Applications In Wearable Devices Research Articles

The integrated smart system to assist elderly at home

Some elders prefer to live independently rather than in a nursing home. However, they need to be assisted because of health and safety reasons. We developed an integrated system consisting of a smart home, a mobile robot, and a wearable device, using message queuing telemetry transport (MQTT) protocol to communicate with each other. The smart home can be monitored and controlled via a mobile application. We use the telepresence robot equipped with a light detection and ranging (LIDAR) sensor to perform simultaneous localization and mapping (SLAM) and autonomous navigation. The wearable device application is used to detect older adults' heart rate, the steps taken, and the burnt calories. We also add pose detection and location estimation using a depth camera powered by an efficient deep-learning algorithm. We also developed an Android application as a dashboard that monitors and controls all system components. Our system can facilitate communication between its various components.

Recovered graphene-hydrogel nanocomposites for multi-modal human motion recognition via optimized triboelectrification and machine learning

Hydrogels have extensive applications in portable, flexible, wearable, and self-powered electronic devices based on triboelectric nanogenerators (TENGs). An important issue with hydrogels is their tendency to dehydrate over time, which leads to a decline in both ionic conductivity and mechanical flexibility. Furthermore, the current techniques used to produce these hydrogels mostly rely on the freeze–thaw process, which has limited ability to modify the polymer conformation. Herein, a novel water-assisted recovered hydrogel is proposed using a simple strategy to prepare high-performance hydrogel-based TENGs by optimizing the cross-linking and crystalline domains. Synthesis of the electrostatic electrode in the TENG involved the incorporation of polyethylene oxide (PEO) into a polyvinyl alcohol (PVA) hydrogel network via cross-linking. Graphene nanoplatelets (GNP) were added to precisely tune the electrical conductivity. GNP constructs the backbone structures in the hydrogel and enhances the charge transport capacity. Electrical conductivity is changed by the GNP concentration and thus, electrical output of the hydrogel can be facilely controlled. The water reabsorption increased density and crystallinity of the cross-linking and allowed the hydrogel to show superior performance compared to the original one. The 7th recovery hydrogel produced around 594 V, 40 μA, and 32 nC. The 7th recovery hydrogel had exceptional endurance, with the capacity to withstand over 16,000 cycles of contact separation. Moreover, it could be stretched up to 541 % of its original length and improved by almost twice as much as that without the recovery process. By combining multi-modal graphene-based TENG sensors with machine learning, a state-of-the-art behavioral monitoring system was created that could reliably detect tapping fingers with an average accuracy rate of 95 %. The findings of this research will pave the way for new approaches to the development of autonomous motion sensors and flexible renewable energy sources.

Flexible Ag2Se Film with Enhanced Thermoelectric Performance.

Flexible thermoelectric devices offer huge potential for wearable electronics due to their ability to generate green energy by using low-grade heat. However, achieving both high thermoelectric performance and flexibility simultaneously remains a challenge for these devices. Here, we present a simple and cost-effective method for fabricating a high-performance flexible inorganic-organic thermoelectric film by depositing Ag2Se on a porous nylon membrane. The resulting Ag2Se/nylon film exhibits an ultrahigh power factor of approximately 3.4 mW/mK2 at 300 K, the highest value reported for flexible thermoelectric films to date. The Ag2Se/nylon film also demonstrates remarkable flexibility, confirming its potential application in wearable electronics. A thermoelectric module constructed using eight strips of the processed Ag2Se/nylon film generates an impressive output voltage of 65 mV and an output power of 30 μW at a 30 K temperature difference. Additionally, the fabricated module maintains strong flexibility, producing more than 2 mV when wrapped around a human arm with a temperature difference of 1.6 K. This work highlights the significant potential of inorganic-organic films for flexible thermoelectric applications in wearable and implantable devices.

High-Strength and Conductive Electrospun Nanofiber Yarns.

In electrospinning, nanofibers are frequently produced in nonwoven web form. Their poor mechanical properties (below 100 MPa) and difficulty in tailoring the fibrous structure have restricted their applications. However, advanced materials must be highly resistant to both deformation and fracture. By combining electrospinning technology with stretching, we have overcome this disadvantage and demonstrated a polyacrylonitrile nanofiber yarn with a tensile strength of 743 ± 20 MPa. The nearly perfect uniaxial orientation of the fibrils under the stretching process is crucial for the remarkable mechanical properties of the yarn. Additionally, the nanofiber yarn was functionalized by a dip-coating process with silver nanowires (AgNWs), imparting conductive properties. This conductive, high-strength nanofiber yarn demonstrates practical applications in flexible and wearable devices. The presented strategy is versatile and can be adapted to create other high-performance nanofiber yarns, with potential uses in fields such as biomedicine and smart textiles.

Thermoelectric power generator module using n-type Sb₂S₃ and p-type Bi₂Te₃-coated cotton fabric for wearable device applications

Antimony trisulfide (Sb₂S₃), a binary metal chalcogenide, exhibits significant promise for energy conversion applications due to its tunable bandgap and exceptional stability under exposure to moisture and air, making it a strong candidate for thermoelectric applications. In this study, Sb₂S₃ was synthesized via co-precipitation method and subsequently coated onto cotton fabric using a formulated ink. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses confirmed its orthorhombic crystalline structure and nanorod-like morphology. Sb₂S₃ was found to possess an indirect bandgap of 1.70 eV in its amorphous phase and 1.52 eV in its crystalline phase. Fourier-transform infrared (FTIR) spectroscopy revealed characteristic peaks at 447 cm⁻1 and 568 cm⁻1, corresponding to the symmetric stretching vibrations of Sb-O and Sb-S bonds, respectively. Current-voltage (I-V) measurements indicated near-ohmic behavior with an electrical conductivity of 2 × 10⁻⁵ S/cm, while Hall effect measurements confirmed its n-type semiconducting nature. The thermoelectric evaluation of Sb₂S₃-coated cotton fabrics demonstrated n-type behavior, with the Seebeck coefficient increasing with temperature, reaching −185 μV/K at 293 K with a notable power factor of 6.845 × 10−4 nW/cmK2. The material also exhibited low thermal conductivity (0.077 W/mK) and an effusivity of 223.95 Ws1/2/m2K. For the first time, a thermoelectric device was successfully fabricated by combining Sb₂S₃ as the n-type material with Bi₂Te₃ as the p-type material. This device, integrated into a wearable hand band, demonstrated an output voltage of 4.7 mV under a temperature difference of approximately 4 °C, highlighting its significant potential for low-power applications in wearable technology. The successful integration of these materials into a flexible substrate underscores their viability in next-generation thermoelectric energy harvesting devices.

Radiation synthesis of high conductivity hydrogel based on tragacanth gum/poly (ionic liquids) for multimodal sensors and supercapacitor

Natural polymer-based hydrogels have found extensive use in flexible sensing, energy storage, and other fields because of their environmental sustainability and biocompatibility. Nonetheless, numerous challenges persist in the development of hydrogels with outstanding conductivity solely from natural polymers. Herein, we have successfully synthesized hydrogels based on natural polymer (tragacanth gum) and ionic liquids (1-vinyl-3-ethylimidazolium bromide) using a convenient and efficient one-step ionizing radiation method (TG/PIL hydrogels). The TG/PIL hydrogels exhibit high ionic conductivity (7.1 S m−1 at 25 °C), and can be used for multimodal sensors, including strain and temperature sensors. It has exceptional capabilities in monitoring human motor behavior, capturing subtle facial expressions and pulses beat. TG/PIL hydrogel can also accurately sense changes in the temperature of the external environment, and have significant thermal sensitivity within the range of 40 to 60 °C (−3.22 % /°C). Furthermore, the high conductivity of TG/PIL hydrogels enables them to exhibit outstanding performance in supercapacitor electrolytes, it has good stability in a certain load bearing range, temperature range, folding angle range. This work offers a straightforward technique for creating a multimodal hydrogel sensor, with promising applications in flexible wearable devices, energy storage, and beyond.

Zinc Ion Hybrid Capacitors: Four Essential Parameters Determining Device Energy Density.

Zinc ion hybrid capacitors (ZIHCs) with Zn metal faradic and carbon capacitive electrodes have potential applications in grid-scale energy storage systems and wearable devices. However, the high specific energy density reported in many recent studies is based on the mass of active carbon materials alone, with deficient device energy density. This perspective article discusses how four crucial parameters influence the device energy density of ZIHCs, including areal mass loading (mc) and specific capacity (Qg,c) of active carbon materials in cathodes, negative-to-positive electrode capacity ratio (N/P), and electrolyte-to-active carbon materials mass ratio (E/C). Using a representative device model, how the device energy density varies when these four parameters change is shown. Detailed analysis indicates that specific parameter windows with the four parameters within narrow ranges (e.g., mc = 10-20mg cm-2, Qg,c > 100 mAh g-1, N/P < 20, and E/C < 5) need to be achieved simultaneously to deliver application-relevant energy density (e.g., >30 Wh kg-1) in ZIHCs. It is hoped that these findings assist in objectively evaluating reported performance data and identifying essential issues for future research development to realize practical applications.

Improved Pyroelectric Nanogenerator Performance of P(VDF-TrFE)/rGO Thin Film by Optimized rGO Reduction.

The pyroelectric nanogenerator (PyNG) has gained increasing attention due to its capability of converting ambient or waste thermal energy into electrical energy. In recent years, nanocomposite films of poly(vinylidene fluoride-co-trifluoro ethylene) (P(VDF-TrFE)) and nanofillers such as reduced graphene oxide (rGO) have been employed due to their high flexibility, good dielectric properties, and high charge mobility for the application of wearable devices. This work investigated the effect of rGO reduction on pyroelectric nanogenerator performance. To prepare rGO, GO was reduced with different reducing agents at various conditions. The resulting rGO samples were characterized by XPS, FT-IR, XRD, and electrical conductivity measurements to obtain quantitative and qualitative information on the change in surface functionalities. Molecularly thin nanocomposite films of P(VDF-TrFE)/rGO were deposited on an ITO-glass substrate by the Langmuir-Schaefer (LS) technique. A PyNG sandwich-like structure was fabricated by arranging the thin films facing each other, and it was subjected to the pyroelectric current test. For various PyNGs of the thin films containing rGO prepared by different methods, the average pyroelectric peak-to-peak current (APC) and the pyroelectric coefficient (p) values were measured. It was found that a more reduced rGO resulted in higher electrical conductivity, and the thin films containing rGO of higher conductivity yielded higher APC and p values and, thus, better energy-harvesting performance. However, the thin films having rGO of too high conductivity produced slightly reduced performance. The Maxwell-Wagner effect in the two-phase system successfully explained these optimization results. In addition, the APC and p values for the thin film with the best performance increased with increasing temperature range. The current PyNG's performance with an energy density of 3.85 mW/cm2 and a p value of 334 μC/(m2∙K) for ΔT = 20 °C was found to be superior to that reported in other studies in the literature. Since the present PyNG showed excellent performance, it is expected to be promising for the application to microelectronics including wearable devices.

An adaptive bionic sensor: enhancing ankle joint tracking with high sensitivity and superior cushioning performance

Flexible sensors are renowned for their rapid responsiveness, high flexibility, and outstanding mechanical properties, making them ideal for applications in wearable devices, sports and health monitoring, and human-machine interfaces. To enhance the sensing performance of these flexible sensors, researchers have drawn inspiration from nature, creating various bionic microstructures. However, these structures often manifest in the macroscopic form of thin films, which do little to improve impact resistance and joint protection. In response, this work achieves a highly sensitive and impact-resistant pressure sensor by integrating bionic principles at both micro and macro levels. Specifically, at the micro level, a muscle-like hydrogel system consisting of MXene nanosheets incorporated into the double network of polyvinyl alcohol and sodium alginate matrix is selected. At the macro level, the bionic prototypes of mimosa leaves and durian spikes with good energy absorption structure, together with octopus’ sucker with good adsorption capacity are selected, and the synergistic construction of the three structures is realized through 3D printing methods. The obtained sensor has an appropriate response range, sensitivity and stability. More importantly, the displacement deformation of the hydrogel can be reduced by 91.22%, while its adhesion strength can be increased by 57.5% compared to the unstructured hydrogel. As a proof-of-concept, the proposed bionic flexible sensor can be used to monitor the motion status of the human ankle joint in real-time, thereby assisting users in making real-time judgments on gait health.

Biomimetic Structural Hydrogels Reinforced by Gradient Twisted Plywood Architectures.

Naturally structural hydrogels such as crustacean exoskeletons possess a remarkable combination of seemingly contradictory properties: high strength, modulus, and toughness coupled with exceptional fatigue resistance, owing to their hierarchical structures across multiple length scales. However, replicating these unique mechanical properties in synthetic hydrogels remains a significant challenge. This work presents a synergistic approach for constructing hierarchical structural hydrogels by employing cholesteric liquid crystal self-assembly followed by nanocrystalline engineering. The resulting hydrogels exhibit a long-range ordered gradient twisted plywood structure with high crystallinity to mimic the design of crustacean exoskeletons. Consequently, the structural hydrogels achieve an unprecedented combination of ultrahigh strength (46±3MPa), modulus (496±25MPa), and toughness (170±14MJ m-3), together with recorded high fatigue threshold (32.5kJ m-2) and superior impact resistance (48±2kJ m-1). Additionally, through controlling geometry and compositional gradients of the hierarchical structures, a programmable shape morphing process allows for the fabrication of complex 3D hydrogels. This study not only offers valuable insights into advanced design strategies applicable to a broad range of promising hierarchical materials, but also pave the ways for load-bearing applications in tissue engineering, wearable devices, and soft robotics.

Low-temperature growth of CuS thin film on flexible substrates for photodetection

Abstract The covellite phase of copper sulfide thin film (CuS), due to its excellent electronic, optical and chemical properties, has attracted enormous attention in cutting-edge research. This is a comprehensive study of the structural, optical, morphological and electrical properties of CuS thin films deposited by chemical bath deposition technique on flexible polyethylene terephthalate (PET) substrates at different deposition temperatures, i.e. 25 °C, 40 °C, 55 °C and 70 °C for the fabrication of flexible photodetectors. X-ray diffraction and Raman spectral studies reveal the presence of hexagonal covellite phase (CuS), whereas the root mean square (RMS) roughness of CuS thin film increases with an increase in deposition temperature. The optical bandgap of CuS thin film is found to be decreased with an increase in deposition temperature. The optimized CuS thin film, deposited at 70 °C, exhibits a homogeneous surface with RMS roughness of 13.72 nm, mobility of 25.09 cm2 V−1s−1 and bandgap of 1.86 eV. The mobility of CuS thin film is found to be increased with the increase in deposition temperature. The flexible CuS photodetector, fabricated at 70 °C, exhibits better photoresponse characteristics, with the highest responsivity of 0.18 mA W−1, specific detectivity of 1.39 × 108 Jones and sensitivity of 173.25 % upon light illumination. The established photocurrent possesses an outstanding dependence on various intensities of illuminated light. Furthermore, the bending test of flexible CuS photodetectors reveals the absence of any sign of deterioration up to bending angle of 30°. This suggests that the Al/CuS-PET/Al photodetector device could be used in various wearable optoelectronic device applications.

Van der Waals GeSe with Strain- and Gate-Tunable Linear Dichroism for Wearable Electronics.

The direct detection of light polarization poses a crucial challenge in the field of optoelectronics and photonics. Herein, the tunable linear dichroism (LD) in GeSe-based polarized photodetectors is presented through electronic and structural asymmetry modulation, and demonstrate their application prospects in wearable electronics. An improvement in the dichroic ratio up to 34% is achieved under a gate voltage of 20V, and the improvement reaches 44% by applying a tensile strain along the zigzag direction. Theoretical calculations reveal that the gate regulation of barrier height between GeSe and Au electrodes is responsible for the electrical-tunable LD, while the anisotropic optical absorption in response to strains leads to the strain-tunable LD. Moreover, flexible GeSe transistors are developed for wearable applications including motion sensors and glucose monitors. This study offers viable approaches for modulating the optical anisotropy of low-dimensional materials and emphasizes the versatility of van der Waals materials for practical applications in wearable electronic devices.

Improvement of Thermal Stability of Charges in Polylactic Acid Electret Films for Biodegradable Electromechanical Sensors.

Eco-friendly sensors fabricated from biocompatible and biodegradable materials are promising candidates for wearable and implantable electronics due to their environmental sustainability and biosafety. This article reports a fully biodegradable electromechanical sensor (FBES) utilizing a sandwich structure with macro ripple structured polylactic acid (PLA) electret films acting as sensitive layers and molybdenum (Mo) sheets serving as electrodes for a wearable device application. The stability of the space charge stored within the PLA film has been enhanced by introducing an internal cellular structure and improving the polarization process. A macro ripple structure of the PLA layer with higher deformation is a great guarantee for boosting the pressure sensitivity. The results indicate that inserting cell microstructures and optimizing the polarization process significantly improve the charge storage stability of PLA films by nearly 55%. This enhancement is attributed to several factors, including the extended charge drift path of the charges in cellular films, a synergy effect of surface charges, and "macroscopic" dipole charges distributed in the cells. The fabricated sensor achieves a high sensitivity of 1000 pC/kPa, a wide pressure detection range of 0.03-62.4 kPa, and satisfactory stability. Such sensors are not only sensitive to body movements but also to subtle physiological signals, satisfying the diverse needs of wearable healthcare. Importantly, all the composition materials of the sensor can be completely degraded after their service, aligning with the environmentally friendly principles of green development.

Stretchable, self-adhesive, and sensitive polyacrylamide-polyvinyl alcohol double network hydrogels for flexible wearable sensors

With the development of artificial intelligence, flexible hydrogel sensors have received widespread attention in fields such as biomedicine, environmental monitoring, and information identification. However, current hydrogels face challenges such as low conductivity, sensitivity, and stability. In this study, we developed a novel PAHS double network hydrogel composed of polyvinyl alcohol (PVA), acrylamide (AM), acrylic acid (AA), chitosan quaternary ammonium salt (HACC-102), and sodium citrate (SC). This hydrogel features a double network structure, combining a chemically cross-linked network of PAMAAC as the soft network to complement the hard network formed by PVA. This unique structure results in an impressive elongation at break of 1140 % and a maximum stress of 490 kPa, indicating superior mechanical properties. The inclusion of SC significantly enhances the hydrogel's conductivity, reaching 0.63 S/m, a 4.8-fold improvement. The hydrogel exhibits a gauge factor of 1.60 under 0 %-100 % strain and 1.97 within the 100 %-400 % strain range. It also demonstrates a quick response time of 155 ms and 160 ms under 1 % strain, ensuring rapid and stable signal transmission. Moreover, the PAHS hydrogel sensor demonstrates quick response capabilities and high sensitivity in monitoring human movements and high precision in handwriting recognition. With its simple preparation method, excellent mechanical properties, and stable signal transmission, the PAHS hydrogel presents a viable strategy for future applications in flexible wearable devices.

Vacuum Filtration-Coated Silver Electrodes Coupled with Stacked Conductive Multi-Walled Carbon Nanotubes/Mulberry Paper Sensing Layers for a Highly Sensitive and Wide-Range Flexible Pressure Sensor.

Flexible pressure sensors based on paper have attracted considerable attention owing to their good performance, low cost, and environmental friendliness. However, effectively expanding the detection range of paper-based sensors with high sensitivities is still a challenge. Herein, we present a paper-based resistive pressure sensor with a sandwich structure consisting of two electrodes and three sensing layers. The silver nanowires were dispersed deposited on a filter paper substrate using the vacuum filtration coating method to prepare the electrode. And the sensing layer was fabricated by coating carbon nanotubes onto a mulberry paper substrate. Waterborne polyurethane was introduced in the process of preparing the sensing layers to enhance the strength of the interface between the carbon nanotubes and the mulberry paper substrate. Therefore, the designed sensor exhibits a good sensing performance by virtue of the rational structure design and proper material selection. Specifically, the rough surfaces of the sensing layers, porous conductive network of silver nanowires on the electrodes, and the multilayer stacked structure of the sensor collaboratively increase the change in the surface contact area under a pressure load, which improves the sensitivity and extends the sensing range simultaneously. Consequently, the designed sensor exhibits a high sensitivity (up to 6.26 kPa-1), wide measurement range (1000 kPa), low detection limit (~1 Pa), and excellent stability (1000 cycles). All these advantages guarantee that the sensor has potential for applications in smart wearable devices and the Internet of Things.

Enhanced performance of flexible BiFeO3 ferroelectric memory with Mica substrate via SrTiO3 buffer layer

BiFeO3 (BFO) application in flexible wearable devices is garnering interest because of its unique ferroelectric and magnetic properties. However, the integration of high-quality BFO films onto flexible substrates presents significant technical challenges. Here, we successfully fabricated high-quality BFO films on mica substrates by using pulsed laser deposition, and report the fatigue characteristics of BFO films on flexible substrates for the first time. The results demonstrated that, after 108 bipolar switching cycles, the polarization only degraded by 0.28%, indicating superior fatigue characteristics compared to previously reported BFO films. Additionally, the device ferroelectric properties remained largely unchanged, with a bending radius of 3.5 mm. The fabricated flexible Pt/BFO/La0.65Sr0.35MnO3(LSMO)/SrTiO3(STO)/mica non-volatile memory devices exhibited mechanical flexibility and fatigue resistance. These findings not only highlight the potential of flexible BFO films for wearable electronic devices and flexible memory devices, they also provide valuable insight for the future development of high-performance flexible ferroelectric materials.

Stretchable printed circuit boards using a silicone substrate of variable stiffness and conventional PCB fabrication methods

Abstract Stretchable printed circuit boards (S-PCBs) offer unique advantages over rigid PCBs such as enabling conformability to changing environments and ergonomic designs with increased lifetime under dynamic loads. This study introduces an innovative fabrication method and a cost-effective solution for rapid prototyping S-PCBs using commercially available materials. By utilizing silicone substrates with different levels of stiffness and structured copper sheets for electrical connections, the S-PCBs feature ‘stiff islands’ embedded in a flexible base material. This fabrication method helps alleviate mechanical strain on strain-sensitive components while allowing local deformation of the S-PCB. The proposed fabrication method does therefore enable to integrate surface mount device components into S-PCBs and facilitates complex circuit designs while maintaining stretchability and fatigue resistance. Through material characterization, video strain analysis, as well as quasi-static and cyclic loading tests, this article demonstrates the efficacy of our approach. Based on the experimental results, we provide insights into failure modes and suggest design principles to further enhance the durability of S-PCBs fabricated with our method. We then conclude by presenting a soft wearable S-PCB demonstrator. The S-PCBs fabricated with this method withstood mechanical strains up to 100% and cyclic loads with 30% strain up to 625 cycles. The results are very promising for applications in soft robotics, wearable devices, and soft sensors and actuators. Overall, our study offers a comprehensive toolkit for fast S-PCB prototyping, paving the way for advancements in stretchable electronics with a high degree of complexity and stretchability.

Mechanically Adaptable High‐Performance p(SBMA‐MMA) Copolymer Hydrogel with Iron (II/III) Perchlorate for Wearable Thermocell Applications

AbstractQuasi‐solid‐state thermocells (QTECs) show promise as a power source for wearable devices by converting body heat into electricity. While significant progress has been made with p‐type elements for QTECs, challenges remain with their n‐type counterparts. Here, a high‐performance n‐type QTEC element is presented, using a copolymer hydrogel that outperforms conventional p‐type elements. This copolymer hydrogel combines hydrophilic zwitterionic sulfobetaine methacrylate (SBMA) for ionic conduction and hydrophobic methyl methacrylate (MMA) for structural stability. By increasing the MMA content from 35 to 100 wt.%, versatile control is achieved over the hydrogel's elastic modulus (72 kPa to 127.7 MPa) and tensile strength (54 kPa to 6.7 MPa). A high mechanical toughness of 7.2 MJ m−3 is also achieved at 68 wt.% MMA. The mechanically robust and high toughness p(SBMA‐MMA) hydrogel is then immersed in Fe(ClO4)2/3 solutions of different concentrations to evaluate its performance as an n‐type QTEC element. The hydrogel with 0.8 M Fe(ClO4)2/3 exhibits a high ionic Seebeck coefficient of −1.7 mV K−1, a power density of 1.1 mW m−2 K−2, and an elastic modulus of 1.6 MPa, which is similar to that of human skin. Finally, the optimized n‐type p(SBMA‐MMA) hydrogels demonstrate the potential application for wearable devices.

Low-temperature fabrication of metal-organic-frameworks/TiO2 photoanode for flexible dye-sensitized solar cells

Metal-organic frameworks (MOFs) are utilized to integrate with TiO2 to enhance the solar-to-electricity conversion efficiency. The porphyrin-based MOF PCN-222 is the focus of the study. The MOF/TiO2 composite is deposited on a flexible ITO-PEN (polyethylene naphthalate) substrate under low-temperature (<150 °C) conditions. The resulting flexible DSSC demonstrates faster electron diffusion and improved charge carrier separation ability, achieving an efficiency of 4.41 % under 100 mW cm−2, AM 1.5 global illumination. In comparison to the traditional FTO-glass-based DSSC, this type of flexible DSSC shows great potential for application in wearable electronic devices.

Customizable metamaterial design for desired strain-dependent Poisson’s ratio using constrained generative inverse design network

Inverse design of metamaterial structures with customized strain-dependent Poisson’s ratio has significant potential across various applications. However, achieving precise control over these mechanical properties presents a challenge due to the complex relationship between geometry and mechanical performance. Here, we present a novel data-driven approach utilizing a constrained generative inverse design network (CGIDN) to address this challenge. The CGIDN uses backpropagation to efficiently navigate the design space and achieve target mechanical properties with high accuracy. Our method starts by generating a comprehensive dataset of Poisson’s ratio-strain curves for various geometries incorporating cuts. These curves are then compressed using principal component analysis (PCA) to reduce dimensionality while preserving essential features. A deep neural network (DNN) is then trained to map input geometric parameters to these principal components, with the architecture optimized using grid search. The CGIDN facilitates the inverse design process by recommending geometric parameters for unit cell designs that match specified target Poisson’s ratio-strain curves. We validated the effectiveness of our approach through Finite Element Analysis (FEA) and experimental verification. The FEA results for the designed unit cells showed high agreement with the target and predicted curves, demonstrating the accuracy of the CGIDN model. Further, tensile tests on specimens confirmed that the inverse-designed structures reproduced the desired mechanical behavior upon scale-up. Our method, which enables efficient and accurate design of metamaterials with tailored mechanical properties, holds promise for applications in wearable devices, soft robotics, and advanced sensor systems.