Multimode Sensor Research Articles

Light-Sheet Skew Ray-Based Microbubble Chemical Sensor for Pb2+ Measurements

A multimode fiber-based sensor is proposed and demonstrated for the detection of lead traces in contaminated water. The sensing mechanism involves using a light sheet to excite a specific group of skew rays that optimizes light absorption. The sensing region features an inline microbubble structure that funnels the skew rays into a tight ring, thereby intensifying the evanescent field. The sensitivity is further refined by incorporating gold nanoparticles, which amplify the evanescent field strength through localized surface plasmon resonance. The gold nanoparticles are functionalized with oxalic acid to improve specificity for lead ion detection. Experiment results demonstrated the significantly enhanced absorption sensitivity of the proposed sensing method for large center offsets, achieving a detection limit of 0.1305 ng/mL (the World Health Organization safety limit is 10 ng/mL) for concentrations ranging from 0.1 to 10 ng/mL.

A flexible proximity-pressure–temperature tri-mode robotic sensor with stimulus discriminability, high sensitivity and wide perception range

Along with the explosive utilization of intelligent and bionic robotics, the rise of somatosensory system with excellent flexibility and multiple biological sensing characteristic emerges as a substantial crux of this domain. Herein, we propose a flexible high-performance multi-mode sensor for real-time proximity–pressure–temperature perception based on a monolithic sensing unit with fingerprint-like hierarchical architecture. The monolithic sensing unit, primarily constituted by a double-permeable ionic liquids/Multi-walled nanotubes conductive network, demonstrates dual-functionality in detecting pressure and temperature. Making use of the further synergy of rational topographical architecture engineering and feasible decoupling algorithm construction, extraordinary progress in sensing performances for both pressure and temperature are attained with negligible mutual interferences. Additionally, the sensor is capable of switching to touchless mode to detect objects at distance up to 200 mm, validating its remarkable proximity sensing ability. The multifunctional nature of sensor is further substantiated through its integration with a robotic hand, highlighting its practical applicability in advanced robotic systems.

Multifunctional Self-Powered Sensors Integrated on a Robot Hand for Detecting Temperature-Pressure Stimuli and Recognizing Objects.

Tactile sensing, especially pressure and temperature recognition, is crucial for both humans and robots in identifying objects. The general solutions, which use piezoresistive, capacitive, and thermal resistance effects, are usually subject to single-mode sensing and an energy supply. Here, we propose a multimode self-powered sensor. The sensor can respond to pressure and temperature stimuli using triboelectric and thermoelectric effects. Furthermore, we developed a sensing system comprising sensors, a deep learning block, and a smart board. The deep learning model can fuse features of triboelectric and thermoelectric signals, enabling a high accuracy of 99.8% in recognizing ten objects. This method may provide the future design of self-powered sensors for object recognition in robotics.

Single-Mode versus Multimode Fiber Bragg Grating Temperature Sensors: A Theoretical Study

This paper aims to enhance understanding regarding the impact of the geometrical parameters of the grating on the transmission spectrum of single-mode and multimode fiber Bragg grating sensors and to compare the performance of both sensors for temperature monitoring. Furthermore, we propose a novel design where we combine between phase shifted and tilted grating in MMFBG sensors to further enhance their sensitivity and make them more suited for temperature sensing applications. In this regard, a numerical simulation using the eigenmode expansion (EME) solver of Lumerical software is conducted. Analysis of the obtained results suggests that the multimode Fiber Bragg grating sensor has the potential to be used as a temperature sensor with good sensitivity when it is well designed.

Flexible multifunctional sensing platform based on a rapid lateral integration strategy for health monitoring with ultralow spatial crosstalk

There has been a widespread demand for the adaptability of flexible strain sensors in the field of human health monitoring. However, the currently manufactured flexible sensors are difficult to adapt to various working conditions since the strain range or the size of the sensors is limited to be altered after production. Additionally, there is an urgent need to quickly integrate flexible multimode sensors to perceive multiple stimuli simultaneously. Thus, a lateral extension strategy is proposed to develop a flexible sensing platform by coupling biomimetic strain-insensitive connectors and individual sensors, making it laterally extended and freely assembled with ultralow spatial crosstalk. The process allows for rapid integration (<300 s) without the additional adhesives. The integrated sensing platform exhibits a fast response time (34 ms) and excellent stability (over 1000 cycles). Furthermore, this technique also enables the quick integration of multimode flexible sensors (pressure and temperature) into a multifunctional sensing platform with accurate signal decoupling capabilities. The proposed lateral extension strategy is expected to provide a new approach for the design and fabrication of a multifunctional sensing platform, as well as advance the application in fields of human-machine interaction and medical diagnostics.

Cladding modes’ interference in MM-tapered SM-MM fiber devices: Experimental demonstration of a high-sensitivity temperature sensor

Here, we report our experimental demonstration of a high-performance temperature sensor fabricated by cascading dissimilar multimode fibers and tapered single mode fiber coated with an index-matching gel of high thermo-optic coefficient. The output power is recorded under varying temperature conditions of the coated material. Besides wavelength-shifting based multimode interferometer sensor, here a unique methodology is adopted where an intensity based fiber temperature sensor is realized. Our optimized design yields a temperature measurement sensitivity of 8.1253 µW/°C, accuracy of ± 0.9 0C, response time of 392 ms and resolution of 0.1 0C within the range of 29 °C to 64 °C. Analytical mode overlap and Ansys Lumerical simulation validate experimental results, affirming the method's effectiveness.

Multimode Fiber-Based Interferometric Sensors With Microwave Photonics

Multimode Fiber-Based Interferometric Sensors With Microwave Photonics

Hydrophobic TPU/CNTs-ILs Ionogel as a Reliable Multimode and Flexible Wearable Sensor for Motion Monitoring, Information Transfer, and Underwater Sensing.

Ionogel-based sensors have gained widespread attention in recent years due to their excellent flexibility, biocompatibility, and multifunctionality. However, the adaptation of ionogel-based sensors in extreme environments (such as humid, acidic, alkaline, and salt environments) has rarely been studied. Here, thermoplastic polyurethane/carbon nanotubes-ionic liquids (TPU/CNTs-ILs) ionogels with a complementary sandpaper morphology on the surface were prepared by a solution-casting method with a simple sandpaper as the template, and the hydrophobic flexible TPU/CNTs-ILs ionogel-based sensor was obtained by modification using nanoparticles modified with cetyltrimethoxysilane. The hydrophobicity improves the environmental resistance of the sensor. The ionogel-based sensor exhibits multimode sensing performance and can accurately detect response signals from strain (0-150%), pressure (0.1-1 kPa), and temperature (30-100 °C) stimuli. Most importantly, the hydrophobic TPU/CNTs-ILs ionogel-based sensors can be used not only as wearable strain sensors to monitor human motion signals but also for information transfer, writing recognition systems, and underwater activity monitoring. Thus, the hydrophobic TPU/CNTs-ILs ionogel-based sensor offers a new strategy for wearable electronics, especially for applications in extreme environments.

Multimode interference methane sensor based on a ZIF-8/PDMS composite film.

A multimode interference methane sensor based on a ZIF-8/PDMS composite film is proposed. The sensing principle is that the refractive index of the ZIF-8/PDMS composite film changes when it adsorbs methane, leading to a measurable optical path difference during the coupling of the cladding higher-order modes and the fundamental mode in the multimode interference fiber (MMI). The environmental methane concentration is then detectable by detecting the wavelength shifts of the interference peaks in the resulted spectrum. Through simulations and experiments aimed at enhancing sensor sensitivity, we optimized three parameters within the sensor structure: the length of the Tapered Single-Mode Fiber (TSMF), the composite film thickness, and the TSMF taper diameter. The experimental results indicate that the sensor's sensitivity reaches a maximum of 0.231 nm%-1. Additionally, the sensor exhibits excellent structural stability and measurement repeatability. The response time is as short as 40 s, and the recovery time ranges between 3 and 5 min. The proposed multimode interferometric methane sensor based on the ZIF-8/PDMS composite film has great potential to support highly sensitive methane concentration detection in many applications.

Humidity Sensing Using a Multimode Fiber Ring Laser with Thermal Compensation

We propose a multimode fiber laser sensor utilizing PI-SMF (polyimide-coated single mode fiber) for low-error relative humidity (RH) measurement, which is temperature compensated based on FBG. The PI-SMF in the laser cavity is used as a sensing element, and its length varies with humidity and temperature by volume-variation induced strain, which leads to frequency shift of the longitudinal mode beat frequency signal (BFS). When the 2000 MHz BFS is selected as the sensing signal, a RH sensitivity of −2.68 kHz/%RH and a temperature sensitivity of −14.05 kHz/°C are achieved. The peak shift of the FBG-based laser emission spectrum is only sensitive to temperature rather than RH with a temperature sensitivity of 9.95 pm/°C, which is used as the temperature compensation for RH measurements. By monitoring the response of the BFS and the laser wavelength, the cross-sensitivity effect of RH and temperature is overcome, and low-error RH measurement in the temperature range of 20 to 65 °C is realized with errors within ±0.67 %RH (25 to 85 %RH). The scheme does not require the design and production of complex structures and hygroscopic material coating processes, owning the advantages of simple structure, easy operation and high accuracy, and is expected to be practically applied in food safety and environmental monitoring.

A Multimode Optical Sensor for Selective and Sensitive Detection of Harmful Heavy Metal Cr(VI) in Fresh Water and Sea Water.

Water pollution originating from heavy metals has shown great impacts on the ecological environment and human health due to their extremely low biodegradability. Hexavalent chromium Cr(VI), as one harmful heavy metal with strong oxidation, high biological permeability, and high carcinogenicity, is becoming an increasingly serious threat to human health. Therefore, conveniently but accurately, monitoring the Cr(VI) level in water to maintain its normal level and ensuring the stability of the ecosystem and human health become very valuable. However, most of these heavy metal sensors reported are turn-off type single-emission sensors. In this work, a ratiometric fluorescence/colorimetry/smartphone triple-mode turn-on optical sensor for Cr(VI) was developed based on a multifunctional metal-organic framework platform. The detection limits for these three mutual verification modes were only 1.28, 4.89, and 68.4 nM, respectively. Additionally, the color changes of the detection system under sunlight can also be observed directly by the naked eye. The accuracy and practicability of this multimode sensor were further proved by the detection of Cr(VI) in actual water and seawater samples, and the recovery rate ranged from 97.308 to 104.041%.

A Wearable Sandwich Heterostructure Multimode Fiber Optic Microbend Sensor for Vital Signal Monitoring.

This work proposes a highly sensitive sandwich heterostructure multimode optical fiber microbend sensor for heart rate (HR), respiratory rate (RR), and ballistocardiography (BCG) monitoring, which is fabricated by combining a sandwich heterostructure multimode fiber Mach-Zehnder interferometer (SHMF-MZI) with a microbend deformer. The parameters of the SHMF-MZI sensor and the microbend deformer were analyzed and optimized in detail, and then the new encapsulated method of the wearable device was put forward. The proposed wearable sensor could greatly enhance the response to the HR signal. The performances for HR, RR, and BCG monitoring were as good as those of the medically approved commercial monitors. The sensor has the advantages of high sensitivity, easy fabrication, and good stability, providing the potential for application in the field of daily supervision and health monitoring.

Strain-insensitive micro torsion and temperature sensor based on a helical taper seven-core fiber structure.

We propose a multimode interference-based optical fiber NHTSN sensor with a helical taper for simultaneous measurement of micro torsion and temperature. The sensor consists of single mode fiber (SMF), no-core fiber (NCF), and seven-core fiber (SCF). A helical taper is fabricated in the SCF using a flame heater, forming the SMF-NCF-Helical Taper SCF-NCF-SMF (NHTSN) structure. Theoretical analysis and experimental results demonstrate that the introduction of helical taper not only imparts directionality to the torsion measurement, but also results in a significant improvement in torsion sensitivity due to the increased inter-mode optical path difference (OPD) and enhanced inter-mode coupling. In the experiment, the torsion sensitivity of the NHTSN sensor reaches -1.255 nm/(rad/m) in the twist rate (TR) range of -3.931 rad/m to 3.931 rad/m, which is a 9-fold improvement over the original structure. Further reduction of the helical taper diameter increases the sensitivity to -1.690 nm/(rad/m). In addition, the sensor has a temperature sensitivity of up to 97 pm/°C from 20 °C to 90 °C, and simultaneous measurement of torsion and temperature is attainable through a dual-parameter measurement matrix. The NHTSN sensor possesses advantages of compact size, high sensitivity, good linearity, and strain-independence, endowing it with potential applications in structural health monitoring (SHM) and engineering machinery.

Multi-mode industrial soft sensor method based on mixture Laplace variational auto-encoder

The industrially collected process data usually exhibit non-Gaussian and multi-mode characteristics. Due to sensor failures, irregular disturbances, and transmission problems, there are unavoidable outliers that make the data exhibit heavy-tailed characteristics. To this end, a variational auto-encoder regression method based on the mixture Laplacian distribution (MLVAER) is proposed, by introducing a type-II multivariate Laplacian distribution in the latent variable space for robust modeling, and further extending it to the mixture form to accommodate multi-mode processes, the corresponding reparameterization trick is finally proposed for the mixture form of this distribution for neural network gradient descent training. The model based on this distribution assumption has higher degrees of freedom than the model based on the traditional multivariate Laplace distribution assumption when the network structure is the same. Numerical simulation and experiments on two industrial examples demonstrate that the proposed algorithm reduces the root mean square error by over 15% compared to other algorithms.

A Multimode Neuromorphic Vision Sensor With Improved Brightness Measurement Performance by Pulse Coding Method

A Multimode Neuromorphic Vision Sensor With Improved Brightness Measurement Performance by Pulse Coding Method

Improvement of a flexible multimode pressure-strain sensor (FMPSS) for blueberry firmness tactile sensing and tamper-evident packaging

Improvement of a flexible multimode pressure-strain sensor (FMPSS) for blueberry firmness tactile sensing and tamper-evident packaging

Exploring Unidentified Aerospace Phenomena Through Instrumented Field Studies: Historical Insights, Current Challenges, and Future Directions

The study of Unidentified Aerospace Phenomena (UAP) requires a shift from a historical, narrative-based approach to a scientific and technology-based study. To conduct unbiased and agnostic research on UAPs, rigorous scientific study is necessary, including the collection of hard data to support credible explanations or scientifically prove the existence of unknown phenomena. Obtaining reliable and valid data requires instrumented observations, including multi-wavelength and multi-mode sensors (e.g., optical, radar, infrared). We present herein an overview of the benefits as well as the strategic and tactical considerations of instrumented field studies, highlighting common limitations and shortcomings with the objective of contributing to the development of future projects. We provide an overview of some past and current UAP military and civilian projects and analyze a timetable of instrumented projects spanning the years 1950-2023, encompassing contributions from both citizen science and professional/academic science. In conclusion, this paper reflects on how UAP field experiments might look going forward. Newer technologies like digital cameras, scientific instruments, computing, big data analytics, artificial intelligence, and satellite imagery are becoming more advanced and cost-effective. This is leading to the growth and progress of technical field studies, complementing local projects with global-scale investigations. Researchers can enhance their chances of success by adopting a more disciplined approach and exploring innovative avenues. Collaboration, transparency, and standardization in data collection and analysis are crucial, while also acknowledging the complex nature of the UAP phenomenon.

Flexible multimode sensors based on hierarchical microstructures enable non-destructive grading of fruits in cold chain logistics

In practical applications, flexible pressure sensors must demonstrate adequate sensitivity, durability, and the ability to detect both dynamic and static forces across a wide range. The objective of this study is to develop a flexible dual-mechanism piezoelectric/piezoresistive sensor (FDMPS) based on layered microstructures to enable versatile detection in real fruit sorting operations. The FDMPS consists of an upper layer featuring planar MXene electrodes on a PDMS film, a mid-layer comprising microstructured Ag electrodes on a PVDF-TrFE/Silica gel/ZnO film, and a lower layer with microstructured MXene electrodes on a PDMS film composition. To ensure a secure fit, the three-layer structure is treated with APTES and plasma. All electrodes are produced using a pneumatic direct-write process, while the PDMS and piezoelectric films are created via a spin-coating process, making them suitable for large-scale production. The flexible FDMPS, with a 10 wt% ZnO content, achieves an optimal piezoelectric output of 3.6 V. Additionally, the FDMPS demonstrates excellent linearity (0.997), resistive sensitivity (23.65 kpa−1), and stability (5000 cycles). The incorporation of microstructures significantly enhances the performance of piezoelectric/piezoresistive sensing. Moreover, the FDMPS can accurately measure bending strain rate and angle within the ranges of 0–90°/s (with a sensitivity of 0.014 V/(°·s−1)) and 0–110° (with a sensitivity of 0.216/°), respectively. In a wireless, real-time mode, the FDMPS proves effective in monitoring the reciprocating motion of a robotic arm and assessing fruit ripeness during the grading process. This advancement promotes the development and application of precision agriculture and wearable sensing technologies.

A dual-mode wearable sensor with coupled ion and pressure sensing

Simultaneous monitoring of the body’s biochemical and biophysical signals via wearable devices can provide a comprehensive assessment of an individual’s health state. However, current multifunctional sensors for synchronous biochemical and biophysical sensing rely on discrete sensing units, posing a limitation in increased complexity in device assembly, signal processing, and system integration. In this study, we report a dual-mode and self-powered wearable sensor with ion and pressure-sensing capabilities by interfacing a hydrogel film with a solid ion-selective electrode. The hydrogel film can not only collect natural sweat from the skin but also offer a piezoionic response to pressure. We show that wrist pulse-induced pressure response can be incorporated into the noise of the response to sweat sodium ions, allowing for the simultaneous measurement of heart rate and sweat electrolytes. This work provides an example of simplifying the development of wearable multimode sensors through the rational design of classic electrochemical sensors.

Fluorometric and colorimetric dual-mode sensing of α-glucosidase based on aggregation-induced emission enhancement of AuNCs.

Herein, a fluorometric and colorimetric dual-mode assay platform used for α-glucosidase (α-Glu) activity sensing based on aggregation-induced emission enhancement (AIEE) of AuNCs was developed for the first time. The quantum yield (QY) and fluorescence lifetime of AuNCs were successfully ameliorated by Ce3+-triggered AIEE (Ce@AuNCs). Subsequently, on the basis of the inner filter effect (IFE) and dynamic quenching effect (DQE) between 2,6-dichlorophenolindophenol (DCIP) and Ce@AuNCs as well as the reduction of DCIP by ascorbic acid (AA) generated from α-Glu-catalyzed hydrolysis of L-ascorbic acid-2-O-α-D-glucopyranosyl (AA2G), the marriage of fluorometric and colorimetric modes applied for α-Glu activity monitoring was achieved. Besides, the feasibility of this dual-mode sensing system was confirmed by the assays versus potential interfering substances and in real samples. In particular, this system was further applied to evaluate natural α-Glu inhibitors (AGIs) including luteolin, apigenin, and hesperidin. Overall, the multi-mode optical sensor newly designed here has the potential for the accurate discovery of natural anti-diabetes drugs and the therapy of diabetes.