Applications Of Terahertz Waves Research Articles

Illegal food chemicals sensing with photonic crystal fiber sensor in the terahertz spectrum

The method by which a photonic crystal is manufactured fiber is detailed throughout the subsequent undertaking, containing a hexahedron core and hazardous dietary additives using a hexagonal cladding. Saccharine, sorbitol, and butyl acetate are used as analytes for sensing purposes. The sensor contains five tiers of circular ventilation holes within the hexagonal framework, as well as two tiers of hexahedron circles in the central area. FEM (Finite Element Method) is implemented in the sensor design of COMSOL software version 4.2. We noticed the response of the PCF sensor to the specific substances. We examined key optical metrics encompassing specifications including V-parameter, Relational sensitivity, effective refractive index, and power fraction to assess the suitability of the sensor for precisely and effectively detecting various food additives. The revised model attains sensitivity values of 90.10%, 91.30%, and 86.60%, respectively, at a frequency of 1 THz, the identification of saccharine (1.550 in the index of refraction), sorbitol (1.375 in the index of refraction), and butyl acetate (1.394 in the index of refraction) is performed. Furthermore, the compositions of saccharine (1.550 in the index of refraction), sorbitol (1.375 in the index of refraction), and butyl acetate (1.394 in the index of refraction) demonstrate losses from confinement of 6.15 × 10−8 dB/m, 7.25 × 10−8 dB/m, and 6.35 × 10−8 dB/m, which are comparatively minimal, and 0.0235 cm−1 is an insignificant effective material loss. These structures are studied at the terahertz frequency spectrum. Owing to its superior wave-guiding properties, this proposed sensor can be used for polarization-preserving terahertz wave applications and detecting dangerous food additives. Besides, because of simple fabrication, high sensitivity, and low confinement loss, we strongly believe this optimized geometrical structure will contribute to real-life applications that lead to safer food and support a circular economy in developing countries.

Metasurface-based sensor with terahertz molecular fingerprint enhancement in trace additives identification

Terahertz (THz) wave has gained considerable interest in biosensing with its unique spectral fingerprint characteristics. However, limited sensitivity confines its applications in trace-amount identification. In this article, a magnetic dipole metamaterial for strengthening molecular fingerprint in virtue of angle-scanning strategy is proposed, which is carefully designed by elaborately arranging symmetric condition of the dipole structures. The physical mechanism is elucidated by the finite-difference time-domain method. In virtue of manipulating the incident angle, the signal of molecular fingerprint is outstandingly elevated. Consequently, three kinds of food additives including azodicarbonamide, sorbic acid and melamine can be simultaneously detected, and the corresponding identification limits are as low as 1.65 μgcm−2 , 1.20 μgcm−2 and 1.66 μgcm−2 , respectively. Our work offers a new train of thought in identifying trace-amount food additives and paves the way for more practical applications of THz wave in food industry.

Application of Terahertz Radiation in Non-Destructive Testing of Military-Designated Composite Materials

The non-destructive testing methods (NDT) are gaining significant attention due to their ability to monitor the objects structure without causing their damage. In recent years, studies focused on NDT have been directed towards imaging with the use of the terahertz (THz) waves. The presented study describes terahertz imaging-based NDT method and testing results on selected military-designated materials with intentionally introduced defects. The main aim of the work was to clearly detect various discontinuities in materials interior and thus, to show the possibilities of the newly developed terahertz-based testing method in transmission mode. The results confirmed high applicability of THz waves for monitoring various materials where each implemented flaw was easily distinguished. Therefore, the presented method looks promising for real applications in everyday practice.

Focused THz wave from a spintronic terahertz Fresnel Zone Plate emitter

Spintronic terahertz emitters (STEs) with the feature of low cost and high performance are considered as one of the most potential terahertz (THz) sources for the future applications of THz waves. At present, the demand for a STE with some additional functions apart from the generation of a THz wave only has become more and more urgent. THz lenses, as a wavefront control device, which is one of the indispensable elements in a THz system, are widely used in THz focus and image systems. However, the common THz lenses are bulky and costly and not applicable for some miniaturization and integration THz systems. Based on two nonferromagnetic film with comparable magnitude of spin Hall angle, but with opposite sign, a binary-phase spintronic terahertz Fresnel Zone Plate emitter (ST-FZPE) is proposed in this paper. Compared with reported THz emitters with a FZP structure, the ST-FZPE is low cost, easy to be fabricated and has a higher efficiency of directing emission focused THz wave. As a planar optical element, the ST-FZPE has tremendous significance to realize integration and miniaturization of THz devices and systems, and it has potential applications in the field of THz bio-sensing, THz imaging and THz communication in the future.

Terahertz polarization detection based on the mode analysis of longitudinally polarized vortices

Polarization detection of terahertz waves is essential for applications of terahertz waves in communication, imaging, and other fields. Here, we propose a novel terahertz polarization detection approach via the mode analysis of transmitted longitudinally polarized vortex field. By finely designing the phase profiles of the proposed all-silicon metasurface, we establish a connection between the generated longitudinally polarized vortices and the polarization parameters of the incident field. Complete polarization parameters are obtained by analyzing the intensity, phase, and mode purity of the longitudinally polarized vortex field. The comparisons between the detected polarization states and the incident states prove the accuracy of the proposed metasurface for polarization detection. Such metasurface polarization detection scheme may further promote the application of terahertz technology.

Pulse Burst Multiwavelength Terahertz-Wave Spectroscopic Measurement Using Parametric Wavelength Conversion

In this study, we developed a multi-wavelength spectroscopic measurement system using a pulse burst-pumped injection-seeded terahertz (THz)-wave parametric generator (is-TPG). Real-time spectroscopy using multi-wavelength simultaneous generation has been demonstrated; however, the ability to make quantitative measurements with this method has been limited by the gain competition between wavelengths. In this study, we divided the pump beam into multiple paths and created pulse bursts with nanosecond intervals via spatial delays. Quasi-multi-wavelength simultaneous generation was achieved by generating different THz wavelengths with each pulse; in principle, this is equal to repetitive single-wavelength generation. The gain competition between multi-wavelengths was suppressed compared to the multi-wavelength is-TPG pumped by a single pump pulse. Pulse-burst pumping improved the “quantitativeness” of real-time spectroscopic measurements using an is-TPG and is expected to expand the scope of THz wave applications.

Millimetre wave antenna for biomedical applications-a review

Terahertz represents the portion of electromagnetic wave between the microwave and IR region. Recent research has been focused on the application of Terahertz waves in biomedical applications such as cancer detection. The current diagnostic methods in cancer treatment involve imaging to MRI and biopsy. Due to the low photon energy that terahertz possess, there are no health threats caused in contrast to traditional methods. Cancer cells can be detected by monitoring the blood supply to the affected tissues and water level in the local tissues. This can be diagnosed using Terahertz imaging. THz radiation can be generated and detected using various commercialized systems. On analysis of various literatures, it is observed that Meta material antennas will be the suitable candidate to enhance the existing terahertz spectroscopy techniques since it has better focusing capabilities. This paper reviews the various implementation techniques of an antenna in THz range. The design and properties of the antenna are also investigated.

Terahertz Schottky Barrier Diodes Based on Aligned Carbon Nanotube Arrays

Carbon nanotubes (CNTs) with superior electrical characteristics are among the most promising candidate materials for constructing millimeter wave and terahertz wave electronic devices. However, the reported Schottky barrier diodes (SBDs) based on CNTs usually exhibited high series resistance and severe mismatch to lower impedance external circuits, which limits the devices for high frequency applications. In this work, CNT SBDs of lateral structure with a rectify current density of -0.78 mA/μm and a short circuit current responsivity of 6.8 A/W are demonstrated based on aligned carbon nanotube arrays (A-CNTs) with high-density and high-semiconducting purity on a quartz substrate. The A-CNT SBD with a width of 10 μm and an L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ch</sub> of 50 nm under zero bias exhibits an ultra-low intrinsic capacitance of 2.5 fF and an intrinsic cutoff frequency <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> of up to 840 GHz, which suggests that CNT-based SBDs are promising for millimeter wave and terahertz wave applications.

High stability with low polarization and confinement loss based new structure of photonic crystal fiber waveguide profile

Abstract Nowadays ethanol is broadly used chemical item in various industrial purpose. So, detection of this organic chemical has become very important task in industrial basis. In this paper, a hexagonal core PCF has constructed in which silica is used as base material. A finite element method is applied and mesh analysis has been done for investigating boundary conditions of proposed PCF sensor. After simulation, 59.48 % sensitivity and an ignorable loss of confinement which is 8·956020 × 10−13 cm−1 at 2.5 THz frequency has been gained. Focusing on easy construction of fiber, conventional fabrication procedures are attainable. Having satisfactory waveguiding attributes, the proposed sensor can be applicable effectively for sensing ethanol and also polarization-based applications of terahertz waves.

Terahertz shaping technology based on coherent beam combining

The generation of terahertz (THz) waves by focusing a femtosecond pulsed laser beam at a distance is able to overcome the strong absorption properties of air and has rapidly attracted the attention of industry. However, the poor directionality of the THz wave radiation generated by this method is not conducive to THz wave applications. By controlling the morphology of the ultrafast laser-excited plasma filament and its electron density distribution through coherent beam combining technology, we achieve direct THz beam shaping and are able to obtain THz wave radiation of Gaussian or arbitrary transverse distribution. The novel experimental approach proposed in this paper opens up the research field of direct THz wave shaping using plasma. Moreover, it innovates multi-parameter convergence algorithms and, by doing so, has the potential to find beam patterns with higher energy conversion efficiency and break the energy limit of THz waves emitted by lasers at high power.

THz Systems Exploiting Photonics and Communications Technologies

Terahertz (THz) systems open up the possibility of new applications of electromagnetic waves. Enormous bandwidths up to several terahertz enable the development of powerful spectroscopy systems that can provide insights into the structure and material of objects with micrometer resolution. New high power and compact THz time-domain spectroscopy (TDS) systems will be presented. The wide bandwidth also enables high-resolution imaging under far-field conditions to analyze arbitrary objects from a distance. In addition, a near-field system-on-a-chip imaging system is presented that achieves a resolution of 10 μm. Additionally, the application of terahertz waves presents challenges due to the low transmit power of the sources, high attenuation in free space, and the high noise figures of the receivers. These challenges can be overcome by antennas with high gain. Since - depending on the application - spatial scanning or focusing in a time-varying direction is required, beam steering is an essential component of many THz systems. In terms of communications, terahertz carrier frequencies offer wide bandwidths, enabling correspondingly high data rates of 100 Gbit/s and more. As a result, the frequency bands between 250 GHz and 450 GHz have already been identified and/or allocated for communication services and are being discussed as a component of 6G mobile communications. Concepts and demonstrations for 6G terahertz mobile communications will be presented. The high bandwidth of terahertz waves can also be used for high-accuracy indoor localization.

Ultrafast Optomechanical Terahertz Modulators Based on Stretchable Carbon Nanotube Thin Films

For terahertz wave applications, tunable and rapid modulation is highly required. When studied by means of optical pump–terahertz probe spectroscopy, single-walled carbon nanotube (SWCNT) thin films demonstrated ultrafast carrier recombination lifetimes with a high relative change in the signal under optical excitation, making them promising candidates for high-speed modulators. Here, combination of SWCNT thin films and stretchable substrates facilitated studies of the SWCNT mechanical properties under strain and enabled the development of a new type of an optomechanical modulator. By applying a certain strain to the SWCNT films, the effective sheet conductance and therefore modulation depth can be fine-tuned to optimize the designed modulator. Modulators exhibited a photoconductivity change of approximately 2 times of magnitude under the strain because of the structural modification in the SWCNT network. Stretching was used to control the terahertz signal with a modulation depth of around 100% without strain and 65% at a high strain operation of 40%. The sensitivity of modulators to beam polarization is also shown, which might also come in handy for the design of a stretchable polarizer. Our results give a fundamental grounding for the design of high-sensitivity stretchable devices based on SWCNT films.

Graphene-based terahertz reconfigurable printed ridge gap waveguide structure

Graphene-based microwave devices have enabled reconfigurability, thus paving the way to the realization of flexible wireless terahertz systems with featured performances. Despite great progress in the development of graphene-based terahertz devices in the literature, high insertion loss and wide tunable range are still significant challenges at such high frequencies. In this work, we introduce the use of graphene to implement a reconfigurable printed ridge gap waveguide (RPRGW) structure over the terahertz frequency range for the first time. This guiding structure is suitable for both millimeter and terahertz wave applications due to its supporting quasi-TEM mode, which exhibits low dispersion compared to other traditional guiding structures. The presented solution is featured with low loss as the signal propagates in a lossless air gap, which is separated from the lossy graphene elements responsible for the reconfigurable behavior. In addition, this guiding structure is deployed to implement a tunable RPPGW power divider as an application example for the proposed structure.

Broadband generation of abruptly autofocusing terahertz ring-Airy beams with all-silicon metasurface

Abruptly autofocusing terahertz (THz) ring-Airy beam has been generated by transmissive plasmonic metasurface at a single frequency in the earlier work. However, the transmission efficiency of it is low. Based on the waveguide effect, a design strategy for broadband generation of THz ring-Airy beams with transmissive all-silicon metasurface is proposed in this paper, which has an improved transmission efficiency and is more favorable in fabrication. Under the linearly polarized plane wave incidence, the amplitude and phase of the cross-polarized transmitted beam can be simultaneously modulated by controlling the rotation angles of the identical rectangular silicon pillars arranged on the silicon substrate. A polarization-independent antireflection square silicon pillar array is also proposed to be patterned at the other side of the substrate. The metasurface promises a working bandwidth from 2.12 to 2.72 THz with the overall transmission efficiency being over 51.18% (the highest transmission efficiency is up to 77.57% at 2.52 THz). The peak intensity positions of the generated beam during the propagation follow a parabolic trajectory. For the generated ring-Airy beam, the focal length is positively proportional to the frequency, while the abruptly autofocusing property and full width at half maximum (FWHM) of the focus are positively and negatively related with the frequency, respectively. This work can be expected to facilitate the applications of terahertz wave in biomedicine and manipulation of particles.

Beam steerable terahertz antenna based on VO&lt;sub&gt;2&lt;/sub&gt;

To realize the diversified applications of terahertz wave, a new method to realize 2-bit (4 states) coding metasurface with only two hybrid units is proposed, which combines the phase transition characteristics of VO&lt;sub&gt;2&lt;/sub&gt; and is different from the traditional metasurface. The metal wire threaded through the patch makes single-line control possible. The method of preparing the VO&lt;sub&gt;2&lt;/sub&gt; thin film and the voltage control mechanism make the design more practical. The highlight of this design is that the fixed structure array can encode different state sequences and then tune the reflected beam. On this basis, a visual design is carried out for the calculation of the coding metasurface array antenna by MATLAB. The state sequence and radiation results are predicted by actively setting the operating frequency, beam deflection angle, etc., so as to achieve active adjustment. The system does not limit the unit structure and is universal to all arrays that meet the coding conditions. In addition, a deep neural network is introduced into the array arrangement, and the structure sequence is predicted by algorithm training and verified by numerical calculation and full-wave simulation. The results show that the proposed method is effective in beam deflection angle and structure arrangement. This study presents a new way of actively and flexibly controlling terahertz waves, which has potential applications in terahertz imaging, phase-controlled radar, communication and other fields.

Nano-printing technology based double-spiral terahertz tunable metasurface

Electromagnetic devices made of artificially constructed metasurfaces can achieve filtering, modulation, sensing, and detection functions in the terahertz frequency band, which is essential for the applications of terahertz waves in the fields of communication and imaging. We design and prepare a flexible and transparent double spiral metasurface based on nano-printing technology, and use the metasurface to construct a rotating tunable filter, which can achieve regular tuning of the terahertz wave transmittance by rotating the metasurface. After rotating 90°, the transmittance at 0.52 THz increases from 8% to 67%, and the transmittance at 0.92 THz decreases from 68% to 3%, thus realizing active tuning with modulation depth greater than 88%. Moreover, the proposed nano-printing metasurfaces have excellent properties of ultra-thinness, flexibility, and visible light transparency, which are conducive to the miniaturization, light-weight and large-area preparation of terahertz tunable devices.

A Review of Feasible Applications of THz Waves in Medical Diagnostics and Treatments.

Introduction: Terahertz (THz) waves with frequencies in the range of 0.1 to 10 THz are electromagnetic radiation with growing applications in various fields of science and technology. Attractive features of this radiation have brought out many novel possibilities for medical diagnostics and treatments with considerable advantages compared to other conventional methods. Methods: In this paper, we present a review of more recent reports on practical applications of THz radiation for diagnostic, biosensing and clinical treatments. The review includes the diagnosis of breast, skin, mouth, cervical, lungs, small intestine, prostate, colon, and stomach cancers, the evaluation of biomolecules, the detection of genetic mutations, the determination of burn depth, the diagnosis of tooth decay, diabetes, and emotional-psychological states, the evaluation of corneal water to diagnose visual diseases, and wound healing monitoring. Further, it embraces the use of THz therapy in reducing the size of the tumor, treating skin cancer, and healing burn wounds, cardiovascular disease, corneal epithelium, angina, and THz heating. Results: This review has emphasized the capabilities of THz waves as a novel tool for future clinical diagnostics and treatments. Conclusion: The paper provides a comprehensive understanding of the feasible potential application of THz waves for clinical purposes and its advantages in comparison with other conventional tools.

Superoscillatory metalens for polarization conversion and broadband tight focusing of terahertz waves

For terahertz wave applications, such as medical imaging, space exploration, security inspection etc., the lens is fundamental for use as the optical focusing element. Far-field subdiffraction focusing devices play a special role in such terahertz applications. Metasurfaces can provide complete control over the amplitude, the phase, and the polarization of the optical field. They also show excellent potential in connection to focusing and polarization conversion devices. In the paper, we propose a group of subwavelengh dielectric birefringent meta-atoms that operate in the terahertz range. Over a full coverage of 2π, they can produce a simultaneous integration of the polarization conversion and the phase modulation. Based on the concept of optical superoscillation, a metalens with a numerical aperture (NA = 0.975) is optimized for a wavelength, λ, of 2500 μm. Under the illumination of linearly polarized waves, the broadband polarization conversion, and the sub-wavelength tight focusing, is achievable between the wavelengths 1900 and 2700 μm. Simulation results demonstrate that the spots have sizes over the range 0.418 λ - 0.556 λ, while the sidelobe ratio (SR) is kept at a low intensity level between 14.3% and 16.2%. Importantly, continuous adjustment of the focal spot size is feasible by changing the incident polarization from 0° to 45° with respect to the axis. For incident polarization angles between 75° and 90°, the inner FWHMs of the hollow dark spot are far smaller than the corresponding super-oscillation criterion. Due to these improved performance characteristics, such superoscillatory metalens have wide potential in many terahertz applications. This approach is shown to open a novel avenue for the polarization conversion and the broadband tight focusing of terahertz waves.

Performance analysis of alcohols sensing with optical sensor procedure using circular photonic crystal fiber (C-PCF) in the terahertz regime

In this study, a TOPAS-based optical sensor for detecting alcohols in drinks and liquids, made of circular air holes (CAH) in the cladding and a hexahedron core is suggested here. In addition, COMSOL Multiphysics program for development and analysis of the sensing qualities of a PCF-based sensor using finite element technical as a solution. In the THz frequency band, the described C-PCF structure has an exceptionally high relative sensitivity of 86.60%, 88.70%, and 84.71%, and low confinement losses (CLs) are 5.75 × 10−08, 6.11 × 10−08 dB/m and 5.70 × 10−08 dB/m for three alcohols such as Ethanol (n = 1.354), Butanol (n = 1.399), and Propanol (n = 1.387), respectively at monitoring region of 1 THz. Alcohol is widely used in both the food and beverage sectors and chemical operations. The detection methods of alcohol thus must be accurate, accurate, and reliable. This content modeling and analysis in the terahertz frequency range is a novel TOPAS-based photonic crystal fiber (C-PCF). Moreover, the total power fraction and effective area are also determined in the terahertz frequency range. Due to its excellent waveguiding characteristics, this suggested sensor has the potential to be employed in alcohols detection as well as polarization preserving terahertz wave applications.

A review on teratronics: from present state to future

Teratronics is an interdisciplinary field of Opto-and Microelectronics embracing the important features of high-speed digital signal processing, high-frequency electronics, and optics and photonics. This is one of the significant challenging fields of solid state physics and technology with the new domains of electronics industry and research. This review outlines the different field of application of terahertz wave in security, medical imaging, chemical and biological sensing and highly emerging field of wide-band telecommunications along with the development of active and passive devices. Discussion encompasses from the founding concept of THz electronics to the development and future scopes. Content of this article will also include the new aspects of terahertz technology with their present contenders in the field of security and telecommunication. Dialogue for the newly evolved devices such as nano-ring and disk transistor along with stacked quantum dots systems also included to provide a novel glimpse for deep and underlying fundamental physical mechanism. All these topics will provide a critical supervision for further innovative stages in this field.