Ultrasonic transducer and parametric speaker including the same

An ultrasonic transducer comprising:

• a first diaphragm;
• at least one frame body extending in a longitudinal direction and joined to the first diaphragm;
• and
• at least one unimorph piezoelectric vibrator, attached to the at least one frame body, and including a piezoelectric body facing the first diaphragm with a space therebetween and a second diaphragm provided on an opposite side of the piezoelectric body from the frame body;
• wherein
• the first diaphragm is configured to resonantly vibrate in a phase opposite to a phase of the at least one unimorph piezoelectric vibrator in a direction orthogonal or substantially orthogonal to the first diaphragm;
• a dimension in the longitudinal direction inside the at least one frame body is about four or more times a dimension in a lateral direction orthogonal or substantially orthogonal to the longitudinal direction inside the at least one frame body;
• and
• the second diaphragm is located in a region interposed, in the lateral direction, between both edges in the lateral direction of an inner peripheral surface of the at least one frame body as viewed in the direction orthogonal or substantially orthogonal to the first diaphragm, and an average distance in the lateral direction between one of the edges in the lateral direction of the inner peripheral surface of the at least one frame body and one of edges in the lateral direction of the second diaphragm and an average distance in the lateral direction between another of the edges in the lateral direction of the inner peripheral surface of the at least one frame body and another of the edges in the lateral direction of the second diaphragm are one sixth or less the dimension in the lateral direction inside the at least one frame body.