Shape memory alloy temperature sensor

• US 6,837,620 B2
• Filed: 06/18/2003
• Issued: 01/04/2005
• Est. Priority Date: 12/05/2001
• Status: Expired due to Fees

• Current Assignee: Mohsen Shahinpoor
• Original Assignee: Mohsen Shahinpoor
• Inventors: Shahinpoor, Mohsen
• Primary Examiner(s): Bennett, G. Bradley
• Assistant Examiner(s): Jagan, Mirellys
• Application Number:
  US10/464,244
• Publication Number:
  US 20040120384A1
• Time in Patent Office: 566 Days
• Field of Search: 374/205, 374/187, 374/194, 374/195, 374/198, 374/199, 374/200, 374/190, 374/159, 116/221
• US Class Current: 374/205
• CPC Class Codes: G01K 5/483 using materials with a configuration memory, e.g. Ni-Ti alloys

Abstract

A sensor provides a persistent indication that it has been exposed to temperatures below a certain critical temperature for a predetermined time period. An element of the sensor made from shape memory alloy changes shape when exposed, even temporarily, to temperatures below the Austenitic start temperature A_s and well into Martensite finish temperature M_f off the shape memory alloy. The shape change of the SMA element causes the sensor to change between two readily distinguishable states. The sensor includes a one-way stop element that creates a persistent indication of the temperature history, allowing the sensor to be manufactured and stored at temperatures above the Austenitic temperature without causing the indication of an over-temperature event.

Claims

1. A temperature history indication apparatus, comprising:

a) A body;

b) A shape memory alloy element having a first length in a first state and a second length in a second state;

c) Means for mounting the shape memory alloy element with the body such that, when the shape memory alloy element transitions from its first length to its second length, the means for mounting prevent the shape memory alloy element from attaining its first length even if the temperature of the shape memory alloy element would otherwise indicate a transition to the first length; and

d) Means for making change in the length of the shape memory alloy element perceptible.

2. The apparatus of claim 1, wherein shape memory alloy is chosen from the group consisting of:

Ag—

Cd, Au—

Cd, Cu—

Al—

Ni, Cu—

Sn, In—

Ti, Ni—

Al, Ni—

Ti, Fe—

Mn—

Si, Cu—

Zn-A, Cu—

Al—

Ni, alloys thereof, shape memory polymers, polyester prepolymers, and polyurethane.

3. A temperature history indication apparatus, comprising:

a) a body, defining a path having a length from an attachment portion thereof to a restraining portion thereof;

b) a sensing element, mounted at a first end with the attachment portion fixed along the direction of the path, and extending along the direction of the path toward the restraining portion, wherein the sensing element comprises a shape memory alloy that, when in its softened state, provides the sensing element with a first length sufficient to extend from the attachment portion to the restraining portion, and, when in its contracted state, provides the sensing element with second length less than the initial length unless constrained by the restraining portion;

c) wherein the restraining portion is adapted to, when the sensing element transitions from a length less than the first length to a length equal to the first length, prevent subsequent shortening of the sensing element without external mechanical intervention.

4. The apparatus of claim 3, wherein shape memory alloy is chosen from the group consisting of:

Ag—

Cd, Au—

Cd, Cu—

Al—

Ni, Cu—

Sn, In—

Ti, Ni—

Al, Ni—

Ti, Fe—

Mn—

Si, Cu—

Zn-A, Cu—

Al—

Ni, alloys thereof, shape memory polymers, polyester prepolymers, and polyurethane.

5. A apparatus for indicating a temperature event below a threshold temperature, comprising:

a) A body;

b) An indicator element mounted with the body, rotatable relative to the body about an axis;

c) A forcing element mounted with the body and with the indicator element, disposed such that the forcing element urges rotation of the indicator element in a first direction;

d) A shape memory alloy element mounted with the body and with the indicator element, disposed such that the shape memory alloy element is in its contracted state when exposed to temperature above the threshold temperature, and when in its contracted state opposes the action of the forcing element with sufficient force to prevent rotation of the indicator element, and such that the shape memory alloy element is in its softened state when exposed to temperatures below the threshold temperature, and when in its softened state does not prevent rotation of the indicator element responsive to the forcing element;

e) Means for preventing the indicator element from rotating opposite the first direction once the indicator element has rotated a first amount in the first direction.

6. An apparatus as in claim 5), wherein the means for preventing comprise an engagement element that prevents rotation opposite the first direction when engaged, wherein the engagement element engages when the indicator element has rotated the first amount in the first direction.

7. An apparatus as in claim 5), wherein the body comprises a first indicator, and wherein the indicator element comprises a second indicator, and wherein the second indicator obscures the first indicator when the indicator element has rotated the first amount in the first direction.

8. An apparatus as in claim 5), wherein the body comprises a first indicator, and wherein the indicator element comprises a second indicator, and wherein the second indicator does not obscure the first indicator when the indicator element has rotated the first amount in the first direction.

9. The apparatus of claim 5, wherein shape memory alloy is chosen from the group consisting of:

Ag—

Cd, Au—

Cd, Cu—

Al—

Ni, Cu—

Sn, In—

Ti, Ni—

Al, Ni—

Ti, Fe—

Mn—

Si, Cu—

Zn-A, Cu—

Al—

Ni alloys thereof, shape memory polymers, polyester prepolymers, and polyurethane.

10. A temperature history indication apparatus, comprising

a) A body;

b) A forcing element mounted with the body;

c) A sensing element comprising a shape memory alloy element having first and second ends, mounted fixedly with the body at the first end, and mounted with the body and the forcing element at the second end in a one-way restraining relationship, wherein the one-way restraining relationship substantially prevents motion of the second end toward the first end once the forcing element has moved the second end a sufficient distance from the first end, and where the forcing element does not supply sufficient force to move the second end the sufficient distance when the shape memory alloy element is in its contracted state; and

d) further comprising a restrainable element mounted with the sensing element, and wherein the body defines a restraining portion adapted to allow motion of the restrainable element therethrough in one direction but not in the other direction once the second end has moved the sufficient distance away from the first end.

11. The apparatus of claim 10, wherein the shape memory alloy element is disposed within the body along a substantially linear path.

12. The apparatus of claim 10, wherein shape memory alloy is chosen from the group consisting of Ag—

Cd, Au—

Cd, Cu—

Al—

Ni, Cu—

Sn, In—

Ti, Ni—

Al, Ni—

Ti, Fe—

Mn—

Si, Cu—

Zn-A, C Cu—

Al—

Ni, alloys thereof, shape memory polymers, polyester prepolymers, and polyurethane.

13. The apparatus of claim 10 wherein the sensing element comprises an indicator that assumes a first state when the second end has moved the sufficient distance, denoted condition a, and assumes a second state when the second end has not moved the sufficient distance, denoted condition b.

14. The apparatus of claim 13 wherein the body comprises a window, and wherein the indicator comprises a region of the sensing element whose appearance through the window when the apparatus is in condition a is distinguishable from its appearance through the window when the apparatus is in condition b.

15. The apparatus of claim 13, wherein the body comprises a signal region, and wherein the indicator obscures the signal region when the apparatus is in one of condition a and condition b, and does not obscure the signal region when the apparatus is in the other condition.

16. A temperature history indication apparatus, comprising:

a) a body, defining a path from an attachment portion thereof to an engagement portion thereof;

b) a sensing element having first and second portions, where the first portion mounts with the attachment portion such that motion of the first portion toward the engagement portion along the path is constrained, and having a temperature responsive element made of a shape memory alloy mounted with the first and second portions such that changes in the temperature responsive element urge motion of the second portion toward the attachment portion along the path;

c) a forcing element, having first and second portions, where the first portion of the forcing element mounts with the second sensing element portion, and where the second portion of the forcing element mounts with the engagement portion of the body;

d) a restraining element mounted with the body such that, when the second portion of the sensing element is in a first position the restraining element substantially prevents motion of the second portion toward the attachment portion;

e) wherein the forcing element is adapted to apply a force to the second sensing element portion having a component of force substantially along the path, wherein the component along the path is sufficient to stretch the temperature responsive element such that the second portion of the sensing element attains the first position when the temperature responsive element is in its Austenitic state but insufficient to stretch the temperature responsive element such that the second portion of the sensing element attains the first position when the temperature responsive element is in its Martensitic state.

17. The apparatus of claim 16, wherein shape memory alloy is chosen from the group consisting of:

Ag—

Cd, Au—

Cd, Cu—

Al—

Ni, Cu—

Sn, In—

Ti, Ni—

Al, Ni—

Ti, Fe—

Mn—

Si, Cu—

Zn-A, Cu—

Al—

Ni, alloys thereof, shape memory polymers, polyester prepolymers, and polyurethane.

18. The apparatus of claim 16, wherein the body has a length greater than 5 cm and less than 15 cm, and wherein the body comprises a first section having a cross-sectional area of less than 27 mm² and a second section wherein temperature-responsive changes in the shape of the shape memory allow are observable.

19. The apparatus of claim 18, wherein the cross-sectional area of the first section changes with distance from the second section, and wherein the cross-sectional area of the first section is at a minimum at its greatest distance from the second section.

20. A method of providing a persistent indication of a temperature history, comprising:

a) Providing a sensing element, comprising a shape memory alloy element having a first length at temperatures below a threshold temperature, contracting to a second length when exposed to a temperature transition from below to above the threshold temperature;

b) Providing a constraining element, mounted with the sensing element such that when the shape memory alloy element is at the first length the constraining element prevents contraction of the shape memory alloy element to the second length;

c) Providing a forcing element, mounted with the sensing element such that the forcing element urges the sensing element to a configuration that engages the constraining element;

d) Then exposing the sensing element to temperatures above the threshold temperature;

e) Then exposing the sensing element to unknown temperatures;

f) Then determining if the sensing element exhibits the first length or the second length, with the sensing element exhibiting the first length corresponding to a temperature history including temperature below the threshold temperature, and the sensing element exhibiting the second length corresponding to a temperature history not including temperature below the threshold temperature.