Tunable Sensor Research Articles

Pixelated graphene-strontium titanate metamaterial supported tunable dual-band temperature sensor

Investigation was made of a certain form of metamaterial structure comprising pixelated graphene-strontium titanate-based metasurface with the aim of designing temperature sensor. Transmission spectral characteristics of the structures were evaluated under different chemical potentials of graphene and ambient temperature. It was found that the proposed structures exhibit sharp transmission minima corresponding to various parametric and operating conditions, which undergo frequency shifts corresponding to varying ambient temperature as well as tuning conditions – the feature that can be exploited in tunable temperature sensing. Furthermore, such features were obtained considering the removal of graphene pixels step-by-step. It was noticed that the elimination of graphene pixels results in reducing the sensitivity of the structure. Moreover, the illustrative case was taken up to demonstrate the polarization-insensitive property of the proposed metamaterial configuration – the characteristic that remains of great significance in the design and operation of optical sensors.

Realization of multi-band perfect absorber in graphene based metal-insulator-metal metamaterials

The graphene based metal-insulator-metal (MIM) metamaterial is numerically investigated to realize an active and adjustable multi-band perfect absorber, which is composed of an asymmetric double T-shaped cavity on the top layer. As the symmetry of T-shaped cavities is broken, the previous dual-band absorption will be converted to tri-band absorber. The corresponding electric field distribution at each resonant position is invesitgated to figure out the physical mechanism. More interestingly, these resonant peaks will split into multiband with further destruction of the central symmetry. In addition, non-contact dynamic control of perfect absorption is explored by tuning the Fermi energy, the polarization angle and the incident angle. Finally, the sensitivity of our proposed design is elaborately examined with different concentrations of CS2 dropped into the cavities. The results demonstrate that the refraction index per unit can reach up to a high value of 1673.33 nm/RIU. Therefore, this work delivers a new strategy to design tunable multi-band absorbers and has potential applications in highly tunable optical switchers, sensors and filters.

On the performance of a tunable grating-based high sensitivity unidirectional plasmonic sensor.

Optical biosensing is currently an intensively active research area, with an increasing demand of highly selective, sensitivity-enhanced and low-cost devices where different plasmonic approaches have been developed. In this work we propose a tunable optimized grating-based gold metasurface that can act both as a high sensitivity sensor device (up to 1500 nm/RIU) and as an unidirectional plasmon source. The theory behind surface plasmon polariton generation is recalled to thoroughly understand the influence that every parameter of the grating source has on the performance of the proposed device. The results and conclusions discussed here offer a key step toward the design of biosensors based on excitation of surface plasmons polaritons by grating-based structures or in the process of creating new nanophotonic circuit devices.

Highly tunable plasmon-induced transparency with Dirac semimetal metamaterials* *Project supported by the Natural Science Foundation of Henan Provincial Educational Committee, China (Grant No. 21A140026).

Based on Dirac semimetal metamaterials, the tunable plasmon induced transparency (PIT) is investigated elaborately in this work. The designed unit cell consists of a strip and a square bracket, which is periodically aligned on the dielectric substrate. Our numerical results illustrate that a pronounced transparency window exists due to near field coupling between two bright modes, which can be dynamically tuned with Fermi energy. Namely, the transparency window demonstrates a distinct blue shift with a larger Fermi energy. Moreover, an on-to-off switch of the PIT transparency window is realized with different polarization angles. In addition, the accompanied slow light property is examined with the calculation of phase and group delay. Finally, a small variation of the refractive index of the substrate can induce a clear movement of the PIT transparency window which delivers a guidance in the application of optical sensing. Thus, this work provides us a new strategy to design compact and adjustable PIT devices and has potential applications in highly tunable optical switchers, sensors, and slow light devices.

A Tunable Plasmonic Refractive Index Sensor with Ultrabroad Sensing Range for Cancer Detection

Contribution of quantum dots (QDs) and nano dots (NDs) in boosting the plasmonic behavior of noble metal nano cavity structure and its refractive index (RI) sensing is proposed across an ultrabroad RI range via first, second, and third near-infrared windows. An optimized refractive index sensor based on plasmonic-photonic interaction arising from the extraordinary optical transmission (EOT) through nano cavity is reported. Herein, the sensing platform comprised of an array of silver square nano disc and ring having cavity in between. By the introduction of dots, the absorption profile of entire system is dramatically modified resulting from the plasmon-exciton/plasmon-plasmon coupling and thereby attains higher tunability in sensing parameters together with an enhanced figure of merit (FOM), all confirmed by finite element method (FEM) stimulations. The tailorable hybrid structure demonstrating absorbance enhancement and resonant peak shift with cavity area, embedded material permittivity, presence of dots, etc., proposes an open platform for optical-based chemical and biosensing applications.

Tunable broadband terahertz absorber based on graphene metamaterials and VO2

A tunable broadband terahertz (THz) absorber is designed in this paper, which is composed of graphene, silica medium and phase change material Vanadium dioxide (VO 2 ). By simultaneously changing the fermi level of graphene and conductivity of VO 2 , the dual-controlled absorber can be realized. The results show that the full width at half maximum of the absorption spectrum is 1.03 THz, the bandwidth with the absorptance above 90% is 0.65 THz, and the absorptance is close to 100% at 1.2 THz. Moreover, the absorptance, transmittance and reflectance of the absorber can be dynamically adjusted from 0 to 99%, 0–65%, and 0–74%, respectively. The large tunability allows the proposed absorber to be used as THz tunable filters, sensors, switches and modulators. • A broadband metamaterial absorber has been proposed based on the patterned graphene resonators. • Dual control and tunability is realized based on graphene array and phase change material vanadium dioxide. • The proposed structure can be dynamically tuned to act as an absorber or reflector. • The structure can be made to work in transmission or absorption mode by changing the conductivity of vanadium dioxide.

Numerical Simulation of Tunable Terahertz Graphene-Based Sensor for Breast Tumor Detection

This article presents a modeling and analysis of a tunable graphene-based sensor for breast tumor detection operating in the terahertz frequency range using the wave concept iterative process (WCIP) method. Through the novel implementation approach of the biological tissues in the WCIP method, we can integrate the normal and tumor of human breast tissues into this algorithm. At the beginning, the details of the algorithms of human breast tissue and graphene modeling in the WCIP method are presented. In order to verify the results obtained by the WCIP algorithm, we presented a comparative study with the CST simulator. Then, using the WCIP method, the numerical simulation results demonstrate the capability of the proposed sensor to detect the normal breast tissue with good sensitivity of 7.11 (THz/RIU) and breast tumor with a high sensitivity of 8.21 THz/RIU and large figure of merits of 17.51 and 20.23 RIU−1, respectively. Finally, the simplicity, efficiency and tunability are the benefits of the proposed sensor, which makes it suitable for breast tumor detection in the THz band.

Design and analysis of a tunable refractive index sensor by using a Ta2O5-coated photonic crystal fiber

A plasmonic refractive index (RI) sensor based on photonic crystal fiber is proposed. A chemically stable thin film of gold (Au) is used as an active plasmonic layer and high RI material Ta2O5 is used as an overlayer over the gold thin film. The effect of Ta2O5 thin film on the sensor performance is analyzed in detail and a novel, as per the authors’ best knowledge, operating analyte RI range tunable property is reported. It is observed that the operating range is tuned toward the lower RI region with increasing Ta2O5 layer thickness. Furthermore, the sensor is optimized and its sensitivity is realized using both wavelength and amplitude interrogation techniques. A maximum wavelength sensitivity and amplitude sensitivity of 16,354 nm/RIU (refractive index unit) and 1574 RIU − 1, respectively, are obtained corresponding to the operating RI range of 1.39 to 1.41 for the optimized structure. Moreover, the detection accuracy of the sensor is found of the order of 10 − 6 with a high figure of merit up to 282 representing an overall good sensing performance. The sensor performance is realized using surface plasmon resonance phenomenon and numerically analyzed using finite element method. Our study, no doubt, provides a new direction of designing RI sensor that could tune the RI range to the desired operating range. In addition, the simple design feasibility, low fabrication cost, and portable nature of the proposed sensor make it suitable for industrial and chemical sensing applications.

High Sensitivity Plasmonic Sensor Based on Fano Resonance with Inverted U-Shaped Resonator.

Herein, we propose a tunable plasmonic sensor with Fano resonators in an inverted U-shaped resonator. By manipulating the sharp asymmetric Fano resonance peaks, a high-sensitivity refractive index sensor can be realized. Using the multimode interference coupled-mode theory and the finite element method, we numerically simulate the influences of geometrical parameters on the plasmonic sensor. Optimizing the structure parameters, we can achieve a high plasmonic sensor with the maximum sensitivity for 840 nm/RIUand figure of merit for 3.9 × 105. The research results provide a reliable theoretical basis for designing high sensitivity to the next generation plasmonic nanosensor.

Modeling of Magnetic Properties of Magnetorheological Elastomers Using JA Hysteresis Model

Magnetorheological elastomers (MREs) are composite materials that consist of magnetically permeable particles in a nonmagnetic polymeric matrix. Under the influence of an external magnetic field, a reversible deformation change occurs in the mechanical properties of these materials. Due to their coupled magnetomechanical response, these materials have been found suitable for a range of applications including tunable vibration absorbers, sensors, and actuators. Notably, improvement of such devices are prerequisites to efficient energy conversion systems, hence the need to understand further the MRE technology. The Jiles-Atherton (JA) theory takes into consideration the magneto-coupling experienced by effective domains in a magnetic material. Algorithm based on the theory yields five model parameters; saturation magnetization (M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> ), domain density (a), domain coupling (α), loss coefficient (k), and reversibility (c). Using JA theory, model parameters were calculated and linked to the physical attributes of Fe powder and isotropic MRE. The results show that the calculated Ms for the MRE is reasonably related to that of the Fe powder by a factor of the particle's volume fraction used in the MRE. The calculated k, a, and α provided support for the reduced pinning factor, domain density, and increased domain coupling in the MRE due to the changes in the domain structure between the two materials. From the calculated JA parameters, finite-element modeling (FEM) of the MRE hysteresis loop was performed. The analysis showed that the modeled magnetic properties including coercivity, remanence, and coordinates of the hysteresis loop tip vary with geometric position.

Ultrasensitive and Tunable Sensor Based on Plasmon-Induced Transparency in a Black Phosphorus Metasurface

We propose an ultrasensitive and tunable mid-infrared sensor based on plasmon-induced transparency (PIT) in a monolayer black phosphorus metasurface. Results show that there are two PIT windows, each of which occurs when the long axis of the metasurface is placed along the MBP’s armchair and zigzag crystal directions, respectively. The corresponding sensors based on these PIT effects show high sensitivities of 7.62 THz/RIU and 7.36 THz/RIU. Both PIT frequencies can be tuned statically by varying the geometric parameters or dynamically by changing the electron doping of monolayer black phosphorus, making the sensors adaptable to tackle with a variety of scenarios. We expect that this work will advance the engineering of metasurfaces based on monolayer black phosphorus and promote their sensing applications.

Highly Sensitive and Tunable Fano-Like Rod-Type Silicon Photonic Crystal Refractive Index Sensor

A highly sensitive and tunable 2D rod-type silicon photonic crystal cavity based biosensor configuration has been designed and numerically analyzed. The structure is optimized so that the light-matter interaction is maximized in the cavity region. Out-of-plane light confinement is achieved by sandwiching the rods between metal plates, and tuning is achieved by introducing an air-gap between on top of the rods and the metal plate. A single rod is positioned in the middle of the waveguide so that the cavity Q-factor is enhanced by obtaining a Fano-like resonance. The air-gap between the rods and the metal plate acts as a slot structure, confining E-field in that small region and simultaneously decreasing mode-volume while making the resonance characteristics highly dependent on the gap size. This creates the opportunity to tune the resonance characteristics by electrostatic actuation via applying voltage to the top and bottom metal plates. The proposed structure has a sensitivity value of 1039 nm/RIU, a mode volume of 0.214 ( $\lambda $ /n)3, flexible tuning capabilities, and is the first tunable 2D PhC rod-type refractive index sensor.

High-sensitive plasmonic sensor based on Mach-Zehnder interferometer

We design a novel, real-time and accurate plasmonic sensor made of asymmetric Mach-Zehnder Interferometer. Our plasmonic structure takes the advantage of surface-plasmon polaritons sub-wavelength confinement at the interfaces to fabricate nano- and micro-scale devices. The waveguides in the Mach-Zehnder Interferometer are made of lossy media, with positive and negative electromagnetic susceptibilities, including metamaterial, metal and graphene, interfaces with dielectrics. We compare the impact of media with different electromagnetic properties in the sensor structure on the sensor sensitivity and performance. The sensor is sensitive to the changes in the sample RI and is capable to work with different liquid and gas samples with different refractive indices. We introduce two configurations for the sensor with the sample in different domains along the structure to expand sensors applicability to different domains; the highest sensitivities reported for this sensor are 67.7THz/RIU, 69THz/RIU and 160THz/RIU for metal-, metamaterials- and graphene-based structures, respectively. We take the advantage of graphene to attain a tunable plasmonic sensor by applying a gate voltage to graphene in the sensor structure that shifts the sensor transmission peak to different frequencies and affects the sensor sensitivity. Our sensor structure has applications in liquid and gas chemical sensing, aerosol sensing, and environmental monitoring.

Multi-parameter tunable phase transition based terahertz graphene plasmons and its application

The active modulation of the amplitude and phase of terahertz wave has been widely adopted in terahertz functional devices. The current metal-insulator-metal metasurface structure combined with two-dimensional materials such as graphene can realize dynamic control of terahertz amplitude/phase, but it has some disadvantages such as less freedom of control (voltage or light intensity), complex processing technology and high price of metasurface structure. In this article, we propose a prism-coupled matel-insulator-graphene (MIG) phase regulation structure. This structure can not only control the phase by adjusting the Fermi level in the usual way, but also change the intrinsic loss and radiation loss of the structure by adjusting the thickness of the air gap and the number of layers of pre-spread graphene, so that the phase of the structure can be controlled, which is determined by the difference between intrinsic loss and radiation loss of the fabric, which is closely related to this structure staying in the under-coupling/over-coupling state. The adjustment of the structural phase can also lead the magnitude of the terahertz Goos–Hänchen(GH) displacement and its positive sign and negative sign to be selected. Furthermore, it is shown that the under-coupling state and the over-coupling state of the structure have an important effect on the coincidence of the Goos–Hanchen (GH) displacement. The results show that by dynamically adjusting the thickness of the air gap and the Fermi level of graphene, and changing the eigenloss and radiation loss of the system, the phase regulation can be achieved. Finally, the transition from overdamped to underdamped state is realized. In this physical process, the GH displacement of the system will also change obviously. This paper puts forward the structure of the process with simple processing technology (no need to microstructure), tunable high degrees of freedom (available graphene Fermi level and air gap dynamic regulation, also could be regulated and controlled by controlling the graphene layers) in comparison with the phase modulator of metal-insulator-metal super surface structure. The results of this paper open up a new way of developing the multi-parameter tunable terahertz sensor components.

The Impact of TiO &lt;sub&gt;2&lt;/sub&gt; Nanoparticle Exposure on Transmembrane Cholesterol Transport and Enhanced Bacterial Infectivity

We have previously shown that exposure to TiO2 nanoparticles (NPs) reduces the resistance of HeLa cells to bacterial infection. Here we demonstrate that the increased infectivity is associated with enhanced asymmetry in the cholesterol distribution. We applied a new live cell imaging method which uses tunable orthogonal cholesterol sensors to visualize and quantify in-situ cholesterol distribution between the two leaflets of the plasma membrane (PM). In the control culture, we found marked transbilayer asymmetry of cholesterol, with the concentration in the outer plasma membrane (OPM) being 12.5(2.2)-fold higher than that in the inner plasma membrane (IPM). Exposure of the culture to 0.1 mg/mL of rutile TiO2 NPs increased the asymmetry such that the concentration in the OPM was 50.8(9.5) times higher, while the total cholesterol content increased only 20.5(2.4)%. This change in cholesterol gradient may explain the increase in bacterial infectivity in HeLa cells exposed to TiO2 NPs since many pathogens, including Staphylococcus aureus used in the present study, require cholesterol for proper membrane attachment and virulence. RT-PCR indicated that exposure to TiO2 was responsible for upregulation of the ABCA1 and ABCG1 mRNAs, which are responsible for the production of the cholesterol transporter proteins that facilitate cholesterol transport across cellular membranes. This was confirmed by the observation of an overall decrease in bacterial infection in ABCA1 knockout or methyl-β-cyclodextrin-treated HeLa cells, as regardless of TiO2 NP exposure. Hence rather than preventing bacterial infection, TiO2 nanoparticles upregulate genes associated with membrane cholesterol production and distribution, hence increasing infectivity.

Near-infrared tunable surface plasmon resonance sensors based on graphene plasmons via electrostatic gating control.

A tunable near-infrared surface plasmon resonance sensor based on graphene plasmons via electrostatic gating control is investigated theoretically. Instead of the traditional refractive index sensing, the sensor can respond sensitively to the change of the chemical potential in graphene caused by the attachment of the analyte molecules. This feature can be potentially used for biological sensing with high sensitivity and high specificity. Theoretical calculations show that the chemical potential sensing sensitivities under wavelength interrogation patterns are 1.5, 2.21, 3, 3.79, 4.64 nm meV−1 at different wavebands with centre wavelengths of 1100, 1310, 1550, 1700, 1900 nm respectively, and the full width half maximum (FWHM) is also evaluated to be 10, 25.5, 43, 55.5, 77 nm at these different wavebands respectively. It can be estimated that the theoretical limit of detection (LOD) in DNA sensing of the proposed sensor can reach the femtomolar level, several orders of magnitude superior to that of noble metal-based SPR sensors (nanomolar or subnanomolar scale), and is comparable to that of noble metal-based SPR sensors with graphene/Au-NPs as a sensitivity enhancement strategy. The FWHM is much smaller than that of the noble metal-based SPR sensors, making the proposed sensor have a potentially higher figure of merit (FOM). This work provides a new way of thinking to detect in an SPR manner the analyte that can cause chemical potential change in graphene and provides a beneficial complement to refractive index sensing SPR sensors.

Gate-bias tunable humidity sensors based on rhenium disulfide field-effect transistors

We investigate the humidity sensing performance and mechanism of few-layer-thick rhenium disulfide (ReS2) field-effect transistors (FETs) under gate bias operation. Consequently, a negative gate bias exhibits the sensor response, exceeding 90% mainly in the low relative humidity (RH) range. Meanwhile, the threshold voltage change was discovered to be a superior sensing parameter to achieve a broad monitoring of RH range with high response and sensitivity. The approach obtained a practical sensitivity of 0.4 V per 1% RH, which exceed a majority of previous studies with the pristine 2D materials. Besides, our devices display reversible adsorption–desorption and long-term stability operations even after a one-month period. This suggests the sensor capacity to function in real-time applications with a short response and recovery times. These outcomes offer support in the development of adaptable tunable humidity sensors based on ReS2 FETs.

Feasibility study of a micro-electro-mechanical-systems threshold-pressure sensor based on parametric resonance: experimental and theoretical investigations

A tunable threshold pressure sensor based on parametric resonance of a microbeam subjected to electrostatic levitation is proposed. Parametric excitation can trigger a large amplitude vibration at twice the natural frequency if the magnitude of the driving force is large enough to overcome energy loss mechanisms in the system such as squeeze film damping. This causes a temporarily unstable response with a significant gain in oscillation amplitude over time until it is eventually capped by nonlinearities in the force or material or geometric properties. The instability divides the frequency region into two regions: distinct responses bounded by the system non-linearity, and trivial responses with very low oscillation amplitudes. It is shown experimentally that the appearance of parametric resonance depends on the pressure, which influences the amount of energy loss from squeeze film damping. Therefore, the distinct difference in the vibration amplitude can be used to detect when the pressure passes a threshold level. The activation of parametric resonance also depends on the amplitude of the driving force (). This voltage amplitude can be set to trigger parametric resonance when the pressure drops below a predetermined threshold. A reduced-order model is developed using the Euler–Bernoulli beam theory to elucidate the non-linear dynamics of the system. The simulation results from the mathematical model are in good agreement with the experimental data. The advantages of the proposed sensor over pull-in based sensors are its reliability and improved resolution from a large signal-to-noise ratio.

Designing Tunable Capacitive Pressure Sensors Based on Material Properties and Microstructure Geometry

Rationally designed pressure sensors for target applications have been in increasing demand. Capacitive pressure sensors with microstructured dielectrics demonstrate a high capability of meeting this demand due to their wide versatility and high tunability by manipulating dielectric layer material and microstructure geometry. However, to streamline the design and fabrication of desirable sensors, a better understanding of how material microstructure and properties of the dielectric layer affect performance is vital. The ability to predict trends in sensor design and performance simplifies the process of designing and fabricating sensors for various applications. A series of equations are presented that can be used to predict trends in initial capacitance, capacitance change, and sensitivity based on dielectric constant and compressive modulus of the dielectric material and base length, interstructural separation, and height of the dielectric layer microstructures. The efficacy of this model has been experimentally and computationally confirmed. The model was then used to illuminate, qualitatively and quantitatively, the relationships between these key material properties and microstructure geometries. Finally, this model demonstrates high tunability and simple implementation for predictive sensor performance for a wide range of designs to help meet the growing demand for highly specialized sensors.

Improved H2 detection performance of GaN sensor with Pt/Sulfide treatment of porous active layer prepared by metal electroless etching

High-performance chemiresistor gas sensor made of sulfide porous GaN decorated with Pt nanoparticles, which shows tunable sensor response and enhanced sensitivity. The fabricated gas sensors show detection of H2 down to 30 ppm at 23 °C after sulfide treatment and Pt decorated porous GaN. The response time and recovery time were equal to 47 s and 113 s, respectively. Density functional theory simulations were used to support the detection mechanism based on sulfide treatment. Adsorption energy calculations showed that H adsorption energy is lowered by the simultaneous presence of S and Pt on the GaN (0001) surface. The density of states (DOS) calculations revealed possibility of bond strengthening when Pt and S is adsorbed on GaN surface along with H, arising from the hybridization of d and p orbitals of Pt and S with that of H 1s orbitals.