Search Results (27)

Planar heaters are designed to deliver uniform heat across broad surfaces and serve as critical components in applications requiring energy efficiency, safety, and mechanical flexibility, such as wearable electronics and smart textiles. However, conventional metal-based heaters are limited by poor adaptability to curved or complex surfaces, low mechanical compliance, and susceptibility to oxidation-induced degradation. To overcome these challenges, we applied a protein-assisted electroless copper (Cu) plating strategy to electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofiber substrates to fabricate flexible, conductive planar heating membranes. For interfacial functionalization, a protein-based engineering approach using bovine serum albumin (BSA) was employed to facilitate palladium ion coordination and seed formation. The resulting membrane exhibited a dense, continuous Cu coating, low sheet resistance, excellent durability under mechanical deformation, and stable heating performance at low voltages. These results demonstrate that the BSA-assisted strategy can be effectively extended to complex three-dimensional fibrous membranes, supporting its scalability and practical potential for next-generation conformal and wearable planar heaters. Full article

Fiber-shaped electrical heaters with high flexibility and excellent adaptability make an ideal candidate for the application of wearable electronics but still suffer from low strength and poor durability. Herein, an all-in-one Joule-heating fiber capable of outstanding mechanical properties, good heating efficiency, and long-term stability is reported by using polymer-assisted metal deposition to firmly coat Cu nanoparticles on high-performance liquid crystal polymer (LCP) fibers. Taking advantage of LCP, the resultant fibers exhibit a satisfying temperature threshold (up to 200 °C) and immense strength (2.94 GPa). By virtue of dense and continuous Cu film, these fibers show low electrical resistance (5.51 Ω/cm) and an ultrafast response rate (12.6 °C·s⁻¹) at low supplied voltages (0.5–3.5 V). Benefiting from the levodopa/polyethyleneimine interface design, such fibers maintain nearly constant resistance after repeatable bending, folding, and even washing (50 cycles). Based on the above-mentioned merits, a wearable patch with a Joule-heating function is knitted by using as-made fibers to offer therapeutic benefits for human body joints. This work demonstrates prospective potential for enriching the challenging applications of fiber-shaped electrical heating systems. Full article

Recent developments in flexible printed heaters (FPHs) for wearable thermal applications, driven by the advancement of printed electronics, show great promise in revolutionizing patient care through the development of wearable flexible heaters for medical applications. Wearable heaters with high thermal stability, heat uniformity, safety, flexibility, comfort, biocompatibility, biodegradability, recyclability, and power efficiency are desirable for standalone medical thermotherapy applications. This paper reviews recent advancements in the design of FPHs for wearable thermal applications. Materials used in the FPHs, fabrication methods, design considerations, temperature control mechanisms, medical applications, and performance analysis of specific FPHs are all thoroughly discussed. Materials used in FPHs, such as conductive and substrate materials, receive special attention along with the heater design parameters. Additionally, the paper addresses the challenges and future directions for the advancement of FPHs in wearable medical applications. Full article

Soft transportation devices with high flexibility, good stability, and quick controllability have attracted increasing attention. However, a smart soft transportation device with tactile perception and a non-contact actuating mode remains a challenge. This work reports a magnetic soft pipeline (MSP) composed of sensor film, a magnetorheological elastomer (MRE) cavity pipeline, and heater film, which can not only respond well to tactile compression stimuli but also be transported by magnetic actuation. Notably, the sensor film was integrated on the upper surface of an MRE pipeline, and the relative resistance change (∆R/R₀) of the MSP was maintained at 55.8% under 2.2 mm compression displacement during 4000 loading cycles. Moreover, the heater film was integrated on the lower surface of the MRE pipeline, which endows the MSP with an electrothermal heating characteristic. The temperature of the MSP can be increased from 26.7 °C to 38.1 °C within 1 min under 0.6 V. Furthermore, the MSP was attracted and deformed under the magnetic field, and the ∆R/R₀ of the MSP reached 69.1% under application of a 165 mT magnetic field density. Benefiting from the excellent perception and magnetic deformation performances, the magnetic actuate transportation of the MSP with self-sensing was successfully achieved. This multi-functional soft pipeline integrated with in situ self-sensing, electrothermal heating, and non-contact magnetic actuating transportation performance possess high potential in smart flexible electronic devices. Full article

The authors explore the development of paper-based electronics using carbon-based composites with a biodegradable matrix based on ethyl cellulose and dibasic ester solvent. The main focus is on screen-printing techniques for creating flexible, eco-friendly electronic devices. This research evaluates the printability with the rheological measurements, electrical properties, flexibility, and adhesion of these composites, considering various compositions, including graphene, graphite, and carbon black. The study finds that certain compositions offer sheet resistance below 1 kΩ/sq and good adhesion to paper substrates with just one layer of screen printing, demonstrating the potential for commercial applications, such as single-use electronics, flexible heaters, etc. The study also shows the impact of cyclic bending on the electrical parameters of the prepared layers. This research emphasizes the importance of the biodegradability of the matrix, contributing to the field of sustainable electronics. Overall, this study provides insights into developing environmentally friendly, flexible electronic components, highlighting the role of biodegradable materials in this evolving industry. Full article

The roll-to-roll (R2R) continuous patterning of silver nanowire-polyvinylpyrrolidone (Ag NW-PVP) composite transparent conductive film (cTCF) is demonstrated in this work by means of slot-die coating followed by selective calendering. The Ag NWs were synthesized by the polyol method, and adequately washed to leave an appropriate amount of PVP to act as a capping agent and dispersant. The as-coated Ag NW-PVP composite film had low electronic conductivity due to the lack of percolation path, which was greatly improved by the calendering process. Moreover, the dispersion of Ag NWs was analyzed with addition of PVP in terms of density and molecular weight. The excellent dispersion led to uniform distribution of Ag NWs in a cTCF. The continuous patterning was conducted using an embossed pattern roll to perform selective calendering. To evaluate the capability of the calendering process, various line widths and spacing patterns were investigated. The minimum pattern dimensions achievable were determined to be a line width of 0.1 mm and a line spacing of 1 mm. Finally, continuous patterning using selective calendering was applied to the fabrication of a flexible heater and a resistive touch sensing panel as flexible electronic devices to demonstrate its versatility. Full article

Nature’s systems have evolved over a long period to operate efficiently, and this provides hints for metal nanoparticle synthesis, including the enhancement, efficient generation, and transport of electrons toward metal ions for nanoparticle synthesis. The organic material-based ink composed of the natural materials used in this study requires low laser power for sintering compared to conventional nanoparticle ink sintering. This suggests applicability in various and sophisticated pattern fabrication applications without incurring substrate damage. An efficient electron transfer mechanism between amino acids (e.g., tryptophan) enables silver patterning on flexible polymer substrates (e.g., PET) by laser-direct writing. The reduction of silver ions to nanoparticles was induced and sintered by simultaneous photo/thermalchemical reactions on substrates. Furthermore, it was possible to fabricate a stable, transparent, and flexible heater that operates under mechanical deformation. Full article

Laser-induced graphene (LIG) films and their derivatives have been regarded as one of the most outstanding functional flexible electrodes in the past decade, which will transform society and enable new devices and developments. The aim of this Special Issue is to provide a scientific platform for scholars in the LIG field to present their recent research towards a deeper understanding of forming mechanism, structure/ morphology, properties and behaviors of LIG films. This Special Issue gives readers the possibility to gain new insights into the applications of LIG films in flexible electronics, including mechanical/temperature/gas/electrochemical sensors, micro-supercapacitors, actuators, electrocatalysis, solid-state triboelectric nanogenerators, Joule heater, etc. We believe that the papers published in this Special Issue will provide a useful guidance for the manufacturing of nanostructured LIG electrodes in flexible electronics. Full article

In a flexible electronic heater (FEH), periodic metal wires are often encapsulated into the soft elastic substrate as heat sources. It is of great significance to develop analytic models on transient heat conduction of such an FEH in order to provide a rapid analysis and preliminary designs based on a rapid parameter analysis. In this study, an analytic model of transient heat conduction for bi-layered FEHs is proposed, which is solved by a novel symplectic superposition method (SSM). In the Laplace transform domain, the Hamiltonian system-based governing equation for transient heat conduction is introduced, and the mathematical techniques incorporating the separation of variables and symplectic eigen expansion are manipulated to yield the temperature solutions of two subproblems, which is followed by superposition for the temperature solution of the general problem. The Laplace inversion gives the eventual temperature solution in the time domain. Comprehensive time-dependent temperatures by the SSM are presented in tables and figures for benchmark use, which agree well with their counterparts by the finite element method. A parameter analysis on the influence of the thermal conductivity ratio is also studied. The exceptional merit of the SSM is on a direct rigorous derivation without any assumption/predetermination of solution forms, and thus, the method may be extended to more heat conduction problems of FEHs with more complex structures. Full article

EHD printing is an advanced deposition technology that is commonly utilized for the direct manufacture of electrical devices. In this study, meander-type resistive electrodes consisting of silver nanoparticles were printed directly on rigid glass and flexible polyethylene terephthalate (PET) substrates. High-resolution patterns of ≈50 µm linewidth were successfully printed on untreated surfaces utilizing a bigger nozzle of 100 µm inner diameter after improving the experimental settings. The manufactured electrodes were evaluated and used as Resistance Temperature Detectors (RTDs) and micro-heaters in a systematic manner. The temperature sensors performed well, with a Temperature Coefficient of Resistivity (TCRs) of 11.5 $\times {10}^{-3}/°\mathrm{C}$ and 13.3 $\times {10}^{-3}/°\mathrm{C}$, for glass and PET substrates, respectively, throughout a wide temperature range of 100 °C and 90 °C. Furthermore, the RTDs had a quick response and recovery time, as well as minimal hysteresis. The electrodes’ measured sensitivities as micro-heaters were 3.3 °C/V for glass and 6.8 °C/V for PET substrates, respectively. The RTDs were utilized for signal conditioning in a Wheatstone bridge circuit with a self-heating temperature of less than 1 °C as a practical demonstration. The micro-heaters have a lot of potential in the field of soft wearable electronics for biomedical applications, while the extremely sensitive RTDs have a lot of potential in industrial situations for temperature monitoring. Full article

Epidermal electronic systems (EESs) are a representative achievement for utilizing the full advantages of ultra-thin, stretchable and conformal attachment of flexible electronics, and are extremely suitable for integration with human physiological systems, especially in medical hyperthermia. The stretchable heater with stable electrical characteristics and a uniform temperature field is an irreplaceable core component. The inorganic stretchable heater has the advantage of maintaining stable electrical characteristics under tensile deformation. However, the space between the patterned electrodes that provides tensile properties causes uneven distribution of the temperature field. Aiming at improving the temperature distribution uniformity of stretchable thermotherapy electrodes, an orthotropic heat transfer substrate for stretchable heaters is proposed in this paper. An analytical model for transient heat conduction of stretchable rectangular heaters based on orthotropic transfer characteristics is established, which is validated by finite element analysis (FEA). The homogenization effect of orthotropic heat transfer characteristics on temperature distribution and its evolutionary relationship with time are investigated based on this model. This study will provide beneficial help for the temperature distribution homogenization design of stretchable heaters and the exploration of its transient heat transfer mechanism. Full article

With the development of flexible electronics, flexible microheaters have been applied in many areas. Low power consumption and fast response microheaters have attracted much attention. In this work, systematic thermal and mechanical analyses were conducted for a kind of flexible microheater with two different wire structures. The microheater consisted of polyethylene terephthalate (PET) substrate and copper electric wire with graphene thin film as the middle layer. The steady-state average temperature and heating efficiency for the two structures were compared and it was shown that the S-shaped wire structure was better for voltage-controlled microheater other than circular-shaped structure. In addition, the maximum thermal stress for both structures was from the boundary of microheaters, which indicated that not only the wire structure but also the shape of micro heaters should be considered to reduce the damage caused by thermal stress. The influence resulting from the thickness of graphene thin film also has been discussed. In all, the heating efficiency for flexible microheaters can be up to 135 °C/W. With the proposed PID voltage control system, the response time for the designed microheater was less than 10 s. Moreover, a feasible fabrication process flow for these proposed structures combing thermal analysis results in this work can provide some clues for flexible microheaters design and fabrication in other application areas. Full article

Thin-film microdevices can be applied to various wearable devices due to their high flexibility compared to conventional bulk-type electronic devices. Among the various microdevice types, many IoT-based sensor devices have been developed recently. In the case of such sensor elements, it is important to control the surrounding environment to optimize the sensing characteristics. Among these environmental factors, temperature often has a great influence. There are cases where temperature significantly affects the sensor characteristics, as is the case for gas sensors. For this purpose, the development of thin-film-type micro-heaters is important. For this study, a wirelessly driven thin-film micro-heater was fabricated on the flexible and stretchable elastomer, a polydimethylsiloxane (PDMS); the antenna was optimized; and the heater was driven at the temperature up to 102 degrees Celsius. The effect of its use on gas-sensing characteristics was compared through the application of the proposed micro-heater to a gas sensor. The heated SnO₂ nanowire gas sensor improved the performance of detecting carbon monoxide (CO) by more than 20%, and the recovery time was reduced to less than half. It is expected that thin-film-type micro-heaters that can be operated wirelessly are suitable for application in various wearable devices, including those for smart sensors and health monitoring. Full article

Stretchable electronic devices must conform to curved surfaces and display highly reproducible and predictable performance over a range of mechanical deformations. Mechanical resilience in stretchable devices arises from the inherent robustness and stretchability of each component, as well as from good adhesive contact between functional and structural components. In this work, we combine bench-top thin film structuring with solvent assisted lift-off transfer to produce flexible and stretchable multi-material thin film devices. Patterned wrinkled thin films made of gold (Au), silicon dioxide (SiO₂), or indium tin oxide (ITO) were produced through thermal shrinking of pre-stressed polystyrene (PS) substrates. The wrinkled films were then transferred from the PS to poly(dimethylsiloxane) (PDMS) substrates through covalent bonding and solvent-assisted dissolution of the PS. Using this approach, different materials and hybrid structures could be lifted off simultaneously from the PS, simplifying the fabrication of multi-material stretchable thin film devices. As proof-of-concept, we used this structuring and transfer method to fabricate flexible and stretchable thin film heaters. Their characterization at a variety of applied voltages and under cyclic tensile strain showed highly reproducible heating performance. We anticipate this fabrication method can aid in the development of flexible and stretchable electronic devices. Full article

Thermal sensors are mainly based on the selective heating of specific areas, which in most cases is a critical feature for both the operation and the performance of the thermal device. In this work, we evaluate the thermoelectrical response of two graphitic materials, namely (a) a commercial 2.4%wt graphene–ethyl cellulose dispersion in cycloxehanone and terpineol (G) and (b) a custom functionalized reduced graphene oxide (f-rGO) ink in the range of −40 to 100 °C. Both inks were printed on a flexible polyimide substrate and the Thermal Coefficients of Resistance (TCR) were extracted as TCR_G = −1.05 × 10⁻³ °C⁻¹ (R² = 0.9938) and TCR_f-rGO = −3.86 × 10⁻³ °C⁻¹ (R² = 0.9967). Afterward, the inkjet-printed devices were evaluated as microheaters, in order to exploit their advantage for cost-effective production with minimal material waste. f-rGO and G printed heaters reached a maximum temperature of 97.5 °C at 242 mW and 89.9 °C at 314 mW, respectively, applied by a constant current source and monitored by an infrared camera. Repeatability experiments were conducted, highlighting the high robustness in long-term use. The power–temperature behavior was extracted by self-heating experiments to demonstrate the ability of the devices to serve as heaters. Both static and dynamic evaluation were performed in order to study the device behaviors and extract the corresponding parameters. After all the experimental processes, the resistance of the samples was again evaluated and found to differ less than 13% from the initial value. In this work, fabrication via inkjet printing and demonstration of efficient and stable microheaters utilizing a custom ink (f-rGO) and a commercial graphene ink are presented. This approach is suitable for fabricating selectively heated geometries on non-planar substrate with high repeatability and endurance in heat cycles. Full article