Reflectometry

<h2 id="radiation-sources">Radiation sources</h2>
<ul><li><a href="/facts/Electromagnetic_radiation/Ynx7ujCW">Electromagnetic radiation</a> of widely varying wavelength is used in many different forms of reflectometry:
<ul><li><a href="/facts/Radar/jk9BTbFA">Radar</a>: Reflections of radiofrequency pulses are used to detect the presence and to measure the location and speed of objects such as aircraft, missiles, ships, vehicles.</li>
<li><a href="/facts/Lidar/b9SPUmLM">Lidar</a>: Reflections of light pulses are used typically to penetrate ground cover by vegetation in <a href="/facts/Aerial_archaeology/C4KygsAW">aerial archaeological surveys</a>.</li>
<li>Characterization of semiconductor and dielectric thin films: Analysis of reflectance data utilizing the <a href="/facts/Forouhi%25E2%2580%2593Bloomer_model/myoPDSmF">Forouhi Bloomer dispersion equations</a> can determine the thickness, <a href="/facts/Refractive_index/yjkzvgeE">refractive index</a>, and <a href="/facts/Complex_index_of_refraction/yjkzvgeE">extinction coefficient</a> of thin films utilized in the <a href="/facts/Semiconductor/zFf3mGTE">semiconductor</a> industry.</li>
<li><a href="/facts/X-ray_reflectometry/CGk7tUHT">X-ray reflectometry</a>: is a surface-sensitive analytical technique used in chemistry, physics, and materials science to characterize surfaces, thin films and multilayers.</li>
<li>Propagation of electric <a href="/facts/Pulse_(signal_processing)/2v5sWtyB">pulses</a> and  <a href="/facts/Signal_reflection/LFqMxKrn">reflection</a> at discontinuities in <a href="/facts/Electric_cable/Dhzlz5hn">cables</a> is used in time domain reflectometry (TDR) to detect and localize defects in electric wiring.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a><a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a></li>
<li><a href="/facts/Skin_reflectance/oEypoFH5">Skin reflectance</a>: In anthropology, reflectometry devices are often used to gauge <a href="/facts/Human_skin_color/nkMestc6">human skin color</a> through the measurement of skin reflectance. These devices are typically pointed at the upper arm or forehead, with the emitted waves then interpreted at various percentages. Lower frequencies represent lower skin reflectance and thus darker pigmentation, whereas higher frequencies represent greater skin reflectance and therefore lighter pigmentation.</li></ul></li>
<li><a href="/facts/Acoustics/2GpQUymy">Acoustic</a> reflectometry: the reflection of sound waves is used. One application is the use of a <a href="/facts/Tympanometer/d28nz5aK">tympanometer</a> (a specialised acoustic reflectometer) to diagnose medical conditions of the ear.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a>
<ul><li><a href="/facts/Ultrasound/31Pa5IH9">Ultrasonic</a> reflectometry: A <a href="/facts/Transducer/YS7zfv9d">transducer</a> generates acoustic waves at ultrasonic frequency which propagate until they reaches the interface between the propagation medium and the sample. The wave is partially reflected at the interface and partially transmitted into the sample. The waves reflected at the interface travel back to the transducer, then the <a href="/facts/Acoustic_impedance/FdXaKVjo">acoustic impedance</a> of the sample is determined by measuring the <a href="/facts/Amplitude/aEckuXJM">amplitude</a> of the wave reflected from the propagation medium/sample interface.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> From the reflected wave, it is possible to determine some properties of the sample that is desired to characterize. Applications include <a href="/facts/Medical_ultrasonography/Ju5BFuuV">medical ultrasonography</a> and <a href="/facts/Nondestructive_testing/Czz0Vt0B">nondestructive testing</a>.</li></ul></li>
<li><a href="/facts/Neutron_reflectometry/S3K8tuEv">Neutron reflectometry</a>: is a <a href="/facts/Neutron_diffraction/fYXAunDW">neutron diffraction</a> technique for measuring the structure of <a href="/facts/Thin_film/nSeoUT4Q">thin films</a>, similar to the often complementary techniques of X-ray reflectivity and <a href="/facts/Ellipsometry/8jHpJ2z8">ellipsometry</a>. The technique provides valuable information over a wide variety of scientific and technological applications including <a href="/facts/Particle_aggregation/GvDNtDVo">chemical aggregation</a>, <a href="/facts/Polymer/eF32E50K">polymer</a> and <a href="/facts/Surfactant/zgVX6g8o">surfactant</a> <a href="/facts/Adsorption/ARH9peYM">adsorption</a>, structure of thin film <a href="/facts/Magnetic_field/Ta8Ev588">magnetic</a> systems, biological membranes.</li></ul>
<h2 id="different-reflectometry-techniques">Different reflectometry techniques</h2>
<p>Many techniques are based on the principle of reflectometry and are distinguished by the type of waves used and the analysis of the reflected signal. Among all these techniques, we can classify the main but not limited to:
</p>
<ul><li>In <a href="/facts/Time-domain_reflectometry/md9VY2JY">time-domain reflectometry</a> (TDR), fast pulses are emitted, and the magnitude, duration and shape of the reflected pulses is analyzed.</li>
<li>Frequency-domain reflectometry (FDR):<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a><a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> this technique is based on the transmission of a set of stepped-frequency sine waves from the sample. As with TDR, these waves propagate to the sample and are reflected at the interface back to the source. There are several types of FDR; they are commonly used in radar applications and for characterization of cables/wires. The changes in frequency between the incident signal and the reflected signal are analyzed.</li>
<li><a href="/facts/Ellipsometry/8jHpJ2z8">Ellipsometry</a> is the polarization-resolved measurement of light reflections from thin films.</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Teppo, Heikki; Revonta, Matti (2009). "Consumer acoustic reflectometry by parents in detecting middle-ear fluid among children undergoing tympanostomy". Scandinavian Journal of Primary Health Care. 27 (3): 167–171. doi:10.1080/02813430903072165. ISSN 0281-3432. PMC 3413189. PMID 19565410. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3413189" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3413189</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Smail, M.K.; Hacib, T.; Pichon, L.; Loete, F. (2011), "Detection and Location of Defects in Wiring Networks Using Time-Domain Reflectometry and Neural Networks", IEEE Transactions on Magnetics, 47 (5): 1502–1505, Bibcode:2011ITM....47.1502S, doi:10.1109/TMAG.2010.2089503, S2CID 30284686 <a href="/wiki/IEEE_Transactions_on_Magnetics" target="_blank">/wiki/IEEE_Transactions_on_Magnetics</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Furse, C.; Haupt, R. (2001), "Down to the wire: The hidden hazard of aging aircraft wiring", IEEE Spectrum, 38 (2): 35–39, doi:10.1109/6.898797 <a href="/wiki/IEEE_Spectrum" target="_blank">/wiki/IEEE_Spectrum</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>Teppo, Heikki; Revonta, Matti (2009). "Consumer acoustic reflectometry by parents in detecting middle-ear fluid among children undergoing tympanostomy". Scandinavian Journal of Primary Health Care. 27 (3): 167–171. doi:10.1080/02813430903072165. ISSN 0281-3432. PMC 3413189. PMID 19565410. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3413189" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3413189</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>McClements, D.J.; Fairley, P. (1990), "Ultrasonic pulse echo reflectometer", Ultrasonics, 29 (1): 58–62, doi:10.1016/0041-624X(91)90174-7 <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>Soller, B.J.; Gifford, D.K.; Wolfe, M.S.; Froggatt, M.E. (2005), "High resolution optical frequency domain reflectometry for characterization of components and assemblies", Optics Express, 13 (2): 666–674, Bibcode:2005OExpr..13..666S, doi:10.1364/OPEX.13.000666, PMID 19488398 <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
<li id="fn:7"><p>Furse, C.; C.C., You; Dangol, R; Nielsen, M.; Mabey, G.; Woodward \first6=R. (2003), "Frequency-Domain Reflectometery for on-Board Testing of Aging Aircraft Wiring", IEEE Trans. Electromagn. Compat., 45 (2): 306–315, doi:10.1109/TEMC.2003.811305{{citation}}:  CS1 maint: numeric names: authors list (link) <a href="/wiki/IEEE_Transactions_on_Electromagnetic_Compatibility" target="_blank">/wiki/IEEE_Transactions_on_Electromagnetic_Compatibility</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li>
</ol>

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Reflectometry