Flexible Array Research Articles

Temperature-Switching Flexible Strain Sensors Based on Vanadium Dioxide for Intelligent Packaging Applications.

Flexible sensors are promising for intelligent packaging and artificial intelligence, but the required multistimulus response is still a challenge in external environments. A candidate material for such multistimulus response is VO2 due to its unique semiconducting properties. Herein, W-doped VO2(M) with a tunable phase transition temperature was prepared by the hydrothermal method, and then, VO2(M)-based flexible sensors were fabricated employing a direct-write strategy, where conductive inks with VO2(M) powders were patterned onto various substrates. These sensors achieve dual responses to temperature and strain and exhibit high stability (over 2000 stretch-release cycles) to accurately monitor various statuses (opening and closing, temperature changes, etc.) of intelligent packaging. The spatial pressure distribution of different objects was discerned by the prepared VO2(M)/poly(dimethylsiloxane) (PDMS) sponge flexible pressure sensor arrays, and the information was successfully edited using the Morse code. The sensing signals from the intelligent packaging were collected and remotely transmitted to intelligent terminals via a wireless local-area network to achieve real-time monitoring of the packaged contents. Therefore, in this work, we not only designed new flexible sensors with multiple stimulus responses but also demonstrated the potential applications of W-doped VO2(M)-based flexible sensors in intelligent packaging.

Origami-inspired soft fluidic actuation for minimally invasive large-area electrocorticography

Electrocorticography is an established neural interfacing technique wherein an array of electrodes enables large-area recording from the cortical surface. Electrocorticography is commonly used for seizure mapping however the implantation of large-area electrocorticography arrays is a highly invasive procedure, requiring a craniotomy larger than the implant area to place the device. In this work, flexible thin-film electrode arrays are combined with concepts from soft robotics, to realize a large-area electrocorticography device that can change shape via integrated fluidic actuators. We show that the 32-electrode device can be packaged using origami-inspired folding into a compressed state and implanted through a small burr-hole craniotomy, then expanded on the surface of the brain for large-area cortical coverage. The implantation, expansion, and recording functionality of the device is confirmed in-vitro and in porcine in-vivo models. The integration of shape actuation into neural implants provides a clinically viable pathway to realize large-area neural interfaces via minimally invasive surgical techniques.

Electrostatic Force-Assisted Transfer of Flexible Silicon Photodetector Focal Plane Arrays for Image Sensors.

Flexible photodetectors are pivotal in contemporary optoelectronic technology applications, such as data reception and image sensing, yet their performance and yield are often hindered by the challenge of heterogeneous integration between photoactive materials and flexible substrates. Here, we showcase the potential of an electrostatic force-assisted transfer printing technique for integrating Si PIN photodiodes onto flexible substrates. This clean and dry process eliminates the need for chemical etchants, making it a highly desirable method for manufacturing high-performance flexible photodetector arrays, expanding their widespread applications in electronic eyes, robotics, and human-machine interaction. As a demonstration, a 5 × 5 flexible Si photodetector focal plane array is constructed for imaging sensors and shaped into a convex semicylindrical form to achieve a π field of view with long-term mechanical and thermal stability. Such an approach provides a high yield rate and consistent performance, with the single photodetector demonstrating exceptional characteristics, including a responsivity of 0.61 A/W, a response speed of 39.77 MHz, a linear dynamic range of 108.53 dB, and a specific detectivity of 2.75 × 1012 Jones at an applied voltage of -3 V at 940 nm.

Ultra-low power carbon nanotube/porphyrin synaptic arrays for persistent photoconductivity and neuromorphic computing

Developing devices with a wide-temperature range persistent photoconductivity (PPC) and ultra-low power consumption remains a significant challenge for optical synaptic devices used in neuromorphic computing. By harnessing the PPC properties in materials, it can achieve optical storage and neuromorphic computing, surpassing the von Neuman architecture-based systems. However, previous research implemented PPC required additional gate voltages and low temperatures, which need additional energy consumption and PPC cannot be achieved across a wide temperature range. Here, we fabricated a simple heterojunctions using zinc(II)-meso-tetraphenyl porphyrin (ZnTPP) and single-walled carbon nanotubes (SWCNTs). By leveraging the strong binding energy at the heterojunction interface and the unique band structure, the heterojunction achieved PPC over an exceptionally wide temperature range (77 K-400 K). Remarkably, it demonstrated nonvolatile storage for up to 2×104 s, without additional gate voltage. The minimum energy consumption for each synaptic event is as low as 6.5 aJ. Furthermore, we successfully demonstrate the feasibility to manufacture a flexible wafer-scale array utilizing this heterojunction. We applied it to autonomous driving under extreme temperatures and achieved as a high impressive accuracy rate as 94.5%. This tunable and stable wide-temperature PPC capability holds promise for ultra-low-power neuromorphic computing.

Investigation on the focusing and separation of polystyrene microbeads in an integrated microfluidic system using magnetized functionalized flexible micro-magnet arrays

Investigation on the focusing and separation of polystyrene microbeads in an integrated microfluidic system using magnetized functionalized flexible micro-magnet arrays

Preparation of W-N-C single atom catalyst and Cu3(HHTP)2 metal-organic framework dual-decorated graphene nanoplatelet flexible electrode arrays for the rapid detection of carbendazim in vegetables

It is highly desirable to develop a low-cost and rapid detection method for trace levels of carbendazim fungicide residues, which would be beneficial for improving human health and mitigating environmental issues. Herein, isolated single tungsten atoms were implanted onto well-organized metal–organic framework (MOF)-derived N-doped carbons to form W-N-C single-site heterojunctions with ultrahigh electrocatalytic activity. The coupling of W-N-C with Cu3(HHTP)2, an electronically conductive MOF with a large surface area and porous structure, exhibited enhanced electrocatalytic performance for the oxidation of carbendazim (CBZ) when they were used for decorating graphene nanoplatelet flexible electrode arrays fabricated via template-assisted scalable filtration. A wide linear range (3.0 nM–50 μM) with an ultra-low detection limit of 0.97 nM and fast response was achieved for CBZ analysis. Moreover, the sensing platform has been utilised to monitor CBZ levels in vegetable samples with satisfactory recovery rates of 97.2–102% and a low relative standard deviation of 1.9%.

Design and Dynamic In Vivo Validation of a Multi-Channel Stretchable Liquid Metal Coil Array.

Recent developments in the field of radiofrequency (RF) coils for magnetic resonance imaging (MRI) offer flexible and patient-friendly solutions. Previously, we demonstrated a proof-of-concept single-element stretchable coil design based on liquid metal and a self-tuning smart geometry. In this work, we numerically analyze and experimentally study a multi-channel stretchable coil array and demonstrate its application in dynamic knee imaging. We also compare our flexible coil array to a commonly used commercial rigid coil array. Our numerical analysis shows that the proposed coil array maintains its resonance frequency (<1% variation) and sensitivity (<6%) at various stretching configurations from 0% to 30%. We experimentally demonstrate that the signal-to-noise ratio (SNR) of the acquired MRI images is improved by up to four times with the stretchable coil array due to its conformal and therefore tight-fitting nature. This stretchable array allows for dynamic knee imaging at different flexion angles, infeasible with traditional, rigid coil arrays. These findings are significant as they address the limitations of current rigid coil technology, offering a solution that enhances patient comfort and image quality, particularly in applications requiring dynamic imaging.

GW-MUSIC focusing algorithm with high accuracy for composite damage diagnosis

The Guided Wave (GW)-based Multiple Signal Classification (MUSIC) method for damage imaging in composite structures offers high-resolution and flexible sensor array placement, demonstrating considerable potential for precise damage localization. However, the application to real aircraft composite structures, characterized by complex structural features, presents substantial challenges. These include complex boundary reflections, pronounced anisotropy, and diminished scattered signals from damage sites. This paper presents a novel single-peak anisotropy-compensated MUSIC method for damage imaging of complex composites. This method, designed for improved localization accuracy, combines a self-excited calibration strategy to mitigate anisotropy with single wave peak focusing to amplify signals and reduce boundary reflections. Experimental validation on a complex composite wing structure demonstrated significant enhancements in localization precision, affirming the method's efficacy.

Stretch-tolerant interconnects derived from silanization-assisted capping layer lamination for smart skin-attachable electronics

Flexible strain sensor arrays hold great promise in on-skin monitoring of human signals and activities. Despite the development of strain-sensitive materials and patterning technologies for improved performance and device integration, the metal film serving as interconnects is always vulnerable upon stretch, which hinders the operation under large strains. Herein, a novel strategy is developed for achieving stretch-tolerant interconnects within a sensor array. Through introducing a high-modulus capping layer for the deposition of Ag interconnects, followed by silanization-assisted lamination onto the stretchable substrate where strain-sensitive graphene patches are inkjet-printed, the deformation of Ag interconnects is largely suppressed upon the global strain of the device, and a high working range of 40 % strain is achieved. Moreover, the chemical bonding between the capping layer and the stretchable substrate ensures a stable contact between the electrode and the sensitive layer under vigorous bending. The as-prepared sensor array demonstrates high sensitivity (gauge factor (GF) > 100) within a wide range (18 %), and could reliably monitor various physiological signals and human activities. A machine learning-assisted wearable gesture recognition system is developed based on the sensor array and a convolutional neural network (CNN), which could distinguish from 10 defined gestures with 100 % accuracy after 14 training processes. The facile and effective strategy could be universally applied for metal interconnects protection under stretch, and dramatically facilitate the design of smart flexible electronics.

Twisted and Disconnected Chains: Flexible Linear Tetracuprous Arrays and a Decanuclear CuI Cluster as Blue- and Green/Yellow-Light Emitters.

Defined arrays of transition metal ions embedded in tailored polydentate ligand scaffolds allow for a systematic design of their physical properties. Such molecular strings of closed-shell transition metal centers are particularly interesting for Group 11 metal ions in the oxidation state +1 if they undergo metallophilic d10···d10 contact interactions since these clusters are oftentimes efficient photoluminescence (PL) emitters. Copper is particularly attractive as a sustainable earth-abundant coinage metal source and because of the ability of several CuI complexes to serve as powerful thermally activated delayed fluorescence (TADF) emitters in molecular/organic light-emitting devices (OLEDs). Our combined synthetic, crystallographic, photophysical, and computational study describes a straight tetracuprous array possessing a centrally disconnected CuI2···CuI2 chain and a continuous helically bent CuI4 complex. This molecular helix undergoes a facile rearrangement in diethyl ether solution, yielding an unprecedented nanosized CuI10 cluster (2.9 × 2.0 nm) upon crystallization. All three clusters show either bright blue phosphorescence, TADF, or green/yellow multiband phosphorescence with quantum yields between 6.5 and 67%, which is persistent under hydrostatic pressure up to 30 kbar. Temperature-dependent PL investigations in combination with time-dependent density-functional theory (TD-DFT) calculations and void space analyses of the crystal packings complement a comprehensive correlation between the molecular structures and photoluminescence properties.

Replicating CD Nanogrooves onto PDMS to Guide Nanowire Growth for Monolithic Flexible Photodetectors with High Bending-Stable UV-vis-NIR Photoresponse.

Guided nanowires grown on polymer surfaces facilitate their seamless integration as flexible devices without post-growth processing steps. However, this is challenging due to the inability of polymer films to provide the required lattice-matching effect. In this work, this challenge is addressed by replicating highly aligned nanogrooves from a compact disc (CD) onto a casted flexible polydimethylsiloxane (PDMS) surface. Leveraging the replicated nanogrooves, copper hexadecafluorophthalocyanine (F16CuPc) and various metal phthalocyanines are guided into large-area, self-aligned nanowires. Subsequently, by employing specifically designed shadow masks during electrode deposition, these nanowires are seamlessly integrated as either a monolithic flexible photodetector with a large sensing area or on-chip flexible photodetector arrays. The resulting flexible photodetectors exhibit millisecond and long-term stable response to UV-vis-NIR light. Notably, they demonstrate exceptional bending stability, retaining stable and sensitive photoresponse even at a curvature radius as low as 0.5cm and after enduring 1000 bending cycles. Furthermore, the photodetector array showcases consistent sensitivity and response speed across the entire array. This work not only proves the viability of guided nanowire growth on flexible polymer surfaces by replicating CD nanogrooves but also underscores the potential for large-scale monolithic integration of guided nanowires as flexible devices.

A Flexible CSRR-Based Array Icing Sensor With Defective Microstrip Structure

A Flexible CSRR-Based Array Icing Sensor With Defective Microstrip Structure

Wide-humidity, anti-freezing and stretchable multifunctional conductive carboxymethyl cellulose-based hydrogels for flexible wearable strain sensors and arrays

Hydrogels play an important role in the design and fabrication of wearable sensors with outstanding flexibility, high sensitivity and versatility. Since hydrogels lose and absorb water during changes in humidity and temperature, it is critical and challenging to obtain hydrogels that function properly under different environmental conditions. Herein, a dual network hydrogel based on tannic acid (TA) reinforced polyacrylamide (PAM) and sodium carboxymethylcellulose (CMC) was constructed, while the introduction of the green solvents Solketal and LiCl endowed the hydrogel with greater possibilities for further modification to improve the water content and consistency of the mechanical properties over 30–90 % RH. This composite hydrogel (PTSL) has long-term stability, excellent mechanical strength, and freezing resistance. As strain sensors, they are linear over the entire strain range (R2 = 0.994) and have a high sensitivity (GF = 2.52 over 0–680 % strain range). Furthermore, the hydrogel's exceptional electrical conductivity and freezing resistance are a result of the synergistic effect of Solketal and LiCl, which intensifies the contact between the water molecules and the colloidal phase. This research could address the suitability of hydrogels over a wide range of humidity and temperature, suggesting great applications for smart flexible wearable electronics in harsh environmental conditions.

Design and application research of a flexible array plantar sensor based on P(VDF-TrFE)/SnO2NPS/GR for Parkinson’s disease diagnosis

ABSTRACT This paper introduces a flexible array Plantar sensor fabricated through the high-voltage electrospinning process of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) ，incorporating stannic oxide nanoparticles （SnO2NPS）and graphene (GR) composite nanofilm. The surface morphology, β-phase crystal content, piezoelectric performance, composition, and structure of the composite piezoelectric films were evaluated using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy, and a vibration platform. Experimental findings reveal that P(VDF-TrFE)/SnO2NPS/GR composite films containing 5% SnO2NPS and 0.1% GR exhibit superior open-circuit voltage and short-circuit current, measuring 22.43 V and 12.95 uA, respectively. These values are approximately 1.59 times and 1.34 times higher than those of the 5% P(VDF-TrFE) composite film and about 2.37 and 2.16 times higher than those of pure P(VDF-TrFE). A flexible piezoelectric sensor was fabricated using this composite film, and the mechanical properties and electrical impedance behavior of the sensor were investigated and analyzed.A multi-channel foot pressure collection and classification system was established based on this sensor, and a Parkinson’s disease machine learning model for multi-channel foot pressure collection was investigated. Various machine learning models for Parkinson’s disease were compared, and a fine K Nearest Neighbors（KNN） Parkinson’s disease classification model with an accuracy of 97.1% was proposed. This offers a novel solution for Parkinson’s disease diagnosis and holds significant reference value.

Wearable multichannel-active pressurized pulse sensing platform

With the modernization of traditional Chinese medicine (TCM), creating devices to digitalize aspects of pulse diagnosis has proved to be challenging. The currently available pulse detection devices usually rely on external pressure devices, which are either bulky or poorly integrated, hindering their practical application. In this work, we propose an innovative wearable active pressure three-channel pulse monitoring device based on TCM pulse diagnosis methods. It combines a flexible pressure sensor array, flexible airbag array, active pressure control unit, advanced machine learning approach, and a companion mobile application for human–computer interaction. Due to the high sensitivity (460.1 kPa−1), high linearity (R2 > 0.999) and flexibility of the flexible pressure sensors, the device can accurately simulate finger pressure to collect pulse waves (Cun, Guan, and Chi) at different external pressures on the wrist. In addition, by measuring the change in pulse wave amplitude at different pressures, an individual’s blood pressure status can be successfully predicted. This enables truly wearable, actively pressurized, continuous wireless dynamic monitoring of wrist pulse health. The innovative and integrated design of this pulse monitoring platform could provide a new paradigm for digitizing aspects of TCM and other smart healthcare systems.

Study of Wind Load Influencing Factors of Flexibly Supported Photovoltaic Panels

Flexible photovoltaic (PV) support structures are limited by the structural system, their tilt angle is generally small, and the effect of various factors on the wind load of flexibly supported PV panels remains unclear. In order to investigate the shape coefficients of the flexibly supported PV panel arrays, the grid-independent validation is carried out first, and then the case study validation is carried out to ensure the accuracy of the method in this paper. The CFD numerical simulation method is used to obtain the wind load variation of the PV panel array with different tilt angles, different spacing ratios, different wind angles, different heights above ground, different regions, and mountainous conditions. The distribution of wind pressure coefficients on the surface of PV panels with different inclination angles at different spacing ratios was investigated. The results show that the wind load shape coefficients with the increase in tilt angle and height above ground are basically a linear growth; the maximum value of PV shape coefficients appears in the wind angle at 30°, and 150° near the different tilt angles of the flexible PV array group shape coefficients distribution law is inconsistent. Different tilt angles of PV modules with the change rule of the spacing ratio of the wind load are inconsistent and have a greater impact on the wind load, so the PV panel array in all wind direction angles under the regional shape coefficients has a recommended value. The proposed value of the regional shape coefficients at all wind angles and the wind load calculation formula introducing height coefficients and spacing ratio coefficients are given.

A 3D imaging method for flexible array SAR based on a distributed POS

ABSTRACT The longer the baseline length of an airborne array synthetic aperture radar (SAR) is, the richer the ground object information can be resolved. The airborne array flexible SAR can overcome the limitation that the baseline length is limited by the belly length by attaching the antenna to the wing. However, fusing the airborne array flexible SAR distributed position and orientation system (POS) data under the wing and the belly is a major difficulty. To address this issue, the paper analyzes the inconsistency of airborne array flexible SAR data with a distributed POS and proposes a three-dimensional imaging method of airborne array flexible SAR based on distributed POS by fusing the Doppler centre, yaw angle and time of the observation data. By using distributed POS data, flexible data can obtain higher resolution than single-POS processing. The experiment of airborne array flexible SAR data proves the superiority of the proposed method.

65‐1: Invited Paper: Biaxially Formed LC Cells and Organic Transistors for 3D Curved Displays for Automotive Applications

Unsurprisingly, the FPD industry began life making flat display panels. In recent years curved displays have entered production, including TVs and foldable smartphone displays built on polyimide. These are manufactured in a flat state, then uniaxially curved.However, many real‐world surfaces have surfaces with biaxial curvature, either for aesthetic or functional reasons, and require biaxially curved displays with active optics that enable these surfaces to actively modulate, steer and focus light.We report on recent developments which show that flexible OTFT arrays, LC cells and Organic LCDs (OLCDs) can be biaxially thermoformed to spherically curved surfaces.

Exposure Factors for Flexible Digital Detector Arrays

Exposure factors (R factors) provide guidance in gamma radiography applications. The exposure time is calculated for a specific source type, activity, thickness of steel, desired exposure factor for a target film density or pixel value, and source-to-detector distance (SDD). R factors to produce target film densities of 2.0, 2.5, 3.0, and 3.5 were published for M100, MX125, T200, AA400, and HS800 films. Digital R factors are now published for Carestream rigid and flexible digital detector array (DDA) products. The flexible DDA’s are bent repeatedly around curved surfaces for single wall viewing, as radiography codes and standards require that the detector be in direct contact with the weld whenever practical. The R factor tables are published along with the supporting data used to calculate them, which are provided in graphical format for each condition. Iridium, selenium, and cobalt radioisotope sources were utilized for the generation of the data. Radiographers utilize the tables provided to enter the R factor into a commercially available phone-based calculator to determine the exposure time required to obtain the target optical density or grey value through the base metal. R factors are meant to be a starting point only, as other factors related to the part geometry and technique impact the required exposure.

Corrosion detection and localisation utilising a novel thin film guided wave sensor sparse array

Detecting and pinpointing corrosion-related damage in infrastructure poses significant financial and technical difficulties. It is simply not feasible to manually inspect all infrastructure for corrosion. Permanently installed systems can monitor critical failure points without the need for manual scanning but these are not always known. Ultrasonic guided wave technology can be used for full system coverage, however, there is a trade-off between range and resolution. This has found a place for long distance monitoring of significant defects, however high- resolution systems require too dense a network to be feasible to install, cost and maintain. This research seeks a middle ground between these two options by employing machine learning and a scalable setup of easy to install, printed detection sensors. A flexible array of printed thin film sensors is placed around two identical mild steel pipes, each 0.5m long with a 6 mm wall thickness and 115 mm outer diameter. Corrosion is then induced artificially in one sample. Two transmit transducers on the top and bottom of the pipes are used to emit an ultrasonic, circumferential guided wave. The transmitted waveform was then received on all sensors throughout the array for data collection. Through machine learning and a search algorithm, sub-millimetre resolution is achieved, detecting millimetre-scale corrosion and localisation to the nearest detection sensor. Crucially, the system maintains scalability for large-scale asset inspection. This technology shows promise in addressing inspection challenges, including Corrosion Under Pipe Supports (CUPS) and Corrosion Under Insulation (CUI). It offers a potential solution to the costly problem of infrastructure damage detection and localisation while retaining scalability and a low-profile design philosophy.