Abstract:
A wireless and batteryless pressure sensor apparatus comprises of a SAW sensor and an antenna mounted on a printed circuit board. Optionally, and RFID tag in used in combination with the SAW sensor. A sensor antenna and a RFID antenna can be located on the printed circuit board such that the antennas communicate electrically with the sensor and the RFID device. The sensor can be interrogated utilizing a radio frequency, which is used to excite a SAW crystal inside the sensor. The interrogation signal causes the SAW to resonate wherein a resonant frequency changes with the pressure and temperature that is applied to the sensor. An interrogator can receive a return (echo) signal representing a change in SAW sensor properties (e.g., diaphragm change). A printed circuit board can be mounted on a stainless steel port and overpackaged with standard processes for hermetically sealing the sensor, or sensor and RFID device with at least one antenna.

Description:
TECHNICAL FIELD 
       [0001]    Embodiments are generally related to sensors, and in particular pressure and temperature sensors and systems. Embodiments are also related to surface acoustic wave (SAW) devices and, more particularly, to a pressure and/or temperature sensor assembled as a self-contained batteryless, transmitterless system. Embodiments are additionally related to wireless and batteryless pressure and/or temperature sensors used in mobile and industrial applications. 
       BACKGROUND OF THE INVENTION 
       [0002]    Surface acoustic wave (SAW) devices used as sensors in measurement system are known, For example, a tire pressure monitoring system (TPMS) helps to avoid accidents by warning the driver about tire pressure problems. TPMS is a vehicle-embedded system detecting the tire pressure by analyzing the difference between the wheel speeds or by measurement of pressure and temperature. System like a direct TPMS system typically consists of one UHF receiver in the vehicle and four sensors mounted on the wheel rim or valve to sense data, to calibrate pressure versus temperature and to organize data transmission to the car body. 
         [0003]    Various other SAW sensor applications are known in the art. In particular, many different techniques have been proposed for sensing the temperature of a component in an industrial process or system. Pressure, as with use in tires and for delivering this information to the operator at a central location on the vehicle, can be used in industrial system to convey pressure differentials during processing operations (e.g., dairy, petroleum, medical, aeronautical, deep sea, etc., applications). 
         [0004]    The majority of prior art sensors are direct active systems, some utilizing a silicon micro-electro-mechanical system (MEMS) based sensor powered by a battery. Where several sensor are utilized throughout a target system, pressure and temperature information is transmitted by radio from each sensor locations (e.g., each of the wheels on a motor vehicle) to an electronic control unit (ECU) and displayed as either a number or a warning indicator. The problem associated with using such prior art systems in, for example, a TPMS environment is that the need to remove the tire for access to the batteries, and the need to rebalance the tires after battery replacement, together with the disposal of worn out batteries are the major shortcomings of direct sensing systems. Batteries inside tires add weight, have limited life and cannot be replaced. Furthermore, they require some sort of electrical connection between the sensor and any remote monitoring device. With a rotating wheel, this electrical connection requires special contacts, complicating the system, introducing added cost and reducing reliability. 
         [0005]    Conventional wireless systems are not durable and are expensive to design and produce. The sensors and transmitters must also be able to withstand the harsh environment, such as when used inside a vehicle tire that includes high temperatures, shock and vibration, and centrifugal forces from tire rotation. Although it has the advantage of wireless communication of the pressure to a remotely placed monitor, it is difficult to install and service, and requires special adaption of the wheel. 
         [0006]    One particular type of sensor, or condition-responsive device, which has recently become desirable for use in certain electronics systems, is an acoustic wave device, such as a surface acoustic wave (SAW) device. SAW devices have desirable properties for certain sensor applications since they are sensitive, use very little power, and can be operated at radio frequencies convenient for relaying information in a wireless fashion. SAW devices may include at least one resonator element made up of interdigitated electrodes deposited on a piezoelectric substrate. One of the problems with current SAW sensor designs, particularly those designs adapted to tire pressure and temperature sensing applications, is the inability of conventional SAW sensing systems to meet the rigorous environment within the environment itself. Such systems are inherently expensive, awkward, and often are not reliable in accurately sensing at least one of tire air pressure and temperature. 
         [0007]    A need therefore exists for an improved wireless and batteryless SAW sensor apparatus and packaging system, which for example can be integrated into a tire and interrogated wirelessly, and that the sensors are ultimately more efficient and sturdier than presently implemented sensors. Such an apparatus is described in greater detail herein. 
       BRIEF SUMMARY 
       [0008]    The following summary is provided to facilitate an understanding of some of the innovative features unique to the embodiments disclosed and is not intended to be a full description. A full appreciation of the various aspects of the embodiments can be gained by taking the entire specification, claims, drawings, and abstract as a whole. 
         [0009]    It is, therefore, one aspect of the present invention to provide for improved sensor methods and systems. 
         [0010]    It is another aspect of the present invention to provide for improved wireless, batteryless and transmitterless SAW pressure sensor with housing options. 
         [0011]    The aforementioned aspects and other objectives and advantages can now be achieved as described herein. A wireless and batteryless pressure sensor apparatus comprises of a SAW sensor and a sensor antenna. The SAW sensor alone in combination with a sensor antenna can adequately operate at short distances from an interrogator, i.e., less than 30 inches. SAW devices are resonator whose resonant frequency changes when strained. Working at radio frequencies, SAW sensing devices can be wirelessly excited with an interrogation pulse and a response (partial echo of the RF from the interrogator) from the SAW sensor can be measured to allow at least one of pressure and/or temperature to be calculated. 
         [0012]    Optionally, an RFID device can be mounted on a printed circuit board with the SAW sensor. An RFID device can be added to the SAW sensor for a total wireless solution with read distances greater than 30 inches. A sensor antenna and an RFID antenna can be located on the printed circuit board such that the antennas communicate electrically with the sensor and the RFID device. As with the SAW sensor only solutions, the sensor can be interrogated utilizing a radio frequency, which can be used to excite a SAW crystal inside the sensor. The interrogation signal causes the SAW to resonate wherein the resonant frequency changes with the pressure and temperature that can be applied to the sensor. The sensor&#39;s resonation frequency/signal is then transmitted by the RFID tag. 
         [0013]    The printed circuit board can be mounted on a stainless steel port and overpackaged with standard processes for hermetically sealing the sensor, the sensor combined with an RFID device. 
         [0014]    Antennas are capable of receiving a radio frequency signal. When the antenna receives the particular signal associated with the sensor, or sensor +RFID device, the measurement generated by the sensor can be directed to and transmitted by the sensor antenna. 
         [0015]    A SAW sensor can be designed in a button package which result in a full line of sensors for use with harsh media. The sensor can be used in a wide variety of pressure ranges, port styles, and termination types. 
         [0016]    A sensor as will be further described herein can be adapted for use as a pressure and/or temperature sensing product for broad use in industrial, commercial, petroleum and automotive markets (e.g., TPMS). In a TPMS application, the sensor housing can be integrated with the valve stem inside the tire, strapped on the rim inside the tire, or mounted to the rim outside the tire. Such a sensor can also be utilized for moving automotive parts such as tires, wheels, suspensions, rotary pumps, pistons, valves, and other pressure tanks or vessels. The SAW pressure sensor apparatus disclosed herein can therefore sense pressure and temperature for use in harsh media and is resistant to the effects of shock, vibration and hostile environments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The accompanying figures, in which like reference numerals refer to identical or functionally-similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate the embodiments and, together with the detailed description, serve to explain the embodiments disclosed herein. 
           [0018]      FIG. 1A  illustrates a top view of a SAW sensor button package, which can be implemented in accordance with a preferred embodiment; 
           [0019]      FIG. 1B  illustrates a side view of the SAW sensor button package, which can be implemented in accordance with a preferred embodiment; 
           [0020]      FIG. 2  illustrates a perspective view of the sensor antenna assembly mounted on a stainless steel port, in accordance with a preferred embodiment embodiment; 
           [0021]      FIG. 3  illustrates an exploded view of a sensor antenna assembly including a SAW sensor and RFID tag, which can be implemented in accordance with a alternative embodiment; 
           [0022]    FIG;  4  illustrates a perspective view of the sensor antenna assembly of  FIG. 3  mounted on a stainless steel port, in accordance with an alternative embodiment; 
           [0023]      FIG. 5  illustrates a perspective view of a packaged pressure sensor apparatus, in accordance with a preferred embodiment; 
           [0024]      FIG. 6  illustrates a perspective view of the pressure sensor apparatus with flush mount port, in accordance with an alternative embodiment; 
           [0025]      FIG. 7  illustrates a perspective view of a strap pressure sensor apparatus, in accordance with an alternative embodiment; and 
           [0026]      FIG. 8  illustrates an exploded view of a tire sensor system, which can be implemented in accordance with an alternative embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0027]    The particular values, configurations and applications discussed in these non-limiting examples can be varied and are cited merely to illustrate at least one embodiment and are not intended to limit the scope thereof. Note that in  FIGS. 1-8  identical parts or elements are generally indicated by identical reference numerals. 
         [0028]    Referring to  FIG. 1A  a top view of a SAW sensor button package  150  is illustrated, which can be implemented in accordance with a preferred embodiment. Pressure sensor package  150  generally includes a package cover  160  that includes a dimple  162  formed at the center of cover  160 . Pressure sensor package  150  can be implemented as a SAW pressure and/or temperature sensor. 
         [0029]    Referring to  FIG. 1B  a side view of the SAW sensor button package  150  is illustrated, which can be implemented in accordance with a preferred embodiment. Cover  160  thus generally includes a dimple  162  formed at the center of cover  160 . A quartz sense element  164  can be located below proximate to dimple  162  and between mounting pins  168  and  172 . Pressure sensor  150  can be implemented as a SAW pressure sensor that includes a quartz sense element  164  (e.g., a SAW chip), and a package base  166 . The sensor diaphragm  174  can be hermetically welded to the front end of the sensing element  164 . The pressure sensor  150  described herein can be utilized to measure pressure and temperature inside monitored systems, such as a vehicle tire (e.g., a passenger car tire or truck tire). When used as A TPMS, the pressure sensor  150  should preferably possess a low cross sectional area and thickness, and be generally lightweight in configuration to be compatible for application within truck tires and passenger car tires. 
         [0030]    Referring to  FIG. 2  an exploded view of a SAW sensor system  100  in accordance with a preferred embodiment of the invention. The sensor system  100  can include a substrate  112  associated with a flexible printed circuit board  110  that can be formed from a high-performance polyimide film material that is currently available and utilized in the electronics arts such as, for example, Kapton®. Kapton® is a registered trademark of the E. I. DuPont de Nemours and Company. The SAW sensor system as depicted includes a SAW sensor  150  and sensor antenna assembly  120  as illustrated, and which can be implemented in accordance with a preferred embodiment of the present invention. The SAW sensor  150  is combined with an antenna  120  on the flexible printed circuit board  110  and assembled in a stainless steel port package  310  for use in various applications. The sensor and antenna portions can then be overmolded to protect them from debris, as will be described in more detail below. 
         [0031]    Referring to  FIG. 3  an exploded view of a SAW sensor system  200  is illustrated, which can be implemented in accordance with an alternative embodiment of the present invention. Sensor package  150  described in  FIG. 2  can be modified for use with radio-frequency identification (RFID) device  130 . The sensor antenna assembly  100  can therefore function as a combined SAW sensor  150  and RFID sensor  130  that permits proximity-based communications between a reader and multiple transponders. Radio frequency identification device (RFID)  130  can be utilized to provide unique identification for a given tire, enabling tracking abilities for a tire. The sensor system  100  can include a substrate  112 , a flexible printed circuit board  110  that can be formed from a high-performance polyimide film material that is currently available and utilized in the electronics arts such as, Kapton®. The assembly  100  can also includes a surface acoustic wave (SAW) sensor  150  and sensor antenna  120  and an RFID  130  and RFID antenna  140 , which can be electronically connected. The SAW sensor antenna  120  and the RFID antenna  140  can be a shared antenna and enable communication or electrical connection between the SAW sensor package  150  and the RFID device  130 . The SAW sensor package  150  can be configured from one or more SAW sensing elements. Such a configuration therefore permits wireless interrogation of SAW sensor package  150  from an external wireless source, such as, for example, a wireless data transmitter and receiver device (e.g., interrogator), which is located external to the sensor assembly  100 . 
         [0032]    Antennas  120  and  140  can be printed on a polyimide substrate  112  such as, for example, Kapton®. Antennas  120  and  140  can therefore constitute flexible circuit antenna configurations and/or antenna ribbons. Antennas  120  and  140  can be printed onto a substrate  112  (or tape) formed from a polyimide film material such as, for example, Kapton®. It can be appreciated that other types of polyimide films can be utilized in place of Kapton® in accordance with alternative embodiments. The use of Kapton® is therefore discussed herein for general illustrative and edification purposes only and is not considered a limiting feature of the embodiments disclosed herein. 
         [0033]    As utilized herein with respect to the invention, the term “RFID device,” and so forth generally can refer to a device that includes a loop antenna of one or more turns coupled to an electronic device, wherein the electronic device both receives signals via the loop antenna and transmits signals via the loop antenna. Specific measurement parameters can also be extracted from certain SAW RFID configurations to produce a passive wireless sensor capable of conveying an identification code if required along with temperature, pressure or other similar measurements back to an interrogation reader. Such uniquely identifiable sensors can be well suited for the automotive industry where a single reader located in an automobile could communicate and monitor pressure, temperature and other useful parameters. 
         [0034]    The received signals with respect to the wireless article may include signals for controlling and/or operating the electronic device and/or for being stored in a memory associated therewith, whether embodied in the same or a separate electronic chip. The transmitted signals with respect to the wireless article may include information that is stored in the memory of or associated with the electronic device and may include information previously received and stored therein. 
         [0035]    Such device or other wireless article may be part of the object to be detected/identified, or may be made on a rigid or flexible substrate that is placed with and/or attached to such object, such as by adhesive or a strap or tie or the like, or by being packaged therewith, either permanently or releasable, as may be desired for a particular application. Where the object is metallic or otherwise electrically conductive the wireless article can be spaced away from the object a sufficient distance, e.g., a few millimeters, to allow operation of its antenna for communication of signals. 
         [0036]    Referring to  FIG. 4  a perspective view of the sensor antenna assembly  100  mounted on a stainless steel port  310  is illustrated, in accordance with an alternative embodiment. The sensor apparatus  300  includes the sensor antenna assembly  100  mounted on a stainless steel port  310 , such as, for example, a stainless steel 17-7 PH material. The sense element  164  of the pressure sensor package  150  is bonded to the stainless steel port  310  in order to measure diaphragm deformations. 
         [0037]    Referring to  FIG. 5  a perspective view of the sensor package assembly  400  with plastic cover  410  is illustrated, in accordance with an alternative embodiment. The sensor assembly  100  can be overpackaged or overmolded with a plastic cover  410  once placed on the stainless steel port  310  for hermetically sealing the sensor package  150 , and the RFID device  130  when included with the SAW sensor in the package  400 . The plastic cover  410  can next be stamped into a circular shape, and deep drawn into a cup configuration. The dimensions of cover  410  may vary, depending on the needs and use of such a device. This SAW sensor package  150  can also be overpackaged by welded into a fitting, threaded port, or automotive style housing and can be utilized in food and beverage, dairy, kidney dialysis, infusion pumps, air compressors, hydraulic controls, transportation, aerospace, agriculture, oil refinery, refrigeration and general industrial applications. 
         [0038]    The sensor apparatus  400  can be interrogated utilizing a radio frequency band of 434 MHz, which is the standard ISM (Industrial, Scientific and Medical) band. The cover  410  of the sensor assembly  100  acts as a diaphragm that applies a force to flex the SAW sensor  150 , which changes the SAW frequency proportional to the applied pressure. A portion of the interrogation signal can be used to excite the SAW sense element  164  inside the sensor  150  as shown in  FIG. 1B . 
         [0039]    After the sensor element  164  reaches resonation, a resonant frequency can be transmitted to the user through the SAW sensor antenna  120 . This resonant frequency changes with the pressure and temperature that is applied to the sensor apparatus  400 . A change in the output signal from the SAW sensor  150 , such as a change in frequency, phase and/or amplitude of the output signal, corresponds to changing characteristics in the propagation path of the SAW sensor apparatus  400 . In some SAW device embodiments, monitoring device frequency and any changes thereto provide sufficient information to determine parameters such as temperature and strain to which a SAW device is subjected. 
         [0040]    Referring to  FIG. 6  a perspective view of a pressure sensor apparatus  500  with flush mount port  510  is illustrated, in accordance with an alternative embodiment. The plastic cover  410  acts as the flush mount diaphragm. The dimple  162  translates external pressure to mechanical force against the sense element  164 . The flush mount port  510  is ideal for medical, beverage and food processing applications where stringent sanitation requirements are necessary. Note that flush mount port  510  can be configured from stainless steel. Referring to  FIG. 7  a perspective view of a strap sensor apparatus  600  is illustrated, in accordance with an alternative embodiment. The sensor antenna assembly  100  with top plastic cover  410  can be placed with and/or attached to a strap  610 . 
         [0041]    Referring to  FIG. 8  an exploded view a tire sensor system  700  is illustrated, which can be implemented in accordance with an alternative embodiment of the present invention. System  700  can be implemented in the context of a tire  710  associated with, for example, a drum-type brake. It can be appreciated, however, that system  700  can be implemented in the context of other brake systems, such as disk brakes, and that the drum-type brake configuration is presented herein for general illustrative and edification purposes only. Tire  710  generally includes a tire rim  720 . System  700  includes a brake drum  730 , which can interact with a backing plate  740 , which in turn surrounds a vehicle axle  750 . 
         [0042]    System  700  also incorporates sensor apparatus  400 ,  500  and  600 , which is described in greater detail herein with respect to  FIGS. 1-7 . System  700  can be utilized to monitor the temperature and pressure of tire  710  by locating sensor apparatus  400 ,  500  and  600  at a particular location within or on tire  710 . In general, sensor apparatus  400 ,  500  and  600  can be placed into tire  710  prior to tire molding thereof. Sensor apparatus  400 ,  500  and  600  can then be “cured into” tire  710 . Sensor apparatus  400 ,  500  and  600  therefore measures air pressure and temperature inside tire  710 . A wireless signal (e.g., radio frequency, low frequency, etc.) can be transmitted to sensor apparatus  400 ,  500  and  600 . Pressure and air temperature data can then be transmitted back for further collection and evaluation. 
         [0043]    The sensor antenna assembly  100 / 200  and the stainless steel port  310  can be utilized as a wireless and batteryless pressure and temperature sensor that can be used in a wide variety of applications. The sensor apparatus  400  utilizes surface acoustic wave (SAW) technology for the sensor technology and, when used, a passive radio frequency identification (RFID) technology for enhanced signal transmission. The key applications may be in Tire Pressure Monitoring Systems (TPMS)  700  where the sensor apparatus  400  can be integrated with the valve stem inside the tire  710 , strapped on the rim  720  inside the tire  710  utilizing sensor apparatus  600 , and mounted to the rim  720  outside the tire  710  utilizing sensor apparatus  500 . 
         [0044]    Each of the two antennas  120  and  140  can be wired to a respective BNC connector (not shown) that protrudes from the top of each antenna block. Note that the term “BNC Connector” as utilized herein generally refers to a type of connector utilized with coaxial cables. The basic BNC connector is a male type mounted at each end of a cable. This connector has a center pin connected to the center cable conductor and a metal tube connected to the outer cable shield. A rotating ring outside the tube locks the cable to any female connector. 
         [0045]    The sensor apparatus such as apparatus  400 ,  500  and  600  is ideal for equipment that has moving parts such as tires, wheels, suspensions, rotary pumps, pistons, valves, and other pressure tanks or vessels. These sensors can be ideal for mobile, portable, or un-stationary equipment. The sensor apparatus can be interrogated with low power RF signals and can be ideal for applications that require intrinsically safe and explosion proof components. The sensor apparatus  400 ,  500  and  600  is resistant to the effects of shock, vibration and hostile environments. A wide variety of pressure ranges, port styles, and termination types can be utilized with respect to the sensor antenna assembly  100 . The wireless technology allows the measurement of pressure and temperature from inside the tire  710  to help truck fleet managers accurately monitor tire pressure for improved fuel efficiency and extended tire life. 
         [0046]    The invention described herein can be implemented, in accordance with one possible embodiment, as a product in a component in a wireless and batteryless tire pressure monitoring system (TPMS). Although described in detail as a possible application, TPMS should not be viewed as a limitation over the present invention as it will be appreciated that many other industrial and commercial applications are possible for the wireless, batteryless sensor described herein. Such an exemplary embodiment as TPMS can be configured as a small-size device, which is also lightweight and based on batteryless operation. The pressure sensor described herein does not consume power when implemented in the context of a TPMS operation. Thus, the present invention can be embodied in a practical and low cost design solution. Such a design can be mass-produced for automotive, heavy-duty vehicles, and commercial markets. 
         [0047]    It will, therefore, be appreciated that variations of the above-disclosed and other features and functions, or alternatives 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.