Patent Publication Number: US-2022221309-A1

Title: Mutual and overlap capacitance based sensor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part (CIP) and claims priority to U.S. Provisional Application Ser. No. 63/153596 filed on Feb. 25, 2021 entitled “SENSOR FOR PROXIMITY, LIGHT TOUCH, AND PRESSURE-BASED GESTURE RECOGNITION” (Atty. Dkt. No. HRA-50529) and claims priority to U.S. Non-Provisional application Ser. No. 17/174226 filed on Feb. 11, 2021 entitled “SYSTEM AND METHOD FOR FABRICATING SOFT SENSORS THAT CONFORM TO ARBITRARY SMOOTH GEOMETRIES” (Atty. Dkt. No. HRA-49574.01), which claims priority to U.S. Provisional Application Ser. No. 63/136428 filed on Jan. 12, 2021 entitled “SYSTEM AND METHOD FOR FABRICATING SOFT SENSORS THAT CONFORM TO ARBITRARY SMOOTH GEOMETRIES” (Atty. Dkt. No. HRA-49574), all of which are expressly incorporated herein by reference. 
    
    
     BACKGROUND 
     The need for soft tactile sensors that conform to arbitrary smooth geometries has been a bottleneck for developing robot hands with dexterous manipulating capabilities. The field requires the sensor to be soft, skin-like, and to conform to the shape of a fingertip and/or a palm. Although, there has been significant development in the field of soft sensors, however, most of them are all in academia. In actual commercial applications several other requirements need to be met especially in the readout electronics segment. For example, adhering soft sensors for robotic purposes may often be a challenge and delamination is often an issue. 
     Additionally, many pressure sensor arrays have difficulty detecting light contacts because signal amplitudes are very small, while highly sensitive force sensors saturate at high-force interactions. 
     BRIEF DESCRIPTION 
     According to one aspect, a system for fabricating soft sensors that conform to arbitrary smooth geometries that includes a top stretchable layer that includes a set of electrodes of soft sensors that are made of an elastic material. The system also includes a bottom flexible layer that is composed of a thin sheet of suitable metal that is patterned using photolithography. The bottom flexible layer is configured to be in conformity with the arbitrary smooth geometries. The top stretchable layer is bonded to the bottom flexible layer to form a sensor substrate. The sensor substrate is configured as a stretchable adhesive film which enables robust adhesion to the arbitrary smooth geometries. 
     According to another aspect, a method for fabricating soft sensors that conform to arbitrary smooth geometries that includes fabricating a top stretchable layer that includes a set of electrodes of soft sensors that are made of an elastic material. The method also includes fabricating a bottom flexible layer that is composed of a thin sheet of suitable metal that is patterned using photolithography. The bottom flexible layer is configured to be in conformity with the arbitrary smooth geometries. The method further includes bonding the top stretchable layer to the bottom flexible layer to form a sensor substrate. The sensor substrate is configured as a stretchable adhesive film which enables robust adhesion to the arbitrary smooth geometries. 
     According to yet another aspect, a system for fabricating soft sensors that conform to arbitrary smooth geometries that includes a sensor substrate that is configured to as a stretchable adhesive film which enables robust adhesion to a robotic device that includes a top stretchable layer that includes a set of electrodes of soft sensors that are made of an elastic material. The sensor substrate also includes a bottom flexible layer that is composed of copper films that are patterned using photolithography. 
     A mutual and overlap capacitance based sensor may include a top stretchable layer including a first electrode configured in a serpentine pattern, a bottom layer including a second electrode, and a dielectric layer positioned between the first electrode and the second electrode. 
     The second electrode may have a line shape which runs perpendicular to a wavelength direction of the first electrode and parallel to an amplitude direction of the of the first electrode. The first electrode may be arranged such that a first portion of the first electrode overlaps the second electrode and the first portion of the first electrode may include a contour. The first electrode may be arranged such that a first portion of the first electrode overlaps the second electrode and a portion of the second electrode may include an exposed area not covered by the first electrode. The first portion of the first electrode may include a contour and a portion of the second electrode may include an exposed area not covered by the first electrode. 
     A first portion of the second electrode may include an exposed area not covered by the first electrode and a second portion of the second electrode may include a covered area covered by the first electrode. The first portion of the second electrode may be associated with a first taxel of the mutual and overlap capacitance based sensor and the second portion of the second electrode may be associated with a second taxel of the mutual and overlap capacitance based sensor. A processor may determine a sensing mode based on a capacitance reading from the first taxel being within a first range, a second range, or between the first range and the second range and a reading from the second taxel. The first taxel may neighbor the second taxel. The sensing mode may be a mutual capacitance mode or an overlap capacitance mode. 
     A mutual and overlap capacitance based sensor may include a top stretchable layer including a first electrode configured in a serpentine pattern, a bottom layer including a second electrode, and a dielectric layer positioned between the first electrode and the second electrode. The second electrode may have a line shape which runs perpendicular to a wavelength direction of the first electrode and parallel to an amplitude direction of the of the first electrode. 
     The first electrode may be arranged such that a first portion of the first electrode overlaps the second electrode and the first portion of the first electrode may include a contour. The first electrode may be arranged such that a first portion of the first electrode overlaps the second electrode and a portion of the second electrode may include an exposed area not covered by the first electrode. The first portion of the first electrode may include a contour and a portion of the second electrode may include an exposed area not covered by the first electrode. A first portion of the second electrode may include an exposed area not covered by the first electrode and a second portion of the second electrode may include a covered area covered by the first electrode. The first portion of the second electrode may be associated with a first taxel of the mutual and overlap capacitance based sensor and the second portion of the second electrode may be associated with a second taxel of the mutual and overlap capacitance based sensor. 
     A system for mutual and overlap capacitance sensing may include a mutual and overlap capacitance based sensor including a top stretchable layer including a first electrode configured in a serpentine pattern, a bottom layer including a second electrode, and a dielectric layer positioned between the first electrode and the second electrode and a processor. The processor may determine a sensing mode for the mutual and overlap capacitance based sensor based on a capacitance reading from a first taxel of the mutual and overlap capacitance based sensor being within a first range, a second range, or between the first range and the second range and a reading from a second taxel of the mutual and overlap capacitance based sensor neighboring the first taxel. 
     The second electrode may have a line shape which runs perpendicular to a wavelength direction of the first electrode and parallel to an amplitude direction of the of the first electrode. The first electrode may be arranged such that a first portion of the first electrode overlaps the second electrode and the first portion of the first electrode may include a contour. The first electrode may be arranged such that a first portion of the first electrode overlaps the second electrode and a portion of the second electrode may include an exposed area not covered by the first electrode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features believed to be characteristic of the disclosure are set forth in the appended claims. In the descriptions that follow, like parts are marked throughout the specification and drawings with the same numerals, respectively. The drawing figures are not necessarily drawn to scale and certain figures may be shown in exaggerated or generalized form in the interest of clarity and conciseness. The disclosure itself, however, as well as a preferred mode of use, further objects and advances thereof, will be best understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a cross-section view of a sensor substrate, according to an exemplary embodiment of the present disclosure; 
         FIG. 2A  is an illustrative overview of the fabrication of a top stretchable layer of the sensor substrate, according to an exemplary embodiment of the present disclosure; 
         FIG. 2B  is a cross-section view of the top stretchable layer of the sensor substrate, according to an exemplary embodiment of the present disclosure; 
         FIG. 3A  is an illustrative overview of a bottom flexible layer of the sensor substrate, according to an exemplary embodiment of the present disclosure; 
         FIG. 3B  is a cross-section view of the bottom flexible layer of the sensor substrate, according to an exemplary embodiment of the present disclosure; 
         FIG. 4  is an illustrative overview of bonding of the top stretchable layer and the bottom flexible layer, according to an exemplary embodiment of the present disclosure; 
         FIG. 5  is an illustrative overview of the bonding of the sensor substrate to an arbitrary smooth geometry, according to an exemplary embodiment of the present disclosure; 
         FIG. 6  is a process flow diagram of a method for fabricating the sensor substrate and attaching the sensor substrate to a robotic device, according to an exemplary embodiment of the present disclosure; 
         FIG. 7  is a process flow diagram of a method for fabricating soft sensors that conform to arbitrary smooth geometries, according to an exemplary embodiment of the present disclosure; 
         FIG. 8  is an illustrative overview of a mutual and overlap capacitance based sensor having a smooth geometry, according to an exemplary embodiment of the present disclosure; 
         FIG. 9  is a cross-sectional view of a mutual and overlap capacitance based sensor having a smooth geometry, according to an exemplary embodiment of the present disclosure; 
         FIG. 10  is an illustrative overview of an exemplary mutual and overlap capacitance based sensor having a smooth geometry, according to an exemplary embodiment of the present disclosure; 
         FIG. 11  is an operation diagram associated with the mutual and overlap capacitance based sensor, according to an exemplary embodiment of the present disclosure; 
         FIG. 12  is a component diagram of an exemplary system for mutual and overlap capacitance based sensing, according to an exemplary embodiment of the present disclosure; 
         FIG. 13  is a flow diagram of an exemplary method for mutual and overlap capacitance based sensing, according to an exemplary embodiment of the present disclosure; 
         FIG. 14  is an illustration of an example computer-readable medium or computer-readable device including processor-executable instructions configured to embody one or more of the provisions set forth herein, according to an exemplary embodiment of the present disclosure; and 
         FIG. 15  is an illustration of an example computing environment where one or more of the provisions set forth herein are implemented, according to an exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     I. System Overview 
     Referring now to the drawings, wherein the showings are for purposes of illustrating one or more exemplary embodiments and not for purposes of limiting same,  FIG. 1  includes a cross-section of the sensor substrate  100  according to an exemplary embodiment of the present disclosure. In one embodiment, a fabrication system may be configured to fabricate the sensor substrate  100  that includes soft sensors to conform to arbitrary smooth geometries to provide a high mechanical robustness and a high level of electronic sensor signal integrity with respect to sensor signals output by the soft sensors. 
     The fabrication system may leverage the advantages of making devices/circuit boards and soft-sensor technology that enables the fabrication of state-of-the-art conformal tactile sensors. In one embodiment, a set of electrodes of soft sensors that may be bonded upon a sensor substrate may be made of flexible material that provides a conformity needed for proper robotic device sensing (e.g., robotic finger sensing) with conventional materials that are solder-able. This configuration may also provide an interface with readout electronics. 
     As described in more detail below, the fabrication system may be configured to utilize an additional set of top electrodes that may be made of stretchable conductor material that renders a top segment of the sensor as soft and compliant. The system may also be configured to form a bottom flexible layer  104  that may be composed of a thin sheet of suitable metal that is patterned using photolithography. In one embodiment, the thin sheet of suitable metal may include copper films that are patterned using photolithography. The bottom flexible layer  104  is configured to be in conformity with the arbitrary smooth geometries with smooth segments of small radii of curvatures, to which a high level of conformity may be achieved with a suitable copper film thickness and copper pattern size and shape. 
     Photolithography is known in the art to have also been implemented in fabricating passive electronic components such as surface mount resistors directly on the circuit boards. The fabrication system may use photolithography as a patterning process to provide a benefit of the process being easily scalable since it may be used to make features in the range of nanometers (used in microchips) all the way to centimeters or larger. Also, the device sizes fabricated using photolithography technology may be scaled all the way from a few millimeters in size to a few meters. The substrate for this fabrication process may be configured as a stretchable adhesive film which enables easy implementation and robust adhesion on a robotic device such as a robot finger/hand. Accordingly, the use of the fabrication method executed by the fabrication system and described in more detail below allows the fabrication of soft sensors that may easily interface with electronics and may provide mechanical and electrical integrity that may be required by a commercial grade product. 
     As shown in  FIG. 1 , the sensor substrate  100  may include a top stretchable layer  102  that may be bonded to a bottom flexible layer  104 . A bottom portion of the sensor substrate  100  may be configured to include an adhesive portion, such that a bottom face of the bottom flexible layer  104  allows the sensor substrate  100  to robustly adhere one or more types of sensors to/upon any arbitrary geometry. As such, the sensor substrate  100  may be configured to adhere one or more types of sensors on robotic applications, such as robotic hands, fingers, and/or additional types of geometries. 
       FIG. 2A  is an illustrative overview of the fabrication of the top stretchable layer  102  of the sensor substrate  100  according to an exemplary embodiment of the present disclosure. As shown, a dielectric layer  202  may be cast as a bottom portion of the top stretchable layer  102 . The dielectric layer  202  may be cast in a mold using an elastic material. Accordingly, the top portion of the top stretchable layer  102  may provide a level of elasticity and pliability that may be useful for various robotic sensing actions. 
     It is appreciated that a wide range of such materials available in the market that range in elastic modulus of 100 kPa (very soft) to 1˜2 MPa (fairly rigid) may be utilized to cast the dielectric layer  202  of the top stretchable layer  102 . Such materials may closely simulate the mechanical properties of human skin. For example, soft elastic materials such as Ecoflex, Dragon Skin, and the like may be utilized to cast the dielectric layer  202  of the top stretchable layer  102 . In some configurations, the dielectric layer  202  may also have structures such as pillars, pyramids, or domes and therefore air gaps, to fine tune the mechanical properties as desired. 
     With continued reference to  FIG. 2A , once the dielectric layer  202  is cast, the fabrication system may pattern the stretchable electrode material into a stretchable electrode pattern  204  with a material using a patterning process of choice. Non-limiting exemplary materials that may be used may include, but may not be limited to, carbon nanotubes, silver nanowires, conducting polymer and/or conducting particle composites. Non-limiting exemplary patterning processes that may be used, but may not be limited to, spray coating shadow masking, and/or screen printing. 
     In one embodiment, upon the patterning of the stretchable electrodes into the stretchable electrode pattern  204 , an encapsulating layer  206  may be cast upon the stretchable electrode pattern  204  using the same or similar elastic material used to cast the dielectric layer  202  of the top stretchable layer  102 . For example, the encapsulating layer  206  may be cast in a mold using Ecoflex, Dragon Skin, or other elastic materials. 
     As shown in  FIG. 2B , a cross-section of the top stretchable layer  102  of the sensor substrate  100  according to an exemplary embodiment of the present disclosure, the encapsulating layer  206  is cast upon the stretchable electrode pattern  204 . As discussed above, the stretchable electrode pattern  204  is disposed atop of the dielectric layer  202  that may be composed of elastic material. 
     With reference to the bottom flexible layer  104 , of the sensor substrate  100 ,  FIG. 3A  includes an illustrative overview of the bottom flexible layer  104  of the sensor substrate  100  according to an exemplary embodiment of the present disclosure. In one embodiment, a bottom portion of the bottom flexible layer  104  and consequently the sensor substrate  100  may be configured as a soft adhesive sheet  302 . In one configuration, the soft adhesive sheet  302  may be configured as a pliable adhesive sheet that may be flexible for robust adhesion to various arbitrary smooth geometries. The soft adhesive sheet  302  may be configured as a double sided acrylic tape sheet adhesive substrate. As an illustrative example, the soft adhesive sheet  302  may include tape dimensions of 12″×12″. It is appreciated that many different sizes of sheets and tape dimensions may be utilized that may include varying properties of mechanical stiffness and chemical stability. 
     With continued reference to  FIG. 3A , a thin sheet of copper film  304  may be laminated upon a top side portion of the soft adhesive sheet  302 . Upon the lamination of the copper film  304  upon the soft adhesive sheet  302 , a dry film photoresist  306  may be laminated upon a top portion of the copper film  304 . In one configuration, the fabrication system may be configured to send instructions to utilize a thermal laminator (not shown) to laminate the dry film photoresist  306  upon the copper film  304 . In one embodiment, the dry film photoresist  306  may be exposed through a mask using an ultraviolet source. 
     In an exemplary embodiment, the fabrication system may be configured to use a developing solution to develop exposed portions of dry film photoresist pattern  308 . The exposed portions of dry film photoresist pattern  308  may be utilized as a mask to etch undesired portions of copper of the copper film  304  previously laminated upon the soft adhesive sheet  302 . Accordingly, the soft adhesive sheet  302  may include etched copper  310  with respective exposed portions of dry film photoresist pattern  308  that remain upon the soft adhesive sheet  302 . 
     In one embodiment, upon the etching of the undesired copper of the copper film  304  to allow the etched copper  310  to remain upon the soft adhesive sheet  302 , the fabrication system may remove the photoresist from the dry film photoresist pattern  308  that remains upon the etched copper  310 . Upon the removal of the photoresist, a patterned copper film may remain upon the etched copper  310  of the bottom flexible layer of a sensor substrate. The patterned copper film may be configured as patterned copper electrodes  312  that may be operably connected to a control board (not shown) that is associated with the sensor substrate  100 . 
       FIG. 3B  is a cross-section view of the bottom flexible layer  104  of the sensor substrate  100  according to an exemplary embodiment of the present disclosure. In an exemplary embodiment, a top layer of elastic material  314  may be cast upon of the soft adhesive sheet  302  that may be configured as an adhesive substrate. As discussed above, the soft adhesive sheet  302  may include the patterned copper electrodes  312  that may remain upon the etched copper  310  of the bottom flexible layer  104  of the sensor substrate  100 . 
       FIG. 4  includes an illustrative overview of the bonding of the top stretchable layer  102  and the bottom flexible layer  104  according to an exemplary embodiment of the present disclosure. In an exemplary embodiment, upon the fabrication of the top stretchable layer  102  of the sensor substrate  100  and the bottom flexible layer  104  of the sensor substrate  100 , the fabrication system may be configured to bond the top stretchable layer  102  to the bottom flexible layer  104  to form the sensor substrate  100 . As shown, the casting of the top layer of elastic material  314  upon the adhesive substrate of the bottom flexible layer  104  may enable a strong adhesion between the dielectric layer  202  that may be composed of elastic material and the layer of elastic material  314  of the bottom flexible layer  104 . Accordingly, the top layer of elastic material  314  may be bonded to the bottom flexible layer  104  to form the sensor substrate  100 . 
       FIG. 5  includes an illustrative overview of the bonding of the sensor substrate  100  to an arbitrary smooth geometry according to an exemplary embodiment of the present disclosure. As represented in  FIG. 5 , upon the fabrication of the sensor substrate  100 , the bottom portion that is configured as a soft adhesive sheet  302  may be configured for robust adhesion to a robotic device such as a robot finger/hand  502 . In other words, once the sensor fabrication is complete, the sensor substrate  100  which is adhesive on a bottom face is used to adhere the sensor substrate  100  on any arbitrary smooth geometry such as to the robot finger/hand  502 . In order to interface with readout electronics, the patterned copper electrodes  312  may include traces that run to the circuit board that is associated with the sensor substrate  100 . In one configuration, the traces may be soldered to consequently form a robust connection between the patterned copper electrodes  312  and the circuit board to communicate sensor signals. 
     In some embodiments, the patterned copper electrodes  312  may be interfaced with copper tape, using crimp connectors on each respective electrode connection trace, and/or using a flexible flat cable connection (exemplary connections not shown). In alternate embodiments, the copper tape and/or the flexible flat cable connection may be soldered on the circuit board. However, it is appreciated that various types of connection techniques may be utilized to operably interface the patterned copper electrodes  312  with the control board that is associated with the sensor substrate  100 . 
     The fabrication system may enable a reduction of the number of interconnects requiring a soft electrode-rigid circuit interface by at least half or even more in case of an asymmetric circuit to enhance the signal integrity by a significant amount. In some configurations, when the sense terminals of the readout hardware are connected using the copper soldered connection, this functionality may provide an additional increase in signal to noise ratio. The utilization of photolithography may enable the fabrication of very complex and dense bottom electrode patterns in asymmetric designs where only one set of electrode patterns need to be more complex than the other. 
     In one embodiment, a stretchable conductor material with electrode materials (such as copper) may be utilized to achieve a higher signal integrity by moving one half or more of the sensor(s) into the solid electrode material domain. The connection of excitation terminals of the readout electronics to the top stretchable layer  102  and the sense terminals to the patterned copper electrodes  312  of the bottom flexible layer  104  is thereby completed. This functionality ensures a higher signal integrity and clean sense signal which delivers a better signal to noise ratio, when compared to a sensor that has both top and bottom electrodes made of stretchable conductor materials. 
     II. Methods Implemented to Fabricate Soft Sensors that Confirm to Arbitrary Geometries 
       FIG. 6  is a process flow diagram of a method  600  for fabricating the sensor substrate  100  and attaching the sensor substrate  100  to a robotic device according to an exemplary embodiment of the present disclosure.  FIG. 6  will be described with reference to the components of  FIGS. 1-5  though it is to be appreciated that the method  600  of  FIG. 6  may be used with other systems/components. In one embodiment, the method  600  may be included as computer implemented instructions that are stored within an electronic memory and may be accessed and executed by a processor of a computing system to operably control mechanical equipment (e.g., machinery) to fabricate the top stretchable layer  102  of the sensor substrate  100  and the bottom flexible layer  104  of the sensor substrate  100 , and to attach the bonded layers that comprise the sensor substrate  100  to a robotic device. 
     The method  600  may begin at block  602 , wherein the method  600  may include casting a dielectric layer  202 . In one embodiment, the fabrication system may begin the fabrication process to fabricate the top stretchable layer  102  of the sensor substrate  100  by casting the dielectric layer  202  as a bottom portion of the top stretchable layer  102 . As discussed above, the dielectric layer  202  may be cast in a mold using an elastic material. In some configurations, the dielectric layer  202  may have structures such as pillars, pyramids, or domes to fine tune mechanical properties as desired. 
     The method  600  may proceed to block  604 , wherein the method  600  may include fabricating a stretchable electrode pattern  204 . In one embodiment, the fabrication system may fabricate the stretchable electrode pattern  204  with a material of choice using a patterning process of choice. For example, spray coating, shadow mask, and/or screen printing may be utilized to pattern carbon nanotubes, silver nanowires, conducting polymer and/or conducting particle composites as materials of the stretchable electrode pattern  204 . 
     The method  600  may proceed to block  606 , wherein the method  600  may include casting an encapsulating layer  206  to complete fabrication of the top stretchable layer  102 . In one embodiment, the encapsulating layer  206  may be cast upon the stretchable electrode pattern  204  using the same or similar elastic material used to cast the dielectric layer  202  of the top stretchable layer  102 . Accordingly, as shown in  FIG. 2B , the encapsulating layer  206  may be cast atop the stretchable electrode pattern  204  which is included upon the dielectric layer  202  to complete fabrication of the top stretchable layer  102 . 
     The method  600  may proceed to block  608 , wherein the method  600  may include fabricating a soft adhesive sheet  302 . In one embodiment, the fabrication system may begin the fabrication process to fabricate the bottom flexible layer  104  of the sensor substrate  100  by fabricating the soft adhesive sheet  302  as a bottom portion of the bottom flexible layer  104 . The soft adhesive sheet  302  may be configured as a double sided acrylic tape sheet that is configured with varying properties of mechanical stiffness and chemical stability. 
     The method  600  may proceed to block  610 , wherein the method  600  may include laminating a copper film  304  upon the soft adhesive sheet  302 . In one embodiment, the fabrication system may laminate the thin sheet of copper film  304  upon a top side portion of the soft adhesive sheet  302 . In one embodiment, the copper film  304  may be patterned using photolithography. This may enable the fabrication of passive electronic components such as surface mount resistors directly on the circuit board associated with the sensor substrate  100 . This functionality enables the ability to design complex electrode designs which otherwise may not be possible to fabricate using alternative processes such as shadow mask patterning of composites. 
     The method  600  may proceed to block  612 , wherein the method  600  may include laminating a dry film photoresist  306  upon a top potion of the copper film  304 . Upon the lamination of the copper film  304  upon the soft adhesive sheet  302 , the fabrication system may utilize a thermal laminator to laminate a dry film photoresist  306  upon a top portion of the copper film  304 . 
     The method  600  may proceed to block  614 , wherein the method  600  may include etching undesired portions of copper of the copper film  304 . In an exemplary embodiment, the fabrication system may utilize the exposed portions of dry film photoresist pattern  308  as a mask to etch undesired portions of copper of the copper film  304  previously laminated upon the soft adhesive sheet  302 . Accordingly, the soft adhesive sheet  302  may include the etched copper  310  with respective portions of dry film photoresist  306  that remain upon the soft adhesive sheet  302 . 
     The method  600  may proceed to block  616 , wherein the method  600  may include enabling patterned copper electrodes to remain upon the etched copper  310  to complete fabrication of the bottom flexible layer  104 . In one embodiment, the fabrication system may remove the photoresist, leaving the patterned copper electrodes  312 . The patterned copper electrodes  312  may include traces that run to the circuit board that is associated with the sensor substrate  100 . Accordingly, as shown in  FIG. 3B , the bottom flexible layer  104  may be fabricated with the soft adhesive sheet  302  that includes the patterned copper electrodes  312  that are included upon the etched copper  310 . The bottom flexible layer  104  may be configured to be in conformity with the arbitrary smooth geometries with smooth segments of small radii of curvatures, to which a high level of conformity may be achieved with a suitable copper film thickness and copper pattern size and shape. 
     The method  600  may proceed to block  618 , wherein the method  600  may include bonding the top stretchable layer  102  to the bottom flexible layer  104  to form the sensor substrate  100 . In one embodiment, upon the fabrication of the top stretchable layer  102  of the sensor substrate  100  (at block  606 ) and the bottom flexible layer  104  of the sensor substrate  100  (at block  616 ), the fabrication system may be configured to bond the top stretchable layer  102  to the bottom flexible layer  104  to form the sensor substrate  100 . In one embodiment, the top layer of elastic material  414  may include an adhesive coating that may enable a strong adhesion between the dielectric layer  202  of the top stretchable layer  102  and the layer of elastic material  414  of the bottom flexible layer  104 . Accordingly, the top stretchable layer  102  may be bonded to the bottom flexible layer  104  to form the sensor substrate  100 . 
     The method  600  may proceed to block  620 , wherein the method  600  may include attaching the sensor substrate  100  to a robotic device. In an exemplary embodiment, upon the completion of the sensor fabrication, the sensor substrate  100 , which is adhesive on the bottom face may be placed upon any arbitrary geometry to be robustly adhered to the arbitrary geometry. As discussed above with respect to  FIG. 5 , once the sensor fabrication is complete, the sensor substrate  100  which is adhesive on a bottom face is used to adhere the sensor substrate  100  on any arbitrary smooth geometry such as to the robot finger/hand  502 . 
     Since the fabrication system utilizes the soft adhesive sheet  302  as the base of the sensor substrate  100 , robust adhesion arbitrary smooth geometry such as to the robot finger/hand  502  is achieved with little risk of delamination as the robotic device interacts with the physical world. Additionally, this functionality also ensures robust adhesion of the patterned copper electrodes  312  on the sensor substrate  100  and also the top elastic layers that are built upon it. 
       FIG. 7  is a process flow diagram of a method for fabricating soft sensors that conform to arbitrary smooth geometries according to an exemplary embodiment of the present disclosure.  FIG. 7  will be described with reference to the components of  FIGS. 1-5  though it is to be appreciated that the method  700  of  FIG. 7  may be used with other systems/components. The method  700  may begin at block  702 , wherein the method  700  may include fabricating a top stretchable layer  102  that includes a set of electrodes of soft sensors that are made of an elastic material. 
     The method  700  may proceed to block  704 , wherein the method  700  includes fabricating a bottom flexible layer  104  that is composed of copper films that are patterned using photolithography. In one embodiment, the bottom flexible layer  104  is configured to be in conformity with the arbitrary smooth geometries. The method  700  may proceed to block  706 , wherein the method  700  includes bonding the top stretchable layer  102  to the bottom flexible layer  104  to form a sensor substrate  100 . In one embodiment, the sensor substrate  100  is configured as a stretchable adhesive film which enables robust adhesion to the arbitrary smooth geometries. 
     The following includes definitions of selected terms employed herein. The definitions include various examples and/or forms of components that fall within the scope of a term and that may be used for implementation. The examples are not intended to be limiting. Further, one having ordinary skill in the art will appreciate that the components discussed herein, may be combined, omitted or organized with other components or organized into different architectures. 
     A “processor”, as used herein, processes signals and performs general computing and arithmetic functions. Signals processed by the processor may include digital signals, data signals, computer instructions, processor instructions, messages, a bit, a bit stream, or other means that may be received, transmitted, and/or detected. Generally, the processor may be a variety of various processors including multiple single and multicore processors and co-processors and other multiple single and multicore processor and co-processor architectures. The processor may include various modules to execute various functions. 
     A “memory”, as used herein, may include volatile memory and/or non-volatile memory. Non-volatile memory may include, for example, ROM (read only memory), PROM (programmable read only memory), EPROM (erasable PROM), and EEPROM (electrically erasable PROM). Volatile memory may include, for example, RAM (random access memory), synchronous RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), and direct RAM bus RAM (DRRAM). The memory may store an operating system that controls or allocates resources of a computing device. 
     A “disk” or “drive”, as used herein, may be a magnetic disk drive, a solid state disk drive, a floppy disk drive, a tape drive, a Zip drive, a flash memory card, and/or a memory stick. Furthermore, the disk may be a CD-ROM (compact disk ROM), a CD recordable drive (CD-R drive), a CD rewritable drive (CD-RW drive), and/or a digital video ROM drive (DVD-ROM). The disk may store an operating system that controls or allocates resources of a computing device. 
     A “bus”, as used herein, refers to an interconnected architecture that is operably connected to other computer components inside a computer or between computers. The bus may transfer data between the computer components. The bus may be a memory bus, a memory controller, a peripheral bus, an external bus, a crossbar switch, and/or a local bus, among others. 
     The aspects discussed herein may be described and implemented in the context of non-transitory computer-readable storage medium storing computer-executable instructions. Non-transitory computer-readable storage media include computer storage media and communication media. For example, flash memory drives, digital versatile discs (DVDs), compact discs (CDs), floppy disks, and tape cassettes. Non-transitory computer-readable storage media may include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, modules, or other data. 
       FIG. 8  is an illustrative overview of a mutual and overlap capacitance based sensor  800  having a smooth geometry, according to an exemplary embodiment of the present disclosure. The mutual and overlap capacitance based sensor of  FIG. 8  may include a top layer  802  and a bottom layer  804 . According to one aspect, the top layer  802  may be, for example, the top stretchable layer  102  described above (e.g., including one or more of the encapsulating layer  206 , the stretchable electrode pattern  204 , and the dielectric layer  202 ) and the bottom layer  804  may be the bottom flexible layer  104  described above (e.g., including one or more of the layer of elastic material  310 , the patterned electrodes  312 , and the soft adhesive sheet  302 ). As seen in  FIG. 4 , the dielectric layer  202  is positioned between the stretchable electrode pattern  204  and the patterned electrodes  312  or otherwise between the first electrode and the second electrode. 
     The top layer  802  may include a first electrode  812 . The bottom layer  804  may include a second electrode  814 . As seen in  FIG. 8 , the second electrode  814  has a line shape or rectangular shape which runs perpendicular to a wavelength direction  816  of the first electrode  812  and parallel to an amplitude direction (i.e., line a-a′) of the first electrode  812 . The top stretchable layer  102  may include the first electrode  812 , which may be the stretchable electrode pattern  204  described above and may be arranged or configured in a serpentine pattern. Described in another way, the first electrode  812  may be shaped similarly to a sine wave. 
     In this way, the first electrode  812  may have an architecture that enables both proximity and pressure sensing without the need for electrode switching while providing the location of the proximity along both horizontal axes. This may be achieved, for example, using a combination of soft stretchable electrodes and copper film electrodes leveraging the advantages of both materials. The conformity and softness may be realized by the dielectric layer  202  made of elastomer (e.g., Ecoflex 00-30) typically used to make face masks for movie props, and the top electrode made of a highly stretchable carbon composite. The bottom layer may include copper film electrodes for robust interconnection with the readout hardware. 
     This shape may be further optimized according to application specific requirements for sensitivity of either mode of sensing, meaning that other shapes are contemplated. For example, an electrode design that maximizes the length of a contour  818  of the top electrode and an overlap area between the top and bottom electrode may be considered. As another example, an electrode design with both overlapping and exposed areas may be utilized. 
     The first electrode  812  may be arranged such that a first portion  822  of the first electrode  812  overlaps the second electrode  814 . The first electrode  812  may be arranged such that the first portion  822  of the first electrode  812  may include a contour. The first electrode  812  may be arranged such that a first portion  832  of the second electrode  814  includes an exposed area not covered by the first electrode  812 . A second portion  834  of the second electrode  814  may include a covered area covered by the first electrode  812  while the first portion  832  of the second electrode  814  may include an exposed area not covered by the first electrode  812 . 
     The first portion  832  of the second electrode  814  may be associated with a first taxel of the mutual and overlap capacitance based sensor and the second portion  834  of the second electrode  814  may be associated with a second taxel of the mutual and overlap capacitance based sensor. 
     A processor, described in greater detail below, may determine a sensing mode based on a capacitance reading from the first taxel being within a first range, a second range, or between the first range and the second range and a reading from the second taxel. The first taxel may neighbor the second taxel. The sensing mode may be a mutual capacitance mode or an overlap capacitance mode. 
     The sensor may utilize a combination of capacitive sensing techniques: 1) mutual capacitance for proximity sensing and 2) overlap capacitance for pressure sensing. The sensor may use a novel electrode architecture that has both exposed and overlapping electrode areas, thereby enabling both mutual and overlap capacitive modes simultaneously, as demonstrated in  FIG. 9 . 
       FIG. 9  is a cross-sectional view of a mutual and overlap capacitance based sensor having a smooth geometry, according to an exemplary embodiment of the present disclosure.  FIG. 9  illustrates that mutual capacitance changes even if the electrodes are not co-planar (e.g., along line a-a′) as long as the bottom electrode is exposed. A serpentine pattern may be implemented for the top electrodes (e.g., the first electrode  812 ) to balance between two modes: 1) for mutual capacitance, the edge contour  818  length of the top electrode  812  may be maximized, according to one aspect, because most of the electric field coupling between the excitation and sense electrodes occurs at the edges and 2) for overlap capacitance, the overlap area  822  may be maximized. 
     The sensor or capacitive sensor described herein has two distinct advantages: 1) a top electrode architecture that allows both proximity and pressure sensing without the need for electrode switching while providing the location of the proximity along both horizontal axes, and 2) a combination of soft stretchable electrodes and copper film electrodes leveraging the advantages of both materials. The conformity and softness are realized by the dielectric layer (e.g.,  202 ) made of elastomer typically used to make face masks for movie props, and the top electrodes made of a highly stretchable carbon composite. The bottom layer may include copper film electrodes for robust interconnection with the readout hardware. The fabrication process combines conventional methods, making it straightforward to work with curved surfaces and scale depending on applications. 
     As seen in  FIG. 9 , the second portion  834  of the second electrode  814  may include a covered area  834  covered by the first electrode  812  while the first portion  832  of the second electrode  814  may include an exposed area  832  not covered by the first electrode  812 . In this way, mutual capacitance and overlap capacitance readings may be provided by the same mutual and overlap capacitance based sensor. The first electrode  812  and the second electrode  814  are stacked in a vertical orientation, but due to the covered area  834  and the exposed area  832 , mutual capacitance still exists between the non-co-planar electrodes, indicated at  910 , as a human finger  912  approaches the sensor  800 . 
     When the finger  912  makes contact with the first electrode  812 , and applies a downward force, overlap capacitance between the first electrode  812  and the second electrode  814  may increase, thereby creating a reading at the associated sensor taxel. 
     According to one aspect, the sensor  800  of  FIG. 8  may be made of soft, stretchable material and is therefore conformable to smooth curved surface of robot links. The sensor  800  may also be fabricated in different sizes from fingertips to torso because the fabrication process employs scalable methods. Recognizing gentle contact gestures often seen in affectionate physical interactions may be possible based on the dual mutual and overlap capacitance detection abilities of this sensor. Further, spatio-temporal information of the 2D capacitance data obtained from the sensor may be applied using deep neural network architectures. 
     The contribution of this sensor  800  may be twofold. First, the multi-modal capacitance-based sensor architecture may detect proximity and near-zero force contacts, as well as large forces. Multi-modal sensing may be achieved by combining two sensing modalities normally used separately: pressure sensing based on overlap capacitance that depends on the distance between two overlapping electrodes (e.g., distance between the second portion  834  of the second electrode  814  and the first electrode  812 ), and proximity sensing based on mutual capacitance (also known as projected capacitance), which may be used in touch-screen devices. Stated another way, this sensor uses a combination of capacitive sensing techniques: 1) mutual capacitance for proximity sensing and 2) overlap capacitance for pressure sensing. 
     Mutual capacitance is the capacitance between two electrodes (e.g., excitation and sense) and may be used in touch screens. Typically, the electrodes may be placed on the same plane and, as a result, the coupling electric field projects out of the plane from the excitation electrode and returns back to the sense electrode. As a human finger approaches the sensor, the electric field couples with the finger and the coupling between the capacitive electrodes, Cs, decreases. The magnitude of the capacitance decrease increases as the finger comes closer to the sensor surface. For a mutual capacitive sensor to function, both excitation and sense electrodes are exposed to enable the electric field to project outward and couple with a finger. 
     Overlap capacitance refers to the capacitance that is inversely proportional to the distance between two overlapping electrodes: C S =eA/d where e is the permittivity, A is the overlap area, and d is the distance between the electrodes. Upon application of a normal force, decrease in d causes an increase in capacitance C S . 
     The mutual and overlap capacitance based sensor  800  may utilize a novel electrode architecture that has both exposed and overlapping electrode areas as shown in  FIGS. 8-9 , thus enabling both mutual and overlap capacitive sensing modes to occur simultaneously.  FIG. 9  illustrates that mutual capacitance changes even if the electrodes  812 ,  814  are not co-planar as long as the bottom electrode is exposed. The selection of a serpentine pattern for the top electrodes enables balance between two modes: 1) for mutual capacitance, the edge contour length  818  of the top electrode may be maximized because most of the electric field coupling between the excitation and sense electrodes occurs at the edges and 2) for overlap capacitance, the overlap area  822  may be maximized. This shape may however be further optimized according to specific application requirements for sensitivity of either mode of sensing. 
       FIG. 10  is an illustration of an exemplary mutual and overlap capacitance based sensor having a smooth geometry, according to an embodiment of the present disclosure. A capacitance-based sensor array architecture for physical human-robot interaction (pHRI) applications that may measure proximity, near-zero-force (NZF) contacts, and pressure between a robot and human body may be provided by duplicating the sensor of  FIG. 8  according to an array architecture, for example. 
     According to one aspect, a carbon composite may be utilized for the top electrodes, while using thin copper film for the bottom electrodes, taking advantage of the fact that the bottom layer may be attached to a rigid robot body part and therefore need to be conformable but not necessarily stretchable. Furthermore, the copper electrodes may be connected to a sense terminal of the readout circuit because the copper may be more critical to signal quality than the excitation terminal. The sensor may utilize crimp connectors for the top electrodes made of stretchable carbon composite. 
     According to one aspect, the mutual and overlap capacitance based sensor  800  may include of top and bottom layers of strip-shaped electrodes  814  running perpendicularly to each other, separated by the dielectric layer  202 . Each intersection of a pair of top and bottom electrodes may provide a capacitance measurement and may be considered or grouped as ‘a taxel’. One implementation may have 160 taxels over an area of 20 cm×15 cm, but the fabrication process may be scalable and therefore suitable for installation on both small (e.g. fingertip) and large (e.g. limbs and torso) areas. The mutual and overlap capacitance based sensor  800  may use stretchable carbon composites for the top electrodes and elastomer for the dielectric layer to make the sensor stretchable and conformable, while using thin films of copper for the bottom electrodes for robust interconnection to readout hardware and hence better signal integrity. 
     Fabrication of the mutual and overlap capacitance based sensor may include I) patterning copper film electrodes, II) fabricating soft top electrodes and dielectric, and III) bonding top and bottom segments. This process may be highly scalable. Also, large area sensors (for full body) may be fabricated just as easily as small area counterparts (for fingertips) by utilizing dry-film photoresists that may be laminated on large substrates. 
     In step I, according to one aspect, a copper film of thickness 100 μm may be laminated on a stretchable adhesive sheet 3M-9495LE of thickness 170 μm. A dry film photoresist may be then thermally laminated using a laminator (e.g., Akiles Pro-Lam) at a temperature of 110° C. at a speed setting of 10 mm/sec. The photoresist may then be exposed through a shadow mask using a UV lamp (365 nm) for 60 sec. The exposed photoresist may be then developed using a developer solution of 1% (wt/wt) NaHCO3. Once exposed, the copper film may be etched using a Ferric Chloride solution (e.g., MG Chemicals). Finally, the photoresist may be stripped using a 1% (wt/wt) NaOH solution. The copper electrodes have extended parts that may be later directly soldered onto a readout system. 
     Step II may include molding the dielectric layer using soft elastomer (e.g., Ecoflex 00-30) in a mold with an inverted pyramid pattern. The pyramids may have a square base of 1.5 mm×1.5 mm, a height of 1.5 mm and a draft of 10 degrees. The pitch of the pyramids may be 1 mm edge to edge. This dielectric architecture provides higher sensitivity to normal forces as opposed to a solid dielectric and may be further tuned to obtain an application-specific elastic modulus. Part A and Part B of Ecoflex may be mixed in equal quantities and poured in the mold. The uncured elastomer may be then degassed in a vacuum chamber until all the air may be removed. The elastomer may be then cured at 60° C. for 20 min. It may be also possible to cure the elastomer at room temperature for 4 hours. Once cured, the stretchable carbon composite may be patterned on top of the surface of the dielectric using a shadow mask to form the top electrodes. The shadow mask may be cut out using a laser cutter (e.g., Dremel LC40). The carbon composite may be formed by mixing 100 mg of Carbon Nanofibers (e.g., Sigma-Aldrich 719781), 300 mg of Carbon Black (e.g., Alfa Aesar—H30253) and 2 gm of Ecoflex 00-30 Part A and 2 gm of Part B. A Thinky planetary centrifuge (e.g., ARE 310) may be used to mix the composite at 2000 rpm for 5 min. The carbon composite pattern may be then cured at 60° C. for 20 min. The terminals of the electrode traces may be wrapped using a standard crimp connector that may then be soldered on to the readout circuit similarly to the copper electrode traces. Finally, an encapsulating layer of the same elastomer may be formed on top of the exposed carbon composite electrodes. 
     Step III may include applying a thin layer of uncured Ecoflex 00-30 mixture on the copper film electrodes and placing the top segment on it. This assembly may be then cured at 60° C. for 20 min ensuring strong adhesion between the top and bottom segments. The adhesive substrate 3M-9495LE, on which the sensor may be built, adheres to smooth curved surface as shown in  FIG. 10 . 
     One issue with this sensor architecture may be an ambiguity between proximity and small pressure, as depicted in  FIG. 11 . When a human finger comes close to or barely touches the sensor (e.g., NZF contact), mutual capacitance decreases compared to the baseline value. As the finger increases the pressure, measured capacitance increases due to increased overlap capacitance and eventually exceeds the baseline. When the measured capacitance is below the baseline, therefore, it may be difficult to distinguish proximity and small pressure using merely the capacitance value of a single taxel. This ambiguity, however, may be resolved using the information from the neighboring taxels that are stimulated due to the proximity effect. 
     In this regard, recognizing contact gestures involving proximity, NZF contacts, and large pressure may be achieved by applying deep neural network (DNN) architectures to time-series capacitance data from the sensor, such as a3D Convolutional Neural Network (3DCNN) and Convolutional Long-Short Term Memory (ConvLSTM) in a class gesture recognition problem including non-contact gestures (e.g., hover and air-stroke), NZF (e.g., light touch, light stroke, tickle), and pressure-based (e.g., hard stroke and massage) gestures, in addition to the baseline (e.g., no interaction), using the system  1200  of  FIG. 12 . According to one experiment between the two models, 3DCNN demonstrated a higher accuracy than the ConvLSTM with a test dataset obtained separately from the training dataset. 
       FIG. 11  is an operation diagram associated with the mutual and overlap capacitance based sensor, according to an exemplary embodiment of the present disclosure. As discussed above, there may be an ambiguity between proximity and light touch when the capacitance of a taxel is below the baseline. Again, this ambiguity may be resolved by applying pattern recognition techniques to the time-varying 2D capacitance data from all neighboring taxels. 
     For example, with reference to a response of an array of 3×3 taxels when a finger approaches and applies a small and a medium pressure to the middle taxel of the 3×3 taxel grid. During approach, the capacitance of the middle taxel decreases while the neighboring taxels experience a smaller decrease due to the larger distances. When the finger touches the middle taxel, the neighboring taxels still continue to register decreased capacitance. From this point on when the finger applies a small pressure, the middle taxel start to see an increase in capacitance since the dielectric thickness decreases while the capacitance at the neighboring taxels further decreases. This continues up to the point where the capacitance of the middle taxel returns to the baseline value. Using the information from the neighboring taxels, the system of  FIG. 12  may therefore differentiate between proximity and small pressure with the same sensor array. In this way, the processor and mode determiner of  FIG. 12  may differentiate between different type of touches or gestures from a user. Two DNN architectures that have been used for similar recognition problems using spatio-temporal data may include ConvLSTM and 3DCNN. However, other models, including classical ones, such as hidden-Markov models (HMM) may be utilized. 
       FIG. 12  is a component diagram of an exemplary system  1200  for mutual and overlap capacitance based sensing, according to an exemplary embodiment of the present disclosure. The system  1200  for mutual and overlap capacitance based sensing may include the mutual and overlap capacitance based sensor  800  of  FIG. 8 , which may include the first electrode  812 , the second electrode  814 , and the dielectric layer  202 . The first electrode  812  may be the stretchable electrode pattern  204  configured in a serpentine pattern or shaped as a sine wave. The system  1200  for mutual and overlap capacitance based sensing may include a processor  1220 , a memory  1222 , and a mode determiner  1230 . 
     The mode determiner  1230  may be implemented via the processor  1220  and the memory  1222  and may determine a sensing mode for the mutual and overlap capacitance based sensor. The mode determiner  1230  may determine the sensing mode to be a mutual capacitance mode or an overlap capacitance mode, for example. According to one aspect, the mode determiner  1230  may determine the sensing mode based on a capacitance reading from a first taxel of the mutual and overlap capacitance based sensor  800  and/or a capacitance reading from a second taxel of the mutual and overlap capacitance based sensor  800 . 
     When the capacitance reading from the first taxel is within a first range, the mode determiner  1230  may set the operating mode of the mutual and overlap capacitance based sensor  800  to be overlap capacitance mode. When the capacitance reading from the first taxel is within a second range, the mode determiner  1230  may set the operating mode of the mutual and overlap capacitance based sensor  800  to be mutual capacitance mode. When the capacitance reading from the first taxel is between the first range and the second range, the mode determiner  1230  may consider the capacitance reading from the second, neighboring taxel prior to setting the operating mode. 
     Specifically, during an approach of a finger, the capacitance of the first taxel decreases, while the neighboring taxels experience a smaller decrease than the first taxel, and thus, the mode determiner  1230  may set the operating mode to be mutual capacitance mode based on the capacitance reading from the first taxel being between the first range and the second range and based on neighboring taxels experiencing a smaller decrease than the first taxel between subsequent readings. 
     Additionally, when the finger applies a small pressure (e.g., NZF), the capacitance of the first taxel increases, while the neighboring taxels experience a decrease, and thus, the mode determiner  1230  may set the operating mode to be the overlap capacitance mode based on the capacitance reading from the first taxel being between the first range and the second range and based on the reading from the first taxel increasing while the readings from neighboring taxels decreasing. 
     According to one aspect, capacitance measurements at 16×10=160 taxels may be recorded at a rate of 8 Hz through a serial port with a baud rate of 115200, although any number of total taxels and different refresh rates may be implemented. The baseline capacitance magnitude at each taxel may be recorded at the beginning of a sequence and may be subtracted from subsequent measurements to effectively ‘zero out’ readings. 
     A training sequence may be obtained for each gesture by recording a single sequence continuously while the gesture may be repeated 30-40 times with a gap of a few seconds in between. Data from all 160 taxels may be recorded during the training sequence of the tickle gesture. Testing dataset may be obtained separately by a similar procedure while the same person performs the gestures with fewer repetitions on a different day. 
     In order to generate the training dataset, each sequence may be first divided into active sections where a gesture may be performed and baseline sections where there may be no interaction. Given the noise level, a frame may be marked as active if the difference from the baseline value of at least one taxel may be equal to or above a threshold. The training dataset may be generated by scanning the active sections using a sliding window of width w with additional p frames of padding from the preceding baseline section in order to detect interactions early. Active sections shorter than w−p may be discarded. 
     Two DNN architectures were tested: 3DCNN and ConvLSTM, although other architectures may be implemented. These models were chosen because they have been used for modeling spatio-temporal information in RGBD data, which is similar to the tactile data obtained by the sensor. A stopping condition for training may be ai+1&lt;al+0.1 where al (%) may be the training accuracy after the i-th epoch. 
     3D CNN 
     Two layers of 3D CNN of kernel size 3×3×3 may be followed by four fully-connected dense layers with the rectified linear unit (ReLU) activation function, whose outputs go through a softmax function to recognize six gestures in addition to the baseline (no interaction) case. The 3D CNN layers may be fully connected and each layer runs 30 sets of CNN operation on a tensor of size 16×10×w, resulting in an output tensor of size 16×10×w×30. The sizes of the dense layers may be determined to achieve high accuracy while preventing overfitting. 
     A popular choice for prediction problems involving time-series data are recurrent neural networks (RNN) such as Long-Short Term Memory (LSTM). A LSTM unit may take the measurement Xt at time t and ht−1 the output of the previous unit as inputs, and calculates the output ht. In order to avoid the vanishing gradient issue and retain long term dependencies, LSTM uses a set of gates to set the significance of a unit, using a state memory. 
     ConvLSTM 
     The sensor may use a variant of LSTM called ConvLSTM as a part of the DNN architecture for gesture recognition. In ConvLSTM, both input-state and state-state transitions may be replaced by the 2D convolution operation. The rest of the architecture may be based on the “peephole connection” variant of the standard LSTM. Spatial and temporal information may be retained by 2D convolution and LSTM architecture, respectively. 
     According to one aspect, each frame goes through 30 sets of 2D convolutional operation before fed into an LSTM unit. Input and output of an LSTM unit therefore has a size of 16×10×30. The sensor may use two layers of LSTM followed by fully-connected dense layers of the same size and activation functions as in the 3D CNN model. However, in this case only the output of the last LSTM unit may be fed into the dense layer network as opposed to a 3D array as in the case of 3DCNN because the 2D array may be expected to retain both spatial and temporal relations. As a result, ConvLSTM requires much fewer parameters to be trained in the dense network. 
       FIG. 13  is a flow diagram of an exemplary method  1300  for mutual and overlap capacitance based sensing, according to an exemplary embodiment of the present disclosure. According to one aspect, the method  1300  for mutual and overlap capacitance based sensing may include receiving  1302  a capacitance reading from a first taxel of a mutual and overlap capacitance based sensor, determining whether the capacitance reading falls within a first range  1304   a , a second range  1304   b , or between the first range and the second range  1304   c , setting  1306  an operating mode to a mutual capacitance mode based on the capacitance reading being within the first range, setting  1308  the operating mode to an overlap capacitance mode based on the capacitance reading being within the second range, receiving  1310  a capacitance reading from a second, neighboring taxel of the mutual and overlap capacitance based sensor when the capacitance reading falls between the first range and the second range, determining  1312  whether the capacitance reading from the second, neighboring taxel decreases less than the capacitance reading from the first taxel between subsequent readings, setting  1314  the operating mode to the mutual capacitance mode based on the capacitance reading of the first taxel being between the first range and the second range and the capacitance reading from the second, neighboring taxel decreasing between subsequent readings, and setting  1316  the operating mode to the overlap capacitance mode based on the capacitance reading of the first taxel being between the first range and the second range and increasing, while the capacitance reading from the second, neighboring taxel decreasing between subsequent readings. 
     Still another aspect involves a computer-readable medium including processor-executable instructions configured to implement one aspect of the techniques presented herein. An aspect of a computer-readable medium or a computer-readable device devised in these ways is illustrated in  FIG. 14 , wherein an implementation  1400  includes a computer-readable medium  1408 , such as a CD-R, DVD-R, flash drive, a platter of a hard disk drive, etc., on which is encoded computer-readable data  1406 . This encoded computer-readable data  1406 , such as binary data including a plurality of zero&#39;s and one&#39;s as shown in  1406 , in turn includes a set of processor-executable computer instructions  1404  configured to operate according to one or more of the principles set forth herein. In this implementation  1400 , the processor-executable computer instructions  1404  may be configured to perform a method  1402 , such as the method  1300  of  FIG. 13 . In another aspect, the processor-executable computer instructions  1404  may be configured to implement a system, such as the system  1200  of  FIG. 12 . Many such computer-readable media may be devised by those of ordinary skill in the art that are configured to operate in accordance with the techniques presented herein. 
     As used in this application, the terms “component”, “module,” “system”, “interface”, and the like are generally intended to refer to a computer-related entity, either hardware, a combination of hardware and software, software, or software in execution. For example, a component may be, but is not limited to being, a process running on a processor, a processing unit, an object, an executable, a thread of execution, a program, or a computer. By way of illustration, both an application running on a controller and the controller may be a component. One or more components residing within a process or thread of execution and a component may be localized on one computer or distributed between two or more computers. 
     Further, the claimed subject matter is implemented as a method, apparatus, or article of manufacture using standard programming or engineering techniques to produce software, firmware, hardware, or any combination thereof to control a computer to implement the disclosed subject matter. The term “article of manufacture” as used herein is intended to encompass a computer program accessible from any computer-readable device, carrier, or media. Of course, many modifications may be made to this configuration without departing from the scope or spirit of the claimed subject matter. 
       FIG. 15  and the following discussion provide a description of a suitable computing environment to implement aspects of one or more of the provisions set forth herein. The operating environment of  FIG. 15  is merely one example of a suitable operating environment and is not intended to suggest any limitation as to the scope of use or functionality of the operating environment. Example computing devices include, but are not limited to, personal computers, server computers, hand-held or laptop devices, mobile devices, such as mobile phones, Personal Digital Assistants (PDAs), media players, and the like, multiprocessor systems, consumer electronics, mini computers, mainframe computers, distributed computing environments that include any of the above systems or devices, etc. 
     Generally, aspects are described in the general context of “computer readable instructions” being executed by one or more computing devices. Computer readable instructions may be distributed via computer readable media as will be discussed below. Computer readable instructions may be implemented as program modules, such as functions, objects, Application Programming Interfaces (APIs), data structures, and the like, that perform one or more tasks or implement one or more abstract data types. Typically, the functionality of the computer readable instructions are combined or distributed as desired in various environments. 
       FIG. 15  illustrates a system  1500  including a computing device  1512  configured to implement one aspect provided herein. In one configuration, the computing device  1512  includes at least one processing unit  1516  and memory  1518 . Depending on the exact configuration and type of computing device, memory  1518  may be volatile, such as RAM, non-volatile, such as ROM, flash memory, etc., or a combination of the two. This configuration is illustrated in  FIG. 15  by dashed line  1514 . 
     In other aspects, the computing device  1512  includes additional features or functionality. For example, the computing device  1512  may include additional storage such as removable storage or non-removable storage, including, but not limited to, magnetic storage, optical storage, etc. Such additional storage is illustrated in  FIG. 15  by storage  1520 . In one aspect, computer readable instructions to implement one aspect provided herein are in storage  1520 . Storage  1520  may store other computer readable instructions to implement an operating system, an application program, etc. Computer readable instructions may be loaded in memory  1518  for execution by processing unit  1516 , for example. 
     The term “computer readable media” as used herein includes computer storage media. Computer storage media includes volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions or other data. Memory  1518  and storage  1520  are examples of computer storage media. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, Digital Versatile Disks (DVDs) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which may be used to store the desired information and which may be accessed by the computing device  1512 . Any such computer storage media is part of the computing device  1512 . 
     The term “computer readable media” includes communication media. Communication media typically embodies computer readable instructions or other data in a “modulated data signal” such as a carrier wave or other transport mechanism and includes any information delivery media. The term “modulated data signal” includes a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. 
     The computing device  1512  includes input device(s)  1524  such as keyboard, mouse, pen, voice input device, touch input device, infrared cameras, video input devices, or any other input device. Output device(s)  1522  such as one or more displays, speakers, printers, or any other output device may be included with the computing device  1512 . Input device(s)  1524  and output device(s)  1522  may be connected to the computing device  1512  via a wired connection, wireless connection, or any combination thereof. In one aspect, an input device or an output device from another computing device may be used as input device(s)  1524  or output device(s)  1522  for the computing device  1512 . The computing device  1512  may include communication connection(s)  1526  to facilitate communications with one or more other devices  1530 , such as through network  1528 , for example. 
     Although the subject matter has been described in language specific to structural features or methodological acts, it is to be understood that the subject matter of the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example aspects. 
     Various operations of aspects are provided herein. The order in which one or more or all of the operations are described should not be construed as to imply that these operations are necessarily order dependent. Alternative ordering will be appreciated based on this description. Further, not all operations may necessarily be present in each aspect provided herein. 
     As used in this application, “or” is intended to mean an inclusive “or” rather than an exclusive “or”. Further, an inclusive “or” may include any combination thereof (e.g., A, B, or any combination thereof). In addition, “a” and “an” as used in this application are generally construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form. Additionally, at least one of A and B and/or the like generally means A or B or both A and B. Further, to the extent that “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”. 
     Further, unless specified otherwise, “first”, “second”, or the like are not intended to imply a temporal aspect, a spatial aspect, an ordering, etc. Rather, such terms are merely used as identifiers, names, etc. for features, elements, items, etc. For example, a first channel and a second channel generally correspond to channel A and channel B or two different or two identical channels or the same channel. Additionally, “comprising”, “comprises”, “including”, “includes”, or the like generally means comprising or including, but not limited to. 
     It should be apparent from the foregoing description that various exemplary embodiments of the disclosure may be implemented in hardware. Furthermore, various exemplary embodiments may be implemented as instructions stored on a non-transitory machine-readable storage medium, such as a volatile or non-volatile memory, which may be read and executed by at least one processor to perform the operations described in detail herein. A machine-readable storage medium may include any mechanism for storing information in a form readable by a machine, such as a personal or laptop computer, a server, or other computing device. Thus, a non-transitory machine-readable storage medium excludes transitory signals but may include both volatile and non-volatile memories, including but not limited to read-only memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash-memory devices, and similar storage media. 
     It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative circuitry embodying the principles of the disclosure. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in machine readable media and so executed by a computer or processor, whether or not such computer or processor is explicitly shown. 
     It will be appreciated that various implementations of the above-disclosed and other features and functions, or alternatives or varieties thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.