Elastic boundary wave device

Abstract

An elastic boundary wave device includes a first medium with piezoelectricity, an electrode exciting an elastic wave and provided on the first medium, a second medium made of a different material from the first medium and provided on the first medium to cover the electrode, and a sound absorbing portion provided on the second medium.

1 . An elastic boundary wave device comprising:
 a first medium with piezoelectricity;   an electrode exciting an elastic wave and provided on the first medium;   a second medium made of a different material from the first medium and provided on the first medium to cover the electrode; and   a sound absorbing portion provided on the second medium.   
   
   
       2 . The elastic boundary wave device as claimed in  claim 1 , further comprising a third medium provided between the second medium and the sound absorbing portion,
 wherein the first medium and the second medium are made of different materials.   
   
   
       3 . An elastic boundary wave device comprising:
 a first medium with piezoelectricity;   an electrode exciting an elastic wave and provided on the first medium;   a second medium made of a different material from the first medium and provided on the first medium to cover the electrode; and   a protrusion provided on the second medium.   
   
   
       4 . The elastic boundary wave device as claimed in  claim 3 , wherein there are provided multiple protrusions having a different periodicity from the electrode. 
   
   
       5 . The elastic boundary wave device as claimed in  claim 3 , wherein there are provided multiple protrusions on an irregular basis. 
   
   
       6 . The elastic boundary wave device as claimed in  claim 3 , wherein the protrusion is made of a same material as the second medium. 
   
   
       7 . The elastic boundary wave device as claimed in  claim 3 , wherein the protrusion is made of a different material from the second medium. 
   
   
       8 . The elastic boundary wave device as claimed in  claim 3 , wherein the there are provided multiple protrusions, and a portion of the multiple protrusions is made of a same material as the second medium and another portion of the multiple protrusions is made of a different material from the second medium. 
   
   
       9 . The elastic boundary wave device as claimed in  claim 3 , further comprising a third medium provided between the second medium and the protrusion,
 wherein the first medium and the second medium are made of different materials.   
   
   
       10 . The elastic boundary wave device as claimed in  claim 9 , wherein the protrusion is made of a same material as the third medium. 
   
   
       11 . The elastic boundary wave device as claimed in  claim 9 , wherein there are provided multiple protrusions, and a portion of the multiple protrusions is made of a same material as the second medium and another portion of the multiple protrusions is made of a same material as the third medium. 
   
   
       12 . An elastic boundary wave device comprising:
 a first medium with piezoelectricity;   an electrode exciting an elastic wave and provided on the first medium;   a second medium made of a different material from the first medium and provided on the first medium to cover the electrode; and   a third medium made of a different material from the first medium and the second medium and provided on the second medium,   wherein the third medium has a thickness of 0.25 times or more of a periodicity of the electrode.