text:
ISO image
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This article is about a file format. For ISO in reference to cameras, see film speed. For other uses, see ISO (disambiguation).
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ISO image
Filename extension
.iso, .img
Internet media type
application/x-iso9660-image
Uniform Type Identifier (UTI)
public.iso-image
Type of format
Disk image
Standard
ISO 9660, UDF
An ISO image is an archive file of an optical disc, a type of disk image composed of the data contents from every written sector on an optical disc, including the optical disc file system.[1] ISO image files usually have a file extension of .iso. The name ISO is taken from the ISO 9660 file system used with CD-ROM media, but what is known as an ISO image might also contain a UDF (ISO/IEC 13346) file system (commonly used by DVDs and Blu-ray Discs).
ISO images can be created from optical discs by disk imaging software, or from a collection of files by optical disc authoring software, or from a different disk image file by means of conversion. Software distributed on bootable discs is often available for download in ISO image format. And like any other ISO image, it may be written to an optical disc such as CD or DVD.
Contents
[hide]
1 Description
2 Limitations
3 See also
4 References
5 External links
Description[edit]
There is no standard definition for ISO image files. ISO disc images are uncompressed and do not use a particular container format; they are a sector-by-sector copy of the data on an optical disc, stored inside a binary file. ISO images are expected to contain the binary image of an optical media file system (usually ISO 9660 and its extensions or UDF), including the data in its files in binary format, copied exactly as they were stored on the disc. The data inside the ISO image will be structured according to the file system that was used on the optical disc from which it was created
ISO files store only the user data from each sector on an optical disc, ignoring the control headers and error correction data, and are therefore slightly smaller than a raw disc image of optical media. Since the size of the user data portion of a sector (logical sector) in data optical discs is 2,048 bytes, the size of an ISO image will be a multiple of 2,048.
The .iso file extension is the one most commonly used for this type of disc images. The .img extension can also be found on some ISO image files, such as in some images from Microsoft DreamSpark; however, IMG files, which also use the .img extension, tend to have slightly different contents. The .udf file extension is sometimes used to indicate that the file system inside the ISO image is actually UDF and not ISO 9660.
Any single-track CD-ROM, DVD or Blu-ray disc can be archived in ISO format as a true digital copy of the original. Unlike a physical optical disc, an image can be transferred over any data link or removable storage medium. An ISO image can be opened with almost every multi-format file archiver. Native support for handling ISO images varies from operating system to operating system.
Hybrid disc formats include the ability to be read by different devices, operating systems, or hardware. In the past, one example of this use was for a disc that supported both Microsoft Windows and Macintosh installations from a single disk image (by containing several file systems).
An ISO can be "mounted" with suitable driver software, i.e. treated by the operating system as if it were a physical optical disc. Most Unix-based operating systems, including Linux and macOS, have built-in capability to mount an ISO. Versions of Windows after and including Windows 8 also have such capability.[2] For other operating systems software drivers can be installed to achieve the same objective.
Since there is no standard defining the ISO disc image file format, the term "ISO image" is sometimes used in a broader sense to refer to any disc image file of an optical disc, independent of the format it uses. Anr 2001
Limitations[edit]
A CD can have multiple tracks, which can contain computer data, audio, or video. File systems such as ISO 9660 are stored inside one of these tracks. Since ISO images are expected to contain a binary copy of the file system and its contents, there is no concept of a "track" inside an ISO image, since a track is a container for the contents of an ISO image. This means that CDs with multiple tracks can't be stored inside a single ISO image; at most, an ISO image will contain the data inside one of those multiple tracks, and only if it is stored inside a standard file system.
This also means that audio CDs, which are usually composed of multiple tracks, can't be stored inside an ISO image. Furthermore, not even a single track of an audio CD can be stored as an ISO image, since audio tracks do not contain a file system inside them, but only a continuous stream of encoded audio data. This audio is stored on sectors of 2352 bytes different than those that store a file system and it is not stored inside files; it is addressed with track numbers, index points and a CD time code that are encoded into the lead-in of each session of the CD-Audio disc.
Video CDs and Super Video CDs require at least two tracks on a CD, so it is also not possible to store an image of one of these discs inside an ISO image file.
Formats such as CUE/BIN, CCD/IMG and MDS/MDF formats can be used to store multi-track disc images, including audio CDs. These formats store a raw disc image of the complete disc, including information from all tracks, along with a companion file describing the multiple tracks and the characteristics of each of those tracks. This would allow an optical media burning tool to have all the information required to correctly burn the image on a new disc. For audio CDs, one can also transfer the audio data into uncompressed audio files like WAV or AIFF, optionally reserving the metadata (see CD ripping).
Most software that is capable of writing from ISO images to hard disks or recordable media (CD / DVD / BD) is generally not able to write from ISO disk images to flash drives. This limitation is more related to the availability of software tools able to perform this task, than to problems in the format itself. However, since 2011, various software has existed to write raw image files to USB flash drives.[3][4]
See also[edit]
Disk image
El Torito (CD-ROM standard) (CD boot)
Joliet (file system)
Live USB
No-disc crack, a patch that eliminates the need for either an ISO image or the physical disc.
References[edit]
Jump up ^ Fisher, Tim. "ISO File". About.com Tech. Retrieved 13 February 2015. Definition: An ISO file, often called an ISO image, is in fact an "image" of an entire CD or DVD. The entire contents of a disc can be represented in a single ISO file.
Jump up ^ "Windows 8 Explorer will support native mounting of ISO and VHD". ExtremeTech. Retrieved 2012-05-21.
Jump up ^ "ISO image to USB conversion". ISO to USB burning tool. Archived from the original on 15 February 2015. Retrieved 15 February 2015.
Jump up ^ "How to Setup Windows 7 or Windows 8 from USB drive?". PowerISO. Retrieved 15 February 2015.
External links[edit]
How to write ISO files to CD, DVD and BD with Linux using genisoimage, wodim, growisofs, etc.
hide
v
t
e
Disk image file formats
Comparison of disc image software
Optical discs
BIN+CUE
CSO
DAA
IMG+CCD+SUB
ISO
ISZ
MDF+MDS
MDX
NRG
UIF
Hard disks
DMG
FVD
IMG
ISO
NDIF
QCOW
UDIF
VDI
VHD
VMDK
WIM
Floppy disks
ADF, ADZ
DC42, DART
DCF
DMS
IMG, IMA, IMZ
VFD
CD-DA
Disc Description Protocol
Convention: Any item in this table that has the form of "A+B" or "A+B+C" indicates a disk format that spans multiple files, where A contains the bulk of the data, and B and C are sidecar files.
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National Institute of Technical Teachers' Training and Research, Kolkata
From Wikipedia, the free encyclopedia
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National Institute of Technical Teachers' Training and Research, Kolkata
Established
1965
Founder
Ministry of Human Resource Development
Location
Kolkata, West Bengal, India
Website
http://www.nitttrkol.ac.in/index.php
National Institute of Technical Teachers' Training and Research, Kolkata , (also known as NITTTR Kolkata) is a technical teacher's training institution situated in the Kolkata, West Bengal, India.[1]
External Links[edit]
http://www.nitttrkol.ac.in/index.php
References[edit]
Jump up ^ "NITTTR". National Institute of Technical Teachers' Training and Research,.
This article about a university or college in West Bengal, India is a stub. You can help Wikipedia by expanding it.
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Retrieved from "https://en.wikipedia.org/w/index.php?title=National_Institute_of_Technical_Teachers%27_Training_and_Research,_Kolkata&oldid=798528519"
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text:
Propagation constant
From Wikipedia, the free encyclopedia
Jump to navigation Jump to search
"Transmission parameter" redirects here. For ABCD transmission parameters, see two-port network § ABCD-parameters. For scattering transfer parameters, see scattering parameters § Scattering transfer parameters.
The propagation constant of a sinusoidal electromagnetic wave is a measure of the change undergone by the amplitude and phase of the wave as it propagates in a given direction. The quantity being measured can be the voltage, the current in a circuit, or a field vector such as electric field strength or flux density. The propagation constant itself measures the change per unit length, but it is otherwise dimensionless. In the context of two-port networks and their cascades, propagation constant measures the change undergone by the source quantity as it propagates from one port to the next.
The propagation constant's value is expressed logarithmically, almost universally to the base e, rather than the more usual base 10 that is used in telecommunications in other situations. The quantity measured, such as voltage, is expressed as a sinusoidal phasor. The phase of the sinusoid varies with distance which results in the propagation constant being a complex number, the imaginary part being caused by the phase change.
Contents
[hide]
1 Alternative names
2 Definition
3 Attenuation constant
3.1 Copper lines
3.2 Optical fibre
4 Phase constant
5 Filters and two-port networks
5.1 Cascaded networks
6 See also
7 Notes
8 References
9 External links
Alternative names[edit]
The term "propagation constant" is somewhat of a misnomer as it usually varies strongly with ω. It is probably the most widely used term but there are a large variety of alternative names used by various authors for this quantity. These include transmission parameter, transmission function, propagation parameter, propagation coefficient and transmission constant. If the plural is used, it suggests that α and β are being referenced separately but collectively as in transmission parameters, propagation parameters, etc. In transmission line theory, α and β are counted among the "secondary coefficients", the term secondary being used to contrast to the primary line coefficients. The primary coefficients are the physical properties of the line, namely R,C,L and G, from which the secondary coefficients may be derived using the telegrapher's equation. Note that in the field of transmission lines, the term transmission coefficient has a different meaning despite the similarity of name: it is the companion of the reflection coefficient.
Definition[edit]
The propagation constant, symbol γ {\displaystyle {\gamma }} , for a given system is defined by the ratio of the complex amplitude at the source of the wave to the complex amplitude at some distance x, such that,
A 0 A x = e γ x {\displaystyle {\frac {A_{0}}{A_{x}}}=e^{\gamma x}}
Since the propagation constant is a complex quantity we can write:
γ = α + i β {\displaystyle \gamma =\alpha +i\beta \,}
where
α, the real part, is called the attenuation constant
β, the imaginary part, is called the phase constant
That β does indeed represent phase can be seen from Euler's formula:
e i θ = cos  θ + i sin  θ {\displaystyle e^{i\theta }=\cos {\theta }+i\sin {\theta }\,\!}
which is a sinusoid which varies in phase as θ varies but does not vary in amplitude because
| e i θ | = cos 2  θ + sin 2  θ = 1 {\displaystyle \left|e^{i\theta }\right|={\sqrt {\cos ^{2}{\theta }+\sin ^{2}{\theta }}}=1}
The reason for the use of base e is also now made clear. The imaginary phase constant, iβ, can be added directly to the attenuation constant, α, to form a single complex number that can be handled in one mathematical operation provided they are to the same base. Angles measured in radians require base e, so the attenuation is likewise in base e.
The propagation constant for copper (or any other conductor) lines can be calculated from the primary line coefficients by means of the relationship
γ = Z Y {\displaystyle \gamma ={\sqrt {ZY}}}
where
Z = R + i ω L {\displaystyle Z=R+i\omega L\,\!} , the series impedance of the line per unit length and,
Y = G + i ω C {\displaystyle Y=G+i\omega C\,\!} , the shunt admittance of the line per unit length.
Attenuation constant[edit]
In telecommunications, the term attenuation constant, also called attenuation parameter or attenuation coefficient, is the attenuation of an electromagnetic wave propagating through a medium per unit distance from the source. It is the real part of the propagation constant and is measured in nepers per metre. A neper is approximately 8.7 dB. Attenuation constant can be defined by the amplitude ratio
| A 0 A x | = e α x {\displaystyle \left|{\frac {A_{0}}{A_{x}}}\right|=e^{\alpha x}}
The propagation constant per unit length is defined as the natural logarithmic of ratio of the sending end current or voltage to the receiving end current or voltage.
Copper lines[edit]
The attenuation constant for copper lines (or ones made of any other conductor) can be calculated from the primary line coefficients as shown above. For a line meeting the distortionless condition, with a conductance G in the insulator, the attenuation constant is given by
α = R G {\displaystyle \alpha ={\sqrt {RG}}\,\!}
however, a real line is unlikely to meet this condition without the addition of loading coils and, furthermore, there are some frequency dependent effects operating on the primary "constants" which cause a frequency dependence of the loss. There are two main components to these losses, the metal loss and the dielectric loss.
The loss of most transmission lines are dominated by the metal loss, which causes a frequency dependency due to finite conductivity of metals, and the skin effect inside a conductor. The skin effect causes R along the conductor to be approximately dependent on frequency according to
R ∝ ω {\displaystyle R\propto {\sqrt {\omega }}}
Losses in the dielectric depend on the loss tangent (tan δ) of the material divided by the wavelength of the signal. Thus they are directly proportional to the frequency.
α d = π ε r λ tan  δ {\displaystyle \alpha _{d}={{\pi }{\sqrt {\varepsilon _{r}}} \over {\lambda }}{\tan \delta }}
Optical fibre[edit]
The attenuation constant for a particular propagation mode in an optical fiber is the real part of the axial propagation constant.
Phase constant[edit]
In electromagnetic theory, the phase constant, also called phase change constant, parameter or coefficient is the imaginary component of the propagation constant for a plane wave. It represents the change in phase per unit length along the path travelled by the wave at any instant and is equal to real part of the angular wavenumber of the wave. It is represented by the symbol β and is measured in units of radians per unit length.
From the definition of (angular) wavenumber for TEM waves:
k = 2 π λ = β {\displaystyle k={\frac {2\pi }{\lambda }}=\beta }
For a transmission line, the Heaviside condition of the telegrapher's equation tells us that the wavenumber must be proportional to frequency for the transmission of the wave to be undistorted in the time domain. This includes, but is not limited to, the ideal case of a lossless line. The reason for this condition can be seen by considering that a useful signal is composed of many different wavelengths in the frequency domain. For there to be no distortion of the waveform, all these waves must travel at the same velocity so that they arrive at the far end of the line at the same time as a group. Since wave phase velocity is given by
v p = λ T = f ν ~ = ω β {\displaystyle v_{p}={\frac {\lambda }{T}}={\frac {f}{\tilde {\nu }}}={\frac {\omega }{\beta }}}
it is proved that β is required to be proportional to ω. In terms of primary coefficients of the line, this yields from the telegrapher's equation for a distortionless line the condition
β = ω L C {\displaystyle \beta =\omega {\sqrt {LC}}}
However, practical lines can only be expected to approximately meet this condition over a limited frequency band.
In particular, the phase constant β {\displaystyle \beta } is not always equivalent to the wavenumber k {\displaystyle k} . Generally speaking, the following relation
β = k {\displaystyle \beta =k}
is tenable to the TEM wave (transverse electromagnetic wave) which travels in free space or TEM-devices such as the coaxial cable and two parallel wires transmission lines. Nevertheless, it is invalid to the TE wave (transverse electric wave) and TM wave (transverse magnetic wave). For example,[1] in a hollow waveguide where the TEM wave cannot exist but TE and TM waves can propagate,
k = ω c {\displaystyle k={\frac {\omega }{c}}}
β = k 1 − ω c 2 ω 2 {\displaystyle \beta =k{\sqrt {1-{\frac {\omega _{c}^{2}}{\omega ^{2}}}}}}
Here ω c {\displaystyle \omega _{c}} is the cutoff frequency.In a rectangular waveguide, the cutoff frequency is
ω c = c ( n π a ) 2 + ( m π b ) 2 , {\displaystyle \omega _{c}=c{\sqrt {\left({\frac {n\pi }{a}}\right)^{2}+\left({\frac {m\pi }{b}}\right)^{2}}},}
where the integers n , m ≥ 0 {\displaystyle n,m\geq 0} are the mode numbers, and a and b the lengths of the sides of the rectangle. For TE modes, n , m ≥ 0 {\displaystyle n,m\geq 0} (but n = m = 0 {\displaystyle n=m=0} is not allowed), while for TM modes n , m ≥ 1 {\displaystyle n,m\geq 1} . The phase velocity equals
v p = ω β = c 1 − ω c 2 ω 2 > c {\displaystyle v_{p}={\frac {\omega }{\beta }}={\frac {c}{\sqrt {1-{\frac {\omega _{\mathrm {c} }^{2}}{\omega ^{2}}}}}}>c}
The phase constant is also an important concept in quantum mechanics because the momentum p {\displaystyle p} of a quantum is directly proportional to it,[2] [3] i.e.
p = ℏ β {\displaystyle p=\hbar \beta }
where ħ is called the reduced Planck constant (pronounced "h-bar"). It is equal to the Planck constant divided by 2π.
Filters and two-port networks[edit]
The term propagation constant or propagation function is applied to filters and other two-port networks used for signal processing. In these cases, however, the attenuation and phase coefficients are expressed in terms of nepers and radians per network section rather than per unit length. Some authors[4] make a distinction between per unit length measures (for which "constant" is used) and per section measures (for which "function" is used).
The propagation constant is a useful concept in filter design which invariably uses a cascaded section topology. In a cascaded topology, the propagation constant, attenuation constant and phase constant of individual sections may be simply added to find the total propagation constant etc.
Cascaded networks[edit]
Three networks with arbitrary propagation constants and impedances connected in cascade. The Zi terms represent image impedance and it is assumed that connections are between matching image impedances.
The ratio of output to input voltage for each network is given by[5]
V 1 V 2 = Z I 1 Z I 2 e γ 1 {\displaystyle {\frac {V_{1}}{V_{2}}}={\sqrt {\frac {Z_{I1}}{Z_{I2}}}}e^{\gamma _{1}}}
V 2 V 3 = Z I 2 Z I 3 e γ 2 {\displaystyle {\frac {V_{2}}{V_{3}}}={\sqrt {\frac {Z_{I2}}{Z_{I3}}}}e^{\gamma _{2}}}
V 3 V 4 = Z I 3 Z I 4 e γ 3 {\displaystyle {\frac {V_{3}}{V_{4}}}={\sqrt {\frac {Z_{I3}}{Z_{I4}}}}e^{\gamma _{3}}}
The terms Z I n Z I m {\displaystyle {\sqrt {\frac {Z_{In}}{Z_{Im}}}}} are impedance scaling terms[6] and their use is explained in the image impedance article.
The overall voltage ratio is given by
V 1 V 4 = V 1 V 2 ⋅ V 2 V 3 ⋅ V 3 V 4 = Z I 1 Z I 4 e γ 1 + γ 2 + γ 3 {\displaystyle {\frac {V_{1}}{V_{4}}}={\frac {V_{1}}{V_{2}}}\cdot {\frac {V_{2}}{V_{3}}}\cdot {\frac {V_{3}}{V_{4}}}={\sqrt {\frac {Z_{I1}}{Z_{I4}}}}e^{\gamma _{1}+\gamma _{2}+\gamma _{3}}}
Thus for n cascaded sections all having matching impedances facing each other, the overall propagation constant is given by
γ t o t a l = γ 1 + γ 2 + γ 3 + ⋯ + γ n {\displaystyle \gamma _{\mathrm {total} }=\gamma _{1}+\gamma _{2}+\gamma _{3}+\cdots +\gamma _{n}}
See also[edit]
The concept of penetration depth is one of many ways to describe the absorption of electromagnetic waves. For the others, and their interrelationships, see the article: Mathematical descriptions of opacity.
Notes[edit]
Jump up ^ Pozar, David (2012). Microwave Engineering (4th ed.). John Wiley &Sons. pp. 62–164. ISBN 978-0-470-63155-3.
Jump up ^ Wang,Z.Y. (2016). "Generalized momentum equation of quantum mechanics". Optical and Quantum Electronics. 48 (2): 1–9. doi:10.1007/s11082-015-0261-8.
Jump up ^ Tremblay,R., Doyon,N., Beaudoin-Bertrand,J. "TE-TM Electromagnetic modes and states in quantum physics". arXiv:1611.01472  . Bibcode:2016arXiv161101472T. CS1 maint: Multiple names: authors list (link)
Jump up ^ Matthaei et al, p49
Jump up ^ Matthaei et al pp51-52
Jump up ^ Matthaei et al pp37-38
References[edit]
This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C"..
Matthaei, Young, Jones Microwave Filters, Impedance-Matching Networks, and Coupling Structures McGraw-Hill 1964.
External links[edit]
"Propagation constant" (Online). Microwave Encyclopedia. 2011. Retrieved February 2, 2011.
Paschotta, Dr. Rüdiger (2011). "Propagation Constant" (Online). Encyclopedia of Laser Physics and Technology. Retrieved February 2011. Check date values in: |accessdate= (help)
Janezic, Michael D.; Jeffrey A. Jargon (February 1999). "Complex Permittivity determination from Propagation Constant measurements" (PDF). Microwave and Guided Wave Letters, IEEE. 9: 76–78. doi:10.1109/75.755052. Retrieved February 2011. Check date values in: |accessdate= (help) Free PDF download is available. There is an updated version dated August 6, 2002.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Propagation_constant&oldid=811216698"
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