Patent Application
20080275356
I. Field of the Invention
This invention relates generally to a respiratory sensing belt which incorporates a piezoelectric film as its sensing element, and more particularly to a uniquely respiratory sensing belt design in which a piezoelectric film is subjected primarily to a stretching stress to generate data.
II. Discussion of the Prior Art
For many years, devices have been sought and developed to help monitor breathing patterns of human beings in an effective way. This is especially true with respect to respiratory sensors in sleep labs which monitor persons with breathing disorders such as sleep apnea. When using this type of sleep monitoring equipment it is well known that it is very important to have an accurate and reliable way to detect breathing variations.
In the past, a variety of materials and methods have been used to detect respiratory patterns. Some of these devices used film transducers such as polyvinylidene fluoride (PVDF) as a sensing element. PVDF is a highly non-reactive and pure fluoropolymer also known under the commercial name KYNAR®. PVDF material may exhibit efficient piezoelectric and pyroelectric properties. PVDF is electrically poled before it exhibits piezo and pyroelectric properties. It has been used in many types of sensor and battery applications. There are several examples of past respiratory sensing devices which use PVDF film. One example utilized a piece of PVDF film affixed proximate a person's airway so that air will impinge upon the film when respiratory gas is inspired or expired. An output signal was thereby produced related to the impingement of respiratory air on the sensor due to temperature changes or vibrations due to snoring.
Other ways of detecting respiration included using devices with belt and transducer arrangements. Such devices used a transducer arrangement where piezoelectric materials were mounted on belts located around a person's chest or abdomen. The sensors coupled to the belt could detect expansion and contraction to produce output signals. These signals would then be used to relay information about a subject's breathing for analysis. A limitation found in many of these devices was that flexing or bending of the PVDF material was required for signal detection. Therefore, if the individual wearing such a respiratory sensing belt was lying on the portion of the belt where the PVDF material was located, the necessary bending and signal generation would not occur and any previously generated signal would effectively disappear.
Further, the attachment arrangements used in many of the past devices were not particularly well suited for measuring a stretching stress on a belt or like device. Likewise, the configuration used was not well suited for manufacture and the PVDF material proved difficult to work with for these designs. Also, the shape of the PVDF or other sensing element was not ideally shaped to detect longitudinal stress and stretching. Because the PVDF is strictly used to measure changes in stress, the amplitude of the signal changes very little when a person lies on the sensor or when the belt is looser or tighter and there is no signal inversion, as exists with the belts using bending of the sensor as a signal generation.
Therefore, it is desirable to have a sensing device that can be used with greater versatility, ease of manufacture, and effectiveness. An improved respiratory belt sensing device is needed which overcomes the problems experienced in past methods and devices.
The present invention relates generally to a respiratory sensing belt. The device includes a film member having piezoelectric properties and first and second metalized major surfaces. The surfaces have a symmetric shape and a plurality of alignment features around their perimeter. The invention also includes a first tabbed lead and a second tabbed lead, respectively attached to the first and second major surfaces of the film member by an electrically conductive adhesive. This assembly may then be sandwiched between thin layers of an elastomeric material such as polyurethane, which is capable of being stretched. A label is used to conceal the film member and assembly which is affixed to the surface of an elastic belt member.
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.
The present invention can be readily understood from
The configuration of the film member 14 is important to the capabilities and manufacturability of the sensor assembly. While this film member is generally PVDF film, a similar piezoelectric film material of related properties may be utilized as well. The PVDF film 14 is a single-piece, flat member having an outline of a central rectangular member with two rectangular ends of slightly larger width. This outline can be described as a “dogbone” or “dumbbell” shape. The corners of the film are rounded, containing a slight radius. A more detailed view of PVDF film member 14 can be seen in
As mentioned above, the perimeter of PVDF member 14 is somewhat dumbbell shaped, having a central rectangular section and two enlarged heads at the ends. Four important alignment points 28 are located where the perimeter of the central rectangular section and the perimeter of the enlarged heads come together. In this embodiment, these alignment points 28 not only serve to properly orient the surrounding sensor structure, but also function as locations at which adhesive is applied to hold the PVDF film 14 against the belt member 12.
Looking again at the exploded view of
Located directly between the tabs 24 and 26 of the tabbed wires and the PVDF film member 14 are pieces of a double-sided, electrically-conductive adhesive tape members 16. One such material is also known under the commercial name ARCLAD®. These ARCLAD pieces 16, like the tabbed wire members 18 and 20, do not make contact with the opposing surfaces of the PVDF film 14 or extend beyond the perimeter of the PVDF film.
Finally, the label 22 is placed over the entire sensor member assembly and joined to the belt 12. This is done by applying an adhesive to the bottom face of the label 22 and placing it in alignment with the outer dimensions of the belt 12. Label 22 may also be made from stretchable material. The final assembled configuration appears as shown in
Once assembled, the device of the present invention generally operates as follows. First, a user places the belt comprising the present invention around his or her chest or abdomen. Next, when the user inhales air and thereby expands his or her chest cavity or abdomen, tension is applied at opposed ends of the PVDF transducer assembly mounted to the belt. Similarly, when a user exhales air, tension is reduced producing a signal reflecting decreased tension. An electrical signal proportional to the tension stress is produced across the tabbed wires 18 and 20. These wires extend to amplifying and wave shaping circuitry which can be used by medical personal to diagnose and analyze the respiratory patterns of the user.
An alternate embodiment of the present invention is set forth in the exploded view of
Once aligned, the urethane members 34 and 34′ are sealed around the perimeter of film 14, foam 30, and wire leads 18 and 20 by an impulse sealing procedure. In such an impulse sealing operation, temperature and pressure are applied to encase the interior assembly. The resulting assembly is an airtight configuration that is resistant to moisture and corrosive substances that might harm the PVDF film member 14
Assembly of this embodiment is completed when the urethane envelope is aligned between a label and the surface of the belt member 12 and these three elements are joined with one another. In this embodiment, such attachment is preferably performed by stitching the ends of the members to the belt 12, but other attachment means can be employed. The stitching 38 generally extends laterally across the width of the belt and sensor assembly at a location corresponding to a second pair of notches 40 at both ends of the urethane layers 34 and 34′. Placing the stitching 38 in this location ensures that the stitches will pass through the ends of the foam members 30, but are just beyond the ends of the PVDF material 14 to avoid any damage to the film. All these members are sized such that when aligned, precise stitching and assembly can take place. The resulting assembled belt has an outside appearance similar to that of
Those skilled in the art will appreciate that the belt sensor of the present invention may be manufactured in a variety of shapes and sizes to accommodate various sizes and types of persons and belt configurations. The components can be composed of any number of suitable materials. Also, the design of the present invention should not be construed to limit its application to only respiratory sensing applications.
The 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.
