Systems, apparatus and methods for monitoring contact of electrosurgical apparatus with a patient’s body via a contacting monitoring unit having a plurality of contacting segments, wherein each of the contacting segments is separate from an active electrode andor return electrode. The HEMT includes a semiconductor layer, a barrier layer on the semiconductor layer, a piezoelectric layer on the barrier layer, a gate on the piezoelectric layer, and a source and a drain at two sides of the gate respectively, wherein each bandgap of the semiconductor layer, the barrier layer, and the piezoelectric layer partially but not entirely overlaps the other two bandgaps. A bearing assembly has inner and outer bearing members in spaced relationship from one another with a plurality of rolling members interposed between the bearing members to permit relative rotation between the bearing members about the rotational axis. The invention further relates to a method and system for decoding extra information embedded in an input signal by comparing it with an original input signal and decoding the differences into the extra information. A filler layer is formed in the first opening. control means operable to control the passage of water and air independently through the water and air conduits respectively, the control means further operable to control the passage of water and air in each body portion independently.