An analytical model of eddy current ferrite-core probes

An analytical model of an axisymmetric eddy current probe with a cylindrical ferrite core above a layered conductive half-space is developed. Initially we consider the magnetic vector potential of a circular filament coaxial with a ferrite core over a layered conducting half-space. The principle of superposition is then used to derive close-form expressions for both the electromagnetic field and the impedance of a coil from the filament field. Rather than locating the probe in infinite space, it is confined coaxially within a circularly cylindrical boundary on which the vector potential field is zero. The radius of this artificial boundary is large in order to ensure that does not interfere substantially with the field near the probe. By using a truncated region in this way, the vector potential in the probe region can be expanded as a series rather than an integral form. Thus the solution of the problem amounts to finding the expansion coeefficients in the series. The numerical predictions of probe impedance have been compared with experimental data showing good agreement

Analysis of a concentric coplanar capacitive sensor using a spectral domain approach

Previously, concentric coplanar capacitive sensors have been developed to quantitatively characterize the permittivity or thickness of one layer in multi‐layered dielectrics. Electrostatic Green’s functions due to a point source at the surface of one‐ to three‐layered test‐pieces were first derived in the spectral domain, under the Hankel transform. Green’s functions in the spatial domain were then obtained by using the appropriate inverse transform. Utilizing the spatial domain Green’s functions, the sensor surface charge density was calculated using the method of moments and the sensor capacitance was calculated from its surface charge. In the current work, the spectral domain Green’s functions are used to derive directly the integral equation for the sensor surface charge density in the spectral domain, using Parseval’s theorem. Then the integral equation is discretized to form matrix equations using the method of moments. It is shown that the spatial domain approach is more computationally efficient, whereas the Green’s function derivation and numerical implementation are easier for the spectral domain approach

An annotated checklist of the birds of Manusela National Park, Seram. Birds recorded on the Operation Raleigh Expedition

Manusela National Park is located in central Seram at 129 deg E, 3 deg S and covers an area of 186 000 ha, about 11% of the surface area of Seram. The Park contains a broad selection of the habitats present in Seram, stretching from the north coast to within 5 km of the south coast. It includes a large portion of the Binaia-Merkele limestone massif with the highest mountain on Seram, Gunung (G). Binaia, at 24.90m, as well as the lower parallel ridge of Gunung (G). Kobipoto (1500 m) to the north, together with a broad section of the lowland alluvial plain where three wide rivers, the Wae Toluorang, Mual and Isal drain northwards to the sea (see fig.1). Observations were made by the authors between 20 July and 25 September 1987 as part of the ornithological research work conducted under the auspices of Operation Raleigh, Seram expedition

Barriers to Foreign Direct Investment in Japan

Recent polls indicate a dramatic surge in anti-Japanese sentiment in the United States. Sources of this sentiment are Japanese purchases of high-profile United States companies and real estate and the lack of similar opportunities for United States firms in Japan. This Note recognizes that although Japanese interest in mergers and acquisitions has increased, this interest focuses on foreign companies. The reason for the lack of activity within Japan are the various legal, structural, and cultural barriers that impede acquisitions, both foreign and Japanese, of Japanese companies. First, this Note considers T. Boone Pickens Jr.\u27s recent battle for seats on the board of directors of Koito Manufacturing as an example of how a confrontational approach to foreign access in Japan can prove unsuccessful. This Note then examines both legal and extralegal barriers to foreign investment. It is suggested that the friendly and successful acquisition by British-based Polly Peck International of fifty-one percent ownership in Sansui Electric Company is a model for future foreign direct investment activity in Japan. This Note concludes that continuing pressure for reform, both in Japan and by the United States under the recently completed Structural Impediments Initiative and proposed legislation, will lead to increased foreign investment activity in Japan in the 1990s

Advances in developing multiscale flaw models for eddy-current NDE

The need to accurately model multiscale phenomena is ubiquitous in eddy-current nondestructive evaluation. By using volume-integral equations, we are able to develop a very simple algorithm for accurately computing the response of a very small anomaly in the presence of a much larger one. We validate the algorithm and its associated code inVIC-3D{copyright, serif} through benchmark data on two test sets: (1) a notch at a bolt hole with an upper surface coil, and (2) a notch in a bolt hole with a plate surface coil

Cross-categorial gradability in Logoori

The central empirical observation of this paper is that there are polysemous lexical items in a number of unrelated languages that have similar, not intuitively related, meanings. These meanings are 'to arrive'/'to reach,' 'to be enough,' and 'must.' The central theoretical claim of this paper is based on a case study of one such polysemous lexical item in Logoori (Bantu, JE 41; Kenya). We argue that these three meanings all arise from a single semantic denotation that is sensitive to a shared gradable component in the semantics of linguistic expressions referring to spatial paths, gradable predicates, measures of plural count nouns/mass nouns, and modals. The main theoretical issue addressed in this paper is the application of ordered, abstract scales in a model of grammar. This paper is an abridged version of Bowler & Gluckman, to appear

Evaluation of the transient eddy current potential drop of a four point probe

The transient electrical potential drop of a four point probe has been calculated for the case where a current pulse is injected into a conductive plate via two surface contact electrodes and the voltage measured between two other contact electrodes. The four contact points can be co‐linear but this is not always case. For example, they can form a rectangle. Usually such probes carry direct current or alternating current and are used to measure electrical conductivity, crack dimensions or variations of conductivity and magnetic permeability with depth. However, the advantage of a current pulse excitation is that information on the variations of material properties with depth can be acquired rapidly and conveniently. What is needed is a means to infer material properties such as the conductivity variations with depth from the transient field measurements. Here, as an initial step in developing this analysis, we report on the evaluation of transient potential drop signals for four point probes on a homogeneous conductive plates

Evaluation of Eddy-current Probe Signal Due to Cracks in Metallic Parts of a Fast Reactors

Eddy current testing to evaluate the condition of metallic parts in a fast reactor under standby conditions is challenging due to the presence of conductive coolant, for example liquid sodium at 250 °C. The eddy current probe should be sensitive enough to capture small signal changes and hence an advanced inspection systems is needed. We have developed new hardware and improved numerical model to predict the eddy current probe signal due to crack in metallic fast reactor parts by using volume integral equation method. The analytical expressions are derived for the quasi-static time-harmonic electromagnetic fields of a circular eddy current coil to take account of the effect of conductive coolant. Naturally, the method of moment is used to approximate the integral equation and obtain the discrete approximation of the field in the crack domain. The simple and accurate analytical method for dealing with the hyper-singularity element evaluation is also provided. The probe impedance variation has been computed for narrow cracks. This model can be used to refine the eddy current probe design and predict the probe signal for comparison with experiment