A joint calibration technique for improving measurement accuracy of voltage and current probes during synchronous operation for RF-based plasma devices

Abstract

This paper presents a joint calibration scheme for voltage (V) and current (I) probes that helps accurately resolve the voltage–current phase differences even when the difference is very close to 90°. The latter has been a major issue with V–I probes when used with miniature RF plasma devices such as the atmospheric pressure plasma jet (APPJ). Since the impedance of such miniature devices is predominantly capacitive, the phase difference between the voltage and current signals is very nearly 90°. It turns out, however, that when V–I probes are used with such devices without joint calibration, these frequently yield phase shifts over 90°. Also, since the power absorption is proportional to the resistive part of the impedance, it becomes very sensitive to the phase difference when it is close to [Formula: see text]. Thus, it is important to be able to accurately resolve the phases. Post-calibration, V–I probes would be indispensable for the electrical characterization of APPJs for determining the average RF power P av, plasma impedance Z p, etc. Typical post-calibration V–I data yield Z p [Formula: see text] 93.6 − j 1139 Ω (81.5 − j 1173 Ω) at P av [Formula: see text] ([Formula: see text] for helium (argon) gas.

A 2D steady state analytical model for atmospheric pressure RF plasma jet

“…av Plasma parameters estimated using the developed plasma model are believed to be more reliable and accurate since the model is well formulated and the associated power measurement process has been made more accurate and robust by elimination of the anomalies that plague V-I probes during RF measurements on miniature devices [41]. Finally, one notes that the power sensitivity of the model along with the calibration scheme for V-I probes [41] provide a comprehensive methodology for determining the basic parameters of APPJs.…”

“…The methodology and experimental procedure for determining P , av the average power fed to the APPJ is also discussed there in detail and will not be discussed here. Typical voltages and currents (after removal of the anomalies) along with the respective P av values for helium jet are reproduced in table 1 here, for completeness from [41]. One notes in particular that the phase difference j between the voltage and current though very close to 90°, never exceeds it.…”

“…Applying the RF power along with gas feed to the plasma device ignites the discharge within the discharge tube, which appears outside as a plasma jet in the ambient air. More details of the experimental setup can be found in the authors' previous publications [18,41,53].…”

“…As already mentioned earlier, even high-quality voltage and current probes when used with miniature devices like plasma jets exhibit considerable anomalies when utilized for synchronous voltage and current measurements. This issue was addressed systematically and carefully by the authors and resolved recently [41]. The methodology and experimental procedure for determining P , av the average power fed to the APPJ is also discussed there in detail and will not be discussed here.…”

“…It may be mentioned that when used with miniature devices like plasma jets, even high-quality voltage and current probes exhibit considerable anomalies when utilized for synchronous voltage and current measurements. This issue was addressed systematically and carefully by the authors and resolved recently [41].…”