Public defence in Micro- and Nanoelectronic Circuit Design, M.Sc. Muhammad Tanweer

The title of the thesis: Eco-friendly disposable sensor node for smart diaper applications 

Thesis defender: Muhammad Tanweer
Opponent: Prof. Leena Ukkonen, Tampere University, Finland
Custos: Prof. Kari Halonen, Aalto University School of Electrical Engineering

An increasing elderly population brings new challenges to incontinence care. Many older individuals, especially those with dementia or mobility limitations, cannot report diaper wetness, leading to prolonged exposure, skin irritation, and urinary tract infections. Current smart diaper systems can help but often use bulky electronics and batteries, which increase cost, require maintenance, and cause environmental concerns when disposed of. 

In this doctoral research, an economical, battery-less, disposable, and flexible sensor node has been developed for smart diapers that operates entirely on energy harvested from urine. The system integrates two printed elements; capacitive sensors on a flexible substrate to detect urination events and quantify the volume of absorbed liquid, and urine-activated energy harvesting electrodes that power the sensor electronics. The capacitive sensors detect changes in fluid levels by measuring variations in dielectric permittivity inside the diaper’s absorbent layers. The energy harvesting electrodes form a galvanic cell using urine as an electrolyte, producing enough power to operate ultra-low-power application-specific integrated circuits (ASICs). These ASICs include a custom capacitance-to-frequency converter, a frequency-to-digital converter, and a power management unit to ensure stable performance. 

Laboratory and in-diaper tests demonstrated reliable detection of multiple urination events, with quantification down to 30 milliliters, and continuous operation for six hours from a single urination of 90 ml or more. This innovation eliminates the need for battery management, reduces electronic waste, and enables comfortable, cost-effective, single-use monitoring products. The results provide a scalable approach for eco-friendly, disposable medical devices and can be adapted to other single-use healthcare or environmental monitoring applications.

Key words: Battery-less sensor nodes, energy harvesting, disposable smart diapers, printed sensors

Thesis available for public display 7 days prior to the defence at Aaltodoc.