Proposed Sensor Structure Research Articles

Graphene-Based Refractive Index Sensor With a 1-D Topological Photonic System

A terahertz refractive index sensor, which relies on utilizing the Tamm plasmon polariton and localized topological edge state, is proposed in a one-dimensional photonic crystal based on graphene. The proposed sensor structure is an active photonic device due to graphene’s tunable Fermi energy and optical properties. High sensitivity and a high figure of merit (FOM) are the results of the topological protection that allows a perfect zero reflection. Furthermore, the study investigates the sensing performance with various structural and material parameters. This refractive index sensor has the potential to be modified for use in industrial and diagnostic applications.

Investigation and performance improvement of optical fiber acoustic sensor based on diaphragm prestress tunable technology

In this paper, sensitivity and response frequency tunable optical fiber acoustic sensor technology is proposed for the first time, in which a C-shape pedestal mounted diaphragm sensor structure is employed for prestress tuning and consequently for the rigidity adjustment of the diaphragm to investigate and improve the performance of single mode-multimode-single mode (SMS) fiber acoustic sensor. By employing the proposed sensor structure, the influence of prestress on the resonance frequency and the sensitivity of optical fiber acoustic sensor can be investigated theoretically and experimentally. The results also confirm that the proposed method provide a simple but effective solution for the performance improvement of acoustic sensor, by which the response range can be extended from 800 Hz to 1500 Hz with a sensitivity fluctuation of 0.7 dB and a value of 0.998 by adjusting the prestress of diaphragm, meanwhile the background noise can be significantly suppressed from −57 dB to −67 dB.

Analytical Evaluation of a Coplanar Interdigitated Sensor Capacitance for 1-N-1 Multilayered Structure

In this article, an analytical expression (model) for the capacitance of coplanar interdigitated (IDT) capacitive sensors of four 1- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> -1 patterns (such as 1-1-1, 1-3-1, 1-5-1, and 1-11-1) based on conformal mapping (CM) techniques has been obtained. An important feature of the proposed model is that it is universal and independent of any specific application. The proposed model can be used for any number of layers (variable permittivity and thickness), finger width, and the gap between the fingers. In general, the capacitance of a particular IDT sensor depends on finger (electrode) length, the number of fingers, potential distribution of the fingers, dielectric permittivity (substrate and sensitive layers), and geometric parameters (nondimensional): 1) the ratio between the finger widths and gap and 2) the ratio between the top sensitive layer thickness and the sensor wavelength (spatial). Keeping these parameters in mind, comparisons with finite element analysis and experimental results have been made. Also, to confirm the effectiveness of the proposed model, different patterns of 1- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> -1 structured IDT sensors have been developed to measure the water droplets on the leaf canopy by a noncontact method. The proposed sensor structure can be said to be a noncontact leaf wetness sensor (LWS), generally employed to quantify the leaf wetness duration (LWD).

Microwave-Based Electrochemical Sensor Design by SRR Approach for ISM Sensing Applications

This paper presents a transmission line and a split ring resonator (SRR) based sensor structure with a high sensitivity capacity to discriminate various methanol mixtures. The height of the dielectric layer and thickness of copper are assigned as 1.6 mm and 0.035 mm, respectively. The overall dimensions of the sensor structure are defined as 16 mm × 16 mm × 1.6 mm . The operating frequency is selected for the ISM bands, especially around 2.45 GHz. Different methanol-water mixtures are prepared at various ratios, and then, the complex permittivity values are measured. Different sensor structures are modelled and investigated using a two-port transmission line approach. Various types of SRR based sensors are designed, and an optimum design is proposed for methanol mixture detection applications. The observed quality factor of the proposed sensor is 16.5. The resonance shifts of the transmission value ( S 21 ) are used for sensing capability around 2.45 GHz at -45 dB and 90 MHz resonance shifts. The sensitivity of the sensor has been evaluated as 1 MHz. Finally, the electric field distributions of the proposed SRR integrated transmission line are investigated. The novelty of the proposed design is to exactly sense the ratio of methanol in water with a very simple design. The proposed sensor structure can be used for methanol detection applications in medical, military, and chemical research.

Construction of multiple anti-resonant light guidance mechanisms in a hollow-core fiber structure for simultaneous measurement of multiple parameters.

The construction of multiple light guidance mechanisms in a hollow-core fiber (HCF) structure is a popular way to realize the simultaneous measurement of multiple parameters. In this work, a partial coating method to excite multiple anti-resonant light guidance mechanisms (ARLGMs) in an HCF structure for the simultaneous measurement of multiple parameters is proposed. As an example, a double ARLGM based on a partially polyimide (PI)-coated HCF structure for the simultaneous measurement of relative humidity (RH) and temperature is demonstrated theoretically and experimentally. The dip (dip II) produced by the PI-coated HCF section shifts linearly with surrounding RH changes with a sensitivity of circa 58.6 ± 0.77 pm/%RH, while the dip (dip I) produced by the bare HCF section (with an air coating layer) is insensitive to RH changes. In addition, both types of dips have linear responses to temperature variations, with similar sensitivities of ∼ 17 pm/°C. Hence, the proposed sensor structure can be used as an RH sensor that is also capable of compensating for local temperature fluctuations. More importantly, the simultaneous measurement of multiple parameters (such as biomarkers) is possible using the proposed method provided the proper sensing materials are partially coated onto the HCF surface.

Paper-Based Piezoresistive Force Encoder for Soft Robotic Applications

This work demonstrates the design, implementation, and experimental results of a low-cost disposable flexible sensor system capable of both impact localization and measurement. The proposed flexible sensor structure utilizes a special series of Bristol paper as the main fabrication material, which is coated with electric paint graphite paste and silver paste. The implemented sensor system uses a planar absolute encoder-like sensing topology to locate the impact and has a low-cost and quick manufacturing process. The size of the structure is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${210}\times {18}.{56}$ </tex-math></inline-formula> mm with a thickness of approximately 340 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> . It has an electronic read-out consisting of three identical Wheatstone bridge circuits and instrumentation amplifiers for each bit. It can detect the external forces in the range of 0.6N to 12N with a spatial resolution of 2.4 cm and 0.55 cm in horizontal and vertical axes, respectively. The proposed sensor structure is tested in a series of experiments using a robotic setup consisted of a pantograph mechanism and a direct drive linear motor. The experiments illustrate the results with measurement sensitivity as small as 1N and proper fatigue resilience against repetitive loads.

Low-cost high-sensitivity pH sensor based on a droplet-shaped single-mode fiber Mach–Zehnder interferometer

In this paper, we present the fabrication of a new fiber-optic pH sensor based on the macro-bending loss properties in a droplet-shaped single-mode fiber (SMF) bending structure for the first time. To form the droplet-shaped probe, a segment of straight SMF is properly bent into a droplet shape using a short length of a thin silica capillary tube and without any splicing. By gradually varying the bending diameter of the droplet-shaped structure, interference results between the core and cladding modes, and a Mach–Zehnder interferometer (MZI) is effectively introduced within the bending section. Sodium hydroxide (NaOH) or hydrochloric acid (HCl) were added to the pH indicator utilizing buffers solution to achieve a wide pH range from 1 to 14. Experimental results show that the proposed sensor exhibits maximum sensitivity of 3.264 nm/pH and 5.336 nm/pH for acidic and alkaline solutions, respectively. In addition to the high sensitivity, the proposed sensor structure provides high sensitivity with a high linear response and good repeatability.

Fiber Acoustic Sensor With Stable Operating-Point Based on a Photo-Thermal Cavity

Ambient temperature fluctuations inevitably affect the stability and accuracy of most of the existing fiber acoustic sensors. To overcome this drawback, a fiber acoustic wave transducer with stable operating-point based on a photo-thermal cavity (PTC) is proposed in this article. The proposed Fabry-Perot interferometer (FPI) is formed by splicing a section of high-attenuation microfiber (HAMF) between a pair of wavelength-matched fiber Bragg gratings (FBGs). The applied acoustic wave would dynamically disturb the medium refractive index (RI) around the HAMF, causing the narrow Fabry-Perot interferometric fringe shift. The wavelength of the probe laser is tuned on the slope of the interferometric fringe. Theoretical analysis and experimental verification had been performed. The HAMF acts as an excellent active compensated component, which can steady the operating-point through adjusting the heating light source power. The proposed sensor structure has a compact size, simple fabrication and especially the stable operating-point, which make it more suitable for in-situ detecting in application of bioimaging or underwater sonar.

A ϕ-Shaped Bending-Optical Fiber Sensor for the Measurement of Radial variation in Cylindrical Structures

This work presents preliminary results of the ϕ -shaped sensor mounted on support designed by additive manufacturing (AM). This sensor is proposed and experimentally demonstrated to measure the radial variation of cylindrical structures. The sensor presents an easy fabrication. The support was developed to work using the principle of leverage. The sensing head is curled between two points so that the dimension associated with the macro bend is changed when there is a radial variation. The results indicate that the proposed sensor structure can monitor radial variation in applications such as pipelines and trees.

Design of High-sensitivity π-PS-LPFG sensor based on SDOR for simultaneous measurement of SRI and temperature

In this paper, a π-phase-shifted long-period fiber grating (π-PS-LPFG) sensor structure operating near phase-match turning point (PMTP) is proposed, which is able to simultaneously detect surrounding refractive index (SRI) and temperature. First, the parameters of film, grating period and grating length are designed by theoretical simulations. Then, a π-phase-shift is introduced to make the single peak of the 25th cladding mode disappear, and two loss peaks are formed in both sides of the original single peak. When the external environment changes, the distance between the center wavelengths of the two loss peaks changes, while a single peak is formed again at the wavelength of the original 25th cladding mode with the change of intensity. Finally, the wavelength spacing of dual-peak and the intensity of the 25th cladding mode resonance peak with SRI and temperature are analyzed, and the results show a good fitting. The simulation results show that the SRI sensitivities based on wavelength modulation and intensity modulation are 9093.3 nm/RIU and −2870 dB/RIU respectively, and the temperature sensitivities based on wavelength modulation and intensity modulation are −0.3 nm/℃ and 0.217 dB/℃ respectively. Compared with other wavelength and intensity modulation based dual-parameter LPFG sensors, the SRI and temperature sensitivities of our proposed sensor structure are at least 10 times and 2 times higher than that of those LPFG sensors that have been reported. Its low fabrication cost, simple configuration, good fitting and high sensitivity make this sensor have potential applications in multi-parameter measurement.

High-Sensitivity and Low-Loss Vector Magnetic Field Sensor Based on the C-Type Optical Fiber

A low-loss all-straight optical fiber vector magnetic field sensor (OFVMS) based on magnetic fluid (MF) is designed and proposed. The sensing structure is composed of a Section of the C-type optical fiber (CTF) embedded in a pair of multi-mode optical fibers (MMF) and wrapped in a capillary with MF. The asymmetry of the CTF provides support for the vector magnetic field measurement whose direction is perpendicular to the optical transmission direction. According to the results of experiments, it can be obtained that the refractive index (RI) sensitivity of the sensing structure is as high as −15716.6072 nm/RIU. In addition, the intensity sensitivity of the OFVMS in the calibrated 90° direction can reach 202.23 pm/G between 0 and 123 G. At the same time, the transmission loss of the proposed sensor structure is not increased by the filling of MF. The sensor demonstrated has dominance in low cost, easy manufacture, and lower loss compared with the same type of sensor device, which has application prospects in vector magnetic field sensing.

Self-Powered, Ultrathin, and Transparent Printed Pressure Sensor for Biosignal Monitoring

Ultrathin sensing devices utilizing piezoelectric materials have emerged as potential candidates to develop highly skin-conformable and energy-efficient continuous biosignal monitoring systems. However, biocompatible, cost-efficient, and simple fabrication processes still need to be investigated to enable wider adoption of such devices. This study proposes a simple two-step printing process for the fabrication of a piezoelectric biosignal sensor that utilizes readily available and biocompatible polymer-based materials for the substrate (i.e., Parylene-C), electroactive layer (i.e., poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE)), and interdigitated electrodes (i.e., poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)). The proposed interdigitated electrode architecture improves upon the conventional metal–insulator–metal architecture by (1) increasing the thickness-normalized output voltage and (2) enabling the detection of bending orientation. The performance of the proposed sensor structure is demonstrated with the measurement of the arterial pulse waveform signal and limb movement detection. The presented results pave the way for cost-effective and continuous unobtrusive on-skin biosignal monitoring.

High sensitivity fiber-optic temperature sensor based on PDMS glue-filled capillary

A high sensitivity fiber-optic sensor based on temperature-sensitive material is proposed and demonstrated experimentally. The sensor consists of single-mode fiber (SMF), silicon capillary tube (SCT) and polydimethylsiloxane (PDMS) film, where the PDMS glue is filled into the SCT and s a temperature-sensitive medium sensing cavity is formed at the end of the SMF. Due to its high thermal expansion and thermo-optic effects, the sensor structure is more sensitive response to the change of ambient temperature. The experiment results demonstrate that the maximum temperature sensitivity of our proposed sensor is 3.449 nm/°C in temperature range of 34–48 °C, and the linearity of fitting curve is 99.9%. Compared with the same structure but filled with ultraviolet (UV) glue, the PDMS-based sensor not only has much higher temperature sensitivity, but also has better stability and repeatability. For the new type of sensor composed of optical fiber microstructure and sensitive material, the proposed sensor structure can increase the measurement temperature range. The sensor structure is simple to fabricate, stable in structure, and possessing good repeatability, which has great potential applications in the temperature sensing fields.

On the sensing performance enhancement in SPR-based Biosensor using specific two-dimensional materials (Borophene and Antimonene)

Antimonene-borophene based surface plasmon resonance (SPR) biosensor for sensitive detection is proposed, simulated, and analyzed. To the best of our knowledge, the antimonene-borophene combination has been studied in the plasmonic sensors for the first time. The proposed sensor utilizes the anisotropy property of black phosphorus (BP)/borophene between graphene/antimonene and gold layer along with the high adsorption efficiency/delocalized orbitals of graphene/antimonene for sensitivity improvement. The thickness of gold layer has been optimized for the rotation angle of the proposed biosensor around the z -axis (in-plane). The sensitivity of proposed sensor structure is as high as 206.26°/RIU. Further, extremely fine detection limit (4.84 × 10 −6 RIU), large propagation length (3220 nm) and large penetration depth (76.73 nm) are achieved for the proposed sensor. The obtained values of above parameters are considerably better than the reported sensors in the literature. • Au-borophene-antimonene based sensor chip exhibits high sensitivity with a detection limit of 4.84×10 -6 RIU. • Au-borophene-antimonene biosensor has higher penetration depth of 76.73nm. • The combination of Au-borophene-antimonene is superior to ultrasensitive detection of biomolecules with finer limit of detection.

Theoretical investigations of Tamm plasmon resonance for monitoring of isoprene traces in the exhaled breath: Towards chronic liver fibrosis disease biomarkers

Detection of blood-carried volatile organic compounds (VOCs) existing in the exhaled breath of humans is an attractive research point for noninvasive diagnosis of diseases. In this research, we have introduced a novel design of photonic crystals (PCs) for the detection of isoprene traces in the exhaled breath as a biomarker for liver fibrosis. To the best of our knowledge, this idea has been introduced for the first time. The proposed sensor structure contains a one-dimensional (1D) PCs covered with a cavity layer of air and a thin metallic layer of Au is attached on the top surface. Hence, the proposed sensor is configured as, [prism/Au/air cavity/(GaN/SiO2)10]. The main idea of the detection procedure is based on the changes in the levels of isoprene traces as the dry exhaled breath (DEB) fills the cavity layer. The transfer matrix method and the Drude model are adopted to calculate the numerical simulations and reflection spectra of the design. The essential key for sensing isoprene levels is the resonant optical Tamm plasmon (TP) states within the photonic bandgap. The obtained numerical results are investigated for both high and low concentrations of the isoprene trances. Due to the optimization route, the designed sensor could receive a relatively high sensitivity (S) of 0.323 nm/ppm or 300000 nm/RIU. Also, we have obtained a quality factor of 980 for ppm levels and a pronounced value of 5042 for ppb levels. This technique can be reducing the risk of infection during the taking of blood samples by syringe. Finally, the imposed gas sensor here could be of potential interest for monitoring several diseases based on the type and level of the exogenous VOC occurring in the exhaled breath.

A monopole microwave-assisted electrochemical sensor for the detection of liquid chemicals

In this paper, a new sensor structure is presented based on a printed circuit board (PCB) monopole antenna with operating frequency of f= 2 GHz. Numerical investigation was performed in order to determine the ethanol alcohol ratio in wine and isopropyl alcohol ratio in disinfectants (sanitizers). Finite Integration Technique (FIT) based commercial high-frequency electromagnetic solver CST Microwave Studio has been used for the simulation study. The loss tangent values and dielectric constants of the samples used in the current study were obtained by KEYSIGHT brand PNA-L N5234A Network Analyzer. The proposed sensor structure was able to greatly differentiate the ethanol alcohol content in the wine and the isopropyl alcohol content in the sanitizer through the return loss values and corresponding graphs. In the design of patch antenna, the electromagnetic permittivity ratios of the samples corresponding to the alcohol ratio and isopropyl ratio are considered and the antenna dimensions along with the working frequency were optimized accordingly. In the related frequency band, permittivity values corresponding to the ethanol alcohol and isopropyl alcohol ratios exhibit a linear variation and make the sensor design possible. According to the obtained results, it was found that the changes in the resonance frequency can be associated with ethanol alcohol and isopropyl alcohol ratio inside the samples. The change of ethanol alcohol amount and isopropyl alcohol in the liquid samples tested at the resonance frequency of patch antenna is proportional to the change in the resonance frequency and they are very close to a linear characteristic.

Water Pollutants p-Cresol Detection Based on Au-ZnO Nanoparticles Modified Tapered Optical Fiber.

In this work, a localized plasmon-based sensor is developed for para-cresol (p-cresol) - a water pollutant detection. A nonadiabatic [Formula: see text] of tapered optical fiber (TOF) has been experimentally fabricated and computationally analyzed using beam propagation method. For optimization of sensor's performance, two probes are proposed, where probe 1 is immobilized with gold nanoparticles (AuNPs) and probe 2 is immobilized with the AuNPs along with zinc oxide nanoparticles (ZnO-NPs). The synthesized metal nanomaterials were characterized by ultraviolet-visible spectrophotometer (UV-vis spectrophotometer) and transmission electron microscope (HR-TEM). The nanomaterials coating on the surface of the sensing probe were characterized by a scanning electron microscope (SEM). Thereafter, to increase the specificity of the sensor, the probes are functionalized with tyrosinase enzyme. Different solutions of p-cresol in the concentration range of [Formula: see text] - [Formula: see text] are prepared in an artificial urine solution for sensing purposes. Different analytes such as uric acid, β -cyclodextrin, L-alanine, and glycine are prepared for selectivity measurement. The linearity range, sensitivity, and limit of detection (LOD) of probe 1 are [Formula: see text] - [Formula: see text], 7.2 nm/mM (accuracy 0.977), and [Formula: see text], respectively; and for probe 2 are [Formula: see text] - [Formula: see text], 5.6 nm/mM (accuracy 0.981), and [Formula: see text], respectively. Thus, the overall performance of probe 2 is quite better due to the inclusion of ZnO-NPs that increase the biocompatibility of sensor probe. The proposed sensor structure has potential applications in the food industry and clinical medicine.

High Sensitivity and High Stability Dual Fabry-Perot Interferometric Fiber-Optic Acoustic Sensor Based on Sandwich-Structure Composite Diaphragm

A dual Fabry-Perot (FP) interferometric fiber-optic acoustic sensor based on sandwich-structure composite diaphragm is proposed, where fixed phase difference is generated by two FP interferometers (FPIs) with different cavity length. An ellipse fitting differential cross multiplication (EF-DCM) interrogation process is applied for phase demodulation to overcome drawbacks of quadrature point based intensity demodulation, such as temperature drifting, optical power jitter and limited dynamic range. Besides, benefiting from the large area sandwich-structure composite diaphragm, high sensitivity and wide flat frequency response are obtained. Experimental results show that phase sensitivity is -121.11 dB re 1 rad/μPa@250 Hz and sensitivity fluctuation is below 0.8 dB between 2-250Hz. To prove the high stability of the demodulation system, acoustic signal test is performed at different wavelength and different optical power and a fluctuation below 3% is observed. Moreover, profiting from the dual FP sensor structure, the acoustic sensor is get rid of influence of temperature drifting which usually leads to variation of cavity length of fiber optic acoustic sensor. The proposed sensor structure also overcomes drawbacks of traditional dual wavelength demodulation such as extra noise introduced by erbium doped fiber amplifier (EDFA) and high cost.

Effect of bending on photonic crystal fibre based surface plasmon resonance biosensor

In this study, the effect of bending on proposed PCF based SPR biosensor has been analysed by employing the Full vectorial Finite Element Method (FVFEM) with Perfectly Matched Layers (PMLs). The spectral interrogation method is chosen to calculate the sensitivity and the resolution of the proposed sensor structure. The blood components (water, cytop, blood plasma, white blood cell (WBC)) refractive index variations are used as a sample. Our numerical results have shown that the overall performance of the proposed sensor can be improved up to 63% by bending. Also, the resonance wavelength of the proposed sensor can be tuned by bending.

Thermal analysis of 22.9-kV crosslinked polyethylene cable joint based on partial discharge using fiber Bragg grating sensors

Thermal effects of power cables are critical factors for determining the remaining lifetime and efficiency of power grids. Herein, we propose a fiber Bragg grating (FBG) sensor package with high-temperature sensitivity. Using polyacetal, which has a higher coefficient of thermal expansion than typical optical fibers, we constructed the proposed sensor structure. The developed sensor exhibited about 14.1 times higher temperature sensitivity than a typical bare FBG sensor. To measure the temperature variation of power cable joints caused by partial discharge, we constructed a mock system similar to a manhole, and we installed the developed sensor at a 22.9-kV crosslinked polyethylene cable joint. The experimental result reveals that even a slight temperature difference of 0.2°C can be measured using PD (300 pC at 20 kV).