Key Literature and References

This section provides a curated list of key literature and references that have informed and supported the development of our project. The selected works cover significant advancements in MEMS technology, ultrasound-based systems, and digital signal processing. Each entry offers insights into the methods and systems that have influenced the design and evolution of our project. Links are provided where available for further reading and exploration.

Anderle, J. (2024, Expected). "HeartWave: A privacy focused ultrasound-based heart rate monitoring System." (Provisional Title).

This project represents the core research and practical work undertaken by Mr. Anderle for his master's thesis, to be submitted in November 2024. The work includes the design, development, and implementation of hardware and software components for a contactless heart rate monitoring system, using digital signal processing techniques. The research presented here forms the foundation of his thesis, ensuring academic transparency and compliance with institutional guidelines.

All work done by Mr. Anderle and presented on this website is part of his master's thesis. The thesis, expected to be submitted in November 2024, encompasses the full scope of his research and development work for this project.

Gneist, N. (2022). "Development of an Ultrasound-Based System Capable of Measuring the Human Heart Rate Non-Invasively and Contactless."

This master's thesis served as a foundational project for the development of a contactless, ultrasound-based heart rate monitoring system. Mr. Nico Gneist's work involved creating a prototype system that utilized MEMS microphones and a ceramic ultrasonic transmitter to perform distance measurements. The system was controlled by the Infineon Aurix Tri-Core 375 microcontroller and was capable of transferring data to Matlab for visualization. While the project demonstrated potential, there were limitations in hardware design, data acquisition, and processing capabilities.

This thesis set the stage for further advancements, with key areas identified for improvement, such as increasing the number of microphones, optimizing data transfer speeds, and refining signal processing algorithms. Building on this foundational work, the current project has significantly improved the robustness of the hardware platform and data acquisition processes. Today, the system features more microphones, faster data transfer, and advanced data processing capabilities, enabling live monitoring of heart pulses.

Wang, A., Nguyen, D., Sridhar, A. R., & Gollakota, S. "Using Smart Speakers to Contactlessly Monitor Heart Rhythms."

This study, published on Nature.com, presents an innovative approach to heart rhythm monitoring using commercially available smart speakers, such as Amazon Echo and Google Home. By leveraging the inherent capabilities of smart speakers to emit sound waves and detect their reflections, the system analyzes minute chest movements caused by heartbeats. The signal processing techniques applied allow the system to detect heart rhythms without any physical contact, demonstrating the potential for non-invasive patient monitoring in a home setting.

This work is particularly significant as it highlights an alternative approach to achieving contactless heart monitoring. Instead of relying on specialized ultrasound hardware, the authors repurposed existing commercial devices, making their solution potentially more accessible to the general public. In comparison to our research, which utilizes ultrasound MEMS microphones and custom hardware, their work serves as a benchmark for understanding the capabilities and limitations of using general-purpose consumer electronics for medical applications.

The results of the study show a high degree of accuracy, but there are limitations in terms of signal resolution and reliability when used in uncontrolled environments. These challenges are addressed in our system, where more sophisticated hardware and refined data processing algorithms enable real-time, high-fidelity monitoring of heart pulses. This research serves as a key reference in our exploration of contactless heart rate monitoring, providing valuable insights into the trade-offs between convenience and precision in non-invasive medical devices.

Ambrosanio, M., Franceschini, S., Grassini, G., & Baselice, F. "A Multi-Channel Ultrasound System for Non-Contact Heart Rate Monitoring."

This paper, published in the IEEE Sensors Journal, introduces a multi-channel ultrasound system for heart rate monitoring that aligns closely with our approach. The authors describe a system that uses multiple ultrasound transducers to detect heartbeats without physical contact. Their research focuses on improving the accuracy of heart rate detection by utilizing multiple channels for signal acquisition, which helps reduce noise and increases the reliability of the measurements in different environments.

The paper details the hardware architecture, where several ultrasound sensors are positioned around the patient to capture the reflections of emitted sound waves. These reflections are then processed to determine heart rate by analyzing the subtle movements of the chest. Their system's multi-channel configuration significantly improves signal quality, reducing the interference caused by environmental noise and motion artifacts, a challenge also addressed in our research.

In comparison to our project, their work validates the effectiveness of using multiple ultrasound channels for non-contact heart monitoring. However, we have taken this a step further by implementing a larger array of MEMS microphones, along with more advanced data acquisition techniques, to achieve even greater precision and real-time monitoring. The insights gained from this study have informed our hardware design choices and data processing algorithms, ensuring that our system provides accurate and reliable results across a variety of settings.

Pasha, S., Lundgren, J., & Ritz, C. "Multi-Channel Electronic Stethoscope for Enhanced Cardiac Auscultation Using Beamforming and Equalisation Techniques."

Presented at EUSIPCO 2020, this paper discusses a multi-channel electronic stethoscope designed to enhance cardiac sound capture through the use of beamforming and equalization techniques. The system aims to improve the clarity and detail of heart sounds captured by multiple microphones arranged in an array, focusing on eliminating noise and interference through advanced signal processing methods.

The beamforming techniques described in this paper are of particular interest to our project. Beamforming allows for the directional focus of sound capture, which can significantly improve the quality of heart signal detection in a non-contact system like ours. By combining the signals from multiple microphones, the system is able to isolate the sound of the heart while minimizing background noise and other unwanted signals. The use of equalization techniques further enhances the system's ability to detect subtle variations in heart sounds, making it a powerful tool for cardiac monitoring.

In our project, while we are focused on capturing ultrasound signals rather than traditional stethoscope sounds, the principles of beamforming and multi-channel signal processing are directly applicable. We have incorporated similar techniques to ensure that our MEMS microphones can accurately detect heart pulses amidst the noise of real-world environments. This paper has influenced the development of our data processing pipeline, where we apply similar strategies to improve signal clarity and reliability in real-time heart rate monitoring.

Anzinger, S., Bretthauer, C., Manz, J., Krumbein, U., & Dehé, A. "Broadband Acoustical MEMS Transceivers for Simultaneous Range Finding and Microphone Applications."

Published in Transducers 2019 - EUROSENSORS XXXIII, this paper explores the use of broadband MEMS transceivers that can simultaneously perform range finding and audio signal capture. The authors present a system that combines these dual functionalities in a single device, leveraging MEMS technology's high sensitivity and accuracy to perform tasks traditionally handled by separate systems.

The dual-purpose functionality described in this paper is directly relevant to our research, as we use MEMS microphones not only to capture ultrasound signals for heart rate monitoring but also to perform distance measurements. This paper provides insights into the design and operation of MEMS transceivers that can handle both tasks efficiently, offering a cost-effective and compact solution for systems requiring both range finding and acoustic analysis.

Our project builds on these concepts by incorporating more advanced MEMS microphones capable of higher resolution signal capture. Additionally, we have optimized the data acquisition and processing workflows to ensure that the system can handle both heart rate detection and environmental monitoring simultaneously. The principles discussed in this paper have informed our hardware selection and system architecture, contributing to the robustness and versatility of our current platform.

Lagler, D., Anzinger, S., Pfann, E., Fusco, A., Bretthauer, C., & Huemer, M. "A Single Ultrasonic Transducer Fast and Robust Short-Range Distance Measurement Method."

This paper, presented at the 2019 IEEE International Ultrasonics Symposium (IUS), introduces a method for fast and robust short-range distance measurement using a single ultrasonic transducer. The system described in the paper uses a combination of signal processing techniques to achieve high accuracy and reliability in short-range applications, even in the presence of noise and environmental interference.

The authors demonstrate that their method can achieve real-time distance measurements with minimal latency, making it highly suitable for applications where precision and speed are critical. Although our project utilizes multiple MEMS microphones for more complex signal capture, the principles of short-range ultrasonic measurement outlined in this paper have informed our approach to optimizing data acquisition and signal processing.

In our system, we employ similar techniques to ensure that the ultrasound signals captured by the MEMS microphones are processed quickly and accurately, allowing for real-time heart rate monitoring. The insights gained from this paper have helped shape our approach to handling the challenges of distance measurement and signal noise, ensuring that our system remains reliable across various conditions.

Di Battista, A., Price, A., Malkin, R., Drinkwater, B. W., Kuberka, P., & Jarrold, C. "The Effects of High-Intensity 40 kHz Ultrasound on Cognitive Function."

This paper, published in Applied Acoustics (2022), examines the cognitive effects of exposure to high-intensity 40kHz ultrasound. Although our system uses 40kHz ultrasound primarily for heart rate detection, this study provides important context on the safety and biological impact of high-frequency ultrasound. Its findings reinforce the harmless nature of the frequencies employed in our system, which are well within safe exposure limits.

Additionally, this research has informed our understanding of the broader applications and implications of using ultrasound in medical devices. While our focus remains on heart rate monitoring, the potential cognitive effects of high-intensity ultrasound highlight the importance of carefully calibrating our system's output to ensure user safety.