MULTIFUNCTIONAL SENSOR

Abstract: Multiple sensors (16, 36) are formed over a common substrate (12). Each sensor is adapted to respond to different stimulants by providing films that are sensitive to the stimulant of interest. The resulting array of sensors may thus be used to provide multifunctional response so a variety of stimulants may be sensed with a single sensor array.

Description: -1- TITLE OF THE INVENTION MULTIFUNCTIONAL SENSOR CROSS REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. provisional patent application No. 60/081,556, filed April 13, 1998, entitled Multi-Functional Sensor. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT Not Applicable BACKGROUND OF THE INVENTION Electronic sensors are known which are used in a variety of applications to detect the presence of a particular stimulant. Such sensors exhibit electrical characteristics, such as resistance, capacitance, and inductance, which vary with the level of stimulant present. Typically an electrical drive signal is applied to the sensor and a control circuit used to measure the particular electrical characteristic which is affected by the stimulant to which this sensor is directed. This electrical drive signal produces a response signal which is indicative of the stimulant present, and the control circuit can then compute a stimulant level based upon the magnitude of the response signal. Typical sensors, however, have a single sensing element which is directed towards a single target -2- stimulant, and are connected to a dedicated control circuit which has predetermined logic for computing the stimulant level based on the response signal magnitude. In order to sense more than one stimulant, it is therefore necessary to orient multiple sensors directed to the different target stimulants, each connected to a dedicated control circuit having the proper logic, within the sensing environment. Further, the need for multiple sensors can hinder simultaneous sensing of more than one stimulant at a single precise location. Moreover, the use of dedicated control circuits, each having predetermined logic directed to a particular stimulant and response signal, adds to the complexity and cost of a system. It would be beneficial, therefore, to develop a multifunctional sensor which includes a plurality of sensing elements, each directed to a particular target stimulant, in which each sensing element delivers a consistent response signal indicative of the stimulant such that the stimulant level can be computed by a common control circuit. BRIEF SUMMARY OF THE INVENTION In accordance with the present invention, a multifunctional sensor is provided which includes a plurality of sensing elements, each of which is constructed to provide a similar response signal, indicative of a particular stimulant, such that the level of the target stimulant can be computed by a common control circuit. Multiple sensing elements, such as conductive sensing -3- films, are disposed on a substrate. Such films are formed such that the electrical resistance or other electrical parameter varies proportionally with the level of a particular target stimulant to which the sensing element is directed. An electrical drive signal is provided to electrical terminals connected to the conductive sensing films. A response signal is provided by each sensing film which is proportional to the stimulant magnitude, and these response signals are received by a signal control circuit. The response signals from the sensing films have similar characteristic curves and can be readily processed by the single control circuit. Preferably the multiple sensors are supported on a common substrate and are connected via shared electrical terminals. Alternatively, the sensing elements may be supported on respective substrates. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING Fig. 1 is a plan view of a first embodiment of the multifunctional sensor as defined by the present invention; Fig. la is a block diagram showing a control circuit coupled to the sensor of Fig. 1; Fig. 2 is a perspective view of the sensor of Fig. 1; Fig. 3 is a side elevation view of the sensor of Fig. 1; Fig. 4a shows a graph of a response signal from a humidity sensing element; Fig. 4b shows a graph of a response signal from a pressure sensing element; -4 - Fig. 4c shows a graph of a response signal from a temperature sensing element; Fig. 5 is a plan view of a second embodiment of the multifunctional sensor as defined by the present invention; Fig. 6 is a side view of the sensor of Fig. 5; and Figs. 7a-c show different mounting structure arrangements of the multifunctional sensor as defined by the present invention. DETAILED DESCRIPTION OF THE INVENTION A first embodiment of a multifunctional sensor as defined herein is shown in Fig. 1. Sensor 10 includes a substrate 12 with electrically conductive traces 14a, 14b, and 14c applied thereto. Individual sensing elements are provided by sensing films 16a and 16b which are applied to the substrate 12 such that each film 16a and 16b overlaps two traces 14, as shown by dotted lines 18. Center trace 14b is common to both films 16a and 16b, which are separated by gap 20 to minimize noise and cross-sensitivity between the two films lβa and 16b. An electrical drive signal is applied to electrodes 22a, 22b, and 22c by which films are energized to generate a response signal, across the same terminals 22a, 22b, and 22c. A control circuit 15 (Fig. la) provides the drive signal and receives and processes the response signals to produce an output indicative of the sensed conditions. Referring again to Fig. 1, terminals 22a and 22b are connected to traces 14a and 14b for receiving a response signal from sensing film 16a, and terminals 22b and 22c are connected to traces 14b -5- and 14c for receiving a response signal from sensing film 16b. Sensing films, 16 generally, are selected for electrical properties which vary in the presence of a particular target stimulant which is to be detected. In the first embodiment, films are selected having a resistance that increases in proportion to the target stimulant level, however other electrical properties, such as capacitance or inductance, can be used. Different films are selected depending on the desired target stimulant, however, the response signal, having a magnitude indicative of the target stimulant level, is substantially similar throughout the desired sensing range regardless of the target stimulant. Referring to Fig. 2, traces 14 and films 16 disposed on both sides of the substrate 12 allows four sensing elements to be placed on a single substrate. The number of sensing elements can be further increased by adding additional traces and films. As shown in Figs 2 and 3, a total of four sensors 16a-16d are shown, placed on both sides of a single substrate and driven by six electrodes 22a-22f, adapted to be connected to a six-pin socket on a circuit board. The side, or elevation, view in Fig. 3 shows sensor films 16a-16d on opposed sides of the substrate 12. Sensor pairs 16a, 16b, and 16c, 16d are diagonally offset, as indicated in Fig. 2, although this diagonal offset is not seen in the elevation view. Since the sensing films exhibit similar response characteristics, these films can share electrical terminals -6- to simplify the electrical interconnection and to permit the sharing of a common control circuit. Referring to Figs. 4a-4c, response signals for typical sensor films are shown. Such films are typically conductive polymers such as polytetrafluoroethylene (PTFE) for sensing humidity, polypropylene for sensing temperature, and polyvinylidene fluoride (PVDF) for sensing pressure. These curves reflect the common response characteristic of the different sensing films. As shown these curves show a resistance change from about lOKohms to about lOOOKohms. Humidity, temperature, and pressure sensing films are shown as examples, however other films can be used which are made responsive to other stimulants by specific doping techniques. For example, in alternative embodiments, films for detection of stimuli such as carbon dioxide, carbon monoxide, methane, formaldehyde, and hydrocarbon can be employed which exhibit similar response characteristics to the particular stimuli. Specifically, Fig. 4a shows the response signal of two sensing films, H-I and H-II, directed to sensing relative humidity, over a stimulant level from a relative humidity of about 0% to 100%. Fig. 4b shows the response signal of sensing films P-I and P-II, directed to sensing pressure, across a stimulant level from about 10 A 6 - 10 A 7 Pa. Fig. 4c shows the response signal of two sensing films T-I and T-II, directed to sensing temperature, across a stimulant range from about 0 degrees Celsius to 100 degrees Celsius. In each case the response signal ranges from about lOKohms to lOOOKohms across the target stimulant range. -7- A second embodiment is shown in Fig. 5, in which four sensors 36a-36d are oriented on the same side of substrate 12. In this embodiment it is necessary that electrodes 42a-42f extend through vias 30 in the substrate 12, and that traces 34a-34f extend only about halfway across the substrate, to allow electrical separation such that each film 36a-36d is disposed across two traces. Such an embodiment provides for flush surface mounting to a printed circuit board or other surface. Further, films 16a-16d can be directly deposited onto a surface such as a circuit board without an intermediate substrate, if such a surface is receptive to film application. A side view of the sensor in Fig. 5 is shown in Fig. 6, illustrating the electrodes 42a-42c extending through vias 30 and connecting to traces 42a-42c which contact sensing films 36a and 36c. Electrodes 42d-42f, traces 34d-34f, and films 36b and 36d are obscured in Fig. 6. The sensor films can be applied to the substrate surface by various methods such as dip coat, brush coat, spray coat, screen print, or pad print, or by other methods known to those skilled in the art. Films are selected for exhibiting electrical properties which exhibit a similar response signal curve over the desired sensing range, to allow for common control circuit logic to compute the stimulant level of the multiple sensing elements on a particular sensor. As indicated above, such sensor films are typically mounted on a substrate, or alternatively applied directly to a surface capable of accepting such a film, such as a printed circuit board. Referring to Figs. 7a-7c, the substrate mounted sensors can be enclosed in a housing to suit a particular application. A vertical mount case 60, as shown in Fig. 7a, includes apertures 62 on both sides to permit exposure of the stimulant to the enclosed sensing films. Perpendicular mounting tabs 64 facilitate attachment to a support surface. Electrodes or terminals 66 extend downward for attachment to a circuit board or other connection to a control circuit. An alternate housing 68 is shown in Fig. 7b for flush, rather than perpendicular, mounting to a surface. Apertures 62 are provided on the top surface to permit exposure of the sensing films to the environment being detected. Electrodes 66 extend downward from the housing. A probe housing is shown in Fig. 7c, and includes a rigid, elongated tube 70 with a cutaway portion or window 72 to allow stimulants to reach the sensor substrate 12 and sensor films 74. Wires 78 extend through the interior of the tube and outwardly of the tube for connection of the electrodes 76 to a control circuit. As other extensions and modifications to the multifunctional sensor disclosed herein may be apparent to those skilled in the art, the present invention is not intended to be limited except by the following claims.

Claims: • 9- CLAIMS What is claimed is 1. A multifunctional sensor comprising: a plurality of sensing elements each responsive to a respective target stimulant and each having a similar response characteristic- each of the sensing elements providing a response signal representative of the magnitude of the respective target stimulant; a plurality of electrical terminals connected to the plurality of sensing elements; and a control circuit connected to the plurality of electrical terminals and operative to provide a drive signal to the plurality of sensing elements and to receive a response signal from each of the sensing elements. 2. The multifunctional sensor of claim 1 further comprising: a substrate; and wherein said plurality of sensing elements are formed on said substrate. 3. The multifunctional sensor of claim 2 wherein the sensing elements are planar sensing elements disposed on said substrate and wherein the plurality of electrical terminals are circuit traces disposed on the substrate in electrical contact with the planar sensing elements. ■ 10 - 4. The multifunctional sensor of claim 3 wherein at least one of said electrical traces is in electrical contact with a plurality of said planar sensing elements. 5. The multifunctional sensor of claim 1 wherein said electrical terminals are connected to electrodes extending through apertures in said substrate. 6. The multifunctional sensor of claim 1 wherein said plurality of sensing elements each comprise a conductive film. 7. The multifunctional sensor of claim 6 wherein said response signal is indicative of the resistance of said conductive film. 8. The multifunctional sensor of claim 7 wherein said resistance varies in accordance with the magnitude of said target stimulant. 9. The multifunctional sensor of claim 1 wherein said response signal is substantially similar for each of said plurality of sensing elements. 10. The multifunctional sensor of claim 9 wherein said response signal from each of said plurality of sensing elements has a similar magnitude over a predetermined response range . ■ 11- 11. The multifunctional sensor of claim 1 wherein said target stimulant is selected from the group consisting of UV radiation, IR radiation, carbon dioxide, carbon monoxide, methane, formaldehyde, and hydrocarbon. 12. A multifunctional sensor for simultaneously detecting the presence of a plurality of target stimulants comprising: a plurality of sensing films disposed on a planar surface, wherein said sensing films are each operative to receive an electrical signal and provide a response signal indicative of a respective target stimulant; a plurality of parallel traces disposed on said planar surface and in electrical contact with said plurality of sensing films; and a control circuit connected to said traces and adapted to provide said electrical signal and receive said response signal, wherein said control circuit is operable to compute a stimulant level in proportion to the magnitude of said response signals. 13. The multifunctional sensor of claim 12 wherein each of said plurality of sensing films is in electrical communication with at least two of said parallel traces . 14. The multifunctional sensor of claim 13 wherein at least one of said parallel traces is in electrical communication with a plurality of said sensing films.

Inventors: CROTZER DAVID R, CROTZER, DAVID, R.
Applicants: IRDAM COMPANY
Application year: 1999
Main classification: G01R27
IPC codes: G01N27