WO2001016484A2

WO2001016484A2 - A magnetically-assisted shape memory alloy actuator

Info

Publication number: WO2001016484A2
Application number: PCT/IB2000/001729
Authority: WO
Inventors: William P. Taylor
Original assignee: Teledyne Technologies, Inc.
Priority date: 1999-09-02
Filing date: 2000-08-30
Publication date: 2001-03-08
Also published as: AU2210901A; WO2001016484A3; WO2001016484A9

Abstract

An actuator (10) including an SMA member (12), a magnetic material portion (14) connected to the SMA member, and a first magnet (16) in magnetic communication with the magnetic material portion.

Description

A MAGNETICALLY-ASSISTED SHAPE MEMORY ALLOY ACTUATOR

Inventor: William P. Taylor

CROSS-REFERENCE TO RELATED APPLICATIONS Not Applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

Not Applicable.

BACKGROUND OF INVENTION

Field of Invention

The present invention is directed to an actuator and, more particularly, to a

magnetically-assisted shape memory alloy actuator.

Description of the Background

A shape memory alloy (SMA) is a material which has the ability to transition

from a deformed state to a predetermined, or memory, shape when heated. When an

SMA is cold, that is, when the SMA is below its phase transition temperature, it has a very low yield strength and can be deformed into a new shape, which the SMA will retain when below the phase transition temperature. When, however, the material is heated through its phase transition temperature, it undergoes a change in crystal structure which

causes it to revert forcefully to its original shape imposed on it during annealing.

SMA materials are advantageous for use in micromachined actuators, also called

microactuators, for several reasons. First, SMA actuating devices can provide an energy

density much greater than other actuating mechanisms. That is, SMA actuators provide a

relatively large force in a relatively small three-dimensional space. Second, SMA

microactuators provide the potential to be fabricated using microelectromechanical

systems (MEMS) fabrication techniques, such as photolithography and selective etching,

as well as according to conventional microelectronic and laminate-based fabrication

methods. Third, SMA actuators may be incorporated on a substrate with electronic

circuitry to share the same power supply as the circuitry.

Relevant art SMA microactuators typically use electrical current or heat resistors

to heat the SMA above its phase transition temperature. Typical relevant art SMA

microactuators employ a biasing spring to bias the SMA in its deformed shape when the

SMA is below it phase transition temperature. The relevant art also discloses the use of a

pressurized fluid at a static pressure to exert a biasing force on the SMA. These biasing

methods are not, however, ideal for batch fabrication of MEMS devices. Rather, the

biasing springs and fluids must be incorporated into the microactuators on an individual

basis, thereby increasing overall fabrication costs of the devices. Accordingly, there exists a need in the relevant art for a SMA microactuator in which the biasing member of the microactuator is capable of fabrication using batch fabrication techniques.

SUMMARY OF THE INVENTION

The present invention is directed to an actuator. The actuator includes an SMA

member, a magnetic material portion connected to the SMA member, and a first magnet

in magnetic communication with the magnetic material portion. According to another

embodiment of the present invention, the actuator includes a second magnet in magnetic communication with the magnetic material portion.

In another embodiment, the present invention is directed to a relay. The relay

includes a substrate, a fixed contact connected to the substrate, a magnetically-assisted

SMA actuator connected to the substrate, and a moving contact connected to the

magnetically-assisted SMA actuator and coupled to the fixed contact when the

magnetically-assisted SMA actuator is in one of an actuated position and a non-actuated

position and not coupled to the fixed contact when the magnetically-assisted SMA

actuator is in another of the actuated position and the non-actuated position.

In another embodiment, the present invention is directed to a valve. The valve

includes a surface defining an opening therethrough and a magnetically-assisted SMA

actuator connected to the surface and having a portion engaged with the surface and

covering the opening when the magnetically-assisted SMA actuator is in one of an

actuated position and a non-actuated position and not engaged with the surface and not covering the opening when the magnetically-assisted SMA actuator is in another of the actuated position and the non-actuated position.

In another embodiment, the present invention is directed to a method of biasing an SMA actuator. The method includes cooling the SMA member to a martensitic phase

and exerting a magnetic force on a magnetic material portion connected to the SMA

member.

In another embodiment, the present invention is directed to a method of switching

a relay having a first contact and a second contact. The method includes connecting the

first contact to an SMA member, transitioning the SMA member between a martensitic

phase and a parent austenitic phase, and biasing the SMA member with a magnetic force

when the SMA member is in the martensitic phase such that the first contact engages the

second contact when the SMA member is in one of the martensitic phase and the parent

austenitic phase and does not engage the second contact when the SMA member is in

another of the martensitic phase and the parent austenitic phase.

In another embodiment, the present invention is directed to a method of operating

a valve having an opening defined by a surface. The method includes transitioning an

SMA member between a martensitic phase and a parent austenitic phase, and biasing the

SMA member with a magnetic force when the SMA member is in the martensitic phase

such that the SMA member engages the surface and covers the opening when the SMA

member is in one of the martensitic phase and the parent austenitic phase and does not

engage the surface and does not cover the opening when the SMA member is in another of the martensitic phase and the parent austenitic phase. The present invention represents an advancement over relevant actuators in that an actuator according to the present invention may be formed using batch fabrication techniques. These and other advantages and benefits of the present invention will become apparent from the Detailed Description of the Invention hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

For the present invention to be clearly understood and readily practiced, the

present invention will be described in conjunction with the following figures, wherein:

Fig. 1 is a combination cross-sectional side-view and block diagram illustrating a

microactuator in the "OFF" position according to the present invention;

Fig. 2 is a combination cross-sectional side-view and block diagram illustrating

the microactuator of Fig. 1 in the "ON" position;

Fig. 3 is a cross-sectional side-view of a microactuator according to another

embodiment of the present invention in the "OFF" position;

Fig. 4 is a cross-sectional side-view of the microactuator of Fig. 3 in the "ON"

position;

Fig. 5 is a combination cross-sectional side-view and block diagram illustrating a

microactuator according to another embodiment of the present invention in the "OFF"

position;

Fig. 6 is a combination cross-sectional side-view and block diagram illustrating

the microactuator of Fig. 5 in the "ON" position; Fig. 7 is a cross-sectional side-view of a microrelay according to the present invention in the "CLOSED" position;

Fig. 8 is a cross-sectional side-view of the microrelay of Fig. 7 in the "OPEN"

position;

Fig. 9 is a cross-sectional side-view of a microrelay according to another

embodiment of the present invention in the "CLOSED" position;

Fig. 10 is a cross-sectional side-view of the microrelay of Fig. 9 in the "OPEN"

position;

Fig. 11 is a cross-sectional side-view of a microrelay according to another

embodiment of the present invention in the "CLOSED" position;

Fig. 12 is a cross-sectional side-view of the microrelay of Fig. 11 in the "OPEN"

position;

Fig. 13 is a cross-sectional side-view of a microvalve according to the present

invention in the "CLOSED" position;

Fig. 14 is a cross-sectional side-view of the microvalve of Fig. 13 in the "OPEN"

position;

Fig. 15 is a cross-sectional side-view of a microvalve according to another

embodiment of the present invention in the "CLOSED" position;

Fig. 16 is a cross-sectional side-view of the microvalve of Fig. 15 in the "OPEN"

position;

Fig. 17 is a cross-sectional side-view of a microvalve according to another

embodiment of the present invention in the "OPEN" position; and Fig. 18 is a top-view of the microvalve of Fig. 17.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that the figures and descriptions of the present invention

have been simplified to illustrate elements that are relevant for a clear understanding of

the present invention, while eliminating, for purposes of clarity, other elements found in a

typical actuator. Those of ordinary skill in the art will recognize that other elements may

be desirable. However, because such elements are well known in the art, and because

they do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein.

Figs. 1 and 2 illustrate a microactuator 10 according to the present invention in the

"OFF" (or non-actuated) and the "ON" (or actuated) positions, respectively. The

microactuator 10 includes a member 12, a magnetic material portion 14, a first magnet

16, a power control 18, a power source 20, and a switch 22. In the "OFF" position, the

magnetic material portion 14 is separated from the first magnet 16 by a distance d,, and in

the "ON" position the distance between the magnetic material portion 14 and the first

magnet 16 is increased to a distance represented by d₂. The microactuator 10 transitions

from the "OFF" position to the "ON" position by heating the member 12. The

microactuator 10 of the present invention may be used in any device requiring remote

actuation, such as, for example, relays, valves, and pumps. The present invention will be

described herein for use in a microactuator, although the benefits of the present invention

may be realized in other applications, such as macroscale actuators. The member 12 is constructed of a shape memory alloy (SMA) such as, for example, titanium nickel (TiNi) or any other joule-effect alloy. A shape memory alloy

material undergoes a thermoelastic phase transformation in passing from a martensitic

phase when at a temperature below the material's phase change temperature to a parent

austenitic phase in a memory shape when heated through its phase change temperature

range. To realize a mechanical translation of such a phase transformation, a particular

mechanical configuration, or memory shape, may be imposed on a SMA at an annealing

temperature, Ta. Below some lower temperature, To, the alloy possesses a particular

crystalline structure, which allows the material to be easily deformed into an arbitrary

shape. The SMA material remains deformed until heated above a temperature Te, where

To < Te < Ta, at which point the SMA undergoes a change in crystalline structure, and

the material forcefully reverts to the memory shape imposed on it during annealing. The

phase change temperature range over which the phase transition occurs is defined as

being To to Te.

To achieve remote actuation using an SMA, the SMA member 12 is deformed

when in its martensitic phase by a biasing force, and then heated through its phase change

temperature range to its parent austenitic phase, causing the SMA member 12 to revert to

its memory shape. According to one embodiment of the present invention, the SMA

member 12 is biased in its deformed shape by the magnetic attraction between the

magnetic material portion 14 and the first magnet 16. The magnetic material portion 14

is attached to a surface of the SMA member 12, and may be, for example, a "soft"

magnetic material such as, for example, nickel iron, nickel, or nickel iron molybdenum. For an embodiment in which the magnetic material portion 14 is a soft magnetic material, the magnetic material portion 14 may also be soft ferrites such as, for example, nickel- zinc or manganese-zinc ferrites. As described hereinbelow in conjunctioawith other embodiments of the present invention, the magnetic material portion 14 may also be a

"hard", or permanent, magnetic material such as, for example, AlNiCo, NdFeB, SmCo,

hard ferrites such as, for example, strontium ferrite, or hard magnetic polymer

composites. According other embodiments of the present invention, the magnetic

material portion 14 may also include an electromagnet. In yet other embodiments of the

present invention, if the SMA member 12 is formed from a magnetic material, the SMA

member 12 and the magnetic portion 14 may be integrated.

According to one embodiment of the present invention, the first magnet 16 and

magnetic material portion 14 are oppositely polarized, and the first magnet 16 is located

relative to the magnetic material portion 14 such that there exists a magnetic attraction

between the magnetic material portion 14 and the first magnet 16. The first magnet 16

may be, for example, a hard, or permanent, magnet or an electromagnet. For an

embodiment in which the first magnet 16 is a permanent magnet, the first magnet 16 may

be constructed of, for example, AlNiCo, NdFeB, SmCo, hard ferrites such as, for

example, strontium ferrite, or hard magnetic polymer composites.

The SMA member 12 may be heated, for example, using electrical current or

resistive heaters. Figs, land 2 illustrate an embodiment of the present invention using electrical current to heat the SMA member 12. The power control 18 modulates the

current flow from the power source 20 to control the heating rate of the SMA member 12, and may be connected to a processor or other control circuit (not shown). The switch 22 controls whether electrical power is supplied to the SMA member 12. The switch 22 may be eliminated if its function is, for example, performed by the power controller 18.

Figs. 3 and 4 illustrate another embodiment of the present invention in which the

SMA member 12 is heated by resistive heaters 24. According to one embodiment of the

present invention, the microactuator 10 illustrated in Figs. 3 and 4 are in the "OFF" (i.e.,

non-actuated) and the "ON" (i.e., actuated) positions, respectively. That is, in Fig. 3 the

SMA member 12 is in its martensitic phase and in its deformed shape, and in Fig. 4 the

SMA member 12 is in its parent austenitic phase and in its memory shape. The illustrated

embodiment includes an insulating layer 26 constructed of, for example, polymers, such

as polyimide. The resistive heaters 24 may be patterned on the insulating layer 26 using,

for example, conventional microfabrication techniques, such as photolithography and

selective etching. In an alternative embodiment, the heaters 24 may be patterned directly

on to the SMA member 12. In addition, the illustrated embodiment includes two resistive

heaters 24, although more or less resistive heaters 24 may also be employed.

The operation of the microactuator 10 will now be described with reference to

Figs. 1 and 2. In Fig. 1, the switch 22 is open, causing no electrical power to be supplied

to the SMA member 12, causing the SMA member 12 to be at an ambient temperature

below its phase change transition temperature. In the martensitic phase, the SMA

member 12 is biased into its deformed state by the magnetic attraction between the

magnetic material portion 14 and the first magnet 16, which are separated by distance d,.

This corresponds to the "OFF" or non-actuated position of the microactuator 10. Subsequently, the switch 22 is closed, as illustrated in Fig. 2, causing electrical current to flow through the SMA member 12 and heat the SMA member 12 through it phase change temperature range, causing the SMA member 12 to revert to its memory shape with a

force great enough to overcome the attractive force of the first magnet 16, thereby pulling

the magnetic material portion 14 away from the first magnet 16 to the distance d₂. This

corresponds to the "ON" or actuated position of the microactuator 10. When the switch

22 is re-opened, the SMA member 12 cools below its phase change temperature, and in

its martensitic phase is again biased into its deformed shape by first magnet 16 as

illustrated in Fig. 1.

In another embodiment of the present invention, the SMA member 12 is annealed

such that its memory shape is that illustrated in Fig. 1, in which case Fig. 1 represents the

"ON" position and Fig. 2 illustrates the "OFF" position. (Note that for such an

embodiment, the switch 22 is closed in Fig. 1 and open in Fig. 2.) According to such an

embodiment, the SMA member 12 assumes the memory shape illustrated in Fig. 1 when

it is heated above its phase change temperature range, i.e., when the switch 22 is closed.

For this embodiment, the magnetic material portion 14 and the first magnet 16 are both

hard magnetic materials and like polarized such that a repulsive force exists between the

two. Once the power is removed from the SMA member 12 and it cools below its phase

change temperature, it is biased into its deformed shape, as illustrated in Fig. 2, by the

repulsive force between the first magnet 16 and magnetic material portion 14.

Utilizing a magnetic biasing force permits the microactuator 10 of the present

invention to be batch fabricated using conventional MEMS fabrication techniques, such as photolithography, selective etching, and screen printing. The present invention may be fabricated by forming thin films on a substrate using conventional microfabrication techniques, including sputtering of an SMA film to form the SMA member 12. In the

present invention, the first magnet 16 may also be formed using conventional MEMS

fabrication techniques, such as photolithography, selective etching, and screen printing.

Thus, the microactuator 10 according to the present invention may be fabricated using

exclusively batch fabrication techniques. In addition, the microactuator 10 of the present

invention may be formed using, for example, conventional microelectronic fabrication techniques and laminate-based fabrication techniques.

The operation of the microactuator 10 using resistive heaters 24 to heat the SMA

member 12, as illustrated in Figs. 3 and 4, is analogous to the operation described

hereinabove with respect to Figs. L and 2. Using resistive heaters 24, when power is

supplied to the heaters 24, the SMA member 12 is heated by the resistive heaters 24

through its phase change temperature range into its memory shape, as illustrated in Fig. 4,

corresponding to the "ON" or actuated position. When no power is supplied to the

heaters 24, the SMA member 12 cools, and the magnetic attraction between the first

magnet 16 and the magnetic material portion 14 biases the SMA member 12 to its

deformed shape as illustrated in Fig. 3, which corresponds to the "OFF" or non-actuated

position.

In an alternative embodiment of the present invention, the SMA member 12 is

annealed such that its deformed shape is that illustrated in Fig. 4. The SMA member 12

is biased to the deformed shape illustrated in Fig. 4 by a repulsive force between the magnetic material portion 14 and the first magnet 16. A repulsive force between the magnetic material portion 14 and the first magnet 16 may be realized where the two are

like polarized, as discussed hereinbefore. According to this embodiment, the "ON"

position is illustrated in Fig. 3 and the "OFF" position is illustrated in Fig. 4.

Figs. 5 and 6 illustrate the microactuator 10 in the "OFF" (i.e., non-actuated) and

"ON" (i.e., actuated) positions respectively according to another embodiment of the

present invention. The microactuator 10 illustrated in Figs. 5 and 6 includes a second

magnet 28, which may be, for example, an electromagnet, such as an electromagnetic

coil. For the illustrated embodiment, the second magnet 28 is located below the first

magnet 16 in relation to the position of the SMA member 12. Alternatively, the first

magnet 16 may be below the second magnet 28 or interleaved with the electromagnetic

coil comprising the second magnet 28. The second magnet 28 may be formed using, for

example, conventional MEMS batch fabrication techniques, microelectronic fabrication

techniques, or laminate-based fabrication techniques.

The magnetic flux force of the second magnet 28 may be oriented to aid or oppose

the magnetic force of the first magnet 16. For example, if the distance d₂ in Fig. 6 is so

great that the magnetic attraction between the magnetic material portion 14 and the first

magnet 16 is not sufficient to deform the SMA member 12 when the member 12 is in its

martensitic phase, the magnetic force of second magnet 28 may be oriented to aid the

magnetic force of the first magnet 16. In combination, the net flux forces of the first

magnet 16 and the second magnet 28 attract the magnetic material portion 14, thereby

biasing the SMA member 12 in its deformed shape. Thereafter, the second magnet 28 may be turned off if the attractive force of the first magnet 16 is sufficiently strong to hold the SMA member 12 at the distance d,. Alternatively, if the attractive force of the first magnet 16 is so great that the SMA member 12 cannot overcome the force of the

first magnet 16 to revert to its memory shape when heated above its phase change

temperature range, the magnetic force of the second magnet 28 may be oriented to oppose

the magnetic force of the first magnet 16. In this embodiment, when the second magnet

28 is energized the attractive force of the first magnet 16 may be effectively canceled,

thereby allowing the SMA member 12 to revert to its memory shape. Thereafter, the second magnet 28 may be turned off.

In another embodiment of the microactuator 10 of the present invention, Fig. 5

illustrates the "ON" (i.e., actuated) position and Fig. 6 illustrates the "OFF" (i.e., non-

actuated) position. According to this embodiment, as discussed hereinbefore, the first

magnet 16 and magnetic material portion 14 are like polarized such that a repulsive

magnetic force exists between the two.

The present invention is also directed to a microrelay employing a magnetically-

assisted SMA microactuator. Figs. 7 and 8 illustrate a microrelay 40 according to one

embodiment the present invention in "CLOSED" and "OPEN" states respectively. The

microrelay 40 is formed on a substrate 42. The substrate 42, which is the lowest layer of

material and any additional or intervening layers or structures formed thereon, may be of

any material on which the microrelay 40 is constructed. The substrate 42 may include a semiconductor material such as, for example, silicon, GaAs, or SiGe, or a non¬

conducting material such as, for example, ceramic, glass, printed circuit board, alumina, or other materials, such as may be used for silicon-on-insulator semiconductor devices. The actuating components of the microrelay 40 include the SMA member 12, the magnetic material portion 14, and the first magnet 16. The microrelay 40 includes a

moving contact 44 and a pair of fixed contacts 46. The contacts 44, 46 may be any

conducting material which ensures reliable switching such as, for example, plated or

sputtered gold metal alloy, silver, platinum, ruthenium, rhodium, or combinations thereof.

An insulator 48 may be provided between the first magnet 16 and the fixed contacts 46.

The insulator 48 may be, for example, silicon nitride, silicon dioxide, glass, air, or

polymers such as, for example, polyimide. The microrelay 40 further includes a support

50 to support the SMA member 12. The support 50 is of sufficient mechanical structure

to support the SMA member 12, and may be constructed of, for example, metal, ceramic,

or polymer. The microrelay 40 may be constructed using, for example, conventional

microfabrication techniques, conventional microelectronic fabrication techniques, and laminate-based fabrication techniques.

According to one embodiment of the present invention, in operation, when the

SMA member 12 is in its martensitic phase, the attractive magnetic force between the

first magnet 16 and the magnetic material portion 14 biases the SMA member 12 into its

deformed shape, thereby causing the moving contact 44 to be in electrical contact with

the fixed contacts 46, as illustrated in Fig. 7, allowing electrical current to flow between

the fixed contacts 46 via the moving contact 44. When the SMA member 12 is heated to

its parent austenitic phase, the member 12 forcefully reverts to its memory shape, as

illustrated in Fig. 8, thereby pulling the moving contact 44 away from the fixed contacts 46 and breaking the electrical connection between the contacts 44, 46. The SMA member 12 may be heated by, for example, electrical current flowing through the member 12 or resistive heaters in close proximity to the member 12, as described hereinbefore with respect to Figs. 1-4.

In another embodiment of the present invention, the SMA member 12 illustrated

in Fig. 7 is in its parent austenitic phase and in its martensitic phase in Fig. 8. According

to this embodiment, as described hereinbefore, the SMA member 12 is biased by a

repulsive magnetic force between the magnetic material portion 14 and the first magnet

16. For such an embodiment, the magnetic material portion 14 may be fabricated as a

hard magnetic material on a first substrate and the first magnet 16 as a hard magnet on a

second substrate, wherein the two are like polarized. Thereafter, the first and second

substrates may be bonded together using conventional wafer bonding techniques to form

the microrelay 40.

Figs. 9 and 10 illustrate another embodiment of a microrelay 40 according to the

present invention. The microrelay 40 illustrated in Figs. 9 and 10 includes a

microactuator as described with respect to Figs. 5 and 6, having a second magnet 28 such

as, for example, an electromagnet. The first magnet 16 may be positioned, for example,

above the second magnet 28 in relation to the position of the SMA member 12, as

illustrated in Figs. 9 and 10. Alternatively, the first magnet 16 may be below the second

magnet 28 or interleaved with the second magnet 28. The magnetic force of the second

magnet 28 may be oriented to aid or oppose the magnetic force of the first magnet 16, as

described hereinbefore. The second magnet 28 may be formed on the substrate 42 using, for example, conventional MEMS fabrication techniques, conventional microelectronic fabrication techniques, or laminate-based fabrication techniques.

In another embodiment of the present invention, the SMA member 12 illustrated

in Fig. 9 is in its parent austenitic phase and in its martensitic phase in Fig. 10.

According to this embodiment, as described hereinbefore, the SMA member 12 is biased

by a repulsive magnetic force between the magnetic material portion 14 and the first

magnet 16.

In another embodiment of the present invention, as illustrated in Figs. 11 and 12,

an upper moving contact 52 is provided on the upper surface of the SMA member 12, and

two upper fixed contacts 54 are provided above the SMA member 12. For this

embodiment, the upper moving contact 52 is in contact with the upper fixed contacts 54

when the SMA member 12 is heated above its phase change temperature range to its

memory shape.

In another embodiment of the microrelay 40 according to the present invention,

the SMA member 12 illustrated in Fig. 11 is in its austenitic phase, and in Fig. 12 it is in

its martensitic phase. According to this embodiment, as described hereinbefore, the SMA

member 12 is biased by a repulsive force between the first magnet 16 and magnetic

material portion 14.

In other embodiments of the microrelay 40 according to the present invention,

various numbers of moving contacts 44 and fixed contacts 46 may be employed such as,

for example, one moving contact 44 and one fixed contact 46. In addition, alternative

embodiments of the present invention contemplate the use of various numbers of upper contacts 52, 54, such as, for example, one upper moving contact 52 and one upper fixed contact 54. In further embodiments of the present invention, the moving contacts may be integrated with the SMA member 12.

The present invention is also directed to a microvalve 60 employing a

magnetically-assisted SMA microactuator. According to one embodiment of the present

invention, Figs. 13 and 14 illustrate a microvalve 60 in the "CLOSED" and "OPEN"

positions respectively. The microvalve 60 is formed on the substrate 42. The microvalve

60 includes a number of ports 62, 63 defining openings in the substrate through which

gas or fluid may enter and exit the microvalve 60. For example, in the illustrated

embodiment, fluid or gas may enter the microvalve 60 through opening 62 and exit via

opening 63. The openings 62 and 63 may be formed using, for example, conventional

MEMS fabrication techniques including, for example, anisotropic etching of a silicon

substrate, etching of a glass substrate, and pre-formed holes cast in an alumina substrate.

The microvalve 60 may further include a seal 64, to better prevent gases and fluids from

entering when the microvalve 60 is closed. The seal 64 may be constructed of, for

example, metal or polymer such as, for example, polyimide. The first magnet 16 may

include, for example, a ring of permanent magnet material around the opening 62, as

illustrated in Figs. 13 and 14. In an alternative embodiment of the present invention

illustrated in Figs. 15 and 16, the first magnet 16 comprises a number of small bar

magnets 66 oriented around the opening 62. The microvalve 60 may be formed on the

substrate 42 using, for example, conventional microfabrication techniques, conventional

microelectronic fabrication techniques, or laminate-based fabrication techniques. According to one embodiment of the present invention, in operation, when the SMA member 12 is in its martensitic phase, the first magnet 16 biases the SMA member 12 to its deformed state, thereby causing the SMA member 12 to engage the seal 64 and

cover the opening 62, as illustrated in Fig. 13. When the SMA member 12 is heated

through its phase change temperature range by, for example, passing electrical current

through the SMA member 12 or heating the SMA member 12 with resistive heaters, as

described hereinbefore with respect to Figs. 1 -4, the SMA member transitions to its

parent austenitic phase and forcefully reverts to its memory shape, thereby opening the

microvalve 60, as illustrated in Fig. 14. Once the heat is removed, the SMA member 12

cools, allowing it to be biased by the magnetic attraction between the first magnet 16 and

the magnetic material portion 14. An advantage of this type of microvalve 60 is that if

the fluid flow is too great when the valve is in the open position, the fluid may cool the

SMA member 12 below its phase change transition temperature range, thereby causing

the SMA member 12 to be biased in its deformed state and closing the valve 60. In an

alternative embodiment, the SMA member 12 is biased by a repulsive force between the

magnetic material portion 14 and the first magnet 16, as described hereinbefore, such that

the SMA member 12 illustrated in Fig. 13 is in its austenitic phase and in its martensitic

phase in Fig. 14.

Figs. 17 and 18 illustrate a microvalve 60 according to another embodiment of the

present invention. According to the embodiment illustrated in Figs. 17 and 18, the

microvalve 60 includes one opening 62. The SMA member 12 is patterned to include a

number of arms 70 supported by the support 50. The microvalve 60 illustrated in Figs. 17 and 18 includes four arms 70, although in other embodiments of the present invention a different number of arms 70 may be employed. According to this embodiment, when the SMA member 12 is not engaged with the seal 64, gas may enter the microvalve 60 through the opening 62 and flow, as illustrated by arrow A and A' in Fig. 17, around the

arms 70 of the SMA member 12 to exit the microvalve 60 at the top. For the illustrated

embodiment of Figs. 17 and 18, the first magnet 16 includes a ring of magnetic material

oriented around the opening 62. In another embodiments, the first magnet may include,

for example, a number of bar magnets oriented around the opening 62, as described hereinbefore with respect to Figs. 15 and 16.

Those of ordinary skill in the art will recognize that many modifications and

variations of the present invention may be implemented. For example, other materials and

processes may also be used to make devices embodying the present invention.

Furthermore, the materials and processes disclosed are illustrative, but are not exhaustive.

In addition, the described sequences of operating and manufacturing the devices

described herein may also be varied. The foregoing description and the following claims

are intended to cover all such modifications and variations.

Claims

CLAIMSWhat is claimed is:

1. An actuator, comprising

an SMA member;

a magnetic material portion connected to the SMA member; and

a first magnet in magnetic communication with the magnetic material portion.

2. The actuator of claim 1, wherein the magnetic material portion is selected

from the group consisting of soft magnetic material and hard magnetic material.

3. The actuator of claim 1, wherein the magnetic material portion includes an

electromagnet.

4. The actuator of claim 1 , wherein the first magnet is selected from the

group consisting of a permanent magnet and an electromagnet.

5. The actuator of claim 1, wherein the magnetic material portion and the

first magnet are like polarized.

6. The actuator of claim 1, wherein the magnetic material portion and the

first magnet are oppositely polarized.

7. The actuator of claim 1 , further comprising a second magnet in magnetic communication with the magnetic material portion.

8. The actuator of claim 7, wherein the first magnet is selected from the

group consisting of a permanent magnet and an electromagnet and the second magnet is

an electromagnet.

9. The actuator of claim 7, wherein a magnetic force of the first magnet and a

magnetic force of the second magnet are oriented in a same direction.

10. The actuator of claim 7, wherein a magnetic force of the first magnet and a

magnetic force of the second magnet are oriented in an- opposite direction.

1 1. The actuator of claim 1 , wherein the SMA member includes nickel

titanium.

12. An actuator, comprising:

an SMA member; and

means for biasing the SMA member with a magnetic force when the SMA

member is in a martensitic phase.

2?

13. The actuator of claim 12, further comprising means for transitioning the

SMA member between the martensitic phase and a parent austenitic phase..

14. A relay, comprising:

a substrate;

a fixed contact connected to the substrate;

a magnetically-assisted SMA actuator connected to the substrate; and

a moving contact connected to the magnetically-assisted SMA actuator and

coupled to the fixed contact when the magnetically-assisted SMA actuator is in one of an

actuated position and a non-actuated position and not coupled to the fixed contact when

the magnetically-assisted SMA actuator is in another of the actuated position and the non-

actuated position.

15. The relay of claim 14, wherein the moving contact is coupled to the fixed

contact when the magnetically-assisted SMA actuator is in the non-actuated position and

not coupled to the fixed contact when the magnetically-assisted SMA actuator is in the

actuated position.

16. The relay of the claim 14, wherein the moving contact is coupled to the

fixed contact when the magnetically-assisted SMA actuator is in the actuated position and not coupled to the fixed contact when the magnetically-assisted SMA actuator is in the non-actuated position.

17. The relay of claim 14, wherein the moving contact includes at least one

moving contact connected to the magnetically-assisted SMA actuator.

18. The relay of claim 17, wherein the fixed contact includes at least one fixed

contact connected to the substrate.

19. The relay of claim 14, wherein the magnetically-assisted SMA actuator

includes:

an SMA member;

a magnetic material portion connected to the SMA member; and

a first magnet in magnetic communication with the magnetic material portion.

20. The relay of claim 19, wherein the first magnet is connected to the

substrate.

21. The relay of claim 19, wherein the magnetically-assisted SMA actuator

further comprises a second magnet in magnetic communication with the magnetic

material portion.

22. The relay of claim 21 , wherein the second magnet is an electromagnet.

23. The relay of claim 21 , wherein the first magnet and the second magnet are

connected to the substrate.

24. The relay of claim 14, further comprising:

an upper moving contact connected to the magnetically-assisted SMA actuator;

and an upper fixed coupled to the upper moving contact when the magnetically-

assisted SMA actuator is in one of the actuated position and the non-actuated position and

not coupled to the upper moving contact when the magnetically-assisted SMA actuator is

in another of the actuated position and the non-actuated position.

25. A valve, comprising:

a surface defining an opening therethrough; and

a magnetically-assisted SMA actuator connected to the surface and having a

portion engaged with the surface and covering the opening when the magnetically-

assisted SMA actuator is in one of an actuated position and a non-actuated position and

not engaged with the surface not covering the opening when the magnetically-assisted

SMA actuator is in another of the actuated position and non-actuated position.

26. The valve of claim 25, wherein the portion of the magnetically-assisted SMA actuator is engaged with the surface and covering the opening when the

magnetically-assisted SMA actuator is in the non-actuated position and not engaged with

the surface and not covering the opening when the magnetically-assisted SMA actuator is

in the actuated position.

27. The valve of claim 25, wherein the portion of the magnetically-assisted

SMA actuator is engaged with the surface and covering the opening when the

magnetically-assisted SMA actuator is in the actuated position and not engaged with the

surface and not covering the opening when the magnetically-assisted SMA actuator is in

the non-actuated position.

28. The valve of claim 25, wherein the surface includes a substrate and a seal

connected to the substrate around the opening.

29. The valve of claim 25, wherein the magnetically-assisted SMA actuator

comprises: an SMA member;

a magnetic material portion connected to the SMA member: and

a first magnet connected in magnetic communication with the magnetic material

portion.

30. The valve of claim 25, wherein the first magnet is connected to the

surface.

31. The valve of claim 29, wherein the portion of the magnetically-assisted

SMA actuator engaged with the surface and covering the opening when the magnetically-

assisted SMA actuator is in one of the actuated position and the non-actuated position

includes the SMA member.

32. The valve of claim 29, wherein the first magnet includes a magnetic ring

around the opening.

33. The valve of claim 29, wherein the first magnet includes a plurality of

magnets oriented around the opening.

34. A method of biasing an SMA member, comprising:

cooling the SMA member to a martensitic phase; and

exerting a magnetic force on a magnetic material portion connected to the SMA

member.

35. The method of claim 34, wherein exerting a magnetic force includes exerting an attractive magnetic force on the magnetic material portion connected to the

SMA member.

36. The method of claim 34, wherein exerting a magnetic force includes

exerting a repulsive magnetic force on the magnetic material portion connected to the

SMA member.

37. The method of claim 34, further comprising heating the SMA member to a

parent austenitic phase.

38. The method of claim 37, wherein heating the SMA member includes

conducting electric current in the SMA member.

39. The method of claim 37, wherein heating the SMA member includes

heating a device in thermal communication with the SMA member.

40. A method of switching a relay having a first contact and a second contact,

comprising:

connecting the first contact to an SMA member;

transitioning the SMA member between a martensitic phase and a parent

austenitic phase; and biasing the SMA member with a magnetic force when the SMA member is in the martensitic phase such that the first contact engages the second contact when the SMA

engage the second contact when the SMA member is in another of the martensitic phase

and the parent austenitic phase.

41. The method of claim 40, wherein biasing the SMA member includes

biasing the SMA member with a magnetic force such that the first contact engages the

second contact when the SMA member is in the martensitic phase and does not engage

the second contact when the SMA member is in the parent austenitic phase.

42. The method of claim 40, wherein biasing the SMA member includes

second contact when the SMA member is in the parent austenitic phase and does not

engage the second contact when the SMA member is in the martensitic phase.

43. The method of claim 40, wherein biasing the SMA member with a

magnetic force includes biasing the SMA member with a magnet having an attractive

magnetic force between the magnet and a magnetic material portion connected to the

SMA member.

44. The method of claim 40, wherein biasing the SMA member with a magnetic force includes biasing the SMA member with a magnet having a repulsive magnetic force between the magnet and a magnetic material portion connected to the

SMA member.

45. A method of operating a valve having an opening defined by a surface,

comprising: transitioning an SMA member between a martensitic phase and a parent austenitic

phase; and biasing the SMA member with a magnetic force when the SMA member is in the

martensitic phase such that the SMA member engages the surface and covers the opening

when the SMA member is in one of the martensitic phase and the parent austenitic phase

and does not engage the surface and does not cover the opening when the SMA member

is in another of the martensitic phase and the parent austenitic phase.

46. The method of claim 45, wherein biasing the SMA member includes

biasing the SMA member such that the SMA member engages the surface and covers the

opening when the SMA member is in the martensitic phase and does not engage the

surface and does not cover the opening when the SMA member is in the parent austenitic

phase.

47. The method of claim 45, wherein biasing the SMA member includes biasing the SMA member such that the SMA member engages the surface and covers the

opening when the SMA member is in the parent austenitic phase and does not engage the

surface and does not cover the opening when the SMA member is in the martensitic

phase.