Search

Thermally stimulated discharge (TSD) technique is a traditional method in dielectric research, especially for electrets. However, in conventional open-circuit and short-circuit TSD techniques, it is difficult to distinguish the surface charge and body charge of dielectric materials. In particular with the test of polymer electrets, the deformation of the polymer film may take place during the measurement process, which will affect the accuracy of the experiment results. In this paper, a glass-assisting TSD (GA-TSD) technique is proposed to solve the above problems. The feasibility of the experimental technique is verified with the GA-TSD spectra of fluorinated ethylene-propylene copolymer electret films. In addition, their theory analysis is also accomplished. The influences of glass thickness, glass dielectric property, and metallizing on the glass on GA-TSD spectra are investigated. The results prove that the GA-TSD spectra can clearly distinguish the difference between surface charge and body charge according to the current direction. The quartz glass with the lowest dielectric constant is best suitable for the GA-TSD technique. The influence of the glass thickness and metallizing on the glass on GA-TSD spectra is little. [ABSTRACT FROM AUTHOR]

Abstract A novel flexible electret membrane, exhibiting persistent electrostatic effect, distinctive temperature stability and outstanding capability of resistance to harsh environment and fatigue, is demonstrated by experiment. Its excellent electret performance is correlated to the synergy of three factors, which are space charge injection, dipole orientation and interfacial polarization according to the analysis of charge storage mechanism. This electret membrane is provided with sandwich configuration PTFE/THV/PTFE, prepared by hot pressing method and thermal charging technology. After wiped its surface with alcohol, its surface potential declines to zero from −550 V, then recovers rapidly to −310 V and finally maintains constant for 800 hours, which shows that its electret performance distinctly precedes traditional electret material such as single PTFE, FEP electret membrane. The measurement of thermal stimulating potentials displays that its surface potential reaches maximum about 5 times initial value at 125 °C. A micro-vibration energy harvester is assembled with this membrane. Its maximum output power reaches 4.66 μW at tapping frequency 5 Hz and keeps stable during over 2000 tapping tests within 100 days, which indicates the long-life service and resistance to harsh environment and fatigue of this electret membrane.

Electrets is a dielectric material that can store electric charge for a long time. Charge in an electrets with the same polarity as the polarizing electric field are called homocharge, while charges with the opposite polarity are called heterocharge. Two copolymers of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride with different component ratios (THV500 and THV815) were used as the research object. The formation and conversion of homocharge and heterocharge in electrets obtained under different thermal polarization conditions are studied. The results show that the polarization electric field is 9.3 MV/m at 32 °C, the two copolymers form heterocharge. When the polarization electric field is 27.3 MV/m, the homocharge is formed. When the polarization electric field is 9.3 MV/m and the polarization temperature rises to near the melting point of polymer, homocharge is in THV500, the heterocharge in THV815. After plated electrode, both form the homocharge. When stored for a little time, the electrets show the homocharge. [ABSTRACT FROM AUTHOR]

Vibrotactile actuators can evoke mechanical stimulations on human skins to induce haptic feedbacks for various human machine interaction applications. However, efforts toward their practical usages encounter several engineering challenges, including wearable comfortability and output abilities. Here, air permeable actuators are developed and embedded in common fabrics for vibrotactile actuation, achieving excellent air permeability of 108 L m−2 s−1, low preload requirement of 10 mN, high output sensitivity of 0.2 mN/V, and good mechanical durability by surviving 11 million testing cycles. As demonstration examples, a wireless haptic feedback glove is shown to distinguish 32 different English characters and symbols with an overall accuracy of 97.8%, and large size actuators (10 × 10 cm2) are also proved for providing haptic feedback for parts of human body. As such, the proposed system opens a new class of wearable vibrotactile actuators for potential applications in wide fields of metaverse, teleoperation, smart textiles, and robotics. [ABSTRACT FROM AUTHOR]

Polylactic acid (PLA) is a biodegradable and biocompatible polymer. Melt‐blown PLA electret fabrics have become attractive materials for air filter applications. Its filtration performance mainly depends on the electrostatic effect originating from electrets. How to improve their electret behavior and then to enhance their filtration efficiency has always been challenging. In this article, three melt‐blown PLA fabrics with different morphological or crystal structure are made from different process conditions or ingredient. The electrets are formed by means of corona charging technology. Their crystalline and morphological structure was analyzed, and filtration performance was measured. Their charge‐trapping feature was studied by thermal stimulating discharge technology. The results proved that the air filtration efficiency of three melt‐blown samples improved a lot when electrets were formed. Different crystalline structures of PLA fabrics will result in differences in their electret charge‐trapping feature. The PLA fabrics with semi‐crystalline characteristics display a regular charge‐trapped level distribution and amorphous structure hints the diversity of charge‐trapped levels. The deference in filtration resistance is mainly ascribed to the different fiber diameters and their distributions. More narrow distribution of fiber diameter leads to more compact fabrics and to higher filtration resistance. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48309. [ABSTRACT FROM AUTHOR]