Three-dimensional scanners

However, it is very difficult to construct a three-dimensional scanner based on bimorphs. An example of such a design is reported by Muralt et al. (1986). It is much more complicated than the tripod scanner. 

Binnig, G., and Smith, D. P. E. (1986). Single-tube three-dimensional scanner for scanning tunneling microscopy. Rev. Sci. Instrum. 57, 1688-1689. 

One particularly interesting type of three-dimensional scanner that uses structured illumination is based on a phenomenon known as the moire effect. The moire effect is a fascinating visual display that often occurs when two periodic patterns are overlaid. It can easily be seen in everyday experiences such as overlapping window curtains or on television when a character wears a shirt with stripes that have nearly the same spacing as the... 

At present, most PET scanners can acquire in both a two-dimensional as well as a three-dimensional mode, whereas SPECT cameras measure in a three-dimensional mode. The physical property of the dual-positron gamma-rays emission lends itself to mathematical reconstruction algorithms to produce three-dimensional images in which the calculations are much closer to exact theoretical ones than those of SPECT. This is, in part, due to the two-photon as opposed to single-photon approach. PET can now achieve resolutions, for example in animal-dedicated scanners, in the order of 1 or 2 mm. The resolution is inherently limited theoretically only by the mean free path or distance in which the positron travels before it annihilates with an electron, e.g. those in biological water 2-8 mm. SPECT, although achieving millimeter resolution with the appropriate instrumentation, cannot quite achieve these levels. 

Simulation of the neutron-induced damages using triple ion beams is schematically shown in Fig. 7. A proton and a helium ion are provided by the ion implanter and the single-ended accelerator, respectively. Heavy ions, such as iron or silicon, accelerated by the tandem accelerator, are injected into the target simultaneously. For example, the SiC/SiC composite was tested under triple ion beam irradiation consisting of a 380-keV proton, a 1.2-MeV helium ion, and a 7.8-MeV Si " ion. The triple irradiation system is equipped with an energy degrader and a beam scanner for uniform three-dimensional (3-D) irradiation. 

Two different operation modes are commonly used. In the topographic mode, images are created by scanning the tip in the xy plane and recording the position required to keep It constant. A three dimensional map z(x, y, It = const.) is recorded. In the constant height mode, the probe scans the surface while the signal at the z-scanner is kept constant, and a three-dimensional image It(x,p,z = const.) is created. 

The mechanical scanner simply scans the array downward in 1 s to capture a full aperture ( 0.75 x 2.0 m) three-dimensional data set. This data set is then reconstructed and displayed using the computer system. 

The most advanced machine vision systems typically involve acquisition and interpretation of three-dimensional information. These systems often require more sophisticated illumination and processing techniques than one- and two-dimensional systems, but their results can be riveting. These scanners can characterize an object s shape three-dimensionally to tolerances of far less than a millimeter. This allows them to do things such as identify three-dimensional object orientation (important for assembly applications), check for subtle surface deformations in high precision machined parts, and generate detailed surface maps used by computer-controlled machining systems to create clones of the scanned object. 

As this isotope decays, positrons are emitted. Recall that when a positron collides with an electron, both are annihilated, and two gamma rays are produced. These gamma rays leave the body and are detected by a scanner. A computer converts the images into a detailed three-dimensional picture of the person s organs. 

Three-dimensional positioning of the scanner is obtained by placing three piezoelectric tubes in an orthogonal arrangement as shown in the illustration of the STM structure (Figure 5.2). The positioning accuracy of the scanner is determined by the characteristics of piezoelectric... 

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