When a piezoelectric transformer (PT) is actuated by a low input voltage (∼10 V), electromechanical coupling leads to a very high (∼10 3 V) surface potential at the distal end that can ionize the surrounding gas and lead to a plasma jet emanating from the surface. PTs are attractive for non-equilibrium plasma generation because of their simple operation, low required input voltage, and low power consumption. In this work, the time-resolved characteristics of the free surface plasma jet generated by a PT operating in open air have been investigated. The temporal evolution of the PT-driven plasma was visualized by using an intensified CCD camera and plasma formation was correlated with the current behavior of the plasma jet. Notably, the plasma formation is a discrete process, appearing at a relatively fixed phase of the sinusoidal input, and the strongest plasma jet appears at the end of the positive half-cycle. Simultaneous measurements of the current show that the discharge current response is consistent with the chaotic mode for a plasma jet and appears statistically about a 1 μs earlier than plasma jet light emission, which indicates that there is a strong afterglow. With a low input voltage required for operation, these types of PT-driven plasma jets could have wide utility in emerging plasma applications beyond the laboratory, such as in healthcare and water treatment.
When a piezoelectric transformer (PT) is actuated at its second harmonic frequency by a low input voltage, the generated electric field at the distal end can be sufficient to breakdown the surrounding gas, making them attractive power sources for non-equilibrium plasma generation. Understanding the potential and electric fields produced in the surrounding medium by the PT is important for effectively designing and using PT plasma devices. In this work, the spatiotemporally resolved characteristics of the electric field generated by a PT operating in open air have been investigated using the femtosecond electric field-induced second harmonic generation (E-FISH) method. Electric field components were determined by simultaneously conducting E-FISH measurements with the incident laser polarized in two orthogonal directions relative to the PT crystal. Results of this work demonstrate the spatial distribution of electric field around the PT’s output distal end and how it evolves as a function of time. Notably, the strongest electric field appears on the face of the PT’s distal surface, near the top and bottom edges and decreases by approximately 70% over 3 mm. The time delay between the PT’s input voltage and measured electric field indicates that there is an about 0.45 phase difference between the PT’s input voltage and output signal.
Moisture susceptibility is one of the key issues of warm mix asphalt (WMA). In this research, the moisture susceptibility of asphalt mixtures and binders containing Sasobit warm mix additive was investigated in comparison to that of hot mixture asphalt (HMA) through laboratory aging experiments. The WMA asphalt mixtures were aged in the laboratory at three aging temperatures and times. The moisture susceptibility of the asphalt mixtures was measured through the laboratory immersed Marshall test and freeze-thaw splitting test. The surface free energy (SFE) of asphalt binders extracted from WMA asphalt mixtures was determined by the sessile drop method. The results show that the aging time and temperature have a significant effect on the improvement in moisture susceptibility in terms of both the freeze-thaw splitting strength ratios and the residual Marshall stability of asphalt mixtures containing Sasobit warm mix additive. The SFE of asphalt binders extracted from Sasobit warm mix increased with the aging time and temperature. The moisture susceptibility of the asphalt mixtures and binders containing Sasobit warm mixes was similar to or even greater than that of HMA aging under certain conditions.
A transient spark discharge is an atmospheric pressure plasma that has applications in pollutant removal, medicine, water treatment, agriculture, bactericides, and nanomaterial synthesis. Conventional methods of generating transient sparks at atmospheric pressure usually require a high voltage input at nanosecond pulses. Piezoelectric crystals offer a path to creating plasma devices that do not require a high voltage power supply to generate high voltage outputs; they directly transform mechanical energy into electrical energy. This work examines a manually-operated piezoelectric mechanical-to-electrical energy conversion plasma device. Electrical characterization of the plasma discharge generated by this device shows that it behaves as a transient spark, discharging 0.96 mJ over approximately 30 ns, with consistent behavior across multiple consecutive discharges. Although this specific device had a low mechanical-to-plasma energy conversion efficiency of 1.54%, the piezoelectric crystal resets to an equilibrium condition after approximately 8 μs, which suggests that it could be operated with a mechanical input of up to nearly 125 kHz. This work shows the potential of generating plasma in off-the-grid situations using piezoelectric crystals. One particular application of a piezoelectric plasma device is for in situ pollution mitigation or plasma-enhanced combustion, embedding such a device on the high-frequency oscillating or rotating components of internal combustion engines and turbomachinery.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.