Abstract:
A combination thermal and vibration sensor for use in sleep monitoring equipment comprises a thin film of plastic exhibiting both pyroelectric and piezoelectric properties. By providing a layer of foam material covering only a predetermined portion of one major surface of the film layer, it is found that the thermal mass of the sensor is changed to the point where the pyroelectric signal can be more readily isolated from the piezoelectric signal using conventional signal processing techniques. Because the layer of foam material is not present on a remaining portion of the piezo/pyro film, the signal output due to the film&#39;s piezoelectric properties is not unduly dampened and attenuated.

Description:
BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     This invention relates generally to electronic sensors for monitoring both temperature change and sound using a single transducer, and more particularly to the construction of such a sensor that more readily allows the temperature signal to be separated from the sound signal using conventional signal processing techniques, e.g., filtering, and which provides a more robust output due to sound vibrations. 
     II. Discussion of the Prior Art 
     In the U.S. Pat. No. 5,311,875, which is hereby incorporated by reference, there is described a system for electronically monitoring breathing patterns and may find use as a sleep sensor in a hospital sleep lab. The system described therein utilizes a plastic film exhibiting both pyroelectric and piezoelectric properties, such as a polyvinylidene fluoride (PVDF) film. The film transducer has a conductive electrode on opposed major surfaces thereof and electrical wires connect the electrodes to an electronics module that is designed to separate the transducer output into two separate channels, one being for temperature and the other being for sound or vibration. 
     As is explained in copending application Ser. No. 09/416,660, filed Oct. 12, 1999, assigned to the assignee of the present invention and which application is hereby incorporated by reference, testing performed by the assignee of the present invention has shown that the signal proportional to temperature variation greatly exceeds that due to noise or vibration by a factor of about 50:1. The temperature-related signal also and is rich in frequency components in the 20 Hz to 50 Hz range during normal exhalation. These properties of earlier sensor designs have caused a difficulty in preventing the thermal component of the transducer from crossing over into the sound channel, often leading to the occurrence of false positives when both sound signals and temperature signals were being simultaneously monitored. The aforereferenced &#39;660 application describes a solution to the problem. By increasing the thermal mass of the sensor, the effective rise-time of the thermal signal can be greatly reduced, while not attenuating the signal amplitude occasioned by sound/vibration of the sensor below a detectable level. 
     As is further described in the aforereferenced &#39;660 application, the thermal mass of the PVDF transducer can be tailored by affixing a layer of plastic foam material onto the transducer film. The plastic foam material is made coextensive with the area of the PVDF film, i.e., it covered the entire surface of the PVDF film. 
     While the invention described in the aforereferenced &#39;660 application resulted in a significant improvement in the performance of the sensor in terms of being able to tailor the rise-time of the thermal signal in relation to the thickness of the foam plastic material applied, it did result in some loss of sensitivity of the transducer to sound/vibration signals. 
     It is, therefore, a principal object of the present invention to provide an improved pyro/piezo PVDF film transducer having a slower rise-time of the thermal signal to the point where it no longer overlaps with the predominant frequency components of the piezo or sound signal, but where the vibration/sound signal is not unduly attenuated. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, control over the thermal mass of the transducer described in the aforereferenced Stasz &#39;875 patent is achieved by affixing a layer of plastic foam material unto the transducer film on at least one surface thereof but where the foam layer need not be coextensive with the PVDF film layer, thus leaving a portion thereof undamped by the plastic foam material. Thus, in accordance with the preferred embodiment of the present invention, the combination thermal and vibratory sensor comprises a plastic film exhibiting pyroelectric and piezoelectric properties and has a predetermined shape configuration with first and second major surfaces. A thin layer of conductive material is disposed on and is coextensive with the first and second major surfaces. A pair of elongated conductors are individually attached at one end thereof to the conductive material on the first and second major surfaces. A layer of a material for changing the thermal mass of the sensor is adhered to the layer of conductive material on at least one of the first and second major surfaces so as to overlay only a predetermined portion of the one major surface while leaving the remainder of that one major surface free of the layer of material. In use as a sleep sensor, the transducer of the present invention may be adhered to the upper lip of a person such that inspiratory and expiratory air flow, via the nasal passages, impinges primarily on the portion of the sensor to which the plastic foam material is adhered while the remainder portion of the transducer that is free of foam material either extends beyond the lips and over the mouth or engages the base of the nasal septum. Noise and vibration which may be caused by a person&#39;s snoring remains undamped, allowing the film to output a more robust piezoelectric signal. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The foregoing features, objects and advantages of the invention will become apparent to those skilled in the art from the following detailed description of a preferred embodiment, especially when considered in conjunction with the accompanying drawings in which: 
     FIG. 1 is a front plan view of a pyro/piezo sensor constructed in accordance with the present invention; 
     FIG. 2 is a side elevation view of the sensor of FIG. 1; 
     FIG. 3 is a front plan view of a pyro/piezo sensor constructed in accordance with an alternative embodiment of the invention; 
     FIG. 4 is a side elevation view of the sensor of FIG. 3; 
     FIG. 5 is a plan view of a further alternative embodiment of the invention; and 
     FIG. 6 is a cross-sectional view taken along line  6 — 6  in FIG.  5 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, there is indicated generally by numeral  10  a transducer element especially designed for use in sleep pattern analysis equipment and constructed in accordance with a first embodiment of the present invention. It comprises a laminated construction having as its active element a layer of plastic film  12  which exhibits both pyroelectric and piezoelectric properties. A polyvinylidine fluoride (PVDF) film, whose thickness may range from about 0.5 to about5 mils is preferred. The film  12  and the layers laminated therewith, and yet to be described in detail, are cut so as to provide a preferred shape like that illustrated in the plan view of FIG.  1 . As is shown, the sensor or transducer  10  includes a generally rectangular midsection  14  with integrally formed, obliquely extending rounded arms  16  and  18  that project from a first end edge of the rectangular midsection  14  along with integrally formed, laterally extending rounded legs  20  and  22  projecting from a second end edge of the rectangular midsection  14 . 
     Examination of the cross-sectional view of FIG. 2 shows that the centrally disposed PVDF film layer  12  has its opposed major surfaces coated with layers  24  and  26 , each being a conductive material sufficiently thin that it can readily flex without cracking. Layers  24  and  26  may comprise carbon coatings on the PVDF film, but conductive materials other than carbon may also be utilized. The layers  24  and  26  constitute electrodes attached to the PVDF film  12 . 
     An elongated flexible conductor  28  electrically connects to the layer  26  and includes a connector  30  at its proximal end that is adapted to be attached to a signal receiver module (not shown). In a similar fashion, an elongated flexible conductor  32  connects to the conductive layer  24  on the opposite side of the film layer  12  and it, too, has a connector  34  adapted to attach to the receiver module. 
     Adhesively bonded onto the conductive layer  26  is a layer of plastic foam material  36  which, in accordance with the aforereferenced &#39;666 application, functions to change the thermal mass of the sensor  10 . However, unlike the sensor disclosed in the &#39;666 application, in accordance with the present invention, the plastic foam layer  36  is not coextensive with the film layer  12 , but instead, covers only a predetermined portion of the transducer film material. More particularly, and as best seen in FIG. 1, the layer of plastic foam  36  only covers the generally rectangular midsection  14  and the obliquely projecting rounded arms  16  and  18 , leaving the laterally extending rounded legs  20  and  22  uncovered. 
     A further layer of plastic foam material  38  is adhesively secured to the conductive layer  24  and it has the same shape configuration as the foam layer  36 . It can, therefore, be seen that only a predetermined portion of the major surfaces of the metallized film layer  12  has the foam layers  36  and  38  affixed thereto with the remainder of the film layer being free of the foam layer. 
     Without limitation, the overall length dimension of the sensor for use on adults may be about 1.25 inch including the obliquely extending rounded arms and the laterally extending rounded leg portions. The width of the leg portion may be about 1.4 inch with the radius of the curved ends being about 0.25 inch. The generally rectangular midsection may measure 0.4 inch in height and 0.7 inch in width. The overall thickness of the sensor will be about 0.10 inch where the foam layers are present but only about 0.005 inch in the remaining portion where only the film thickness is involved. 
     The sensor  10  is especially designed so as to be attached to the upper lip of a person during the course of a respiratory analysis, such as in a sleep lab. As such, the film layer  36  may be provided with a layer of skin compatible, pressure sensitive adhesive  40  which, prior to use, may be shielded from contamination by a layer  42  of release paper. The release paper  42  is, of course, stripped from the transducer at the time of application to expose the adhesive layer  40 . 
     In use, the sensor  10  is attached to the patient&#39;s upper lip with the rounded arms  16  and  18  directly below the nasal openings and the dimensions are such that the laterally extending leg portions  20  and  22  will extend over the edge of the upper lip so as to overlay the mouth opening. The portion of the sensor overlaying the mouth opening, being void of plastic foam material is more directly responsive to sound vibrations occasioned by episodes of snoring and, therefore, capable of producing a more robust piezoelectric response than when the entire transducer is foam covered. 
     The embodiments of FIGS. 3 and 4 show an adaptation of the present invention to a breathing sensor for newborns and small infants. It is indicated generally by numeral  50  and in the plan view is generally rectangular, but having rounded comers. Without limitation, the height dimension may be approximately 0.55 inch and the length dimension 0.515 inch. The rounded comers may have a radius of ⅛ inch. 
     In the cross-sectional view of FIG. 4, the PVDF film layer  52  has conductive electrodes  54  and  56  on opposed major surfaces thereof and they are coextensive with those major surfaces. First and second elongated conductive leads  58  and  60  are individually connected at a first end thereof to the conductive layers  54  and  56  and adhesively bonded to the conductive layers are layers  62  and  64  capable of changing (increasing) the thermal mass of the sensor. The layers  62  and  64  are preferably not coextensive with the film layer  52 , but instead, only overlay a predetermined portion of the PVDF film layer, leaving the remainder free of such material. A workable sensor can be realized, however, by making only foam layer  62  coextensive with the film layer. Again, it is intended that the transducer illustrated in FIG. 3 be adhesively affixed to the newborn&#39;s upper lip and, in this regard, a layer of non-irritating, skin compatible, medical-grade adhesive  72  is applied to the exposed surface of foam layer  64  and that adhesive layer is shielded by a release paper  76  until just prior to its application to the infant. 
     While in the embodiments illustrated, a layer of foam plastic material is disposed on each of the major surfaces of the PVDF film layers, the invention can also be implemented with a single layer of plastic foam, such as foam layer  36  in the embodiment of FIG.  2  and plastic foam layer  62  in the embodiment of FIG.  4 . In such an arrangement, the adhesive for adhering the transducer to the subject&#39;s upper lip would be applied directly to one major surface of the conductive layer, i.e., the major surface not having the foam layer adhered to it. 
     When the transducer patch of FIG. 3 is affixed to an infant or newborn, inspiratory and expiratory gases passing through the infant&#39;s nasal orifices will impinge upon the portion of the transducer  50  carrying the plastic foam layer  62  whereas the lower portion  70  that is free of any plastic foam material overlaying the infant&#39;s mouth will sense the air being inhaled and exhaled through the mouth. During inspiratory flow, the affected portion of the transducer will have relatively cool ambient temperature air pass over it while during expiratory flow, the air impinging on the transducer will be higher—about body temperature. Thus, with normal breathing, the output signal from the transducer should vary rhythmically. However, if coughing, choking or noises attributed to partially occluded air passages should occur, the transducer will output a signal based upon its piezoelectric properties. Because the portion  70  of the transducer  50  does not carry the foam material used to modify the thermal mass, the transducer is capable of producing a more robust signal related to sound and vibration. 
     FIGS. 5 and 6 illustrate yet another embodiment of the pyro/piezo sensor of the present invention which is designed to enhance its sound response. The device is similar in shape to the embodiment or FIG. 1, but instead of leaving the laterally extending legs  20  and  22  devoid of plastic foam, the plastic foam layers  36  and  38  extend over the laterally extending legs. The PVDF film layer  12  is cut so to provide a generally rectangular tab  80  that extends outward between the obliquely extending arms  16  and  18  and which is folded back upon itself to form a loop  82  as best seen in the cross-sectional view of FIG. 6. A layer of pressure-sensitive, skin-compatible adhesive  40  is again adhered to the foam layer  36  to facilitate attachment of the sensor to an upper lip of a person. As with the embodiment of FIG. 1, the obliquely extending arms  16  and  18  will be positioned directly in line with the user&#39;s nasal openings and the loop  82  is designed to press against the base of the nasal septum. When thus-placed, the laterally extending legs  20  and  22  overhang the upper lip and subtend the wearer&#39;s mouth and the loop is in a dead zone relative to inspiratory and expiratory air flow. 
     The positioning of the loop  82  and the fact that it is devoid of the foam material  36  results in an enhanced piezoelectric output from the sensor occasioned by the wearer&#39;s snoring episodes because it is more intimately in contact with the nasal septum and/or with the skin under the nasal septum where snoring vibrations are more intense. 
     This invention has been described herein in considerable detail in order to comply with the patent statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by specifically different equipment and devices, and that various modifications, both as to the equipment and operating procedures, can be accomplished without departing from the scope of the invention itself