In recent years, non-contact physiological monitoring technology has gradually become an important development direction in the medical field due to its convenience and high precision. In this wave of technology, Professor Chen Yan's team at the University of Science and Technology of China has made a major breakthrough, successfully using millimeter-wave radar technology to achieve non-contact cardiac activity monitoring, and control the heart rate monitoring error rate to only 26.1 milliseconds under respiratory interference conditions. This achievement not only solves the key challenges faced by traditional non-contact monitoring, but also provides a new solution for cardiovascular health management.
Technical background: The challenges of contactless monitoring
Cardiovascular disease is one of the leading causes of death worldwide. According to the World Health Organization (WHO), ischemic heart disease kills about 8.9 million people each year, accounting for 16% of all deaths worldwide. At the same time, long-term cardiac activity monitoring plays a key role in the early prevention, diagnosis and rehabilitation management of diseases.
Traditional cardiac monitoring methods, such as electrocardiogram (ECG) and photoplethysmography (PPG), have high monitoring accuracy, but they rely on contact sensors and need to attach electrodes or optical sensors, which have problems such as wearing discomfort, risk of infection, and poor compliance with long-term monitoring. Non-contact technologies, such as millimeter-wave radar, overcome the above shortcomings, but due to the interference of respiratory motion, the monitoring accuracy is often difficult to meet the actual needs.
In order to solve this problem, Professor Chen Yan's team at the University of Science and Technology of China proposed a new signal extraction method based on cardiac mechanical activity harmonics through innovative research, which was successfully applied to the millimeter-wave radar cardiac monitoring system.
Technical principle: innovative application of beat frequency effect and higher-order harmonics
1. Discovery of the beat effect
Professor Chen's team first used millimeter-wave radar to capture the weak vibration signals of the human chest, which are mainly caused by the mechanical activity of the heart and the movement of breathing. However, under far-field monitoring conditions, low-frequency vibrations induced by respiration tend to mask the heartbeat signal, resulting in a decrease in monitoring accuracy.
To this end, the team delved into the spectral properties of cardiac activity and discovered and exploited the beat frequency effect for the first time. When two harmonics of similar frequencies are superimposed, a beat signal with a frequency equal to the difference between the frequencies of the two harmonics is generated. In cardiac monitoring, adjacent heartbeat harmonics are superimposed to generate a new heart rate signature signal with a frequency that precisely corresponds to the heartbeat frequency.
This discovery provides a new idea for millimeter-wave radar signal denoising, and successfully separates the heart rate signal from the complex background.
Figure: Schematic diagram of the flow of the non-contact cardiac activity monitoring system
2. Utilization of higher-order harmonics
Further studies have shown that the harmonic attenuation of the signal caused by respiration is slower, especially in the low frequency band, and the effect is more significant. However, with the increase of frequency, the attenuation of respiratory harmonics accelerates, while the heartbeat signal remains stable in the higher-order harmonic band.
Based on this feature, the research team shifted the heartbeat signal extraction frequency band from the fundamental frequency to the higher-order harmonic frequency band (about 10 octaves). This method effectively avoids the interference of respiratory movement, which enables millimeter-wave radar to achieve high-precision cardiac monitoring in far-field conditions.
Experimental verification: the error rate is only 26.1 milliseconds
In order to verify the effectiveness of the technology, Professor Chen Yan's team conducted large-scale experiments in different scenarios:
1. Hospital scenario: 6222 participants were monitored, and the median error of the system was 26.1 milliseconds
2. Daily scenario: Tested in a home environment for 21 consecutive nights, the median error was 34.1 ms.
The experimental results show that even under complex conditions such as breathing interference and environmental noise, the millimeter-wave radar system still shows extremely high accuracy. This breakthrough enables the accuracy of non-contact cardiac monitoring to reach clinically available standards for the first time.
Technical advantages: the unique value of non-contact millimeter-wave radar
1. High accuracy: Through the beat frequency effect and the high-order harmonic extraction method, the system achieves monitoring accuracy comparable to that of contact sensors.
2. Contactless: No need to wear electrodes or sensors, the test subject can be monitored in their natural state, significantly improving the user experience.
3. Far-field monitoring: Millimeter-wave radar can capture small chest vibrations from a distance of several meters, which is suitable for various scenarios such as medical institutions, homes, and smart health devices.
4. High safety: millimeter wave signal has good penetration, no impact on skin and clothing, and no radiation hazards.
Application prospects: Broad potential for medical and health management
1. Clinical diagnosis and monitoring
Millimeter-wave radar cardiac monitoring technology can be applied to hospital intensive care units (ICUs), cardiovascular clinics and other scenarios to provide continuous and accurate cardiac activity monitoring. At the same time, the technology can be combined with telemedicine systems to help doctors achieve remote diagnosis and real-time monitoring.
2. Family health management
For the elderly and people at high risk of cardiovascular disease, the non-contact monitoring system can achieve long-term, non-sensory health management and timely detection of potential cardiac abnormalities.
3. Smart device integration
With the characteristics of miniaturization and low power consumption, millimeter-wave radar technology can be integrated into consumer electronics products such as smart home devices and wearable devices, and has become the core technology of next-generation intelligent health monitoring.
Global Cardiovascular Health Status and Market Opportunities
The number of patients with cardiovascular disease continues to grow globally, and the need for monitoring is increasing. In 2021, an estimated 19.91 million people died from cardiovascular diseases worldwide, demonstrating the severity of this health problem.
At the same time, the global health surveillance market is growing rapidly. According to market research institutions, the market size of non-contact physiological monitoring will exceed $12 billion by 2026, with a compound annual growth rate of more than 15%. In this context, the breakthrough of millimeter-wave radar technology of USTC undoubtedly has important market competitiveness and application prospects.
Future Prospects: Technology Optimization and Development Direction
Despite the remarkable achievements, there is still room for further optimization of mmWave radar cardiac monitoring technology:
1. Algorithm improvement: The signal processing algorithm is further optimized to improve the adaptability and accuracy of the system in different groups of people and different postures.
2. Equipment miniaturization: Promote the integration and miniaturization of millimeter-wave radar modules, reduce costs, and promote commercialization.
3. Multi-parameter monitoring: Study the feasibility of millimeter-wave radar in the synchronous monitoring of multiple physiological parameters such as blood oxygen saturation and respiratory rate, and create a comprehensive health monitoring system.
Conclusion: Technological breakthroughs lead to a healthy future
Professor Chen Yan's team at the University of Science and Technology of China successfully overcame the technical bottleneck of respiratory interference in non-contact cardiac monitoring through innovative beat frequency effect and high-order harmonic extraction method, and controlled the error rate to 26.1 milliseconds. This breakthrough marks a key step forward for millimeter-wave radar technology in the field of medical and health care, showing broad clinical and market application prospects.
With the continuous development and commercialization of the technology, this innovation is expected to provide strong support for the prevention and management of cardiovascular diseases around the world, and help health monitoring move towards a more intelligent and universal future.
Link to the original paper: Monitoring long-term cardiac activity with contactless radio frequency signals
