Abstract:
A flexible capacitance sensor having multiple layers for communicating signals to a data acquisition system for reconstructing an image of an area or object located in a subject being sensed, the flexible capacitance sensor having a flexible layer of capacitance plates; a flexible shielding ground layer next to the layer of capacitance plates; a flexible layer of signal traces next to the shielding ground layer, where the layer of signal traces has a plurality of trace lines; and where the capacitance sensor is flexible and adapted to be wrapped around the subject being sensed. The sensor is adapted to communicate signals via the plurality of trace lines to a data acquisition system for providing an image of the area or object between the capacitance plates.

Description:
BACKGROUND OF THE INVENTIVE FIELD 
     Electrical Capacitance Tomography (ECT) is the reconstruction of material concentrations of dielectric physical properties in the imaging domain by inversion of capacitance data from a capacitance sensor. 
     Volume capacitance imaging or ECVT is the direct 3D reconstruction of volume concentration or physical properties in the imaging domain utilizing 3D features in the ECVT sensor design. 
     Adaptive ECVT is an advanced technology that introduces a new dimension into 3D sensor design by applying voltages of different frequencies, amplitudes, and/or phases to capacitance plate segments. Adaptive sensors can provide a virtually infinite number of independent capacitance measurements of the flow field or imaging volume through which high resolution images can be obtained. 
     ECVT sensors were developed to distribute electric field in three dimensions for reconstruction of dielectric constant distribution in an imaging domain. 
     ECVT sensors can utilize different plate shapes and distributions in multiple layers to target a volume for imaging. 
     SUMMARY OF THE EXEMPLARY EMBODIMENTS 
     The present invention is directed to process tomography and, in particular, to Electrical Capacitance Volume Tomography (ECVT) and adaptive ECVT sensors and using design techniques for realizing flexible, wearable, stretchable, and modular ECVT sensors. 
     Dynamic ECVT is a technology that senses measured capacitances between sensor plates to generate a whole volume image of the region. ECVT technology has been applied in providing images of objects moving through a pipe for example. ECVT has provided insight into multiphase flow phenomena in many industrial processes, including pneumatic conveying, oil pipe lines, fluidized beds, bubble columns and many other chemical and biochemical processes (the multiphase flow often being in a combination of gas, liquid, and solid states). ECVT may also be used for imaging biological processes and tissues. 
     Capacitance sensing sensors were designed previously to address fixed structure applications surrounding a dynamic flow component. The design of the present invention includes the integration of all plates, connectors, resistors, and shielding layers into one flexible or stretchable element. The present invention provides an innovative design with features through which the sensor can be used repeatedly and on different subjects (columns, pipes, organs, or limbs, etc.) through relatively simple installations. Specifically, features of the preferred embodiment of the present invention includes the integration of all components of a capacitance sensor into one element (of multiple layers) for handling by users, a modular feature where different plates configurations can be easily assembled, a wearable feature where sensors can be placed by users at different parts of the human body, and stretchable feature where sensors can be expanded in different directions. Details of these features are described below. 
     The integrative design of the present invention combines all elements of a capacitance sensor into one flexible sheet that can be used repeatedly. This flexible sheet in the preferred embodiment contains multiple layers including the layers of capacitance plates, isolated signal traces, ground shielding, isolative/resistive layers between conductive layers, a ground layer and low profile connectors for connecting signal traces to low profile coaxial cables. The plate layer contains design of capacitance sensors aimed at distributing the electric field in three dimensions. Traces can be separated from each other by ground to reduce capacitive coupling. The isolative/resistive layer preferably provides separation between plate layer, signal trace layer, and shield/ground layer. The resistance provides a path for discharge of static charges. The shielding ground layer preferably provides isolation for the capacitance sensors from outside capacitance coupling or electric noise. In one embodiment, the low profile connectors connect the sensor plates to data acquisition system through signal traces separated by ground. The ground between traces is aimed at reducing coupling between capacitance plates. The integrative design here enables capacitance sensors to be used easily for wrapping around different geometries. It also provides a means for a wearable feature where sensors can be placed on the human body in a low profile manner. It also provides a stretchable sensor where sensor elements can be extended for applications where object intended for imaging may change in size or geometry. This integrative approach can be applied for ECVT sensors of different designs and varying number of plates. 
     The integrative design of the present invention also preferably includes a modular feature where plates fabricated in an integrative approach can be layered separately for forming an equivalent plate. Such feature enables changing sensor design using modular sensors/plates. 
     The present invention also preferably includes a stretchable feature where sensor plates and layers are fabricated from stretchable materials. For example, stretchable materials can be a formed of stretchable flexible boards or flexible metal meshes used for fabricating conductive layers. The flexibility can also be provided by connecting flexible integrative sensor sections using stretchable connections. Flexibility can also be provided using conductive spray on stretchable isolative materials (like rubber or elastic material or even stretchable fabric) to form layers of integrative sensors as explained above. 
     The interactive design of the present invention also preferably includes a combination of traditional solid layered printed circuit boards and flexible or stretchable sensors. Applications of such combination include addressing an object for imaging where a part of it is fixed and another is expanding. 
     The integrative design of the present invention also enables measuring of capacitance signals from an Adaptive Electrical Capacitance Volume Tomography (AECVT) sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of an exemplary embodiment will be obtained from a reading of the following detailed description and the accompanying drawings wherein identical reference characters refer to identical parts and in which: 
         FIG. 1  illustrates one embodiment of a flexible integrative sensor design of the present invention. 
         FIG. 2  illustrates one embodiment for a sensor with a 2D profile that shows the different layers in the integrative sensor design depicted in  FIG. 1 . 
         FIG. 3  illustrates one embodiment of the sensor with through holes for interfacing coaxial cables with plates. 
         FIGS. 4A-E  illustrate one embodiment of a 24 channel sensor with layers separated out individually for illustration. 
         FIGS. 5A-B  illustrate one embodiment of an integrated flexible capacitance sensor for ECVT applications. 
         FIGS. 6A-B  illustrate one embodiment of a sensor of the present invention configured into one capacitance plate by combining multiple flexible integrative sensors into one equivalent plate. 
         FIGS. 7A-B  illustrate one sensor embodiment for an expandable sensor design with modular plates. 
         FIG. 8  illustrates one embodiment of a capacitance sensor of the present invention having integrative elements connected using stretchable connectors. 
         FIG. 9  illustrates on embodiment of a capacitive sensor of the present invention applied on a pre-stretched elastic substrate for forming a stretchable ECVT sensor. 
         FIG. 10  illustrates one embodiment of a modular and removable section. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates one embodiment of an integrative sensor design  10  of the present invention having with two capacitance plates  12 . More plates can be incorporated using the concepts discussed herein to form virtually any number of sensor configurations of differing shapes and sizes. In the preferred embodiment, the capacitance sensor includes multiple layers for forming a capacitance sensor. For example, the layers may include a flexible insulation layer  11 , plate layer  14 , isolative/resistor layer  16 , a shielding ground layer  18 , a second isolative layer  20 , a flex signal trace layer  21 , an insulation layer  22  and a ground layer  24  and connectors integrated into one flexible board  10 . The plates are preferably made up of conductive material such as copper (metals), conductive liquid, conductive ink, or conductive spray. In the preferred embodiment, signal traces are used in a separate layer with ground shielding in between them for isolation of capacitance coupling. A trace is a conductive line that is imbedded in one of the sensors layers and acts as a means to conduct electric signals from plates to data acquisition system or from plates to low profile connectors. Low profile connectors are preferably used for interfacing strip-lines with coaxial cables for connecting with a data acquisition system for collection sensor readings. 
     In the embodiment shown in 1, the first insulation layer  11  separates the capacitance plates from the object or flow being imaged. The second layer is the capacitance plates layer  14 . Capacitance plates  12  are preferably composed of conductive material and are typically made from metals. In one embodiment, the plates can be made from conductive spray on a nonconductive layer. The third layer is an isolative layer  16  or resistive layer. This layer separates the plates from the ground layer. The isolative layer can be made resistive so it provides a path to discharge static charges from the plates to the ground. The fourth ground layer  18  separates the traces from the plates so they don&#39;t couple. The fifth layer is again an isolative layer  20  that separates the ground layer from the traces layer. The sixth layer is the traces layer  21 . In this layer trace lines  25  are introduced to communicate electric signals from the plates to data acquisition system or from plates to low profile connectors. Gaps between traces in this layer are preferably filled with ground lines to reduce coupling between trace lines. The seventh layer is again isolative  22 . The eighth layer is a ground layer  24  to shield the sensor from outside interference and from trace lines cross-coupling. In the preferred embodiment, all layers are connected together by a thin layer of adhesive typically used in flexible circuit boards technology. The adhesive layer can also serve as an isolative layer. Another embodiment involves plates, ground, and traces sprayed or printed on separate layers using conductive spray or ink and then layering those layers with insulation between them. Such separate layers can be elastic of stretchable materials. 
       FIG. 2  illustrates one embodiment for a sensor with a 2D profile that shows the different layers in integrative sensor design depicted in  FIG. 1 . 
       FIG. 3  illustrates one embodiment of the sensor with through holes  26  for interfacing coaxial cables with plates. 
       FIGS. 4A-E  illustrate one embodiment of a 24 channel sensor with layers separated out individually for illustration. Layers are preferably separated by isolative material and they include  FIG. 4A  plates layer  28 ,  FIG. 4B  ground layer  30 ,  FIG. 4C  signal trace layer  32 , and  FIG. 4D  ground shielding layer  34 . The integrated sensor with the layers combined is shown in the  FIG. 4E  at  36 . 
       FIGS. 5A-B  illustrate one embodiment of an integrated flexible capacitance sensor for ECVT applications.  FIGS. 5A and 5B  illustrate the front and back sides of the fabricated design of  FIG. 4E , respectively, with the layers and components of an ECVT sensor integrated in one flexible circuit. 
       FIGS. 6A-B  illustrate one embodiment of a sensor of the present invention configured into one capacitance plate by combining multiple flexible integrative sensors  42  into one equivalent plate. This modular approach can be used for sensors with multiple plates to form a modular ECVT sensor. Modular sections  42  are combined together by connecting plates, traces, and ground of each modular section to another modular section. Through holes  44  provide means to connecting inner layers of a modular section. For example, a through hole for the trace of a modular section provides a path directly to the trace and bypassing in-between layers. Modular sections also can be connecting through low profile PCB connectors where each layer in one modular section is connected to the same (equivalent) layer of another modular section. Modular sections can also be connected through stretchable lines for introducing elasticity to the design. An equivalent resulting sensor plate from combining modular sections is shown at  46 . 
       FIGS. 7A-B  illustrate one sensor embodiment for an expandable sensor design where modular plates  48  are connected to form an equivalent plate  50  where the equivalent plate can change in size by moving modular plates with respect to each other. Through holes  52  provide paths to different layers in each modular section. Layers from each modular section are preferably connected together using corresponding through holes. Lines used to connect different modular sections can be flexible or stretchable to provide room for movement of modular plates. Modular plates can be of any shape or size. 
       FIG. 8  illustrates one embodiment of a capacitance sensor of the present invention having integrative elements connected using stretchable connectors  54  for forming a stretchable ECVT sensor. Here, modular elements similar to ones described in  FIGS. 7A and 7B  are connected using stretchable lines to connect through holes of different modular section together. The stretchability of connecting lines renders the new formed plate as stretchable. Stretchable lines can be made of elastic material soaked in conductive liquid. Or they can be made of zigzagged conductors. For example, U.S. Pat. No. 8,469,741 describes examples of stretchable connectors. 
       FIG. 9  illustrates on embodiment of a capacitive sensor of the present invention applied on a pre-stretched elastic substrate  58  for forming a stretchable ECVT sensor. Conductive spray, liquid, or ink is applied to pre-stretched layer for forming conductive elements of integrative sensor layers. Elastic substrate can also be soaked in conductive liquid to form conductive parts of any layer in an integrative sensor. This concept can also be applied to the application of the signal traces. 
     Further details regarding the theory and application of ECVT, sensor design, image reconstruction, and deployment of an ECVT system are found in the U.S. Patent Application Publication US 2010/0097374 (application Ser. No. 11/909,548), the relevant disclosures of which are included by reference thereto as if fully set forth herein. 
     As depicted in FIGS. 1A and 1B of the U.S. Patent Application Publication US 2010/0097374 referenced herein, an array of electrodes (e.g., capacitance plates) are arranged to form a capacitance sensor. In one application, this sensor may be placed around a pipe or vent to detect movement within the receptacle to provide imaging data. In a conventional ECVT system, the sensor is made up of capacitance plates where the capacitance is measure between a selected pair of plates. The principle of the basic measuring circuit involves connecting one plate (source electrode or sending electrode) of the sensor to a voltage (e.g., Vi) and another plate (detecting electrode or receiving electrode) to a capacitance measurement circuit. 
     In the preferred embodiment, the ECVT plates (i.e., electrodes) are comprised of an array of smaller capacitance segments that may be individually addressed. The shape of the capacitance segments can be made up various shapes where each plate can be activated with the same or different voltages, frequencies, or phase shifts. Segments of each electrode are preferably connected together in parallel, with voltage control applied independently to each segment. Segments of interest chosen to form sender or receiver plates can be activated by electronic switches that open or close to connect a particular segment in parallel with others chosen in same plate. For example, each segment may be activated with different amplitudes, phase shifts, or frequency to provide the desired sensitivity matrix distribution. In one embodiment, the array of selected capacitance segments can form many pairs of capacitance electrodes or plates without reducing overall plate size. The capacitance segments can also be joined in different configurations to provide different designs. 
     The sensor electronics of the present invention is designed to detect and measure the capacitance for the adaptive ECVT sensor of the present invention. For example, the difference in electrical energy stored in the adaptive ECVT sensor would be measured between an empty state and a state where an object is introduced into the imaging domain (e.g., between the electrodes). The change in overall energy of the system due to the introduction of a dielectric material in the imaging domain is used to calculate the change in capacitance related to the dielectric material. The change in capacitance can be calculated from the change in stored energy. Sensor electronics can also be designed by placing individual segment circuits in parallel yielding a summation of currents representing total capacitance between segments under interrogation. By individually addressing the capacitance segments of the electrodes of the present invention, electric field distribution inside the imaging domain can be controlled to provide the desired sensitivity matrix, focus the electric field, and increase overall resolution of reconstructed images. 
       FIG. 10  illustrates one embodiment of a modular and removable section  60  through which the integrative flexible sensor of the present invention can be placed on the outside or on the inside. Removable sections are introduced as means of placing integrative sensors on fixed structures.