# SDBD Flexible Plasma Actuator with Ag-Ink Electrodes: Experimental Assessment
## 2 Experimental Setup  
Figure 1 shows the experimental setup, including the plasma actuator itself and the diagnostics employed in the present work. The actuator design is illustrated in detail in  
Figure 2: Design of the plasma actuator. (**a**) Top view depicting the high-voltage-driven electrode details. The inset defines the coordinate system that is used hereafter. The system origin coincides with the actuator surface (z = 0), the edge of the discharge gap toward the grounded electrode side (x = 0), and the middle of the grounded electrode length (y = 0). (**b**) Bottom view depicting the grounded electrode details. The stack of Kapton® polyimide films has a total thickness of 0.425 mm, whereas the epoxy resin (No_7c in Figure 1) is not shown for simplicity purposes. Figure 1: Conceptual diagram of the experimental setup. 1: signal generator; 2: audio power amplifier; 3: oscilloscope; 4: current monitor; 5: ferrite core, step up transformer; 6: high-voltage probe; 7: SDBD actuator; 7a: painted electrodes; 7b: flexible dielectric barrier; 7c: epoxy resin; 8: pitot-like tube on x–y–z, linear, micro-translation stage; 9: pitot-like tube hardware and interface; 10: optical fiber; 11: optical matcher; 12: monochromator; 13,14: photo-electron multiplier tube; 15: data acquisition unit; 16: personal computer. The high voltage is generated by amplifying a reference sinusoidal signal (10 kHz) and supplying the primary winding of a specially designed, ferrite core, step-up transformer. The output high voltage, v(t), is permanently monitored with a passive probe (Tektronix; P6015; DC-75 MHz). The DBD current, i(t), is recorded with a wideband current transformer (Pearson Electronics; 6585; 400 Hz-200 MHz). The wavelength- and space-integrated light, emitted from the plasma, is collected with a high-grade fused silica optical fiber (Newport; 77576; 260-2200 nm), and then, it becomes time-resolved with a photo-electron multiplier tube (PMT; Hamamatsu R928; 185-900 nm). All waveforms are recorded by a four-channel, wideband, digital oscilloscope (LeCroy; WaveRunner 44 Xi-A; 400 MHz; 5 GSamples s\({}^{-1}\)). The mean electric power consumed by the actuator is calculated by integrating the product [v(t\({\rm{t}}\) + 5T) \(\times\) i(t\({\rm{t}}\) + 5T)] over five sequential voltage periods, i.e., ST, and by dividing the result by this factor. The process is repeated for five independent [v(t\({\rm{t}}\) + 5T) \(\times\) i(t\({\rm{t}}\) + 5T)] products. Two such measurement sets are realized on different dates. Hence, in total, 10 instantaneous power waveforms (5T duration each) are considered for extracting mean values and standard deviations (error bars in the graphs) of the electric power. The time- and space-integrated light is guided by the abovementioned optical fiber to a monochromator (Jobin Yvon; THR 1000; 170-750 nm; 2400 grooves mm\({}^{-1}\)) and the optical emission spectrum is thus identified. The wavelength calibration of this unit is carried out with an Hg (Ar) pencil-style lamp (Newport; 6035). Special attention is paid to calibrating the relative spectral efficiency of the entire optical system. This is accomplished with a quartz-tungsten-halogen lamp (Newport; 6334 NS; 250 W) operated at 3400 K. The rotational temperature of principal excited molecular species is estimated by fitting their experimental rotational distributions to the corresponding theoretical ones, using a lab-built software [22]. In addition, a 0.25 m imaging spectrograph (Newport; MS260i) is used for exploring wider wavelength ranges. It is equipped with two motorized gratings: one holographic (2400 grooves mm\({}^{-1}\); blaze wavelength 250 nm; 180-700 nm) and one ruled (600 grooves mm\({}^{-1}\); blaze wavelength 400 nm; 250-1300 nm). The photodetector of this spectrograph is a linear CCD array (200-1100 nm). Optical matchers are used in both cases (monochromator and spectrograph) for optimal alignment of the fiber image.