BMS INSTITUTE OF TECHNOLOGY
Avalahalli, Doddabalapur Road,
Bangalore-64

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

TERAHERTZ TECHNOLOGY AND ITS APPLICATIONS
Subject Title: Microwaves & Radar
Name: Hamsini Poovamma B S USN: 1BY12EC014
Batch & Sem: V A
Staff Incharge: Mrs Rashmi N, Asst.Professor Dept. of Electronics and Communication BMS Institute of Technology

Signature of Student Signature of Faculty Signature of HOD
TERAHERTZ TECHNOLOGY AND ITS APPLICATIONS

Terahertz (THz) is Far-Infrared radiation located between microwaves and infrared in the electromagnetic spectrum. It is low-energy, non-ionizing radiation which can penetrate many non-polar, non-conducting materials such as clothing, paper, masonry or plastic. They can penetrate fog and clouds. Their wavelength corresponds revealingly with bio molecular vibrations. Terahertz radiation, also known as t-rays, has wavelength of 3-100 cm-1.

Terahertz radiation was discovered in 1896. Unless they're at a temperature of absolute zero (−273.16°C), all objects, animate and inanimate, give off terahertz radiation (called T-rays), the heat from molecular vibrations. No one knew how to make T-rays bright enough to actually use in the everyday world. Attempts with semiconductors produced only wimpy T-rays, 1/2,000th of a watt at most. One way to make terahertz radiation is based on an ultra-fast laser.
The THz band were initially being referred as “terahertz gap” due to two reasons. Firstly, there were not any proper and affordable signal sources, which are capable of transmitting signals in those frequencies, and secondly the neighbour frequencies around this frequency range are being used in electronics and optical technologies. Recently, with the developments in silicon CMOS signal sources having sufficient transmission energy at those frequencies, and the emergence of front-end circuits, the interest in usage of THz band for communications has increased. In addition, since the best way to increase peak data rate is to increase the bandwidth, the studies on THz waves and communications have been accelerated. For this purpose, 60 GHz range has been chosen as the first target. ECMA-387, IEEE 802.15.3c and IEEE 802.11ad standards all have been developed for this frequency band.
Sources of terahertz radiation * Electronic & Electromagnetic sources, free electron lasers * Optical generation and laser-driven sources * Quantum cascade lasers Emerging applications of Terahertz Radiation * Medicine & Biological * Civilian Security * Defence * Manufacturing * Wireless communications * Research, environmental and space science

Medical imaging:
Terahertz radiation is non-ionizing, and thus is not expected to damage tissues and DNA, unlike X-rays. Some frequencies of terahertz radiation can penetrate several millimeters of tissue with low water content (e.g. fatty tissue) and reflect back. Terahertz radiation can also detect differences in water content and density of a tissue. Such methods could allow effective detection of epithelial cancer with a safer and less invasive or painful system using imaging.
Some frequencies of terahertz radiation can be used for 3D imaging of teeth and may be more accurate and safer than conventional X-ray imaging in dentistry.
Security:
Terahertz radiation can penetrate fabrics and plastics, so it can be used in surveillance, such as security screening, to uncover concealed weapons on a person, remotely. This is of particular interest because many materials of interest have unique spectral "fingerprints" in the terahertz range. This offers the possibility to combine spectral identification with imaging. Passive detection of Terahertz signatures avoid the bodily privacy concerns of other detection by being targeted to a very specific range of materials and objects.
Scientific use and imaging:
Spectroscopy in terahertz radiation could provide novel information in chemistry and biochemistry.
Recently developed methods of THz time-domain spectroscopy (THz TDS) and THz tomography have been shown to be able to perform measurements on, and obtain images of, samples which are opaque in the visible and near-infrared regions of the spectrum. The utility of THz-TDS is limited when the sample is very thin, or has a low absorbance, since it is very difficult to distinguish changes in the THz pulse caused by the sample from those caused by long term fluctuations in the driving laser source or experiment. However, THz-TDS produces radiation that is both coherent and spectrally broad, so such images can contain far more information than a conventional image formed with a single-frequency source.
Terahertz radiation could let art historians see murals hidden beneath coats of plaster or paint in centuries-old building, without harming the artwork.
Communication:
Potential uses exist in high-altitude telecommunications, above altitudes where water vapor causes signal absorption: aircraft to satellite, or satellite to satellite.
Manufacturing:
Many possible uses of terahertz sensing and imaging are proposed in manufacturing, quality control, and process monitoring. These generally exploit the traits of plastics and cardboard being transparent to terahertz radiation, making it possible to inspect packaged goods.
Despite many valuable useful applications, the adoption of terahertz waves has been slow because of the limited output power from currently available sources. Terahertz waves lie between the optical and the microwave spectrum and cannot be efficiently generated by either scaling down optical sources like lasers or scaling up conventional microwave sources such as klystrons. Current moderate size terahertz sources can only generate a few mill watts of average power and hence most require expensive and complicated schemes for detection.
Therefore, the lack of commercially available sources and detector for this frequency region, other than the Advanced Photonix, T-4000, and the Bridge12 gyrotron, lead to the "Terahertz Gap". ‘Li-Fi’, is the commonly used nomenclature for bi-directional, networked wireless communications using visible light, as opposed to traditional radio frequencies. Visible Light Communication (VLC) is essentially Wi-Fi — but using terahertz radiation (light) instead of microwaves (Wi-Fi). Instead of oscillating a Wi-Fi transmitter, VLC oscillates an LED bulb — and, on the receiving end there’s a photo detector instead of an antenna.
It is a 5G visible light communication system that uses light from light-emitting diodes (LEDs) as a medium to deliver networked, mobile, high-speed communication in a similar manner as Wi-Fi.
With Li-Fi, we can connect to the internet simply by being within range of an LED beam, or we could conceivably transmit data using the car headlights. The ramifications of this are huge, especially with the internet of things in full swing and the much mooted spectrum crunch expected to bite increasingly hard in the coming years. Li-Fi has the advantage of being useful in electromagnetic sensitive areas such as in aircraft cabins, hospitals and nuclear power plants without causing electromagnetic interference.
LTE (Long-Term Evolution), commonly marketed as 4G LTE, is a standard for wireless communication of high-speed data for mobile phones and data terminals. It is based on the GSM/EDGE and UMTS/HSPA network technologies, increasing the capacity and speed using a different radio interface together with core network improvements.
As opposed to earlier generations, a 4G system does not support traditional circuit-switched telephony service, but all-Internet Protocol (IP) based communication such as IP telephony. The spread spectrum radio technology used in 3G systems, is abandoned in all 4G candidate systems and replaced by OFDMA multi-carrier transmission and other frequency-domain equalization (FDE) schemes, making it possible to transfer very high bit rates despite extensive multi-path radio propagation (echoes).
The peak bit rate is further improved by smart antenna arrays for multiple-input multiple-output (MIMO) communications.