A Low Power Fully Autonomous Wireless Health Monitoring System For Urinary Tract Infection Screening

Recent advancements of health monitoring sensing technologies are enabling plethora of new applications in a variety of biomedical areas. In this work, we present a new sensing technology that enables a fully autonomous monitoring of urinary tract infection (UTI). UTI is the second most common infection in the human body caused by bacterial pathogens, and costs millions of dollars each year to the patients and the health care industry. UTI is easily treatable using antibiotics if identified in early stages. However, when early stage identification is missed, UTI can be a major source of serious complications such as ascending infections, loss of kidney function, bacteremia, and sepsis. Unfortunately, the limitations of existing UTI monitoring technologies such as high cost, time-intensive sample preparation, and relatively high false alarm rate prohibit reliable detection of UTI in early stages. The problem becomes more serious in certain patient groups such as infants and geriatric patients suffering from neurodegenerative diseases, who have difficulties in realizing the symptoms and communicating the symptoms with their caregivers. In addition to the aforementioned difficulties, the fact that UTI is often asymptomatic makes early stage identifications quite challenging, and the reliable monitoring and detection of UTI in early stages remain as a serious problem.

To address these issues, we propose a diaper-embedded, self-powered, and fully autonomous UTI monitoring sensor module that enables autonomous monitoring and detection of UTI in early stages with minimal effort. The sensor module consists of a paper-based colorimetric nitrite sensor, urine-activated batteries, a boost dc-dc converter, a low-power sensor interface utilizing pulse width modulation, a Bluetooth low energy module for wireless transmission, and a software performing calibration at run-time.

To further optimize the sensor module, a new fully integrated DC-DC converter with low-profile and low ripple is developed. The proposed DC-DC converter maintains an extremely low level of output voltage ripples in the face of different battery output voltages, which is crucial for realizing low-noise sensor interfaces. Since the DC-DC converter is a part of a module embedded into a diaper, it is highly desirable for the DC-DC converter to have a small physical form factor in both area and height. To address this issue, the proposed DC-DC converter adopts a new charge recycling technique that enables a fully integrated design without utilizing any off-chip components. In addition, the DC-DC converter utilizes sub-module sharing techniques – multiple modules share a voltage buffer and a recycle capacitor to reduce power consumption and save chip area. The DC-DC converter provides a regulated voltage of 1.2V and achieves a maximum efficiency of 80% with a 300ohm load resistance. The output voltage ripple is in the range of 19.6mV to 26.6mV for an input voltage ranging from 0.66 to 0.86V.