A method and apparatus for calibrating a sensor for determination of the concentration of a sterilant, e. In one aspect, power control commands for a plurality of base stations are combined to form a single command to control the plurality of base control. The droplet discharging head is preferably an electrostatic drive or piezoelectric drive type. RFID transponders, which operate without making galvanic contact. This can be done by etching at a layer interface, such as a silicon-germanium interface in an over-etch step.