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WO2002071504A1 - Dispositifs piézo-électriques à cisaillement - Google Patents

Dispositifs piézo-électriques à cisaillement Download PDF

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Publication number
WO2002071504A1
WO2002071504A1 PCT/GB2002/001003 GB0201003W WO02071504A1 WO 2002071504 A1 WO2002071504 A1 WO 2002071504A1 GB 0201003 W GB0201003 W GB 0201003W WO 02071504 A1 WO02071504 A1 WO 02071504A1
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WIPO (PCT)
Prior art keywords
portions
electrodes
activation
active
piezoelectric
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PCT/GB2002/001003
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English (en)
Inventor
Mark Richard Shepherd
Ursula Ruth Lenel
Gareth Mckevitt
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1 Ltd
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1 Ltd
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Priority to GB0322650A priority Critical patent/GB2391109B/en
Publication of WO2002071504A1 publication Critical patent/WO2002071504A1/fr
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/20—Piezoelectric or electrostrictive devices with electrical input and mechanical output, e.g. functioning as actuators or vibrators
    • H10N30/208—Piezoelectric or electrostrictive devices with electrical input and mechanical output, e.g. functioning as actuators or vibrators using shear or torsion displacement, e.g. d15 type devices
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/01—Manufacture or treatment
    • H10N30/08—Shaping or machining of piezoelectric or electrostrictive bodies
    • H10N30/085—Shaping or machining of piezoelectric or electrostrictive bodies by machining
    • H10N30/088—Shaping or machining of piezoelectric or electrostrictive bodies by machining by cutting or dicing

Definitions

  • This invention relates to piezoelectric devices comprising a plurality of piezoelectric elements operable in shear mode coupled together to combine the relative displacements created on activation of each element.
  • Piezoelectric material deforms in response to an applied electric field and vice versa.
  • a member of piezoelectric material is provided with a pair of electrodes on opposed surfaces for creating an electric field on activation by application of an activation voltage across the electrodes.
  • the type of deformation depends on the direction of polarization of the piezoelectric material, relative to the direction of the applied electric field.
  • the piezoelectric material may be activated in shear mode, in which case the deformation of the piezoelectric material is a shear, by using an electric field with a direction perpendicular to the polarization direction.
  • the deformation of a single member of piezoelectric material on activation is relatively small.
  • EP-A-0,565,883 proposes a device comprising a plurality of piezoelectric elements operable in shear mode. The elements are coupled together in series by electrodes extending between adjacent piezoelectric elements, to combine the relative displacement created by the shear of each element on activation. Accordingly, the overall relative displacement created by the device is a multiple of the displacement created by the shear of each element. Thus large displacements may be achieved.
  • a piezoelectric device comprising a plurality of piezoelectric elements coupled together, each piezoelectric element comprising a unitary member of piezoelectric material having a plurality of portions including at least one active portion and at least one further portion, the at least one active portion having a pair of electrodes on opposed surfaces for creating an electric field therebetween on activation by application of an activation voltage across the electrodes and having a polarisation direction for activation in shear mode to create relative displacement between two coupling portions of the member, wherein the piezoelectric elements are coupled together by said coupling portions in series to combine the relative displacement created by each element on activation.
  • Such a piezoelectric device is easier to manufacture than the device proposed in EP-A-0,565,883.
  • the piezoelectric device has a construction in which the members of piezoelectric material are coupled together directly by coupling portions of the same unitary member as is operable in shear mode to create the relative displacement.
  • it is not necessary to interpose any additional components between the members of piezoelectric material such as the electrodes in the device proposed in EP-A-0,565,883.
  • this makes it easier both to arrange the individual piezoelectric elements into the desired arrangement and to couple the piezoelectric elements together.
  • the present invention allows the device to have a simple arrangement which eases manufacture.
  • the elements are planar and arranged in a stack with the elements extending parallel to one another.
  • the individual elements, including the coupling portions because the coupling portions which couple the elements together are portions of unitary member of piezoelectric material which also has portions operable in shear mode to create the relative displacement.
  • the displacement of piezoelectric elements is combined together, a large total displacement on activation may be achieved on activation. Any desired displacement may be achieved simply by providing the device with an appropriate number of elements.
  • the individual piezoelectric elements may be formed in a variety of different shapes and arrangements of active and/or inactive portions, provided that at least one active portion is operable in shear mode to create relative displacement between the coupling portions.
  • the members have at least three portions. This is advantageous because it allows simple constructions of piezoelectric devices to be formed, for example with two or more coupling portions and an uncoupled portion intermediate each pair of adjacent coupled portions.
  • the at least one further portion may be inactive. This may be achieved by the at least one further portion having no electrodes.
  • the at least one further portion may be active and activatable in shear mode to shear in a direction antiparallel to the direction in which the first mentioned at least one active portion shears on activation.
  • This may be achieved by the at least one further portion having a pair of electrodes, isolated from the electrodes of the first mentioned at least one active portions, on opposed surfaces for creating an electric field therebetween on activation by application of an activation voltage across the electrodes.
  • this may be achieved by at least one further portion being polarised in an opposite direction from the at least one active portion.
  • the at least one further portion comprises at least two inactive portions which constitute said coupling portions and the at least one active portion of each member includes an active portion intermediate each pair of adjacent coupling portions.
  • an active portion is intermediate to each pair of inactive coupling portions.
  • said plurality of piezoelectric elements are constituted by a unitary block of piezoelectric material having parallel planar slits extending from alternate sides of the block and overlapping to form the beams between the slits, the portions of the beams between the overlapping portions of the slits constituting said active portions and having said electrodes on the facing surfaces of the slits, and the portions of the block beyond the end of the slits constituting said inactive portions.
  • a piezoelectric device comprising a block of piezoelectric material having parallel planar slits extending from alternate sides of the block and overlapping to split the block into parallel members coupled at alternate ends by the portions of piezoelectric material beyond the end of the slits, each member having a pair of electrodes extending on opposed surfaces of the members along the portion of the member between the overlapping slits for creating an electric field therebetween on activation by application of an activation voltage across the electrodes in a direction for activation in shear mode to create relative displacement between the portions of the piezoelectric material beyond the end of the slits.
  • Such a piezoelectric device comprising a block of piezoelectric material is particularly easy to manufacture, simply by making the slits and applying the electrodes. However, it is not essential for the coupling portions to be inactive. In a second type of arrangement, the active portions of the members constitute the coupling portions.
  • each member includes an inactive portion intermediate each pair of adjacent coupling portions, and the active portions are arranged to shear on activation in a direction normal to the interface between the active portions and the further portions.
  • the shearing of the active coupling portions on activation causes the interface between the active coupling portions and the intermediate inactive portion to rotate, because the active coupling portions shear, but the inactive portions are not deformed.
  • the direction in which the active portions are arranged to shear on activation is normal to the interface between the active portions and the further portions.
  • the shear of the active coupling portions is concomitant with rotation of the intermediate inactive portion. This in turn is concomitant with relative displacement of the active coupling portions in a direction perpendicular to the direction of shear.
  • the at least one further portion includes an uncoupled active portion intermediate each pair of adjacent coupled active portions, the uncoupled active portion having a pair of electrodes, isolated from the electrodes of the coupled active portions, on opposed surfaces for creating an electric field therebetween on activation by application of an activation voltage across the electrodes and being polarised to be activatable in shear mode to shear in a direction antiparallel to the direction in which the coupled active portions shear on activation, the coupling and uncoupled active portions being arranged to shear on activation in a direction normal to the interface between the coupling active portions and the further uncoupled active portions.
  • the shear of the active coupled portions causes the interface between the active coupled portions and the active uncoupled portions to relatively rotate.
  • the shear of the uncoupled portions on activation causes the uncoupled active portions to rotate relative to that interface.
  • the coupled and uncoupled active portions are arranged to shear in anti parallel directions, the coupled and uncoupled active portions relatively rotate by an angle equal to the sum of the rotational angles generated by the shear of each element.
  • the coupled active portions are relatively displaced in a direction perpendicular to the direction in which the coupled active portions shear by an amount greater than the first alternative discussed above.
  • the relative rotation of the uncoupled active portions is double the relative rotation of the uncoupled inactive portion in the first alternative.
  • the relative displacement of the coupled active portions is twice the relative displacement of the coupled active portions in the first alternative.
  • inactive portions may be formed simply by arranging the electrodes extending along the active portions not to extend along the inactive portion.
  • the inactivity results from the fact that the electric field created between the electrodes on activation does not create a significant effect in the inactive portions.
  • Electrically isolated active portions may be formed simply by forming separate electrodes in each active portion.
  • the members In simple piezoelectric elements, the members have a single uncoupled portion intermediate each adjacent pair of coupled portions. However, this is not essential and there may be plural uncoupled portions intermediate each adjacent pair of coupled portions.
  • the piezoelectric elements have two coupling portions. However, the piezoelectric elements may equally have more than two coupling portions.
  • the piezoelectric elements may be formed in a plurality of different shapes.
  • each member is a beam.
  • the beam is in manufacture and is a convenient building block from which to design and construct different piezoelectric devices.
  • each member is an annulus or disk, the piezoelectric material being polarised radially of the annulus or disk.
  • This form of piezoelectric element is advantageous for a number of reasons. It may easily be formed by slicing a commercially available tubular piezoelectric block polarised radially through the tube wall. The configuration of the annulus naturally provides rigidity in all directions around the annulus.
  • Fig. 1 is a perspective view of a piezoelectric element in the form of a beam
  • Fig. 2 is a cross-sectional view of the piezoelectric element shown in Fig. 1 on activation, the cross-section being taken along the direction in which the beam extends;
  • Fig. 3 is a side view of a piezoelectric device comprising a plurality of the elements shown in Fig. 1 ;
  • Fig. 4 is a side view of the piezoelectric device of Fig. 3 on activation;
  • Fig. 5 is a cross-sectional view of a further piezoelectric element in the form of a beam, the cross-section being taken along the direction in which the beam extends;
  • Fig. 6 is a side view of a piezoelectric element comprising a plurality of the elements shown in Fig. 5;
  • Fig. 7 is a side view of the piezoelectric device of Fig. 6 on activation;
  • Fig. 8 is a perspective view of a further piezoelectric element in the form of a beam
  • Fig. 9 is a cross-sectional view of the piezoelectric element shown in Fig. 8, on activation, the cross-section being taken along the direction in which the beam extends;
  • Fig. 10 is a side view of a piezoelectric device comprising a plurality of the elements shown in Fig. 8;
  • Fig. 11 is a side view of the piezoelectric device of Fig. 10 on activation;
  • Fig. 12 is a perspective view of a yet further piezoelectric element in the form of a beam;
  • Fig. 13 is a cross-sectional view of the piezoelectric element shown in Fig. 12 on activation, the cross-section being taken along the direction in which the beam extends;
  • Fig. 14 is a side view of a piezoelectric device comprising a plurality of the elements shown in Fig. 12;
  • Fig. 15 is a side view of the piezoelectric device of Fig. 14 on activation;
  • Fig. 16 is a perspective view of another piezoelectric element in the form of a beam
  • Fig. 17 is a cross-sectional view of the piezoelectric element shown in Fig. 16 on activation, the cross-section being taken along the direction in which the beam extends;
  • Fig. 18 is a perspective view of a piezoelectric device formed from a block of piezoelectric element material
  • Fig. 19 is a perspective view of the piezoelectric device shown in Fig. 18 on activation
  • Fig. 20 is a perspective view of a piezoelectric element in the fo ⁇ n of an annulus
  • Fig. 21 is a perspective view of the piezoelectric element of Fig. 20 on activation
  • Fig. 22 is a cross-sectional view of a piezoelectric device comprising a plurality of the piezoelectric elements shown in Fig. 20, the cross-section being taken radially of the annulus; and
  • Fig. 23 is a cross-sectional view of the piezoelectric element device shown in Fig. 22 on activation.
  • the piezoelectric element comprises a unitary member of piezoelectric material, that is a single piece of material so all the portions of the member are unitary. Any suitable piezoelectric material may be used. It may be a piezoelectric ceramic such as lead zirconate titanate (PZT) or a polymer such as polyvinylidine flouride (PNDF).
  • PZT lead zirconate titanate
  • PNDF polyvinylidine flouride
  • Fig. 1 illustrates a piezoelectric element 1 which may be used in a piezoelectric device in accordance with the present invention.
  • the element 1 comprises a member of a piezoelectric material in the form of a beam 2 extending in a given direction 3.
  • the beam 2 has a pair of electrodes 4 arranged on respective opposed surfaces 5 of the beam 2, which surfaces 5 extend parallel to the direction 3 along which the beam 2 extends.
  • the thicknesses of the electrodes 4 are shown grossly exaggerated for clarity.
  • the electrodes 4 are arranged to create, on application of an activation voltage across the electrodes 4, an electric field therebetween in the active portion 6 of the beam 2 positioned between the dotted lines 7 (which are imaginary lines).
  • the electrodes 4 extend only partially along the length of the beam 2.
  • the portions 8 of the beam 2 which protrude beyond the electrodes 4 are inactive, because the electric field in these portions 8 is not sufficient to activate them. Although there is some leakage of the electric field into the inactive portions 8 at the edges of the electrode 4, this does not cause significant activation of the inactive portions 8 when considered on a macroscopic scale.
  • the inactive portions 8 are used as coupling portions, as will be described below.
  • the element 1 has two inactive coupling portions 8 and a single active portion 6 intermediate the two inactive coupling portions 8.
  • the beam 2 of piezoelectric material is easily manufactured because it is a simple piece of piezoelectric material. For example it may be cut from a sheet of commercially available material.
  • the electrodes 4 may be applied using any conventional technique, for example by electroless plating or by printing. Before or after applying the electrodes 4, the material of the beam 2 is polarised along the direction 3 by applying an electric field along the direction 3 along which the beam 2 extends effective to polarise the crystals of the material in the beam 2. Therefore the inactive portions 8 are at the ends of the beam 2 when viewed in the polarisation direction.
  • the piezoelectric element 1 is operated by applying an activation voltage across the pair of electrodes 4 from an electrical source 9, as illustrated in Fig. 2 which is a cross-sectional view of the element 1 taken along the direction 3 in which the beam 2 extends.
  • the active portion 6 of the beam 2 is thus activated in shear mode (d 51 ), rather than extension-contraction mode (d 31 ) as used in a bender construction, because the electric field created between the electrodes 4 is perpendicular to the direction 3 in which the material of the beam 2 is polarised.
  • the beam 2 shears in the active portion 6 where the electric field is created. This may be viewed as a shear in the direction of the applied electric field.
  • the amount d is shown exaggerated in Fig. 2 for clarity. Typically achievable shears are much smaller, perhaps a fraction of a degree. It is advantageous that this relative displacement d is linear and is not rotational as in the case of a bender construction.
  • the piezoelectric elements 1 of Fig. 1 maybe coupled together by the inactive portions 8 which act as coupling portions to form a piezoelectric device 10 in accordance with the present invention as illustrated in Fig. 3, which is a side view of the device.
  • the device 10 is shown in Fig. 3 as comprising four elements 1, for illustration, but any number of elements 1 may in fact be used.
  • the device 10 comprises a plurality of piezoelectric elements 1 arranged in a stack with the beams 2 extending parallel to one another and the electrodes 4 on each element 1 facing one another. Adjacent elements 1 in the stack are coupled together in series by couplings 11 between the inactive portions 8 of adjacent elements 1 at alternate ends through the stack.
  • the couplings 11 are preferably adhesive, but may alternatively be any other suitable coupling, for example a mechanical coupling.
  • the device 10 is operated by applying activation voltages to the pairs of electrode 4 of each element 1 in the same manner as illustrated for a single element 1 in Fig. 2.
  • the activation voltages for the respective elements 1 are selected relative to the polarisation direction of each element 1 to cause the relative displacement of the inactive coupling portions 8 to combine together. For example, if all the beams 2 are polarised in the parallel directions, then the activation voltages are of opposite polarity for alternate beams 2 in the stack.
  • the device 10 extends with the displacement d of each element 1 combining and accumulating to produce a large overall relative displacement between the free inactive coupling portions 8a and 8b of the elements 2 at either end of the stack of elements 2 in the device 10 which are not coupled to adjacent elements 2.
  • These free coupling portions 8a and 8b may be coupled to other components in a larger device.
  • the beams 2 are coupled together by the inactive portions. Firstly, as the inactive portions 8 undergo no change in shape, no additional strain is placed upon the couplings 11 which therefore improves the strength of the coupling. Secondly, as the inactive portions 8 of any given beam 2 do not undergo any relative rotation, the displacements of each element 1 accumulate in the same linear direction without any rotation of the device 10.
  • Fig. 5 is a cross-sectional view of a further element 15 comprising a member of piezoelectric material in the form of a beam 16.
  • the arrangement of the element 15 is identical to that of element 1 except that instead of having two inactive coupling portions 8, the element 15 has three coupling portions 19 and 20. This is achieved by the element 15 being provided with two pairs of electrodes 17 and 18 which are separated along the direction in which the beam 16 extends.
  • the beam 16 has inactive portions 19, 20 protruding beyond the electrodes 17, 18 which are inactive for the same reasons as inactive portions 8 of the element 1, because they are outside the active portions 21 between the respective pairs of electrodes 17, 18 in which a significant electric field is created on application of an activation voltage.
  • the inactive portions 19, 20 include portions 19 protruding at each end of the beam beyond the respective pair of electrodes 17, 18 and a central portion 20 extends between the two pairs of electrode 17, 18. Thus there is a simple active portion 21 between each pair of adjacent inactive portions 19 and 20 along the length of the beam 20.
  • the beam 16 is polarised along the direction in which it extends, that is perpendicular to the direction of the electric field created by applying an activation voltage across the respective pairs of electrodes 17, 18.
  • the beam 16 shears in the active portion 21 where the electric field is created. This may be viewed as a shear in the direction of the applied electric field.
  • the inactive portions 19, 20 do not deform significantly. Therefore, the shear in the active portions 21 relatively displaces the central inactive portion 20 with respect to the inactive portions 19 at the ends of the beam 16.
  • Fig. 6 illustrates a device 25 comprising a plurality of the piezoelectric elements 15 shown in Fig. 5.
  • the device 25 is shown in Fig. 6 as comprising five elements 15, but any number of elements 15 may in fact be provided.
  • the device 25 comprises a plurality of element 15 arranged in a stack with the beams 16 extending parallel to one another with the electrodes 17, 18 of adjacent beams 16 facing one another.
  • the beams 16 are coupled together in series by couplings 26 between the inactive portions 19, 20 arranged alternately through the stack (1) at both ends of the elements 25 coupled to the inactive end portions 19 and (2) between the two pairs of electrodes 17, 18 coupled to the central inactive portion 20 of the beams 25.
  • the couplings 26 are preferably adhesive, but may alternatively be any other suitable type of coupling, for example a mechanical coupling.
  • the piezoelectric device 25 is operated in the same manner as the piezoelectric device 10 by applying activation voltages across each of the pairs of electrodes 17, 18 of each element 10.
  • the activation voltages for the respective elements 15 are selected relative to the polarisation direction of each element 15 the relative displacement of the central inactive portion 20 with respect to the end inactive portions 19 to combine together.
  • the electroactive element 15 may be operated by applying activation voltages of equal magnitude but opposite polarity to the two pairs of electrodes 17, 18. Therefore the relative displacement of the elements 15 occurs in the same direction, adding in series through the device 25, as shown in Fig. 7. This therefore causes the device 25 to extend with the displacement of each element 15 accumulating to provide a large total displacement between the free inactive coupling portions 19a and 19b of the elements 15 at the ends of the stack the device 10 of Fig. 3. but the device 10 of Fig.3, the device 25 has the advantage of increased stability and better load distribution as a result of the device 25 being symmetrical about the couplings 26 to the central inactive portion 20.
  • Fig. 8 illustrates a piezoelectric element 50 having a second arrangement of active and inactive portions different from the piezoelectric element 1 of Fig. 1.
  • the element 50 comprises a member of piezoelectric material in the form of a beam 51 extending in a given direction 52.
  • the beam 51 has two pairs of electrodes 53, 54.
  • the electrodes 53, 54 of each pair are arranged on respective opposed surfaces 55 of the beam 51, which surfaces 55 extend parallel to the direction 53 along which the beam 51 extends.
  • the thicknesses of the electrodes 53, 54 are shown grossly exaggerated for clarity.
  • the two pairs of electrodes 53, 54 are arranged at opposite ends of the beam 51 to create, on application of an activation voltage across the respective pairs of electrodes 53, 54, an electric field therebetween in the active portions 56 of the beam positioned outside the dotted lines 57 (which are imaginary lines).
  • the further portion 58 of the beam 51 intermediate the active portions 56 is inactive because the electric field in this portion 58 is not sufficient to activate it. Although there is some leakage of the electric field into the inactive portion 58 at the edges of the electrodes 53, 54, this does not cause significant activation of the inactive portion 58 when considered on a macroscopic scale.
  • the active portions 56 are used as coupling portions, as will be described below.
  • the element 50 has two active coupling portions 56 and a single inactive portion 58 intermediate the two active coupling portions 56.
  • the beam 51 is easily manufactured in the same manner as the beam 2 of the element 1 of Fig. 1 described above.
  • the beam 51 is polarised along the direction 52 perpendicular to the electric field created by applying activation voltages across the respective pairs of electrodes 53, 54.
  • the piezoelectric element 50 is operated by applying an activation voltage across each pair of electrodes 53, 54 from an electrical source 59 as shown in Fig. 9.
  • the active portions 56 of the beam 51 are thus activated in shear mode, because the electrical field created between the pairs of electrodes 53, 54 is perpendicular to the direction 53 in which the material of the beam 51 is polarised.
  • the active portions 56 shear in a direction normal to the lines 57 which represent the interfaces between the active portions 56 and the inactive portion 58.
  • the inactive portion 58 does not deform significantly. Therefore the shear in the active portions 56 of the beam relatively rotates the inactive portion 58 by an angle ⁇ , this being the angle by which the end surfaces of the active portions 56 rotate. This causes the active coupling portions 56 to be displaced by an amount d as illustrated in Fig. 9. The amount d is shown exaggerated in Fig. 9 for clarity. Typical achievable shears are much smaller, perhaps a fraction of a degree. Therefore, where the length of the inactive portion 58 is L, then the displacement d is approximately L ⁇ (where ⁇ is in radians).
  • the piezoelectric elements 50 of Fig. 8 may be coupled together by the active portions 56.
  • the device 60 is shown in Fig. 10 as comprising three elements 50, but any number of elements 50 may in fact be used.
  • the device 60 comprises a plurality of piezoelectric elements 60 arranged in a stack with the beams 51 extending parallel to one another and with the electrodes 53, 54 on each element 51 facing one another (although for clarity the electrodes 53 are not illustrated in Fig. 10).
  • Adjacent elements 50 in the stack are coupled together in series by couplings 61 between the active coupling portions 56 of adjacent elements 60 at alternate ends through the stack.
  • the couplings 61 are preferably adhesive, but may alternatively be any other suitable coupling, for example a mechanical coupling.
  • the device 60 is operated by applying activation voltages to the pairs of electrodes 53, 54 of each element 50.
  • the activation voltages for the respective elements 50 are selected relative to the polarisation direction of each element 50 to cause the relative displacement of the elements 50 to combine together. For example, if all the beams 51 are polarised in parallel directions, then the activation voltages are of opposite polarity for alternate beams 51 in the stack.
  • the device 60 extends, with the displacement d of each element 50 combining and accumulating to produce a large overall relative displacement between the free active coupling portions 56a and 56b at either end of the stack of elements 50.
  • the free coupling portions 56a and 56b may be coupled to other components in a larger device.
  • Fig. 12 illustrates a piezoelectric element 70 having a similar arrangement of active portions to the piezoelectric element 50 of Fig. 8 but with an alternative intermediate uncoupled portion which is active, unlike the inactive central portion 58 of the element 50.
  • the element 70 comprises a member of piezoelectric material in the form of a beam 71 extending in a given direction 72.
  • the beam 71 has three pairs of electrodes 73, 82 and 74.
  • the electrodes 73, 82 and 74 of each pair are arranged on respective opposed surfaces 75 of the beam 71, which surfaces 75 extend parallel to the direction 73 along which the beam 71 extends.
  • the thicknesses of the electrodes 73, 82 and 74 are shown grossly exaggerated for clarity.
  • the adjacent electrodes 73, 82 and 74 are electrically isolated along the length of the beam 71 by providing a small gap therebetween
  • the beam 71 is easily manufactured in the same manner as the beam 22 of the element 1 of Fig. 1 described above.
  • the beam 71 is polarised along the direction 72 perpendicular to the electric field created by applying activation voltages across the respective pairs of electrodes 73, 74.
  • Each pair of electrodes 73, 82 and 74 creates, on application of an activation voltage thereacross, an electric field therebetween in respective active portions 76 and 78 of the beam 71 between the respective pairs of electrodes 73, 82 and 74.
  • the interfaces between the respective active portions 76 and 78 are shown by the dotted lines 77 (which are imaginary lines).
  • the respective pairs of electrodes 73 and 74 create an electric field in active portions 76 which are used as coupling portions, as will be described below.
  • the pair of electrodes 82 creates an electric field.
  • the piezoelectric element 70 is operated by applying an activation voltage across each pair of electrodes 73, 82 and 74 from an electrical source 79 as shown in Fig. 13.
  • the activation voltage applied to the pairs of electrodes 73, 74 at the ends of the beam 71 are of opposite polarity to the activation voltages applied across the pair of electrodes 82 adjacent the intermediate portion active 78.
  • all the active portions 76 and 78 are activated in shear mode, because the electric field is perpendicular to the polarisation direction and the active portions 76 and 78 shear in a direction normal to the lines 77 which represent the interfaces between the coupling portions 76 and the intermediate portions 78. However, the uncoupled intermediate portions 78 shear in a direction antiparallel to the coupling portions 76.
  • activation of the element 71 causes the intermediate uncoupled portion 78 to rotate relative to the active coupling portions 76.
  • the angle of shear of the active coupling portions 76 is ⁇ and the angle of shear of the intermediate uncoupled portion 78 is ⁇ , then the angle of relative rotation is ( ⁇ + ⁇ ).
  • This causes the active coupling portions 76 to be displaced by an amount d as illustrated in Fig. 13.
  • the amount d is shown exaggerated in Fig. 13 for clarity. Typical achievable shears are much smaller, perhaps a fraction of a degree. Therefore, where the length of the intermediate uncoupled portion 78 is L, then the displacement d is approximately L( ⁇ + ⁇ ) (where ⁇ and ⁇ are in radians).
  • the beam 71 is polarised in a first direction in the active coupling portions 76 and in an antiparallel, second direction in the intermediate further active portion 78.
  • the activation voltages applied across each of the pairs of electrodes 73, 74 is of the same polarity. This would also make it possible for the pairs of electrodes 73, 74 to be replaced by a single pair of electrodes extending across each of the regions 76 and 78.
  • the piezoelectric elements 70 of Fig. 12 may be coupled together by the active coupling portions 76.
  • the device 80 is shown in Fig. 14 as comprising three elements 70, but any number of elements 70 may in fact be used.
  • the device 80 comprises a plurality of piezoelectric elements 80 arranged in a stack with the beams 71 extending parallel to one another and with the electrodes 73, 74 on each element 71 facing one another (although for clarity the electrodes 73 are not illustrated in Fig. 14).
  • Adjacent elements 70 in the stack are coupled together in series by couplings 81 between the active coupling portions 76 of adjacent elements 80 at alternate ends through the stack.
  • the couplings 81 are preferably adhesive, but may alternatively be any other suitable coupling, for example a mechanical coupling.
  • the device 80 is operated by applying activation voltages to the pairs of electrodes 73, 82 and 74 of each element 70.
  • the activation voltages for the respective elements 70 are selected relative to the polarisation direction of each element 70 to cause the relative displacement of the elements 70 to combine together. For example, if all the beams 71 are polarised in parallel directions, then the activation voltages are of opposite polarity for alternate beams 71 in the stack.
  • the device 80 extends with the displacement d of each element 70 combining and accumulating to produce a large overall relative displacement between the free active coupling portions 76a and 76b at either end of the stack of elements 70.
  • the free coupling portions 76a and 76b may be coupled to other components in a larger device.
  • the piezoelectric elements described above have a single further portion intermediate each pair of adjacent coupling portion. However, this is not essential and there may be more than one such further intermediate portion.
  • An example of such an element is the element 90 illustrated in Fig. 16.
  • the element 90 comprises a member of piezoelectric material in the form of a beam 91 extending in a given direction 92.
  • the beam has five portions 93, 94 and 95 along its length, namely two active portions 93; a further active portion 94 adjacent each active portion 93; and an inactive portion 95 intermediate the active portions 94.
  • the active portions 93 and 94 each have a respective pair of electrodes 96 and 97 on opposed surfaces which cause operation in the same manner as the active portions of the elements described above.
  • the inactive portion 95 has no electrodes and so is not activated.
  • the element 90 is operated by applying activation voltages to the respective pairs of electrodes 96 and 97 in fundamentally the same manner as the element 70 of Fig. 12, as described above. This causes a relative displacement of the active coupling portions 93 as shown in Fig. 17 (in which the electrodes are omitted for clarity).
  • the length of the intermediate active portions 94 is L
  • the length of the intermediate inactive portion 95 is L 2
  • the angle of shear of the active coupling portions 93 is ⁇
  • the angle of shear of the intermediate active portion 94 is ⁇
  • the displacement d is approximately (2L,( ⁇ + ⁇ ) + L 2 ⁇ ).
  • FIGs. 18 and 19 illustrate a device 30 in which a plurality of piezoelectric elements 31 are constituted by a single block 37 of piezoelectric material.
  • the device 30 is manufactured from a cuboid block 37 of piezoelectric material.
  • the block 37 is polarised in the direction 32 illustrated in Fig. 18 extending between two faces of the block.
  • planar slits 33 are formed in the block parallel to the polarisation direction 32.
  • the slits 33 are formed extending from alternate sides of the block 37 and overlap one another. Whilst the slits 33 extend most of the way through the block 37 they do not sever the block 37. Thus a portion 34 of piezoelectric material remains beyond the end of each slit 33. Consequently, the slits 33 divide the block into a stack of beams 35 extending parallel to one another and coupled at alternate ends through the portions 34 of piezoelectric material remaining beyond the end of the slits 33.
  • Electrodes 36 are formed on the opposed surfaces of each beam 35 formed by the slits 33.
  • the electrodes may be formed in any convenient manner, for example by evaporation, electroless deposition or infiltration into the slits 33.
  • each beam 35 with its associated pair of electrodes 36 constitutes an individual piezoelectric element 1 which is similar to the element 1 of Fig.1 and the device 30 has an overall arrangement which is similar to the device 10 of Fig. 3, except that all the beams 35 are unitary, being part of a single block 37.
  • the portions 38 of the beams 35 between the overlapping portions of the slits 33 constitute active portions 38 for responding to the active portions 6 of the element 1 of Fig. 1.
  • the portions 34 of piezoelectric material beyond the ends of the slits 33 constitute inactive portions 34 corresponding to the inactive portions 8 of the element 1 of Fig. 1.
  • the arrangement of the individual beams 35 in the device 30 is the same as the arrangement of the beams 2 in the device 10 of Fig. 3.
  • the electrodes 36 extend across the inactive portions 34, the inactive portions 34 are not activated in use, because the voltages applied to the electrodes 36 of either side of each inactive portion 34 (spanning across two beams 35 and forming the coupling portion for each beam 35) is necessarily at the same potential.
  • each individual piezoelectric element 31 is operated by applying activation voltages across the pair of electrodes 36 of that element 31. This causes activation in exactly the same manner as the device 10 of Fig. 3 as described above.
  • the active portions 38 are activated in shear mode, because the direction of the electric field created by the applied activation voltage is perpendicular to the polarisation direction 32. As a result, the active portions 38 shear.
  • the inactive portions 34 do not deform significantly. Therefore, the shear in the active portions 38 relatively displaces the inactive portions 34 in a direction parallel to the direction in which the active portions 38 shear as shown in Fig. 2, although the degree of displacement is exaggerated in Fig. 2 for clarity.
  • the polarity of the activation voltages causes the relative displacement of the inactive coupling portions 34 to combine together.
  • the beams 35 are all polarised in the same direction 32, this means that the activation voltages are of opposite polarity for each element 31.
  • the electrodes 36 on adjacent beams 35 facing one another are at the same potential during activation. This is convenient because it would be difficult to electrically isolate those two electrodes 36.
  • the device 30 extends with the displacement of each beam 35 combining and accumulating to produce a large overall relative displacement between the free ends 39 at either end of the device. These free ends 39 may be coupled to other components in a larger device.
  • the portions 34 of piezoelectric material beyond the end of the slits 33 are inactive because no significant electric field is created in those portions 34 as the electrodes 36 on the opposite surfaces of these portions 34 are at the same potential. Furthermore, the activation voltages for all the slits 33 extending from a first side of the block 37 are of the same polarity. The activation voltages for all the slits 33 extending from the opposite side of the block 37 are of the same polarity opposite from that of the first side.
  • the electrodes 36 in the slits 33 on each side of the block 37 can be applied as a continuous electrode with portions extending around the ends 38 of the inactive portions 34. This simplifies manufacture and also means that only two external terminals are necessary.
  • the device 30 of Fig. 18 may have any number of slits 33 and have any number of elements 31.
  • piezoelectric members in the form of a beam such as the beams 2, 16, 51, 71 and 91 may have any width (ie in the direction perpendicular to both the polarisation direction and the direction of the applied electric field), as the width does not affect the magnitude of the displacement for an applied electric field. Therefore the width may be freely selected to control the stiffness of the element.
  • the piezoelectric element may take many forms other than a beam.
  • Fig. 20 illustrates a piezoelectric element 40 comprising a member of piezoelectric material in the form of an annulus 41.
  • the piezoelectric element 40 may be considered to be the same as the element 1 of Fig. 1 but with circular symmetry. Therefore the discussion above applies equally to the element 40 of Fig. 20.
  • a pair of annular electrodes 42 are disposed on the opposed planar surfaces of the annulus 41 for creating an electric field axially of the annulus 41 on application of an activation voltage across the electrodes 42.
  • the piezoelectric material of the annulus 41 is polarised radially, that is in direction 43.
  • the annulus 41 includes annular coupling portions 44, 45 which protrude radially beyond the electrodes 42 at an inner radial position and an outer radial position, respectively. Accordingly, the annular coupling portions 44, 45 protruding beyond the electrodes 42 are inactive because they are not affected by the electric field created in the region between the electrodes 42 to a significant extent.
  • the piezoelectric element 40 is activated by applying an activation voltage across the pair of electrodes 42.
  • the activation portion of the annulus 41 between the electrodes 42 shears parallel to the electric field as illustrated in Fig. 21, the element 40 taking a frusto-conical form.
  • the annulus 41 is an advantageous form for a piezoelectric element because it provides strength in all directions around the annulus as a result of the circular extent and symmetry.
  • the inactive annular portions 44, 45 are displaced axially relative to one another.
  • a device 47 comprising a plurality of the elements 40 shown in Fig. 20 is illustrated in Fig. 22, which is a cross sectional view taken radially of the annulus 40.
  • the device 47 is illustrated in Fig.
  • the annuluses 40 are arranged in a stack with the annuluses coaxial and parallel to one another. Adjacent elements 40 are coupled together alternately at inner and outer radial positions by couplings 46 coupled to the inactive and portions 44 and 45.
  • the couplings 46 are preferably adhesive but alternatively may be any suitable coupling.
  • the device 47 is operated by applying activation voltages across the pairs of electrodes 42 of each element 40 which cause the annuluses 41 to shear away from each other as illustrated in Fig. 23. Accordingly, the displacement of each annulus 41 accumulates to create a large total displacement along the axis of the annuluses 41.
  • the element 40 may be manufactured from a tubular block of piezoelectric material which is readily available commercially.
  • the tubular block of piezoelectric material is polarised radially for example using cylindrical electrodes, one inserted in the central aperture of the tubular block and the other positioned around the tubular block.
  • the tubular block is sliced radially to create individual annuluses 41 of piezoelectric material.
  • electrodes 42 are applied to the annuluses 41 by any suitable technique, for example by electroless plating or by printing and the annuluses 41 couples together. As an alternative, the coupling may occur before the electrodes 42 are applied.
  • the annuluses 42 are polarised in the same radial direction, then the activation voltages are in opposite directions for adjacent elements 40 in the device
  • the activation voltages for electrodes 42 which are adjacent to one another are at the same polarity which avoids the need for electrical isolation and assists application of the electrodes 42 after coupling.
  • the electrodes 42 may extend across the inactive portions 44, 45 on the opposite side of the annulus 41 from the couplings 46.
  • the individual elements 40 may be formed as a disc, in which case the aperture 47 present in the annulus 41 is absent.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • General Electrical Machinery Utilizing Piezoelectricity, Electrostriction Or Magnetostriction (AREA)

Abstract

La présente invention concerne un dispositif piézo-électrique comprenant une pluralité d'éléments piézo-électriques (1) couplés entre eux. Chaque élément piézo-électrique (1) comprend un élément unitaire (2) fait en matériau piézo-électrique, une pluralité de partie à raison d'au moins une partie active (6) et au moins une autre partie (8). Les deux faces opposées d'une telle partie active (6) comportent une paire d'électrode (4) de façon à créer un champ électrique entre deux lors de l'activation par application entre les électrodes (4) d'une tension d'activation. En outre, ces parties actives (6) sont caractérisées par un sens de polarisation pour que l'activation en mode cisaillement crée un déplacement relatif entre les deux parties de couplage de l'élément. Les éléments piézo-électriques (1) sont couplés ensemble en série par ces parties de couplage de façon à combiner le déplacement relatif créé par chaque élément (1) à l'activation. Selon un mode de réalisation, on a au moins deux autres parties qui sont inactives (8) et constituent les parties de couplage considérées, avec une partie active (6) venant entre chaque paire de parties de couplage adjacentes. Selon un autre mode de réalisation, ce sont les parties actives (56) des éléments (51) qui constituent les parties de couplage considérées, avec d'autres parties (58) entre les parties de couplage qui sont, soit inactives, soit active et capable de fonctionner en mode cisaillement de façon à ce cisailler dans un sens antiparallèle aux parties de couplage.
PCT/GB2002/001003 2001-03-07 2002-03-06 Dispositifs piézo-électriques à cisaillement Ceased WO2002071504A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB0322650A GB2391109B (en) 2001-03-07 2002-03-06 Piezoelectric shear mode devices

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GBGB0105618.3A GB0105618D0 (en) 2001-03-07 2001-03-07 Piezoelectric devices
GB0105618.3 2001-03-07

Publications (1)

Publication Number Publication Date
WO2002071504A1 true WO2002071504A1 (fr) 2002-09-12

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GB (2) GB0105618D0 (fr)
WO (1) WO2002071504A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1821399A4 (fr) * 2004-10-19 2011-04-27 Panasonic Corp Actionneur piézo-électrique, et dispositif de déplacement d'élément capteur d'image et dispositif de capteur d'image utilisant un tel actionneur piézo-électrique
EP2838127A4 (fr) * 2012-03-08 2015-11-18 Konica Minolta Inc Dispositif piézoélectrique, sonde à ultrasons, dispositif de décharge de gouttelettes, et procédé de fabrication de dispositif piézoélectrique

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1989008240A1 (fr) * 1988-02-29 1989-09-08 Spectra, Inc. Transducteur en mode cisaillement pour systemes a jet d'encre
EP0565883A2 (fr) * 1992-03-16 1993-10-20 Rockwell International Corporation Transducteur anisotropique
WO1999005778A1 (fr) * 1997-07-25 1999-02-04 Materials Systems Incorporated Actionneur lineaire piezoelectrique a coupe en serpentin

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1989008240A1 (fr) * 1988-02-29 1989-09-08 Spectra, Inc. Transducteur en mode cisaillement pour systemes a jet d'encre
EP0565883A2 (fr) * 1992-03-16 1993-10-20 Rockwell International Corporation Transducteur anisotropique
WO1999005778A1 (fr) * 1997-07-25 1999-02-04 Materials Systems Incorporated Actionneur lineaire piezoelectrique a coupe en serpentin

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1821399A4 (fr) * 2004-10-19 2011-04-27 Panasonic Corp Actionneur piézo-électrique, et dispositif de déplacement d'élément capteur d'image et dispositif de capteur d'image utilisant un tel actionneur piézo-électrique
EP2838127A4 (fr) * 2012-03-08 2015-11-18 Konica Minolta Inc Dispositif piézoélectrique, sonde à ultrasons, dispositif de décharge de gouttelettes, et procédé de fabrication de dispositif piézoélectrique
US9634229B2 (en) 2012-03-08 2017-04-25 Konica Minolta, Inc. Piezoelectric device, ultrasound probe, droplet discharge device, and piezoelectric device fabrication method

Also Published As

Publication number Publication date
GB2391109B (en) 2004-09-15
GB0105618D0 (en) 2001-04-25
GB0322650D0 (en) 2003-10-29
GB2391109A (en) 2004-01-28

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