Flexible Optical Sensor Research Articles

Optical and electrical analysis of Rhodamine 110 chloride/PVA-PEG for smart and flexible optical sensor technology

Polyvinyl alcohol (PVA)/Polyethylene glycol (PEG) (90:10 wt%) polymeric nanocomposite films were prepared via a simple casting technique with Rhodamine 110 chloride (Rh-110) dye for optoelectronics with various weight ratio percentages (0, 0.06, 0.1,0.2, 0.4, 0.6 1.25, 2 and 4.0 wt%) of Rh-110 doped PVA/PEG polymeric blend composite films. The produced films have been studied with instruments like (XRD and FT-IR) spectroscopic methods, UV-visible-NIR spectrophotometer, and dielectric spectroscopy. The absorbance (Abs) and transmittance T(λ) were measured and analyzed. Absorption spectra in multiple bands are generated between 215 and 620 nm when Rh-110 is added to the PVA-PEG matrix, according to the examination of transmittance curves of Rh-110 /PVA-PEG. Rh-110/PVA-PEG has a transmittance CUT-OFF in the 200–550 nm wavelength range, making it ideal for He–Ne lasers with wavelengths of 532.8 nm. The optical properties of the Rh-110/PVA-PEG polymeric composite films were computed. Moss, Reddy, Anani, and Kumar-Singh relationships have been employed to determine the refractive index values of the materials. Analyses were performed on various electrical properties, including AC conductivity, dielectric constant, and dielectric loss. As a result, the synthesized Rh-110/PVA-PEG polymeric films may be used in various promising and practical optoelectronic applications, including lasers, optical filters, optical communication, light-emitting diodes, and optical switching.

Real-Time Estimation of Human Arm Dynamic Parameters Based on Optical

Abstract A flexible optical intensity sensor is designed in this study to address the poor adaptability of fixed-value parameters in exoskeleton research, which makes it difficult to handle system changes and uncertainties. The light transmission portion of the sensor is made of TPU and PET, exhibiting flexibility and bendable deformation characteristics, as well as good sensitivity, anti-interference capability, and stability. The flexible optical sensor is fixed on the side of the binding device, which is installed on the biceps brachii to collect the optical intensity loss signals after sensor bending. By utilizing this method, parameters such as the cross-sectional radius, arm centroid, and moment of inertia can be estimated in real-time. Finally, the estimated radius values are compared with theoretical values, and the accuracy is verified by combining the kinematic model. Experimental results demonstrate that the proposed method achieves a parameter information error of less than 8.63% and a stability better than 4.3%. Compared to the traditional fixed parameter method, the stability has improved by 25.06%, and the accuracy has improved by 9.04%.

Packaged Elastomeric Optical Fiber Sensors for Healthcare Monitoring and Human‐Machine Interaction

Elastomeric polymer optical fiber (EPOF) enabled flexible optical sensors have been attracting intensive research interest due to their excellent stretchability, sensing performance, and anti‐electromagnetic interference. However, a soft EPOF without effective protection tends to be damaged, which may undermine its long‐term stability, and thus, limit its practical applications. In this work, a strategy for packaging a section of EPOF is proposed, a light‐emitting diode (LED), and a photodiode (PD) into a stretchable and flexible silicone patch for both healthcare and human‐machine interaction applications. The silicone package not only protects the EPOF from environmental disturbance, providing a compact sensing approach for conformal attachment on flexible or curved surfaces but also offers an effective manner to adjust the sensitivity and working range of the EPOF sensors. Typically, an EPOF sensor is sensitive to pressure, strain, or bending. As a proof‐of‐concept demonstration, a laryngoscope equipped with a packaged EPOF sensor that can bear a pressure of 60 MPa is developed. It can effectively avoid teeth damage by real‐time monitoring the contact force during the operation. Furthermore, a data glove with five packaged EPOF sensors for hand gesture recognition and remote control of a micro‐vehicle is fabricated.

Optical Properties of TiO2 Doped ZnO-PVA Nanocomposites

One of the materials with the greatest potential for use in flexible devices is semiconductor nanocomposite material. In this paper, we report the synthesis of ZnO-PVA-TiO2 nanocomposite to be applied as a flexible optical sensor device. The optical property of ZnO-PVA nanocomposite is improved by the addition of TiO2 in this work. The optical characteristics of the ZnO-PVA nanocomposite depend on the concentration of TiO2. Spin coating method was successfully used to synthesize ZnO-PVA-TiO2 with various TiO2 concentrations of 1%, 2%, and 3% w/v, respectively. The absorbance spectrum of ZnO-PVA-TiO2 nanocomposite changes with the addition of TiO2. The absorbance peaks of ZnO-PVA-TiO2 nanocomposites were shifting to a lower wavelength, resulting in increasing the nanocomposite band gap energy. According to this result, future applications of the flexible optical sensor are one of the potential devices based on this study.

Highly sensitive photodetector based on laser-generated graphene with 3D heterogeneous multiscale porous structures

Graphene holds great promise in optoelectronics because of its high broadband light absorption across a wide range of wavelengths. Despite low optical absorption, various techniques have been devised to address this challenge. This study presents a new highly sensitive, photodetector based on three-dimensional (3D) porous graphene derived from fluorinated polyimide (fPI-3DPG). This material is produced via a laser photothermal process and features micro- and nanopore structures that increase the light absorbing area and support optically resonant structures. The resulting fPI-3DPG photodetectors display high photoresponsivity of 4.4 mA W−1 in the visible light range, an ultrahigh signal-to-noise ratio of ∼208, and a noise equivalent power of 0.54 × 10−11 W Hz−1/2. These photodetectors are also mechanically durable, surviving 10,000 cycles of bending and twisting. The laser photothermal method used in this study enables fast, cost effective production of wearable and flexible optical sensors for imaging and spectroscopy applications, making this 3D graphene a promising functional material for sensing technologies.

Flexible optical sensor composited by bisphenol-A acrylate for perceptual detection with high sensitivity

In this paper, a flexible optical sensor based on bisphenol-A acrylate polymer fiber (BAA-POF) is fabricated and demonstrated. The BAA-POF is composed of bisphenol-A acrylate monomers and additives in a certain proportion. When the pressure is applied to the BAA-POF, or the BAA-POF is bent by an angle, the sensor can perceive variations of the output spectrum loss caused by the sensor sensing accordingly. Experimental results show that the sensor has good linear responses to pressure and bending perception with negligible temperature and humidity cross-impact. The pressure sensitivity is 1.24 dB/N and the bending sensitivity is 0.08 dB/°. Moreover, the sensor is also proved for application in activity perception of the elbow joint.

On Dy+3 Nobbled ZnO-Reinforced PVDF for Flexible Optical Sensor

On Dy+3 Nobbled ZnO-Reinforced PVDF for Flexible Optical Sensor

Responsive Liquid‐Crystal Microlaser Arrays with Tactile Perception

AbstractFlexible photonics has the potential to develop artificial skins with superior sensing capabilities. As an essential skin function, the tactile simulation is, however, still challenging due to the difficulty in combining high pressure sensitivity and resolution in sensor networks. Here, this work designs flexible artificial photonic skins for the vivid tactile perception based on responsive cholesteric liquid‐crystal (CLC) vertical‐cavity microlaser arrays. Controllable liquid‐crystal molecule arrangement is explored to synthesize the elastic CLC vertical microcavity lasers, which support a strong correlation between the laser output signals and the external pressures. Large‐scale integration of the CLC microlaser‐based mechanical sensors enables the spatially resolved detection of pressures. As a proof‐of‐concept demonstration of vivid tactile simulation, the flexible photonic chip consisting of a CLC microlaser array is used to identify the contact objects. These results present a significant advance in the construction of high‐performance flexible optical sensor networks, thus providing valuable guidance for the design of novel photonic skins.

Highly Sensitive Strain Sensor Based on Microfiber Coupler for Wearable Photonics Healthcare

Flexible strain sensors are essential components of wearable smart devices that perceive and respond to strain stimulations. However, the sensitivity and response time of most sensors require further improvement to detect subtle strains related to human bodies. Herein, an ultrasensitive flexible optical sensor with fast response time has been built based on a microfiber coupler encapsulated in polydimethylsiloxane. Benefiting from dramatic change of coupling ratio of the microfiber coupler under weak strain, this flexible strain sensor exhibits ultrahigh strain sensitivity (gauge factor, GF = 900), low detection limit (0.001%), ultrafast response time (<0.167 ms), wide sensing range (0.45%), and superior durability and stability (>10 000 cycles). Real‐time capturing and recognizing of respiration, broadband sound signals, and pulse waves at different sites of human body have been demonstrated based on this highly sensitive microfiber coupler sensor. Moreover, simultaneous detection of the wrist pulse and human voice has been achieved based on the frequency division multiplexing technology. This flexible photonics strain sensor could serve as the prototype of ultrasensitive flexible optical sensors with fast response time for the development of high performance and wearable healthcare devices.

A bioinspired flexible optical sensor for force and orientation sensing

A bioinspired flexible optical sensor for force and orientation sensing

Flexible random laser from a porous polymer film

Flexible random lasers have attracted a great deal of interest due to their potential in light-weight, flexible optical sensors and devices. Among many alternatives, flexible thin film random lasers are very interesting because they can be easily fabricated via a simple solution-based process. Herein, we demonstrate a dye-doped porous polyvinyl alcohol film that can work as a flexible random laser source under optical pumping. The film is fabricated by a drop cast technique and has a nearly circular shape with a diameter of ∼5 mm. Owing to the inverted photonic glass structure that is air voids in the polymer matrix, light emission from dye molecules is multiple scattering and lasing emission is achieved. In the central area, the film laser works reliably with the lasing threshold of ∼166μJ/mm2 and lasing wavelength of around 595 nm. In the edge area, the lasing properties are more fluctuated indicating that the structure may not be uniform. It is found that the lasing wavelength in the edge area is 4.5 nm red-shifted compared to that in the central area of the film. Interestingly, the thin film laser can operate well under bending conditions with a minor change in the lasing wavelength.

Highly sensitive and wide-range flexible sensor based on hybrid BaWO4@CS nanocomposite

Flexible photoelectronic devices are in demand right now. In this work, a new family of biopolymer-based photodetectors is described. Chitosan (CS) was utilized as a safe, biodegradable host biopolymer, and nanostructured barium tungstate (BaWO4) particles were used as the nanofiller of the biopolymer matrix to prepare flexible optical sensors. The co-precipitation process was used to produce the filler powders, which were then dried at room temperature without using any surfactants or hazardous solvents. The fabricated sensor showed high flexibility and sensitivity to UV/proton/alpha and laser irradiation. X-ray diffraction (XRD), XPS, FTIR, EDX-map analysis also confirmed the successful synthesis, related chemical binding, and elements in the nanocomposite structure. According to the TEM images, the average particle size of synthesized BaWO4 NPs was obtained at about 110 nm. A considerable luminescence emission was observed in the constructed sensor's blue/green and ultraviolet spectral regions under various excitation sources. The developed sensor was nontoxic to the cells and provided soft, thin, antibacterial activity, flexible, and comfortable contact with skin, and promising ionizing ray detection applications in flexible optical sensors.

Lead (Pb2+) ion sensor development using optical fiber gratings and nanocomposite materials

Research on compact, flexible optical sensors for water quality monitoring, specifically targeting heavy metal ion monitoring, has become extremely important due to the increasing number of water pollution incidents seen worldwide where such heavy metals are involved. Optical fiber-based sensors provide an excellent basis for creating new sensing solutions across a wide area, including for energy, healthcare, structural monitoring, defense and importantly here for environmental monitoring. An innovative, cost-optimized sensor solution to better heavy metal detection is proposed, by introducing a hybrid optical fiber grating sensor system based on concatenating a Long Period Grating (LPG) and Fiber Bragg Grating (FBG) for the concurrent detection of an important, specific heavy metal ion pollutant (in this case lead (Pb2+)). The approach uses the functionalization of an optical fiber grating with a chemically synthesized novel nanocomposite material (together with temperature sensing to allow such corrections to be applied). Such a method not only significantly enhances the system sensitivity (achieving 2.547 nm/nM), with a detection limit (0.5 nM), and high selectivity to the Pb2+ ions, but also mitigates the shortcomings of cross-sensitivity seen with many such sensors. Furthermore, in this work, the incorporation of a forward Artificial Neural Network (ANN)-based predictive algorithm has been incorporated to create an effective, well-calibrated system whose characteristics as an intelligent, highly sensitive system has been demonstrated in the detection of the sub-nanomolar concentration of Pb2+ ion in drinking water.

Multifunctional flexible optical waveguide sensor: on the bioinspiration for ultrasensitive sensors development

This paper presents the development of a bioinspired multifunctional flexible optical sensor (BioMFOS) as an ultrasensitive tool for force (intensity and location) and orientation sensing. The sensor structure is bioinspired in orb webs, which are multifunctional devices for prey capturing and vibration transmission. The multifunctional feature of the structure is achieved by using transparent resins that present both mechanical and optical properties for structural integrity and strain/deflection transmission as well as the optical signal transmission properties with core/cladding configuration of a waveguide. In this case, photocurable and polydimethylsiloxane (PDMS) resins are used for the core and cladding, respectively. The optical transmission, tensile tests, and dynamic mechanical analysis are performed in the resins and show the possibility of light transmission at the visible wavelength range in conjunction with high flexibility and a dynamic range up to 150 Hz, suitable for wearable applications. The BioMFOS has small dimensions (around 2 cm) and lightweight (0.8 g), making it suitable for wearable application and clothing integration. Characterization tests are performed in the structure by means of applying forces at different locations of the structure. The results show an ultra-high sensitivity and resolution, where forces in the μN range can be detected and the location of the applied force can also be detected with a sub-millimeter spatial resolution. Then, the BioMFOS is tested on the orientation detection in 3D plane, where a correlation coefficient higher than 0.9 is obtained when compared with a gold-standard inertial measurement unit (IMU). Furthermore, the device also shows its capabilities on the movement analysis and classification in two protocols: finger position detection (with the BioMFOS positioned on the top of the hand) and trunk orientation assessment (with the sensor integrated on the clothing). In both cases, the sensor is able of classifying the movement, especially when analyzed in conjunction with preprocessing and clustering techniques. As another wearable application, the respiratory rate is successfully estimated with the BioMFOS integrated into the clothing. Thus, the proposed multifunctional device opens new avenues for novel bioinspired photonic devices and can be used in many applications of biomedical, biomechanics, and micro/nanotechnology.

Finger‐Skin‐Inspired Flexible Optical Sensor for Force Sensing and Slip Detection in Robotic Grasping

AbstractThe finger skin of human plays a key role in amplifying and transferring tactile signals to sensory receptors, and it provides design guidelines for next‐generation flexible tactile sensors. To enable robotic applications such as dexterous manipulation and tactile feedback, the functions of force sensing and slip detection are crucial for flexible tactile sensors. Here, a finger‐skin inspired flexible optical (FIFO) sensor based on optical microfiber is reported, and this sensor has fingerprint‐like surface with parallel ridges and resin/polydimethylsiloxane multilayer structure with different stiffness, mimicking the structural characteristics of human finger skin. With these design features, the sensor is capable of measuring force with high durability and detecting slip with high sensitivity and short response time. Time‐resolved response curve and its wavelet transform provide useful information related to grasping and slipping when the sensor is in contact with objects with different shapes and materials. As a proof‐of‐concept demonstration, the sensor directly attached onto a robotic gripper is capable of measuring grasping force and monitoring object slippage during manipulation tasks, indicating its potential applications in advanced robotics.

Active‐Matrix‐Based Flexible Optical Image Sensor

AbstractOwing to the demand for the development of Internet of things devices, multiple sensor platforms are of great interest to society and its future electronics. One of these emerging devices is a mechanically flexible sensor system that can attach and conform to nonplanar surfaces, unlike conventional inflexible sensor chips. To realize this concept, a variety of flexible sensor systems must be developed from materials to system integrations. This study proposes a flexible sensor system as one of the candidates: an active‐matrix‐based flexible optical image sensor that uses a stacked nanosheet film formed by a solution process and transistors. The results show that the sensor can be utilized as an optical imager because it detects enough optical stimuli. In addition to the sensitivity, the mechanical flexibility of the active‐matrix optical sensor is tested, and the results exhibit good electrical stability even after 1000 bending cycles and 0.85 cm bending radius. The mapping of light distribution is successfully demonstrated under both flat and curved conditions. This flexible optical sensor array shows the high possibility to image the light distribution for high‐resolution and low power mapping realized by active matrix circuit integration.

Exploring Plasmonic Resonances Toward “Large‐Scale” Flexible Optical Sensors with Deformation Stability

AbstractThe next generation of sensors requires a simple yet compact lab on chip‐based precise optical detection mechanism where data interpretation can be achieved with minimum effort. Hereby, cost‐efficient strategies of manufacturing both propagating surface plasmon polariton (SPP) and localized surface plasmon resonance (LSPR) sensors on flexible platforms are explored via mechanical instabilities and oblique‐angled metal evaporation. Centimeter scaled dielectric grating structures produced by plasma oxidation of pre‐stressed polydimethylsiloxane film have comprised the substrates, thus imparting inherent flexibility. Subsequently, both continuous and discontinuous 1D‐metallic lattices are obtained via vapor deposition of gold at different angles. The optical isotropy (gold surface‐grating) and anisotropy (gold edge‐grating) are distinctly observed as a difference between forward and backward diffraction efficiencies, backed by analytical correlation to the observed orders. Supported with electromagnetic modeling, the SPP and LSPR excitations are experimentally characterized under reflectance and transmittance measurements, along with a demonstration of their sensing capabilities. The LSPR supported flexible sensor provides superiority in terms of sensitivity, which is investigated under mechanical deformations to exhibit consistency of the resonant wavelength. Such consistency is strategically unraveled via “finite element method” based approaches, thus providing a new paradigm of cost‐efficient, large‐scaled flexible sensors.

Electrospinning Superassembled Mesoporous AIEgen-Organosilica Frameworks Featuring Diversified Forms and Superstability for Wearable and Washable Solid-State Fluorescence Smart Sensors.

Flexible optical sensors are widely studied and applied in many fields. However, developing highly stable and washable wearable sensors in optics is still facing significant challenges. Here, we demonstrate an AIEgen-organosilica framework (TPEPMO) hybrid nanostructure-based flexible optical sensor, which is prepared by a two-step co-condensation and electrospinning superassembly process. Organosilica precursors with aggregation-induced emission (AIE) features are covalently linked into periodic mesoporous organosilica (PMO) frameworks with high fluorescent efficiency due to the restriction of intramolecular motion. The three-dimensional space of ordered porous materials provides abundant reaction sites, allowing rapid and sensitive monitoring of analytes. TPEPMOs exhibit good properties as acidic pH fluorescent sensors with a pKa of 4.3. A flexible film is obtained by dispersing TPEPMO nanospheres in a poly(lactic-co-glycolic acid) (PLGA) and polyacrylonitrile (PAN) hybrid fibrous matrix (TPEPMO-CFs) using the electrospinning superassembly technique and is successfully served as an efficient fluorescent probe for the naked eye detection of ammonia gas and HCl vapor by emission changes. The fluorescence of TPEPMO-CFs can be reversed in the presence of volatile acidic/alkaline gas for more than five cycles, exhibiting excellent recyclability. In addition, TPEPMO-CF sensors show excellent washability and long-term photostability (fluorescence was maintained above 94% after washing 10 times). These stimuli-responsive AIEgen-organosilica frameworks featuring diversified forms and superstability for wearable and washable solid-state fluorescence exhibit great potential for smart gas sensors, wearable devices, and solid-state lighting applications.

SnOx and a-Si thin-films based photodiode in a flexible substrate for visible spectral region

Thin-films based photodiodes are an advantageous alternative to the photodetectors based on semiconductor doping processes, especially in optical sensors implemented on non-semiconductor substrates. This is the first report of a p-i-n junction photodiode, based on n-SnOx/p-SnOx and amorphous silicon (a-Si) thin-films, fabricated in a polymeric, flexible and photosensitive substrate, only considering different annealing conditions and thicknesses of evaporated metallic Sn and sputtered a-Si. Seebeck coefficient measurements were performed, using a custom-built setup, to assess the implementation of n- and p-type thin-films. The obtained Seebeck coefficients were −167 µV/K and +266 µV/K for the n-SnOx and p-SnOx, respectively. X–ray diffraction (XRD) analysis also confirmed the deposition of an a-Si thin-film as the intrinsic layer of the p-i-n junction. The photodiode responsivity and response times were measured, using a custom-built optical setup for the visible spectral region. The measured responsivity (at 0 V reverse bias) was 2.8µA/W at 572 nm and the rise and fall times were 0.203 s and 0.312 s, respectively. The developed photodiode provides a promising solution for high level light detection applications in flexible optical sensors.

Wet-spinning of fluorescent fibers based on gold nanoclusters-loaded alginate for sensing of heavy metal ions and anti-counterfeiting.

Fluorescent and robust fibers based on gold nanoclusters-loaded alginate were successfully prepared by wet spinning of gold nanoclusters and alginate. The relationship between process conditions, mechanical properties, and fluorescent properties of fibers was investigated. The as-prepared fibers exhibited high mechanical strength (up to 7.09 cN/dtex) and remarkable red emission under ultraviolet excitation. The fibers could be used as a simple, low-cost, and high-selectivity fluorescent sensor for detecting Cu2+ and Hg2+ among various metal ions in aqueous solution, with a detection limit as low as 187.99nM for Cu2+ and 82.14nM for Hg2+, respectively. Furthermore, the novel fluorescent fibers were used as an anti-counterfeiting label through knitting into textile materials. The wet-spun functional fibers may be applied to the design of smart wearable sensors and flexible optical sensors.