AIAA-2005-565-450Acoustic Testing of the dielectric barrier(6)

推进器的声波特性

Figure 8: Polar plot of Vmpp comparing acoustic emissions for different actuator sizes at Vfpp of 7 kV and 5 kHzNext the forcing voltage waveform was changed while using the 30x8 cm actuator. A forcing voltage of 7 kV was used at a frequency of 5 kHz. The waveforms used included square, negative ramp, positive sawtooth, triangle, and the sinusoidal waveform. These results showed that the square waveform produced the highest amplitude and the negative sawtooth the lowest amplitude. Previous force measurements16 showed an opposite relationship for the measured forces. The square wave produced the least amount of tangential thrust while the positive sawtooth produced the most. The directional characteristics of the acoustic emissions for all five forcing voltage waveforms were fairly consistent with a frontal lobe and a smaller back lobe similar to the patterns shown above. The next set of measurements used the second experimental apparatus described above (Figure 3). For these measurements the actuator forcing voltage was sinusoidal at 5 kV and an actuator size of 30x8 cm was used. The measured directional characteristics are shown in figure 9. A similar bimodal pattern was observed.Figure 9: Polar plot of Vmpp comparing acoustic emissions for different forcing frequencies at a Vfpp of 5 kV.Since this similar bimodal pattern is seen in the polar plots for both set of measurements it is concluded that the effects of acoustic reflections, if any, are minimal. The results in figure 9 were obtained in a different environment, with a different apparatus, microphone and set-up. In the measurements with this second apparatus the waveform for a single cycle was recorded. The waveform was recorded at two frequencies and at angles of ten degree increments from zero to 180 degrees. Figure 10 shows the effect of the frequency change from 5 to 8 kHz on the measured waveform at an angle near the peak of the frontal lobe (40 degrees). 6 American Institute of Aeronautics and Astronautics