Sensor Layer Research Articles

Multi-crack damage identification and quantification using Lamb wave-based structural health monitoring

The simultaneous presence of multi-crack damage in a structural component is a crucial issue affecting system safety. To address the accurate and quantitative monitoring of multi-crack damage in an aeronautical structure, an innovative multi-crack damage localization, orientation and quantification algorithm using Lamb wave-based structural health monitoring is presented in this paper. An improved Hausdorff distance-based weighted average imaging methodology is introduced for precise multi-crack damage position identifications. To account for the critical role of crack orientation in damage quantification, a cross-orthogonality-based method is developed, enabling orientation detection at arbitrary positions and angles while simplifying the problem into a mathematical formulation. A wave scattering sources-based quantification algorithm incorporating the estimated position and orientation information is further proposed to estimate the multi-crack lengths. Additionally, a singular elliptic trajectories removal scheme is presented to suppress useless ambient noise and enhance the damage information discriminability. Experiments on the aircraft wing-box structure of a real airplane are implemented to substantiate the proposed techniques. Due to the outstanding properties, such as flexibility, electrically stabilized and applicability to complex structures, the sensor layer with built-in PZT sensor network surface-installed on the monitored structure is adopted to generate and receive Lamb wave signal. The results manifest that the proposed monitoring algorithm, without prior information or calibration required, is effective and straightforward for detecting multi-crack damage. This study can also provide a feasible technique for accurately locating and quantitatively identifying cracks in some concealed parts or inside the structure.

Multi-Level High Entropy-Dissipative Structure Enables Efficient Self-Decoupling of Triple Signals.

The theory of high entropy-dissipative structure is confined to high-entropy alloys and their oxide materials under harsh conditions, but it is very difficult to obtain high entropy-dissipative structure for smart sensors based on polymers and metal oxides under mild conditions. Moreover, multiple signal coupling effect heavily hinder the sensor applications, and current multimodal integrated devices can solve two signal-decoupling, but need very complicated process way. In this work, new synthesis concept is the first time to fabricate high entropy-dissipative conductive layer of smart sensors with triple-signal response and self-decoupling ability within poly-pyrrole/zinc oxide (PPy/ZnO) system. The sensor (SPZ20) amplifies pressure (17.54%/kPa) and gas (0.37%/ppm), reduces humidity (0.41%/% RH) and temperature (0.12%/°C) signals, simultaneously achieving the triple self-decoupling effect of pressure and gas in the complex temperature-humidity field because of the enlarged pressure-contact area, enhanced gas-responsive sites, altered vapor path and its own heat insulation function. Additionally, it inherits the strong robustness (500 rubbing, washing, and heating or freezing cycles) and endurance (10000 photo-purification cycles) of traditional high-entropy materials for information transmission and smart alarms in emergencies or harsh environments. This work gives a new insight into the multiple-signal response and smart flexible electronic design from natural fibers.

A Unified Shear Deformation Theory for Piezoelectric Beams with Geometric Nonlinearities—Analytical Modelling and Bending Analysis

The objective of the present paper is to demonstrate the effects of shear deformation and large deflections on the piezoelectric materials and structures which often serve as substrate layers of multilayer composite sensors and actuators. Based on a displacement-unified high-order shear deformation theory and the von Kármán geometric nonlinearity, a general theory (governing equations and associated boundary conditions) for the analysis of piezoelectric beams is developed using Hamilton’s principle. Nonlinear effects due to the coupling between extensional and bending responses in beams with moderately large rotations but small strains are included. A bending problem for a piezoelectric beam is solved analytically, and the obtained results are compared to the results available in the literature. The numerical results show that both shear deformation effects and von Kármán geometric nonlinearity have a stiffening effect and therefore reduce the displacements. The influence of geometric nonlinearity is more prominent in the case of thin beams, while the effects of shear deformation dominate in the case of thick beams. The proposed unified methodology for the analysis of bending problems is independent of the thickness of the piezoelectric beam.

Poly(3,4-ethylenedioxythiophene) and Poly(3-octylthiophene-2,5-diyl) Molecules as Composite Transducers in Potentiometric Sensors-Synthesis and Application.

The aim of this paper is to investigate the influence of the molecules of conducting polymers on the properties of potentiometric sensors. Two conducting polymers, poly(3-octylthiophene-2,5-diyl) and poly(3,4-ethylene-1,4-dioxythiophene), were compared in the context of the design of ion-selective electrodes. This study offers a comparison of the most popular conducting polymers in the context of the design of potentiometric sensors. Firstly, the properties of both materials, such as their microstructure, electrical performance, wettability, and thermic properties, were examined. Subsequently, conducting polymers were applied as transducer layers in potassium-selective sensors. The properties of both groups of sensors were evaluated using the potentiometry method. Research has shown that the presence of poly(3-octylthiophene-2,5-diyl) (POT) in the transducer layer makes it superhydrophobic, leading to a long lifetime of sensors. On the other hand, the addition of poly(3,4-ethylene-1,4-dioxythiophene) polystyrene sulfonate (PEDOT:PSS) allows for the enhancement of electrical capacitance parameter values, which beneficially influence the stability of the potentiometric response of sensors. Both examined conducting polymers turned out to be perfect materials for transducer layers in potentiometric sensors, each being responsible for enhancing different properties of electrodes.

A stunning sensitive isopropanol gas sensor based on ZnMn2O4 microspheres

The pure porous ZnMn2O4 microspheres were prepared by a one-step hydrothermal technique with different concentrations of Urea (ZU). Various techniques including XRD, FESEM, PL, UV–Vis, FT-IR and EDS were used to study the structural and morphological properties of the obtained samples. The results show that the obtained samples have high purity and by changing the concentration of urea, the microspheres have rough surfaces, which is useful for gas sensing properties. Then, the gas sensor properties of the fabricated sensor layers were investigated for isopropanol vapor with different concentrations at different working temperatures. Gas sensing results confirm that the ZU films exhibit a high response of 5.54 for ZU3 (500 ppm isopropanol), a very fast response time of 2.5 s for ZU2 (400 ppm) and ZU3 (300 ppm), and excellent selectivity with a difference of approximately 107 % compared to DMF at a relatively low temperature. In addition, the gas sensing mechanism was also thoroughly discussed.

Alumina ceramic insulation layer for strain sensor fabricated by direct laser deposition

ABSTRACT Strain sensors are often used to monitor the use of critical components. The bond strength between the strain sensor and the gear teeth is particularly critical. There is a problem of insufficient bond strength between separated strain sensors and parts. The strain sensor is prone to loosening and flaking in the working environment. Therefore, a method of preparing the ceramic insulation layer of the strain sensor by direct laser deposition (DLD) is proposed. The effects of laser scanning trajectories, laser power, and scanning speed on forming quality were investigated experimentally. In addition, the phase analysis, microstructure characterization, and insulation properties of the insulating layers prepared at different overlap rates were researched. The research shows that the ceramic insulation layer has good insulation properties and hardness. The maximum hardness can reach 2405.74MPa, and the insulation resistance increases with the number of layers. The surface of the ceramic insulation layer is dense and has no cracks.

Influence of Layer’s Annealing Temperature on Sensing Properties of Spin-Coated SBS Layer Exposed to Alcohol Vapor

QCM-based alcohol vapor sensors have been widely researched, and various materials have been deposited onto the sensor surface to serve as a functional layer. However, non-conductive polymers such as SBS as a functional layer for alcohol sensors are still minimally reported. In this study, the SBS was deposited on 1 side of the QCM using the spin coating technique. After deposition, the layer was annealed for 1 h. The annealing temperatures are 100, 150 and 200 °C. The concentrations of exposed alcohol vapor were 5, 10, 15, 20, 25, 50, 75 and 100 ppm. This study demonstrated that the SBS layer has the potential to be a functional layer of alcohol sensors. SBS 200 °C is an optimum functional layer for alcohol vapor sensors due to its high ∆f and sensitivity. Meanwhile, SBS 100 °C has poor ∆f and sensitivity. This is due to the morphology of 200 °C SBS, which consists of more valleys that perform as interaction sites for SBS and alcohol molecules. However, one of the limitations of SBS as a functional sensor layer for alcohol sensors is its low selectivity, which is a characteristic of rubbery polymers. HIGHLIGHTS The SBS layer annealed at higher temperatures has more valleys than the SBS layer annealed at low temperatures. The valleys in the morphology of the SBS layer act as interaction sites for alcohol molecules, where each site interacts with an alcohol molecule. It is based on the sensor response and proved by fitting the Langmuir model. The SBS layer annealed at 200 ᵒC has a high ∆f, sensitivity, and longer response time. The selectivity of SBS was relatively low, a characteristic of rubbery polymers. The interaction between SBS and methanol is physisorption. GRAPHICAL ABSTRACT

All‐Paper‐Based, Flexible, and Bio‐Degradable Pressure Sensor with High Moisture Tolerance and Breathability Through Conformally Surface Coating

AbstractHighlighted with bio‐degradability, paper‐based flexible pressure sensors receive significant attention in the field of wearable devices for a sustainable future. However, it remains a challenge to possess considerable sensing performance in high humidity and underwater environments, because its structure rapidly breaks down after the hydrophilic cellulose absorbs water. In this study, a facile chemical vapor deposition method is employed to conformally coat a thin hydrophobic layer onto the cellulose fibers, resulting in an encapsulating paper with high moisture tolerance. The well‐maintained porous structure reserves the superior breathability of the paper. A micro‐convex‐structured sensor layer impregnated with MXene serves as the sensing layer. As a result, an all‐paper‐based pressure sensor with high moisture tolerance and breathability is fabricated. This sensor features a broad sensing range (0–60 kPa), acceptable sensitivities (39.58 kPa−1 (0–1.01 kPa), 11.95 kPa−1 (1.01–60 kPa)), a low detection limit of ≈2.8 Pa, response and recovery time (93 and 69 ms), reliable hydrophobic breathability, and excellent repeatability (10 000 cycles). Moreover, this sensor can be safely worn on human skin and can monitor physiological signals in real‐time in different environments (including air, humid environments, and even underwater), providing a reliable, economical, and environmentally friendly solution for wearable technology.

Additively manufactured micro-lattice dielectrics for multiaxial capacitive sensors.

Soft sensors that can perceive multiaxial forces, such as normal and shear, are of interest for dexterous robotic manipulation and monitoring of human performance. Typical planar fabrication techniques have substantial design constraints that often prohibit the creation of functionally compelling and complex architectures. Moreover, they often require multiple-step operations for production. Here, we use an additive manufacturing process based on continuous liquid interface production to create high-resolution (30-micrometer) three-dimensional elastomeric polyurethane lattices for use as dielectric layers in capacitive sensors. We show that the capacitive responses and sensitivities are highly tunable through designs of lattice type, thickness, and material-void volume percentage. Microcomputed tomography and finite element simulation are used to elucidate the influence of lattice design on the deformation mechanism and concomitant sensing behavior. The advantage of three-dimensional printing is exhibited with examples of fully printed representative athletic equipment with integrated sensors.

High-Entropy Sulfide (FeCoNiCrMn)S2 for Room Temperature NO2 Sensors.

Metal sulfides have been extensively studied in the field of chemical sensors working at room temperature (RT). However, compared to metal oxides, metal sulfides often suffer from incomplete recovery and unsatisfactory selectivity. In this work, we for the first time report the high-entropy sulfide (HES) (FeCoNiCrMn)S2, prepared by the solvothermal method, is a promising candidate for utilization as the sensitive layer in gas sensors. Unlike traditional single-metal sulfides, this HES (FeCoNiCrMn)S2 exhibits reversible recovery for NO2 at RT as well as excellent selectivity. To unveil the sensing mechanism, we simulated the adsorption and charge transfer between (FeCoNiCrMn)S2 and gas molecules by the density functional theory (DFT) calculation, revealing the reason (FeCoNiCrMn)S2 is uniquely selective to NO2. This work explores the application potential of HES (FeCoNiCrMn)S2 as an RT sensor and enriches the material selection for NO2 sensors.

Gas sensing performance regulating of ZIF-8 encapsulated WO3 nanosheets

Reasonably regulating the adsorption properties on the surface of metal oxide semiconductors (MOS) to enhance sensor selectivity remains a challenge, limiting their application in detecting diseases biomarkers in human exhaled gas. To address this, we proposed a metal-organic frameworks (MOFs) encapsulated strategy to provide a gas-selective permeable nano-filtration layer for MOS gas sensors. By adjusting the coating thickness of ZIF-8, we successfully modulate the sensing properties of WO₃ to different potential biomarkers. The optimized WO₃/ZIF-8 composite shows improved selectivity and response to various disease biomarkers compared to WO₃ alone. The unique porous structure of ZIF-8 and the heterojunction of WO3/ZIF-8 synergistically promote the gas adsorption performance. QCM test results confirm that ZIF-8 modification effectively regulates gas adsorption on the WO₃ surface. This study provides a valuable reference for designing exhaled gas sensor arrays for detecting serious diseases.

Dynamic buckling active control of FGM spherical shell with piezoelectric sensor and actuator layers

The mechanical snap-through phenomenon represents one of the buckling modes inherent in shallow shells, exemplifying the shell's reaction to external loads, which can potentially have detrimental effects on structural performance. This article delves into the study of this phenomenon within the context of spherical shells. Leveraging functionally graded material (FGM) in the main layer of this structure proves instrumental in enhancing the shell's performance against rapid mechanical loads. Furthermore, the strategic placement of piezoelectric layers, both symmetrically and asymmetrically, coupled with the implementation of a proportional and derivative control system, facilitates the control of the shell's response. The formulation of displacement field and electric potential is grounded in the first-order shear deformation theory (FSDT) and second-order distribution, respectively. The strong form of nonlinear dynamic and electrostatic equations is derived using Hamilton's principle. Solving these equations is achieved through the implementation of the generalized differential quadrature (GDQ) method in the spatial domain and Newmark in the time domain. Additionally, the Newton-Raphson method is employed to tackle the inherent nonlinearity of the problem. The Budiansky's criterion is employed for the assessment of the load necessary for the buckling of the shell. Following the validation of results against numerical, analytical, and laboratory outcomes, a set of parametric results is presented. These results underscore the remarkable impact of the control system in mitigating shell deformation under time-dependent mechanical loads, as well as in postponing the occurrence of the snap-through phenomenon and damping the vibrations.

Enhanced Sensing of Diseased Blood Samples through One-Dimensional MgO-SiO2 Photonic Crystal Sensor

In this investigation, we present a tailored one-dimensional photonic crystal sensor (1D PCS), magnesium oxide (MgO) and silicon dioxide (SiO2) layers designed for the specific detection of diseased blood samples components, including plasma, platelets, red blood cells, and uric acid concentrations. The sensor structure is architecturally optimized for 6, 8,10,12,14, and 20 periods, encapsulating a central defect cavity that facilitates the interaction with the blood samples. Upon introducing the blood samples into this cavity, the transmittance spectrum is meticulously analyzed using the transfer matrix method to observe the variations in the defect mode’s wavelength. The study is conducted over a range of incident waves from wavelength 450 to 750 μm, enhancing the understanding of the sensor’s effect on the detection mechanism. In this context, our sensor demonstrates a remarkable sensitivity of approximately 815 nm per refractive index unit (RIU-1). It achieves a detection limit of 10–5, showcasing an exceptional ability to detect low concentrations of the infected blood components.Moreover, Q Factor of 3795 and FOM of 3369.18 indicate the sensor’s high precision in differentiating between healthy and infected blood samples.These findings underscore the potential of the proposed MgO-SiO2-based 1D PhC sensor in serving as a high-fidelity tool for biosensing application.

Mobile Device Security: A Two-Layered Approach with Blockchain and Sensor Technology for Theft Prevention

In the backdrop of the escalating incidents of mobile device theft and associated security challenges, a resilient and innovative solution is imperative. The traditional security mechanisms, largely reliant on the International Mobile Equipment Identity (IMEI), have been fraught with vulnerabilities, leading to a surge in incidents of device theft and data breaches. Addressing this pressing issue, we present a novel, two-tiered approach integrating sensor technology and blockchain to bolster mobile device security. This work aims to create and assess a dual-layered security strategy that uses blockchain and sensor technologies in a complementary way. Based on a rigorous conceptual framework, it explores a two-tiered security model that intricately combines sensor and blockchain technologies. This collaborative integration aims to provide an effective solution to the widespread challenges of theft and security breaches in mobile devices. The methodology employs a sensor layer for real-time data collection and processing to detect potential thefts, and activating alerts. The blockchain layer, invoked upon these alerts, initiates secure, transparent, and decentralized transactions for verification and validation across network nodes. This dual mechanism ensures swift and secure anti-theft actions, supported by an enhanced encryption standard. Our result analysis reveals the proposed system’s superiority in computational time, energy consumption, and overall security levels when compared to existing protocols. The integration of real-time processing and blockchain’s immutable nature promises reduced false positives and enhanced data integrity. The findings indicate that this integrative approach not only mitigates theft but also ensures data security, marking a significant stride in mobile security technology. In conclusion, this two-layered system promises a scalable, efficient, and robust solution to mobile device theft and data breaches, with potential impacts transcending individual device security to influence broader data privacy and security paradigms, thus signifying a pivotal development in the field of mobile security.

Task Scheduling Algorithm for Power Minimization in Low-Cost Disaster Monitoring System: A Heuristic Approach

This study investigates the optimization of a low-cost IoT-based weather station designed for disaster monitoring, focusing on minimizing power consumption. The system architecture includes application, middleware, communication, and sensor layers, with solar power as the primary energy source. A novel task scheduling algorithm was developed to reduce power usage by efficiently managing the sensing and data transmission periods. Experiments compared the energy consumption of polling and deep sleep techniques, revealing that deep sleep is more energy-efficient (4.73% at 15 s time intervals and 16.45% at 150 s time intervals). Current consumption was analyzed across different test scenarios, confirming that efficient task scheduling significantly reduces power consumption. The energy consumption models were developed to quantify power usage during the sensing and transmission phases. This study concludes that the proposed system, utilizing affordable hardware and solar power, is an effective and sustainable solution for disaster monitoring. Despite using non-low-power devices, the results demonstrate the importance of adaptive task scheduling in extending the operational life of IoT devices. Future work will focus on implementing dynamic scheduling and low-power routing algorithms to enhance system functionality in resource-constrained environments.

Optimization by Hydrogen Plasma Treatment of a-CH and Hydrogen/Nitrogen-Assisted a-CH Layers for SAW Sensors

Optimization by Hydrogen Plasma Treatment of a-CH and Hydrogen/Nitrogen-Assisted a-CH Layers for SAW Sensors

ZnO Hexagonal Nano- and Microplates Modified with Nanomaterials as a Gas-Sensitive Material for DMS Detection-Extended Studies.

The detection of dimethyl sulphide (DMS) at levels between ppb and ppm is a significant area of research due to the necessity of monitoring the presence of this gas in a variety of environments. These include environmental protection, industrial safety and medical diagnostics. Issues related to certain uncertainties concerning the influence of high humidity on DMS measurements with resistive gas sensors, e.g., in the detection of this marker in exhaled air, of the still unsatisfactory lower detection limit of DMS are the subject of intensive research. This paper presents the results of modifying the composition of the ZnO-based sensor layer to develop a DMS sensor with higher sensitivity and lower detection limit (LOD). Improved performance was achieved by using ZnO in the form of hexagonal nano- and microplates doped with gold nanoparticles (0.75 wt.%) and by using a well-proven sepiolite-based passive filter. The modification of the layer composition with respect to the authors' previous studies contributed to the development of a sensor that is highly sensitive to 1 ppm DMS (S = 11.4) and achieves an LOD of up to 406 ppb, despite the presence of a high water vapour content (90% RH) in the analysed atmosphere.

Highly Sensitive and Flexible Capacitive Pressure Sensors Combined with Porous Structure and Hole Array Using Sacrificial Templates and Laser Ablation.

Flexible, wearable pressure sensors offer numerous benefits, including superior sensing capabilities, a lightweight and compact design, and exceptional conformal properties, making them highly sought after in various applications including medical monitoring, human-computer interactions, and electronic skins. Because of their excellent characteristics, such as simple fabrication, low power consumption, and short response time, capacitive pressure sensors have received widespread attention. As a flexible polymer material, polydimethylsiloxane (PDMS) is widely used in the preparation of dielectric layers for capacitive pressure sensors. The Young's modulus of the flexible polymer can be effectively decreased through the synergistic application of sacrificial template and laser ablation techniques, thereby improving the functionality of capacitive pressure sensors. In this study, a novel sensor was introduced. Its dielectric layer was developed through a series of processes, including the use of a sacrificial template method using NaCl microparticles and subsequent CO2 laser ablation. This porous PDMS dielectric layer, featuring an array of holes, was then sandwiched between two flexible electrodes to create a capacitive pressure sensor. The sensor demonstrates a sensitivity of 0.694 kPa-1 within the pressure range of 0-1 kPa and can effectively detect pressures ranging from 3 Pa to 200 kPa. The sensor demonstrates stability for up to 500 cycles, with a rapid response time of 96 ms and a recovery time of 118 ms, coupled with a low hysteresis of 6.8%. Furthermore, our testing indicates that the sensor possesses limitless potential for use in detecting human physiological activities and delivering signals.

4D-STEM and Eels Analysis of Complex C-Based Sensor Architectures

Transforming high-carbon precursors into open-porous carbon foams and coatings via thermal processes is gaining attention as a sustainable method for various applications, including catalysis, energy utilization, and sensing [1]. In this research, we adopt a one-step laser patterning approach to selectively pyrolyze doctor-bladed ink coatings on flexible PET substrates, thereby producing highly porous, intricately designed CO2 sensor structures with a thickness of about 50 µm. Our ink formulation includes glucose as a pore-forming agent and adenine as a nitrogen source to enhance sensing capabilities. Laser processing in an oxygen-rich setting results in flexible, highly porous sensor heterostructures characterized by distinct areas enriched with nitrogen and oxygen functionalities. The laser intensity’s attenuation with depth leads to the development of a distinctly porous graphitic surface layer (serving as the electrical transducer layer) and a denser nitrogen-enriched lower sensor layer, linked by a narrow transitional region [2]. To understand the formation and functionality of these sensors, we conducted an in-depth TEM analysis of cross-sections of the complete device, prepared through ultramicrotomy cross-sectioning. STEM-EELS elemental distribution maps distinctly show the chemical composition differences between the upper and lower layers of the sensor. Principal component analysis was utilized to separate the complex sensor structures into their constituent crystalline and amorphous carbon and nitrogen-containing phases. 4D-STEM analysis exposed the arrangement of the crystalline graphitic phase and the orientation of graphite basal planes adjacent to the pores of the open-porous sensor. Analyzing these structural parameters is essential for understanding the electrical performance of the sensor, as depicted in Figure 1 [3]. Figure 1: A (top)) SEM micrograph of sensor embedded in epoxy, (bottom) depth-dependent thermal laser intensity attenuation; B (left)) HA ADF-STEM micrograph showing different sensor layers, (middle) STEM-EELS nitrogen distribution map, (right) PCA bond analysis, C) HRTEM images of sensor from transducer (top) and sensor (bottom) layers with SAED image of respective ROIs (inset); D) 4D-STEM analysis depicting misalignment angle between graphitic carbon basal plane normal relative to the pore surface normalReferences[1] M. Hepp, et al. npj Flexible Electronics 6, 1-9 (2022)[2] H. Wang, et al. Advanced Functional Materials 32, 2207406 (2022)[3] C. Ophus, et al. Microscopy and Microanalysis 28, 390-403 (2022) Acknowledgements: We acknowledge use of the DFG-funded Micro-and Nanoanalytics Facility (MNaF) at the University of Siegen (INST 221/131-1). Figure 1

Dynamic Tactile Synthetic Tissue: from Soft Robotics to Hybrid Surgical Simulators

Surgical simulators are valuable educational tools for physicians, enhancing their proficiency and improving patient safety. However, they typically still suffer from a lack of realism as they do not emulate dynamic tissue biomechanics haptically and fail to convincingly mimic real‐time physiological reactions. This study presents a dynamic tactile synthetic tissue, integrating both sensory and actuatory capabilities within a fully soft unit, as a core component for soft robotics and future hybrid surgical simulators utilizing dynamic physical phantoms. The adaptive surface of the tissue replica, actuated via hydraulics, is assessed by an embedded carbon black silicone sensor layer using electrical impedance tomography to determine internally or externally induced deformations. The integrated fluid chambers enable pressure and force measurements. The combination of these principles enables real‐time tissue feedback as well as closed loop operation, allowing optimal interaction with the environment. Based on the concepts of soft robotics, such artificial tissues find broad applicability, demonstrated via a soft gripper and surgical simulation applications including a dynamic, artificial brain phantom as well as a synthetic, beating heart. These advancements pave the way toward enhanced realism in surgical simulators including reliable performance evaluation and bear the potential to transform the future of surgical training methodologies.