Comparison with Other Fiber Optic Distributed Sensing Techniques

Comparison with other fiber optic distributed sensing techniques

Comparison with Other Fiber Optic Distributed Sensing Techniques 1

Distributed acoustic sensing relies on light which is Rayleigh backscattered from small variations in the refractive index of the fiber. The backscattered light has the same frequency as the transmitted light. There are a number of other distributed fiber sensing techniques that rely on different scattering mechanisms and can be used to measure other parameters. Brillouin scatter occurs due to the interaction between the light and acoustic phonons travelling in the fiber. As the light is scattered by a moving phonon, its frequency is shifted by the Doppler effect by around 10 GHz. Light is generated at both above (anti-Stokes shift) and below (Stokes shift) the original optical frequency. The intensity and frequency shifts of the two components are dependent on both temperature and strain and by measuring the shifts, absolute values of the two parameters can be calculated using a distributed temperature and strain sensing (DTSS) system. Brillouin scatter is much weaker than Rayleigh scatter and so the reflections from a number of pulses must be summed together to enable the measurements to be made. Therefore, the maximum frequency at which changes can be measured using Brillouin scatter is typically a few tens of Hz. Raman scatter occurs when light is scattered in interaction with molecular vibrations in the fiber. As with Brillouin scattering, both Stokes and anti-Stokes components are produced and these are shifted from the wavelength of the incident light by several tens of nanometers. By measuring the ratio in intensity between the Stokes and anti-Stokes components, an absolute value of temperature can be measured by a distributed temperature sensing (DTS) system. The larger wavelength shifts compared to Brillouin scatter mean that it is easier to separate the scattered Raman light from the un-shifted Rayleigh scattered component. However the intensity of the Raman scatter is even lower than the Brillouin scatter and so it is normally necessary to average for many seconds or even minutes in order to get reasonable results. Therefore, Raman-based systems are only suitable for measuring slowly varying temperatures. Phase-sensitive coherent optical time-domain reflectometryPhase-sensitive coherent optical time-domain reflectometry (Ï•-OTDR) is a technique that can provide sufficient sensitivity and resolution for these distributed acoustic sensing systems. Standard optical time-domain reflectometry techniques use light sources with coherence lengths, which are shorter than pulse lengths. This can yield a sum of backscattered intensities from each scattering center, which allows monitoring splices and breaks in fiber optic cables. On the contrary, in Ï•-OTDR-based sensors, the coherence length of lasers is longer than their pulse length. An event near the fiber generates an acoustic wave that affects the optical fiber by changing the phases of the backscattering centers. An analysis of such signals can reveal their impact on the sensor and monitor located near fiber objects.

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Long-fiber-reinforced thermoplastic

Long-fiber-reinforced thermoplastic (LFRTs) is a type of easily mouldable thermoplastic used to create a variety of components used primarily in the automotive industry. LFRTs are one of the fastest growing categories in thermoplastic technologies. Leading this expansion is one of the oldest forms, glass mat thermoplastic (GMT) and two of the segment's newest: precompounded (pelletized) LFRTs (long-fiber-reinforced thermoplastics), also known as LFTs, and inline compounded (ILC) or direct LFTs (D-LFTs). LFRTs differ from the composite structures used in the aerospace industry for components such as aircraft parts. The fibers in LFRTs are relatively short (6.35 mm/0.25 in. or greater) compared to the fibres contained in composite aircraft components. High performance composites usually contain fibers as long as the component itself (6 metres or longer). Their structural properties and low cost per part have enabled LFRTs to replace metal parts in the automotive industry. In addition, some new organic fibers can even be recyclable. With the independence of choosing the reinforcement from a wide range of fibers and the matrix from a wide range of thermoplastics polymer in the LFRTs, its property can be changed according to customer needs. LFRTs have become an increasingly valuable and popular part of building envelope components such as windows and doors.

Comparison with Other Fiber Optic Distributed Sensing Techniques 2

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Fiber

As with the Pygora breed, the fiber is classified into three types, A, B and C, depending on the length and type of the fibers.:358 Type A is Angora-type mohair, long and lustrous; type B is "cashgora", which combines mohair with cashmere-type undercoat and is of medium length; type C is like cashmere and is shorter.:49

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Have You Ever Used Tape Storage
As long as it is related to technology, "never say impossible" to technologies that seem to be outdated. When one day there is a "change of Dynasty", it may "make a comeback", or even become more usable or attractive, and become a good way to solve new problems.It can't be true? Are we stepping into the time machine now? Everyone knows that "tape" is... "Antique" technology! Don't all storage applications now use solid state disk (SSD) or hard disk drive (HDD) memory?The answer is not exactly right. In a recent article in the Wall Street Journal - "companies look to an old technology to protect against new threats", it is mentioned that many companies store data on tape again in case. This is not just an anecdote: there are some powerful data certificates in the market, the unit shipment of tape has increased, and more and more data is stored on tape.Although tape is not as easy to access as SSD or HDD memory, this attribute is also an advantage, especially when the "worst" situation occurs, it can show its strong and slow recovery mechanism. In addition, because tapes cannot be "online", hackers are unlikely to access them. The Wall Street Journal article pointed out that "the government, financial services companies, medical insurance companies and other regulated industries still use tape as a backup system for digital records. Now, some companies are turning back to tape technology because hackers are becoming more and more powerful in penetrating their preventive measures."If you still stick to the old idea that tape is a large volume of disk, it is really out of date; In fact, there are only some archive disks left, and we are lucky to find the playback device. At present, the tape industry has standardized on the easy-to-use tape cartridge, so that it can play and rewind through the manipulator under the large array configuration of the tape drive "field", as shown in the table. Even with the assistance of the international tape storage Council, some standards began to appear, focusing on defining overall dimensions and formats, etc. Tape storage Council is an industry organization established in 2012 to promote the technological innovation and application of tape storage industry.Modern tape drives (lto-7) can be equipped with backup and restore performance up to 750mb / S (2.7tb / HR), and each cartridge can support 15tb of data (source: quantum Corp.)Two key criteria: ltfs and LTOThe two key standards of tape technology are linear tape file system (ltfs) - which can make tape "almost" like HDD; And the linear tape open (LTO) standard developed in the late 1990s as an alternative to the then proprietary tape format. In the "technology advances promote tape to new markets" report recently published by the tape storage Council, it briefly describes the latest progress and application of tape technology.The comparison of tape with SDD or HDD is not limited to security; The tape storage Council believes that reliability and bit error rate (BER) also deserve attention. As shown in the figure below, the quantum lto-7 has an error every 1019 bits, while the HDD of the top gauge has an average error of 1016 bits. The difference of up to three orders of magnitude is really impressive. Other performance comparisons between tape and HDD are also noteworthy, and may even break the traditional myth.Comparing different data storage media shows that high-performance tape provides the lowest bit error rate, even 1000 times better than other technologies (source: tape storage Council)The tape system is also a miniature analog signal and wireless transmission link, even if the stored data is digital. In many ways, it is similar to RF channel, except that RF is replaced by magnetic field for energy transmission. In addition, it also has all the problems that affect the RF "wireless" link, such as jitter, signal-to-noise ratio (SNR), inter symbol interference, signal strength change and so on.Of course, the reading channel starts with the analog preamplifier (installed as close to the reading head itself as possible) and the variable gain amplifier (VGA). But that is only the beginning of analog signal processing, because advanced tape systems use read channels with partial response, maximum likelihood (PRML) signal detection circuits to maximize the chance of successful and zero error data restoration (although the channel is irregular). Although the physical scale may be much smaller than the RF link, the signal path blocks are similar.There seems to be a development element contrary to "going back to the future". Tape is not only the first high-density data storage mechanism (much earlier than HDD), but also an early "amateur" - personal computers (PCS) use Philips Consumer audio tape cartridges as low-cost storage media (of course, low-speed and low-capacity), load the operating system and store programs and data through the "boot loader". Today, tape is not cost-effective for hobbies and business applications, especially high-density HDDs, which are more affordable and random access, but potential tape technology still plays a vital role - and even the trend of "comeback".As usual, I would like to reiterate once again: as long as it is related to technology, it is "never impossible" to say what seems to be outdated technology. When one day the "dynasty changes", it may "reappear in the Jianghu", or even become more usable or attractive, and become a good way to solve new problems.Have you used advanced LTO / ltfs tape technology? Or have you ever used tape storage before?
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