BACKGROUND OF THE INVENTION
Field of the Invention
One or more embodiments of the invention are related to the field of measuring instruments. More particularly, but not by way of limitation, one or more embodiments of the invention enable a sensor array integrated into a fabric that may be attached to or placed near an object to be measured. The fabric may include integrated data analysis capabilities and an integrated display.
Description of the Related Art
Sensor arrays are known in the art. For example, phased array radar systems are in widespread use. Microphone arrays for reception and processing of acoustic signals are also known. An array of sensors provides several potential advantages over individual sensors, including for example improved directionality of signal reception. These radar and microphone arrays are typically large, expensive instruments that are installed into a site or an area.
Sensors that can be attached to a surface of an object are also known in the art. For example, relatively low-cost, wearable sensing devices exist for selected applications. These devices generally contain individual sensors, such as motion sensors or heartbeat sensors. They are often designed as rigid components that are attached to a user for example using a wristband.
Piezoelectric sensors offer several benefits, including compact size and lack of a requirement for an external power source. While piezoelectric sensors are known in the art, they have not been integrated into a sensor array in a flexible fabric that may for example include integrated processing or display layers.
Combining the technological advantages of sensor arrays with the convenience and cost efficiency of surface mountable or wearable devices offers several potential benefits. There are no known devices that provide these solutions.
For at least the limitations described above there is a need for a surface mountable piezoelectric sensor array fabric.
BRIEF SUMMARY OF THE INVENTION
One or more embodiments described in the specification are related to a surface mountable piezoelectric sensor array fabric. Embodiments of the system measure one or more properties of an object using a sensor array embedded into a fabric that is attached to or placed near the object.
One or more embodiments of the system include a fabric that can be mounted to or placed near or in proximity to a surface of an object to be measured. The fabric may comprise a sheet of material that may contain one or more laminar layers. The bottom side of the sheet may be attached to or placed near the surface of the object to be measured; the top side of the sheet may be visible to a viewer looking at the mounted sheet. Various components of the system may be integrated into one or more of the layers. One or more layers may contain a sensor array, which comprises sensors of any type, configured to measure any property or properties of the object. One or more layers may contain a communications array with electrical connections to the sensors of the sensor array. The communications array may read sensor data from each sensor in the array; in one or more embodiments it may also provide power or control signals to the sensors in the sensor array. Sensor data may be transferred to a sensor data analysis subsystem that comprises one or more processors. These processors may be external to the sheet, or integrated into one or more layers of the sheet. The sensor data analysis subsystem may generate one or more outputs using any analysis or data transformation techniques; these outputs may be transferred to a display subsystem comprising one or more displays. The displays may be external to the sheet, or integrated into one or more layers of the sheet.
One or more embodiments may include a display integrated into one or more layers and visible to a viewer that looks at the top side of the sheet. For example, an integrated display may be a liquid crystal display with a layer of liquid crystal cells that form pixels of the display. One or more embodiments may include additional display layers such as power, control, and communication lines; light polarizers; and reflective, transmissive, or transflective layers.
Sensor arrays in embodiments may measure any property or set of properties in any region or regions of the object. In one or more embodiments sensor arrays are configured to measure a grid of object regions, for example by associating a subset of the array with each region of the object. These configurations may for example provide a map of a property across the object. For example, sensor array elements may be partitioned into subarrays that each measure a region of the object located below or near the subarray when the sheet is placed on or near the object. In embodiments with an integrated display layer, the display may show the object property or an output derived from this property for the region of the object directly below or near each pixel or region of the display. This configuration in a sense effectively allows a viewer to look through the surface of the object to observe the object's underlying properties. As an illustrative example, one or more embodiments may have an array of temperature sensors, and a corresponding array of display pixels in a display layer. The fabric may then provide a temperature map for the surface of the object (or for regions below the surface), where the output on the display (such as a color for example) corresponds to the temperature of the object directly below that portion of the display.
One or more embodiments may use one or more processors for sensor data analysis. These processors may be integrated into one or more layers of the sheet, or they may be external to the sheet. In one or more embodiments there may be both integrated processors in one or more layers and external processors. One or more embodiments may use any type or types of processors, including for example, without limitation, a microprocessor, an array of microprocessors, a digital signal processor, an array of digital signal processors, an analog filter circuit, an array of analog filter circuits, a computer, a laptop computer, a tablet computer, a desktop computer, a server computer, a network of computers, a mobile device, and a network of mobile devices.
In one or more embodiments a sensor data analysis subsystem may use any technique or techniques to analyze sensor data and to create one or more outputs for display or for further analysis. For example, without limitation, data analysis may include application of beamforming signal processing methods to sensor data. Beamforming may be used for example to amplify signals arriving from one set of directions and to attenuate signals arriving from another set of directions. Data analysis may also include for example, without limitation, application of one or more of a band-pass filter, a band-stop filter, a high-pass filter, or a low-pass filter to sensor data or to the output of other analysis stages.
One or more embodiments may have a large number of sensors in a sensor array, for example 100 sensors, 1000 sensors, or more. One or more embodiments may have a high density of sensors per square centimeter of surface area of the sheet, for example 10 sensors per square centimeter, 1000 sensors per square centimeter, or more. For example, 3D printing technology may be used to create one or more embodiments with small sensor cells and high-density sensor arrays.
Embodiments may have sensor arrays with any type or types of sensors. One or more embodiments include acoustic sensors, which may be for example, without limitation, piezoelectric acoustic sensors. One or more embodiments may generate piezoelectric acoustic sensors from two adjacent layers, one of which contains cells of calcium carbonate, and the other of which contains corresponding cells of potassium bitartrate.
One or more embodiments may have an inner cladding layer located on the bottom side of the sheet, which is adjacent to the surface of the object to be measured. One or more embodiments may have an outer cladding layer located on the top side of the sheet. Cladding layers may for example protect components of the sheet from the environment. An inner cladding layer may provide material that attaches to or interfaces with the object to be measured.
In one or more embodiments the sheet may be configured to be attached to or placed near a person, and the sensor array may measure one more biological properties of one or more body parts. Biological properties measured may include for example, without limitation, sound, pressure, temperature, sweat rate, electric resistance, electric conductivity, electrical voltage, electrical current, electromagnetic field, motion, orientation, fluid flow, strain, pH, tissue type, tissue composition, cell type, and chemical composition.
One or more embodiments may include acoustic sensors that measure the sound of blood flow. These sounds may be used for example to measure the presence or size of blood vessels beneath the sheet. An integrated display may be included to show the blood vessels directly on the sheet. A potential application for a blood vessel detecting sheet is phlebotomy, where the attached sheet allows a clinician to visualize blood vessels beneath the skin.
One or more embodiments may include a piezoelectric sensor array integrated into one or more layers of the fabric. A communications array may have one or more electric connections to the sensor array layer or layers. A display layer may be integrated into the fabric. The piezoelectric sensor array may be constructed from discrete piezoelectric ceramic elements, from piezoelectric particles embedded in a matrix, from piezoelectric fibers, or from any combination thereof. Piezoelectric materials may include for example, without limitation, lead zirconate titanate (PZT) or similar ceramics. They may include lead-free piezoelectric materials such as for example, without limitation, barium titanate (BT), bismuth sodium titanate (BNT), bismuth potassium titanate (BKT), potassium sodium niobate (KNN), and a composite of barium zirconate titanate and barium calcium titanate (BZT-BCT).
For piezoelectric sensor arrays with piezoelectric particles embedded in a matrix, the matrix may be formed from various polymers, including for example passive polymers such as methyacrylic, acrylic, polyurethane, epoxy, and lacquer, and piezoelectrically active polymers such as polyvinylidene fluoride (PVDF) and polyvinylidene fluoride trifluoroethylene (PVDF-TrFE). In one or more embodiments the particles and matrix may form a 0-3 composite, although other connectivity configurations may also be used.
In one or more embodiments, the piezoelectric sensor array may be formed from piezoelectric fibers, which may for example be woven into any desired shape. Fibers may be formed for example, without limitation, from a piezoelectrically active polymer, from a multilayer polymer-carbon nanotube-electrode composite piezoelectric fiber, from an aligned lead zirconate titanate ceramic fiber, and from an aligned lead zirconate titanate ceramic fiber and polymer composite.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other aspects, features and advantages of the invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein:
FIG. 1 illustrates an embodiment of the invention that embeds a sensor array into a patch placed on a pipeline; the sensor array measures and reports the flow rate through the pipeline.
FIG. 2 illustrates an embodiment of the invention with a sensor array integrated into the fabric, and with processing and display elements external to the fabric.
FIG. 3 illustrates an embodiment of the invention with a display integrated into the fabric.
FIG. 4 illustrates an embodiment of an integrated display that uses a liquid crystal display constructed from multiple layers of the fabric.
FIG. 5 illustrates an embodiment of the invention with data processors integrated into the fabric.
FIG. 6 illustrates an embodiment of the data analysis subsystem, which uses beamforming techniques to achieve directional reception of signals, and applies a band-pass filter to the result.
FIG. 7 illustrates an embodiment of the sensor array that uses piezoelectric acoustic sensors formed from adjacent layers of calcium carbonate and potassium bitartrate.
FIG. 8 illustrates an embodiment that uses a piezoelectric acoustic sensor array to measure blood flow, and displays the location of blood vessels on a display integrated into the fabric.
FIG. 9 shows a view of the embodiment of FIG. 8 placed on a hand.
FIG. 10 illustrates a high-density sensor array constructed using a 3D printer.
FIG. 11 illustrates an embodiment of the invention with an array of piezoelectric sensors that are formed from discrete ceramic sensor elements deposited on a flexible substrate layer.
FIG. 12 illustrates an embodiment of the invention that uses piezoelectric ceramic particles embedded in a polymer matrix as the sensor array.
FIG. 13 illustrates an embodiment of the invention that uses piezoelectric fibers woven into a flexible layer as the sensor array.
DETAILED DESCRIPTION OF THE INVENTION
A surface mountable piezoelectric sensor array fabric will now be described. In the following exemplary description numerous specific details are set forth in order to provide a more thorough understanding of embodiments of the invention. It will be apparent, however, to an artisan of ordinary skill that the present invention may be practiced without incorporating all aspects of the specific details described herein. In other instances, specific features, quantities, or measurements well known to those of ordinary skill in the art have not been described in detail so as not to obscure the invention. Readers should note that although examples of the invention are set forth herein, the claims, and the full scope of any equivalents, are what define the metes and bounds of the invention.
FIG. 1 shows an illustrative embodiment of the invention configured to be placed on the surface of a pipeline 110. One or more embodiments of the invention may be configured to be placed on, near, or in the vicinity of a surface or surfaces of any type of object or objects to be measured. This embodiment comprises a fabric 100 with at least three layers: sensor array layer 101, inner cladding layer 102, and outer cladding layer 103. These layers are illustrative; one or more embodiments may comprise a fabric with any number of layers comprising any number and types of components in each layer. Fabric layers may be made of any material or materials. For example, in one or more embodiments some of the fabric layers may be cotton or other wearable materials. In one or more embodiments a sensor array may comprise multiple layers. In one or more embodiments there may be multiple inner cladding layers or multiple outer cladding layers. One or more embodiments may not have an inner cladding layer. One or more embodiments may not have an outer cladding layer.
Cladding materials for inner or outer cladding layers may be for example chosen to protect inner layers from the environment. Inner cladding layers may be selected for example to attach the fabric to the object being measured, such as pipeline 110 of FIG. 1. Outer cladding layers may be selected to be transparent in one or more embodiments, for example to show inner layers or elements such as an integrated display. One or more embodiments may use any type of material or materials of any size, shape, thickness, or consistency for cladding layers.
Layer 101 of the fabric shown in FIG. 1 contains a sensor array 104. This sensor array comprises a grid of sensors, configured in any desired shape or pattern. The regular rectangular grid illustrated in FIG. 1 for sensor array 104 is illustrative; one or more embodiments may use sensor arrays in any geometric pattern, including for example, without limitation, linear, polygonal, circular, elliptical, random, polar, or tiled in any periodic or non-periodic tiling pattern. One or more embodiments may arrange sensors into a non-orthogonal array, such as for example a polar array. A polar array may for example position sensors at grid points that have r and θ polar coordinates spaced at regular intervals or in any desired sequence. One or more embodiments may use a polar array, or any other non-orthogonal array, for example in order to minimize aliasing artifacts or phasing anomalies. One or more embodiments may arrange sensors into concentric circles, with any desired radial spacing between the circles and any desired angular spacing between sensors on the same circle. One or more embodiments may arrange sensors into an irregular pattern, for example with random offsets from a grid, in order to minimize aliasing artifacts or phasing anomalies. One or more embodiments may combine non-orthogonal arrays (such as polar arrays for example) with random offsets. One or more embodiments may have sensor arrays in three-dimensional patterns where the sensors in the array do not all lie on the same plane or the same surface. Sensors in a sensor array may be of any size, shape, or type. A sensor array may have any number of sensors. Sensors may measure any property or properties of an object, including for example, without limitation, position, orientation, motion, rotation, sound, vibration, temperature, charge, voltage, current, flow, chemical composition, chemical reaction, mass, weight, force, tension, stress, strain, luminance, color, density, viscosity, pressure, or electromagnetic field. One or more embodiments may have multiple types of sensors that measure different properties of an object, or that measure a single property using different modalities.
In the embodiment shown in FIG. 1, data is transmitted from fabric 100 over network 105 to computer 106, which processes the sensor data and displays output 107. One or more embodiments may transmit data over any wired or wireless network or connection. One or more embodiments may process sensor data using any algorithms or techniques to generate one or more outputs. The output 107 shows a flow rate. This output is illustrative; one or more embodiments may generate any output or outputs from sensor data. In the embodiment of FIG. 1, sensor data processing and output display are external to the fabric 100. In one or more embodiments one or more of these functions are integrated into the fabric.
FIG. 2 shows an exploded block diagram of an embodiment of the invention. Fabric 200 is configured to measure object 210. In this illustrative embodiment, fabric 200 comprises four layers, shown in an exploded view in FIG. 2. The thickness shown for the layers is for ease of illustration only; one or more embodiments may comprise layers that are arbitrarily thin, with thickness much smaller than their surface areas, for example. The bottom surface of 200 is the surface that is adjacent to or attached to object 210; inner cladding layer 102 lies along this bottom surface. The top surface of 200 is the surface opposite the bottom surface; outer cladding 103 lies along this top surface. Layer 201 comprises an array of sensors. Layer 202 comprises a communications network of electric connections to these sensors. For example, connection 203 in the network of layer 202 connects to sensor 204 in sensor array layer 201. One or more embodiments may employ one or more layers to supply power to sensors, to supply control signals to sensors, or to read data from sensors. One or more embodiments may use wireless connections to sensors instead of or in addition to wired connections to sensors. One or more embodiments may use connections between sensors to consolidate data from the sensor array in a smaller number of hub sensors, and then communicate between these hub sensors and other layers.
The connection network of layer 202 reads data from the sensor array (in addition to possibly providing power and control signals), and transmits this data to processor 220 for analysis. In the embodiment shown in FIG. 2, processor 220 is external to fabric 200. This configuration is illustrative; one or more embodiments may include one or more processors in the fabric, for example in one or more processing layers. Processor 220 may be for example, without limitation, a microprocessor, a microcontroller, a computer, a laptop computer, a notebook computer, a tablet computer, a desktop computer, a server computer, a mobile device, a digital signal processor, an analog signal processor, or any combination of the above. Processor 220 may be a network or array of processors, connected via any wired or wireless connections. In the embodiment of FIG. 2, sensor data is sent from the connection network 202 to processor 220 over wireless connection 230 by antenna 231; the antenna may for example be integrated into the connection layer 202 or into any other layer. In one or more embodiments data may be transmitted from the fabric 200 to processor 220 via a wired connection or via any combination of wired and wireless connections. Processor 220 analyzes the sensor data from sensor array 201 and generates one or more outputs. These outputs are transmitted to display 240. In the embodiment of FIG. 2, display 240 is external to fabric 200; in one or more embodiments the display may be included in the fabric for example as one or more layers.
In the embodiment of FIG. 2, each sensor in sensor array 201 is configured to measure a property of a region of object 210. For example, sensor 204 measures a property of region 211 in object 210. The value of the property is illustrated in FIG. 2 as the shading of the region; it may for example correspond to the temperature, pressure, or vibration in that region, or to any other property. In this example, the region of the object measured by the sensor is the region of the object adjacent to the sensor. This is illustrative; in one or more embodiments any sensor may measure any region or regions of any objects. The outputs displayed on display 240 correspond to the properties measured for the corresponding regions of the object. For example, pixel 241 in the display shows the measured property of region 211 of the object, and pixel 242 shows the measured property of region 212 of the object. In this configuration the outputs and the display pixels provide a map of the measured property across the object. In one or more embodiments, data from multiple sensors may be combined into a smaller number of outputs, or even into a single output as for example illustrated in FIG. 1.
FIG. 3 illustrates an embodiment of the invention in which the display is integrated into the fabric. Fabric 300 contains layers 102, 201, and 202 as in FIG. 2. It also contains display layer or layers 301, which integrate pixels displaying outputs from processor 220 into the fabric. In this embodiment processor 220 is external to the fabric; thus wireless link 230 may send sensor data to processor 220, which analyzes the data and sends outputs back to the display 301 over the same wireless link. The embodiment illustrated in FIG. 3 uses connection and communication network layer 202 for both reading sensor data and for writing outputs to the display layer. One or more embodiments may use separate connection and communication layers for sensors and for displays. Outer cladding layer 103a may for example be transparent so that viewer 310 can view display layer 301 when looking at the top surface of fabric 300. One or more embodiments may use an integrated display layer or layers using any display technology. Display technologies may include for example, without limitation, liquid crystals, LEDs, OLEDs, Bragg cells, electrostatic displays, thermoluminescent displays, and thermochromic displays. Integrated display layers may use any number and arrangement of pixels. Integrated displays may be for example color displays, black and white displays, or grayscale displays.
One or more embodiments may use liquid crystal displays integrated into the fabric. FIG. 4 illustrates an exploded view of an embodiment with several layers that form a liquid crystal display. This configuration is illustrative; one or more embodiments may use any layer or layers to generate a liquid crystal display or a display using any other technology. The bottom display layer is a reflective layer 401 that reflects incoming light. This illustrative example uses a reflective LCD display; one or more embodiments may use transmissive or transflective LCD. The liquid crystal cells and the signaling lines to these cells are sandwiched between polarizing layers 402 and 405. Layer 403 contains an array of liquid crystal cells, each corresponding to a pixel of the display. As an illustration, the chemical composition 406 of the liquid crystal cells may for example contain cholesteryl benzoate (C34H50O2). One or more embodiments may use any chemical or chemicals that generate a liquid crystal. Layer 404 contains signaling lines to control the liquid crystal cells. In the embodiment of FIG. 4, the processor 220 is external to the fabric; thus the signaling layer 404 receives output data from the processor 220 via input 407, which may be for example a wireless antenna, or a wired connection.
In one or more embodiments the fabric may contain one or more layers that include a processor or processors that analyze sensor data and generate outputs for display. FIG. 5 illustrates an embodiment with a processor layer 501. For illustration, this layer contains two microprocessors, 502 and 503. One or more embodiments may include any number of processors of any type in one or more layers. The processor layer has connections such as 504 to the layer 202 that reads sensor data from the sensor array layer 201, and connections such as 505 to the display layers. The embodiment illustrated in FIG. 5 is completely self-contained; no external processor or display is required. One or more embodiments may provide self-contained fabrics that also support transfer of data from the fabric to other components such as an external display or an external processor for further analysis.
Processing layers or external processors may perform any type of data analysis on sensor data. FIG. 6 shows an illustrative data analysis performed by one or more embodiments. Sensor data received from sensor array 201 is transformed from the time domain to the frequency domain via Fourier transform 601. One or more embodiments may use any transform techniques, including for example, without limitation, continuous or discrete Fourier transform, FFT, z-transform, Laplace transform, or any integral transform with any kernel. One or more embodiments may perform data analysis in the time domain or space domain instead of or in addition to the frequency domain. In FIG. 6, the result of transform 601 is an array of frequency-domain signals 602. This array is weighted by an array of weighting factors or weighting functions 603, and the resulting product array is summed 604. Weighting factors 603 may in general be complex, with both an amplitude 605 and a phase 606. This general framework includes for example a class of beamforming techniques known in the art. These beamforming techniques may for example modify the directionality of a sensor array, to increase the gain of signals received from a specific direction or directions, and to attenuate the gain of signals received from other directions. For example, the weighting factor array 603 may be structured to rotate the main lobe of peak reception 610 for the sensor array to a different direction such as 611. One or more embodiments may use beamforming techniques to direct the receptivity of the sensor array in a particular direction, or to reject or attenuate data from certain directions. Beamforming techniques are known in the art; one or more embodiments may use any of these well-known techniques to process data from a sensor array.
The data analysis example shown in FIG. 6 further processes the signal 607 using a frequency-domain filter 608. The filter 608 shown is a band-pass filter; this is illustrative and one or more embodiments may use any desired filter, including for example, without limitation, a band-pass filter, a band-stop filter, a high-pass filter, a low-pass filter. A band-pass filter may be desirable, for example, when the data of interest falls within a known frequency range, and noise or undesired signals fall largely outside of this frequency range. The resulting output 609 may be further processed via additional algorithms or filters as desired.
One or more embodiments may use sensor arrays of any type, to measure any desired property or properties of an object. One or more embodiments may use acoustic sensors to measure sound or vibration emitted from, reflected from, or transmitted through an object or a portion of an object. In particular, one or more embodiments may use piezoelectric acoustic sensors that transform pressure variations into electrical signals. FIG. 7 illustrates an embodiment with an array 201a of piezoelectric acoustic sensors, such as cell 701 in the array. In one or more embodiments, an array of piezoelectric acoustic sensors may be formed from a pair of adjacent layers with specific chemical compositions in the adjacent cells to generate a piezoelectric effect. In FIG. 7, array 201a is formed from adjacent layers 702 and 703. Cells of layer 702 contain potassium bitartrate 704 (KC4H5O6); corresponding adjacent cells of layer 703 contain calcium carbonate 705 (CaCO3). The interaction of the adjacent potassium bitartrate and calcium carbonate cells generates a piezoelectric sensor 701 in each cell of array 201a. This configuration is illustrative; one or more embodiments may use any layers of any chemical composition to form piezoelectric sensors or any other type of sensors.
One or more embodiments of the fabric may be used to measure one or more biological properties of a human body. For example, one or more embodiments may use acoustic sensors to detect blood flow, and may use this information to map the location of blood vessels. A potential application for a blood vessel mapping fabric may be phlebotomy, for example: a phlebotomist may for instance attach a fabric with sensors to a patient's skin to visualize the underlying vessels prior to drawing blood. FIG. 8 illustrates an embodiment of the invention that measures the presence of blood vessels 801 in a portion 210a of a human body. The flow of blood through vessels 801 generates sounds 802 that are detected by array 201a of acoustic sensors. In the embodiment shown, processing is performed within the fabric in processor layer 501, and outputs are transmitted to display layer 301a. Data analysis performed by the processor layer may for example include beamforming to focus the sensor array to the region directly beneath the skin, or to another region of interest. Data analysis may also for example include frequency filtering to eliminate or attenuate sound signals outside the expected frequencies generated by the blood flow. One or more embodiments may perform processing or display external to the fabric. The pattern displayed on display layer 301a recreates the location of blood vessels 801 beneath the fabric. For a phlebotomy application, the outer cladding layer 103a may for example be a transparent, compliant, layer that can be easily pierced by a needle for a blood draw; the inner cladding 102a may for example contain an adhesive for attachment to a patient's skin.
FIG. 9 illustrates a diagram of the embodiment shown in FIG. 8, where the fabric 901 is attached to the hand 210a of a patient to visualize the underlying blood vessels.
One or more embodiments may use very small cells for sensor arrays, displays, processors, or other components embedded into the laminar layers. For example, one or more embodiments may use sensor cells with widths less than or equal to 300 micrometers. This illustrative cell width may for example provide sensor density of more than 1000 sensors per square centimeter of sheet surface area. This density is illustrative; one or more embodiments may use sensors of any size and density. Embodiments may have sheets of any desired size. For example, a sheet of 100 square centimeters in area may have more than 100,000 total sensors in the sheet's sensor array. Cell widths of 300 micrometers or less may be achieved for example using readily available 3D printing technologies, which can achieve resolution of less than 20 micrometers. FIG. 10 shows an illustrative process for generating high density sensor arrays. 3D printer 1001 includes three axis actuators 1002, 1003, and 1004, and a material deposition head 1005. The figure illustrates deposition of sensor material onto sensor array layer 201. Close up 1010 of a portion of layer 201 shows that cell widths may be for example 20 micrometers, a resolution that is readily achievable by current 3D printing technology.
In one or more embodiments the sensor array may include any type or types of piezoelectric sensors. These piezoelectric sensors may use any piezoelectric materials and piezoelectric technologies, including but not limited to any piezoelectric materials and technologies known in the art. One or more embodiments may use piezoelectric arrays as actuators instead of or in addition to using them as sensors. Piezoelectric materials may be used in a flexible sensor array, for example to create smart textiles and fabrics. A grid of piezoelectric sensors can be produced in any desired shape or pattern using one or more of several fabrication techniques.
Piezoelectric sensor arrays used in one or more embodiments may include for example, without limitation, discrete ceramic piezoelectric sensor elements, piezoelectric particles embedded in a matrix of passive or piezoelectrically active polymer, or piezoelectric fibers. FIG. 11 illustrates an embodiment with a sensor array formed from discrete ceramic elements made of piezoelectric material. The embodiment illustrated uses piezoelectric sensors to detect blood flow, as in FIG. 8; this application is illustrative, and one or more embodiments may use piezoelectric sensors for any desired application and sensor modality. In the embodiment shown in FIG. 11, piezoelectric sensors are in sensor array layer 201b. This layer includes sensor elements such as element 1101, which in this illustrative example is a discrete cell made of a piezoelectric ceramic material. The material may be for example lead zirconate titanate (PZT), or any other piezoelectrically active material, including composite materials. In this example each sensor element is physically continuous and is separated by a gap or by another material from other sensor elements. Each sensor element has a discrete connection such as connection 1103 to a communications array, which allows the system to read individual sensor values from each sensor element. The discrete sensor elements may be deposited on or in a substrate such as substrate 1102. This substrate may be electrically active or electrically passive. It may be flexible, for example to conform to an irregular or curved surface when the fabric is placed on or near an object such as object 210a. For example, without limitation, the substrate may be a flexible printed circuit board, as described for example in international patent publication WO 2008/137030, “A Flexible Conformal Ultrasonic Imaging Transducer and System.”
FIG. 11 illustrates an embodiment with discrete piezoelectric sensor elements. In one or more embodiments the piezoelectric sensors may be dispersed throughout a medium, and one or more electric connections to the medium may measure piezoelectrically generated voltages resulting from the dispersed sensors near each connection. FIG. 12 illustrates an embodiment where the sensor array layer 201c is formed from a polymer matrix 1202 into which piezoelectric particles such as particle 1201 are embedded. The particles may be dispersed throughout the medium 1202. This configuration of piezoelectric particles embedded in a continuous medium is referred to in the art as a 0-3 composite, which designates the number of dimensions through which the piezoelectric material (first number) and the medium (second number) are continuous. One or more embodiments may use a 0-3 composite of piezoelectric particles and medium, or any other configuration such as for example, without limitation, a 1-3 composite, a 3-3 composite, or a 2-2 composite. An example of a 0-3 composite that has been studied in the art is described in Elkjaer et. Al., “Integrated Sensor Arrays based on PiezoPaint™ for SHM Applications,” Annual Conference of the Prognostics and Health Management Society, 2013. One or more embodiments may use a paint or similar composite as described in this paper, or similar composites known in the art.
The piezoelectric particles such as 1201 embedded in medium 1202 may be made of any desired piezoelectrically active material, including for example, without limitation, 1203 (PZT) or similar piezoelectric ceramics that contain lead. Because of the environmental and health hazards of lead, lead-free piezoelectric materials are increasingly being studied and used. See for example P. K. Panda & B. Sahoo (2015), PZT to Lead Free Piezo Ceramics: A Review, Ferroelectrics, 474:1, 128-143. One or more embodiments may use any lead-free piezoelectric material, including for example, without limitation, any of the materials 1204, which includes barium titanate (BT), bismuth sodium titanate (BNT), bismuth potassium titanate (BKT), potassium sodium niobate (KNN), and barium zirconate titanate—barium calcium titanate (BZT-BCT).
Medium 1202 that contains piezoelectric particles may be made of materials that include, without limitation, passive polymers such as those listed in 1206 (methyacrylic, acrylic, polyurethane, epoxy, and lacquer), and piezoelectrically active polymers such as those listed in 1205 (polyvinylidene fluoride [PVDF] and polyvinylidene fluoride trifluoroethylene [PVDF-TrFE]).
In one or more embodiments the layer 201c containing the polymer matrix and the piezoelectric particles may be a thick film, such as for example a paint. In one or more embodiments the layer 201c may be a layer of any desired thickness, shape, and consistency. A great range of piezo behavior can be produced with composite thick films. Different composition piezo ceramic particles can be embedded in a wide range of matrix materials and the ratio between the piezo ceramic particles and the polymer content can be varied to tune the piezo activity.
Thick films may be applied by a variety of techniques such as screen printing, pad printing, stenciling or ink-jet printing. Various fabric substrates may be used as long as the matrix polymer wets the fabric well to make full contact. In one or more embodiments the final array assembly may be composed of multiple layers that allow a wide range of electrodes and interconnects.
In one or more embodiments, a sensor array may be formed from piezoelectric fibers. These fibers may be woven for example into wearable textiles, or arranged in any other pattern to provide a flexible fabric containing piezoelectric sensors. FIG. 13 illustrates an embodiment with a sensor array layer 201d that contains piezoelectric fibers such as fiber 1301. Fibers may be of any desired shape, diameter, length, and size. Fibers may be arranged for example in parallel configurations, in random configuration, or in a cross weave pattern as illustrated in FIG. 13. Fibers may be formed of any piezoelectric material or composite, including for example, without limitation, any of the materials 1302. For example, fibers may be PVDF-TrFE nanofibers, as described for instance in Baniasadi et. al., Thermo-electromechanical Behavior of Piezoelectric Nanofibers, ACS Applied Materials and Interfaces, 2016, 8, 2540-2551. Fibers may be a multilayer polymer-carbon nanotube-electrode composite piezoelectric fiber, as described for example in Sim et. al., Flexible, Stretchable and Weavable Piezoelectric Fiber, Advanced Engineering Materials 2015, 17, No. 9, 1270-1275. Fibers may be an aligned PZT ceramic fiber and/or a ceramic fiber-polymer composite. Fibers may be produced for example using methods such as those described in U.S. Pat. No. 5,072,035, “Method for Making Piezoelectric Ceramic Fibers,” and in U.S. Pat. No. 5,827,797, “Method for Producing Refractory Filaments.”
While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.
Patent Application
20170146493
