Ultrasonic device including acoustically matched regions therein
Ultrasonic devices include a transducer having a piezoelectric element therein that may operate as an acoustic signal receiving surface and/or an acoustic signal generating surface. At least one acoustic matching layer is provided on the piezoelectric element. This at least one acoustic matching layer may be configured as a composite of N acoustic matching layers, with a first of the N acoustic matching layers contacting the primary surface of the piezoelectric element. This first acoustic matching layer may have an acoustic impedance equivalent to Z L1 , where N is a positive integer greater than zero. In some embodiments of the invention, the magnitude of Z L1 may be defined as: 0.75 ((Z p ) N+1 (Z g )) 1/(N+2) ≤Z L1 ≤1.25 ((Z p ) N+1 (Z g )) 1/(N+2) , where Z p is the acoustic impedance of the piezoelectric element (e.g., lead zirconate titanate (PZT)) and Z g is the acoustic impedance of a compatible gas.
1. An ultrasonic device, comprising:
a transducer having a piezoelectric element therein;
at least one acoustic matching layer on the piezoelectric element, said at least one acoustic matching layer comprising a composite of N acoustic matching layers, with a first of the N acoustic matching layers contacting the piezoelectric element and having an acoustic impedance equivalent to Z L1 , where N is a positive integer greater than zero and Z L1 is defined as:
0.75(( Z p ) N+1 ( Z g )) 1/(N+2) ≤Z L1 ≤1.25(( Z p ) N+1 ( Z g )) 1/(N+2) ,
where Z p is the acoustic impedance of the piezoelectric element and Z g is the acoustic impedance of a compatible gas; and
a protective layer on said at least one acoustic matching layer.
2. The ultrasonic device of claim 1 , wherein said protective layer has an acoustic impedance equivalent to Z pl , where:
0.5(( Z p )( Z g ) N+1 ) 1/(N+2) ≤Z pl ≤1.5(( Z p )( Z g ) N+1 ) 1/(N+2) .
3. The ultrasonic device of claim 2 , wherein said protective layer comprises polyethylene terephthalate (PET).
4. The ultrasonic device of claim 3 , where N equals two and a second of the N acoustic matching layers, which extends between said protective layer and the first of the N acoustic matching layers, has an acoustic impedance equivalent to Z L2 , where Z L2 is defined as:
0.75(( Z p ) 2 ( Z g ) 2 ) 0.25 ≤Z L2 ≤1.25(( Z p ) 2 ( Z g ) 2 ) 0.25 .
5. The ultrasonic device of claim 4 , wherein the second of the N acoustic matching layers comprises polyethersulfone (PES).
6. The ultrasonic device of claim 5 , wherein the piezoelectric element comprises lead zirconate titanate (PZT).
7. The ultrasonic device of claim 2 , where N equals two and a second of the N acoustic matching layers, which extends between said protective layer and the first of the N acoustic matching layers, has an acoustic impedance equivalent to Z L2 , where Z L2 is defined as:
0.75(( Z p ) 2 ( Z g ) 2 ) 0.25 ≤Z L2 ≤1.25(( Z p ) 2 ( Z g ) 2 ) 0.25 .
8. The ultrasonic device of claim 1 , where N equals two and a second of the N acoustic matching layers, which extends between said protective layer and the first of the N acoustic matching layers, has an acoustic impedance equivalent to Z L2 , where Z L2 is defined as:
0.75(( Z p ) 2 ( Z g ) 2 ) 0.25 ≤Z L2 ≤1.25(( Z p ) 2 ( Z g ) 2 ) 0.25 .
9. The ultrasonic device of claim 2 , wherein said protective layer comprises a polyethylene terephthalate (PET) layer metalized with aluminum (Al).
10. The ultrasonic device of claim 9 , wherein the first of the N acoustic matching layers is a PET layer.
11. The ultrasonic device of claim 2 , wherein said protective layer is a polymer layer having a thickness of less than about 20 microns.
12. The ultrasonic device of claim 2 , wherein the first of the N acoustic matching layers comprises polyethersulfone (PES).
13. The ultrasonic device of claim 1 further comprising:
a second of the N acoustic matching layers comprising PET extending between said first of the N acoustic matching layers and the piezoelectric element.
14. The ultrasonic device of claim 13 , wherein said second of the N acoustic matching layers is bonded to the piezoelectric element and said protective layer is bonded to said first of the N acoustic matching layers.
15. The ultrasonic device of claim 14 , wherein said protective layer is metalized with aluminum.
16. The ultrasonic device of claim 1 , wherein the first of the N acoustic matching layers comprises a first acoustic matching layer bonded to the piezoelectric element and the protective layer is bonded to said first of the N acoustic matching layers.