Abstract:
A method of making a gaseous fluid data sensor assembly for acquiring data regarding the ambient environment adjacent a surface of an airframe with adjacent air speeds below 40 knots (or another aerodynamic structure with low speed gaseous fluid flow adjacent thereto) having a flexible substrate adhesively conforming to the airframe surface, a conformable cover layer and a relatively thin air data sensor for sensing air pressure between the substrate and the cover layer. The method includes forming a flexible printed circuit on a polymeric film, attaching thin air data sensor to the printed circuit and attaching a flexible substrate to form a conformal air data sensor. The method may also include attaching a data acquisition circuit to the printed circuit and may still further include providing an optical interconnection between the air data sensor and the data acquisition circuit.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a division of U.S. patent application Ser. No. 09/757,443, titled Conformal Fluid Data Sensor, filed Jan. 9, 2001 now U.S. Pat. No. 6,662,647. This application claims the benefit of and expressly incorporates by reference the entirety of U.S. patent application Ser. No. 09/757,443. 

   FIELD OF THE INVENTION 
   The present invention relates to the field of fluid data sensing, including airborne vehicle instrumentation, more particularly, to sensors for measuring one or more ambient air parameters adjacent an airflow structure such as an airfoil of an aeronautical structure or an airflow structure in a gaseous fluid flow apparatus such as (but not limited to) a forced air convection heating system. 
   BACKGROUND OF THE INVENTION 
   The aviation community has needed ambient air parameter measurements since the advent of instrumented flight. However, prior art sensor technology was typically not able to provide sufficient resolution in a utilitarian form and at an affordable cost for measurement of dynamic pressures associated with air speeds below 40 knots. For this reason, helicopters and V/STOL (vertical/short takeoff and landing) aircraft used active sensing technologies such as radar and laser optical systems with consequent increases in complexity and cost and attendant issues of reliability. In addition, prior art air data sensors characteristically had salient (projecting) profiles with respect to the structural members to which they were attached. The present invention overcomes such shortcomings of the prior art by providing an apparatus capable of measuring temperature and pressure with high resolution regardless of dynamic pressure, in harsh environments and at extreme temperatures while having a streamlined profile integrated with or conforming to the aerodynamic structure on which it is mounted. As used herein, airborne vehicle and aeronautical structure each mean any apparatus intended for passage through air, around which air may be conducted, or through which air is intended to pass, such as aircraft (whether fixed wing or rotary wing), spacecraft, self-powered and un-powered- projectiles (such as missiles and artillery projectiles), and gaseous fluid propulsion machinery (such as turbo-machinery, jet engines, rocket engines, and the like). 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view from below, forward and to the right of an AV-8B Harrier II aircraft useful in the practice of the present invention. 
       FIG. 2  is a view similar to that of  FIG. 1 , except from above, slightly aft and to the right to illustrate an example application of the present invention on the upper surface of the wing of the aircraft. 
       FIG. 3  is a simplified enlarged, fragmentary perspective view of a wing showing an application of the present invention. 
       FIG. 4  is a cross sectional view of the present invention as it would appear installed on a wing as shown in  FIGS. 2 and 3 . 
       FIG. 5  is a simplified block diagram of a system interconnection useful in the practice of the present invention. 
       FIG. 6  is a side view of an airframe structure such as a wing carrying an array of air data sensors of the present invention. 
       FIG. 7  is a simplified block diagram of the array of  FIG. 6  connected to a data reduction and processing block similar to that shown in  FIG. 5 . 
       FIG. 8  is a simplified perspective view resonant microbeam sensor useful in the practice of the present invention. 
       FIG. 9  is a side view of the sensor of  FIG. 8  in a relaxed state and in a deflected state. 
       FIG. 10  is a plot of the gain and phase response versus frequency of the sensor shown in  FIGS. 8 and 9 . 
       FIG. 11  is an enlarged view of an optical fiber interface useful in the practice of the present invention. 
       FIG. 12  is a section view of a cantilevered microbeam shown to illustrate a temperature sensor useful in the practice of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the Figures, and most particularly to  FIGS. 1 and 2 , an AV-8B Harrier V/STOL type aircraft  10 , as manufactured by The Boeing Company, is shown. Referring now also to  FIG. 3 , the present invention is shown as a relatively thin patch  12  or layer over part of a wing  14  of the aircraft  10 . It is to be understood that the present invention is useful in connection with various airborne vehicles, such as aircraft, rockets and missiles, and projectiles. Such vehicles may be manned or unmanned. The Harrier aircraft is used as an illustration or example application inasmuch as it operates at airspeeds below 40 knots during takeoff and landing. The streamlined aspect of the present invention is useful at higher airspeeds to reduce drag and turbulence. 
   Referring now most particularly to  FIG. 4 , a cross-section view of the air data sensor assembly  12  may be seen. In this view, the assembly  12  is bonded to a portion  16  of the wing  14  via an adhesive layer  18 . A pressure sensor  20  is located within the assembly  12 . A data acquisition circuit  22  and battery  24  are also preferably located within assembly  12 . The sensor  20 , circuit  22 , and battery  24  are mechanically and electrically interconnected via a flexible printed circuit layer  26 . Battery  24  is preferably a ½ mil thick polymer rechargeable lithium battery available from Ultralife Battery, Inc. having an address at 2000 Technology Parkway, Newark, N.Y. 14513 as part number: EL 27. 
   As shown in  FIG. 5  in a preferred embodiment of the present invention, an array or plurality  26  of sensors such as sensor  20  are co-located below a fluoropolymer layer  34  having a total thickness of 6–10 mil. Such sensors could be temperature and pressure sensors, or other air data sensors, as desired. It is to be understood that temperature is necessary to correct the air pressure readings. One example of an absolute pressure transducer is disclosed in U.S. Pat. No. 5,808,210. The sensors provide data via a network of optical fibers in an optical fiber layer  28  to an electronic data reduction and processing block  30  (see  FIGS. 5 and 7 ). The optical fiber layer  28  also can be used to provide power to the sensors  20 . The resonating integrated microstructure sensors may be optically energized by an embedded photodiode located in the microbeam structure. As incident light is coupled to the sensor via an optical fiber and a collimating graded index lens, the photodiode establishes an “etalon effect” causing the microbeam to be excited into a resonant mode of operation. The principle of operation for the optical sense and drive for such a sensor is presented in U.S. Pat. No. 5,808,210. 
   The optical fibers in layer  28  may be collected and terminated in standard optical fiber cable connectors. The optical fiber cable connectors are connected to a universal signal conditioner and remote input/output unit in block  30 . Block  30  converts the optical signals to air temperature and pressure signals, which are used by the Air Data Computation Block  32  to compute altitude and airspeed from the pressure and temperature according to well-known techniques. 
   The present invention may be used to provide a minimally invasive pressure measuring instrument for characterizing the boundary layer fluid flow on an aerodynamic surface such as an airplane wing or a inside turbo-machinery such as a turbine engine. By conforming closely to the contour of the surface to which it is attached, there will be minimal or even negligible effect on the fluid flow characteristics in the boundary layer being sensed. 
   In the practice of the present invention, the air data sensor (such as an air pressure sensor  20 ), a data communications network (in layer  28 ), data acquisition circuits  22  and mechanical support are all combined in a single ultra low profile conforming package  12 . The package or patch  12  includes a conformal layer  34  for environmental protection which includes a plurality of ports or apertures  36 . Layer  34  is preferably a fluoropolymer film such as that manufactured by the 3M Company of St. Paul, Minnesota under the product number 500 as aircraft paint replacement film in thicknesses of 3.5 to 10 mils. In addition to providing a protective cover, film  34  serves as a flexible layer for mounting the components of the system in a manner to be described infra. 
   Referring now again to  FIG. 4 , the instrument package  12  is preferably adhesively bonded to an airframe surface  38 . An adhesive layer  40 , preferably in the form of a pressure sensitive adhesive formed in a commercially available acrylate process to a thickness of about 1.5 mils initially has a backing or release layer (not shown) which is removed immediately prior to installation on the surface  38 . The air data sensor  20 , data acquisition circuit  22  and conformal rechargeable battery  24  are all preferably mounted on film  34  which eventually will form a conformable cover layer for the instrument package  12 . It is to be understood that one or more sensors  20  (which may include pressure sensors and temperature sensors), circuit  22 , and battery  24  are each connected electrically and mechanically to cover layer  34 . The conformable assembly  12  is preferably about 6–10 mils thick, with layer  34  acting as a base for a flexible printed circuit, providing electrical interconnects and mechanical relief support, in addition to being an environmental cover. The flexible printed circuit on layer  34  is preferably a 1 mil thick conductive polymer thick film  41 , deposited on the backside of layer  34  using stencil, screen printing, or ink-jet processing techniques. The electrical components and pressure sensor are preferably interconnected to the flexible printed circuit using conventional surface mounting techniques utilizing solder bumps  42 . Additional mechanical support may be provided by adding a layer  44  of about 0.5 mils thick epoxy coating compound to bond the sensors  20  and related components to layer the polymer film layer  41  and cover layer  34 . 
   The optical fiber layer  28  is a flexible substrate preferably formed of polyimide about 200 microns thick to provide optical interconnections between the sensors  20  and the data acquisition circuit  22  and to an optical fiber to waveguide coupler  46 , which has a strain relief  48  for a multimode fiber optic cable  50  connecting the instrument package  12  to high temperature data processor  32  (see  FIG. 5 ). Using fiber optic interconnects enhances electromagnetic interference immunity, by limiting effects to the local processing area only. It is to be understood that the data acquisition circuit  22  converts the optical signals to one or more (preferably digital) electrical signals for further processing. 
   Referring now to  FIGS. 8 ,  9  and  10 , certain aspects of one embodiment for the air data sensor  20  for sensing pressure may be seen. In  FIGS. 8 and 9  a resonant microbeam sensor assembly  60  are illustrated.  FIG. 8  is a partially cut away view of the sensor assembly  60  having a cantilever mounting arm  62  having a vacuum cavity enclosure  64 , a drive electrode  66 , a microbeam  68 , and a sense resistor  70 . As illustrated in  FIG. 9 , when the cantilever mounting arm  62  is deflected a distance  72  by an applied force  74 , the resonating microbeam  68  will have a resulting axial force increase, indicated by arrow  76 . 
     FIG. 10  shows the gain and phase response for the assembly  60 . As force  74  is applied, the resonant frequency and frequency at which the phase shift occurs will change, with the frequency increasing with an increase in applied force. The change in air pressure sensed at port  36  results in a change in force  74  applied to arm  62 , detected as a shift in the resonant frequency  78  along the abscissa or horizontal axis  80  of response characteristics  82  of the resonating microbeam  68 . 
   The instrument package  12  is fabricated by creating the flexible printed circuit  41  on cover layer or film  42 , after which components  20 ,  22 , and  24  are electrically connected via solder connections  42 . Epoxy layer or flexible potting compound  44  is applied to fill the spaces adjacent components  20 ,  22 , and  24 , and the optical fiber interconnect layer  28  with coupler  46  is attached to the components and epoxy layer. The coupler  46  and the pressure sensitive adhesive layer  40  may be attached to the flexible substrate layer  28  before or after assembly to the remainder of package  12 . 
   Referring now to  FIG. 11 , an enlarged view of an optical fiber interface or coupler  46  useful in the practice of the present invention may be seen. Optical fiber cable  50  is received in the strain relief  48  within a gradient index lens  54  which is optically coupled to an optical waveguide or etched cavity  56  in silicon chip subsystem  58 . Incident light is indicated by arrow  52 . 
   Referring now to  FIG. 12 , a simplified view of a microbeam temperature sensor  90  useful in the practice of the present invention may be seen. The measurement of air temperature to provide correction of air pressure readings may be accomplished by incorporating an additional resonating integrated microstructure sensor  90  into the air data sensor system. Resonant microbeam temperature sensing is known from U.S. Pat. No. 5,772,322. The structure for temperature sensor  90  includes a conforming metallization layer  92  of a precious metal such as gold or platinum applied to one side  94  of a bulk silicon cantilever beam  96  via a sputtering process or equivalent semiconductor method. The coefficients of thermal expansion of the two dissimilar layers causes the mechanical stiffness of the cantilever beam  96  to change according to the temperature to which the beam  96  is exposed. The air data and temperature sensor  90  is preferably packaged as an array of two active devices located adjacent to each other on a common silica substrate  98 . Beam  96  also preferably carries resonating integrated microstructure  100 . The active devices are interrogated by a further optical fiber (not shown) co-located with the air pressure optical fiber  50  at the end of the conformal sensor package  12 . Static compensation of resonant microbeam sensor technology is disclosed in U.S. Pat. No. 5,458,000. 
   In practice, the instrument package  12  of the present invention may be fabricated and stored in roll form with the release layer attached, until it is desired to install the package  12  on an airframe member, at which time the package and release layer is unrolled, the release layer removed, and the package or patch  12  applied by hand pressure to the surface adjacent which air data is to be taken. The cable  50  is preferably connected via conventional fiber optic cable connectors to data processing equipment (not shown) to provide air data for the boundary layer adjacent the surface to which patch  12  is attached. The overall thickness of instrument package  12  is about 10 mils or 0.010 inches thick. 
   This invention is not to be taken as limited to all of the details thereof as modifications and variations thereof may be made without departing from the spirit or scope of the invention. For example, the present invention may be used to advantage on an interior surface of a turbine engine or other structure requiring streamlined airflow. Furthermore, the present invention may be used in conventional gaseous fluid flow structures such as process equipment and space heating.