1,721,035 research outputs found
Tactile sensor devices exploiting the tunnelling conduction in piezoresistive composites
Full text linkThe thesis reports on the preparation of three piezoresistive composites using different metal particles as filler in a silicone (PDMS) matrix. The results obtained from the functional characterizations performed under compressive and tensile stresses are well supported by the theoretical models and showed that the conduction mechanism in the metal-polymer composites is based on a quantum tunnelling effect. The phenomenon is further enhanced by the sharp tip morphology of the metal particles used. In particular when using spiky nickel particles, the composites undergo a variation of resistance up to nine orders of magnitude under an applied pressure. The possibility to obtain a huge variation in resistance upon a small deformation of the samples makes these composites a
well performing functional material for sensor applications. Moreover the simplicity of the synthesis process, the low cost of the materials and the mechanical flexibility favor their choice among the possible sensing materials for tactile sensors.
Piezoresistive composites were subsequently implemented in two different sensor architectures. The first measures the resistance variation of a 8x8 array of sensing element and reproduces the pressure distribution on a 3D graphic software. The second exploits both the resistance and capacitance variation of the tunnelling conductive material with an extremely low power quasi-digital frequency converter methods. Thanks to this measuring methods, the sensor was able to resolve 1 gr of applied load
Spiky nanostructured metal particles as filler of polymeric composites showing tunable electrical conductivity
No full textHighly sensitive PDMS-Ag nanoflakes porous pressure sensors prepared by templating and molding approaches for wearable applications
Full text linkThe rise of information technologies has led to the need for collecting vast amounts of multidisciplinary data related to human habits, social interactions, and physical activities. This demand has intensified the challenge of integrating rigid electronics with the flexibility of human tissue. Wearable sensors have emerged as a solution to detect several biometric signals from human body. Among these applications, pressure sensing is particularly crucial. In this work, we present a flexible, sandwich-structured pressure sensor based on a porous PDMS sponge. Two distinct fabrication methods were investigated with a critical analysis of their advantages and limitations. A templating technique using a common sugar cube as a sacrificial mold, and a molding method where a sugar-PDMS slurry was shaped using a predefined mold. While the templating approach offers simplicity and accessibility, the molding method provides greater control over geometry and customization. All fabricated sensors demonstrated excellent piezocapacitive performance under mechanical compression, characterized by minimal hysteresis during cyclic loading—an essential feature for consistent and reliable sensing. To boost sensitivity, silver nanoflakes were incorporated into the polymer matrix, resulting in a 65 % increase in pressure sensitivity, achieving up to 0.047 kPa−1 , one of the highest value reached by PDMS-based foam sensors, and lowering the detection threshold to just 0.6 g (40 Pa). The successful implementation of these sensors in wearable formats underscores their potential as lightweight, scalable, and cost-effective platforms for continuous biometric monitoring in real-world applications
Electronic Applications
No full textIn the last years, additive manufacturing technologies have been widely implemented in the production of electronic components. The possibility of incorporating electronic functionalities in complex-shaped devices together with the multimaterial and multilayered fabrication capability has brought to the realization by 3D printing approaches of passive elements such as resistors, capacitors, and conductive traces, active elements like transistors and LEDs (light-emitting diodes), and also multiple examples of sensors and actuators. Compared to traditional production, 3D printing electronics resulted as one of the most promising technologies for producing parts in a more effective and efficient manner.
Here, we review the state of the art related to the research activity in fabricating electronic passive elements and active elements. We also focus on 3D printed sensors and actuators, discussing both the physical working principles and the application fields of the different components
3D Printed Metallic Pillar Nanomechanical Resonators Decorated with TiO2 Nanotubes for Highly Sensitive Environmental Applications
Full text linkMicro and nanomechanical devices offer enhanced sensing capabilities for detecting biological and chemical small molecules. However, miniaturization necessitates advanced fabrication processes and complex measurement systems, hindering routine sensor analysis. While alternative methods like 3D printing show promise, challenges such as low device resolution persist due to intrinsic damping of polymer inks. In this study, an array of micrometric pillar resonators is fabricated in Ti6Al4 V alloy using additive manufacturing based on laser powder bed fusion technology. These metallic nanomechanical resonators exhibit a very high quality factor with minimal difference between air and vacuum measurements due to low intrinsic damping. Furthermore, titania nanotubes grown on the pillars via anodic oxidation heighten sensitivity for molecular dye degradation evaluation. Leveraging the weak coupling phenomenon among the pillars in the array, these devices facilitate large-scale parallelized measurements, here demonstrated with real-time analysis of dye degradation process. This approach to creating mass sensing devices via metallic additive manufacturing can usher in a new generation of highly performing resonating sensor arrays, offering a cost-effective and efficient alternative to traditional silicon microfabrication methods
Effect of intramodal and intermodal nonlinearities on the flexural resonant frequencies of cantilevered beams
No full textSensing applications that utilize nanomechanical resonators require careful control of nonlinear effects in
their eigenmodes to ensure robust measurement. While the effect of intra- and intermodal nonlinearities on the
resonant frequencies of doubly clamped elastic beams have been widely studied using theory and experiment,
commensurate studies on cantilevered beams are limited in comparison. Here, we present such a detailed study
that includes an explicit and simple formula for the flexural resonant frequencies of slender cantilevered beams
that accounts for intra- and intermodal nonlinearities. Using this general theory, numerical results for the modal
nonlinear coefficients are tabulated for the first 20 flexural eigenmodes of cantilevered beams possessing uniform
cross sections. The accuracy of this theory, and the effect of cantilever aspect ratio (length/width) on these
nonlinear coefficients, is explored using high-accuracy laser Doppler vibrometry experiments. We anticipate that
these results will find utility in single- and multimode applications, where the effect of finite oscillation amplitude
on the cantilever resonant frequencies can significantly impact measurement design and interpretation
Multi-responsive 3D printable organohydrogel for the fabrication of durable and low-hysteresis flexible sensors
Full text linkIonically conductive hydrogels have emerged as promising candidates for sensors in wearables and prosthetics due to their high flexibility and stretchability. However, those suffers intrinsically of a strong limitation which is water evaporation, that over time alters their mechanical and electrical properties, restricting their usage. On the other hand, the use of organohydrogels limits this drawback, controlling rate of evaporation and thus preserving the device properties. This study introduces a double-network, conductive, 3D-printable hydrogel where water is partially replaced by glycerol using a solvent replacement strategy to prevent evaporation and preserve electrical and sensing properties. This organohydrogel exhibits excellent stretchability (up to 350 %), high strain and pressure sensitivity, and negligible hysteresis. Moreover, the mechanical and electrical characteristics of the organohydrogel remain stable for more than six months. The sensor demonstrates an outstanding strain detection limit of 0.05 % and a pressure detection limit of 1.5 Pa, enabling the evaluation of micrometric deformations across a wide temperature range, including below room temperature. The use of glycerol, a high boiling point and biocompatible solvent, allows both temperature and humidity sensing, enhancing the versatility of this organohydrogel. Since the solvent replacement strategy is applied to the already formed hydrogel, its 3D printability remains unaffected, enabling the enhancement of sensing properties through complex 3D structuring. The excellent time stability of mechanical and sensing properties, combined with sensitivity to both micro and macro deformations, temperature and humidity responsiveness, highlights the potential of this organohydrogel in a broad spectrum of flexible sensing applications
Coffee-Ring Effect-Based Three Dimensional Patterning of Micro/Nanoparticle Assembly with a Single Droplet
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