Terahertz Applications Research Articles

THz radiation distribution for the identification of infiltrating ductal carcinoma in human breast model: a computational study

With numerous biomedical applications of terahertz (THz) imaging, spectroscopy, and sensing, the THz regime of the spectrum is quickly emerging as an important area of research with the potential to usher in a new era in the healthcare industry. In the medical field, THz radiation has been explored to diagnose and monitor several ailments, including foot diabetes, skin dryness, wounds, and burns. Compared to X-rays, THz waves' phase sensitivity to bodily fluid levels and water results in superior contrast and stronger absorption. This feature makes THz potentially useful for the diagnosis of various malignant tumor forms because cancerous tumors have higher water molecule contents than healthy tissues. The current study presents a computational analysis of a CW-THz point-by-point scanning technique for breast cancer detection. COMSOL multiphysics platform was utilized to create a multilayer three-dimensional breast model containing an irregular-shaped infiltrating ductal carcinoma in the glandular layer. The propagation of the THz radiation in the constructed breast model was simulated based on the radio frequency module and electromagnetic waves in the frequency domain interface. Furthermore, different volumes and locations of the induced tumor were examined. The results demonstrated significant disparities in the acquired electric distribution at different tumor sizes and sites between normal and diseased breasts. The resultant electric field for healthy breast ranged from 1.1 × 10–5 to 0.61 V/m, however, the electric field ranges following tumor addition fluctuate based on its volume and location. Additionally, the position of the THz source and detector array influences the reflected THz signal.

A Graphene Gold Metasurface Inspired Surface Plasmon Resonance Sensor Designed for Terahertz Applications in Sensing and Detection of Heavy Metals in Water

A Graphene Gold Metasurface Inspired Surface Plasmon Resonance Sensor Designed for Terahertz Applications in Sensing and Detection of Heavy Metals in Water

Design of High-Gain Antenna Arrays for Terahertz Applications.

A terahertz band (0.1-10 THz) has the characteristics of rich spectrum resources, high transmission speed, strong penetration, and clear directionality. However, the terahertz signal will suffer serious attenuation and absorption during transmission. Therefore, a terahertz antenna with high gain, high efficiency, and wide bandwidth is an indispensable key component of terahertz wireless systems and has become a research hotspot in the field of antennas. In this paper, a high-gain broadband antenna is presented for terahertz applications. The antenna is a three-layer structure, fed by a grounded coplanar waveguide (GCPW), using polytetrafluoroethylene (PTFE) material as the dielectric substrate, and the metal through-hole of the dielectric substrate forms a substrate-integrated waveguide (SIW) structure. The metal fence structure is introduced to reduce the coupling effect between the radiation patches and increase the radiation bandwidth and gain. The center frequency is 0.6366 THz, the operating bandwidth is 0.61-0.68 THz, the minimum value of the voltage standing wave ratio (VSWR) is 1.00158, and the peak gain is 13.14 dBi. In addition, the performance of the designed antenna with a different isolation structure, the length of the connection line, the height of the substrate, the radius of the through-hole, and the thickness of the patch is also studied.

Comments on “Numerical investigation and circuit analysis of interdigitated photoconductive antenna for terahertz applications”

Comments on “Numerical investigation and circuit analysis of interdigitated photoconductive antenna for terahertz applications”

Terahertz Radiation – the Dawn of a New Information Era

This mini-review article explores the evolution of wireless communication technologies, emphasizing the crucial role played by advancements in information transfer over long distances with minimal errors. Tracing developments from submergible cables to the current 5G technology, the review discusses the potential of 6G, offering insights into the transformative applications it could enable, such as holographic real-time communication and autonomous transport infrastructure. Exploring the applications of Terahertz (THz) frequencies, the article presents the limitations of current wireless speeds and proposes solutions, including the use of spintronic terahertz emitters (STEs) and antiferromagnetic materials, concluding on the challenges and prospects of integrating these technologies into practical applications.

Design and Analysis of Terahertz Antenna for Breast Tumor Detection

In this paper, two different types of rectangular patch antennas are designed for broadband gigahertz and terahertz applications. First, a patch antenna is modeled using PEC for gigahertz applications. Secondly, a patch antenna is modeled using graphene for terahertz applications. Without exposing the patient to ionizing radiations, malignant lesions can be detected by using the dielectric discontinuities in the tissues. The simulation results show a degraded reflection coefficient due to the use of PEC and graphene. Therefore, the reflection coefficient is above -10 dB at 33 GHz and at 2.6 THz and also VSWR is less than 2 dB in both gigahertz and terahertz. The purpose of this work is to develop a simple, low-cost miniaturized mmWave imaging antenna sensor that can be used to detection of breast tumors or cancers in women by monitoring the changes in the antenna’s S11 parameter. The time-domain solver of CST MWS software is used to evaluate the performance of the patch antennas in both gigahertz and terahertz frequency. In gigahertz we can absorb deflection in the resonant frequency within 1 GHz bandwidth and in terahertz we can absorb deflection in the resonant frequency about 0.005THz bandwidth. The antenna is capable of detecting tiny malignant tumors that size ≥1 mm inside the breast fantom. Other factors like S21,E-Field and farfield are also simulated to measure the efficiency of the antennas designed in both gigahertz and terahertz frequencies. By these results we conclude the antenna can detect tumor presence

Bipolar electron waveguides in two-dimensional materials with tilted Dirac cones

We show that the (2+1)-dimensional massless Dirac equation, which includes a tilt term, can be reduced to the biconfluent Heun equation for a broad range of scalar confining potentials, including the well-known Morse potential. Applying these solutions, we investigate a bipolar electron waveguide in 8–Pmmn borophene, formed by a well and barrier, both described by the Morse potential. We demonstrate that the ability of two-dimensional materials with tilted Dirac cones to localize electrons in both a barrier and a well can be harnessed to create pseudogaps in their electronic spectrum. These pseudogaps can be tuned through varying the applied top-gate voltage. Potential opto-valleytronic and terahertz applications are discussed.

Multifield-Modulated Spintronic Terahertz Emitter Based on a Vanadium Dioxide Phase Transition.

The efficient generation and active modulation of terahertz (THz) waves are strongly required for the development of various THz applications such as THz imaging/spectroscopy and THz communication. In addition, due to the increasing degree of integration for the THz optoelectronic devices, miniaturizing the complex THz system into a compact unit is also important and necessary. Today, integrating the THz source with the modulator to develop a powerful, easy-to-adjust, and scalable or on-chip THz emitter is still a challenge. As a new type of THz emitter, a spintronic THz emitter has attracted a great deal of attention due to its advantages of high efficiency, ultrawide band, low cost, and easy integration. In this study, we have proposed a multifield-modulated spintronic THz emitter based on the VO2/Ni/Pt multilayer film structure with a wide band region of 0-3 THz. Because of the pronounced phase transition of the integrated VO2 layer, the fabricated THz emitter can be efficiently modulated via thermal or electric stimuli with a modulation depth of about one order of magnitude; the modulation depths under thermal stimulation and electrical stimulation were 91.8% and 97.3%, respectively. It is believed that this multifield modulated spintronic THz emitter will provide various possibilities for the integration of next-generation on-chip THz sources and THz modulators.

Wafer-level substrate-free YIG single crystal film for a broadband tunable terahertz isolator

Yttrium iron garnet (YIG) is a promising material for various terahertz applications due to its special optical properties. At present, a high-quality YIG wafer is the desire of terahertz communities and it is still challenging to prepare substrate-free YIG single crystal films. In this work, we prepared wafer-level substrate-free La:YIG single crystal films, for the first time, to our knowledge. Terahertz optical and magneto-optical properties of La:YIG films were characterized by terahertz time domain spectroscopy (THz-TDS). Results show that the as-prepared La:YIG film has an insertion loss of less than 3 dB and a low absorption coefficient of less than 10 cm−1 below 1.6 THz. Benefitting from the thickness of the substrate-free YIG films and low insertion loss, their terahertz properties could be further manipulated by simply using a wafer-stacking technique. When four La:YIG films were stacked, there was an insertion loss of less than 10 dB in the range of 0.1−1.2 THz. The Faraday rotation angle of the four-layer-stacked La:YIG films reached 19°, and the isolation could reach 17 dB. By further increasing the stacking number to eight pieces, a remarkable Faraday rotation angle of 45° was achieved with an isolation of 23 dB, which is important for practical application in the THz band. This material may provide a milestone opportunity to make various non-reciprocal devices, such as isolators and phase shifters.

Microstructure and dielectric properties of low-temperature sintered MgO-based ceramics at millimeter wave and terahertz frequencies

Low-temperature co-fired ceramics (LTCC) applied in millimeter/microwave and terahertz frequencies (5G/6G) have attracted a lot of attention recently. In this study, MgO-based dielectric ceramics were successfully sintered at 950∘C with the sintering aids: x wt.% of LiF fluoride ([Formula: see text], 4, 6, 8, 10) and 0.5[Formula: see text]wt.% of BBSZ (Bi2O3–B2O3–SiO2–ZnO) glass. BBSZ glass was introduced as another sintering aid to facilitate the sintering and densification. Crystalline structure and micro-morphology were investigated and analyzed. Dielectric properties ([Formula: see text], [Formula: see text], [Formula: see text]) at millimeter/microwave and terahertz wave frequencies were also studied. The ionic characteristics of Mg–O bond ([Formula: see text]), the lattice energy (U) and the bond energy (E) were calculated and analyzed. It is suggested that the optimal [Formula: see text], where [Formula: see text], [Formula: see text][Formula: see text]GHz (@12[Formula: see text]GHz) and [Formula: see text][Formula: see text]ppm/∘C at millimeter/microwave range. When the frequency was up to terahertz (1.0[Formula: see text]THz), the [Formula: see text] values were 8.8–9.35 and the tan[Formula: see text] were [Formula: see text]–[Formula: see text]. The experimental results indicated that the low-temperature sintered MgO-based ceramics have potential for millimeter/microwave and terahertz communication applications.

Actively switchable spintronic terahertz emission with arbitrary polarization states

Flexible manipulation of the polarization state is essential for the practical application of terahertz (THz) waves in many fields. However, the lack of effective, high-quality polarization-tunable THz sources hinders the further development of THz technology. Here, we demonstrate an actively switchable spintronic THz source with polarization states among linear, circular, and elliptical states in the CoFeB/Pt/SiO2(sub)/Ta/Co/IrMn structure by using the antiferromagnet/ferromagnet exchange bias effect, as well as a temporary magnetic field to combine the magnetization directions, and designing the thickness of the substrate to achieve a suitable phase difference. In addition, the chirality, ellipticity, and azimuth of the THz waves can be manipulated arbitrarily by controlling the magnetization combination. More importantly, using rotating motors and electromagnets enables fully automated operations. This highly efficient, polarization-tunable THz source meets most of the existing needs, and its low cost and small size make it more suitable for integration into various devices. It paves the way for accelerating THz spintronic devices and unveiling mechanisms in condensed matter physics.

Metasurface-empowered high-efficiency and broadband terahertz vortex beam plates

Metasurfaces have been continuously garnering attention in both scientific and industrial fields owing to their unprecedented wavefront manipulation capabilities using arranged subwavelength artificial structures. Terahertz vortex beams have become a focus of research in recent years due to their prominent role in many cutting-edge applications. However, traditional terahertz vortex beam plates are often faced with challenges including large size, low efficiency, and limited working bandwidth. Here, we propose and experimentally demonstrate highly efficient and broadband vortex beam plates based on metasurface in the terahertz region. The experimental results well verify that the designed metasurfaces can efficiently generate terahertz vortex beams with different orbital angular momentum topological charges in the range of 0.5–1 THz. Notably, the maximum efficiency can reach about 65% at 0.5 THz. The proposed devices may play a vital role in developing vortex beams-related terahertz applications.

Asymmetric CPW-fed patch antenna with slits at terahertz applications for 6G wireless communications

Asymmetric CPW-fed patch antenna with slits at terahertz applications for 6G wireless communications

An Ultra-high Quality Factor Terahertz Photonic Crystal Cavity

High quality factor Terahertz (THz) cavities are highly desired for many THz applications. This paper presents an ultra-high quality factor terahertz planar photonic crystal cavity at 300 GHz range. Two approaches are employed to reduce the losses in the cavity increasing the quality factor of the cavity. Firstly, short embedded photonic crystal waveguides are employed to reduce the in – plane loss. Secondly, a novel way of hole displacement is adopted for four edged holes of the L3 – type photonic crystal cavity to decrease the radiation loss. An ultra – high quality factor of 65000 at a resonant frequency of 315.3 GHz was achieved for the designed cavity. This result could enable promising applications such as THz sensing.

Investigation of Gliding Walled Multilayer Waveguides

This article suggests a new waveguide design that utilizes a “walled” architecture. Instead of relying on conventional gap waveguide structures to create electronic bandgaps and prevent field leakage, the proposed design introduces a “walled” guiding mechanism. This technique preserves transmission while maintaining the multilayer approach and eliminates the need for nails or chemical bonds to attach the layers. Simulations were carried out in the W-band (75–110 GHz) and D-band (110–170 GHz) using several metals, and measurements were performed in the W-band using aluminum. The simulation results show that the reflection coefficient was less than −40 dB over the entire D-band. At the same time, the average insertion loss was around 0.0054 dB/mm and around 0.0065 dB/mm for silver and gold, respectively. Similarly, the reflection coefficient was less than −45 dB over the 75–110 GHz range, with an average insertion loss of 0.0018 dB/mm for silver and 0.003 dB/mm for gold, respectively. The aluminum model’s reflection coefficient was less than −35 dB, and the average insertion loss was 0.0035 dB/mm. The experimental results achieved a reflection coefficient of less than –30 dB and the average transmission coefficient was −0.2 dB, with an insertion loss of 0.002 dB/mm. The simple stacking ability of the weightless walled metal plates and easy fabrication makes the proposed transmission line a promising technology in mmWave and Terahertz applications.

RF/Analog Performance Optimization and Assessing Linearity/Distortion FoMs of HDDP-DG-NCFET for Terahertz Applications

RF/Analog Performance Optimization and Assessing Linearity/Distortion FoMs of HDDP-DG-NCFET for Terahertz Applications

Fabrication and Characterization of 2D Nonlinear Structures Based on DAST Nanocrystals and SU-8 Photoresist for Terahertz Application.

We demonstrate a method for the realization of highly nonlinear optical 4-(4-dimethylaminostyryl)- 1-methylpyridinium tosylate (DAST) two-dimensional structures by a double-step technique. The desired polymeric structures were first fabricated by using the multiple exposure of the two-beam interference technique, and the DAST nanoscrystals were then prepared inside the air-voids of these photoresist templates, resulting in nonlinear periodic structures. The nonlinear properties were characterized by optical and scanning microscopies, as well as by second-harmonic generation technique. This nonlinear modulation is very promising for the enhancement of nonlinear conversion rates, such as terahertz generation, by using the quasi-phase matching technique.

Active multi-focus vortex beam terahertz encoding metasurface based on Dirac semimetals.

An electromagnetic wavefront can be flexibly manipulated by discrete phase coding on the coding unit. In this paper, we designed two coding metasurfaces with 1-bit and 3-bit based on active tuning of Dirac semimetals by controlling the Fermi level (E F) with an external polarization voltage. The size and structure of the metasurface remain unchanged with this strategy. Both designs were found to be dynamically tunable. The 1-bit coding metasurface enables beam conversion, single-focus switching, and switching between single-focus and multi-focus. On the other hand, the 3-bit coding metasurface enables the switching between vortex beams and single-beam mirror reflections. These proposed structures have potential applications in terahertz (THz) communications and terahertz-focused imaging, opening up new possibilities for the dynamic modulation of THz waves.

Terajet-assisted time-domain super-resolution imaging

Large-scale applications of real-time terahertz (THz) imaging are often limited by the spatial resolution of a THz microscope. One of the simplest approaches to circumvent this problem in practice and achieve resolution below the diffraction limit consists in placing a dielectric particle with a size comparable to the radiation wavelength in the vicinity of the focal plane of the THz imaging system. Here, we theoretically consider the transmittance of a THz Gaussian beam through a Teflon sphere to further analyze experimental results on THz superresolution imaging. We address the resolution beyond the diffraction limit (the experimentally determined value is 0.38λ at 0.46 THz) through the superlens effect of the terajet generated by the mesoscale sphere owing to propagating and evanescent partial waves in the terajet. Due to the coupling of the dielectric sphere and time-domain THz spectrometer, we can detect a 10 µm thick PTFE film, which is almost transparent (98% transmittance) in the THz frequency range. The correlation between the transmittance spectrum of the dielectric sphere and the quality of THz images of thin, nonconducting films collected at different frequencies has been demonstrated experimentally and considered analytically. Our study is relevant for hyperspectral imaging applications and further development of the sphere-coupled time-domain THz imaging technique.

Dispersion‐Compensated Terahertz Ultra‐Broadband Quarter and Half Wave Plates in a Dielectric‐Metal Hybrid Metadevice

AbstractManipulating terahertz (THz) polarization in an efficient and broadband manner is of great significance to facilitating THz applications, including communications, imaging, defense, and homeland security. In this work, a dispersion compensation scheme is proposed for high‐efficiency and ultra‐broadband THz polarization manipulation using an anisotropic dielectric‐metal hybrid metadevice. The operating bandwidth is broadened by dispersion compensation, where the dielectric grating provides an artificial birefringence with a phase dispersion of positive slope and the metallic grating provides a phase dispersion of negative slope. Experimental results show that the device achieves two ultra‐broadband dispersion compensation, corresponding to the achromatic quarter‐wave plate in the lower frequency band (QWP: 0.5–2.0 THz, PCR >0.95) and the achromatic half‐wave plate in the higher frequency band (HWP: 1.0–2.1 THz, PCR >0.9), respectively. Theoretically, the bandwidth of QWP can be further improved to 2.6 THz by optimizing the grating dispersion, which brings huge application space to cover most of the THz radiation. This hybrid metadevice configuration offers a versatile platform for engineering electromagnetic waves, and the strategy of phase compensation can be generalized to extend the bandwidth of the metadevice in imaging and communications.