SAR of a birdcage coil with variable number of rungs at 300 MHz

The specific absorption rate produced in a rat’s brain phantom inside of quadrature birdcage coil as a function of the rung number was studied at 300 MHz. Electromagnetic field simulations and specific absorption rate and loss return responses were performed using a rat’s brain phantom weighing 100 mg. To assure optimal simulations and to evaluate coil performance, S-parameters were simulated and compared with experimentally data. Simulations showed that magnetic field uniformity improves and that electric field is increased with the number of rungs. Specific absorption rate and temperature values obtained from axial bi-dimensional maps increase as the number of rungs grows. These results corroborated very well with published data. A quadrature 16-rung birdcage coil was developed for comparison and phantom images were acquired to show its feasibility. The presented approach yields information on specific absorption rate allowing to previously develop RF coils and their possible effects on the biological sample.     

Frictional force microscopic detection of anisotropy at NaCl (1 0 0), (1 1 0) and (1 1 1) surfaces

Frictional coefficients were measured at atom-flat NaCl (1 0 0), (1 1 0) and (1 1 1) surfaces with frictional force microscopy. At the electrically neutral (1 0 0) and (1 1 0) surfaces in 15% relative humidity, lower friction was detected along 1 1 0 direction where the same kind of ions are aligned, than along 1 0 0 direction where different ions alternate. Low and isotropic friction was observed at the polar (1 1 1) surface. The results were explained by the gradients of electrostatic interaction potentials between a dipole at the tip and the ions at the surface. Toward higher relative humidity up to 60%, frictions at the (1 0 0) surface decreased indicating lubrication effect by water. The changes observed for the (1 1 0) surface suggested presence of adsorbed water in stripe pattern along the 1 1 0 direction. In the higher humidity range, frictional force increased at all the surfaces, probably due to larger normal force caused by the meniscus force.     

Weighing system with low evaporation error for liquid microflow down to 1 mg/min

A static weighing system for a liquid microflow calibration rig, whose minimum flow rate is 1 mg/min (equivalent to 1 μL/min for water), was designed and evaluated. The developed weighing system, which can collect over 10 g of water, has two features: (i) an automatic detachable device with a sealing and wiper mechanism in contact with a needle and (ii) a flexible air bag to contain the air from the weighing vessel. Having these two features, the weighing system succeeds in reducing the evaporation effect as well as preventing tension on the weighing scale. However, uncertainty due to the mass difference of adhering liquid on the outside surface of needle before needle insertion and after needle extraction should be considered. Theoretical and experimental analysis were conducted. The mass difference due to the adhering liquid on the needle was estimated to be smaller than 1/3 of the target standard uncertainty of mass measurement set at 0.1 mg, indicating that the detachable procedure was not a dominant uncertainty source for mass measurement. The evaporation rate during collection was experimentally estimated to be less than 0.001 mg/min, which corresponds to less than 0.1% for the lowest flow rate of 1 mg/min.     

Mass calibration designs for a robotic comparator loading three weights at most

Mass calibration designs for a mass comparator loading three weights at most were searched for a weight series of 10–5–5′–2–2′–1–1′. Under exclusive consideration of Type A variance, the criteria of A-optimality was applied to the designs by minimizing the sum of the variances. A design introduced for the comparator by its manufacturer but not originally intended for the comparator was compared with an A-optimality design that can reduce the average variance by 33%.     

SIM force standards comparison up to 10 kN

A comparison in the quantity of force was carried out among the Interamerican Metrology System (SIM) national laboratories in order to estimate the level of agreement for the realization of the quantity and the uncertainty associated to its measurement. This comparison was carried out up to 10 kN. The equipment used consisted on two force transducers (load cells); both with the same measuring range (10 kN). With the purpose of obtaining maximum accuracy on the transducers, the comparison range was selected from 4 kN up to 10 kN. This comparison (SIM comparison number SIM 7.7) has an overlap with the force steps used in the CIPM key comparison CCM.F-K1.a and CCM.F-K1.b. The results obtained, as well as the reference values selected for the comparison are included in this document. Two different methods were used to analyze the level of agreement and to state the conformity declaration.     

International comparison of volume measurement for a 1 kg silicon sphere between KRISS and NMIJ

1 kg single-crystal silicon spheres are presently used as primary density standards in many countries. The absolute density of the spheres is determined from the measurements of their mass and volume in conformity with the definitions of the SI base units. Since the mass of the spheres is almost 1 kg, a mass comparison with the prototype of the kilogram can be performed with very low uncertainty. Absolute volume measurements for the spheres therefore have a crucial role in realizing a reliable density traceability system. To confirm the reliability of the volume measurement, the volume of a silicon sphere was measured independently using optical interferometers at the Korea Research Institute of Standards and Science (KRISS, Korea) and the National Metrology Institute of Japan (NMIJ, Japan). An optical interferometer with an etalon scanning system was used at KRISS. On the other hand, an optical interferometer with an optical frequency scanning system was used at NMIJ. The volume was measured at 20 °C and 0 Pa, and the results are in agreement with each other within their uncertainties. Details of the two interferometers and the comparison results are described.     

Uncertainty evaluation of the 20 kN m deadweight torque standard machine

A deadweight-type torque standard machine of 20 kN m rated capacity (20 kN m-DWTSM) has been designed and developed by the National Metrology Institute of Japan (NMIJ) at the National Institute of Advanced Industrial Science and Technology (AIST). Each uncertainty contribution comes mainly from the performance of each mechanical part of the 20 kN m-DWTSM. Authors evaluated the uncertainty of the mass of the linkage weights, local acceleration of gravity, influence of air buoyancy on deadweight loading, initial moment-arm length (including CMM measurement and temperature compensation), and sensitivity of the fulcrum. This report deals especially with evaluation of the remaining contributions, namely the influence of arm flexure and reference line variation at the end of the moment-arm on best measurement capability (BMC). Estimation of BMC in the 20 kN m-DWTSM gave a relative expanded uncertainty of less than 7.0 · 10⁻⁵ (k = 2) for the calibration range from 200 N m to 20 kN m.     

Large scale spectrum survey in rural and urban environments within the 50 MHz–6 GHz bands

In-depth spectrum measurement was conducted in rural and urban locations, covering 50 MHz–6 GHz bands, during the weekdays and weekends. A modified duty cycle metric is presented by introducing a space variable into the existing metrics available today. An adaptive energy detection threshold technique was employed, the results indicate the average spectral occupancy of 0.18%, and 5.08% in rural and urban locations respectively during weekdays and 1.45% on weekends for urban locations. Furthermore, short and long term temporal variations of the duty cycle for each of the bands were studied, and it was found that GSM 900 shows significant temporal variation when compared with GSM 1800. It was also found that the choice of the detection threshold would significantly affect the duty cycle as GSM 900 and 1800 give exponential decay with increase in detection threshold while TV band shows very sharp exponential decay which becomes invariant after −85 dBm.     

A new vacuum interferometric comparator for calibrating the fine linear encoders and scales

A new one-dimensional laser interferometric comparator has been developed for the calibration of the fine linear encoders and scales up to 1600 mm. In the comparator, the interferometer is fully arranged in vacuum and the calibration objects are mounted under atmospheric conditions. The Abbe’s principle on the alignment of workpiece with the measuring beam is satisfied in the structure of a long measuring range. A travelling slide table, on which the calibration objects are mounted, is supported on guide rails by the air bearing and is driven through a recirculating ballscrew. The exhaust of the air bearing is guided to the exterior of the booth in which the comparator is placed. The travel of the table is measured by a reference interferometer with a beam path in vacuum shielded by an evacuated metal bellow, so that the effect of refractive index is eliminated. The laser beam is led by a polarization plane maintaining glass fiber from a self-designed stabilised He–Ne laser, which is placed in an adjacency room, to the beam inlet of the main unit. The measurement system can input the interferometer signal by the encoder signal or the scale signal, and input the encoder or scale data by the interferometer signal. The system resolution is approximately 0.8 nm and maximum travelling measurement speed is 20 mm/s at continuous measurement. The uncertainly (k=2) of measurement is approximately 30 nm in linear encoders of 500 mm length and, approximately 40 nm in scales of 500 mm, although it depends on the length and the characteristics of encoders and scales. It is successful such a high accuracy that the uncertainty of measurement system is smaller than 40 nm in encoders of 1 m length.     

Compact maglev stage system for nanometer-scale positioning

Semiconductor manufacturing systems and ultra-precise machine tools now require nanometer-scale positioning accuracy. To improve positioning accuracy, it is efficient to support the top table with a noncontact guide system to prevent guide friction and heat transfer from the lower table or base. A magnetic levitation (maglev) stage can accomplish ultra-precise positioning accuracy with six-degrees-of-freedom (6DOF) control even in vacuum conditions. However, if the gravity of the levitated table is supported by the thrust of a linear motor, heat generation from the motor coil dramatically increases. In addition, a larger motor is required, which causes the moving mass to increase and the mechanical response to deteriorate. We aimed to develop a compact maglev stage for which the levitated mass is less than 1 kg and that is dramatically more lightweight than existing maglev stages. This compact feature was enabled by our newly proposed gravity compensation system with repellent force and a planar motor structure. The developed stage system also has long strokes, specifically 200 mm in the X and Y-directions on a horizontal plane. We designed a maglev stage with the following design concepts to create its compact structure: (1) Reduce top-table mass to minimize the motor dimensions and enable a light weight and high responsiveness. (2) Measure the top-table position from the base to eliminate positioning error and isolate vibrations of the coarse stage. (3) Install a motor in a symmetrical layout in view from the Z-axis to enable the same driving characteristics between the X and Y axes. The results of the performance evaluation showed that the developed maglev stage system with a compact structure with 0.81 kg levitated mass has ±10 nm positioning stability.     

High-precision and high-speed positioning of 100 G linear synchronous motor

The present paper describes a moving permanent magnet linear synchronous motor (MPM LSM) that can move with an acceleration above 100 G (=980 m/s²), and is also capable of high-precision and high-speed positioning. The MPM LSM consists of a mover including permanent magnets and a double-sided electromagnet stator. It can produce a thrust of 4.56 × 10³ N and has a working range wider than 1 m. The MPM LSM mover is improved for light weight and is driven using a suitable phase lead for flux weakening. The combination of the improved mover and the suitable phase lead provides motion at an acceleration above 100 G and a velocity above 12 m/s. The positioning characteristics of the improved MPM LSM are examined using a controller with two suitable phase lead functions. The control system shows a positioning accuracy and a positioning resolution of 500 nm, which is similar to the vibration amplitude of the sensor output in open loop. In 300-mm step positioning, the improved MPM LSM shows an acceleration above 660 m/s² and a velocity above 8.3 m/s. It takes less than 101 ms to reduce the positioning error to less than 5 μm. The temperature rise during positioning is also examined experimentally. Continuous positioning for longer than 30 minutes increases the temperature of the MPM LSM, but by less than 6 °C.     

Differential pressure comparison from 5 Pa to 500 Pa with a liquid column manometer between CENAM (Mexico) and INTI – Fisica y Metrologia (Argentina)

A differential pressure comparison was performed between CENAM (Mexico) and INTI (Argentina) by means of a liquid column manometer. The measuring range was 5–500 Pa. CENAM calibrated the transfer standard at the beginning and at the end of the comparison. The transfer standard used was a Dwyer liquid column manometer model Microtector with an accuracy class of 0.013% of the reading. The compared pressure points were (5, 75, 125, 200, 250, 300, 350, 400, 450, 500) Pa. The uncertainty sources to be evaluated included at least the following: (a) Uncertainty due to the standard used by the laboratory; (b) Uncertainty due to repeatability; (c) Uncertainty due to resolution; (d) Uncertainty due to hysteresis; (e) Uncertainty due to zero drift. The criteria used to compare the results obtained were the normalized error equation (E_n). The results obtained by the laboratories were compatible according to the criteria |E_n| ? 1.     

1 Ω and 10 kΩ high precision transportable setup to calibrate multifunction electrical instruments

A temperature controlled 1 Ω and 10 kΩ transportable setup was developed at National Institute of Metrological Research (INRIM) for the calibration and adjustment of multifunction electrical instruments as digital multimeters (DMMs) and multifunction calibrators (MFCs). The two standards are made of two 10 Ω and 100 kΩ resistor nets connected in parallel and inserted in a temperature controlled aluminum structure. Novelties of the realization are the oil insertion of the 1 Ω net with the internal side of the connectors lowering the thermo-electromotive forces (EMFs) effects, and the possibility to know instantly the temperatures of the environment, of the internal of the structure and the last calibration values of the 1 Ω and10 kΩ standards. Short- and mid-term stabilities of the setup standards resulted on the order and in some cases better than other metrology-grade 1 Ω and 10 kΩ commercial items. The transport of the setup even turning off its temperature control did not cause appreciable measurement variations on the two standards. The standards uncertainties meet those requested by DMMs and MFCs manufacturers to calibrate and adjust these instruments. A test to adjust a MFC gave satisfactory results.     

Errors due to magnetic effects in 1 kg primary mass comparators

A revised draft of OIML Recommendation 111 has been approved recently. Among the many notable changes to the previous edition are specific requirements for both the magnetic susceptibility and residual magnetization of weights used in legal metrology. The highest class of such weights is E₁, for which a 1 kg weight has a manufacturing tolerance of ±0.5 mg. It therefore follows that better magnetic properties might be needed for weights having mass uncertainties substantially better than E₁ tolerances. The work presented below shows how this problem was approached at the BIPM and supports our conclusion that alloys meeting the new Class E₁ specifications for 1 kg weights have magnetic properties sufficient for the needs of the BIPM.     

Bilateral comparisons of measurement capabilities for the calibration of low nominal capacity torque measuring devices between NMIJ and PTB in the range from 0.1 N m to 10 N m using different procedures

Bilateral comparisons of the calibration of low nominal capacity torque measuring devices (TMDs) were conducted between NMIJ and PTB for the first time. A 10 N m deadweight torque standard machine (TSM) newly developed at NMIJ was compared with PTB’s two TSMs with nominal capacities of 1 N m and 1 kN m, in the range from 0.1 N m to 10 N m. The transfer measurement devices used had nominal capacities of 1 N m and 10 N m. The comparisons were made using two calibration procedures: one based on the CCM.T-K2 Key Comparison procedure and the other according to the daily calibration procedure adopted at each institute. As a result, the torque realized by the TSM at NMIJ was shown to be equivalent to that realized by the two TSMs at PTB. In addition, it was confirmed that the daily calibration procedures of both institutes yielded consistent results in the calibration of low nominal capacity TMDs.     

Estimation of femoral neck bone mineral density by ultrasound scanning: Preliminary results and feasibility

Aim of this paper was to assess the diagnostic accuracy of a novel ultrasound (US) approach for femoral neck densitometry. A total of 173 female patients (56–75 years) were recruited and all of them underwent a dual X-ray absorptiometry (DXA) of the proximal femur and an US scan of the same anatomical district. Acquired US data were analysed through a novel algorithm that performed a series of spectral and statistical analyses in order to calculate bone mineral density employing an innovative method. Diagnostic accuracy of US investigations was quantitatively assessed through a direct comparison with DXA results. The average diagnostic agreement resulted pretty good (85.55%), with a maximum (88.00%) in correspondence of the youngest investigated patients (56–60 y). Overall, diagnostic accuracy showed only minimal variations with patient age, indicating that the proposed approach has the potential to be effectively employable for osteoporosis diagnosis in the whole considered age interval.     

Surface electronic structure of Ti-covered W(1 1 1) by photofield emission

Photofield emission (PFE) measurements are employed to examine modifications of the surface electronic structure of the tungsten (1 1 1) facet upon deposition of thin films (1–3 monolayers) of titanium. With the help of DFT simulations, the observed PFE features are interpreted as adsorbate-induced resonance states with energies just below the Fermi level, localized predominantly at the exposed surface atoms. Comparison between the computed surface DOS distributions and the measured PFE spectra is also used to verify various possible arrangements of the Ti adatoms, supporting the DFT-favored model of Ti growth in registry with the W(1 1 1) substrate until a full physical overlayer of the adsorbate is completed.     

Dry wear and friction behaviour of plasma nitrided Ti–6AL–4 V alloy after explosive shock treatment

The unlubricated wear behaviour of explosive shock treated and, subsequently plasma nitrided Ti–6Al–4 V alloy was studied using a ball-on-disc wear tester. Plasma nitriding was carried out at three different temperatures (700, 800 and 900 °C) for 3, 6, 9 and 12 h. Plasma nitriding after explosive shock treatment enabled a reduction in the wear rate of two orders of magnitude. Detailed investigations of this improved wear performance dependent on the nitriding temperature and time were carried out. The friction and wear data showed a clear breakthrough transition from the nitrided layer to the core of the Ti–6Al–4 V alloy matrix. The lowest wear volume was obtained for the sample, nitrided at 900 °C for 12 h, especially at loads of 2.5, 5 and 7.5 N. Obviously, the hard nitride layers were intimately associated with low wear rate, providing a smooth low friction surface. The coefficient of friction reduced from 0.46 to 0.2 due to a thick and hard compound layer resulting from a high nitrogen diffusion rate caused by explosive shock treatment that expected to increase point defects in the alloy. Detailed examination of the wear tracks showed that plasma nitriding changes the mechanism of wear from one of adhesion for untreated Ti–6Al–4 V to both delamination and mild abrasive.     

Evaluation of newly developed 50 N dead-weight type force standard machine using tuning-fork type force transducer

A 50 N dead-weight type force standard machine (DWM) was developed by the National Metrology Institute of Japan to expand the lower end of calibration force from 10 N to 1 N. The weights of the DWM consisted of a loading frame and a linkage-weight stack. The loading frame applied a gravitational force of 1 N to a force transducer under calibration. The calibration and measurement capability of the 50 N DWM was verified to be 2 × 10⁻⁵ relative using a tuning-fork type force transducer in accordance with ISO 376. The equivalence between the 50 N and 500 N DWMs was confirmed by performing an intralaboratory comparison using the tuning-fork type force transducer. Moreover, the competence of the transducer for the evaluation of DWMs was demonstrated.     

NMC–NMIJ bilateral comparison of millimeter-wave attenuation in WR-15 waveguide band at 50 GHz and 54 GHz

This paper reports on a bilateral comparison of millimeter-wave attenuation in WR-15 waveguide band between the National Metrology Institute of Japan (NMIJ) and the National Metrology Centre, A1STAR (NMC). Different types of attenuation measurement systems were independently developed at both laboratories. The systems are based on a stabilized single-channel intermediate frequency (IF) substitution method at NMIJ, and a dual-channel audio frequency substitution method at NMC. A comparison was carried out at 50 GHz and 54 GHz using a programmable step attenuator fitted with precision coaxial to waveguide adaptors as a traveling standard. Good agreement of the measurement results between both laboratories was verified in the attenuation range up to 60 dB.