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| | Let me initial start by introducing myself. My name is Boyd Butts even though it is not the name on my birth certification. Since she was 18 she's been working as a meter reader but she's usually needed her own business. What I love performing is playing baseball but I haven't produced a dime with it. Her family members life in Minnesota.<br><br>my blog - at home std test; [http://Www.Fuguporn.com/user/RMitchell such a good point], |
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| {{Orphan|date=August 2008|few=April 2013}}
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| [[Acoustic wave]]s emitted by [[Ultrasound|ultrasonic]]s '''transducer''' crystals exhibit a property known as '''self-focusing''' (or ''natural focusing''). Note that this is distinct from the electronically controlled focusing employed in diagnostic [[ultrasound]] devices which employ arrays of transducers. The self-focusing effect exists even for a single [[crystal]].
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| Self-focusing refers to the narrowing of the ultrasonic beam in the near-field. The effect occurs because,
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| if the ultrasound wave generated by the crystal is [[Coherence (physics)|coherent]],
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| the edges of the emitting surface generate [[wavelet]]s that constructively interfere with the plane wave that is generated.
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| The volume near the transducer which exhibits this phenomenon is called the [[near and far field|near field]],
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| as opposed to the [[far field]] where wave intensity decays approximately exponentially.
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| The near-field size is usually approximated
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| by <math>D = \frac{d^2}{4 \lambda}</math> where <math>d = </math>crystal diameter and <math>\lambda =</math>[[wavelength]] of the emitted wave.
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| At the edge of the near-field, where the focusing reaches its maximum, the beam width reaches <math> \frac{d}{2}</math>.
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| However, there exist techniques, such as [[apodization]] that may be used to reduce the near field size.<ref>{{cite journal|title=Investigations of compact self focusing transducers using stacked piezoelectric elements for strong sound pulses in therapy|author=Dreyer, T.; Krauss, W.; Bauer, E.; & Riedlinger, R.E.|location=Ultrasonics Symposium, 2000|publisher=[[IEEE]]|volume=2|date=October 2000|pages=1239–1242|url=http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/7345/19924/00921547.pdf?tp=&isnumber=&arnumber=921547/|accessdate=2008-05-06}}</ref>
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| ==References==
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| {{reflist}}
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| {{DEFAULTSORT:Self-Focusing Transducers}}
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| [[Category:Ultrasound]]
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| [[Category:Nondestructive testing]]
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| {{physics-stub}}
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Let me initial start by introducing myself. My name is Boyd Butts even though it is not the name on my birth certification. Since she was 18 she's been working as a meter reader but she's usually needed her own business. What I love performing is playing baseball but I haven't produced a dime with it. Her family members life in Minnesota.
my blog - at home std test; such a good point,