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

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 degrees. 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 degrees. It turns out, however, that when V-I probes are used with such devices without joint calibration, these frequently yield phase shifts over 90 degrees. 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 approximate to 90 degrees. 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) approximate to 93.6 - j 1139 Omega (81.5 - j 1173 Omega) at P-av approximate to 9.8 W (approximate to 7.7 W) for helium (argon) gas. Published under an exclusive license by AIP Publishing.

Automated summary

This paper presents a joint calibration scheme for voltage and current probes to accurately resolve voltage-current phase differences, even when the difference is very close to 90 degrees. This has been a major issue with V-I probes used with miniature RF plasma devices. The proposed scheme improves the accuracy of phase resolution and provides indispensable tools for electrical characterization of RF plasma devices.