Recently, one of the most successful commercial aircraft, the Boeing 777, uses piezoelectric ceramic materials for the 60 ultrasonic fuel tank probes on each aircraft. Ultrasonic transducers are installed at multiple locations in each fuel tank. A pulsed electric field is applied to the ceramic material. The ceramic material responds by oscillating. The resulting sound waves are reflected from the surface of the fuel and accepted by the piezoelectric ceramic transducer. The digital signal processor interprets the "time of flight" of the sound waves to continuously indicate the presence The amount of fuel. Similar ultrasonic fuel detectors are also used in fighter jets and other levels of sensing applications because they can provide highly accurate readings regardless of the orientation of the aircraft.