Absolute Probe Research Articles

Direct comparison of photoemission spectroscopy and in situ Kelvin probe work function measurements on indium tin oxide films

The work function of commercially available indium tin oxide (ITO) films on glass substrates was measured using photoemission spectroscopy (PES) and ultra-high vacuum (UHV) Kelvin probe in direct comparison. Absolute Kelvin probe work function values were determined via calibration of the measured contact potential difference (CPD) using an in situ sputtered Au reference sample. The Kelvin probe data confirmed that ultraviolet photoemission spectroscopy (UPS) measurements change the work function of ITO surfaces previously exposed to ambient environment, when measured without in situ surface cleaning procedures. The results also demonstrate that both Kelvin probe and PES yield virtually identical work function values, as long as the Kelvin probe data are calibrated against a known standard. As a consequence, previously reported higher work function values determined with Kelvin probe as compared to values obtained with UPS on similar samples are likely related to a photochemically generated surface dipole during UPS measurements. Comparison between Kelvin probe and low intensity X-ray photoemission spectroscopy (LIXPS) work function measurements demonstrated that accurate work function measurements on ITO previously exposed to the ambient are possible with PES.

Numerical Analysis of Compound ECT Signals due to Various Tube Defects near Support Plate in Steam Generator

In this paper, eddy current signals from various anomalous defects in the steam generator tube are numerically predicted and their signal slope characteristics are investigated. The signal variations due to increased frequencies are also observed. Based on the accumulated knowledge, the analysis of compound signal is attempted which includes the effect of support plate. Both differential and absolute bobbin probe signals are analyzed. For the signal prediction, axisymmetric finite element modeling is used and this leads us to the utilization of slope angle analysis of the signal. Results show that differential signals are useful for locating the position of defect under the support plate, while absolute signals are easy to presume and interpret even though the effect of support plate is mixed. Combined use of these two types of signals will help us accomplish a more reliable inspection.

System for 3D Visualization of Flaws for Eddy Current Inspection

This paper presents a novel method for 3D visualization of flaws detected during Eddy Current (EC) inspection. The EC data was acquired using an automated scanning system equipped with precise eddy current probe positioning. The method was tested on a single frequency instrument with an absolute probe. The EC inspection procedure is implemented statically by registering the operating point of the instrument at each equidistant point on a tested object.The paper describes a data processing method based on the Fourier transform enabling 3D visualization of flaws. This three-dimensional image of the result of a scan enables the position of flaws to be determined, and the size and bevel (angle to the surface) of each detected flaw to be estimated. This research investigated flaws rising from the surface of the tested object, and flaw depth was not evaluated in this work. This method of visualization is simple to implement and is currently targeted for application in EC scanning devices.

Automated classification of eddy current signatures during manual inspection

This article presents a novel method for automatic evaluation of flaws during a manual eddy current (EC) inspection procedure. In manual scanning, a signal related to impedance change in the complex plane is affected by large and unpredictable variations of scanning speed and alterations of probe position. This paper introduces a robust EC signal normalization method using non-linear filtration based on evaluation of the distance between consecutive samples in the complex plane and median based tracking of the EC signature. Feature extraction was performed using normalized Fourier and complex discrete wavelet descriptors. The classification was performed using six different methods: nearest-mean classifier, k-nearest neighborhood classifier, the standard multi-layer feed forward neural network with backpropagation, radial basis network, support vector machines and the adaptive-network-based fuzzy inference system. The method was tested on a single frequency instrument with an absolute probe and a dual frequency instrument with a probe for fast testing of rivets in layered structures. The results obtained using this approach demonstrate the effectiveness of the proposed system.

Study of high- and low-work-function surfaces for hyperthermal surface ionization using an absolute Kelvin probe

We have performed a study of high- (>6 eV) and low- (<3 eV) work-function surfaces in order to identify suitable target materials as an ion source for a new type of mass spectrometer technique based on hyperthermal surface ionization (HSI). In this application a molecular beam of neutral gas molecules is ionized by supersonic collision on a target surface. High-work-function surfaces produce positive ions (pHSI), and low-work-function surfaces negative ions (nHSI). Analytical merits of HSI include very high sensitivity, atmospheric pressure inlet, and informative mass spectra. As this technique does not use electron-impact filaments, the amount of cracking products is substantially reduced. The ultra-high-vacuum (UHV) scanning Kelvin probe is a technique producing relative work-function topographies between a scanning reference tip and the sample in a truly noninvasive fashion with high accuracy (1–2 meV). We demonstrate a novel extension of this technique, using photoelectric determination, which produces absolute work-function data even if the tip work function is not known. Using this hybrid probe, together with scanning electron microscopy and Auger electron spectroscopy, we have followed (a) work-function topographies of clean surfaces in UHV, (b) changes in work function with oxidation that are related to surface cleaning processes, (c) the temperature-dependent oxidation kinetics of polycrystalline metal surfaces (Re, Pt, Mo, W, and Pd) for pHSI, and (d) the stability of Ca, Gd, and LaB6 under residual gases for nHSI. We will report the optimum parameters for target stability and performance under both pHSI and nHSI operating conditions. We will also illustrate informative mass spectra produced by time-of-flight HSI.

Modeling of eddy current probe response for steam generator tubes

Sample calculations were performed with a three-dimensional (3D) finite-element model to describe the response of an eddy current (EC) probe to defects in steam generator (SG) tubing. Such calculations could be very helpful in understanding and interpreting EC probe response to complex tube/defect geometries associated with the inservice inspection (ISI) of SG tubes. The governing field equations are in terms of coupled magnetic vector and electric scalar potentials in conducting media and of total or reduced scalar potentials in nonconducting regions. To establish the validity of the model, comparisons of the theoretical and experimental responses of an absolute bobbin probe are given for two types of calibration standard defects. Simulation results are also presented on the effect of ligament size in axial cracks on bobbin probe response.

A practical hole testing technique using a meter display eddy current instrument

A practical technique for the detection of cracks emanating from holes was investigated for non-ferrous materials using the eddy current method. This technique is suggested when more appropriate test equipment is not available. An unshielded absolute pencil probe and a meter display instrument were utilized in the study. It was determined that holes with a minimum diameter of 6.5 mm can be tested efficiently for the detection of cracks at least 0.15 mm deep. For the equipment used, the hole depth that can be tested is limited about 11 mm if access from the other side is not possible. The detection capability was confirmed by an impedance plane display instrument using rotary differential probes.

Free-space electro-optic sampling with a high-repetition-rate regenerative amplified laser

The use of a high-repetition-rate (250 kHz) regenerative amplified laser with μJ pulse energy in a free-space THz beam electro-optic sampling system has produced a significant improvement in both the signal-to-noise ratio (>105) and absolute probe beam photomodulation depth (>19%). Focal plane images of the electric field distribution (strength and polarity) in dipole and quadrupole planar photoconductive emitters are presented. Preliminary results of real-time 2D THz images of moving objects have also been obtained.

Reconstruction of differential probe signals from absolute probe signals in eddy current testing : Rao, B.P.C.; Babu, Rao, C.B. Non-Destructive Evaluation and Quality Assurance. Edited by C.R.L. Murthy, B. Raj, O. Prabhakar and A. Sreenivasulu. pp. 181–190. Interline Publishing (1993) ISBN 81-7296-010-7

Reconstruction of differential probe signals from absolute probe signals in eddy current testing : Rao, B.P.C.; Babu, Rao, C.B. Non-Destructive Evaluation and Quality Assurance. Edited by C.R.L. Murthy, B. Raj, O. Prabhakar and A. Sreenivasulu. pp. 181–190. Interline Publishing (1993) ISBN 81-7296-010-7

Accurate probe-response calculation in eddy current NDE by finite element method

A method is presented to evaluate flaw signals in eddy current NDE using the finite element technique. The analysis of the electromagnetic field is based on a three-dimensional finite element scheme that computes directly the electromagnetic field distortions due to defects. This direct field-distortion calculation together with an accurate unflawed field calculation provides accurate total field values in general three-dimensional geometries. The paper shows that the application of the reaction concept and the reciprocity theory allows computations of the probe responses by performing integrals over the flaw region only, even if the analysis is performed by a finite element scheme. Two benchmark problems—a plate with rectangular slot scanned by a differential probe and a tube with axial and circumferential slots scanned by an absolute probe—have been solved to demonstrate the validity and the efficiency of the method. The calculated probe responses show good agreement with the measured trajectories. In order to reach better quantitative agreement, a calibration algorithm that adjusts the parameters of the cylindrical coil model and the lift-off within the range of the geometrical tolerances has been developed.

Reconstruction of differential probe signals from absolute probe signals in eddy current testing : Rao, B.P.C.; Babu, Rao, C.B. Non-Destructive Evaluation and Quality Assurance. Edited by C.R.L. Murthy, B. Raj, O. Prabhakar and A. Sreenivasulu. pp. 181–190. Interline Publishing (1993) ISBN 81-7296-010-7

Reconstruction of differential probe signals from absolute probe signals in eddy current testing : Rao, B.P.C.; Babu, Rao, C.B. Non-Destructive Evaluation and Quality Assurance. Edited by C.R.L. Murthy, B. Raj, O. Prabhakar and A. Sreenivasulu. pp. 181–190. Interline Publishing (1993) ISBN 81-7296-010-7

A probe manipulator for wind tunnel experiments

This paper describes the development of a seven-axis probe manipulator which is now in service in a wind tunnel facility at the National Taiwan Institute of Technology. The manipulator is composed of commercially available components, and is controlled by an IBM PC based servomotor controller that implements a robust control algorithm. A precision, non-contact calibration method is developed to align the probe manipulator with experimental coordinates and to measure some of the probe positioning errors. An absolute probe positioning accuracy better than 0.05 mm in all directions is achieved. Integrated with measurement instruments and capable of translation and rotation in three orthogonal directions, this computer controlled probe manipulator provides a dramatic improvement in experimental capability, as demonstrated by a flow fluctuation measurement.

NMR of water protons. The detection of their nuclear-spin noise, and a simple determination of absolute probe sensitivity based on radiation damping

NMR of water protons. The detection of their nuclear-spin noise, and a simple determination of absolute probe sensitivity based on radiation damping

Gated blood pool scintigraphic monitoring of doxorubicin cardiomyopathy: Comparison of camera and computerized probe results in 101 patients

Serial gated blood pool scintigraphic monitoring of cardiac function with both a nonimaging scintillation probe and a conventional gamma camera-computer imaging system was performed in 101 patients receiving doxorubicin hydrochloride (Adriamycin) chemotherapy. Comparison of probe- and camera-derived ejection fractions (n = 287) correlated significantly (r = 0.70, p less than 0.005) as did the interstudy (n = 183) change in ejection fraction (r = 0.76, p greater than 0.005). Significant discordance in probe- and camera-derived ejection fraction change occurred in 3 (1.6%) of 183 interstudy intervals. Average intrastudy variability of absolute probe-derived ejection fraction was 2.9%. This variability was unrelated to the level of cardiac function. Thirteen patients (13%) developed clinical cardiotoxicity, including four at cumulative Adriamycin levels less than 450 mg/m2. Mean absolute camera ejection fraction decline for these patients was 21% from baseline evaluation, and mean absolute probe ejection fraction decline was 22%. The minimal absolute ejection fraction decline was 11% for patients with clinical congestive heart failure. Eight asymptomatic patients had therapy terminated before the development of clinical cardiotoxicity after a mean decline in absolute camera ejection fraction of 19 +/- 4% (SD) and in probe ejection fraction of 19 +/- 9% into abnormal ranges (a decline in magnitude equivalent to that in patients developing congestive failure). None of these five asymptomatic patients available for clinical follow-up at 6 months after termination of Adriamycin therapy subsequently developed signs of ventricular dysfunction. The majority of patients (83%) studied at 450 mg/m2 cumulative dose levels did not have a 15% or greater decline from baseline into the abnormal range.(ABSTRACT TRUNCATED AT 250 WORDS)

Field Mapping of the IUCF 200 MeV Cyclotron

Magnetic field mapping of the Indiana main stage cyclotron is performed on a Cartesian grid using a 4 by 4 array of Hall probes. The apparatus, driven by torque motor-assisted, high-speed stepping motors, maps one eighth of the cyclotron beam area in 6 hours. Positioning accuracy is maintained by encoders attached to the stepping motor drive shafts and absolute probe locations are determined using magnetic fiducials on the magnet pole tip. The mapper is interfaced to a digital computer for automatic position control and for field data acquisition, reduction and storage. On-line data reduction includes conversion of Hall voltages to field values, allowing for individual differences in the sensitivity and non-linearity of the probes, and corrections in the fields for measured errors in the relative probe positions. Examples of the field data quality obtained are presented.