Abstract:In this paper, we present a pulse pressure waveform sensor that does not constrain a wearer's daily activity; the sensor uses hetero-core fiber optics. Hetero-core fiber sensors have been found to be sensitive to moderate bending. To detect minute pulse pressure changes from the radial artery at the wrist, we devised a fiber sensor arrangement using three-point bending supports. We analyzed and evaluated the measurement validity using wavelet transformation, which is well-suited for biological signal processing. It was confirmed that the detected pulse waveform had a fundamental mode frequency of around 1.25 Hz over the timevarying waveform. A band-pass filter with a range of frequencies from 0.85 to 1.7 Hz was used to pick up the fundamental mode. In addition, a high-pass filter with 0.85 Hz frequency eliminated arm motion artifacts; consequently, we achieved high signal-to-noise ratio. For unrestricted daily health management, it is desirable that pulse pressure monitoring can be achieved by simply placing a device on the hand without the sensor being noticed. Two types of arrangements were developed and demonstrated in which the pulse sensors were either embedded in a base, such as an armrest, or in a wearable device. A wearable device without cuff pressure using a sensitivity-enhanced fiber sensor was successfully achieved with a sensitivity of 0.07-0.3 dB with a noise floor lower than 0.01 dB or multiple subjects.

In this paper, we proposed a hetero-core optic nerve pulse sensor made by softly silicone rubber sheet for unconstrained monitoring. An optical fiber has several advantages such as lightweight, minimal material, resistance to corrosion and electromagnetic interference. Additionally, a hetero-core optic fiber sensor is only sensitive to be bending action of the sensing portion and the transmission line is unaffected to external disturbance as pressure and temperature fluctuation because of its single-mode stable propagation scheme. Therefore, the hetero-core optic fiber sensor could be suitable for the pulse pressure sensing in unconstrained human activities and be placed in various sites such as a sofa and bath, and wearable device at the wrist. The proposed pulse sensor was devised to have high sensitivity by means of adding two spacers to the both ends of a hetero-core portion. Additionally, the pulse sensor was devised to have detectable area in the pulse pressure to be relatively wide with high sensitivity due to several hetero-core optic fiber sensors arranged in the pulse sensor. We successfully demonstrated to be adjustable to sensitivity and the sensing area, and some participants could detect the pulse signal due to a hetero-core optic nerve pulse sensor.