Development of Biomedical Transducer by Use of Optical Fiber Sensor and Actuator

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Fiber optic sensors have advantages in a number of application, especially in the medical field. An optical power-feed system has been designed to supply power to devices which can be used in hazardous and noisy environment such as high voltage power systems. However, the available power of the earlier reported system was around 150 muW and was too low for the power supply to conventional devices. The aim of this work is to develop an optical power-feed system in order to sypply enough power to a conventional sensor element such as temperature monitors.Laser light was transmitted to solar cells where the energy is accumulated. A laser diode (SLD304XT, the wave length 813 mm, maximum optical power 800 mW) was used as a light source. A laser diode with graded-index fiber (230mum in core diameter) was used. Eight solar cells connected in series are assembled around the fiber end. Each solar cell (S-4V, United Detector Technology) had an active area was 0.5 x 0.27 cm. The maximum optical power measured in the tip of a graded-index optical fiber was 800 mW. The temperature measurement circuit with IC temperature sensor was tested. The output signal was converted into a digitized, coded signal by the optical transmitting circuit. The digitized signal was transmitted along another optical fiber to the light-measuring instrument. A light link diode (SFH 751, Siemens) was used for optical signal transmission.The open-circuit voltage of the eight solar cell was about 4 V and the short-circuit was about 6 mA. Total current consumption of the sensor circuit was about 3 mA. The digitized signal could be trans-mitted by a light-link diode feeded with less than 2 mA. The result indicates that the system can be used as power supply for conventional sensor elements, especially with potentially long transmission distance and immunity to electromagnetic interference.