310 / | HD | ELECTRICAL GENERATOR OR MOTOR STRUCTURE |
300 | DF | NON-DYNAMOELECTRIC {4} |
311 | DF | .~ Piezoelectric elements and devices {17} |
313 R | DF | .~.~ Surface acoustic wave devices {2} |
313 B | DF | .~.~.~ Interdigitated electrodes {2} |
313 C | .~.~.~.~ Envelope or apodized |