WO2020056463A1

WO2020056463A1 - Sensor array and sensor array system

Info

Publication number: WO2020056463A1
Application number: PCT/AU2019/051004
Authority: WO
Inventors: Adin Ming TAN; Yehuda WEIZMAN; Franz Konstantin Fuss
Original assignee: Swinburne University Of Technology
Priority date: 2018-09-19
Filing date: 2019-09-19
Publication date: 2020-03-26

Abstract

A sensor array comprising a plurality of sensors distributed over one or more functional layers. Each functional layer includes a plurality of sensor regions, a plurality of first electrode and one or more second electrodes, arranged on and retained between a first substrate and a second substrate. The plurality of first electrodes and one or more second electrodes are arranged to overlap sensor regions to cause each sensor to be electrically connected via a first and a second electrode when the first substrate and second substrate are adhered together. The sensor array can also be incorporated into a system including a controller configured to be electrically connected to each one of the first electrodes and second electrodes of each functional layer to sample signals from the sensor array. The sensor array and system components can be incorporated into garments and equipment.

Description

Sensor Array and Sensor Array System

Technical field:

The field of the invention is pressure sensor arrays, in particular, wearable sensor arrays. An example of an application of a wearable pressure sensor array is use in footwear for biofeedback, for example, for gait analysis.

Background:

Wearable sensor arrays, such as those for innersoles for shoes can provide useful biofeedback. However, the practical applications of such sensor arrays can be limited by poor resolution due to distance between sensors and physical robustness of the sensor arrays.

A typical example of a multiplexed solution is described in WO201500321 1. This system provides a sensor array, particularly for placement in shoe innersoles. The system comprises a sensor grid comprising an array of sensors that may be any conventional sensor type such as pressure sensitive material which has resistive, capacitive or piezoelectric properties, with a grid of wires or electrode strips on either side of the pressure sensitive material, or on one side of the pressure sensitive material only, to provide a pressure sensitive grid. If the grid is located on one side of the pressure sensitive material only, insulating material is provided at the intersection of wires or strip electrodes running perpendicular to each other. Space must be left between the sensors for adhesive to glue the layers of the sensor together, thus resulting in a trade-off between sensing area and glue area. Pressure measurements are made by sampling the signals of each pressure sensor.

In this sensor array all sensor are connected to each other, row by row and column by column, and multiplexing is done at the sensor level.

Although the design described above, and disclosed in WO201500321 1 , seems to be advantageous, it is affected by many problems, mainly related to the grid connected sensor array and usage of such designed sensor systems:

1 ) The sensor grid is not durable, specifically when subjected to cyclic or repetitive high forces (e.g. impact), shear forces, and deformation such as bending. All of which are typical in some applications such as athletic shoes. The plastic sheets on which the tracks and sensors are printed tend to delaminate and separate at the point where top and bottom plastic sheets are glued together. This causes electrical failure of the array, by either loss of electrical contact, distortion of electrical signals, or shorting. Failures are common specifically at the through-hole locations.

2) Failure of a single pressure senor in the array will cause loss of signals from the linked sensors in the same row and column as the faulty sensor. This means that a single sensor failure results in the loss of X + Y - 1 sensors. Sensor failure can be prevalent due to low durability of the physical array structure as discussed above.

3) Design-wise, space is required for the tracks to run from the sensor grid array to the connector. This can happen outside, at the outskirts of the sensor grid array, or, if there is no space left in e.g. confined spaces, then the tracks have to run between the sensors. This reduces the sensor size and requires through-holes, so that tracks can pass from one side of the flexible PCB to the other side, or insulating bridges, so that tracks can cross each other. This adds further manufacturing processes to the complexity of sensor array printing.

Furthermore, through-holes are unreliable, prone to failure (specifically on delamination). Delamination does not usually affect the through-holes. However, the applied conductive paint connecting the top and bottom faces of the substrate is prone to mechanical failure such as cracking, when stress is applied to the flexible substrate. Through holes can also be difficult to manufacture when incorporated together with the printing process. Track bridges can also cause track failure.

4) The sensors of the sensor matrix can never cover the entire area to be scanned. The reason for this is twofold. First, gaps between the sensors are required to glue top and bottom plastic sheets together to maintain the electrical integrity of the flexible PCB. Second, gaps allow tracks to be placed between the sensor cells. However, maximum area coverage is important, specifically if the sensors measure pressure and the overall normal force has to be calculated from all pressure sensors.

5) The sensor array system is affected by sensor cross-talk. All sensors are interconnected by the row/column track system, and therefore, the current does not only go through the sensor to be measured, but also through the neighbouring sensors simultaneously.

Therefore, if the measured sensor experiences a low pressure and a neighbouring cell a high one, then the signal on the measured cell is higher than expected. There are electronic methods for reduction of cross-talk but it can never be completely eliminated.

6) All the sensors of the array system are scanned one after the other, which affects the data sampling rate: the more sensors, the slower the sampling rate.

There is a need for improved wearable sensor arrays. Summary of the invention:

According to one aspect there is provides a sensor array comprising a plurality of sensors distributed over one or more functional layers, each functional layer comprising: a plurality of sensor regions, a plurality of first electrode and one or more second electrodes, arranged on and retained between a first substrate and a second substrate, wherein the plurality of first electrodes and one or more second electrodes are arranged to overlap sensor regions to cause each sensor to be electrically connected via a first and a second electrode when the first substrate and second substrate are adhered together.

In some embodiments the plurality of first electrodes and the one or more second electrodes are arranged in an interdigitating pattern in regions for connection to sensor material.

In some embodiments the sensor array comprises two or more functional layers, and wherein the first or the second substrate layer of one functional layer can also be a first or second substrate for another functional layer.

In some embodiments the sensors are arranged in a plurality of rows or columns distributed over different functional layers without overlapping of the sensor regions.

In some embodiments the sensors are printed on the substrate.

In some embodiments each of the first substrate and second substrate comprise flexible polymer material. In some embodiments where the substrate is a fibre composite the sensors can be formed by soaking or coating regions of the fibre composite with sensor material.

In some embodiments the sensor material is one of: piezoresistive, piezoelectric, or capacitive, the sensor material being configured to provide electrically readable outputs indicative of any one or more of: pressure, force, stretch, bend, displacement, temperature, or humidity.

In some embodiments the first and second electrodes are printed on the first or second substrate.

In an embodiment for each functional layer: the plurality of first electrodes and one or more second electrodes are formed on the first substrate; and the plurality of sensor regions are formed on the second substrate.

In an alternative embodiment for each functional layer: the plurality of first electrodes are formed on the first substrate; the one or more second electrodes are formed on the second substrate; and the plurality of sensor regions are formed on at least one of the first substrate and second substrate overlaying the printed electrodes to provide a plurality of sensor regions.

In some embodiments one or more of the first substrate and second substrate further comprise a printed glue layer for adhering the first substrate and second substrate together to form the electrical connection between the sensors and first and second electrodes.

In an embodiment for each functional layer: the plurality of first electrodes and one or more second electrodes are formed on the first substrate; the plurality of sensor regions are formed on the first substrate overlaying the first and second electrodes, and a glue layer is provided on the second substrate. In some embodiments the glue layer further comprises additional thickness of glue for adhesion between the sensor regions. In some alternative embodiments glue regions are formed between sensor regions on the first substrate.

According to another aspect there is provided a sensor array system comprising: a sensor array in accordance with an embodiment as described above; and a controller configured to be electrically connected to each one of the first electrodes and second electrodes of each functional layer to sample signals from the sensor array.

In some embodiments the controller is configured to multiplex sampled signals from the plurality of sensors.

In some embodiments the controller is further configured to analyse the sampled signals from the plurality of sensors.

Brief Description of the Drawings:

Figure 1 is a representative of block diagram of a simple embodiment of a sensor array system.

Figure 2 is a legend for the patterns used consistently in array cross sections of Figures 3a to 7b.

Figures 3a and 3b illustrate a cross section of a single functional layer embodiment.

Figures 3c and 3d illustrate a cross section of an alternative single functional layer embodiment.

Figures 4a and 4b illustrate a cross section of a dual functional layer embodiment.

Figures 5a to 5c illustrate a cross section of an alternative dual functional layer embodiment. Figures 6a and 6b illustrate a cross section of a triple functional layer embodiment. Figures 7a and 7b illustrate different manufacturing approaches to achieve the same resulting functional layer structure.

Figure 8 shows a 3-layer solution of a smart insole sensor array, showing each functional layer separately.

Figure 9 shows the 3 layers of the smart innersole sensor array of Figure 8 as assembled, with each layer shown in a different shade of grey.

Figure 10 is an exploded view of the smart innersole sensor array of Figure 8, to illustrate assembly, with each layer shown in a different shade of grey.

Figure 1 1 illustrates an example of interdigitating power and sensor electrodes.

Figure 12a illustrates a simple example of construction of a functional layer (showing facing sides of substrate layer which are arranged to be placed together like a sandwich or closing a book to form functional layers).

Figure 12b illustrates an alternative simple example of construction of a functional layer (showing an arrangement where the substrates are such that these are slid over each other to be overlayed to functional layers).

Figure 13 illustrates a simple example of construction of a functional layer where electrodes are arranged on opposite sides of the sensor material.

Figure 14 illustrates an alternative example of construction of a functional layer.

Detailed Description:

Embodiments of the present invention provide a sensor array and a sensor array system comprising a plurality of sensors distributed over one or more functional layers. Each functional layer comprises a plurality of sensor regions, a plurality of first electrodes and one or more second electrodes arranged on and retained between a first substrate and a second substrate. The plurality of first electrodes and one or more second electrodes are arranged to overlap sensor regions to cause each sensor to be electrically connected via a first and a second electrode when the first substrate and second substrate are adhered together. The sensors and tracks are arranged on one or the other of the first and second substrates, with the arrangement varying between embodiments.

The system also includes a controller configured to be electrically connected to each one of the first electrodes and second electrodes of each functional layer and sample signals from the sensor array. In the preferred embodiments the sensor material is pressure sensitive material, but other types of sensor materials are considered within the scope of the present application.

Figure 1 is a representative of block diagram of a simple embodiment of a sensor array system. The system 100 comprises a controller 1 10 and a sensor array 120. The sensor array 120 comprises a plurality of sensors 140a-d distributed over one or more functional layers 130. The sensors and sensor electrodes are arranged on substrates which are adhered together to form a functional layer (the functional layer construction is discussed further below). Note that although glue is referred to as the means for adhesion in the embodiments discussed other methods of adhesion can also be used, for example fusing, welding or physical fasteners, all feasible alternatives are considered within the scope of the sensor array embodiments. Each one of the sensors 140a-d is electrically connected via a common electrode 150, (for example to supply power to the sensors via a power output 155 of the controller) and an individual sensor electrode 160a-d (for reading the sensor signal). The array electrodes 150, 160a-d are connected 150’,160’a-d to the controller 1 10 and optionally multiplexed. In some embodiments the controller 1 10 may be a single chip microcontroller for controlling sampling, supporting circuitry and power supply. Alternatively, the controller 1 10 may be a controller unit comprising a microcontroller and other

components, for example a processor for analysing samples signals and/or wireless communication interface for communicating with external devices or systems. In some embodiments the microcontroller may be configured to multiplex sampled signals or an additional multiplexer. The controller configuration may vary between embodiments depending on the sensor array application and nature of the wearable carrying the array. In some embodiments, there may be a physical multiplexer for each functional layer.

The array comprises one or more functional layers, each layer comprising plurality of first electrodes and one or more second electrodes are arranged to overlap sensor regions between a first and a second substrate. The electrodes may be formed by printing on the substrate layers. The sensors material may be printed onto one or the other of the substrate layers. Alternatively, fibre composites may be used with sensors formed by soaking or coating regions of the fibre composite with sensor material.

Figures 2 to 7b illustrate cross sections of some possible arrangements of functional layers of sensor arrays, in which Figure 2 is a legend for the patterns used consistently to represent sensors 201 , electrodes or tracks 202, glue 203 and substrates 204 in the array cross sections of Figures 3a to 7b.

Figures 3a and 3b illustrate a single functional layer embodiment having 2 sub-layers, with 1 substrate, each shown separately 305 (for example in an intermediate stage of manufacture) in Figure 3a and fully assembled in a functional layer 310 in Figure 3b. The top sublayer 310 comprising the first substrate 204, supporting the sensors 201 and glue area 203, and the bottom layer 320 comprising the second substrate 204 supporting the first and second electrodes 202. In this example the area of the sensors is maximised at the expense of the glue area which is insufficiently large and, in this configuration, represents a risk of delamination. This arrangement may be feasible for a linear array where extra glue may be provided adjacent the sensor regions for improved adhesion of the layers, however the risk of delamination in the sensor regions remains. Alternatively, sensor area may be sacrificed to increase the adhesion area. Figures 3c and 3d, show a single functional layer embodiment (in two separate sublayers 315 in Figure 3c and as an assembled functional layer 320 in Figure 3d), similar to Figures 3a and 3b. Flowever, in this example in the functional layer 315 the area of the sensors 201 is as large as the glue area 203, the sensor area is reduced to 50%. In this example adhesion in the final functional layer 320 is improved at the cost of sensor area coverage. For some applications this may provide insufficient sensor area coverage.

By using two or more functional layers 320 and distributing the sensor regions over the two or more functional layers it becomes feasible to achieve 100% sensor area coverage.

Further, distributing the sensor areas over multiple functional layers can allow greater area for glue and hence reduce delamination risks. Figure 4a illustrates two functional layers 325 each having two substrates 204. The sensor 201 and glue 203 areas of the respective substrates are aligned such that the total sensor 201 area is 100% when both functional layers are combined and glued together as shown in Figure 4b. Note in this embodiment the assembled sensor array has two substrates 204 glued together 203 through the middle of the array.

Figure 5a illustrates another embodiment having three sub-layers 335, with 1 substrate each. In this example the top sublayer comprises a substrate 204t having sensors 2011 and glue 203t area. The centre layer is a substrate 204c with electrodes and tracks 202c formed on one side, arranged adjacent to the top sub-layer, and sensors 201 c and glue 203c on the other side of the substrate 204c. The bottom layer bears tracks and electrodes 202b arranged opposite the sensors 201 c and glue 203c arranged on the centre layer substrate 204c. The sensors 2011 of top layer and sensors 201c of centre layer are arranged alternatingly so that the total sensor area is 100%. Figure 5b shows the assembled dual functional layer sensor array 340. From a comparison of Figure 4b and 5b is can be observed that the sensor array of figure 5b is thinner, having one less substrate than figure 4b. Figure 5c illustrates an alternative sublayer formation 345 to achieve the sensor array configuration of Figure 5b. In Figure 5c the bottom sublayer 204b has the tracks and electrodes 202b formed on the substrate 204b and glue sections 203b arranged on top of the tracks and electrodes 202b to adhere between the sensor regions 201 c formed on the adjacent side of the centre layer substrate 204c. Although not shown, the top and centre layer may use a similar configuration. Figure 5c illustrates that it is the final order and arrangement of the sensors glue and tracks that is important, not the intermediary arrangement of these component parts on the first and second substrates that is critical to the functionality of the sensor array. Flowever, the order and arrangement for forming the tracks and electrodes, sensors and glue on the first and second substrates may be modified based on manufacture preferences, equipment restrictions, efficiencies, or ease of assembly.

Figure 6a and 6b illustrate an embodiment comprising 3 functional layers 350, formed using 4 sub-layers, with 1 substrate 204 each. The top sub-layer having a substrate 204, sensors 201 and glue 203 areas, two similar centre layers each having a substrate 204 with sensors 201 and glue 203 on one side and tracks/electrodes 202 on the other side of the substrate 204. The bottom layer has a substrate 204 supporting tracks and electrodes 202. The sensors 201 of top and the 2 centre layers are arranged alternatingly so that the total sensor area is 100%. Figure 6b illustrates the layers of Figure 6a assembled together in a triple functional layer sensor array 355.

In some embodiments the sensors, electrodes/tracks and glue can be printed on the first and second substrates. Figures 7a and 7b illustrate different manufacturing approaches to achieve the same resulting functional layer and array structure. These examples show single functional layers (even though this is inefficient or lacks robustness in a practical embodiment, a single functional layer is useful for illustrative purposes) which could be combined into multi-functional layer embodiments similarly to figures 4a-6b. Figure 7a illustrates an embodiment of a preassembled functional layer 360 where the first (upper) substrate 204 is first printed with electrodes and tracks 202, for example using screen printing or inkjet printing using electrically conductive inks. On top of the electrically conductive electrodes 202 on the substrate 204 the sensors 201 are printed, for example screen printing sensor regions using piezo-resistive ink. The second substrate 204 layer is printed with glue 203, which may cover the entire second (bottom) substrate, with additional thickness of glue 203 for adhesion between the sensor regions 201 . In the preassembled functional layer 365 of Figure 7b, the first (upper) substrate 204 is first printed with electrodes and tracks 202, for example using screen printing. On top of the electrode layer 202, sensor regions 201 are printed, and glue regions 203t are printed between the sensor regions 201. The second (lower) substrate 204 is simply printed with glue 203b to adhere to the first sub-layer on the first substrate 204. It should be appreciated that in this

embodiment the array structure will be robust due to the full layer coverable of glue.

Embodiments may also be configured to have electrodes formed on both the first and second substrates such that the electrodes will be on either side of the sensor (not shown).

In an embodiment these sensor array systems can be printed on e.g. polymer sheets as a flexible printed circuitry board (PCB), either by screen printing or ink-jet printing. The printed sensors can be, electrically seen, for example piezoresistive, piezoelectric, or capacitive, that measure for example quantities such as pressure, force, stretch, bend, displacement, temperature, humidity. In alternative embodiments, instead of polymer sheets the substrate on which the sensor array is printed may be wood, metal (with insulating coating), fabric etc. Combinations of materials may also be used. Any material able to be compressed by external force to activate the sensor material may be used in various embodiments.

Embodiments of the sensor array may be incorporated into garments, sporting equipment or other objects (hats, helmets, gloves, pads, bats, guards, jerseys, jackets, body armour, shoes etc) and the materials for the sensor array may be chosen based o functional requirements of the garment, equipment or object.

The substrate does not need to be a plastic or polymer material, other materials may be used. The sensors are not necessarily printed on the substrate. Different sensor compounds can be used. For example, fibre composite sensor arrays can be affected by problems such as lacking robustness and delamination, similarly to printed sensors. A problem associates with fibre composite sensors is when a glass fibre fabric (substrate) is coated or soaked by piezoresistive ink (to form a sensor), then the epoxy or resin (glue) can no longer penetrate the fabric (substrate). This weakens the composite structure and can leave layers at risk of delamination. In fibre composite embodiments the tracks/electrodes must be in direct contact with the sensor material, any epoxy/resin/glue between electrodes and sensors acts as an insulator, degrading performance of the array.

The sensor cells are distributed over, and printed or otherwise formed on, different functional layers, without multiplexing of rows and columns, but rather multiplexing of individual sensor cells.

An example of an embodiment of a sensor array for application in an innersole is shown in Figures 8, 9 and 10. Figures 8, 9 and 10 illustrate an example of a printed sensor array comprising three functional layers for application in an innersole. Figure 8 shows each of the three functional layers separately. The first functional layer 210 has sensors substantially arranged in two columns 240, 245 with each sensor, for example sensor 215, having a sensor electrode 260 and a common (power supply) electrode 255. In this example, all of the sensors 215 in one functional layer 210 share a common electrode connection 255. However, the sensor electrodes 260 for each sensor 215 are separately connected. Figure 8 illustrates tracks connecting the individual sensor electrodes following paths between the sensors and forming a parallel bus 250 or external connection. The tracks are printed on a flexible substrate using an electrically conductive material.

Each of the functional layers 210, 220, 230 are electrically insulated from each other. It should be apparent from the illustrated functional layers 210, 220, 230 that the tracks 260 on one layer can follow a path that is overlapped by the sensors of another functional layer.

This is perhaps more apparent from Figures 9 and 10. Figure 9 shows the three layers as assembled, with each layer shown in a different shade of grey. Figure 10 shows an exploded view of the smart innersole sensor array, to illustrate assembly, again with each layer shown in a different shade of grey.

This configuration enables sensors to be densely packed as tracks can run behind sensors on different functional layers, so there is no need to leave space between sensors for laying tracks.

Figure 1 1 illustrates an arrangement of the sensor and common power electrodes in the sensor regions. The sensor electrodes 510 and common electrodes 520 are interdigitated in the region behind the sensor material 530. These electrodes are arranged to pick up electrical signals from the sensor material. The interdigitating arrangement can improve the accuracy of detection of the sensor signals. This arrangement of electrodes 510, 520 can also be readily screen printed along with the tracks 515, 525. As can be seen from Figure 1 1 , all of the power electrodes 520 are connected via a common track 525, whereas sensor electrodes 510, 540, for sampling the sensor signals, are connected by one track 515, 545 for each sensor region.

In embodiments of the invention a functional layer (FL) can comprise several sublayers. Figure 12a illustrates one example of these sublayers.

In a first example of a shunt mode version (electrodes on one side of the sensor) as shown in Figure 12a for each functional layer: a) plastic layer A 610, provides a first substrate. In this example the substrate is flexible plastic or polymer material, but other materials may also be used. The amount of flexibility in the substrate may also vary based on the requirements for the application of the sensor array. b) electrodes (interdigitating at sensor contact) printed on plastic layer A 610. These include a common track and interdigitating electrodes 630 for each sensor region and individual tracks and interdigitating sensor electrodes 640, 642, 644 for each sensor. These tracks and electrodes are printed directly onto the plastic layer 610. c) sensor 650 and glue layer 660, both printed on plastic layer B 620 (space between sensors filled up with glue) on the side to be placed facing the first substrate. The sensors can be printed using a printable sensor material having piezoresistive, piezoelectric, or capacitive properties, to provide electrically readable outputs. Depending on the nature and properties of the sensor material the output may be indicative of any one or more of:

pressure, force, stretch, bend, displacement, temperature, or humidity. d) plastic layer B 620, provides the second substrate layer on which the sensors 650 and glue 660 are printed. The two substrate layers 610, 620 are arranged with sides bearing sensors 650 and electrodes 630, 640, 643, 644 placed together, with the sensors and electrodes overlapping, and adhered together using the glue 660. Figure 12a shows the surfaces of plastic layers 610, 620 and 670, 680 that are adhered together, like two sides of a sandwich or pages of a book. Thus, the sensors and tracks are prepared mirroring, to align once the substrates are assembled. It should be appreciated that this configuration allows for a substantial area of the substrate to be covered with the glue to provide good adhesion. This can provide good durability and resistance to delamination compared to the prior art sensor matrix discussed in the background section. In some embodiments glue may be printed on both of the substrates.

In the case of 2 or more functional layers, two adjacent functional layers can share one plastic layer. For example, as shown in Figure 12, one of substrate 680 or 670 may be the rear side of one of the other substrates 610 or 620. Therefore, the minimum number of plastic layers (A and B) required equals FL+1 (whereas the maximum number would be 2^*FL).

In a second example of a shunt mode version (electrodes on one side of the sensor) as shown in Figure 12bfor each functional layer: a) plastic layer A 810, provides a first substrate. In this example the substrate 810 is flexible plastic or polymer material, but other materials may also be used. The amount of flexibility in the substrate may also vary based on the requirements for the application of the sensor array. b) electrodes 830, 840, 842, 844 (interdigitating at sensor contact) printed on plastic layer A. These include a common track and electrodes 830 for each sensor region and individual tracks and sensor electrodes 840, 842, 844 for each sensor. These tracks and electrodes are printed directly onto the plastic layer. c) sensor regions 850 are printed onto plastic layer A 810 over the first and second electrodes 830,040, 042, 844. The sensors can be printed using a printable sensor material having piezoresistive, piezoelectric, or capacitive properties, to provide electrically readable outputs. Depending on the nature and properties of the sensor material the output may be indicative of any one or more of: pressure, force, stretch, bend, displacement, temperature, or humidity; d) a glue layer is printed either on layer A 810 (as shown) or on a plastic (or other material) layer B 870 to overlay layer A. This glue layer may include thicker portions corresponding with spaces between sensor regions (space between sensors filled up with glue). Plastic layer B 870, provides the second substrate layer (adhering to layer A 810 using the glue). The substrate sensor array structure is sandwiched between two substrate layers. e) The two substrate layers are adhered together using the glue. It should be appreciated that this configuration allows for the entire area of the substrate B to be covered with the glue (on the surface to face substrate layer A) to provide good adhesion. This can provide good durability and resistance to delamination compared to the prior art sensor matrix discussed in the background section. In some embodiments glue may be printed on both of the substrates, for example instead of thicker regions of glue on plastic later B, glue may be printed between the sensors on plastic layer A.

The outer surface of plastic layer B 870 may also be used for a substrate for another set of electrodes and sensors, offset from those sandwiched between substrate layers A and B, to increase the sensor coverage area, as illustrated in Figure 12b.

In an alternative embodiment, sensor regions 850 may be formed in a substrate (for example woven or impregnated material) or on an underside of the substrate, which is then slid over the substrate layer 810 on which the electrodes are printed to connect with the electrodes when adhered to the substrate 810 to form a functional layer.

It should be noted that although interdigitating electrodes are shown in the exemplary embodiment, the electrodes need not be interdigitating other configurations where both a first and second electrode are provided for each sensor region are contemplated for embodiments of the sensor array.

Figure 14 shows two examples of sensor and electrode arrangements where the electrodes do not cover substantially all of the sensor area, but rather are place toward the edge of the sensor area at opposite edges. In a first example, common electrode 930 and sensor electrodes 940, 942, 944 are printed or otherwise formed on a first substrate 910, and three sensor areas 950 are printed on or formed in a substrate 920 to align with the electrodes 930, 940, 942, 944 and the two substrates secured together with glue 960 to form the functional layer. Alternatively, the sensor and electrodes may be carried on the one substrate, for example by forming the sensor and printing eth electrodes over the top, or vice versa. In another embodiment an elongate sensor area 985 is printed on or otherwise formed in a substrate 980, and two electrodes 972, 975 are formed on a second substrate 970 to, once the two substrates are adhered together, align in contact with the sensor 985 proximate two opposite edges. Alternatively, the sensor and electrodes may be formed on the same substrate. The sensor may be in front or behind the sensors and may be aligned toward the top and bottom or opposite die edges. All such alternatives are contemplated within the scope of embodiments of the sensor array. Although Figure 14 illustrates a shunt mode arrangement of these sensors and electrodes, this can similarly apply to through mode embodiments.

In an example of a through mode version (electrodes on both sides of the sensor), the construction of this functional layer and an example of a process for manufacturing this functional layer is illustrated in Figure 13. Each functional layer can comprise: a) plastic layer A 710 b) electrodes 720 printed on plastic layer A 710, in the illustrated example these are common power electrodes 720 (but could alternatively be sensor electrodes) c) sensor 730 and glue 740 layer; one side of the sensor 730 comprising the sensor material is printed on plastic layer A 750, in this instance over the common electrodes 720. The other side of the sensor, the track for reading 760-765 are printed on plastic layer B 750. The space between sensors 730 (parallel to the plane of the plastic layers) is filled up with glue 740. The glue can be printed either on layer A 710 or B 750 or both (thereby printing the glue on top of the electrode tracks). d) electrodes printed on plastic layer B 750 to provide the sensor electrodes 760-765, forming the second sides of the sensors. e) plastic layer B 750

In this example as the electrodes 720, 760-765 are provided on opposite sides of the sensors the electrodes will typically not have an interdigitating configuration as this is not required in these embodiments as the electrical connection is made between the electrodes on either side of the sensor layer. In some embodiments the electrodes may not cover the whole of the sensor area as shown. For example, the electrodes may be formed as fingers or patterned to cover only a small part of the sensor (although sufficient to receive the sensor signal transmitted through the sensor material), in other embodiments the electrode may cover a substantial area of the sensor.

In some through mode embodiments, the sensor material is divided into two parts, where on substrate A, electrodes, and one side of the sensor are printed; and on substrate B, electrodes and the other side of the sensors are printed. Substrates A and B are joined such that the two sensor parts overlap, with an air gap between the two parts of a sensor.

Pressure or bending is detected by contact being made between the two sides of the sensor.

As in the shunt mode version, two adjacent functional layers can share one plastic layer.

These sensor array systems are printed on e.g. polymer sheets as a flexible printed circuitry board (PCB), either by screen printing or ink-jet printing. The printed sensors can be, electrically seen, for example piezoresistive, piezoelectric, or capacitive, that measure for example quantities such as pressure, force, stretch, bend, displacement, temperature, humidity.

In some embodiments the substrate may be wood. For example, for an embodiment where the sensor array is incorporated into a bat, board, deck or floor wood wooden panels, thin wooden planks or veneer sheets may be used as a substrate, having the properties of being flexible to enable compression of the sensor material. The sensor may be distributed between different wooden layer levels, which are connected with glue to provide a multilayer laminated wooden structure. Such an embodiment may be highly suitable for flooring or decking. In another alternative embodiment a substrate may be metal with insulating coating. Similarly to the wood embodiment, multiple layers may be used to build a laminated structure.

Array configurations as discussed above can be used in fibre composite array embodiments (sometimes referred to as“smart” fibre composite arrays). For example, embodiments using fibrous material for substrate or sensor layers, for example glass fibres, coated carbon fibres, Kevlar fibres, aramid fibres, polymer or natural fibres may be used as substrates or for the active components (sensor and electrode) in the functional layers. Hybrid

composites, such as glass/carbon fibres on different layers may also be used.

For example, for fabrication of a fibre composite array first a fibre substrate (for example glass fibre fabric) is coated or soaked in sensor regions with sensor ink (for example, piezoresistive ink). Alternatively, a paste or slurry of sensor ink may be applied to the fibre substrate in sensor regions. An advantage of using a paste or slurry is this is less likely to be absorbed into the fibres or spread (bleed) along the fabric fibres. This forms the sensor regions on the fibre substrate. Next the electrode and tracks are formed on top of the sensors by coating or printing, for example, using conductive paste, silver paste; with e.g. ink jet printer, screen printing, etc. It should be noted that a dedicated electrode/track sub-layer in the form of glass fibre fabric embroidered with electrodes and tracks is not feasible for embodiments using adhesives such as epoxy/resin as the adhesive can creep into the fabric and thus between electrodes and sensors, thereby creating an insulating layer and degrading performance. In this fibre composite embodiment one single functional layer comprises a fabric substrate, sensors distributed on or absorbed in the fibre substrate (i.e. on the surface of the fibre substrate or soaked through the fibre substrate), electrodes on top of the sensor regions and tracks formed on non-sensor regions of the fibre substrate, and an adhesive layer (i.e. epoxy/resin) on one side of the fabric substrate for adhesion to other functional layers.

These functional layers are then stacked and consequently glued together by the adhesive layer. Epoxy/resin of the adhesive layer creeps into the fabric to improve bonding. The adhesive layer can also insulate the layers from each other. Alternatively or additionally, a substrate fabric layer (i.e. a sheet of fabric, without sensors / tracks) can be inserted between the functional layers as an additional‘substrate’ sub-layer.

The sensors are distributed across different functional layers in order to maximize the available glue area (epoxy/resin area) without overlap of the sensor areas to enable up to 100% sensor area in total, with the sensors distributed over different functional layers. By distributing the sensors over different functional layers, the adhesion area is increased, reducing the risk of delamination, although delamination is not the only problem associated with fibre composite embodiments.

Fibre composite sensor arrays having pressure sensors incorporated in fibre composites would not only measure the pressure applied, or force distributed across, the composite. These sensor arrays can also respond to bending and buckling, for example as layers are pressed against each other on bending. These sensor arrays can also be used for detection of penetration. These sensor arrays can also be used to localise the point or area of impact or distributed force. For distributed force, the sensor array can be used to determine the centre of pressure (COP), about which all the sensor moments are in equilibrium (sensor moment = sensor force [i.e. sensor pressure times sensor area] times distance between COP and sensor). In embodiments of the present invention the sensor cells are distributed over, and printed on, different functional layers, without multiplexing of rows and columns, but rather multiplexing of individual sensor cells.

Embodiments provide printed sensor array systems, with sensors arranged in rows and columns that are multiplexed at the microcontroller level. Each sensor cell is supplied by 2 tracks (electrodes). One track is in contact with the specific sensor to be measured as well as all other cells in the same row of the sensor matrix. The other track is in contact with the specific sensor to be measured as well as all other cells in the same column of the sensor matrix. This electrode design keeps the overall number of tracks to the absolute minimum, by scanning one cell after the other.

For example, if the array has X rows and Y columns, the number of cells Z is: Z = X ^* Y. In an embodiment, the X row tracks can be connected to the output digital ports of the microcontroller, and the Y column tracks to the input analogue ports of the microcontroller. The number of tracks T on the band cable, or connection, between the sensor array matrix and the microcontroller is therefore: T = X + Y.

Advantages of this arrangement can include:

1 ) Increased surface area for adhesion because of more than one functional layer. By distributing sensors over more than one functional layer, space between sensors on each layer is increased, thus increasing adhesion area. Two layers increase the adhesion area from a minimum to at least 50%; and three layers to at least 67%. This prevents the delamination problem, e.g. shear failure of the sensor matrix. This also solves the manufacturing problem, as two sub-layers can be easily glued together without high precision printing.

2) Maximising the surface area of each printed sensor to be printed through reduction of gaps between sensors (which otherwise were required for adhesive purposes). This also improves the accuracy of the sensor matrix, as a maximum amount of area is covered by sensors, ideally by reducing the gaps between sensors to zero. For example, gaps between adjacent cells (that are not necessarily on the same layer) can be reduced to a minimum, preferably within a range of 0-1 mm, for maximal sensor area coverage.

3) Reduction of the width of the connecting band cable, as the tracks are distributed across several layers. This solves the problem inherent to the individual sensing solution, i.e. the requirement of 2 electrodes per sensor and therefore the number of tracks on the connecting band cable is twice the number of sensors. 4) Simplification of the manufacturing process as precision printing of tracks at through-holes and bridges, or in between cells, is no longer necessary. This solves the problem of ruggedness and reliability, and prevents shear failure of the sensor matrix. This also results in cheaper manufacturing costs.

5) In the event of a faulty cell, the fault localised instead of affecting an entire column plus an entire row within the sensor matrix. The number of faults is thereby kept to a minimum which improves the reliability and accuracy of the sensor matrix.

6) The sensor matrix is more shear resistant because of the increased adhesion area. This reduces the long-term failure problem such as shear delamination, resulting in loss of sensor-electrode contact, short-circuiting (through-mode version), and open-loop circuit if through-hole electrical connection is lost.

7) The individual-cell sensing method electrically isolates each cell and consequently avoids cross-talk entirely, and thereby improves the output data accuracy of the sensor matrix.

8) Also, the sampling rate is improved (compared to the multiplexing method with row and column electrodes). An example is given below.

The following example compares sampling sensor signals using the present sensor array connection configuration described above with the inferior prior art solution wherein sensors are interconnected via row and column electrodes.

In this example a sensor matrix compromises of X rows and Y columns; then number of sensor cells Z is therefore: Z = X^*Y.

Inferior (prior art) solution using row and column electrodes connecting each sensor: the rows and column electrodes are scanned by X digital ports and Y analog ports, respectively, by the microcontroller. The number of tracks T is therefore X + Y. The number of

consecutive reading steps R required to scan the entire matrix is R = Z. The number of simultaneous reading steps is 0.

Superior (current) individual sensing solution: Z number of cells are supplied by Z + 1 tracks (where the extra track is the driver, e.g. supplying 5 V)

If number of functional layers FL > 1 is then:

Each layer has cells such that _{= z} where the symbols

L

and J denote the ceiling and floor functions, respectively, i.e. rounding a number to the next higher or lower integer, respectively, and the symbol v denotes“or”. The number of tracks T per FL is: i , or maximally j = -i ; this

FL

number also depends on the size of multiplexor The total number of tracks is then (if a multiplexor can handle

+ 1

FL tracks)

There are tracks before the multiplexor; and after the multiplexor:

W+3 tracks (where _w , and‘3’ = 1 ground / GND track, 1 power track, 1 analog

track); a number of FL analog tracks are read in parallel (simultaneously) which improves to the sampling speed as follows: the number of FL parallel, i.e. simultaneous, reads happen at the same time (and not one after the other) and are therefore equivalent to 1 consecutive read. However, this 1 read per unit of time happens Z/FL times consecutively for scanning the entire matrix, so that the effective number of consecutive reading steps R required to scan the entire matrix is R = Z/FL.

For example, a sensor matrix consists of 9 columns and 20 rows, resulting in 180 sensor cells.

Inferior solution with row and column electrodes: there are 9 analog channels and 20 digital ones; the tracks are read and multiplexed at the same time, but not in parallel; 9 are read (not in parallel) 20 times (20 are switched); this results in a total of 180 consecutive reads for scanning the entire matrix. The connecting band cable has 29 tracks.

Superior individual sensing solution: 6 layers at 30 cells per layer are chosen as a design solution. There are 6 analog reads in parallel (simultaneously after multiplexing; therefore, 6 reads are reduced, and equivalent, to 1 read from a time perspective. However, this 1 read happens 30 times. Consequently, we obtain 30 consecutive reading steps for scanning the entire sensor matrix. The connecting band cable has 6 layers with 31 tracks each (before the

, 180

multiplexor). There are 8 tracks after the multiplexor, i.e. lo —

6 + 3

log 2

Comparing the two solutions, the number of 180 reads per scan (inferior solution) is reduced to 30 reading steps (superior solution), thereby increasing the reading speed considerably by sixfold, whereas the width of the band cable does not increase by sixfold, but rather marginally from 30 to 31 tracks.

The summary of advantages of the individual sensing solutions include any one or more of: cheaper, more accurate (no cross talk, minimised gaps), easier to manufacture, more robust and rugged, faster data sampling, reduced band cable, more reliable, less sensor failures.

The apparent disadvantage of the individual sensing solution, namely a very wide band cable (because the problem of increased number of tracks) is mitigated by printing on different functional layers.

It should be appreciated that embodiments of the disclosed sensor arrays and sensor array system may be configured for application in many alternative areas than for innersoles as is disclosed in the example. For example, arrays may be configured for integration into sporting clothing and equipment for measuring impact or other forces. Examples include but are not limited to: helmets, jackets, pants, guards/pads, surfaces (such as grip surfaces, handles, saddles and seats), racquets, bats, clubs, gloves (such as palm and dorsum, punching gloves, cricket gloves, catchers’ mitts etc.) and other equipment. Applications may also include medical or therapeutic equipment, or even industrial application. For example, embodiments may be used for sensor mats for wheelchair seats, or beds. Sensors for braces (for example scoliosis braces), splints, slings or prostheses. The sensor array could be used in smart mats and smart flooring, for example to enable monitoring of foot traffic. Sensor arrays may be integrated into gym equipment to provide additional feedback to users, for example regarding balance, asymmetry, stability etc while using the equipment. It should be appreciated that the number of sensors, number of layers and distribution of sensors over the layers may be varied based on requirements for the array application.

It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the invention.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as“comprises” or“comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

Claims

1. A sensor array comprising :

a plurality of sensors distributed over one or more functional layers,

each functional layer comprising:

a plurality of sensor regions, a plurality of first electrode and one or more second electrodes, arranged on and retained between a first substrate and a second substrate, wherein the plurality of first electrodes and one or more second electrodes are arranged to overlap sensor regions to cause each sensor to be electrically connected via a first and a second electrode when the first substrate and second substrate are adhered together.

2. A sensor array as claimed in claim 1 wherein the plurality of first electrodes and the one or more second electrodes are arranged in an interdigitating pattern in regions for connection to sensor material.

3. A sensor array as claimed in claim 1 or claim 2 wherein the sensor array comprises two or more functional layers, and wherein the first or the second substrate layer of one functional layer can also be a first or second substrate for another functional layer.

4. A sensor array as claimed in any one of claims 1 to 3 wherein the sensors are arranged in a plurality of rows or columns distributed over different functional layers without overlapping of the sensor regions.

5. A sensor array as claimed in any one of claims 1 to 4 wherein the sensors are printed on the substrate.

6. A printable array as claimed in any one of claims 1 to 5 wherein each of the first substrate and second substrate comprise flexible polymer material.

7. A sensor array as claimed in any one of claims 1 to 4 wherein the substrate is a fibre composite and the sensors are formed by soaking or coating regions of the fibre composite with sensor material.

8. A printable array as claimed in any one of claims 1 to 7 wherein the sensor material is one of: piezoresistive, piezoelectric, or capacitive, the sensor material being configured to provide electrically readable outputs indicative of any one or more of: pressure, force, stretch, bend, displacement, temperature, or humidity.

9. A sensor array as claimed in any one of claims 1 to 8 wherein the first and second electrodes are printed on the first or second substrate.

10. A sensor array as claimed in any one of claims 1 to 9 wherein for each functional layer:

the plurality of first electrodes and one or more second electrodes are formed on the first substrate; and

the plurality of sensor regions are formed on the second substrate.

1 1 . A sensor array as claimed in any one of claims 1 to 9 wherein for each functional layer:

the plurality of first electrodes are formed on the first substrate; the one or more second electrodes are formed on the second substrate; and the plurality of sensor regions are formed on at least one of the first substrate and second substrate overlaying the printed electrodes to provide a plurality of sensor regions.

12. A sensor array as claimed in any one of claims 1 to 1 1 wherein one or more of the first substrate and second substrate further comprise a printed glue layer for adhering the first substrate and second substrate together to form the electrical connection between the sensors and first and second electrodes.

13. A sensor array as claimed in any one of claims 1 to 9 wherein for each functional layer:

the plurality of first electrodes and one or more second electrodes are formed on the first substrate;

the plurality of sensor regions are formed on the first substrate overlaying the first and second electrodes, and

a glue layer is provided on the second substrate.

14. A sensor array as clamed in claim 13 wherein the glue layer further comprises additional thickness of glue for adhesion between the sensor regions.

15. A sensor array as claimed in claim 13 further comprising glue regions formed between sensor regions on the first substrate.

16. A sensor array system comprising:

a sensor array as claimed in any one of the preceding claims; and

a controller configured to be electrically connected to each one of the first electrodes and second electrodes of each functional layer to sample signals from the sensor array.

17. A sensor array system as claimed in claim 16 wherein the controller is configured to multiplex sampled signals from the plurality of sensors.

18. A sensor array system as claimed in claim 16 or 17 wherein the controller is further configured to analyse the sampled signals from the plurality of sensors.