Fabian Michler

Local Pulse Wave Detection Using Continuous Wave Radar Systems

Although a lot of research has been done into radar-based heartbeat detection over the past few years, it is still unknown which physiological effects truly underlie these measurement signals. This paper investigates the cardiovascular system, as well as the effects due to the antenna characteristics, and establishes a connection to the variety of heartbeat signals that can be found in comparable publications. For the first time, the cause of the diverging signal shapes is researched, revealing the locally specific pulse wave curves named sphygmograms. Three different types are investigated: the carotid, the venous, and the ventricle sphygmogram. Verification of the measured signal shapes is ensured by a laser sensor. Afterward, the influence of the filtering on the sphygmograms is researched, as well as the influence of the antenna characteristics on the radar signal. Finally, all novel insights are combined to substantiate the variety of published heartbeat signal curves.

Radar-Based Heart Sound Detection

This paper introduces heart sound detection by radar systems, which enables touch-free and continuous monitoring of heart sounds. The proposed measurement principle entails two enhancements in modern vital sign monitoring. First, common touch-based auscultation with a phonocardiograph can be simplified by using biomedical radar systems. Second, detecting heart sounds offers a further feasibility in radar-based heartbeat monitoring. To analyse the performance of the proposed measurement principle, 9930 seconds of eleven persons-under-tests’ vital signs were acquired and stored in a database using multiple, synchronised sensors: a continuous wave radar system, a phonocardiograph (PCG), an electrocardiograph (ECG), and a temperature-based respiration sensor. A hidden semi-Markov model is utilised to detect the heart sounds in the phonocardiograph and radar data and additionally, an advanced template matching (ATM) algorithm is used for state-of-the-art radar-based heartbeat detection. The feasibility of the proposed measurement principle is shown by a morphology analysis between the data acquired by radar and PCG for the dominant heart sounds S1 and S2: The correlation is 82.97u2009±u200911.15% for 5274 used occurrences of S1 and 80.72u2009±u200912.16% for 5277 used occurrences of S2. The performance of the proposed detection method is evaluated by comparing the F-scores for radar and PCG-based heart sound detection with ECG as reference: Achieving an F1 value of 92.22u2009±u20092.07%, the radar system approximates the score of 94.15u2009±u20091.61% for the PCG. The accuracy regarding the detection timing of heartbeat occurrences is analysed by means of the root-mean-square error: In comparison to the ATM algorithm (144.9 ms) and the PCG-based variant (59.4 ms), the proposed method has the lowest error value (44.2 ms). Based on these results, utilising the detected heart sounds considerably improves radar-based heartbeat monitoring, while the achieved performance is also competitive to phonocardiography.

Microw(h)att?! Ultralow-Power Six-Port Radar: Realizing Highly Integrated Portable Radar Systems with Good Motion Sensitivity at Relatively Low Cost

Short-range noncontact microwave radar systems have undergone significant development in recent years [1]. Driven by advances in modern monolithic microwave integrated circuitry, printed circuit board (PCB) technologies, and embedded computing, highly integrated portable radar systems with good motion sensitivity can today be realized at relatively low cost. Radar systems have emerged in a variety of new application fields including industrial sensing [2], [3], human vital-sign detection [4], [5], and structural health monitoring [6].