Ultrasonic transducer and parametric speaker including the same
An ultrasonic transducer includes a diaphragm, one or more frame bodies extending in a longitudinal direction and bonded to the diaphragm, and one or more ultrasonic vibrators attached to the respective one or more frame bodies and facing the diaphragm with a space in between. The diaphragm is structured to resonate and vibrate in a direction orthogonal to the diaphragm in a phase opposite to a phase of the one or more ultrasonic vibrators. A dimension in the longitudinal direction inside the one or more frame bodies is larger than a dimension in a lateral direction orthogonal to the longitudinal direction inside the one or more frame bodies. One or more cavities cause an external space on an opposite side from the one or more frame bodies with respect to the diaphragm and an internal space inside the one or more frame bodies to communicate with each other.
1 . An ultrasonic transducer, comprising:
a first diaphragm;
one or more frame bodies extending in a longitudinal direction and bonded to the first diaphragm; and
one or more ultrasonic vibrators attached to the respective one or more frame bodies and facing the first diaphragm with a space in between; wherein
the first diaphragm is structured to resonate and vibrate in a direction orthogonal to the first diaphragm in a phase opposite to a phase of the one or more ultrasonic vibrators;
a dimension in the longitudinal direction inside the one or more frame bodies is larger than a dimension in a lateral direction orthogonal to the longitudinal direction inside the one or more frame bodies; and
one or more cavities cause an external space on an opposite side from the one or more frame bodies with respect to the first diaphragm and an internal space inside the one or more frame bodies to communicate with each other.
2 . The ultrasonic transducer according to claim 1 , wherein the one or more cavities are in the first diaphragm.
3 . The ultrasonic transducer according to claim 2 , wherein each of the one or more cavities includes a slit extending in the lateral direction.
4 . The ultrasonic transducer according to claim 3 , wherein the one or more cavities extend to be equal to or larger than the dimension in the lateral direction inside the one or more frame bodies.
5 . The ultrasonic transducer according to claim 1 , wherein one cavity of the one or more cavities is open at one of both end portions in the longitudinal direction inside the one or more frame bodies.
6 . The ultrasonic transducer according to claim 1 , wherein two cavities of the one or more cavities are open at respective both end portions in the longitudinal direction inside the one or more frame bodies.
7 . The ultrasonic transducer according to claim 1 , wherein each of the one or more ultrasonic vibrators includes a piezoelectric element including a piezoelectric body.
8 . The ultrasonic transducer according to claim 1 , wherein the first diaphragm and the one or more ultrasonic vibrators have resonant frequencies equal to or higher than about 100 kHz.
9 . The ultrasonic transducer according to claim 7 , wherein a relationship of 0.25CpTp/Cv≤Tv≤0.6CpTp/Cv is satisfied, where Cv is an acoustic velocity of a transverse wave of the first diaphragm, Cp is an acoustic velocity of a transverse wave of the piezoelectric body, Tv is a thickness dimension of the first diaphragm, and Tp is a thickness dimension of the piezoelectric body.
10 . The ultrasonic transducer according to claim 7 , wherein a relationship of 0.7CpTp/Cv≤Tv≤1.3CpTp/Cv is satisfied, where Cv is an acoustic velocity of a transverse wave of the first diaphragm, Cp is an acoustic velocity of a transverse wave of the piezoelectric body, Tv is a thickness dimension of the first diaphragm, and Tp is a thickness dimension of the piezoelectric body.
11 . The ultrasonic transducer according to claim 1 , wherein
the one or more frame bodies are aligned in the lateral direction and are bonded to the first diaphragm; and
some of the one or more frame bodies adjacent to each other in the lateral direction are connected to each other at both end portions in the longitudinal direction.
12 . The ultrasonic transducer according to claim 7 , wherein
the one or more ultrasonic vibrators are each a unimorph-type piezoelectric vibrator; and
a second diaphragm is provided on a side of the piezoelectric body opposite to a frame body side.
13 . The ultrasonic transducer according to claim 5 , wherein the dimension in the longitudinal direction inside the one or more frame bodies is equal to or greater than twice the dimension in the lateral direction inside the one or more frame bodies.
14 . The ultrasonic transducer according to claim 1 , wherein a dimension of the one or more cavities in the lateral direction is equal to or greater than about 60% and equal to or less than about 95% of the dimension in the lateral direction inside the one or more frame bodies.
15 . A parametric speaker, comprising
the ultrasonic transducer according to claim 1 ; wherein
an audible sound is reproducible by modulation driving of the ultrasonic transducer.
16 . The parametric speaker according to claim 15 , wherein the one or more cavities are in the first diaphragm.
17 . The parametric speaker according to claim 16 , wherein each of the one or more cavities includes a slit extending in the lateral direction.
18 . The parametric speaker according to claim 17 , wherein the one or more cavities extend to be equal to or larger than the dimension in the lateral direction inside the one or more frame bodies.
19 . The parametric speaker according to claim 15 , wherein one cavity of the one or more cavities is open at one of both end portions in the longitudinal direction inside the one or more frame bodies.
20 . The parametric speaker according to claim 15 , wherein two cavities of the one or more cavities are open at respective both end portions in the longitudinal direction inside the one or more frame bodies.