Abstract:
To monitor temperature variations over a surface, the present invention employs a grid of thermoelectric wires imbedded into a carrier or body patch. The thermoelectric wires form a thermopile with “hot” junctions distributed over the central section of the body patch, while the “cold” junctions” are positioned at the periphery of the patch. The patch may be a wound dressing application. The thermopile is connected to an amplifier and subsequently to a threshold detector. Crossing a threshold activates a radio transmitter that sends a signal to a remote receiver. The carrier (patch) is applied to a monitored surface (examples are machinery enclosures and patient skin or wound) in such a manner that the peripheral portion of the patch is outside of the monitored area.

Description:
FIELD OF INVENTION  
       [0001]     The present invention relates to sensors for continuous monitoring of temperature gradients being developed over an object&#39;s surface and specifically to medical sensors for monitoring development of cutaneous or subcutaneous thermogenic inflammations. It is based on U.S. Provisional Patent Application No. 60/615,388 filed on Oct. 4, 2004.  
       DESCRIPTION OF PRIOR ART  
       [0002]     Detection of temperature gradients in industrial applications may help to uncovers troublesome conditions that are manifested in increased heat production or heat conduction at a specific surface of a machinery or equipment. Examples include measuring hot spots in engines where excessive friction results in heat production. This condition should be detected before it may cause a damage.  
         [0003]     In medical applications, subcutaneous and even cutaneous injuries or inflammations may lead to pyrogenic processes. In other words, surface temperature increases with infection or injury. In veterinary medicine, detection of a horse leg temperature has been used for many years to identify internal injuries without a need to employ X-ray or other imaging devices. A common method in both industry and medicine has been use of infrared imaging equipment or just infrared thermometers. An example is a temperature scanner of U.S. Pat. No. 4,797,840 issued to Fraden. That and similar scanners are moved over the object of interest and remotely detect changes in intensity of infrared (IR) emission from the surface. The IR emission is stronger from a warmer surface and thus is an indicator of the surface temperature increase and subsequently of an increased heat production or conduction.  
         [0004]     When employed with stationary objects, the IR thermometers or imagers can be optically aimed at the area of interest and provide continuous monitoring. However, when the equipment is moving, or ambient conditions are not suitable for the IR monitoring, or, in medicine, when a continuous monitoring is required from a patient&#39;s body surface, this method is impractical. It would be highly desirable to provide a simple detector that could be attached to a surface of interest and on a continuous basis to provide a signal indicative of an increased heat production. Particularly in medicine, this may be used during thermal treatments of subcutaneous tissues, in wound dressings to detect onsets of inflammation and other applications where thermal gradient may develop between different areas on the skin.  
         [0005]     It is therefore an object of this invention to provide a contact sensor for detecting thermal gradient over a surface.  
         [0006]     It is another object of the invention to provide a thermal gradient sensor that substantially is not responsive to absolute temperature of the surface and responsive to a spatial thermal gradient.  
         [0007]     Another object of the invention is to provide a temperature gradient detector that is simple, inexpensive to produce, doesn&#39;t require calibration, has long shelf life and can be sterilized without degrading its&#39; performance.  
         [0008]     An another object of this invention is to provide a medical skin cover that detects heat production and transmits a signal to a remote monitor.  
       SUMMARY OF INVENTION  
       [0009]     The present invention employs a grid of thermoelectric wires imbedded into a carrier or body patch. The thermoelectric wires form a thermopile with “hot” junctions distributed over the central section of the body patch, while the “cold” junctions” are positioned at the periphery of the patch. The thermopile is connected to an amplifier and subsequently to a threshold detector. Crossing a threshold activates a radio transmitter that sends a signal to a remote receiver. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0010]      FIG. 1  is a grid sensor attached to an object  
         [0011]      FIG. 2  shows a step in preparation of a grid sensor  
         [0012]      FIG. 3  is a grid sensor with cut wires  
         [0013]      FIG. 4  shows a thermopile detector with a block diagram of the circuit  
         [0014]      FIG. 5  is a side view of the temperature gradient detecting patch  
         [0015]      FIG. 6  shows a patch with an indicator  
         [0016]      FIG. 7  is a schematic diagram of a patch with thermistors  
     
    
     DESCRIPTION OF PREFERRED EMBODIMENT  
       [0017]     Several methods of a contact detection of thermal gradients are known in art. Some are based on use of absolute temperature sensors such as thermistors or RTDs, some use the IR emission detectors. However, temperature detectors belonging to a class of relative sensors appear to be more suitable for the task. A relative sensor by definition responds to a temperature difference between different parts of the sensor. The most popular is a sensor based on a thermoelectric effect, better known as a thermocouple. The variance of a thermocouple is a thermopile which is a serially connected multiple thermocouple junctions. Thermopiles are better known by their designs used for the mid and far infrared detection (See J. Fraden,  Handbook of Modern Sensors . Springer Verlag. 3 rd  ed., 2004). A thermopile was originally invented by Joule for the purpose of increasing the output signal of a thermocouple. Each thermocouple consists of two dissimilar conductors which are joined together at two junctions—one is often called “hot” and the other is called “cold”. In a thermopile, all hot and all cold junctions are electrically connected. Separating spatially the hot and cold junctions may be used for detection of warm or cold spots within the respective areas. This works even if not all but as little as just one junction of a thermopile is exposed to a thermal anomaly.  
         [0018]      FIG. 1  shows object  1  whose temperature gradient is measured. It is expected that area  7  may develop a thermal anomaly—it may become either cooler or warmer than its surroundings. Carrier  2  supports a wire grid composed of two dissimilar wires (conductors). For example, one wire may be made of alloy Constantan (first wire  3 ) while the other is made of iron (second wire  4 ). Wires are welded or otherwise joined together at the intersection joints and cut at the appropriate spots to form a thermopile.  FIG. 2  illustrates how such a sensor can be fabricated. Two dissimilar wires  3  and  4  and attached (for example, with a glue) to carrier  2 . The wires are welded at intersection spots  6 . Then, as illustrated in  FIG. 3 , wires are cut in specific spots (in area  8 ) to form a continuous chain (a loop) of joints between terminals  5 . Note that terminals  5  are fabricated of the same type of a conductor (wires  3 ), for example, either constantan or iron. A continuous chain of junctions allows detection of temperature gradients between the first group of junctions  18  and  18 ′ (called “cold” junctions) and the second group  17  (called “hot” junctions).  
         [0019]     When at least one active junction in a chain is subjected to an elevated or reduced temperature with respect to other junctions, thermally induced voltage will appear between terminals  5  and will be amplified by electronic amplifier  20 . Unlike in a traditional thermopile where respectively all hot junctions and all cold junctions are thermally coupled with one another, the hot and cold junctions of this invention need to be separated from one another and spread over wider monitored areas  17  and  18  respectively. Within each such area, the combined thermoelectric voltage represents the average temperature of many junctions, thus the output signal from amplifier  20  represents an average thermal gradient between areas  18  plus 18′ and 17. The hot or cold junctions do not need to be subjected to the same respective temperatures as in traditional thermopiles. In fact, just one of the “hot” junctions need to be over the warm spot to produce a useful signal.  
         [0020]     The application of the device is illustrated in a medical wound dressing patch  40  shown in  FIG. 4 . It can be used for detecting an onset of inflammation at a patient skin or wound. Patch  40  is a carrier for the conductors and thermoelectric junctions. It has two distinct areas: peripheral area  16  and active area  15 . Peripheral area  16  is to be placed over a healthy skin of a patient, while active area  15  is to be placed over a wound or a suspected injured spot. Thus, the patch should have an appropriate size to cover the entire monitored area. The carrier patch may be a wound dressing assembly comprising several sterile layers of absorbing and insulating materials, possibly with some imbedded medications, such as silver ions which may help in fighting infection.  
         [0021]     The thermocouple wires are imbedded into the body of patch  40  in such a manner as to form most or all “cold” junctions  80  (white spots) over peripheral area  16  and to form all “hot” junctions  70  (black spots) over active area  15 . For the illustration, only five pairs of junctions are shown. However, there is no limitation on the number of pairs. For the monitoring, terminal  51  is electrically attached to a reference potential, for example, to chassis  19 , while terminal  52  is connected to an input of amplifier  20 . The thermopile sensor generates a rather small signal. It can be as little as 50 microvolts per degree C. of a gradient. Amplifier  20  should have a low offset voltage and a substantial voltage gain, typically over 100, so its output voltage can be applied to a threshold circuit  21 . When the amplified voltage exceeds a predetermined level due to a thermal gradient, threshold circuit  21  will generate indicating signal applied to transmitter  22 . The entire electronic circuit in the patch is designated by number  26 . The transmitter may be of any kind ranging from a simple wire connection to a radio transmitter. If it is a radio transmitter, it will generate an RF signal in its transmitting antenna  23 . The signal will be received by a remote receiving antenna  25  and processed by receiving unit  24 .  
         [0022]     A side view of patch  40  is shown in  FIG. 5 . Its bottom portion  27  has peripheral areas  16  and active area  15  where the thermopile conductors  29  are imbedded. At least a portion of surface  30  may contain adhesive for attaching the patch to the patient&#39;s skin. A dressing layer  28  placed over the thermopile should have a low thermal conductivity to reduce influence of the ambient temperature. Electronic circuit  26  is positioned outside and may contain a small battery (not sown). It should be noted that thermopile conductors do not need to touch a monitored surface and thus can be imbedded inside the carrier (patch). In addition, the conductors may be given a protective electrically insulating coating to more reliably separate them from the patient&#39;s tissue.  
         [0023]     In some applications, a remote transmission of the signal may not be required. Then, patch  32  ( FIG. 6 ) will contain an external indicator  33  that shows a signal indicating presence of a thermal anomaly. Indicator  33  may be of any kind, for example it may contain liquid crystals which either change in color or form symbols with are indicative of a temperature gradient. In the simplest form, electronic circuit  26  may contain just a couple of electrodes connected to a liquid crystal layer to cause the indication. Alternatively, patch  32  may contain a light emitting device which will flash when a thermal gradient is detected. All these indicators are of common and of a well known nature.  
         [0024]     Still, the same function to detect a thermal gradient inside a wound dressing patch may be achieved by use of the absolute temperature sensors, like thermistors as illustrated in  FIG. 7 . Thermistors  41  and  42  are serially connected, while  42  is positioned on a peripheral area  16  and  41  is on active area  15 . The thermistors are serially connected and supplied with reference voltage  43 . Since thermistors produce much larger signals than the thermopiles, an amplifier may not be needed. Comparator  21  is supplied with a threshold voltage  45  to produce an indicative signal  21  when a thermal disbalance occurs between thermistors  41  and  42 . The thermistors may be of a discrete or distributed nature. For example, each thermistor  41  or  42  may be a combination of several serially connected individual thermistors or each thermistor may be a screen printed layer having a relatively large area.  
         [0025]     While the above description contains several specifics, these specifics should not be construed as limitations on the scope of the invention, but merely as exemplifications of preferred embodiments thereof. Those skilled in the art will envision many other possible variations that are within the scope and spirit of the invention.