Development and Diagnostic Performance Evaluation of a Wireless Digital Fetal Heart Rate Monitoring System Using Ultrasonic Doppler with Digital Filter-Based Noise Reduction

Muhammad Ridha Makruf; Roichatun Nashichah; Lusiana; Verry Angriawan

doi:10.33019/

Authors

Muhammad Ridha Makruf Department of Medical Electronics Technology, Poltekkes Kemenkes Surabaya
Roichatun Nashichah Department of Medical Electronics Technology, Poltekkes Kemenkes Surabaya
Lusiana Department of Medical Electronics Technology, Poltekkes Kemenkes Surabaya
Verry Angriawan Department of Medical Electronics Technology, Poltekkes Kemenkes Surabaya

DOI:

https://doi.org/10.33019/

Keywords:

Fetal Heart Rate Monitoring, Doppler Ultrasound, Wireless Communication, ESP32, Digital Signal Processing, Low-Pass Filter, Real-Time Monitoring

Abstract

Early fetal heart rate (FHR) monitoring is essential for assessing fetal well-being and enabling the early detection of fetal distress during pregnancy. However, existing fetal Doppler systems commonly rely on wired communication and remain susceptible to signal noise, limiting monitoring flexibility and measurement reliability. This study aimed to develop and evaluate a wireless fetal heart rate monitoring system with enhanced signal quality and reliable real-time communication. The proposed system integrates an ultrasonic Doppler sensor, ESP32 microcontrollers communicating through the ESP-NOW protocol, and digital signal processing using a Butterworth low-pass filter and a smoothing algorithm to suppress noise and improve signal clarity. System performance was evaluated using sampling frequencies ranging from 200 to 1000 Hz and baud rates from 300 to 250,000 bps. Communication reliability was assessed by transmitting 1,500 ADC packets for each sampling-frequency configuration and 1,000 ADC packets for each baud-rate configuration while monitoring packet sequence numbers to identify transmission loss. Experimental results showed that no packet loss was observed under all tested configurations. The developed system achieved BPM measurement errors ranging from 0.56% to 0.89% and improved signal quality, with the highest signal-to-noise ratio of 18.70 ± 0.17 dB obtained using a 0.5–20 Hz Butterworth filter. Higher sampling frequencies produced more detailed waveform representations, whereas higher baud rates improved transmission responsiveness without affecting waveform integrity within the tested range. These findings demonstrate that the proposed system provides an accurate, reliable, and portable solution for real-time wireless fetal heart rate monitoring.

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