Proposed Sensor Structure Research Articles

Sensitivity of Reflecting Terahertz Sensors of Aqueous Solutions

Sensitivity of sensors of aqueous solutions in which a terahertz signal is reflected from a structure consisting of a dielectric film and solution is studied. The maximum sensitivity is reached at angles of incidence and radiation frequencies that provide zero reflection of monochromatic radiation from the specified structure. Conditions for such reflection are determined for the s- and p-polarized radiation. The calculated results are proven by experimental data for a sensor of glucose in water in which a thin silicon film separates the solution from air. For the time-domain terahertz spectroscopy, the proposed sensor structure allows reliable detection and identification of glucose at concentrations of 10 and 30 g/L.

High-performance refractive index sensor for oil derivatives based on MWCNT photonic crystal microcavity

In this paper, we propose a new all-optical sensor based on a two-dimensional (2D) regular array of multi-walled carbon nanotubes (MWCNTs) for the refractive index sensing of oil derivatives, for the first time. The interaction of optical wave with the desirable oil derivatives is enhanced using the slow light effect that makes the group velocity go down. We consider the geometric feature for the proposed sensor structure as a photonic crystal (PhC) with a line defect formed by missing some rows of MWCNT elements. The difference of refractive index △n = 0.1418 between Butanol (C4H10O) and Nitrobenzene (C6H5NO2) host materials results in a wavelength shift of 149 nm, and indicates a sensitivity of 1050 nm/RIU, which can be widely used for the bio/chemical detection and environmental monitoring. To achieve the physical stability of the proposed sensor, MWCNTs are considered to be grown in the AAO (Al2O3) template. By removing one or two rows of the MWCNTs and creating a linear defect within the sensor structure, whereas oil derivatives are injected into the defect area. We have achieved a sensitivity up to 870 nm/RIU. This proposed sensor with un-reactive structure of MWCNTs can be used in environments with high temperature and pressure such as oil refinery industry and other chemical processes industries under wide range of different reaction conditions.

A New Planar Microwave Sensor for Building Materials Complex Permittivity Characterization.

A new microwave sensor is proposed to characterize the complex relative permittivity of building non-magnetic materials and used in the characterization of three concrete samples. The proposed sensor structure consists of a log-periodic planar antenna with microstrip elements tilted forward by an angle β and printed, alternately, on the top and bottom sides of a dielectric layer. The operation principle is based on the measurement of the scattering parameters S11 and S21 in a free space propagation transmitter-receiver setup, for both cases with the material under test (MUT) sample (non-line-of-sight, NLOS) and without it (line-of-sight, LOS). A prototype is fabricated and measured to determine the scattering parameters of concrete samples. After measurements, the obtained results are used in the efficient and accurate Nicolson–Ross–Weir (NRW) method, making it possible to estimate the values of the complex relative permittivity of the concrete blocks. The sensor design is demonstrated from initial simulations to measurements for validation of the developed prototype. The obtained results for the complex relative permittivity of concrete are in agreement with those available in the literature and the difference between the simulated and measurement results for the sensor antenna resonant frequency is 4.71%. The used measurement setup can be applied to characterize different types of solid or liquid dielectric materials.

Plasmonic sensor utilizing Ti3C2Tx MXene layer and fluoride glass substrate for bio- and gas-sensing applications: Performance evaluation

The two-dimensional (2D) heterostructure of black phosphorus (BP)–MXene shows great stability in liquid and gaseous environments. Sensitivity enhancement of a surface plasmon resonance (SPR) sensor utilizing BP and Ti3C2Tx MXene layer is proposed in this work. A CaF2 glass prism is considered as the coupling substrate and 2D Ti3C2Tx MXene as analyte interacting layer. The sensor’s performance is demonstrated in terms of sensitivity and figure-of-merit (FOM) values at an operating wavelength of 633 nm. An extremely high angular sensitivity of 322.46°/RIU is obtained, with a significant FOM value of 55.596/RIU (analyte refractive index ∼ 1.33) for three-layer BP–Ti3C2Tx MXene monolayer based SPR sensor. Further, the sensing of gaseous analyte using the proposed sensor structure is also explored. This work will open new avenues for application of BP–MXene heterostructure in various optoelectronic devices.

Au-nanoshells modified surface field enhanced LRSPR biosensor with low LOD for highly sensitive hIgG sensing

A high sensitivity side polished fiber long-range surface plasmon resonance (LRSPR) biosensor with electronic field enhanced through surface modified with Au-nanoshells is proposed to detect human immunoglobulin G (hIgG). LRSPR which has high penetration depth and long propagation distance can effectively detect biomacromolecules. The plasmon coupling effect between the Au-nanoshells and Au-film can enhance the electric field intensity on the surface of the sensor, which makes the proposed sensor structure have a lower limit of detection (LOD) and higher sensitivity. The experimental results show that the sensitivity as well as LOD of side-polished-fiber (SPF)/dielectric-matching-layer (DML)/Au-film/Au-nanoshells sensor is 1.84 nm/(µg/mL) and 0.20 µg/mL, which indicates better responses to hIgG with a concentration range of 1–40 µg/ml compared with the SPF/DML/Au-film sensor. The LRSPR sensor modified by Au-nanoshells was used to detect chicken serum samples and the calculated recovery is 107.62%, showing good practicality and superior self-referenced function. The biosensor has the advantages of small volume, high sensitivity and long-distance detection, and has good practicability in the field of biochemical sensing.

Perovskite Color Detectors: Approaching the Efficiency Limit.

Color image sensing by a smartphone or digital camera employs sensor elements with an array of color filters for capturing basic blue, green, and red color information. However, the normalized optical efficiency of such color filter-based sensor elements is limited to only one-third. Optical detectors based on perovskites are described, which can overcome this limitation. An efficient color sensor design has been proposed in this study that uses a vertically stacked arrangement of perovskite diodes. As compared to the conventional color filter-based sensors, the proposed sensor structure can potentially reach normalized optical efficiency approaching 100%. In addition, the proposed sensor design does not exhibit color aliasing or color Moiré effects, which is one of the main limitations for the filter-based sensors. Furthermore, up to our knowledge, for the first time, it could be theoretically shown that both vertically arranged sensor and conventional color filter-based sensor provide almost comparable color errors. The optical properties of the perovskite materials are determined by optical measurements in combination with an energy shift model. The optics of the stacked perovskite sensors is investigated by threedimensional finite-difference timedomain simulations. Finally, colorimetric characterization was carried out to determine the color error of the sensors.

Grease oil humidity sensor by using metamaterial

Interaction between water and lubrication grease oil is not desirable, but it is not inevitable. The operational life of the machine component is influenced by humid grease oil. Metameterial-based transmission line sensor application is proposed and its operation is validated both numerically and experimentally by inserting grease oil samples in the sample holder. The proposed sensor structure is able to determine the humidity ratio of grease oil samples. The proposed structure shifts resonance frequency to react to the grease oil’s dielectric constant. The frequency shift of grease oil samples is monitored as about 300 MHz’s. Linearity characteristic between resonant frequency and dielectric constant value is validated. The novelty of this article is that no such study has been conducted by employing non-destructive methods which provide long-term stability of the sensor structure.

Performance analysis of optical fiber surface plasmon resonance sensor in single-mode operation region

Abstract A new approach for studying the performance of single-mode optical fiber surface plasmon resonance sensor for refractive index sensing is presented. Intensity interrogation technique is used to observe and examine the effect of changing the value of the operating wavelength, within the single-mode operation region, on sensor performance. Effect of changing metal thickness, which is a critical parameter of the sensor structure, is also investigated. The results show that the selected operating wavelength within the mentioned region plays a very important role and has a significant impact on the sensor sensitivity. As the operating wavelength increases beyond the cut-off wavelength, above which the first higher-order mode disappears, the sensitivity increases while the refractive index range, for which the sensitivity is above its half maximum value, becomes narrower. In the proposed sensor structure, for a metal thickness of 25 nm, the maximum sensitivity reaches 2554 RIU−1 for analyte refractive index of 1.439 at a wavelength of 1500 nm. This sensitivity corresponds to a resolution of order 106 RIU by assuming 1% minimum reflectivity variation. The operating wavelength should be carefully selected and changed according to the refractive index values intended to be measured to ensure high sensor sensitivity at these values. The analysis provided in this paper enables to select and change the desired range of the sensed refractive index using low cost technique by just changing the operating wavelength in the single-mode operation region.

Etched multicore fiber sensor using copper oxide and gold nanoparticles decorated graphene oxide structure for cancer cells detection

A compact, portable, label-free, and ultra-sensitive sensor is proposed to detect cancerous cells based on Multi-Core Fiber (MCF) comprising of seven cores arranged in a hexagonal shape spliced with Single-Mode Fiber (SMF). Here, cytosensing based on fiber optic Localized Surface Plasmon Resonance (LSPR) is used for the efficient detection of different types of cancer cells. The proposed sensor structure is etched in a controlled manner to increase the evanescent wave (EWs) and coupling of modes between the cores of MCF. The etched MCF based LSPR probe has high refractive index sensitivity (RIS). To further increase the sensitivity, the sensor structure is immobilized with different nanomaterials (NMs) such as optimized size of gold nanoparticles (AuNPs), graphene oxide (GO), and copper oxide nanoflowers (CuO-NFs). AuNPs increase the sensitivity using LSPR, whereas, GO and CuO-NFs helps to increase the biocompatibility of sensor. The developed probe is further coated with 2-deoxy-D-glucose (2-DG) over NMs that are specific for the detection of cancer cells. In this work, various cancerous cell lines i.e. HepG2, Hepa 1–6, MCF-7, A549, and normal cell lines i.e. NCF and LO2 are detected using the developed sensing probe. Various analysis of proposed sensor such as selectivity, reusability, anti-interference ability, and involvement of GLUT receptor in detection has also been performed. The proposed etched sensor is ultra-sensitive for detection of HepG2, Hepa1 6, A549, MCF-7, LO2, and NCF cell lines with a limit of detection (LoD) of 3, 2, 2, 2, 4, 10 cells/mL, respectively in the linear range of 1 × 102–1 × 106 cells/mL.

Negative Curvature Hollow Core Fiber Based All-Fiber Interferometer and Its Sensing Applications to Temperature and Strain.

Negative curvature hollow core fiber (NCHCF) is a promising candidate for sensing applications; however, research on NCHCF based fiber sensors starts only in the recent two years. In this work, an all-fiber interferometer based on an NCHCF structure is proposed for the first time. The interferometer was fabricated by simple fusion splicing of a short section of an NCHCF between two singlemode fibers (SMFs). Both simulation and experimental results show that multiple modes and modal interferences are excited within the NCHCF structure. Periodic transmission dips with high spectral extinction ratio (up to 30 dB) and wide free spectral range (FSR) are produced, which is mainly introduced by the modes coupling between HE11 and HE12. A small portion of light guiding by means of Anti-resonant reflecting optical waveguide (ARROW) mechanism is also observed. The transmission dips, resulting from multimode interferences (MMI) and ARROW effect have a big difference in sensitivities to strain and temperature, thus making it possible to monitor these two parameters with a single sensor head by using a characteristic matrix approach. In addition, the proposed sensor structure is experimentally proven to have a good reproducibility.

Photonic crystal sensor based on Fano resonances for simultaneous detection of refractive index and temperature

A structure for simultaneous measurement of refractive index (RI) and temperature (T) is proposed based on photonic crystal (PhC) beam structures. The sensor structure consists of three parallel 1D PhC cavities, in which the middle cavity 1 has a wide linewidth, and cavity 2 and cavity 3 on both sides have a narrow linewidth. By changing the RI of the analyte and the T of the ambient, we explored the linear relationship between the two parameters and resonant wavelengths, respectively. For cavity 2 with air mode, the RI and T sensitivities are 377.2 nm/RIU and 101 pm/K, respectively. For cavity 3 with dielectric mode, the RI and T sensitivities are 194 nm/RIU and 261 pm/K, respectively. In addition, we also discussed the crosstalk between two adjacent cavities at different RI and T, and all crosstalk values are lower than −7 dB and −6 dB for RI and T, respectively. Compared with previous sensor structures, the proposed sensor structure could be used in simultaneous RI and T sensing with higher sensitivity and lower crosstalk values.

Time response characteristics of a highly sensitive barometric pressure change sensor based on MEMS piezoresistive cantilevers

This paper describes the frequency characteristics of a highly sensitive barometric pressure change sensor. Here, we propose a method to measure pressure changes based on microelectromechanical systems piezoresistive cantilevers and an air chamber. The proposed sensor structure realizes a mechanical high pass filter to eliminate the influence of the barometric pressure change due to meteorological variations. The experimental frequency characteristics indicate that the proposed sensor unit with a high resolution of less than 0.1 Pa from 0.1 to 10 Hz responds to pressure changes with a high pass filter property according to the chamber volume size.

Optical Pixel Sensor Based on a-Si:H TFTs to Detect Combined Optical Signals for Multiuser Interactive Displays

This article presents new optical pixel sensors that are based on hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs) for detecting secondary color optical signals to increase the number of colors of sensed light. Three types of series-connected structure with different photo TFTs enable the sensors to receive secondary color optical input signals that combine any two primary colors, such as magenta (blue and red), cyan (green and blue), and yellow (red and green). The secondary color optical sensors also prevent from being affected by light of a single color to integrate with primary color optical sensors for realizing a six-color sensing mechanism. Moreover, only one photo TFT is used to suppress the effect of ambient white light by compensating photocurrents without increasing the complexity of the proposed sensor structure. The measurements demonstrate that the difference in the output voltages is 15.6 V even under ambient white light with an intensity of 10000 lux, proving that the proposed sensor can yield significantly different sensing results with and without an optical input signal under intense ambient white light. Thus, the proposed sensors increase the number of sensed color light that can be integrated with a large TFT-LCD panel for multiuser interaction.

High Sensitivity Refractive Index Sensor Based on the Excitation of Long-Range Surface Plasmon Polaritons in H-Shaped Optical Fiber.

In this paper, we propose and numerically analyze a novel design for a high sensitivity refractive index (RI) sensor based on long-range surface plasmon resonance in H-shaped microstructured optical fiber with symmetrical dielectric–metal–dielectric waveguide (DMDW). The influences of geometrical and optical characteristics of the DMDW on the sensor performance are investigated theoretically. A large RI analyte range from 1.33 to 1.39 is evaluated to study the sensing characteristics of the proposed structure. The obtained results show that the DMDW improves the coupling between the fiber core mode and the plasmonic mode. The best configuration shows 27 nm of full width at half maximum with a resolution close to 1.3 × 10 nm, a high sensitivity of 7540 nm/RIU and a figure of merit of 280 RIU. Additionally, the proposed device has potential for multi-analyte sensing and self-reference when dissimilar DMDWs are deposited on the inner walls of the side holes. The proposed sensor structure is simple and presents very competitive sensing parameters, which demonstrates that this device is a promising alternative and could be used in a wide range of application areas.

Design of thin-film lithium niobate structure for integrated filtering and sensing applications

Lithium Niobate (LN) is a premium material with strong electro-optic coefficient and low-loss transparency window covering from visible to mid-infrared wavelength regions. Thin-film LN on Insulator (LNOI) is an emerging integrated photonic platform with excellent optical properties of LN and large refractive index contrast, which has attracted considerable research interests in the field of integrated optics. In this paper, we present an integrated structure on LNOI platform, which could serve as an electro-optic tuning filter with ultra-narrow bandwidth and large wavelength-tuning range. Moreover, the wavelength-tuning sensitivity reaches ~37.25 pm/V, which is about 8 times higher than that of the LN-based tunable filter proposed in our previous study. In addition, a method to expose this structure under external applied for sensing applications is proposed. Q-factor of our proposed sensor structure reaches 106 or even higher. When the refractive index of sensing materials changes by an order of 10−4, this sensor still exhibits observable transmission spectral responses. Structural flexibility and ease of integration make the proposed sensor a promising candidate for potential applications in the fields of optical communications, biological and chemical sensing.

Integrated optic-fiber sensor based on enclosed EFPI and structural phase-shift for discriminating measurement of temperature, pressure and RI

An optic-fiber sensor based on integration of extrinsic Fabry–Pérot interferometer (EFPI) and phase-shifted fiber Bragg grating (PS-FBG) is depicted and demonstrated. The proposed sensor structure mainly consists of an enclosed EFPI fabricated with photosensitive adhesive between two end-faces of a halved FBG. Since the periodic refractive index (RI) distribution of FBG is interrupted and resulted in a structural PS-FBG in the middle of FBG. Consequently, the enclosed EFPI is capable of measuring the variations of temperature, pressure and RI due to optical cavity length changes, whereas the notch wavelength of introduced structural phase-shift spectrum is only sensitive to temperature, and the intensity of structural phase-shift spectrum is only insensitive to pressure. Therefore, the discriminating measurement of temperature, pressure and RI can be realized, due to using the methods of wavelength modulation and intensity modulation. The relative errors of temperature, pressure and RI, between the analysis results and measurement values, are 1.4%, 4.1% and 0.1%. The proposed integrated sensor with cost-effective merit has a promising research prospect in the field of the multiple parameters distinguish measurement.

A Fiber Bragg Grating Force Sensor with Sensitization Structure

This article presents a fiber Bragg grating (FBG) force sensor with enhanced sensitivity. a strain-reinforcing mechanism comprised of a linear structure and loop-shaped structure is proposed. When external tension is applied, the strain directions are opposite in the two structures. Two FBGs were adhered to the surfaces of positive and negative strain bodies and sensor data were compared. Then, the sensing principle of the FBG force sensor was deduced based on the theory of material mechanics. Results of theoretical calculations and finite element analysis (FEA) show that sensitivity of the proposed sensor is about 5.07 times higher than an FBG directly adhered to the surface of the substrate. Comprehensive testing of the sensor prototype was conducted. Experimental results show that the sensor can achieve a sensitivity of 38.25 pm/kN with a repeatability error and hysteresis error of 2.11% and 1.76%, respectively. The enhanced coefficient is 4.84, which is basically consistent with theoretical design value of 5.07. In addition, favorable temperature compensation and creep resistance were obtained during performance tests. Good capability for alternating strain measurement has also been demonstrated. Our results demonstrate the potential for superior structural health monitoring in civil engineering applications using the proposed sensor structure.

Sensitivity enhancement of an SPR biosensor with a graphene and blue phosphorene/transition metal dichalcogenides hybrid nanostructure.

A novel surface plasmon resonance (SPR) biosensor based on Ag-Au bimetallic films with a hybrid structure of blue phosphorene (BlueP)/transition metal dichalcogenides (TMDCs) and graphene is presented. In order to improve the sensitivity, the thickness of silver and gold films is optimized to achieve minimum reflectivity and an adequate level of sensitivity; further, sensitivity for the monolayer BlueP/MoS2 and graphene structure is enhanced by 19.73%, with respect to a traditional sensor. Besides, the effect of layers of different Blue/TMDCs heterostructures to the sensitivity of the SPR biosensor is investigated, and the highest sensitivity with 335.4°/RIU for the bilayer BlueP/WS2 is obtained. Furthermore, distributions of the electric field and the changes of resonance angle to the refractive index of the sensing medium and prism in the visible regime are illustrated at optimal configuration. In virtue of highly sensitive characteristics, the proposed sensor structure will be a much better option to be employed for further biological detection.

Refractive index sensor based on selectively liquid infiltrated birefringent photonic crystal fiber

We propose a highly sensitive micro-fluidic refractive index (RI) sensor based on birefringent photonic crystal fiber (B-PCF) in this article. A single microchannel is infiltrated with liquid analyte, situated next to the core to attract mode field with analyte. The proposed sensor structure works on total internal reflection (TIR) mechanism. It is optimized and its sensitivity is numerically analyzed in detail using Finite Element Method (FEM). All the simulation results apprise that the structural parameter variation influences a little on the sensitivity of the refractive index sensor which suppress the necessity of the precise processing. A high sensitivity of 15428.50nm/RIU is achieved by this sensor with birefringence ∼ 10-4 in the RI range from 1.36 to 1.41 with a resolution of 5×10-6 RIU. The proposed highly sensitive RI sensor may be a potential candidate for chemical and industrial sensing applications.

An inductive-capacitive-circuit-based micro-electromechanical system wireless capacitive pressure sensor for avionic applications: Preliminary investigations, theoretical modelling and simulation examination of newly proposed methodology

Pressure is a key unit of measure in aerospace industries. Spontaneous precise measurement of pressure has to be compassed at locations where it is futile and impractical to couple the pressure responsive constituent to the conditional electronics or computational circuit by practicing standard cables and measurements prone to harsh environment. This paper introduces the design of a wireless pressure-monitoring system for aerospace applications in harsh environment. Traditionally, applied pressure deflects a delicate silicon diaphragm, altering the capacitance developed between it and metal electrode firm on a substrate. The LC circuit translates the pressure variation into the LC resonant frequency shift. This change is sensed remotely by virtue of inductance coupling, expelling the compulsion for wire connection rooted telemetry circuits. Novelty of our work rests in the fact that contrary to examining shift in the resonant frequency due to the applied pressure, we have put in effort to maintain resonant shifting equal to zero by varying the capacitance at the observer unit. This will allow pressure variations to be measured directly in terms of the capacitance variation at a fixed resonant frequency, which is 7.92 MHz in our context. According to the application domain (avionics), the proposed sensor structure is designed for functioning in the pressure range between (100 and 1140) mbar. The choice of design values for sensor parameters has been validated. The sensitivity is measured to be 1.746e−17 F/Pa over specified linear range which is shown to match a theoretical estimate realized by mathematical model. An in-depth, step by step derivation of performance parameters to achieve above-stated objective is shown for sensor under study. The results generated are modelled and examined using MATLAB. The analysis conducted dovetail perfectly with the modelled results.