Metamaterial Sensor Research Articles

A review of terahertz metamaterial sensors and their applications

Terahertz (THz) waves possess unique characteristics such as high transmission, strong absorption, and low photon energy. THz metamaterial sensors, as label-free and rapid optical sensors, offer significant advantages in detection technology. These sensors enable high-sensitivity, efficient, non-destructive, and low-dose sensing due to the properties of THz waves, the sensitivity of metamaterial devices to changes in the surrounding dielectric environment and the characteristic fingerprint spectrum of biochemical molecules. THz metamaterial sensors hold great potential for applications in biomedicine, non-destructive testing, as well as the food and agricultural sectors. This paper provides a comprehensive review of various detection methods employed by THz metamaterial sensors, which consists of THz refractive index sensors, biometric fingerprint (characteristic absorption peak) sensors and biomass sensors. The study critically discusses different device structures and modulation principles used in these sensors, analyzing their respective strengths weaknesses and development trend. This review represents a broad introduction for beginners.

High quality factor double negative metamaterial for textile fabric and fabric moisture sensing applications

This study introduces an innovative high-Quality factor (Q-factor) double negative (DNG) metamaterial sensor designed for textile fabric and fabric moisture sensing applications in the dynamic realm of textile innovation. The sensor is specifically designed to detect the dielectric properties and moisture content of different textile fabrics. The high Q-factor of this metamaterial structure ensures heightened sensitivity and accuracy in fabric sensing, facilitating precise detection of even subtle changes in fabric properties. By measuring frequency shifting and analyzing S21 values, the sensor provides crucial information about the fabric’s dielectric characteristics. Sensing experiments conducted on various fabrics, including cotton, denim, corduroy, organza, and polyester unveil distinctive patterns of frequency shifting and Q-factors, establishing a nuanced link between fabric structure and sensor performance. The proposed sensor is capable of detecting fabrics with a very low dielectric constant variation of 0.05. In the experiment, the high-dielectric fabric denim (1.7) exhibited frequency shifting and Q-factor of 6970 and 834.87, respectively. Moreover, it is worth noting that the low-dielectric fabric organza (1.03) exhibits frequency shifting and Q factors of 2190 and 1367.03, respectively. Experimental results affirm the prominent efficacy of the proposed sensor in fabric and fabric moisture sensing. Its high Q-factor empowers the sensor to accurately detect and monitor fabric properties, rendering it highly suitable for critical tasks such as quality control, energy efficiency optimization, and process enhancement within the textile industry. The proposed metamaterial sensor (MMS) can significantly contribute to the development of a smart textile sensing technology and pave the way for innovative applications in the textile industry.

Microstrip and Metamaterial Embedded Patch Antenna Sensors for Determination of Moisture in Rice, Wheat, and Pulse Grains

Moisture Content determination inside the grains is essential for grain processing activities including harvesting, storing, inspecting, and transporting. In this paper, microstrip and metamaterial embedded patch sensors were developed to determine the moisture content and mean relative error (MRE) of rice, wheat, and pulse. The sensors were simulated in HFSS, prototypes were fabricated and the measurement was done using VNA and anechoic chamber. The Microstrip sensor was operating at a frequency of 5.2 GHz and the metamaterial-embedded sensor was operating at 4.5 GHz. Calibration equations were obtained by using the values of reflection coefficients and moisture content ranging from 11.76% to 25%. For analyzing the efficacy of designed sensors, predicted moisture content (PMC) and actual moisture content (AMC) have been compared and the lowest mean relative error has been determined. The analysis shows that the metamaterial embedded sensor has better sensitivity and accuracy than the microstrip sensor. The lowest mean relative error in moisture prediction for metamaterial sensor was 1.07% for rice, 1.13% for wheat, and 1.47% for pulse respectively. A comparison of the proposed metamaterial embedded sensor with earlier designed sensor in literature was also presented in this work and it was found that the proposed sensor had more accuracy and sensitivity than earlier designs.

Using Mirror-based Terahertz Metamaterial Sensor to Chiral Identification and Detection of D-/L- Serine

Using Mirror-based Terahertz Metamaterial Sensor to Chiral Identification and Detection of D-/L- Serine

A carbon nanotube metamaterial sensor showing slow light properties based on double plasmon-induced transparency.

In this study, we proposed a bifunctional sensor of high sensitivity and slow light based on carbon nanotubes (CNTs). An array of left semicircular ring (LSR), right semicircular ring (RSR), and circular ring (CR) resonators are utilized to form the proposed metamaterial. The proposed structure can achieve double plasmon-induced transparency (PIT) effects under the excitation of a TM-polarization wave. The double PIT originated from the destructive interference between two bright modes and a dark mode. A coupled harmonic oscillator model is used to describe the destructive interference between the two bright modes and a dark mode, and the simulation results agree well with the calculated results. Moreover, we investigate the influence of the coupling distance, period, and flare angle on the PIT spectra. The relationship between the resonant frequencies, full width at half maximum (FWHM), amplitudes, quality factors (Q), and the coupling distance is also studied. Finally, a high sensitivity of 1.02 THz RIU-1 is obtained, and the transmission performance can be maintained at a good level when the incident angle is less than 40°. Thus, the sensor can cope with situations where electromagnetic waves are not perpendicular to the structure's surface. The maximum figure of merit (FOM) can reach about 8.26 RIU-1; to verify the slow light property of the device, the slow light performance of the proposed structure is investigated, and a maximum time delay (TD) of 22.26 ps is obtained. The proposed CNT-based metamaterial can be used in electromagnetically induced transparency applications, such as sensors, optical memory devices, and flexible terahertz functional devices.

3D-Printed Terahertz Metamaterial Sensor with Polarization-Independent High-Q Resonance Based on Bound States in the Continuum

3D-Printed Terahertz Metamaterial Sensor with Polarization-Independent High-Q Resonance Based on Bound States in the Continuum

A high Q-factor metamaterial sensor based on electromagnetically induced transparency-like

This paper proposes an electromagnetically induced transparency-like (EIT-like) metamaterial with a high-quality factor (143.54), which is composed of a square ring resonator (SRR) and a cross-shaped resonator (CR). The designed metamaterial generates a sharp transparency peak at 15.79 GHz. The electric field distributions reveal that appearance of the transparency window results from the coupling between bright mode and dark mode. Moreover, analysis of the surface current distributions verifies that the EIT-like effect is induced by the destructive interference of the electric dipoles . Furthermore, the metamaterial is equated to a circuit model, which provides a better fit to the simulated transmission spectrum. These theories fully explain the generation mechanism of the EIT-like phenomenon. In addition, the EIT-like metamaterial is able to detect the dielectric constant of the target analyte (glucose solution), and the sensing performance is evaluated. The results demonstrate that the sensitivity (S) is 4.80 GHz R−1IU−1 and the figure of merit (FOM) reaches 43.71. The proposed EIT-like metamaterial shows prominent sensing abilities, consequently it has potential applications in environmental monitoring, biological and chemical measurements.

A Terahertz Metamaterial Sensor Based on Dual Resonant Mode and Enhancement of Sensing Performance

A Terahertz Metamaterial Sensor Based on Dual Resonant Mode and Enhancement of Sensing Performance

Swift 4D printing of thermoresponsive shape-memory polymers using vat photopolymerization

Shape-memory polymers (SMPs) are smart materials that have gained significant attention in recent years owing to their widespread application in smart structures and devices. Digital light processing (DLP), a vat-photopolymerization-based technique, is a significantly faster technology for printing a complete layer in a single step. The current study reports a facile and fast method for the 3D printing of SMP-based smart structures using a DLP 3D printer and a customized resin. A liquid crystal (LC, RM257) was combined with the resin to introduce shape-memory properties. The combination of LCs in photocurable resin provides the opportunity to directly 3D-print thermoresponsive structures, avoiding the complexity of SMP resin preparation. The structures were printed with different geometries, and the shape-memory response was measured. Lattice structures were fabricated and programmed to obtain tunable mechanical properties. Furthermore, the strain-sensing response was measured to demonstrate the utility of these lattice structures as smart patches for joint-movement sensing. The SMPs can be prepared conveniently and can potentially be used for various applications, such as smart tools, toys, and meta-material sensors.

Hybridization chain reaction assisted terahertz metamaterial biosensor for highly sensitive detection of microRNAs

MicroRNA (miRNA) is closely related to the occurrence and development of cancer. Accurate determination of the miRNA concentration is of great significance for early cancer diagnosis. However, due to the short sequence and low concentration of miRNA, it is still a challenge to achieve low-concentration detection. In this work, we proposed a method for the highly sensitive detection of miRNA-21 using a terahertz (THz) metamaterial sensor combined with a Hybridization chain reaction (HCR). First, a capture hairpin probe was combined with gold nanoparticles (AuNPs), which were then modified to the surface of the sensor for specific binding of miRNA-21. Then the signal amplification technique of HCR is used to amplify the trace amount of miRNA, and the super-long dendritic DNA macromolecules are formed on the surface of the sensor. This changes the dielectric environment of the sensor surface, and the resonance frequency of the sensor is shifted. The method has good specificity and sensitivity, and the concentration of miRNA-21 in the range of 100 aM to 10 nM shows excellent linear relationship with frequency shift. Most importantly, it paves the way for low-cost, easy-to-operate and marker-free miRNA detection.

Minimal microfluidic metamaterial sensor for concentration detection

The design of high sensitivity and minimal size sensors for liquid concentration detection has significant importance in biomedical and chemical engineering. In this paper, we present a microfluidic liquid sensor for concentration detection based on metamaterial, with a minimal size of 20 × 16 mm2. The sensor consists of a modified square split-ring resonator (SRR) and a microstrip transmission line (MTL), integrated with a microfluidic device. The operating frequency of the sensor is 4.38 GHz. Experimental results demonstrate that the resonant frequency of the water–ethanol mixture with concentrations ranging from 0 to 100 % has a linear shift of 290 MHz. A mathematical model is established by examining the relationship between the transmission parameters and the complex dielectric constant, the maximum deviation between the ethanol solution concentration predicted by this model and the actual concentration is 0.5 %. The sensor exhibits a sensitivity of 2.14 × 10^-3 dB/(mg/dL) to aqueous glucose solutions with 0–––400 mg/dL. A fitting formula is derived from the transmission parameters to predict unknown concentrations of aqueous glucose solutions, could detect the change of 1 mg/dL glucose solution accurately with a maximum error of 0.7 %.

Metamaterial microwave sensor with ultrahigh Q-factor based on narrow-band absorption

A novel metamaterial sensor with ultrahigh Q-factor of 665.85 and 1883.3 at 5.46 GHz and 11.3 GHz is presented in this paper, which consists of a metal pattern with cross structure and ring (CSR), a dielectric slab FR4 and a metal backplate. Based on the principle of the absorber, the Q-factor of the two resonance frequency points is improved by optimizing the ring and cross structure to strengthen the resonance. It is because of its wide angle incidence, insensitive polarization, and narrow-band absorptivity greater than 90 %, which is very conducive to the design of material refractive index sensor. Equivalent circuit method is used to analyze the characteristic of the metamaterial structure and the experimental results are in good agreement with the simulations. By loading three giving materials, the sensing function is analyzed and verified in experiments. The design has the advantages of ultrahigh Q-factor, angle and polarization insensitivity, and has potential application prospects in metamaterial sensing.

Design of self-coupled plasmonic hyperbolic metamaterials refractive index sensor based on intensity shift

Achieving efficient, accurate, label-free, and real-time biodetection is urgently required; hence, we propose a miniaturized, easily integrated, high-sensitivity plasmonic metamaterial light intensity refractive index sensor. The main structure of the sensor is layered hyperbolic metamaterial grating comprises eight pairs of Au/Al2O3 thin film, and the highly sensitive bulk plasmon polaritons can be effectively excited inside by the self-coupled effect without external prism or nanograting. The periodic fishnet arrays built in the layered HMM structure can not only be used as nanograting to achieve efficient coupling between incident light and layered HMM, but also increase the volume of the sensing, and the measured substance can get full interaction with the enhancement field to obtain high sensitivity. By detecting the change of reflected optical intensity with the ambient refractive index, the sensor exhibits intensity sensitivity of 36 RIU−1 (refractive index unit) and figure of merit of 403; moreover, the full width at half maximum of resonant peak is low at 5 nm. The sensing performances indicate that the sensor we designed has a significant potential to achieve portable, highly sensitive sensing platforms for precise detection.

A Metamaterial Computational Multi-Sensor of Grip-Strength Properties with Point-of-Care Human-Computer Interaction.

Grip strength is a biomarker of frailty and an evaluation indicator of brain health, cardiovascular morbidity, and psychological health. Yet, the development of a reliable, interactive, and point-of-care device for comprehensive multi-sensing of hand grip status is challenging. Here, a relation between soft buckling metamaterial deformations and built piezoelectric voltage signals is uncovered to achieve multiple sensing of maximal grip force, grip speed, grip impulse, and endurance indicators. A metamaterial computational sensor design is established by hyperelastic model that governs the mechanical characterization, machine learning models for computational sensing, and graphical user interface to provide visual cues. A exemplify grip measurement for left and right hands of seven elderly campus workers is conducted. By taking indicators of grip status as input parameters, human-computer interactive games are incorporated into the computational sensor to improve the user compliance with measurement protocols. Two elderly female schizophrenic patients are participated in the real-time interactive point-of-care grip assessment and training for potentially sarcopenia screening. The attractive features of this advanced intelligent metamaterial computational sensing system are crucial to establish a point-of-care biomechanical platform and advancing the human-computer interactive healthcare, ultimately contributing to a global health ecosystem.

A dual-band terahertz metamaterial sensor with high Q-factor and sensitivity

A dual-band terahertz metamaterial sensor with high Q-factor and sensitivity

Terahertz metamaterials for biomolecule sensing based on symmetry-broken unit resonators

Terahertz waves have gained attention owing to their potential for various bio-applications, including broadband spectroscopy, imaging, and sensing. For development of practical applications in clinical fields, highly sensitive molecular detection is essential. Notably, the molecular sensitivity of optical sensing can be enhanced by utilizing localized electromagnetic waves in metallic optical resonators. In this study, we theoretically design terahertz (THz) metamaterial sensors based on the Fano resonance, enabling highly sensitive and selective molecular sensing without additional molecular labeling. The metamaterial sensors consisting of symmetry-broken unit resonators are designed to support Fano resonances with strongly localized electromagnetic waves through coupling of the resonators. The key concept behind the design is to match the Fano resonance with the characteristic resonance in the target molecules, leading to pronounced changes in the transmission spectra of THz waves through the metamaterial with the analytes. We numerically demonstrate the sensing performance by considering steroids as the target molecules and explain the sensing mechanism using both temporal coupled-mode theory and FDTD numerical simulations.

Terahertz Metamaterial Sensor Based on Electromagnetic Induced Transparency

A graphene-based terahertz electromagnetically induced transparency (EIT) metamaterial sensor is proposed and studied. The sensor is made up of two bright modes: a graphene strip resonator and a 7-shape resonator. In a terahertz metamaterial sensor based on EIT, the metamaterial structure is designed to have two resonant modes that are coupled through a common resonator. When terahertz radiation hits the metamaterial, the two resonant modes interact, creating a window of transparency in the transmission spectrum. It illuminated that the physical mechanism of the EIT effect lay in the recombination effect of the conductive resonators. By changing the carrier relaxation lifetime or the Fermi energy of the graphene, the amplitude or the location of the EIT window could be actively tuned. The terahertz metamaterial sensors based on EIT have the potential to provide highly accurate and sensitive measurements in a wide range of fields and could lead to important advances in medical diagnostics.

Metamaterial Sensor With Large Incident Angle Based on Electromagnetically Induced Transparency Effect

Metamaterial Sensor With Large Incident Angle Based on Electromagnetically Induced Transparency Effect

High-selectivity terahertz metamaterial nitric oxide sensor based on ZnTiO3 perovskite membrane

Human exhaled gases contain a wide range of volatile organic compounds, offering the potential for detecting physiological, cardiovascular, and endocrine disorders. For instance, nitric oxide (NO) concentration can be indicative of chronic obstructive pulmonary disease. Analyzing exhaled gases provides a noninvasive approach to disease detection without posing any risks to individuals. While electronic sensors have been developed over the past two decades for NO detection at high temperatures, few studies have explored optical detection in the ultraviolet to visible light range, which may have adverse effects on the skin. In this study, we designed a split-ring resonator metamaterial tailored for operation within the terahertz (THz) frequency range. Specifically, the metamaterial was designed to resonate at the NO frequency of 0.257 THz. To enhance gas absorption capacity, we incorporated a composite film layer consisting of ZnTiO3 and reduced graphene oxide onto the metamaterial. By sintering ZnTiO3 powder at different temperatures, we achieved an increase in component sensitivity (ΔT/T) from 2% to 16.4%. Overall, the proposed metamaterial holds promise for both physical monitoring applications and the development of wearable electronic devices.

Numerical research on supercavity sensing driven by guided resonance in a terahertz all-metal metamaterial absorber

Terahertz metamaterial sensing features high sensitivity and rich fingerprint spectrum, which shows an application potential of the great significance. However, limited by low-quality resonances and insufficient sensitivity, the sensing performance of terahertz metamaterials remains at a moderate level. In this paper, we numerical investigate a high-performance terahertz sensor based on plasmonic supercavity sensing. The proposed metamaterial sensor features an adjustable high quality absorption resonance ascribed to guided resonance excited by band-folding effect. Also, the terahertz plasmonic sensor inherently characterizes a high sensitivity owing to the all-metal design, which can limit the resonant field within the structured metal surface to fully couple with analyte. Based on these advantages, the proposed all-metal sensor demonstrates the maximum resonance frequency shift, sensitivity and sensing figure of merit are about 66%, 1.6 THz/RIU and 218, respectively, substantiating the sensing superiority. The proposed metamaterial absorber shows potential in spectroscopy, in addition to being a multifunctional absorber and sensor.