Capacitive Nappy Sensor for Liquid Quantity and Faeces Detection
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Solution Overview
Problem
Conventional enuresis and incontinence products emit instant alarms upon detecting liquid, lacking differentiated measurement methods for urine and faeces, which do not allow for adaptive alarm levels and fail to provide continuous monitoring of liquid quantity in absorbing materials.
Innovation Solution
A system using capacitive sensors with a data logger that applies an alternating voltage across electrodes to measure capacitance, allowing for continuous liquid quantity estimation and faeces detection, with optional features like temperature measurement, GPS tracking, and wireless signal transmission for remote monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional resistive instant alarm sensors are used to detect liquid presence, then alarm response speed is improved, but measurement precision of liquid quantity and differentiation between urine and faeces deteriorates
Solution Approach 1:
The patent replaces conventional resistive sensors with capacitive sensors that measure changes in capacitance rather than electrical resistance. This substitution enables continuous monitoring of liquid quantity with higher precision while maintaining rapid detection capability. The capacitive measurement principle allows differentiation between urine and faeces based on their distinct dielectric properties, resolving the contradiction between fast alarm response and precise measurement.
Solution Approach 2:
The patent changes the measurement parameter from electrical resistance to capacitance. By measuring capacitance changes in response to liquid presence, the system achieves both rapid detection (maintaining the speed advantage) and precise quantification of liquid amount (improving measurement precision). The system also utilizes dielectric constant variations to differentiate between urine and faeces, further enhancing measurement precision.
2Speed
If conventional instant alarm systems are used, then alarm activation speed is improved, but adaptability for different alarm levels and user needs deteriorates
Solution Approach 1:
The patent implements a dynamic alarm system that can adapt to different user needs and situations. The system provides continuous liquid quantity monitoring with multiple detectable states, allowing alarm thresholds and sensitivity levels to be adjusted based on individual requirements. This dynamic capability enables the same rapid detection technology to serve diverse applications from immediate alarm needs to gradual monitoring preferences.
Solution Approach 2:
The capacitive sensor system serves multiple functions: rapid liquid detection, continuous quantity monitoring, differentiation between urine and faeces, and adaptive alarm level adjustment. This multi-functionality allows a single system design to accommodate various user needs and alarm preferences without sacrificing response speed.
3Speed
If conventional urine sensors are used for instant alarm, then detection speed is improved, but ability to detect and differentiate faeces deteriorates
Solution Approach 1:
The patent utilizes the dielectric constant parameter to differentiate between urine and faeces. Capacitive sensors measure changes in dielectric properties, and since faeces and urine have distinctly different dielectric constants, the system can reliably distinguish between them while maintaining rapid detection speed. This parameter-based differentiation resolves the difficulty of detecting and measuring faeces separately from urine.
Solution Approach 2:
The replacement of resistive sensing with capacitive sensing enables faeces detection capability. Resistive sensors primarily detect liquid presence through conductivity, while capacitive sensors detect changes in dielectric properties, which differ significantly between urine and faeces. This substitution transforms the system from urine-only detection to multi-substance detection with maintained speed.
4Measurement precision
If embedded sensors in liquid-absorbing material are used, then liquid quantity monitoring capability is improved, but device complexity and manufacturing difficulty deteriorates
Solution Approach 1:
The patent segments the sensor system into distinct functional components: capacitive sensing elements, signal processing circuitry, and alarm/control modules. This segmentation allows for standardized manufacturing of sensor modules that can be integrated into nappies without requiring complex custom fabrication processes. The modular approach maintains measurement precision while reducing overall device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables adaptive alarm levels, continuous monitoring of liquid quantity, and detection of faeces, enhancing awareness of when a nappy needs changing and providing improved care for users with impaired cognitive functions.
Implementation Method 1
to measure capacitance between the two electrodes of the first pair of electrodes and to calculate, based on the measured capacitance, an estimate of the quantity of liquid
Implementation Method 2
to measure capacitance between the two electrodes of the second pair of electrodes and to estimate, based on the measured capacitance, whether faeces are present
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A system is disclosed for measuring and recording a quantity of liquid in an absorbing material (16), such as the quantity of urine in a nappy, which system comprises a sensor (1) comprising a first pair of electrodes (4, 7) for measuring the quantity of liquid, which first pair of electrodes is arranged to be placed around the absorbing material in, for example, a nappy, and a data logger (10), which is arranged to apply an alternating voltage across the first pair of electrodes and, concurrently herewith, to measure the capacitance between the two electrodes of the first pair of electrodes and to calculate, based on the measured capacitance, an estimate of the quantity of liquid in the absorbing material. In an embodiment, the system further comprises a second pair of electrodes (6, 8) for estimating the presence of a substance, such as faeces, there between using a similar method.