Annular array sensors

• US 4,992,692 A
• Filed: 05/16/1989
• Issued: 02/12/1991
• Est. Priority Date: 05/16/1989
• Status: Expired due to Fees

• Current Assignee: Agilent Technologies, Inc.
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Dias, J. Fleming
• Primary Examiner(s): Williams, Hezron E.
• Assistant Examiner(s): Arana, Louis M.
• Application Number:
  US07/352,526
• Time in Patent Office: 637 Days
• Field of Search: 73/632, 73/625, 310/334, 310/335, 310/369, 310/366, 29/25.35
• US Class Current: 310/335
• CPC Class Codes: B06B 1/0625 Annular array
• CPC Class Codes: Y10T 29/42 Piezoelectric device making

Abstract

An improved annular array sensor [10] that facilitates hermetic sealing and uses optimum acoustic matching layers is disclosed. The key to the performance improvement obtained in the present invention is the method of forming the annular elements [38,40] of the array. In one approach, the elements [38,40] are not quite separated from one another at the concave side [14] of the sensor shell [12]. A series of cuts [34] are made into a shell [12] of piezoelectric material from its convex side [16]. These cuts [34] are made almost entirely through the shell [12] so that a small amount of material [20] remains between the cut and the concave side [14]. After poling, the resulting ultrasonic sensor [10] has the basic electrical properties of a conventional sensor in which the cuts are made completely through the shell [12]. However, the continuous concave side [14] of the ultrasonic sensor [10] need not be sealed. A conductive coating [32] on the concave side [14] serves as a common ground for all the array elements [38,40]. In another embodiment, the concave side is grooved and plated with a conductive layer [60]. Then a series of thin-kerfed circular cuts [62] are made from the convex side [16] so that they intersect the relatively thick grooves [56]. The thick conducting layer [60] serves as both common ground and mechanical support structure. In the previous art, the conductive coating would be required to have good impedance matching properties, in addition to adequate conductivity. In either embodiment of the present invention, when an impedance matching layer [41] is selected for application to the concave side [14], no compromises need be made in its properties. Therefore the impedance match can be optimized, and the material used need not be an electrical conductor. To complete the sensor array, individal electrical conductors [42] are connected to the annuli [40] and central disc [38], at the convex side [16]. An acousitically attenuating layer [41] may be used on the convex side [16].

Claims

1. A method of fabricating an ultrasonic sensor array comprising the steps of:

a. fabricating a circular shell of piezoelectric material, said shell having a concave side, a convex side, and a shell edge;

b. attaching said shell snugly inside a conductive ring, said ring having an inner side, a bottom edge, an outer side, and a top edge, so that said concave surface is aligned with said bottom edge;

c. cutting at least one circular concentric cut into said convex side;

said cut extending almost to said concave side, so that a portion of said shell in proximity to said concave remains uncut;

d. forming a central disc and at least one concentric annulus, said uncut portion having a thickness dimension which is adequate to retain stable alignment between said concentric annulus and said central disc;

e. attaching a conductive coating to said concave side, to said convex side, and to said bottom edge;

f. connecting a conductor to said central disc and to each of said annuli at said convex side;

g. poling each of said annuli and said central disc by applying a DC potential between said conductive coating and each of said conductors; and

h. sealing said top edge with a hermetic seal so that said convex side is sealed and each of said conductors emerges through said seal.

2. A method of fabricating an ultrasonic sensor array [10] as in claim 1, comprising the additional step of affixing a layer [41] having an acoustic matching impedance over said conductive coating [32].

3. A method of fabricating an ultrasonic sensor array [10] as in claim 2, comprising the additional step of affixing an acoustically attenuating layer [41] to said convex side [16].

4. An ultrasonic sensor array [10] comprising:

a. a piezoelectric shell [12] having a concave side [14], a convex side [16], and a shell edge [15];

b. said convex side [16] being dissected into a central disc [38] and at least one concentric annulus [40] by at least one circular cut, [34], said cut [34] extending from said convex side [16] toward said concave side [14], so that a region [36] in proximity to said concave side [14], so that a region [36] in proximity to said concave side [14] remains uncut;

c. a conductive ring [18], having an outer edge [24], an inner edge [20], a lower end [22], and an upper end [25], said ring [18] being affixed around said piezoelectric shell [12] so that said piezoelectric shell [12] fits snugly inside said ring [18], with said lower end [22] aligned with said concave side [14];

d. a conductive coating [32] applied over said concave side [14] and said lower end [22];

e. a seal [44] applied over said upper end [25] of said ring [18], thereby forming an open space [54], between said seal [44] and said convex side [16], said open space [54] being hermetically sealed; and

f. an electrical connection [42] to said central disc [38] and to each of said concentric annuli [40];

said electrical connections [42] being made within said open space [54], at said convex side [16] of said piezoelectric shell [12], said connections [42] passing through said seal [44] to permit external connection.

5. An ultrasonic sensor array as in claim 4, in which said piezoelectric material is chosen from the group comprising lead zirconate titanate [PZT] and modified lead titanate (PbTiO₃).

6. An ultrasonic sensor array as in claim 5, in which at least one impedance matching layer [41] is bonded to said conductive coating [32] on said concave side [14].

7. An ultrasonic sensor array as in claim 6, in which said conductive coating [26] extends across said bottom edge [22], and over said outer side [24].

8. An ultrasonic sensor array as in claim 7, in which said seal [44] is a cup shaped membrane affixed to said top edge [25] of said ring [18], said seal [44] having a non-conducting layer [48], and at least one conductive layer [46,50];

said seal [44] thereby enclosing said convex side [16];

said conductive layer [46,50] extending over said outer side [24] of said ring [18];

said conductive layer [46,50] being hermetically bonded to said outer side [24].

9. An ultrasonic sensor array as in claim 8, in which said membrane is penetrated by pass-throughs [52] for said conductors [42], said pass-throughs [42] being hermetically sealed in said non-conducting central layer [48].

10. An ultrasonic sensor array as in claim 9, in which said passthroughs [42] are formed photolithographically.

11. An ultrasonic sensor array as in claim 10, in which an acoustically attenuating layer [54] is applied to said convex side [16].

12. A method of fabricating an ultrasonic sensor array comprising the steps of:

a. fabricating a shell of piezoelectric material;

said shell being essentially round, and having a concave side, a convex side and a shell edge;

b. cutting at least one circular groove into said concave side, concentric with a center of said shell, said groove have a groove width;

c. depositing a conductive coating over said concave side of said array, said coating essentially filling said circular groove;

d. cutting at least one circular concentric cut into said convex side;

said cut having a radius the same as that of said circular groove, and kerf width narrower than that of said groove width, said cut being aligned radially with said circular groove;

e. extending said cut to contact said conductive coating in said circular groove, thereby forming a central disc and at least one annulus which are separated from one another and maintained in position by said conductive coating;

f. attaching a conductor to said central disc and to each of said annuli at said convex side;

g. poling each of said annuli and said central disc by applying a DC potential between said conductive coating and each of said conductors; and

h. sealing said top edge with a hermetic seal, so that said convex side is sealed and each of said conductors emerges through said seal.

13. A method of fabricating an ultrasonic sensor array [10] as in claim 12, comprising the additional step of affixing a layer [41] having an acoustic matching impedance over said conductive coating [60].

14. A method of fabricating an ultrasonic sensor array [10] as in claim 13 comprising the additional step of affixing an acoustically attenuating layer [41] to said convex side [16].