Split memory element

• US 4,918,919 A
• Filed: 07/19/1989
• Issued: 04/24/1990
• Est. Priority Date: 10/02/1987
• Status: Expired due to Term

• Current Assignee: Catheter Research Incorporated
• Original Assignee: Catheter Research Incorporated
• Inventors: Cole, Gregory, Small, James E., McCoy, William C.
• Primary Examiner(s): Ostrager, Allen M.
• Application Number:
  US07/383,233
• Time in Patent Office: 279 Days
• Field of Search: 60/527, 60/528, 60/529
• US Class Current: 60/528
• CPC Class Codes: C21D 10/00 Modifying the physical properties by methods other than heat treatment or deformation
• CPC Class Codes: C21D 2201/01 Shape memory effect
• CPC Class Codes: C22F 1/006 Resulting in heat recoverable alloys with a memory effect
• CPC Class Codes: C22F 3/00 Changing the physical structure of non-ferrous metals or alloys by special physical methods, e.g. treatment with neutrons
• CPC Class Codes: G11C 13/02 using elements whose operation depends upon chemical change G11C13/0009 takes precedence

Abstract

A memory element of the present invention is split to minimize the magnitude of electrical current flowing therethrough as the split memory element is being heated to its transitional temperature, thereby permitting the cross-sectional area of the lead wires used to conduct an electric current to the memory element to be minimized. The split memory element includes a tip member and first and second strip members aligned in side-by-side relation. Each of the tip member, first strip member, and second strip member are made of a shape-memory alloy and have a characteristic internal structure. Each strip member includes a shape-memory portion coupled to the tip member, a lead-attachment portion, and partition means for interconnecting the shape-memory and lead-attachment portions. Each partition means has an internal structure which is dissimilar to the characteristic internal structure of the tip member and the first and second strip members so that certain ions originating in the electrically conductive wire lead coupled to the lead-attachment portions are substantially isolated or otherwise contained in the lead-attachment portions to prevent contamination of the shape-memory portions.

Claims

1. A memory element comprising

a tip member, and

first and second strip members aligned in side-by-side relation, each of the tip member, first strip member, and second strip member being made of a shape-memory alloy and having a characteristic internal structure, each strip member including a proximal portion coupled to the tip member, a distal portion, and partition means for interconnecting the proximal and distal portions, each partition means having an internal structure which is dissimilar to the characteristic internal structure of the tip member and the first and second strip members.

2. The memory element of claim 1, wherein the dissimilar internal structure in each strip member is configured to block transmigration of selected ions between its proximal and distal portions.

3. The memory element of claim 1, further comprising an electrically conductive lead connected to each of the distal portions, the dissimilar internal structures of the partition means cooperating to provide means for blocking transmigration between the distal portions and the first strip, second strip, and tip members of selected ions indigenous to the electrically conductive leads to control the concentration of said selected ions in the first strip, second strip, and tip members.

4. The memory element of claim 1, wherein the distal portions cooperate to define a lead-attachment part, the tip member and the proximal portions cooperate to define a shape-memory part, at least the shape-memory part moves to assume a predetermined shape when heated to a predetermined temperature, and the partition means includes means for communicating energy from the lead-attachment part to heat the shape-memory part to its predetermined temperature so that at least the shape-memory part assumes its predetermined shape.

5. The memory element of claim 1, wherein the first and second strip members are aligned relative to one another to define a space therebetween extending between the tip member and the terminal ends of both distal portions.

6. The memory element of claim 1, further comprising insulator means disposed between the first and second strip members for blocking conduction of electrical current between the first and second strip members along a path bypassing the tip member.

7. The memory element of claim 6, wherein the first and second strip members cooperate to define a space therebetween extending between the tip member and the terminal ends of both distal portions and the insulator means is situated in the space.

8. The memory element of claim 7, wherein the insulator means is arranged substantially to fill said space.

9. The memory element of claim 6, wherein the insulator means includes means for bonding the first and second strip members together so that at least the proximal portions of the first and second strip members move in unison to assume a predetermined shape when heated to a predetermined temperature.

10. The memory element of claim 9, further comprising first and second electrically conductive leads, first connection means for coupling the first electrically conductive lead to the distal portion of the first strip member to permit introduction of an electrical current into the first strip member, and second connection means for coupling the second electrically conductive lead to the distal portion of the second strip member to ground the second strip member, the dissimilar internal structure of the partition means in the first strip member being configured to provide means for communicating electrical current introduced into the distal portion of the first strip member to the proximal portion of the first strip member, and the dissimilar internal structure of the partition means in the second strip member being configured to provide means for communicating electrical current conducted into the proximal portion of the second strip member via the proximal portion of the first strip member and the tip member to the grounded distal portion of the second strip member so that at least the tip member and the proximal portions of the first and second strip members move to assume the predetermined shape when heated to the predetermined temperature by electrical current being conducted therethrough.

11. The memory element of claim 1, further comprising first and second electrically conductive leads, first connection means for coupling the first electrically conductive lead to the distal portion of the first strip member to permit introduction of an electrical current into the first strip member, and second connection means for coupling the second electrically conductive lead to the distal portion of the second strip member to ground the second strip member, the dissimilar internal structure of the partition means in the first strip member being configured to provide means for communicating electrical current introduced into the distal portion of the first strip member to the proximal portion of the first strip member, and the dissimilar internal structure of the partition means in the second strip member being configured to provide means for communicating electrical current conducted into the proximal portion of the second strip member via the proximal portion of the first strip member and the tip member to the grounded distal portion of the second strip member so that at least the tip member and the proximal portions of the first and second strip members move to assume the predetermined shape when heated to the predetermined temperature by the electrical current being conducted therethrough.

12. A memory element comprising

first and second lead-attachment portions,

a U-shaped shape-memory portion including first and second leg members, each leg member including a proximal end and a distal end, and a bight member interconnecting the proximal ends of the first and second leg members,

first barrier means interconnecting the first lead-attachment portion and the distal end of the first leg member for blocking transmigration of selected ions from the first lead-attachment portion to the shape-memory portion to control the concentration of said selected ions in the shape-memory portion, and

second barrier means interconnecting the second lead attachment portion and the distal end of the second leg member for blocking transmigration of the selected ions from the second lead-attachment portion to the shape-memory portion to control the concentration of said selected ions in the shape-memory portion, the lead-attachment portions, the shape-memory portion, and the first and second barrier means being made of a shape-memory alloy.

13. The memory element of claim 12, wherein each of the shape-memory and lead-attachment portions has a characteristic internal structure and the first and second barrier means have a dissimilar internal structure.

14. The memory element of claim 12, further comprising insulator means disposed between the first and second strip members for blocking conduction of electrical current between a first element section including the first leg member and the first lead-attachment portion and a second element section including the second leg member and the second lead-attachment portion along a path bypassing the bight member.

15. The memory element of claim 12, further comprising insulator means for bonding the first leg member to the second leg member without establishing an electrically conductive path between the first and second leg members which bypasses the bight member.

16. The memory element of claim 12, further comprising insulator means for bonding the first lead-attachment portion to the second lead-attachment portion without establishing an electrically conductive path between the first and second lead-attachment portion which bypasses the bight member.

17. The memory element of claim 12, further comprising first and second electrically conductive leads, first connection means for coupling the first electrically conductive lead to the first lead-attachment portion to apply an electrical current to the memory element, and second connection means for coupling the second electrically conductive lead to the second lead-attachment portion to ground the memory element.

18. The memory element of claim 17, wherein the first barrier means is configured to provide means for communicating electrical current introduced into the first lead-attachment portion to the first leg member and the second barrier means is configure to provide means for communicating electrical current, conducted into the second leg member to the grounded second lead-attachment portion so that at least the shape-memory portion moves to assume a predetermined shape when heated to a predetermined temperature by electrical current being conducted therethrough.

19. A memory element comprising

a first strip member made of a shape-memory alloy and including a first lead-attachment portion, a first shape-memory portion, and first partition means for interconnecting the first lead-attachment and shape-memory portions,

a second strip member made of the shape-memory alloy and including a second lead-attachment portion, a second shape-memory portion, and second partition means for interconnecting the second lead-attachment and shape-memory portions, and

means interconnecting the first and second shape-memory portions for conducting electrical current in the first shape-memory portion to the second shape-memory portion.

20. The memory element of claim 19, wherein the shape-memory alloy has a first internal structure, each lead-attachment portion and each shape-memory portion have said first internal structure, each partition means has a dissimilar second internal structure, the first partition means is formed by exposing a selected portion of the first internal structure between the first lead-attachment and shape-memory portions to an energy source and the second partition means is formed by exposing a selected portion of the first internal structure between the second lead-attachment and shape-memory portions to an energy source.

21. The memory element of claim 20, wherein each energy source is a laser.

22. The memory element of claim 19, wherein the conducting means and the first and second strip members are unitarily formed of a single member made of shape-memory alloy.

23. The memory element of claim 22, wherein the single member is U-shaped, the first and second strip members cooperate to define legs of the U-shaped member, and the conducting means is configured to define a bight interconnecting the legs of the U-shaped member.

24. The memory element of claim 23, wherein the first and second strip members are disposed in spaced-apart parallel relation, and further comprising insulator means for preventing establishment of an electrical connection of the lead-attachment and shape-memory portions of the first strip member with the lead-attachment and shape-memory portions of the second strip member apart from an electrical connection provided by the conducting means, the insulator means being disposed in a space defined between the spaced-apart first and second strip members.

25. The memory element of claim 24, wherein the insulator means includes means for bonding at least the first and second shape-memory portions together so that at least the conducting means and the first and second shape-memory portions move in unison to assume a predetermined shape when heated to a predetermined temperature.

26. The memory element of claim 19, wherein the conducting means is formed by welding a distal end of the first shape-memory portion to a distal end of the second shape-memory portion while the first and second shape-memory portions are aligned in side-by-side, spaced-apart relation.

27. The memory element of claim 26, wherein the conducting means and the first and second strip members cooperate to define a substantially U-shaped member having a longitudinally extending apace, provided between the first and second strip members.

28. The memory element of claim 27, further comprising insulator means disposed in the longitudinally extending space for blocking electrical communication between adjacent lead-attachment portions and between adjacent shape-memory portions along any path bypassing the conducting means.

29. The memory element of claim 28, wherein the insulator means includes means for bonding at least the first and second shape-memory portions together so that at least the conducting means and the first and second shape-memory portions move in unison to assume a predetermined shape when heated to a predetermined temperature.

30. A method of making a temperature-activated memory element, the method comprising the steps of

providing an elongated U-shaped mechanism made of a shape-memory alloy having a crystalline structure and a slit extending along the longitudinal axis of the mechanism from one of the ends of the mechanism to a point in close proximity to the other of the ends of the mechanism to define a pair of longitudinally extending legs and a bight interconnecting the pair of legs,

exposing a first selected portion of the first leg of the mechanism to an energy source to divide the first leg into a proximal first shape-memory portion coupled to the bight and a distal first lead-attachment portion,

exposing a second selected portion of the second leg of the mechanism to the energy source to divide the second leg into a proximal second shape-memory portion coupled to the bight and a distal second lead-attachment portion, and

continuing the exposing steps for at least a predetermined period of time sufficient to disrupt the crystalline structure of the first and second selected portions to alter the crystalline structure to provide a dissimilar structure configured to block transmigration of selected ions between each lead-attachment portion and its companion shape-memory portion.

31. The method of claim 30, further comprising the step of inserting an insulator into the slit to block electrical communication between the pair of legs along a path extending across the slit.

32. The method of claim 30, wherein the providing step includes the steps of furnishing a unitary sample of a shape-memory alloy and cutting the unitary sample along its longitudinal axis to define the slit so that the pair of longitudinally extending legs and the bight are formed.

33. The method of claim 30, wherein the providing step includes the steps of furnishing a pair of elongated strips made of the shape-memory alloy, aligning the strips in side-by-side relation so that a distal end of the first shape-memory portion is adjacent to a distal end of the second shape-memory portion, and welding the distal ends of the first and second shape-memory portions together to define the bight.

34. The method of claim 30, further comprising the steps of connecting one electrically conductive lead to the first lead-attachment portion and connecting another electrically conductive lead to the second lead-attachment portion, the connecting steps occurring after the exposing and continuing steps to provide means for applying an electric current to the mechanism, each of the first and second selected portions providing a partition intermediate its companion lead-attachment and shape-memory portions to isolate in the lead-attachment portion selected ions communicated from the electrically conductive lead to the lead-attachment portion.