Search Results (576)

To address the challenges of traditional flexible humidity sensors, such as reliance on external power supply, complex fabrication processes, and poor adaptability to energy-limited scenarios, this study successfully developed a low-cost, easily scalable, self-powered flexible humidity sensor based on hydroxypropyl trimethyl ammonium chitosan/lithium chloride (HACC/LiCl) composite electrolyte using a screen-printing process. The device employs A4 paper as the flexible substrate, and interdigitated manganese dioxide (MnO₂) positive electrodes, zinc (Zn) negative electrodes, and HACC/LiCl composite electrolyte layers are sequentially fabricated via screen-printing, ultimately constructing a simple primary battery structure. Through a series of performance screening and optimization, 0.1 mol/L LiCl-modified HACC (HL-1) is identified as the optimal electrolyte system. The test results show that the HL-1 sensor exhibits a wide humidity detection range of 11~97% relative humidity (RH), with the output voltage displaying a good quadratic function relationship with humidity (R² = 0.996), and a peak output voltage of up to 1.2 V. The device possesses excellent cyclic stability and long-term stability, with no significant fluctuation in output voltage under different bending deformation states. This sensor demonstrates broad application prospects in fields such as respiratory monitoring and non-contact sensing, providing a feasible technical path for the development of low-cost passive humidity monitoring equipment. Full article

Printed electronics offer a scalable and sustainable route for integrating sensing systems into everyday environments; however, the use of flexography remains highly limited, and fully printed sensors fabricated exclusively with industrial flexographic technology have not been previously reported. This study evaluates the feasibility and practical limits of fabricating resistive humidity sensors for relative humidity (RH) measurements using flexography only, relying on commercial infrastructure, packaging-grade substrates, and low-temperature processing. Silver interdigitated electrodes and a carbon-based sensing layer were printed using solvent-based electronic inks, industrial aniloxes (12 and 20 cm³/m²), and standard flexographic conditions (10 m/min, ≤120 °C drying), without any post-processing. The sensing layer was optionally modified with adsorptive additives (≤5 wt% MgO; additionally, Al₂O₃ and Al) to enhance moisture interaction while maintaining rheological compatibility. Sensors were fabricated on recyclable paper substrates and PET for comparison. Under controlled conditions (10%–90% RH at 23 °C), devices exhibited a maximum relative resistance change of ~75% at 90% RH (referenced to 40% RH), low hysteresis (≤~5%), rapid visible response (<1 min), and stabilization within ~30 min. MgO increased relative response by 20%–233%, depending on humidity. Paper-based sensors showed higher responses but single-use behavior under flooding, while PET enabled repeatable cycling. Rather than targeting state-of-the-art performance, this work defines the functionality reliably achievable using flexography only, clarifying trade-offs among substrate choice, layer thickness, and additives for sustainable, humidity and disposable flood monitoring. Full article

A novel capacitive interdigital electrode (IDE) sensor for the in-situ measurement of soil moisture is presented. Two planar electrode configurations, spiral and embracing, were designed and evaluated through modeling, simulation, fabrication, and experimental validation. Compared with conventional circular and square electrodes, the proposed structures exhibited higher sensitivity and greater electric field penetration, with the spiral configuration offering the advantage of easier fabrication. The experimental results demonstrated that the calibrated spiral IDE sensor achieved a coefficient of determination (R²) of 0.9976 and a mean squared error (MSE) of 0.859, indicating good stability and repeatability over the tested period. Furthermore, comparison with a commercial moisture sensor showed that the proposed sensor reached a higher R² value of 0.9995, exhibiting closer agreement with gravimetric measurements. These findings confirm that the developed sensor holds strong potential for in situ monitoring of soil moisture and can provide valuable technical support for landslide monitoring and prevention. Full article

This study presents a wide-linear-range flexible pressure sensor based on a gradient non-uniform porous structure. Through co-optimization of material composition and structural parameters, the sensor integrates high sensitivity, a broad linear response range, and excellent stability. The sensing layer is fabricated using a PVC/CNT composite slurry, with interdigital silver electrodes screen-printed on a PET substrate. A porous architecture is constructed via solution blending and a template method. Innovatively, orthogonal experiments were employed to optimize the conductive filler concentration and porosity. A mixed sugar template comprising particles of 50–75 μm and 125–150 μm was introduced to form a gradient non-uniform porous structure, effectively expanding the linear response range. Experimental results demonstrate that the sensor exhibits outstanding linearity (R² > 0.99) and high sensitivity (5.57 kPa⁻¹) over a broad pressure range of 0–120 kPa. It also shows a dynamic response speed of 50 ms, cyclic stability exceeding 500 cycles, and signal fluctuation of less than 5%. Scanning electron microscopy (SEM) analysis reveals the synergistic mechanism of the non-uniform pores, confirming the effectiveness of this design in reconciling the trade-off between sensitivity and linear range. This study offers new insights into the performance optimization of flexible pressure sensors and demonstrates significant potential for applications in health monitoring and electronic skin (E-skin). Full article

In radiofrequency filters, there is an increasing demand for high-frequency, wide-bandwidth operation. Recently, laterally excited A₁-mode Lamb wave resonators (XBARs) have attracted significant attention; however, freestanding structures are mechanically fragile, limiting their practical implementation. To address this challenge, a novel bonded membrane structure consisting of a lithium niobate (LiNbO₃; LN) thin plate supported by a silicon carbide (SiC) layer is proposed to realize high-frequency, high-performance, and thermally robust acoustic resonators. Finite element simulations were performed to analyze the excitation and propagation of A₁-mode Lamb waves in the LN/SiC membrane, clarifying the distinct behavior compared with XBARs. The influence of the bonded SiC thin layer on A₁-mode Lamb waves was systematically evaluated in terms of coupling coefficient and phase velocity, and design guidelines were established based on these insights. A fabricated LN/SiC resonator with an interdigital electrode pitch of 12 µm exhibited a clear A₁-mode response near 1.2 GHz, showing an effective electromechanical coupling coefficient of 24% and a phase velocity exceeding 14,000 m/s. These results demonstrate the feasibility of the bonded LN/SiC membrane as a promising platform for high electromechanical coupling, high-speed, and thermally stable acoustic devices. Full article

The characterization of cancer and other diseases can be aided by the development of reusable electrochemical sensors that provide broad biomarker expression information in real time. We describe an interdigitated electrode (IDE) sensor array that can be used for rapid detection of multiple biomarkers, including human midkine (MDK), HIV gp41 peptide, mAb 7B2, and single-stranded DNA (ssDNA), using electrochemical impedance spectroscopy (EIS) with coated nanoparticles (NPs). These targets represent potential biomarkers for identifying malignant cancer, HIV infection, and DNA mutation. Targets were detected by coating NPs with an antibody, a protein, and ssDNA to capture them from solution. Interacting proteins attached to the nanoparticles were then analyzed with EIS to identify interaction on the surface. In many biological contexts, more than one partner can interact with selected targets, so the determination of the identity of the interacting component is critical for interpretation. In a controlled system, we verify impedance data clusters based on the identity of the protein coated on the surface of the NPs. Data clusters corresponding to protein identity were clearly bifurcated using the impedance spectrum and unsupervised principal component analysis (PCA). NPs clustered based on surface modification, suggesting individual proteins have unique EIS spectral characteristics that can be used for identification. Full article

We present a flexible pH sensor which leverages the unique properties of reduced graphene oxide/polyaniline (rGO/PANI) composite films through an efficient and scalable hybrid microfabrication approach, wherein the rGO/PANI films are conformally coated on flexible polyethylene terephthalate (PET) substrates via dip-coating and thereafter lithographically patterned into precise arrays of interdigitated electrodes (IDEs), serving both as the pH-active medium and the electrical interface. Upon dip-coating, a thermal reduction process is performed to yield uniform rGO/PANI composite layers on PET substrates, where the PANI content is adjusted to 20% to optimize conductivity and protonation-driven response. Composition optimization is first performed using inkjet-printed silver (Ag) contacts and a conductometric readout mechanism is employed to explore pH-dependent behavior. Subsequently, IDE arrays are defined in the rGO/PANI using photolithography and oxygen-plasma etching, demonstrating clean pattern transfer and dimensional control on flexible substrates. Eliminating separate contact metals in the final design simplifies the stack and reduces cost. A set of IDE geometries is evaluated through I–V measurements in buffers of different pH values, revealing a consistent, monotonic change in electrical characteristics with pH and geometry-tunable response. The present study demonstrated that the most precise pH measurement was achieved with an 80:20 rGO/PANI composition within the pH 2–10 range. These results establish rGO/PANI IDEs as a scalable route to low-cost, miniaturized, and mechanically compliant pH sensors for field and in-line monitoring applications. Full article

Nowadays, the development of efficient water treatment processes is increasingly driven by the need to provide solutions for contaminants of emerging concern. Electrochemical advanced oxidation processes (EAOPs) based on diamond electrodes can be part of innovative removal concepts. However, expensive substrates, energy-intensive chemical vapor deposition (CVD) of diamond, and market availability complicate matters for diamond electrodes to gain traction in the water treatment sector. In addition, it has to be stated that the mining and complex processing of necessary substrates like Si, Ti, Nb, or Ta need a significant amount of fresh water, which counteracts the need for more sustainability in the field of EAOPs. In this context, a ceramic-based boron-doped diamond (BDD) electrode is presented, which addresses this dilemma. The presented concept of the so-called interdigitated double diamond electrode (iDDE) consumes 14–46% less energy in batch-mode experiments to degrade an organic model molecule compared to standard BDD technology in a poorly conductive electrolyte (κ < 350 µS/cm). Laser-induced micro-structuring of the BDD layer reduces the interelectrode spacing (IES) of the iDDE to below 50 µm. The structuring approach at the micrometer scale enables the treatment of electrically low-conductivity electrolytes more energy efficiently, while reducing the need for a supporting electrolyte or a proton exchange membrane. Degradation experiments and Raman measurements reveal different properties of an iDDE compared to standard BDD technology. The iDDE concept highlights the need to understand the significance of non-uniform current density distributions on the general electrochemical activity of BDD electrodes. Full article

The progressive aging of the population requires reliable, non-invasive, and real-time tools to monitor hydration, prevent dehydration-related complications, and promote active aging in elderly patients. Wearable sensors based on interdigitated electrodes (IDEs) and on Electrochemical Impedance Spectroscopy (EIS) represent a promising tool thanks to their miniaturization, sensitivity to dielectric variations with humidity, and compatibility with flexible substrates. This study reports the design, fabrication, and metrological characterization of inkjet-printed IDEs for skin hydration monitoring, as a building block of a multisensor wearable device. IDEs were fabricated on polyimide substrates using silver nanoparticle-based ink. Their characterization involved the following: (i) morphological evaluation by scanning electron microscopy; (ii) EIS measurements in KCl solutions, leading to developing a regression model to correlate impedance with salt concentration; (iii) in vitro EIS validation on agar gel samples, which demonstrated a robust linear relationship between the impedance phase shift at 199.5 $\mathrm{Hz}$ and water loss, with consistent sensitivity values across sensors. The results confirm the feasibility of IDEs for hydration monitoring, identifying optimal frequency ranges and validating regression models. These findings represent a critical step toward the development of multisensor wearable devices for elderly monitoring, enabling decentralized and continuous health monitoring to improve healthcare sustainability and telemedicine. Full article

This research demonstrates, for the first time, the integration of aero-titania material in sensor devices. An innovative approach for the practical application of aero-titania (aero-TiO₂) materials in photodetectors and the characterization under ultraviolet irradiation was assessed. The fabrication of aero-materials was carried out through the atomic layer deposition (ALD) of titanium dioxide ultrathin layers on a sacrificial network consisting of zinc oxide micro-tetrapods. This process was followed by a selective etching of the sacrificial ZnO template and formation of aero-titania hollow micro-tetrapods. The obtained material has been characterized using UV-Vis spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) analysis. The development of photodetectors was achieved through the sequential spin-coating deposition of aero-TiO₂ onto an interdigitated ceramic electrode. The obtained results show that, for high-intensity ultraviolet, the maximum sensitivity was reached for the two-deposited-layer aero-TiO₂ sensor at about 23, since for the low-intensity UV the highest sensitivity was recorded for the one-deposited-layer aero-TiO₂ sensor at about 12. In terms of the responsivity, the highest response was obtained for the one-deposited-layer aero-TiO₂ sensor under low-intensity illumination, reaching about 1.23 × 10⁻⁴ A W⁻¹ cm⁻². Thus, the aero-TiO₂ structure demonstrates the practical viability and application potential of this emerging class of materials in advanced sensing technologies. Full article

This paper investigates the capacitance characteristics of a glass-embedded interdigitated capacitive sensor (IDCS) for touch-sensing applications. The study analyzes both baseline (no-touch) and touch-induced capacitance variations through a combination of analytical modeling and experimental validation. A multilayer analytical model is first employed to calculate the baseline capacitance of the proposed structure, followed by experimental measurements for model verification. Subsequently, an equivalent circuit model of the touched state is introduced to represent the interaction between the human fingertip, sensor electrodes, and earth-ground, explaining the observed capacitance reduction during a finger touch. Sensor prototypes with electrode finger widths of 1.4, 2.0, 2.4, and 3.0 mm were fabricated within a 40 × 40 mm² sensing area. The baseline capacitance decreased from 28.6 pF at 1.4 mm to 12 pF at 3.0 mm electrode finger width, while the capacitance change upon touch ranged from 0.6–0.9 pF. Touch sensitivity for three test persons increased from about 1.7–4.6% at 1.4 mm to 5–7.6% at 3.0 mm electrode finger width. The results confirm that narrower-electrode designs yield higher absolute capacitance, whereas wider electrodes enhance touch sensitivity and provide greater uniformity within the defined sensing area. Overall, the findings validate the proposed IDCS configuration as a practical approach for realizing glass-integrated touch sensors and offer practical guidelines for optimizing electrode geometry in touch-based smart-glass applications. Full article

In recent years, the development of stretchable electronic devices with mechanical properties similar to those of human tissues has attracted increasing research interest in biomedical engineering, wearables, and other fields. These devices have demonstrated, and some other researchers have already shown, promising advancements towards applications that span from measurements of the disruption of model barrier tissues to wearable or implantable devices, soft robotics, and the development of flexible and stretchable batteries. For example, models of barrier tissues, consisting of two compartments separated by a porous membrane, have been used to measure their integrity as well as to investigate the passage of drugs, toxins, and cancer cells through these tissues. Some of these models include an elastomeric membrane which can be stretched to model processes such as breathing and gut peristalsis, while others include electrodes for real-time measurement of barrier tissue integrity. However, to date, microelectrodes have not been fabricated directly on a porous elastomeric membrane. Here, we present lithographically patterned gold electrodes on porous PDMS membranes that enable electronic sensing capabilities in addition to mechanical manipulation. These membranes are incorporated into vacuum-actuated devices which impart cyclic mechanical strain, and their suitability for electrical impedance measurements, even after 1000 stretching cycles under fluids similar to cell culture media, is demonstrated. In the future, we expect to use these electrodes to measure the disruption in model cell barriers as well as to dielectrophoretically trap cells in a region of interest for more rapid assembly of a model tissue. Other areas like wearables, robotics, and power sources will greatly benefit from the further development of this technology. Full article

Current photoconductive antennas (PCAs) fail to maximize the use of photogenerated carriers at the electrode edges. To address this limitation, we designed a novel PCA structure featuring a ring electrode and a disc electrode. The positive and negative electrodes are positioned on opposite sides of the substrate, and eight metal tips are incorporated into the ring electrode to enhance performance. The PCA-1 photoconductive antenna with both positive and negative electrodes on the same side of the substrate generates a peak current of about 18 μA, whereas under the same simulation parameters, the peak current generated by the PCA-1 and the conventional interdigitated photoconductive antenna are equal, and the PCA-2 photoconductive antenna with positive and negative electrodes on the top and bottom sides of the substrate generates a current nearly 1.45 times higher than that generated by the PCA-1. The PCA-3 photoconductive antenna with positive and negative electrodes on the top and bottom of the substrate and eight additional metal tips on the circular electrodes is nearly twice the peak current generated by the PCA-1, and the terahertz radiated power of the designed PCA-3 is four times that of the PCA-1, which suggests that the designed THz-PCA can improve the optical-terahertz conversion efficiency, and it has a great prospect of popularizing terahertz technology based on the THz-PCA. Full article

Mg-doped gallium oxide films were prepared on single crystal sapphire substrates through radio frequency magnetron sputtering technology, and then AlN films of different thicknesses were deposited on them as passivation layers. Finally, Pt interdigitated electrodes were prepared through mask plate and ion sputtering technology to make metal–insulator–semiconductor–insulator–metal (MISIM) photodetectors. The influence of the AlN passivation layer on the optical properties and photodetection performance of the device was investigated using UV-Vis (ultraviolet-visible absorption spectroscopy) spectrophotometer and a Keith 4200 semiconductor tester. The device’s performance was significantly enhanced. Among them, the MISIM-structured device achieves a responsivity of 2.17 A/W, an external quantum efficiency (EQE) of 1100%, a specific detectivity (D*) of 1.09 × 10¹² Jones, and a photo-to-dark current ratio (PDCR) of 2200. The results show that different thicknesses of AlN passivation layers have an effect on the detection performance of Mg-doped β-Ga₂O₃ films in the UV detection of the solar-blind UV region. The AlN’s thickness has little effect on the bandgap when it is 3 nm and 5 nm, and the bandgap increases at 10 nm. The transmittance of the film increases with the increase in AlN thickness and decreases when the AlN’s thickness increases to 10 nm. The photocurrent exhibits a non-monotonic dependence on AlN thickness at 10 V, and the dark current gradually decreases. The thickness of the AlN passivation layer also has a significant impact on the response characteristics of the detector, and the response characteristics of the device are best when the thickness of the AlN passivation layer is 5 nm. The responsiveness, detection rate, and external quantum efficiency of the device first increase and then decrease with the thickness of the AlN layer, and comprehensive performance is best when the thickness of the AlN passivation layer is 5 nm. The reason is that the AlN layer plays a passivating role on the surface of Ga₂O₃ films, reducing surface defects and inhibiting its capture of photogenerated carriers, while the appropriate thickness of the AlN layer increases the barrier height at the semiconductor interface, forming a built-in electric field and improving the response speed. Finally, the AlN layer inhibits the adsorption and desorption processes between the photogenerated electron–hole pair and O₂, thereby retaining more photogenerated non-equilibrium carriers, which also helps enhance photoelectric detection performance. Full article

The detection and monitoring of ions are essential for a broad range of applications, including industrial process control and biomedical diagnostics. Traditional ion-sensitive field-effect transistors require bulky and expensive reference electrodes, which face several limitations, including device miniaturization, high fabrication costs, and incompatibility with semiconductor manufacturing processes. Here, we introduce a reference-less semiconductor ion sensor (RELESIS) that utilizes anodic aluminum oxide film as both the sensitive and dielectric layer. The RELESIS is composed of a metal-oxide-semiconductor field-effect transistor and an interdigital electrode, which fundamentally eliminates the need for a reference electrode, thereby enabling device miniaturization. During fabrication, the anodic oxidation process is employed in place of the expensive atomic layer deposition method, significantly reducing manufacturing costs while maintaining high surface quality. In practical measurements, the RELESIS device demonstrated an excellent pH sensitivity of 57.8 mV/pH with a low hysteresis of 7 mV. As a proof-of-concept application, the RELESIS device was employed for real-time, non-destructive monitoring of milk freshness, accurately detecting pH changes from fresh to spoiled in milk samples. The combination of reference-less structure, low-cost fabrication, and superior sensing performance positions this technology as a promising platform for next-generation portable ion sensing systems in food safety, environmental monitoring, and point-of-care diagnostics. Full article