Reflectometry

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Reflectometry uses the reflection of waves at surfaces and interfaces to detect or characterize objects.

There are many different forms of reflectometry. They can be classified in several ways: by the used radiation (electromagnetic, ultrasound, particle beams), by the geometry of wave propagation (unguided versus wave guides or cables), by the involved length scales (wavelength and penetration depth versus size of the investigated object), by the method of measurement (continuous versus pulsed, polarization resolved, ...), and by the application domain.

Used radiation[edit]

Electromagnetic radiation of widely varying wavelength is used in many different forms of reflectometry:

  • Radar and Lidar: Reflections of electromagnetic pulses are used to detect the presence and to measure the location and speed of objects like aircraft, missiles, ships, cars.
  • Characterization of Semiconductor and Dielectric Thin Films: Analysis of reflectance data utilizing the Forouhi Bloomer dispersion equations can determine the thickness, refractive index, and extinction coefficient of thin films utilized in the semiconductor industry.
  • X-ray reflectometry: is a surface-sensitive analytical technique used in chemistry, physics, and materials science to characterize surfaces, thin films and multilayers.

Propagation of electric pulses in cables is used to detect and localize defects in electric wiring.[1][2]

Ultrasonic reflectometry: A transducer generates ultrasonic waves which propagates until it 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 impedance of a sample is determined by measuring the amplitude of the wave reflected from the propagation medium/sample interface.[3] From the reflected wave, it is possible to determine some properties of the sample that is desired to characterize. Applications include medical ultrasonography and nondestructive testing.

Neutron reflectometry: is a neutron diffraction technique for measuring the structure of thin films, similar to the often complementary techniques of X-ray reflectivity and ellipsometry. The technique provides valuable information over a wide variety of scientific and technological applications including chemical aggregation, polymer and surfactant adsorption, structure of thin film magnetic systems, biological membranes.

Skin reflectance[edit]

In anthropology, reflectometry devices are often used to gauge human skin color 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.[4]

Below are global estimates of observed or predicted skin reflectance frequencies in various countries, populations and areas:

# Country/Population/Area Hemisphere Reflectance site Observed reflectance at 685 nm Predicted reflectance at 685 nm
1 Afghanistan/Iran[4] Northern hemisphere Upper inner arm 55.70 45.55
2 Algeria (Aures)[4] Northern hemisphere Upper inner arm 58.05 47.91
3 Australia (Darwin)[4] Southern hemisphere Upper inner arm 19.30 36.24
4 Belgium[4] Northern hemisphere Upper inner arm 63.14 65.66
5 Botswana (San)[4] Southern hemisphere Upper inner arm 42.40 39.45
6 Brazil (Caingan)[4] Southern hemisphere Upper inner arm 49.40 48.53
7 Brazil (Guaraní)[4] Southern hemisphere Upper inner arm 47.20 45.29
8 Burkina Faso (Kurumba)[4] Northern hemisphere Upper inner arm 28.60 34.23
9 Cambodia[4] Northern hemisphere Upper inner arm 54.00 38.99
10 Cameroon (Fali)[4] Northern hemisphere Upper inner arm 21.50 34.37
11 Chad (Sara)[4] Northern hemisphere Upper inner arm 24.60 34.77
12 China (Southern)[4] Northern hemisphere Upper inner arm 59.17 50.49
13 China (Tibet)[4] Northern hemisphere Upper inner arm 54.70 41.78
14 Ethiopia[4] Northern hemisphere Upper inner arm 31.70 32.70
15 Ethiopia (Highland)[4] Northern hemisphere Upper inner arm 33.55 31.35
16 Germany (Mainz)[4] Northern hemisphere Upper inner arm 66.90 65.21
17 Greenland (Southern)[4] Northern hemisphere Upper inner arm 55.70 70.31
18 India[4] Northern hemisphere Upper inner arm 44.60 48.85
19 India (Bengal)[4] Northern hemisphere Upper inner arm 49.73 44.33
20 India (Goa)[4] Northern hemisphere Upper inner arm 46.40 38.93
21 India (Nagpur)[4] Northern hemisphere Upper inner arm 41.30 41.53
22 India (Northern)[4] Northern hemisphere Upper inner arm 53.26 44.23
23 India (Orissa)[4] Northern hemisphere Upper inner arm 32.05 41.52
24 India (Punjab)[4] Northern hemisphere Upper inner arm 54.24 47.89
25 India (Rajasthan)[4] Northern hemisphere Upper inner arm 52.00 42.19
26 India (Southern)[4] Northern hemisphere Upper inner arm 46.70 37.60
27 Iraq/Syria (Kurds)[4] Northern hemisphere Upper inner arm 61.12 51.50
28 Ireland (Ballinlough)[4] Northern hemisphere Upper inner arm 65.20 67.11
29 Ireland (Carnew)[4] Northern hemisphere Upper inner arm 64.50 65.84
30 Ireland (Longford)[4] Northern hemisphere Upper inner arm 65.00 66.99
31 Ireland (Rossmore)[4] Northern hemisphere Upper inner arm 64.75 66.73
32 Israel[4] Northern hemisphere Upper inner arm 58.20 48.67
33 Israel (Kurdish Jews)[5] Northern hemisphere Medial aspect of upper arm 54.89-60.02
34 Israel (Yemeni Jews)[5] Northern hemisphere Medial aspect of upper arm 53.15-56.94
35 Japan (Central)[4] Northern hemisphere Upper inner arm 55.42 58.51
36 Japan (Hidakka)[4] Northern hemisphere Upper inner arm 59.10 63.58
37 Japan (Northern)[4] Northern hemisphere Upper inner arm 54.90 61.34
38 Japan (Southwest)[4] Northern hemisphere Upper inner arm 53.55 56.68
39 Jordan[4] Northern hemisphere Upper inner arm 55.42 58.51
40 Jordan (Arabs)[6] Northern hemisphere Forehead 44.2-47.1
41 Jordan (Arabs)[6] Northern hemisphere Medial aspect of upper arm 48.0-52.7
42 Jordan (Chechen)[6] Northern hemisphere Forehead 50.9-52.5
43 Jordan (Chechen)[6] Northern hemisphere Medial aspect of upper arm 51.9-55.0
44 Jordan (Druze, males)[6] Northern hemisphere Forehead 48.5
45 Jordan (Druze, males)[6] Northern hemisphere Medial aspect of upper arm 52.8
46 Kenya[4] Northern hemisphere Upper inner arm 32.40 34.21
47 Lebanon[4] Northern hemisphere Upper inner arm 58.20 50.74
48 Liberia[4] Northern hemisphere Upper inner arm 29.40 40.52
49 Libya (Cyrenaica)[4] Northern hemisphere Upper inner arm 53.50 44.19
50 Libya (Fezzan)[4] Northern hemisphere Upper inner arm 44.00 41.31
51 Libya (Tripoli)[4] Northern hemisphere Upper inner arm 54.40 48.83
52 Malawi[4] Southern hemisphere Upper inner arm 27.00 38.67
53 Mali (Dogon)[4] Northern hemisphere Upper inner arm 34.10 34.54
54 Morocco[4] Northern hemisphere Upper inner arm 54.85 49.09
55 Mozambique (Chopi)[4] Southern hemisphere Upper inner arm 19.45 43.84
56 Namibia[4] Southern hemisphere Upper inner arm 25.55 38.29
57 Namibia (Okavango)[4] Southern hemisphere Upper inner arm 22.92 38.63
58 Namibia (Reheboth Baster)[4] Southern hemisphere Upper inner arm 32.90 36.49
59 Nepal (Eastern)[4] Northern hemisphere Upper inner arm 50.42 46.31
60 Netherlands[4] Northern hemisphere Upper inner arm 67.37 65.94
61 Nigeria (Ebo)[4] Northern hemisphere Upper inner arm 28.20 41.86
62 Nigeria (Yoruba)[4] Northern hemisphere Upper inner arm 27.40 39.62
63 Pakistan[4] Northern hemisphere Upper inner arm 52.30 44.15
64 Papua New Guinea[4] Southern hemisphere Upper inner arm 35.30 37.26
65 Papua New Guinea (Goroka)[4] Southern hemisphere Upper inner arm 33.30 34.20
66 Papua New Guinea (Karker)[4] Southern hemisphere Upper inner arm 32.00 37.25
67 Papua New Guinea (Lufa)[4] Southern hemisphere Upper inner arm 31.20 36.88
68 Papua New Guinea (Mount Hagan)[4] Southern hemisphere Upper inner arm 35.35 31.56
69 Papua New Guinea (Port Moresby)[4] Southern hemisphere Upper inner arm 41.00 35.45
70 Peru (Maranon)[4] Southern hemisphere Upper inner arm 43.05 42.28
71 Peru (Nunoa)[4] Southern hemisphere Upper inner arm 47.70 34.89
72 Philippines (Manila)[4] Northern hemisphere Upper inner arm 54.10 41.53
73 Russia (Chechen)[4] Northern hemisphere Upper inner arm 53.45 59.04
74 Saudi Arabia[4] Northern hemisphere Upper inner arm 52.50 38.65
75 South Africa[4] Northern hemisphere Upper inner arm 42.50 45.67
76 South Africa (Cape)[4] Northern hemisphere Upper inner arm 50.96 50.71
77 South Africa (Hottentot)[4] Northern hemisphere Upper inner arm 46.80 43.91
78 South Africa (San Central)[4] Northern hemisphere Upper inner arm 43.75 41.14
79 Spain (Basques)[4] Northern hemisphere Upper inner arm 65.70 62.38
80 Spain (Leon)[4] Northern hemisphere Upper inner arm 64.66 60.80
81 Sudan[4] Northern hemisphere Upper inner arm 35.50 33.45
82 Swaziland[4] Northern hemisphere Upper inner arm 35.60 44.62
83 Tanzania (Nyatura)[4] Northern hemisphere Upper inner arm 25.80 34.12
84 Tanzania (Sandewe)[4] Northern hemisphere Upper inner arm 28.90 32.13
85 Tunisia[4] Northern hemisphere Upper inner arm 56.30 52.03
86 Turkey[4] Northern hemisphere Upper inner arm 59.15 55.56
87 United Kingdom (Cumberland)[4] Northern hemisphere Upper inner arm 66.75 66.99
88 United Kingdom (London)[4] Northern hemisphere Upper inner arm 62.30 65.84
89 United Kingdom (Northern)[4] Northern hemisphere Upper inner arm 66.10 67.49
90 United Kingdom (Wales)[4] Northern hemisphere Upper inner arm 65.00 66.15
91 Vietnam[4] Northern hemisphere Upper inner arm 55.90 43.59
92 Zaire[4] Northern hemisphere Upper inner arm 33.20 37.46
93 Zaire (Konda)[4] Northern hemisphere Upper inner arm 29.40 39.43

Different reflectometry techniques[edit]

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:

  • In time-domain reflectometry (TDR), one emits a train of fast pulses, and analyzes the magnitude, duration and shape of the reflected pulses.
  • Frequency-domain reflectometry (FDR):[7][8] this technique is based on the transmission of a set of stepped-frequency sine waves from the sample. As for the TDR, these waves propagate until the sample and are reflected back to the source. Several types of FDR exist and are commonly used in radar applications or characterization of cables/wires. The signal analysis is focused rather on the changes in frequency between the incident signal and the reflected signal.
  • Ellipsometry is the polarization-resolved measurement of light reflections from thin films.

References[edit]

  1. ^ 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, doi:10.1109/TMAG.2010.2089503 
  2. ^ 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 
  3. ^ McClements, D.J.; Fairley, P. (1990), "Ultrasonic pulse echo reflectometer", Ultrasonics, 29 (1): 58–62, doi:10.1016/0041-624X(91)90174-7 
  4. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay az ba bb bc bd be bf bg bh bi bj bk bl bm bn bo bp bq br bs bt bu bv bw bx by bz ca cb cc cd ce cf cg ch Jablonski, N. G., and G. Chaplin (2000). "The evolution of human skin coloration" (PDF). Journal of Human Evolution. 39 (1): 57. Retrieved 30 August 2017. 
  5. ^ a b J. A. Lourie (1973). "Physical characteristics of Yemenite and Kurdish Jews in Israel". Philosophical Transactions of the Royal Society of London B: Biological Sciences. 266 (876): 101–112. Retrieved 30 August 2017. 
  6. ^ a b c d e f Sunderland, E., and Elizabeth Coope (1973). "Genetic studies in Jordan". Philosophical Transactions of the Royal Society of London B: Series B, Biological Sciences: 207–220. Retrieved 30 August 2017. 
  7. ^ 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, doi:10.1364/OPEX.13.000666 
  8. ^ 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 Transactions on electromagnetic compatibility, 45 (2): 306–315, doi:10.1109/TEMC.2003.811305