. Phys. E: Sci. Instrum. 19 876 Tag this article

  Article References Full text PDF (392 KB)

  In NMR imaging the rapid switching of magnetic field gradients can induce currents in surrounding conductors, thus creating undesirable reflected fields which are spatially and temporally inhomogeneous. For certain types of gradient switching it is possible to screen the magnetic fields completely, using a thick cylindrical conductor, within which the gradient uniformity may be re-established using simple changes in coil separations. Details are presented for the analytic treatment of this problem, with results for the cases of the Maxwell pair, a modified Maxwell pair and saddle coils. These results are also applicable when active screening is used.

• Open/close A critical study of the open-ended coaxial line sensor technique for RF and microwave complex permittivity measurements

  J P Grant et al 1989 J. Phys. E: Sci. Instrum. 22 757 Tag this article

  Article References Full text PDF (1.35 MB)

  An HP 8510 automatic network analyser and a six-port reflectometer have been used with a purpose-built calculable open-ended coaxial line sensor to measure the reflection coefficients of various materials, including dielectric reference liquids, in the frequency range 50 MHz-2.0 GHz. Factors crucial for calculable measurements have been identified including associated measurement uncertainties. The reference material measurements have been used in critical studies of: a commonly employed lumped equivalent circuit model of the fringing fields of the sensor; and a numerical point-matching theory of the propagating and evanescent modes, at the termination of the sensor. It is concluded that the inverse point-matching theory should enable a more widespread and accurate exploitation of the sensor technique for various applications including those in biomedicine and industrial quality control.