Philips Journal of Research最新文献

This paper reviews the research done on soft-magnetic fluxguide materials for use in sandwich heads and in thin-film recording heads for digital magnetic recording. After dealing with the basic principles of magnetic recording, the requirements on modern soft-magnetic materials are discussed. The roles of magnetic anistropy and magnetostriction in relation to permeability are discussed. Next, we review the recent advances in soft-magnetic materials processing, in particular for amorphous cobalt (CoNbZr) and nanocrystalline iron alloys, such as FeMX, with M being group IVa-Va metals such as Zr, Hf, Nb, Ta, etc., and X being N and O.

In radiotherapy, portal images are used to ensure a correct patient position during every radiation session. A reliable on-line verification is of clinical interest to interrupt the radiation in time in case the patient is not at the right position. A great problem for successful image registration is the poor image quality of portal images. They are corrupted by noise and of very low contrast. A method directly based on the grey levels is not sufficient. Therefore a structure-based method was developed which is almost insensitive to distrubances (air bubbles, noise, slowly varying grey levels). In most cases the selection of a region of interest (ROI) can be omitted. Besides the automatical segmentation of the radiation field, only the structures relevant for matching the anatomy are enhanced by using a bandpass filter. It is possible to detect the maximum correlation between different image modalities reliably (simulator image, digitally reconstructed radiograph, portal image). By using Fast Fourier Transformation (FFT), the calculation time is smaller than five seconds, which enables a clinical on-line verification. We have matched 1139 pairs of images of different modalities and various regions of the body (pelvis, nasopharyngeal space, head, lung). The success rate is greater than 95%.

Metal-films for precision resistors combine a very low temperature dependence of the electrical resistance with a tolerance of the resistance of only 0.1%. Corrosion resistance and adhesion to the substrate are of major importance. There are different classes of materials being utilised. For low ohmic applications, we use Cu-Ni alloys with a composition of about 65 at. % (atomic percent) of Cu. For this special alloy, the low temperature coefficient of the resistance (TCR) is a stable, intrinsic property. For most alloys, however, annealing is essential to approach the state of zero TCR. This is the case for the NiCrAl alloys, used for the mid-range of resistances and for SiCrN for high ohmic applications. In high ohmic films, metals are often combined with non-metallic substances like oxides or nitrides. Variation of alloy composition, sputtering conditions and annealing procedures are important for obtaining optimum thin-film properties. Important tools for thin-film characterisation are electron microscopy and related techniques together with high-temperature resistance measurement.

Functional polymers are increasingly being used in the electronics industry. The advantages are ease of processing, tailor-made materials and unique properties. The technology used is spin-coating of PPV derivatives which are made soluble by side chains attached to the polymer. The polymer light-emitting diode build-up is discussed as well as some typical results for brightness, efficiency and stability. On this basis, extension to application areas where larger flat devices are required, is considered. Of most direct importance are LCD backlights and displays based on the light-emitting polymer itself. Upon comparison with existing technologies, light-emitting polymers turn out to yield most promising solutions.

A layered motion estimation algorithm is proposed that permits quasisimultaneous motion estimation/segmentation up to a fixed maximum number of layers. The estimation results in one motion parameter set per layer, and a segmentation map that assigns these sets to different parts of the image (motion layers). Motion in a layer is modelled with at maximum four parameters capable of describing pan, tilt and zoom. The concept shows some hierarchy, i.e. a ranking of the motion layers. In this way the motion parameter estimation concerning one layer excludes those parts of the image that have been described by a layer ranked higher in the hierarchy and are not polluted by parts of the image that are better described by layers ranked lower in the hierarchy. The concept results in a very low operations count. It has been shown to perform well even in critical scan rate conversion applications, particularly in picture rate up-conversion. A variant including three layers has been scheduled to run in real-time on a Philips TriMedia processor.

This paper develops a Bayesian motion estimation algorithm for motion-compensated temporally recursive filtering of moving low-dose X-ray images (X-ray fluoroscopy). These images often exhibit a very low signal-to-noise ratio. The described motion estimation algorithm is made robust against noise by spatial and temporal regularization. A priori expectations about the spatial and temporal smoothness of the motion vector field are expressed by a generalized Gauss-Markov random field. The advantage of using a generalized Gauss-Markov random field is that, apart from smoothness, it also captures motion edges without requiring an edge detection threshold. The costs of edges are controlled by a single parameter, by means of which the influence of the regularization can be tuned from a median-filter-like behaviour to a linear-filter-like one.

Although Magnetic Resonance Imaging (MRI) has faced a dramatic increase in real-time capabilities over the last year, acceptable image quality still limits the actually achievable acquisition speed. This paper presents a motion-compensated noise filter that, on the basis of hierarchical motion estimation and edge-preserving adaptive weighted averaging, has been integrated into a segmented radial MR acquisition scheme. In several studies of moving joints, the proposed approach led to significant reductions in the noise level without introducing motion blur. The improved image quality would, in principle, allow more than double the acquisition speed, retaining the original image quality.

The trend of miniaturization of electronic products has had an effect on the development of passive components. A solution to the problems that are generated by size reduction of discrete passive components is to integrate resistors, capacitors and inductors into a functional passive circuit on one substrate. Various conditions have to be fulfilled in order to justify this integration. Important aspects are manufacturing cost, assembly cost, miniaturization, reliability, functionality and performance. Thin film technology can offer many advantages in all these aspects.

Digital tape recording systems show the same trend as hard-disk drives: a large increase of storage density with time. The use of advanced media and highly sensitive thin-film heads with magnetoresistive (MR) readout will increase the storage density dramatically. Key improvements are narrower tracks, more sensitive MR elements attained by applying the giant magnetoresistance effect, high-saturation flux density pole materials, advanced metal powder tape, intimate head-to-tape contact, and accurate tracking. By increasing the number of channels in the multitrack thin-film head, high data rates can be obtained as well. The basics of digital magnetic recording are discussed and a short historical overview is given of the Philips activities on thin-film heads for tape recording. An outlook on future improvements is given.