Passive UHF RFID Diaper Moisture Sensor with Extended Read Range
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Solution Overview
Problem
Current diaper moisture sensors are either bulky and costly or have limited read ranges, and existing passive RFID-based sensors are not practical for smart diaper applications due to limitations in read range and reliability, posing risks of skin breakdown and infections from delayed diaper changes.
Innovation Solution
A flexible, battery-free, and reusable passive RFID tag attached to the diaper that uses a single interrogator antenna to detect urine presence by a sharp decline in Received Signal Strength Indicator (RSSI), with a read range of 4.4 meters, allowing for instant notification and monitoring of multiple users, and incorporates a reference tag to address ambiguities from user movement or external blockages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of stationary object
If passive RFID-based sensors are used, then the sensor is light and cheap, but the read range is limited
Solution Approach 1:
The patent changes the operating frequency parameter from traditional HF (13.56 MHz) to UHF (902-928 MHz) band, which fundamentally alters the propagation characteristics and extends the read range from centimeters to meters while maintaining the passive RFID architecture
Solution Approach 2:
The RFID tag antenna serves dual functions: it acts as both the identification tag antenna and the moisture sensing element. The same antenna structure detects urine presence through dielectric constant changes, eliminating the need for separate sensing components
2Measurement precision
If chip detuning-based sensing is used, then liquid level can be detected, but the distance between reader and tag must be fixed
Solution Approach 1:
The system continuously monitors the reflected power or RSSI from the RFID tag and compares it against threshold values to detect moisture presence. This feedback mechanism enables dynamic detection without requiring fixed distance, as the system adapts to varying reader-tag separations
Solution Approach 2:
The patent replaces the mechanical constraint of fixed distance with an electromagnetic field-based detection system. The UHF RFID system uses electromagnetic coupling and dielectric constant measurement to detect moisture, eliminating the need for precise mechanical positioning
3Reliability
If active or semi-passive sensors are used, then sensing capability is improved, but the device becomes bulky and costly
Solution Approach 1:
The passive RFID tag harvests energy from the reader's electromagnetic field to power its own operation and sensing functions. The tag autonomously detects moisture through dielectric constant changes and modulates its reflection without requiring external power sources, achieving reliable sensing with minimal complexity
Solution Approach 2:
The patent utilizes changes in the dielectric constant parameter of the urine-soaked diaper material to detect moisture. This parameter change naturally modulates the RFID tag's reflected power, providing reliable detection without additional active sensing components
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
The solution provides a cost-effective, environmentally friendly, and reliable system with the longest read range among UHF RFID smart diapers, reducing the risk of diaper-related infections by enabling immediate diaper changes and allowing for efficient monitoring of multiple patients, with the ability to detect moisture accurately and automatically store urination data for health insights.
Implementation Method 1
The IC can track antenna detuning due to the proximity of liquid
Data Source
AI summary
A passive UHF (Ultra High Frequency, 902-928 MHz) RFID-based fabric (such as a diaper) moisture sensor is low-cost, user-friendly, reusable, washable, environment-friendly and comes with an extended on-body read range of 3.6 meters with baby diapers and 4.4 meters with adult diapers. The external reader unit is connected to the internet or a local network, and may automatically notify the parents or caregivers as soon as the presence of moisture is detected.