Pencil
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Pencil (optics)
In optics, a pencil or pencil of rays is a geometric construct used to describe a beam or portion of a beam of electromagnetic radiation or charged particles, typically in the form of a narrow cone or cylinder.
Antennas which strongly bundle in azimuth and elevation are often described as "pencil-beam" antennas. For example a phased array antenna can send out a beam that is extremely thin. Such antennas are used for tracking radar.
In optics, the focusing action of a lens is often described in terms of pencils of rays. In addition to conical and cylindrical pencils, optics deals with astigmatic pencils as well.[1]
In electron optics, scanning electron microscopes use narrow pencil beams to achieve a deep depth of field.[2]
Ionizing radiation used in radiation therapy, whether photons or charged particles, such as proton therapy and electron therapy machines, is sometimes delivered through the use of pencil beam scanning.[3]
See also
- Pencil (mathematics), a family of geometric objects having a common property such as passage through a given point.
- Fan beam
- Pencil beam scanning (Medical physics)
References
- ^ Edward L, Nichols and William S. Franklin (1903). The Elements of Physics: A College Text-book. Macmillan Co. p. 77. http://books.google.com/books?id=WK0IAAAAIAAJ&pg=PA77&dq=pencil-of-rays++lens+astigmatic-pencil&lr=&as_brr=1&as_pt=ALLTYPES&ei=wVh-Saa6OZacyATy5oWrDg.
- ^ Nick Johnson (19 May 1983). "The art of seeing the very small". New Scientist 98 (1358): 472. http://books.google.com/books?id=z0Z3DxacC9IC&pg=PA472&dq=electrons+%22pencil-beam%22+sem&hl=en&ei=V7oFTemaKYmosQOqhMCsDQ&sa=X&oi=book_result&ct=result&resnum=1&ved=0CCkQ6AEwAA#v=onepage&q=electrons%20%22pencil-beam%22%20sem&f=false.
- ^ Faiz M. Khan (2009). The Physics of Radiation Therapy (4th ed.). Lippincott Williams & Wilkins. p. 521–522. ISBN 978-0-7817-8856-4. http://books.google.com/books?id=pWDQnxd-r1UC&pg=PA521.
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