GB2591240A

GB2591240A - Sensing and actuating laminate material

Info

Publication number: GB2591240A
Application number: GB2000864.5A
Authority: GB
Inventors: Sebastian Tobon Conde Juan
Original assignee: Hyve Dynamics Holdings Ltd
Current assignee: Hyve Dynamics Holdings Ltd
Priority date: 2020-01-21
Filing date: 2020-01-21
Publication date: 2021-07-28
Anticipated expiration: 2040-01-21
Also published as: GB202000864D0; GB2591240B

Abstract

A laminate material 10 comprises an array of sensors on a stretchable sensor layer 12 and a plurality of elongate actuators on an actuation layer 14. The actuators deform the laminate material 10 by measurements taken from the sensors. The actuators may comprise piezoelectric fibres and may be controlled by interdigitated electrodes on the actuation layer 14. The laminate material may comprise a plurality of actuation layers wherein a given layer’s actuators are angularly offset from another layer’s actuators. The laminate material 10 may comprise a host material 16 (e.g. a fibre, carbon or lattice structure composite). The sensors may measure temperature, pressure or in-plane strain and may comprise bidirectional pressure sensors. The laminate material 10 may be incorporated into an aircraft. Also provided is a method of deforming a layered material comprising a layer 14 of computer-controlled piezoelectric actuators to deform the material based on measurements from a stretchable sensor layer 12.

Description

SENSING AND ACTUATING LAMINATE MATERIAL

This invention relates generally to a sensing and actuating laminate material More particularly, the invention relates to a sensing and actuating laminate material having a stretchable sensor layer and at least one reversibly deformable actuation layer.

Furthermore, the invention relates to a method of deforming a deformable region of a layered material. More particularly, the invention relates to a method of deforming a deformable region of a layered material by using a stretchable sensor to control a plurality of elongate piezoelectric actuators to deform the reversibly deformable region.

BACKGROUND TO THE INVENTION

There has been much development of materials which can reversibly change shape. One area of research has been into shape-memory alloys (SMAs) which utilise a reversible crystalline phase transformation to recover their original heat-treated shape when heated above a critical transformation temperature range. One use has been to deform a surface which interfaces with a flowing fluid. For example, US5662294 discusses using SMA wires to alter the curvature and shape of an air foil. In another example, US8434293 uses an SMA actuated aerostructure to change the shape of a variable area fan nozzle according to flight conditions. It does this by deforming an SMA actuator attached to two sheets. However, there are various limitations which have prevented SMAs from achieving success within multiple fields. For example, the SMAs may be subject to structural fatigue and/or asymmetric actuation caused by a relatively short actuation time and slow deactuation time.

Another solution is the use of discrete actuators to deform a reversibly deformable skin. For example, US8473122 discloses using small discontinuously applied actuators to produce a set deformation in an elastic skin. The disclosed system uses feedback from sensors located in various locations, or a single optical sensor in the form of an optical fibre extending around some of the deformable surface, to control piezoelectric actuators to deform the elastic skin to set positions.

Other examples include 1JS8402739 and US8727267. These disclose a means to deform an inlet lip section of a gas turbine engine. In both, the deformation is performed by actuator arms acting on discrete sections of the inlet lip. A sensor detecting operability conditions, such as take-off or climbing, of the aircraft communicates with a controller which determines the deformation to apply from a given set of predetermined deformations.

In the above examples, the actuators can only deform discrete areas to pre-set deformations based on a limited number of sensor measurements, which may or may not be in close proximity to the deformation area Having sensors remote to the deformation area, or inadequate measurements within the area, can lead to incorrect deformations being applied.

Multi-layered composites which can function as both a sensor and an actuator are known, but they have limited sensing and actuating capability. For example, U S 7935414 discloses a multilayer el ectroactive composite material. Each layer has a unique dielectric, electrical and mechanical property with respect to each of the other layers. The unique properties define a predetermined electromechanical operation of each layer when affected by an external stimulus. Each layer is a carbon nanotube polymer composite. The electromechanical operation of the layers may be a sensing operation or an actuating operation. However, each sensing layer acts as a single sensor giving a single reading. The document discloses using a 4-probe technique to monitor the change in resistance to determine strain.

A recent area of great interest in sensor technology, primarily in the biomedical field, has been flexible and/or stretchable sensors. These commonly have an array of sensors which allows for multiple readings over an area effectively allowing for spatial-temporal distribution of physical parameters to be measured.

It is an object of the present invention to reduce or substantially obviate the aforementioned problems.

STATEMENT OF INVENTION

According to a first aspect of the present invention, there is provided a sensing and actuating laminate material comprising a plurality of reversibly deformable layers, the plurality of reversibly deformable layers comprising at least one stretchable sensor layer comprising an array of sensors, and at least one actuation layer having a plurality of elongate actuators for reversibly deforming the laminate material based on measurements taken from the at least one stretchable sensor layer.

The invention allows for physical parameters to be measured in the location of the deformation before, during and after the deformation caused by the elongate actuators. The stretchable sensor provides a spatial-temporal picture of the physical parameters within the location of deformation. Furthermore, the invention provides for I 0 a light material.

The plurality of reversibly deformable layers may be in a stack.

The array of sensors may be disposed in or on an elastomeric material.

The plurality of elongate actuators may be a plurality of substantially parallel spaced apart elongate actuators. The plurality of elongate actuators may be disposed in a matrix material. The plurality of elongate actuators may be disposed in an elastomeric material.

Each layer of the plurality of deformable layers may be bonded to at least one other layer of the deformable layers.

Each actuator of the plurality of actuators may comprise a piezoelectric fibre.

The elongate actuators in the or each actuation layer may be controlled by a first comb-like electrode structure and a second comb-like electrode structure. The first and second comb-like electrode structures may form an addressable interdigitated electrode pair. The comb-like electrode structure may be formed from a first conductor line and a plurality of conductor fingers connected to and extending orthogonally from the first conductor line.

The first conductor line may be substantially parallel with the elongate actuators. The plurality of conductor fingers may be substantially orthogonal to the elongate actuators The spacing between the conductor fingers of the first comb-like structure and the second comb-like structure, the width of each conductor finger, and the thickness of the actuation layer may be selected so as to achieve a desired strain and/or operational voltage By providing interdigitated electrodes it is possible to deliver the electric field required to activate the piezoelectric effect in the actuators and produce a stronger longitudinal piezoelectric effect along the length of the elongate actuators.

A first surface of the or each actuation layer may comprise at least one set of interdigitated electrode pairs for controlling the elongate actuators A second surface of the or each actuation layer may comprise at least one further set of interdigitated electrode pairs for controlling the elongate actuators. The interdigitated electrode pairs on the second surface may substantially align to the interdigitated electrode pairs on the first surface By providing a number of interdigitated electrode pairs it is possible to apply a voltage and therefore a strain in the specific region of the electrode pairs.

Each set of interdigitated electrode pairs may be individually addressable A deformable cell may be defined as a single interdigitated electrode pair disposed on the first surface of the actuation layer, and the elongate actuators within the region of the single interdigitated electrode pair.

The deformable cell may further comprise a single interdigitated electrode pair on the second surface of the actuation layer which aligns with the single interdigitated electrode pair on the first surface By having individually addressable interdigitated electrode pairs a particular region for deformation may be targeted.

The elongate actuators of one layer may be angularly offset from the elongate actuators of another layer. The angular offset may be with respect to the stacked parallel planes of the actuation layers.

The elongate actuators of one layer may be parallel to the elongate actuators in another layer. I 0

The material of both the elongate actuators and matrix material in one actuation layer may be different to the material of the elongate actuators and matrix material in another.

The actuation layers, particularly the disclosed piezoelectric actuators, are capable of a high in-plane blocking force and a low in-plane strain, or deformation, when compared with other forms of actuators. It is possible to place the actuators in the actuation layer in such a way that when energised the resultant force vector can exhibit a distributed bending moment.

The plurality of deformable layers may further comprise at least one layer of a host material. When there is a plurality of layers of host material at least some of them may be different. Alternatively, each layer of host material may be the same.

The host material may be a fibre composite, a carbon composite, lattice structure composite or combination thereof.

The host material may be part of the host structure. For example, the host material may be the skin of an aircraft. Alternatively, the host material may be a separate material to that of the host structure.

Inclusion of a host material can have added benefits such as providing an offset between the local centroid of the laminate and the net resultant actuating force of the actuator creating a bending moment. The thickness of the host material may be chosen to have the desired local centroid offset.

Furthermore, the host material can reduce any non-linear behavioural characteristics of the actuators, particularly piezoelectric actuators.

The at least one sensor layer may be an external layer of the laminate material. The external layer improves the accuracy of the readings.

The or each of the at least one stretchable sensor(s) may be adapted to measure at least one of pressure, temperature and strain.

The stretchable sensor may comprise a stretchable sensing laminate structure having an array of sensors for measuring pressure. This may be a bidirectional pressure sensor.

The bidirectional pressure sensor may comprise a first elastomeric sheet made from a dielectric material, with a series of conductor lines disposed on or in the elastomeric sheet; a second elastomeric sheet made from a dielectric material, with a series of conductor lines disposed on or in the elastomeric sheet; wherein the conductor lines of the first elastomeric sheet are substantially orthogonal to the conductor lines of the second elastomeric sheet; a microstructure comprising a plurality of elastomeric pillars made from a dielectric material, wherein the microstructure is bonded to the first and second elastomeric sheets so that the bidirectional sensor can register positive and negative pressure by the movement of the first and second elastomeric sheets.

The microstructure may be an array of spaced apart repeating structures used to separate two electrodes.

Advantageously, a bidirectional pressure sensor with a microstructure that is bonded to both elastomeric sheets provides high sensitivity on registering both positive and negative pressures. Because of the high sensitivity from this construction, low Reynold conditions are no longer a challenge.

The series of conductor lines in each of the first and second elastomeric sheets may be formed from carbon nanotubes The series of conductor lines may be in direct contact with the microstructure or have an intervening layer, such as the elastomeric sheet.

Advantageously, this type of conductive material allows for the electrical properties of the conductor lines to be maintained when the sheets are stretched or deformed. The number of conductor lines in the series, as well as the type of conductor material, may be selected based on the required sensor specifications (resolution, sensitivity, or etc). For example, the number of conductor lines may be increased to improve the resolution of the sensor.

Each pillar may be located at a crossing point between the first elastomeric sheet's conductor lines and the second elastomeric sheet's conductor lines. The combination of a pillar and crossing point forms a pixel. The number of pixels determines the resolution of the sensor. Each pixel can provide a measurement, but the combination of pixels creates a sensing area over which pressure is measured.

The or each stretchable sensor(s) may comprise a stretchable sensing lamina structure having an array of sensors for measuring in-plane strain.

The sensing and actuating laminate material may comprise a stretchable sensing laminate structure having an array of sensors for measuring pressure; and a stretchable sensing lamina structure having an array of sensors for measuring in-plane strain. The stretchable structures may form a stack.

It is possible to measure a variety of variables within a specific area by providing stacked stretchable structures. Furthermore, by allowing each stretchable structure to measure a single variable it is possible to improve the resolution. This is because the array of sensors for detecting a particular variable do not have to compete for space with other sensors. The in-plane strain experienced by the first lamina structure is the equivalent to the strain over a surface the multi-layered sensing apparatus may be attached to.

The stretchable sensing lamina structure having an array of sensors for measuring in-plane strain may comprise at least one row of strain gauges connected together by stretchable electrodes.

The strain gauges and/or the stretchable electrodes may be disposed on a dielectric elastomeric material. The strain gauges and/or stretchable electrodes may be embedded in a dielectric elastomeric material I 0 The stretchable electrodes may be either serpentine electrodes or be formed from carbon nanotubes.

By providing stretchable electrodes it is possible to maintain electrical connection between the strain gauges despite any deformation to the first stretchable lamina structure Moreover, the electrical properties of the stretchable electrodes are maintained.

The strain gauges may be formed from a strain-sensitive conductive structure.

These structures allow for the structure to have a minimal thickness.

Furthermore, it ensures that the lamina structure can be deformed to a greater degree without damaging the ability to sense the in-plane strain The strain-sensitive conductive structure may be formed from one or more conductive filaments arranged in a continuous pattern. The continuous pattern may be formed so that the resistance changes when deformed. By providing conductive filaments in a continuous pattern a minimal thickness of lamina structure is ensured. Moreover, it is possible to deform the lamina structure without damaging electrical connectivity.

The strain-sensitive conductive structures may comprise a first number of strain-sensitive conductive structures located in a first orientation and a second number of strain-sensitive conductive structures in a second orientation. Furthermore, the strain-sensitive conductive structures may be divided into sets. Each set may have a different orientation when compared to another set.

The strain-sensitive conductive structure may be made from a material with a predetermined thermal expansion coefficient. The material may be selected to minimise the apparent strain (thermal output) independent of a mechanical load. The material may have a thermal expansion coefficient which matches or is similar to the material of the surface the multi-layered apparatus will be attached to.

The pattern of the strain-sensitive conductive structure may be a low temperature-sensitive strain-sensitive pattern. Low temperature-sensitive strain-sensitive patterns have a minimal resistance change due to a change in temperature.

The or each stretchable sensor(s) may comprise a stretchable sensing lamina structure having an array of sensors for measuring temperature.

The sensing and actuating laminate material may comprise a stretchable sensing laminate structure having an an-ay of sensors for measuring pressure; a first stretchable sensing lamina structure having an array of sensors for measuring in-plane strain, and a second stretchable sensing lamina stmcture having an array of sensors for measuring temperature. The stretchable structures may form a stack.

The second sensing lamina structure may be the middle laminate structure.

By providing a second lamina structure it is possible to measure the temperature of the environment or an object. Alternatively, the temperature data could be used to compensate other measured variables The third stretchable sensing lamina structure may be disposed between the stretchable sensing laminate structure and the first stretchable sensing lamina structure.

By placing the second stretchable sensing lamina structure between the other stretchable structures it is possible to maintain high sensitivity to the measured variables.

Alternatively, the sensing laminate structure for measuring pressure may be disposed between the first and second stretchable sensing lamina structures. This arrangement improves the sensitivity of the array of temperature sensors as they would register less strain as there is an intermediate structure providing a buffer. However, it would lower the sensitivity of the stretchable sensing laminate structure.

The array of sensors for measuring temperature may comprise at least one row of temperature sensors connected together by stretchable electrodes. The temperature sensors and or stretchable electrodes may be disposed on a dielectric elastomeric material. The temperature sensors and/or stretchable electrodes may be embedded in a dielectric elastomeric material.

The stretchable electrodes may either be serpentine electrodes or formed from carbon nanotubes By providing stretchable electrodes it is possible to maintain electrical connection between the temperature sensors despite any deformation to the lamina structure. Moreover, the electrical properties of the stretchable electrodes are 20 maintained.

The temperature sensors may be formed from a temperature-sensitive structure. The temperature-sensitive structure may be formed from one or more conductive filaments arranged in a continuous pattern. The continuous pattern may be formed so that the resistance changes when deformed by temperature expanding the conductor.

These structures allow for a minimal thickness of lamina structure. Furthermore, it ensures that the laminate can be deformed to a greater degree without damaging the ability to sense temperature. Moreover, it is possible to deform the lamina structure without damaging electrical connectivity.

The pattern of the temperature-sensitive structure may be a low strain-sensitive temperature-sensitive pattern. Low strain-sensitive temperature-sensitive patterns have a minimal resistance change due to deformation caused by strain.

The temperature-sensitive structure may be constructed from a material with minimal resistance change due to deformation.

The pattern of the strain-sensitive conductive structure may be similar to the pattern of the temperature-sensitive conductive structure.

Alternatively, the pattern of the strain-sensitive conductive structure may be different to the pattern of the temperature sensitive conductive structure The first stretchable sensing lamina structure may be a strain-sensitive laminate structure formed from multiple lamina structures The second stretchable sensing lamina structure may be a temperature-sensitive laminate structure formed from multiple lamina structures.

The first stretchable sensing lamina structure may be known as the bottom stretchable sensing lamina structure because it is in contact with or attached to a surface of the actuation layer or host material layer.

The sensing and actuating laminate material may be used in or on an aircraft.

In another aspect of the present invention there is provided a method of deforming a deformable region of a layered material, comprising the steps of using a controller or computer to control a plurality of parallel running elongate piezoelectric actuators based on measurements taken from a stretchable senor, the stretchable sensor forming one of the layers of the layered material within the deformable region, and the piezoelectric actuators forming another layer of the layered material within the deformable region

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made by way of example only to the accompanying drawings, in which: Figure 1 shows an exploded schematic view of the sensing and actuating laminate material according to an embodiment of the present invention; Figure 2 shows a perspective view of a stretchable sensor layer according to an embodiment of the present invention; Figure 3 shows an exploded schematic view of a bidirectional pressure sensor according to an embodiment of the present invention; Figure 4 shows a plan view of the bidirectional pressure sensor according to an embodiment of the invention; Figure 5 shows a magnified view of the bidirectional pressure sensor in figure Figure 6 shows an exploded schematic view of a plurality of stretchable sensing layers according to an embodiment of the invention; Figure 7 shows an array of strain-sensitive conductive structures used in an embodiment of the invention; Figure 8 shows an array of temperature-sensitive conductive structures used in an embodiment of the present invention; Figure 9 shows a perspective view of an actuation layer according to an embodiment of the present invention; Figure 10 shows a plan view of a deformable cell forming part of an actuation layer according to an embodiment of the present invention; Figure 11 shows an exploded schematic view of a sensing and actuating laminate material according to an embodiment of the present invention; Figure 12 shows a schematic view of the sensing and actuating laminate material according to another embodiment of the present invention Figure 13 shows a schematic view of the sensing and actuating laminate material according to another embodiment of the present invention; and Figure 14 shows a schematic view of a wing of an aircraft according to an embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring firstly to Figure 1, a first embodiment of the sensing and actuating laminate material is generally indicated at 10. The sensing and actuating laminate material 10 comprises a plurality of deformable layers. The uppermost layer is a stretchable sensor layer 12, the middle layer is an actuation layer 14, and the bottom layer is a host material 16. Although not apparent from the exploded view in Figure 1, the host material 16 is attached to the actuation layer 14 which is attached to the stretchable sensor layer 12.

As shown in Figure 2, the stretchable sensor layer 12 comprises a first dielectric elastomeric sheet 121, a second dielectric elastomeric sheet 123, and an array of sensors. The array of sensors is formed by a first series of parallel running conductor lines disposed on or in the first elastomeric sheet and a second series of conductor lines disposed on or in the second elastomeric sheet. The first series of conductor lines are orthogonal to the second series of conductor lines.

Each conductor line of the first series of conductor lines is connected to a different electrode 125 and each conductor line of the second series of conductor lines is connected to a different electrode 127. In other embodiments, each conductor line of the first series of conductor lines may be connected to the same first serpentine electrode and each conductor line of the second series of conductor lines may be connected to the same second serpentine electrode.

In some embodiments, the first dielectric sheet 121 is separated from the second dielectric sheet 123 by an intervening dielectric structure such as a microstructure or a continuous structure The first elastomeric sheet 121 is bonded, either directly or indirectly through an intervening dielectric structure, to the second elastomeric sheet 123 so that the array of sensors can register strain orthogonal to the surface of the sensor. The registered strain can be representative of both a positive and negative pressure external to the laminate material 10.

In the embodiment shown in Figure 2, the conductor lines are formed from carbon nanotubes, however any conductive material which is known to the skilled person as being flexible and deformable while maintaining its electrical properties would be suitable.

Figure 3 shows an exploded view of a stretchable bidirectional pressure sensor, generally indicated at 20, forming at least a region of the stretchable sensor layer. The stretchable bidirectional pressure sensor 20 comprises a first elastomeric sheet 22, a microstructure 24, and a second elastomeric sheet 26. The first elastomeric sheet 22 and second elastomeric sheet 26 are made from a dielectric material. A series of parallel running conductor lines 221 is disposed on or in the first elastomeric sheet 22. The microstructure 24 comprises a plurality of elastomeric pillars 241 made from a dielectric material. Each pillar in the present embodiment is a cuboid, preferably a rectangular cuboid with a width of approximately 6 p.m and a height less than 300 p.m.

Although not apparent from the exploded view in figure 1, two opposite faces of the cuboid pillars are bonded, either indirectly or directly, to the first elastomeric sheet 22 and the second elastomeric sheet 26. A series of parallel running conductor lines 261 are disposed on or in the second elastomeric sheet 26. The series of conductor lines of the first elastomeric sheet 221 are orthogonal to the series of conductor lines of the second elastomeric sheet 261.

Thought the conductor lines in Figure 3 are shown as solid lines, the skilled person will recognise that this is not indicative of the type of material used. In preferable embodiments the conductor lines are formed from carbon nanotubes, however any conductive material which is known to the skilled person as being flexible arid deformable while maintaining its electrical properties would be suitable.

Each of the elastomeric sheets 22 and 26 are laminate structures with a PDMS laminate layer. Both the first elastomeric sheet and the second elastomeric sheet are essentially identical in construction. Therefore, when the stretchable bidirectional capacitive pressure sensor 20 is constructed the elastomeric sheets may be orthogonally disposed.

Both elastomeric sheets include a stretchable electrode disposed on an edge, in the current embodiment this is a serpentine electrode 28 made from copper. Each serpentine electrode 28 is connected to the ends of all the conductor lines in the series on its respective sheet. Furthermore, the serpentine electrode of the first elastomeric sheet is perpendicular to the serpentine electrode of the second elastomeric sheet.

Figures 4 and 5 both show the stretchable bidirectional capacitive pressure sensor viewed in plan. In the present embodiment, the elastomeric sheets and pillars are translucent or transparent allowing for both series of conductor lines and serpentine electrodes to be seen. However, in other embodiments the elastomeric sheets may be opaque. The stretchable bidirectional capacitive pressure sensor 20 comprises a first elastomeric sheet 22 having a series of conductor lines 221, a microstructure, and a second elastomeric sheet having a series of conductor lines 26L Each elastomeric sheet comprises a series of conductor lines 221 and 261 formed from carbon nanotubes. The series of conductor lines in the first elastomeric sheet are orthogonal to the series of conductor lines in the second elastomeric sheet. This provides for crossing points 29, or apparent intersections, between the conductor lines. Although not visible in Figure 4 or Figure 5, the microstructure comprises a plurality of pillars bonded either directly or indirectly to the elastomeric sheets. Each pillar is disposed and bonded at a crossing point 29. The magnified view of the stretchable bidirectional pressure sensor provided in Figure 4 shows in broken lines the approximate outline of two pillars located and bonded at crossing points. The serpentine electrodes 28 are connected to each conductor line in a series of conductor lines.

Figure 6 shows an exploded schematic view of a stretchable multi-layered sensing apparatus, generally indicated at 30. The stretchable multi-layered sensing apparatus is formed from a plurality of stretchable sensor layers of the sensing and actuating material.

In the current embodiment, the stretchable multi-layered sensing apparatus 30 comprises a stretchable laminate structure 32, a second stretchable lamina structure 34 and a first stretchable lamina structure 36. The stretchable structures 32, 34 & 36 form a stack. The laminate structure 32 may form the surface of the apparatus and therefore the surface of the sensing and actuating material. In other embodiments the stretchable multi-layered sensing apparatus 30 only needs to have stretchable sensing laminate structure 32 and the first stretchable sensing lamina structure 36.

Although not apparent from the exploded schematic view in Figure 6, the first stretchable lamina structure 36 is attached to the second stretchable lamina structure 34 which is attached to the stretchable laminate structure 32. In other embodiments, the first stretchable lamina structure 36 is attached to the stretchable laminate structure 32.

The stretchable laminate structure 32 has a first dielectric elastomeric sheet 321, a second dielectric elastomeric sheet 323 and a microstructure formed by a plurality of dielectric elastomeric pillars 325. Each pillar in the present embodiment is preferably a cuboid. Although not apparent from the exploded view in Figure 6, two opposite faces of the cuboid pillars are bonded, either indirectly or directly, to the first dielectric elastomeric sheet 321 and the second dielectric elastomeric sheet 323.

The stretchable laminate structure 32 has an array of sensors for measuring strain orthogonal to the surface of the apparatus. The sensors are formed by a first series of parallel running conductor lines 327 disposed on or in the first dielectric elastomeric sheet 321, a second series of parallel running conductor lines 329 disposed on or in the second dielectric elastomeric sheet 323, and the plurality of dielectric elastomeric pillars 325. The first series of conductor lines 321 are orthogonal to the second series of conductor lines 323. Each pillar 325 of the microstructure is bonded to both the first and second dielectric elastomeric sheets so that the array of sensors can register strain orthogonal to the surface. The registered strain can be representative of both a positive and negative pressure external to the apparatus, particularly the pressure along the surface of the apparatus or the first dielectric el astom eri c sheet 321.

Each pillar 325 is located at a crossing point between conductor lines of the first series 327 and second series of conductor lines 329. There is no point at which the conductor lines of the first and second series are in physical contact, however there is a point at which they cross when the apparatus is viewed from above or below. The combination of pillar and conductor line crossing point form the sensor.

C = 7 [1] Where the capacitance (C) is inversely proportional to the distance between the orthogonal conductor lines (L), and directly proportional to the area formed by conductor lines at the crossing point (A), relative permittivity of the dielectric material (er) and the permittivity in a vacuum (E0). By calculating the change in capacitance, it is possible to calculate the location and intensity of the force.

The first series and second series of conductor lines 327, 329 are schematically represented by solid lines in Figure 6, this is not indicative of the structure or type of material. In preferable embodiments the conductor lines may be formed from carbon nanotubes, however any conductive material which is known to the skilled person as being flexible and deformable while maintaining its electrical properties would be suitable.

The first dielectric el astomeric sheet 321 and second dielectric el astomeri c sheet 323 of the laminate structure 32 may each include a stretchable electrode in the form of a serpentine electrode 331 made from copper. Each serpentine electrode 331 is connected to the ends of all the conductor lines in the series on its respective sheet.

In the embodiment shown in Figures 3 to 6, the bidirectional pressure sensor uses a capacitive sensing mechanism. An external force causes the pillars to deform either by compressor or extension. This deformation causes a change in capacitance as the distance between the conductor lines change. The capacitance of each pillar and conductor line crossing point is calculated by equation 1.

Eo ErA Furthermore, the serpentine electrode of the first elastomeric sheet is perpendicular to the serpentine electrode of the second elastomeric sheet.

The second lamina structure 34 comprises a dielectric elastomeric sheet 341 with an array of sensors 343 for measuring temperature. The array of sensors 343 are disposed on the dielectric elastomeric sheet 341. In other embodiments, the sensors may be embedded within the dielectric elastomeric sheet 343 or another sheet. Additionally, the sensors may be encapsulated by an additional layer of dielectric elastomeric material.

The array of sensors for measuring temperature 343 are arranged in five rows of three sensors. In other embodiments the number of sensors within a row and the number of rows may vary. Each sensor 343 has an electrical property which varies based on temperature. For example, a thermistor or at least one conductive filament arranged in a known pattern in which the resistance changes based on a temperature.

See Figure 8 for an example of a conductive filament pattern.

Each sensor 343 is represented schematically as blocks; however, this is not indicative of the type of sensor. For example, a sensor may be constructed from a temperature-sensitive conductive filament pattern. The electrical resistance of the pattern changes based on deformation of the pattern due to temperature. See Figure 8 for an example of a conductive filament pattern.

Each sensor in the row is connected to another in the same row by stretchable electrodes 345. The stretchable electrodes 345 are represented schematically by solid lines in Figure 6, but this is not indicative of the structure or type of material. The stretchable electrodes 345 may be any construction which allow for the electrical properties to be maintained while being flexible and/or deformable. For example, they may be serpentine electrodes or electrodes formed from carbon nanotubes as shown in Figures 7 and 8.

The first lamina structure 36 comprises a dielectric elastomeric sheet 361 with an array of sensors 363 for measuring strain. The array of sensors 363 are disposed on the dielectric elastomeric sheet 361. In other embodiments, the sensors may be embedded within the dielectric elastomeric sheet 361 or another sheet. The sensors may also be encapsulated by an additional layer of dielectric el astomeri c material. The first lamina structure 36 has an adhesive layer 367 which allows the sensor 30 to be attached to an object.

The array of sensors for measuring strain 363 are arranged in five rows of three sensors. In other embodiments the number of sensors within a row and the number of rows may vary. Each sensor is represented schematically as blocks; however, this is not indicative of the type of sensor. For example, a sensor may be constructed from a strain- 1 0 sensitive conductive filament pattern. The electrical resistance of the pattern changes based on deformation of the pattern. See Figure 7 for an example of a conductive filament pattern.

Each sensor in the row is connected to another in the same row by stretchable electrodes 365. The stretchable electrodes 365 are represented schematically by solid lines in Figure 6, but this is not indicative of the structure or material. The stretchable electrodes 365 may be any construction which allow for the electrical properties to be maintained while being flexible and/or deformable. For example, they may be serpentine electrodes or electrodes formed from carbon nanotubes as shown in Figures 7 and 8.

Figure 7 shows an array of sensors 40 from the first lamina structure. The array of sensors is constructed from a plurality of sensor rows. Each row comprises a series of sensors 42 connected by stretchable electrodes 44. The sensors shown are strain-sensitives structures constructed from a conductive filament arranged in a known pattern. A conductive filament pattern will use a property of electrical conductance and its dependence on the conductor's geometry to determine strain. When the conductive filament is deformed or stretched, within limits of the material's elasticity, it becomes narrower and longer resulting in an increase in electrical resistance. Conversely, when compressed the conductive filament will broaden and shorten, decreasing its electrical resistance. The electrical resistance is indicative of the strain. A typical pattern for a strain-sensitive conductive filament is a series of parallel conductor runs. Each parallel run is connected to another parallel run by an orthogonal conductor run at its end. The parallel runs are closely spaces and may vary in length. There are other known patterns which involve complex shapes and/or curved conductor runs.

The stretchable electrodes 44 are serpentine electrodes made from a conductive material such as copper. In other embodiments, the stretchable electrodes 44 can be formed from carbon nanotubes (similar to Figure 8) applied to the elastomeric material in the first lamina structure. The stretchable electrodes 44 maintain their electrical properties when stretched or deformed.

Figure 8 shows an array of sensors 50 from the second lamina structure. The array of sensors is constructed from a plurality of sensor rows. Each row comprises a series of sensors 52 connected by stretchable electrodes 54. The sensors shown are temperature-sensitive structures constructed from a conductive filament arranged in a known pattern. A conductive filament pattern will use a property of electrical conductance and its dependence on the conductor's geometry to determine temperature.

When the conductive filament experiences a change in temperature the resistivity of the material will change. The change in resistivity is indicative of the change in temperature. The patterns used for temperature sensing may be similar to those used for strain gauges, however they may be different.

The stretchable electrodes 54 are formed from carbon nanotubes. In other embodiments, the stretchable electrodes 54 may be formed from serpentine electrodes (similar to Figure 7). The stretchable electrodes 54 maintain their electrical properties when stretched or deformed.

As shown in Figure 9, the actuation layer 14 comprises a plurality of parallel running piezoelectric fibres 141 disposed in a deformable matrix material 143 and electrodes (not shown) for controlling the piezoelectric fibres. In the current embodiment, the piezoelectric fibres are lead zirconate titanate fibres, however the type of material used for both the piezoelectric fibre and deformable material may be varied based on individual requirements, such as the required deformation, forces and mechanical properties Figure 10 shows a single deformable cell forming part of an actuation layer 14. The actuation layer 14 is comprised of many copies of the deformable cell, which may be formed integrally and continuously. The deformable cell is formed by a first interdigitated electrode pair and a plurality of parallel piezoelectric fibres 141 disposed in a deformable matrix material 143 within the region of the first interdigitated electrode pair. The first interdigitated electrode pair is formed by a first comb-like conductor 145 and a second comb-like conductor 147. Each comb-like conductor is disposed on or in the first surface of the actuation layer and is formed from a conductor line running parallel to the piezoelectric fibres and a plurality of finger conductors extending orthogonally from the conductor line. The piezoelectric fibres in the actuation layer 14 preferably pass through the full extent of the actuation layer, through multiple deformable cells. The deformable matrix material may be continuous across the multiple deformable cells. A deformable cell is not to be understood as necessarily being a part in its own right, but is simply a description of an arrangement which is repeated multiple times to form the actuation layer. The actuation layer may comprise a plurality of deformable cells in the sense that each deformable cell is individually addressable by a computer or controller.

The first comb-like conductor may be the positive electrode and the second comb-like conductor may be the negative electrode, or vice versa. When a voltage is applied across the comb-like conductors in the interdigitated electrode pair an electrical field is formed between each of the finger conductors of the comb-like conductors. This causes a contraction in the actuators 141.

In other embodiments, the deformable cell may include a first interdigitated electrode pair disposed on or in the first surface of the actuation layer, a second interdigitated electrode pair disposed on or in a second surface of the actuation layer and a plurality of parallel piezoelectric fibres disposed in a deformable matrix material within the region of the first and second interdigitated electrode pairs. Each of the first and second interdigitated electrode pairs comprise a first comb-like conductor and a second comb-like conductor. Each comb-like conductor is formed from a conductor line running parallel to the piezoelectric fibres and a plurality of finger conductors extending orthogonally from the conductor line. The first comb-like conductor of the second interdigitated electrode pair correspond with the first comb-like conductor of the first interdigitated electrode pair. The finger conductors in each of the first comb-like conductors align when viewed in cross section. The second comb-like conductor of the second interdigitated electrode pair correspond with the second comb-like conductor of the first interdigitated electrode pair. The finger conductors in each of the second comb-like conductors align when viewed in cross section.

The first comb-like conductors on both the first surface and second surface may be the positive electrode and the second comb-like conductors on both the first surface and second surface may be the negative electrode, or vice versa.

Referring to Figure 11, a further embodiment of the sensing and actuating laminate structure is generally indicated at 60. The sensing and actuating laminate structure comprises a sensing layer 12, a first actuation layer 14a, a host material layer 16 and a second actuation layer 14b. The sensing layer is attached to the first actuation layer 14a which is attached to the host material layer 16 which is attached to the second actuation layer 14b.

The parallel running piezoelectric fibres in the first actuation layer 14a are orthogonal to the parallel running piezoelectric fibres in the second actuation layer 14b.

In other embodiments, the angular offset between the parallel running piezoelectric fibres can vary based on the deformation requirements.

Referring to Figure 12, a further embodiment of the sensing and actuating laminate structure is generally indicated at 70. The sensing and actuating laminate structure comprises a sensing layer 12 and at least two actuating layers 14a, 14b. There may be a number of layers between the first actuating layer 14a and the second actuating layer 14b, as indicated by the separation in between Na and 14b in the figure. The sensing layer 12 is the uppermost layer and is attached to the first actuating layer 14a which is attached to a subsequent layer. The second actuating layer 14b is attached to a previous layer. In the current embodiment, the sensing layer 12 has a layer of dielectric material between the first elastomeric sheet and the second elastomeric sheet. Although not apparent from the schematic drawings, the piezoelectric fibres in the middle actuating layer 14a may be angularly offset from the bottom actuating layer 14b.

Referring to Figure 13, a further embodiment of the sensing and actuating laminate structure is generally indicated at 80. The sensing laminate structure comprises a top sensing layer 12, at least two host material layers 16a, 16b and at least two actuation layers Na, 14b. There may be a number of layers between the first actuating layer 14a and the second actuating layer 14b, as indicated by the separation between 14a and 14b in Figure 13. The sensing layer 12 is the uppermost layer and is attached to the first host material layer 16a which is attached to the first actuating layer 14a which is attached to any subsequent layers. The second actuating layer 14b is attached to a previous layer and the second host material layer 16b. In the current embodiment, the sensing layer 12 has a layer of dielectric material between the first el astomeri c sheet and the second elastomeric sheet. Although not apparent from the schematic drawings, the piezoelectric fibres in the middle actuating layer 14a may be angularly offset from the bottom actuating layer 14b.

Figure 14 shows the sensing and actuating laminate material according to any embodiment applied to a wing of an aircraft 90. A plurality of deformable regions 92 are provided on the aircraft wing 90. Each deformable area comprises a sensing and actuating laminate material according to the present invention. The sensing and actuating laminate material may include a portion of the skin of the wing as at least one of the host material layers or the sensing and actuating laminate structure may form a portion of the skin of the wing. The sensing layer is the outermost layer of the wing.

In one embodiment, a controller or computer (not shown) receives measurements taken from the sensing layer, such as pressure, temperature and/or in-plane strain. The measurements provide a spatial-temporal distribution of the physical parameters. Based on the measurements, the controller or computer determines which deformable region 92 to deform and how much deformation to apply. The actuation layers in the deformable regions 92 may have a plurality of individually addressable interdigitated electrode pairs. The controller or computer can determine which interdigitated electrode pairs should be controlled to deform the deformable region 92 to the required deformation. The controller or computer may also use other measurements, readings and information to determine deformation.

The embodiments described above are provided by way of example only, and various changes and modifications will be apparent to persons skilled in the art without departing from the scope of the present invention as defined by the appended claims

Claims

CLAIMS1 A sensing and actuating laminate material comprising a plurality of deformable layers, the plurality of deformable layers comprising: at least one stretchable sensor layer comprising an array of sensors; and at least one actuation layer having a plurality of elongate actuators for deforming the laminate material based on measurements taken from the at least one stretchable sensor layer.
2. A sensing and actuating laminate material claimed in claim 1, in which each actuator comprises a piezoelectric fibre, and the actuation layer comprise interdigitated electrodes for controlling the actuators
3. A sensing and actuating laminate material claimed in claim 1 or claim 2, in which there are a plurality of actuation layers.
4. A sensing and actuating laminate material as claimed in claim 3, in which the elongate actuators of one layer are angularly offset from the elongate actuators of another layer.
A sensing and actuating laminate material as claimed in any preceding claim, in which the plurality of reversibly deformable layers further comprises at least one layer of a host material
6. A sensing and actuating laminate material as claimed in claim 5, in which the host material is a fibre composite, a carbon composite or lattice structure composite.
7. A sensing and actuating laminate material as claimed in claim 5 or claim 6, in which the host material is part of a host structure.
8 A sensing and actuating laminate material as claimed in any preceding claim, in which at least one stretchable sensor layer is an external layer of the material.
9. A sensing and actuating laminate material as claimed in any preceding claims, in which the or each of the at least one stretchable sensor(s) is adapted to measure at least one of pressure, temperature and in-plane strain
10 A sensing and actuating laminate material as claimed in any preceding claims, in which the at least one stretchable sensor comprises bidirectional pressure sensors.
11. An aircraft comprising a sensing and actuating laminate material as claimed in any preceding claim.
12. A method of deforming a deformable region of a layered material, comprising the steps of a controller or computer controlling a plurality of elongate piezoelectric actuators to deform the deformable region based on measurements from a stretchable sensor, the stretchable sensor forming one of the layers of the layered material within the deformable region, and the piezoelectric actuators forming another layer of the layered material within the deformable region.