Terahertz Sensors Research Articles

Design and fabrication of PCF‐based terahertz sensor for breast cancer cell detection

AbstractBreast cancer is a type of cancer that is common in women worldwide, which emphasises its significance in identification with preventative treatment methods. The invented Photonic Crystal Fibre (PCF) exhibits outstanding performance in detecting Breast Cancer. The suggested model of the authors includes Hybrid layout within clad surface alongside Square Core. Introduced PCF detector exhibits max Relative Sensitivity (RS) of 96.82% as well 96.74% for breast cancer cell MCF‐7 as well MDA‐MB‐231 correspondingly. The authors also investigated the Confinement Loss of 1.642 × 10−10 dB/m, 2.461 × 10−10 dB/m with Effective Material Loss of 0.0473, 0.0565 cm−1 for the mentioned cells. Increased outcomes, customised therapy, plus quick action are made possible by swift identification in breast carcinoma. Timely malignancy detection reduces requirements to severe therapy by enabling simpler medicines. Additionally, making continuous illness detection easier, improving patient treatment. Furthermore, reliable evaluation contributes for investigating advancements that improve worldwide recognition as well as therapy alternatives. The introduced PCF Perhaps crucial in quick identification of these deadly cells as it has an extraordinary sensing ability. In conclusion, it has numerous possibilities in the healthcare sector.

Magnetic Field Enhanced Frequency‐Selective Terahertz Detection via 3D Printing Micro‐Helical Stepped and MoTe2 Coated Arrays

AbstractRecent advancements in wireless communication have markedly increased data throughput and decreased latency in progressing toward sixth‐generation (6G) networks, wherein the terahertz (THz) waveband offers significant potential. However, conventional THz sensors often suffer from high noise, low responsivity, and low spectrum efficiency, limiting their effectiveness for THz applications. Here, to address these challenges, a magnetic‐enhanced frequency‐selective is developed THz sensor by depositing an Au‐enhanced active layer of MoTe2 on a designed 3D printing high‐depth micro‐helical stepped structure. This sensor, featuring four characteristic frequency points and an effective area of 107.12 mm2, demonstrated noticeable improvements under a 0.145 mT magnetic field at 0.1 THz: optical responsivity improved by 413.23% (from 3.32 to 17.03 MV W−1), noise equivalent power decreased by 80.51% (from 49.16 to 9.58 pW Hz−1/2), and the detectivity reached 3.30 × 1010 cm·Hz1/2·W−1. This work highlights the potential of integrating 3D microstructures with novel topological materials for practical 6G communication.

A triple plasmon-induced transparency terahertz sensor based on graphene metamaterials

A metamaterial-based terahertz sensor design is presented in this paper. The metamaterial unit structure comprises a graphene cross and three sets of graphene strips, which collectively achieve a triple plasmon-induced transparency (PIT) in both polarization directions. The theoretical results based on the Lorentz resonance theoretical model are in good agreement with finite difference time domain (FDTD) simulations. The sensor is polarization-independent and changes in the angle of incidence between 0° and 10° have a negligible impact on the sensing performance. Furthermore, the sensor exhibits a notable slow-light effect, with a maximum sensitivity of 1.65 THz/RIU and a FOM value of 4.74/RIU for the triple PIT, which is superior to that of comparable devices.

Viscous terahertz photoconductivity of hydrodynamic electrons in graphene.

Light incident upon materials can induce changes in their electrical conductivity, a phenomenon referred to as photoresistance. In semiconductors, the photoresistance is negative, as light-induced promotion of electrons across the bandgap enhances the number of charge carriers participating in transport. In superconductors and normal metals, the photoresistance is positive because of the destruction of the superconducting state and enhanced momentum-relaxing scattering, respectively. Here we report a qualitative deviation from the standard behaviour in doped metallic graphene. We show that Dirac electrons exposed to continuous-wave terahertz (THz) radiation can be thermally decoupled from the lattice, which activates hydrodynamic electron transport. In this regime, the resistance of graphene constrictions experiences a decrease caused by the THz-driven superballistic flow of correlated electrons. We analyse the dependencies of the negative photoresistance on the carrier density, and the radiation power, and show that our superballistic devices operate as sensitive phonon-cooled bolometers and can thus offer, in principle, a picosecond-scale response time. Beyond their fundamental implications, our findings underscore the practicality of electron hydrodynamics in designing ultra-fast THz sensors and electron thermometers.

The high-Q THz stereo metasurface sensor based on double toroidal dipole with wide operating angle bandwidth

A highly sensitive terahertz stereo metasurface sensor, characterized by a high quality factor (Q-factor) and based on dual toroidal dipole (TD) resonance, has been proposed. The optimal structural parameters are ascertained by comparing the pertinent parameters of the stereo and planar structures in relation to TD modal excitation. The effective excitation of the TD mode is demonstrated using the calculations of multipole scattered power, reflection spectra, surface currents, electric fields, and magnetic field distributions. It is crucial that the stereo metasurface exhibits simplicity and that the dual TD resonance can be readily excited through simple adjustments in the distance and height of the intermediate gap. It also demonstrates exceptionally high sensitivity and Q-factor, both of which are essential for sensing applications. Moreover, the proposed stereo terahertz metasurface sensor still shows excellent sensing performance in a wide range of incidence angles (±40°), which is of great significance for practical applications. In conclusion, this structure offers a novel design framework for high-performance terahertz sensors based on the TD mode.

A Chirped Characteristic-Tunable Terahertz Source for Terahertz Sensing.

In broadband terahertz waves generated by femtosecond lasers, spatial chirp will be simultaneously produced with the introduction of angular dispersion. The chirp characteristics of the terahertz wave will directly affect the frequency response, bandwidth response, and intensity response of the terahertz sensor. To enhance the capability of terahertz sensors, it is necessary to control and improve the chirped characteristics of broadband terahertz sources. We generate a chirped terahertz wave via optical rectification in a LiNbO3 prism using the technique of pulse front tilt. The effect of the pump-beam spot size on THz generation is systematically studied. The pump's spot size is manipulated using a telescope system. With a pump spot diameter of 1.8 mm, the scanning spectrum of the THz pulse is narrower and is divided into multiple distinct peaks. In contrast, using a pump spot diameter of 3.7 mm leads to increased efficiency in the generation of THz pulses. Also, we investigate the underlying properties governing the generation of chirped terahertz pulses using varying pump pulse spot diameters.

Stretchable terahertz metasurface based on laser induced graphene for contactless deformation sensing

In this paper, a 1D stretchable terahertz (THz) metasurface based on laser-induced graphene (LIG) for deformation sensing is developed with low cost, good sensitivity and robustness. After the LIG metasurface is fabricated by laser-direct writing on a polyimide film, it is divided into columns and bonded to a medical polyurethane (PU) tape, thus endowed with high elasticity due to the excellent flexibility of PU. Because LIG supports surface plasmon polaritons in the THz band, a plasmonic resonance is introduced in the reflection spectrum and red shifts with lateral stretching. Experimental results show that the device can realize a resonant frequency shift of 336 GHz at a deformation of 0-14 mm, and the linearity reaches 0.988, achieving a sensitivity of 24 GHz/mm and excellent robustness (>1000 repetitions). The LIG-based stretchable THz sensor has great application potential for contactless deformation sensing in aerospace, industrial manufacturing, and related fields.

A high-efficiency terahertz sensor based on surface lattice resonance metasurface for biochemical detection

Metasurfaces have demonstrated their sensing capabilities in the terahertz (THz) region. However, the practical application of these technologies is constrained by the complexity of their structural design and the randomness of their sensing performance. In this work, we propose a novel THz sensor based on a surface lattice resonance (SLR) metasurface with high refractive index (RI) sensitivity (502.8 GHz/RIU), high-quality factor (Q) (164.4), and simple structural design. The high sensing performance is attributed to the SLR generated by the coupling of Rayleigh anomaly (RA) diffraction and spoof localized surface plasmons in the metasurface. In the experiment, 0.9 % (0.1538 mol/L) sodium chloride (NaCl) solution with human physiological concentration can cause a 246.8 GHz shift of the SLR peak. Furthermore, the sensor demonstrates a blue-shift of the SLR peak with the decrease of the structural period of the metasurface, and meanwhile, its RI sensitivity increases with regularity. This work provides a new method for detecting health indicators of human physiological concentration by designing highly sensitive THz metasurface for a specific frequency.

Asynchronous optical sampling of on-chip terahertz devices for real-time sensing and imaging applications.

We demonstrate that asynchronous optical sampling (ASOPS) can be used to measure the propagation of terahertz (THz) bandwidth pulses in a coplanar waveguide device with integrated photoconductive switches used for signal excitation and detection. We assess the performance of the ASOPS technique as a function of measurement duration, showing the ability to acquire full THz time-domain traces at rates up to 100 Hz. We observe a peak dynamic range of 40 dB for the shortest measurement duration of 10 ms, increasing to 88 dB with a measurement time of 500 s. Our work opens a route to real-time video-rate imaging via modalities using scanned THz waveguides, as well as real-time THz sensing of small volume analytes; we benchmark our on-chip ASOPS measurements against previously published simulations of scanning THz sensor devices, demonstrating sufficient dynamic range to underpin future video-rate THz spectroscopy measurements with these devices.

Graphene-based polarization insensitive structure of ultra-wideband terahertz wave absorber

Graphene, a new smart material, has gained a lot of attention recently because of its tunable band structure and strong light-matter interaction. In comparison with typical absorbers, graphene absorbers have emerged as a highly attractive substitute for various types of applications. To broaden the absorption bandwidth, a two-dimensional graphene-based ultra-wideband and polarization-insensitive novel terahertz (THz) absorber with absorption over 95 % from 3.0 THz to 8.5 THz is proposed, with peak absorption of 99.9 % at 6.6 THz and average absorption of 98.4 % for the 5.5 THz bandwidth. The surface plasmon increased by the gold-graphene structure, the Mei resonance, and the interference cancellation between metasurfaces collectively contribute to the ultra-wideband absorption. To obtain nearly perfect broadband terahertz absorption, a single layer of graphene is used. The finite difference time domain (FDTD) approach is used for absorber analysis. In addition, the absorber is insensitive to the polarization angles and incidence angles of incident electromagnetic waves. The proposed graphene-based absorber dominates previously reported wideband THz absorbers in terms of over 95 % bandwidth, absorption peak value, and overall volume. This research will present a novel idea for the design of an ultra-wideband absorber, which can be considered a suitable candidate for different potential applications in terahertz imaging, sensors, photodetectors, and modulators.

Multi-channel switch and sensing applications based on multilayered annular graphene metamaterials at terahertz frequency

In this study, a novel silica-graphene–silica periodic graphene structure consisting of six graphene semi-rings is proposed. The structure is based on a three-layer graphene metamaterial with a semicircular ring that achieves a tunable double plasmon-induced transparency (PIT) effect. In the proposed structure, the double-PIT window can be switched simultaneously at multiple frequencies through the dynamic tunability of graphene. Besides, the sensitivities of the refractive index for the PIT windows are investigated with the maximum values of 1.42 THz RIU−1 and 1.09 THz RIU−1, respectively, indicating the structure’s performance as a terahertz sensor. Overall, it shows the potential of PIT effect in graphene metamaterials in controlling electromagnetic field responses. It has made positive contributions to the development of terahertz technology and related fields.

Design of optically pumped ultrahigh-performance terahertz sensors based on graphene metamaterials

The surface conductivity of graphene can be precisely adjusted to approach the sigma-near-zero (SNZ) point by manipulating the quasi-Fermi level via optical pumping. This capability holds great promise for advanced graphene metamaterials-based terahertz (THz) sensors. In this study, we present a rational approach for designing two distinct types of patterned graphene THz sensors, each tailored to specific requirements regarding the quasi-Fermi level, resonance frequency, and Q-factor. The first sensor type operates in transmission mode and is well-suited for analytes with refractive indices ranging from 1 to 2. With a fixed analyte thickness of 40 nm, it achieves a frequency sensitivity of 1.036 THz/RIU, a Q-factor between 230 and 360, and a figure of merit (FOM) ranging from 51/RIU to 74/RIU. The second sensor type operates in reflection mode and is optimized for detecting biomolecules with refractive indices between 1.5 and 1.7. It exhibits a significant frequency shift of approximately 0.16 THz and a reflectance variation as high as 0.941 when the bio-analyte thickness is 100 nm. Numerical simulations of the sensing performances confirm the potential of these designed sensors for applications in detecting thin dielectric films and biosensing.

In Situ Leaf Water Status Sensor Using Resonant Tunneling Diodes as Terahertz Source and Sensor

In Situ Leaf Water Status Sensor Using Resonant Tunneling Diodes as Terahertz Source and Sensor

Hybrid amorphous strontium titanate and terahertz metasurface for ultra-sensitive temperature sensing.

In this study, a hybrid amorphous strontium titanate (STO) and terahertz metasurface were studied. Because of the excellent physical properties of amorphous STO, such as its dielectric properties and high transmittance in the terahertz region, it plays a core role in realizing a novel terahertz (THz) temperature sensor with high performance in the temperature range of 500-608 K. A blue shift of the absorption peaks appeared for the THz wave as the temperature increased, which confirmed the temperature-sensing function. The physical mechanisms underlying this phenomenon were also investigated. After optimization, the best THz temperature sensor with a sensitivity of 2.08 GHz/K was obtained, in which the thickness of the amorphous strontium titanate film was approximately 0.36 µm. This study provides a new opportunity for amorphous STO materials to be applied in THz sensors and demonstrates the realization of amorphous STO-based THz temperature sensors with high performance, low cost, and simple processes.

A comprehensive study of ferroelectric, dielectric and optical properties of europium-doped SBD metal- organic framework

The synthesis of Europium-doped Strontium based benzene dicarboxylate dimethylformamide metal–organic framework- Eu([Sr(μ-BDC)(DMF)])- with short form as Eu:SBD@MOF was carried out using the solvothermal method. The investigation involved characterization techniques such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), CHN analysis, and energy-dispersive X-ray (EDX) elemental analysis. The results confirmed the formation of metal–organic crystals in the framework. The XRD characterization shows good alignment with the simulated pattern of SBD. The experimental absorption spectrum displays distinct transitions of the Eu (III) ion alongside transitions of the ligands. Calculations of line strengths for all observed transitions have been conducted. The Judd-Ofelt theory has been employed to determine intensity parameters, transition probabilities, branching ratios, and radiative lifetimes for the Eu: SBD@MOF. These JO parameters further aid in calculating various excited state properties. When excited by ultraviolet and visible photons, the complex exhibits emission in the red region respectively. The crystal’s dielectric loss and dielectric constant were investigated for their frequency dependence. It was observed that by virtue of DMF, a molecule linked to the crystal, a synthesized MOF exhibits a good dielectric characteristic and when the temperature is raised to 558 K, the dielectric constant drops sharply as DMF molecule could not stand after this temperature. Further ferroelectric studies reveal that the Eu: SBD@MOF has maximum polarization of 0.27 C/cm2 which is greater than Rochelle salt and other MOF’s. Exploring the broadband dielectric response of metal–organic frameworks (MOFs) open up new avenues in research, potentially leading to innovative applications in smart optoelectronics, terahertz sensors, high-speed telecommunications, and microelectronics.

VO2 based multi-functional ultra-wideband terahertz meta-absorber for EMI shielding application

ABSTRACT This paper presents a multifunctional tuneable wideband metasurface absorber based on phase-changing Vanadium dioxide (VO2). The ‘quad isotropic VO2 circular sectors’ are constructed on amorphous silicon dioxide (SiO2), backed with 0.2 µm-thick gold layer to design the proposed absorber. This novel wideband tunable structure can independently be used as a reflector and absorber as an EMI shield; hence, this multi-functionality in a single structure proves novel and unique in the terahertz frequency range. This unit cell offers a bandwidth of 3.5 THz with more than 90% of absorptivity under normal wave incidence. The equivalent circuit model, surface currents, and field distributions are further investigated to provide a better understanding of structural evolution. Moreover, a wideband absorption has been observed up to the 60° incident angle for both the transverse modes, showing a polarization-insensitive behavior due to the symmetricity in the structure. The parametric study explores, optimizes, and demonstrates various other main characteristics and parameters of the proposed absorber. The novel structure offers shielding effectiveness (SE) higher than 40 dB throughout the frequency band under both normal and oblique incidence. This outstanding performance makes it a strong contender for EMI-EMC applications. Furthermore, it shows great potential in the field of terahertz technology, such as terahertz imagers, detectors, sensors, and other wideband applications.

Four-band terahertz perfect-absorption and high-sensitivity sensor based on tunable Dirac semimetal

In this paper, we designed a dynamically tunable four-band perfect sensor based on bulk Dirac semimetal (BDS). The sensor comprises a top BDS layer, a bottom Au layer, and an intermediate dielectric layer. Four resonant modes with >98 % absorption are achieved in the range of 9–11.8 THz. Due to the rotationally symmetric design, the sensor is polarization insensitive. The formation mechanism of perfect absorption is explained using the principles of impedance matching. We also determined the effects of structural parameters and Fermi energy of the BDS on the absorption spectra. We explain the blue-shift and red-shift phenomena of the resonant frequency based on equivalent circuits. Additionally, we define the refractive index sensitivity (S) and find that the maximum sensitivity is 516 GHz/RIU. Due to these excellent properties, our design provides a way of thinking about actively tunable terahertz sensors and expands their application scope.

A Flexible Terahertz Metamaterial Sensor for Pesticide Sensing and Detection.

Terahertz (THz) waves have garnered significant interest across various fields, particularly in high-sensitivity sensing applications. Metamaterials can be employed in THz sensors, specifically for refractive index sensing and pesticide detection due to their high-sensitivity characteristics. In this Article, a dual-band flexible THz metamaterial sensor based on polyimide is proposed for refractive index and pesticide sensing, which is fabricated using ultraviolet (UV) lithography technology and measured by a THz time-domain spectroscope (TDS) system. The resonant frequencies of the sensor are at 0.37 and 1.13 THz, with transmission rates of 2.9% and 0.3%, respectively. With an analyte layer attached to the sensor's surface, the sensitivity of refractive index sensing can be calculated as 0.09 and 0.28 THz/RIU (refractive index unit) at the two resonant frequencies. In order to validate the exceptional pesticide sensing performance of the sensor, chlorpyrifos-methyl acetone solutions with various concentrations are added on it. Furthermore, a monolayer of graphene is coated on the sensor's surface, which is proved capable of improving pesticide sensing sensitivity at low concentrations due to strong π-π stacking interactions with π-electrons in chlorpyrifos-methyl solutions. Therefore, the graphene-coated sensor can be utilized in detecting pesticide solutions with low concentrations, and the sensor without graphene is preferred for high concentration detection. This work provides a novel option for the THz metamaterial sensor with high sensitivity covering a wide pesticide concentration range.

High-Q factor terahertz metamaterial sensor based on quasi-BIC

In this paper, we proposed a terahertz (THz) metamaterial sensor, which consists of an array with two mirrored double split ring resonators (DSRRs) in one unit cell deposited on a lossless polyimide substrate. The THz spectral response show that when the two DSRRs in one unit cell are mirror symmetric and center symmetric simultaneously, two types of symmetry-protected bound states in the continuum (BICs) can be generated with the incident polarization unchanged. When the gaps are on the short or long arms of DSRRs, different modes of BIC can be observed. By breaking the symmetry of the structure with the gaps deviating from the center line of the DSRRs, quasi-BICs can be achieved, which can provide high Q-factors for our designed THz metamaterial sensor. The performance of the sensor is also evaluated, which has the characteristics of high Q-factor, high sensitivity, and high linearity. The integration of quasi-BIC and THz sensing technology will help solve the problems faced in the design of ultra-high Q-factor THz sensors and further expand the applications of terahertz technology.

Terahertz Biosensor Engineering Based on Quasi-BIC Metasurface with Ultrasensitive Detection.

Terahertz (THz) sensors have attracted great attention in the biological field due to their nondestructive and contact-free biochemical samples. Recently, the concept of a quasi-bound state in the continuum (QBIC) has gained significant attention in designing biosensors with ultrahigh sensitivity. QBIC-based metasurfaces (MSs) achieve excellent performance in various applications, including sensing, optical switching, and laser, providing a reliable platform for biomaterial sensors with terahertz radiation. In this study, a structure-engineered THz MS consisting of a "double C" array has been designed, in which an asymmetry parameter α is introduced into the structure by changing the length of one subunit; the Q-factor of the QBIC device can be optimized by engineering the asymmetry parameter α. Theoretical calculation with coupling equations can well reproduce the THz transmission spectra of the designed THz QBIC MS obtained from the numerical simulation. Experimentally, we adopt an MS with α = 0.44 for testing arginine molecules. The experimental results show that different concentrations of arginine molecules lead to significant transmission changes near QBIC resonant frequencies, and the amplitude change is shown to be 16 times higher than that of the classical dipole resonance. The direct limit of detection for arginine molecules on the QBIC MS reaches 0.36 ng/mL. This work provides a new way to realize rapid, accurate, and nondestructive sensing of trace molecules and has potential application in biomaterial detection.