Wearable Bio-Sensors
Recent advancements in miniature devices have fostered a dramatic growth of interest of wearable technology. Wearable Bio-Sensors (WBS) will permit continuous cardiovascular (CV) monitoring in a number of novel settings. WBS could play an important role in the wireless surveillance of people during hazardous operations (military, firefighting, etc) or such sensors could be dispensed during a mass civilian casualty occurrence. They typically rely on wireless, miniature sensors enclosed in ring or a shirt. They take advantage of handheld units to temporarily store physiological data and then periodically upload that data to a database server via wireless LAN or a cradle that allow Internet connection and used for clinical diagnosis. DEVELOPMENT OF WEARABLE BIOSENSOR
RING SENSOR
It is a pulse oximetry sensor that allows one to continuously monitor heart rate and oxygen saturation in a totally unobtrusive way. The device is shaped like a ring and thus it can be worn for long periods of time without any discomfort to the subject. The ring sensor is equipped with a low power transceiver that accomplishes bi-directional communication with a base station, and to upload date at any point in time.[1]
BASIC PRINCIPLE OF RING SENSOR
Each time the heart muscle contracts, blood is ejected from the ventricles and a pulse of pressure is transmitted through the circulatory system.
This pressure pulse when traveling through the vessels, causes vessel wall displacement which is measurable at various points inorder to detect pulsatile blood volume changes by photoelectric method, photo conductors are used normally photo resistors are used, for amplification purpose photo transistors are used.[3]
Light is emitted by LED and transmitted through the artery and the resistance of photo resistor is determined by the amount of light reaching it. with each contraction of heart, blood is forced to the extremities and the amount of blood in the finger increases. It alters the optical density with the result that the light transmission through the finger reduces and the resistance of the photo resistor increases accordingly. The photoresistor is connected as a part of voltage divider circuit and produces a voltage that varies with the amount of blood in the finger.This voltage that closely follows the pressure pulse
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2.1.2WORKING
The LEDs and PD are placed on the flanks of the finger either reflective or transmittal type can be used. For avoiding motion disturbances quite stable transmittal method is used. Transmittal type has a powerful LED for transmitting light across the finger.
