We propose a novel continuous blood pressure monitoring system which is based on an autonomic nervous system and which considers blood volume simultaneously since both affect blood pressure. An autonomic nervous system regulates blood pressure while blood volume is known to be proportional to the photoplethysmography (PPG) signal. To overcome the limitation of taking blood pressure using a conventional cuff inflating instrument, we designed a system which can achieve continuous blood pressure monitoring. In this research, we used a set of near-infrared light source (940nm) to create a divergent light which was collimated as a uniform beam incident to a wrist surface through a Fourier optics designed transfer lens. We found that the signals became more stable due to the uniform illumination and could be received by a detector. From the signals, we found that the blood volume when converted from blood velocity as measured by an ultrasound probe, showed a strong correlation with the signals. The heart rate variability analyzed from the signals, including time-domain (HR and SDNN) and frequency-domain (LF and HF) indices, could be viewed as physical models since these indices reflect the functions of an autonomic nervous system. Moreover, the research derived regression models can estimate blood pressure. Although it is not common to assess blood pressure from the perspective of an autonomic nervous system and blood flow simultaneously, our research approach seems logical. Our results show the potential for this novel system to be used for blood pressure health monitoring.

The traveling waves of linear traveling wave type piezoelectric motors are not easy to stabilize due to its finite boundary structure. The traditional two-mode excitation method is a method which can excite two modes to generate traveling waves in a finite structure. However, the drawback of the traditional method is that it does not allow for adjustment of the final output velocity. Also, this method is characterized by having low efficiency. The velocity of the generated traveling waves is constant unless the excited modes are changed. In this paper, we propose a novel method, called a two-frequency two-mode excitation method which uses a piezoelectric actuator to simultaneously excite two modes to generate traveling waves. The two frequencies chosen possess a ratio where the excited frequencies are close to two resonant modes. In addition, the two excited frequencies are simultaneously an integer ratio to a specific frequency and have a least one common multiple as small as possible. This approach can generate stable traveling waves such that the velocity of the traveling waves can be adjusted by the two frequencies. Our theoretical predictions were validated by numerical calculations and experimental data. A Hilbert transform was used to optimize the traveling waves generated. A morphological opening was used to track the traveling wave trajectories. The obtained results show that this method can generate stable traveling waves where the wave velocity can be adjusted by mixing the frequency signals.

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