Multilayer backing absorber for ultrasonic transducer

1. A backing absorber for use with an ultrasonic transducer, comprising:

a first elemental multilayer having at least one homogeneous metal layer and at least one adhesive layer; and

a second elemental multilayer having at least one homogeneous metal layer and at least one adhesive layer,

wherein one of said at least one homogeneous metal layer and said at least one adhesive layer of said second multilayer is bonded to the other of said at least one homogeneous metal layer and said at least one adhesive layer of said first multilayer,

wherein a planar surface of said backing absorber is adapted to be coupled to a corresponding planar surface of a vibrating layer of said ultrasonic transducer,

wherein said plurality of elemental multilayers are effective to dampen ultrasonic signals emitted by said vibrating layer when said backing absorber is coupled to said vibrating layer, and

wherein each elemental multilayer further includes a polymer layer.

2. The backing absorber of claim 1 , wherein the backing absorber further comprises at least a third elemental multilayer having at least one homogeneous metal layer and at least one adhesive layer.

3. The backing absorber of claim 2 , wherein each of said at least one homogeneous metal layers is deposited on a corresponding one of said polymer layers to form a periodic grating of metal strips wherein the direction and period of the grating is the same for each elemental layer.

4. The backing absorber of claim 2 , wherein each of said at least one homogeneous metal layers is deposited on a corresponding one of said polymer layers to form a periodic grating of metal strips wherein the direction or period of the grating is different for each elemental layer.

5. The backing absorber of claim 4 , wherein said direction of said grating is positioned at a 90 degree angle relative to the direction of the grating of each adjacent multilayer.

6. The backing absorber of claim 2 , wherein each of said at least one homogeneous metal layers is partially deposited on a selected area of a corresponding one of said polymer layers to form a boundary grading for reflecting backwards waves in such a way as to increase effective attenuation.

7. The backing absorber of claim 1 , wherein the vibrating layer comprises one of a monolithic PZT plate, a 1-3 PZT composite, and a 2-2 PZT composite.

8. The backing absorber of claim 3 , wherein the vibrating layer comprises a 2-2 PZT composite having a plurality of elongated bars of PZT material and wherein the direction of the elongated metal area of the grating is perpendicular to said PZT bars.

9. A method of making a backing absorber for an ultrasonic transducer, comprising:

forming a first multilayer element by coupling a first homogeneous metal layer to a first adhesive layer;

forming a second multilayer element by coupling a second homogeneous metal layer to a second adhesive layer; and

coupling at least one of said second homogeneous metal layer and said second adhesive layer to the other of said first homogeneous metal layer and said first adhesive layer,

wherein a planar surface of said first multilayer element is configured to be coupled to a corresponding planar surface of a vibrating layer of said ultrasonic transducer for absorbing ultrasonic waves,

wherein said forming further comprises first coupling a first and a second polymer layer to said first and second homogeneous metal layers, respectively.

10. The method of claim 9 further comprising:

forming an additional multilayer element by coupling a third homogeneous metal layer to a third adhesive layer; and

bonding said additional multilayer element to said first multilayer element.

11. The method of claim 10 further comprising:

repeating said forming of said additional multilayers and said bonding of said additional multilayer elements until a predetermined acoustic absorption value has been reached.

12. The method of claim 11 , wherein said forming further comprises depositing said homogeneous metal layer on a polymer layer to form a periodic grating of metal strips wherein the direction and period of the grating is the same for each elemental multilayer.

13. The method of claim 11 , wherein said forming further comprises depositing said homogeneous metal layer on a polymer layer to form a periodic grating of metal strips wherein the direction or period of the grating is different for each elemental multilayer.

14. The method of claim 13 , wherein said direction of said grating is positioned at a 90 degree angle relative to the direction of the grating of each adjacent multilayer.

15. The method of claim 10 , wherein said forming further comprises partially depositing said homogeneous metal layer on a selected area of each of said at least one polymer layers to form a boundary grading for reflecting waves in such a way as to increase effective attenuation.

16. An ultrasonic transducer assembly, comprising:

a vibrating layer for generating ultrasonic waves; and

a backing absorber coupled to said vibrating layer for absorbing said ultrasonic waves, said backing absorber having a plurality of elemental multilayers, each elemental multilayer including:

a homogeneous metal layer,

a polymer layer, and

an adhesive layer.

17. The ultrasonic transducer assembly of claim 16 , wherein the vibrating layer comprises one of a monolithic PZT plate, a 1-3 PZT composite, and a 2-2 PZT composite.

18. A method of making an ultrasonic transducer assembly, comprising:

providing a vibrating layer for generating acoustic ultrasonic waves;

forming a plurality of multilayer elements wherein each multilayer element is formed by depositing a homogeneous metal layer on a polymer layer;

bonding said plurality of multilayer elements to one another by use of a plurality of adhesive layers to form a backing absorber; and

bonding a planar surface of said backing absorber to a corresponding backplane of said vibrating layer to absorb said acoustic ultrasonic waves.