ABSTRACT
Airborne sound absorption in porous materials involves complex mechanisms of converting mechanical acoustic energy into heat. In this work, the effective piezoelectric properties of polyethylene ferroelectret foams on sound absorption were investigated by comparable samples with and without the piezoelectric response. Corona poling and thermal annealing treatments were applied to the samples in order to enable and remove the piezoelectric property, respectively, while the microstructure and the mechanical properties remained substantially unchanged. The effective piezoelectric properties and airborne sound absorption coefficients of the polyethylene foam samples before and after material treatments were measured and analyzed. Our experimental results and theoretical analysis showed that the open-cell ferroelectret polymer foam with an effective piezoelectric property provides an additional electromechanical energy conversion mechanism to enhance the airborne acoustic absorption performance.
ABSTRACT
Soft conductive elastomers with low hysteresis over a wide range of stretchability are desirable in various applications. Such applications include soft sensors with a long measurement range, motion recognition, and electronic skin, just to name a few. Even though the measurement capability of the sensors based on soft materials has been greatly improved compared to the traditional ones in recent years, hysteresis in the loading and unloading states has limited the applications of these sensors, thereby negatively affecting their accuracy and reliability. In this work, conductive elastomers with near-zero hysteresis have been formulated and fabricated using 3D printing. These elastomers are made by combining highly stretchable dielectric elastomer formulations with a polar hydrophobic ionic liquid and polymerizing under ultraviolet light. High-performance piezoresistive sensors have been fabricated and characterized, with a 10-fold stretchability and low hysteresis (1.2%) over long-term stability (more than 10â¯000 cycles under cyclic stress) with a 20 ms response time. Additionally, the current elastomers displayed fast mechanical and electrical self-healing properties. Using 3D printing in conjunction with some of our structural innovations, we have fabricated smart gloves to show this material's wide range of applications in soft robots, motion detection, wearable devices, and medical care.
ABSTRACT
Lead-free potassium and sodium niobate (KNN) nanofiber webs with random and aligned configurations were prepared by the electrospinning process from polymer-modified chemical solution. The crystallization process, structure, composition, dielectric, ferroelectric, and piezoelectric properties of the nanofibers and nanofiber webs were investigated. Theoretical analysis and experimental results showed that the surface-induced heterogeneous nucleation resulted in the remarkable lower crystallization temperature for the KNN nanofibers with the {100} orientation of the perovskite phase in contrast to the bulk KNN gel and thus well-controlled chemical stoichiometry. Low dielectric loss, large electric polarization, and high piezoelectric performance were obtained in the nanofiber webs. In particular, the aligned nanofiber web exhibited further improved piezoelectric strain and voltage coefficients and higher FOM than their thin film counterparts and is promising for high-performance electromechanical sensor and transducer applications.
