電網(wǎng)絡(luò)經(jīng)典補充tera hz

1、Title:Tera Hz RadiationsBy Idris KhanTera HzIn physics, terahertz radiation, also called submillimeter radiation, terahertz waves, tremendously high frequency, T-rays, T-waves, T-light, T-lux, or THz, consists of electromagnetic waves within the ITU-designated band of frequencies from 0.3 to 3 terah

2、ertz Wavelengths of radiation in the Terahertz band correspondingly range from 1 mm to 0.1 mm (or 100 m). Because terahertz radiation begins at a wavelength of one millimeter and proceeds into shorter wavelengths, it is sometimes known as the submillimeter band, and its radiation as submillimeter wa

3、ves, especially in astronomy.Tera Hz Radiation SpectrumTerahertz radiation falls in between infrared radiation and microwave radiation in the electromagnetic spectrum, and it shares some properties with each of these. Like infrared and microwave radiation, terahertz radiation travels in a line of si

4、ght and is non-ionizing. Like microwave radiation, terahertz radiation can penetrate a wide variety of non-conducting materials.NaturalTerahertz radiation is emitted as part of the black-body radiation from anything with temperatures greater than about 10 kelvin. While this thermal emission is very

5、weak, observations at these frequencies are important for characterizing the cold 1020K dust in the interstellar medium in the Milky Way galaxy, and in distant starburst galaxies. Telescopes operating in this band include the James Clerk Maxwell Telescope, the Caltech Submillimeter Observatory and t

6、he Submillimeter Array at the Mauna Kea Observatory in Hawaii, the BLAST balloon borne telescope, the Herschel Space Observatory, and the Heinrich Hertz Submillimeter Telescope at the Mount Graham International Observatory in Arizona. The Atacama Large Millimeter Array, under construction, will oper

7、ate in the submillimeter range. The opacity of the Earths atmosphere to submillimeter radiation restricts these observatories to very high altitude sites, or to space.SourcesArtificialthe gyrotronthe backward wave oscillator (BWO)the far infrared laser (FIR laser)Schottky diode multipliers 3varactor

8、 (varicap) multipliersquantum cascade laser4567the free electron laser (FEL)synchrotron light sourcesphotomixing sourcessingle-cycle sources used in terahertz time domain spectroscopy such as photoconductive, surface field, photo-Dember and optical rectification emittersHistoryIn 2012, a source was

9、announced that used a resonant tunneling diode (RTD) to produce waves in the terahertz band at 542 GHz,The first images generated using terahertz radiation date from the 1960s; however, in 1995, images generated using terahertz time-domain spectroscopy generated a great deal of interest, and sparked

10、 a rapid growth in the field of terahertz science and technology. This excitement, along with the associated coining of the term T-rays, even showed up in a contemporary novel by Tom Clancy.In 2002 the European Space Agency (ESA) Star Tiger team,9 based at the Rutherford Appleton Laboratory (Oxfords

11、hire, UK), produced the first passive terahertz image of a hand.10 By 2004, ThruVision Ltd, a spin-out from the Council for the Central Laboratory of the Research Councils (CCLRC) Rutherford Appleton Laboratory, had demonstrated the worlds first compact THz camera for security screening applications

12、. The prototype system successfully imaged guns and explosives concealed under clothingIn mid-2007, scientists at the U.S. Department of Energys Argonne National Laboratory, along with collaborators in Turkey and Japan, announced the creation of a compact device that can lead to portable, battery-op

13、erated sources of T-rays, or terahertz radiation. The group was led by Ulrich Welp of Argonnes Materials Science Division.12 This new T-ray source uses high-temperature superconducting crystals grown at the University of Tsukuba, Japan. These crystals comprise stacks of Josephson junctions that exhi

14、bit a unique electrical property: When an external voltage is applied, an alternating current will flow back and forth across the junctions at a frequency proportional to the strength of the voltage; this phenomenon is known as the Josephson effect. These alternating currents then produce electromag

15、netic fields whose frequency is tuned by the applied voltage. Even a small voltage around two millivolts per junction can induce frequencies in the terahertz range, according to Welp.In 2008, engineers at Harvard University demonstrated that room temperature emission of several hundred nanowatts of

16、coherent terahertz radiation could be achieved with a semiconductor source. THz radiation was generated by nonlinear mixing of two modes in a mid-infrared quantum cascade laser. Until then, sources had required cryogenic cooling, greatly limiting their use in everyday applications.13In 2009, it was

17、shown that T-waves are produced when unpeeling adhesive tape. The observed spectrum of this terahertz radiation exhibits a peak at 2 THz and a broader peak at 18 THz. The radiation is not polarized. The mechanism of terahertz radiation is tribocharging of the adhesive tape and subsequent In 2011, Ja

18、panese electronic parts maker Rohm and a research team at Osaka University produced a chip capable of transmitting 1.5 Gbit/s using terahertz radiation.15In 2013, researchers at Georgia Institute of Technologys Broadband Wireless Networking Laboratory and the Polytechnic University of Catalonia deve

19、loped a method to create a graphene antenna: an antenna that would be shaped into graphene strips from 10 to 100 nanometers wide and one micrometer long. Such an antenna would broadcast in the terahertz frequency rangeApplications:1)Pharmaceutical IndustryTeraView Pharma Innovations team has demonst

20、rated terahertz instruments produce 3D coating thickness maps for multiple coating layers and structural features models allowing better understanding and control of product scale up and manufacture. The analytical performance of 3D TPI measurements is equivalent or better than traditional technique

21、sSolid Dosage-forms Analysis of Tablets with Terahertz ImagingCross section of tablet with terahertz imaging Pharmaceutical tablet coatings control the release of active pharmaceutical ingredients (API) to ensure the bioavailability, safety and efficacy of the drug product. These functions may be se

22、verely compromised if a coating is non-uniform or has defects. From this standpoint, it is critical to assess coating integrity in coated tablets, both within a single tablet and across an entire batch to ensure product quality and monitor and control coating operations.Terahertz Pulsed Imaging (TPI

23、) provides the ability to non-destructively and rapidly analyze the coating layer thickness and quality of coated pharmaceutical tablets. Because it is nondestructive, tablets can be re-examined at later times to monitor coating stability or used for further functional studies with prior knowledge o

24、f the coating uniformity.Medical Imaging1) The potential of terahertz pulsed imaging (TPI) in medical markets is huge. Due in part to its ability to recognize spectral fingerprints, TPI provides good contrast between different types of soft tissue, and is a sensitive means of detecting the degree of

25、 water content as well as other markers of cancer and other diseases.Terahertz Detection Of Skin, Mouth And Epithelial CancersTPI is non-ionising and less hazardous to use than X-ray and the power levels are generally lower than background terahertz radiation encountered in everyday life. It has the

26、 potential for:Earlier detection of epithelial tumorsReduced treatment costsLower morbidity ratesSince 1999, TeraView has pioneered the use of terahertz waves for the detection of skin and other surface cancers. Terahertz waves are a safe, non-ionising form of electromagnetic radiation. As such they

27、 are ideal for using in the detection of cancer.Terahertz for Homeland Security and DefenseThere are applications of terahertz technology in defense and homeland security since its inception. Tera Hz technology can safely, non-invasively and quickly image through different types of clothing and othe

28、r concealment and confusion materialsDetection of explosivesExplosive materials absorb THz light strongly at certain terahertz frequencies but not at others, and this terahertz fingerprint can be used to identify an explosive, and distinguish it from clothing or other inert materials. Because clothi

29、ng is transparent at terahertz frequencies, the THz light can pass through several layers, including common garments and shoes.Terahertz for Personnel ScreeningThe imaging ability of the technology has led to proof of principle demonstrations of shoe scanning, as well as the worlds first practical t

30、erahertz system, based on a hand held wand that operates much like a metal detector, but capable of detecting non metallic weapons and certain explosives. Terahertz Detection of Noxious GasesTerahertz Continuous Wave (CW) spectroscopy has been shown to give superior resolution when compared to infra

31、 red or ion mobility type techniques. This superiority combined with the speed of analysis enables the detection of noxious or dangerous gases to be fully automated, whilst maintaining a very low false alarms level.Terahertz for Security Mail ScreeningFor mail screening terahertz can be used for two

32、 different applications. In the example below, text was applied to paper using pencil, ballpoint and a laser printer. The pages were then placed in an envelope and scanned using TPI. The terahertz images obtained are shown below. Whichever way the text was generated, TPI was able to “read” the scrip

33、t from outside the package. In addition to mail screening, this technology can be used to read the contents of valuable or delicate documents without having to unfold or open the item where damage might occur.In other mail screening applications, the aim is to identify materials or substances contai

34、ned in a letter. These substances may be hazardous and cause harm to the recipient or could also be controlled substances being sent through the mail system. In either case, TPI is able to detect the presence of such materials. An added benefit of this technology is that most materials have distinct

35、 spectral fingerprints in the terahertz region. So the presence of the substance can be detected using TPI and terahertz spectroscopy can be used to determine its chemical identity.Terahertz for the Semiconductor IndustryTerahertz waves can be used to quickly image cracks and defects at depth within

36、 silicon and hence has the potential to substantially improve process yields and reduce waste.Terahertz for Car Paint and Automotive Coatings AnalysisTerahertz technology has major advantages over existing commercially available car paint thickness meters and monitors because it allows non-contact rapid characterization of painting defects. Furthermore, 3D TPI provides the unique ability to identify the presence and to investigate the origins of defects in multi-layered painted car panels with both metallic and plastic (sheet-moulded compo