Abstract: A device (15) including a piezoelectric sensor (16). The piezoelectric sensor (16) includes a layer of piezoelectric material (7) disposed between a number of sensing electrodes (4, 12, 13) and at least one counter electrode (3). The device (15) also includes a controller (17) connected to the piezoelectric sensor (16). The sensing electrodes (4, 12, 13) are arranged to form one or more active regions (19). Each active region (19) includes one or more primary sensing electrodes (4,12) and one or more secondary sensing electrodes (4, 13). The secondary sensing electrodes (4, 13) are separated from the primary sensing electrodes (4, 12) by a perimeter (14). The controller (17) is configured, for each active region (19), to monitor primary piezoelectric charges induced on each primary sensing electrode (4, 12) and to monitor secondary piezoelectric charges induced on each secondary sensing electrode (4, 13).

Abstract: Microwave-Electro-Thermal thrusters produce a high temperature rocket exhaust by sending microwaves into a resonant cavity where an excited mode then creates an electrodeless discharge that heats gaseous fuel. Heretofore, the microwave power coupling between the microwave generator and the resonant cavity and plasma has consisted of rigid waveguide with impedance matching equipment. This waveguide and impedance matching hardware greatly adds to the weight and size of the system making it impractical for spaceflight. The foregoing problems are overcome by greatly reducing or eliminating the waveguide and impedance matching equipment.