It is desirable for care givers of individual children to change wet diapers as soon as possible for a variety of reasons. Hygiene, avoidance of diaper rash, and containing the moisture contents are but a few reasons. In institutional settings where one care giver is responsible for larger numbers of diapered children, the ability to alert the care giver of a child with a wet diaper enables the care giver to better manage their time, as well as to enable them to avoid tactile checking of each child's diapers. Tactile checking is preferably performed with the care giver washing hands between the time that each child's diaper is checked. The time involved usually prevents this proper procedure. Where this procedure is not followed, germs from one child are passed to the other children as the checking progresses.
Several solutions to the above problem have been proposed, but none have gained wide acceptance. U.S. Pat. No. 5,570,082 to Mahgerefteh et al, uses an electromagnetic field large enough that the presence of water in the urine couples the field to react with a non linear element to create harmonics which are detected by a receiver within the device creating the field. The device in essence uses a powerful transceiver to blast an electromagnetic signal at a child's diaper containing an antenna system. Wetting on the antenna changes its natural re-radiating frequency so that the receiver of the transceiver picks up a shifted frequency which is re-radiated from a transmitter antenna within the diaper on which the child wets. Subsequent science has shown that where the body is exposed to electromagnetic radiation, the weaker the power and the less frequent the duty cycle, the better it is.
U.S. Pat. No. 5,291,181 discloses a multiple circuit resistance triggered electrode system within a diaper, connected to an individualized transmitter and then to a nurses station. The contact is made using a large rectangular flexible sheet of material which uncomfortably fits within the diaper.
U.S. Pat. No. 5,395,358 discloses a pointed device, having a blade and which cuts into a diaper to detect moisture. Once moisture is detected, music is played to draw attention to the wet diaper.
U.S. Pat. No. 5,264,830 discloses snaps which connect a device surrounded by a cushioning housing. The device outputs an audible alarm. The circuit uses the interruption of an oscillator to trigger the alarm.
U.S. Pat. No. 4,704,108 to Okada et al discloses a diaper having a water permeable inner sheet, water absorber and water impermeable outer sheet. Metal layers are formed on opposite sides of the water impermeable sheet at the time the diaper is formed. A wicking layer of tissue paper is taught to be disposed between a water content sensing layer and an outer layer. Since the metal conductors are oppositely disposed, wetness in contact with one conductor must be present sufficiently to flow around an impermeable layer to contact the second electrode on the back side of the impermeable layer. The problem with this design is that a large amount of urine is necessary in order to trigger a metal sensor which is custom built into a diaper. Where the child urinates only a little, or where the child is lying on its side, the design of Okada will probably not trigger. Where the object is to keep the child as dry as possible, or to prevent re-inflammation of diaper rash, the Okada design will fail.
In addition, the above sensor structure designs are built into custom made diapers at the time the diaper is manufactured. This will drive up the cost for the diapers considerably given that the conductive or resonant structure will need to be built into and match a given brand of sensor circuit. Shelf space storage increases and the unit cost rises. Where specialty diapers have to be constructed, the additional built in value combines with the shelf space occupied to prohibitively increase the price and decrease availability.
U.S. Patent to Fisher et al., discloses a bed wetting device having sharp alligator clips which attach a large plastic carrier loosely to the adult's pants. The assembly includes a layer with oppositely disposed conductors and a complex carrier and attachment assembly which would be completely unsafe and inappropriate for children. The interchange ability and disposability combined are awkward and do not facilitate quick changeability as would be experienced in diaper changing.
The above set forth structures also fail in their attempt to provide a physical separation of the measurement conductors to prevent shorting out with movement and wear, and also fail to provide a more sensitive indicator of moisture.
Given that diapers are already available in cloth and paper versions which vary greatly in quality and construction and given that the product and product channels are already established, what is needed is a system for wetness monitoring which utilizes the existing market products and quality array. If pre-existing diapers can be utilized, the manufacturing cost can be reduced and the diapers themselves will present only a competitive cost item in the system.
What is needed is a wetness sensor which is easy to construct and which will alert a care provider even if only a small amount of urine is present. The care giver should be notified without a noise near the child which would be startling. The ideal alert system will be a transmitter which is modest in both transmit power and duration to avoid adverse affects on the child's body. The transmitter should ideally operate by short pulses of low duty cycle, and battery conservation should be important.