Application of Optical Fiber Sensor in Monitoring the breathing

With the rising standard of living humans, qualified technology is required in all fields. One of the things that should […]

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With the rising standard of living humans, qualified technology is required in all fields. One of the things that should always be improved is technology in the health field, both in the diagnosis or treatment. This increase could be the better the accuracy of the tool or tools that are increasingly small size and portable. The utilization of optical technology in the health field have already been examined for a long time, given the nature of the optical technologies are non-destructive (does not damage body tissues). One of the popular forms of optical technologies are fiber optic sensors.

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Optical fiber sensor [1]

The sensor is an important component in measurements. Sensor serves as a translator signal quantity into quantity that can be measured and displayed, e.g. electrical signals. Measurement results can be either the amplitude, frequency, or phase of the electrical signal that shows the value of the measured quantity. For example, the concentration of oxygen in the blood can be measured from the amplitude of the light wave is absorbed by the blood. Fiber optic sensors can measure temperature, pressure, vibration, displacement (displacement), and the motion of rotation. The working principle of optical fiber sensors are very diverse, which is basically comparing the behavior of light before and after passing through an optical fiber.

Some of the parameters that must be considered in the selection of the sensor is the accuracy, the working range (span), a resolution (the smallest value that can be read), the repeatability (repeatability of results), and its performance when affected by certain environmental conditions.

Fiber optic sensors can be classified based on some way. According to the location of the sensors, fiber optic sensor is differentiated into intrinsic and extrinsic sensors. On the intrinsic properties of the sensor the light intensity, i.e. the phase polarity, or turned against the magnitudes measured directly such as temperature. While in the extrinsic sensors, there is a modulator of light that pass on information from the variables being measured so that there is no direct relationship between light and variable. This way of working can be described in Figure 2.

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Fiber optic sensor of extrinsic (a) and (b) [1]

Figure 2. Fiber optic sensor of extrinsic (a) and (b) [1]

Based on the principle of its operation, the fiber optic sensor is divided into 3:

1. Intensity-based

Intensity/power light input and output on the optical fiber is measured to know a decrease in intensity. The value can be calibrated to know the value of the quantity being measured. Generally applied to the load sensor and temperature sensor.

2. Polarization-based

Change the properties of the polarization of the light used to detect changes in certain parameters. For example, stress/pressure sensor using components of the polarizer and analyzer to calculate external stress.

3. Phase-based

The most responsive sensor is sensor-based fiber optic phase modulation. The phase of the light waves passing through optical fiber physical length depends on the fiber, the optical path length, refractive index and index profile the propagation of light. In Figure 4, the optical sensor-based phase Interferometer shown by Michelson and Mach-Zehnder.

Fiber optic sensors in the field of medical

Optical fiber sensor used in the medical field because some of the excess. Its small size allows it to be inserted into the body without causing damage is fatal. Optical fiber is also immune to the influence of electromagnetic waves and electricity. Applications of fiber optic sensors can be grouped into:

  1. In-vitro (outside the body). example: analysis of gases, fluids, tissue samples
  2. In-vivo (directly on the body), non-invasive. Example: optrodes placed on the skin
  3. In-vivo, invasive. Example: cathether, endoscopy

The respiratory rate is one of the important parameters in the human body that have successfully measured with optical fiber sensors. To be able to know the intensity of breathing of a person, used the principle of micro bending, IE a small dent on the optical fiber that is causing the loss of power. The movement of the body when the patient in breathing causes the micro bending of optical fiber sensor on. The power loss is a decrease in the intensity of the light after passing the power optical fiber with a specific length. In addition due to the length of the optical fiber, the presence of grooves, bengkokan, or warming up on fiber can cause a loss of power. This power loss is required for later analysis.

In an experiment conducted by a team from Northeastern University, Shenyang, China, in the year 2016 transducer used in the form of two boards with sawtooth surface (sawtooth-shaped) that is placed on the seat as shown below:

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Set Up An Experiment [2]

The use of the transducer in the shape of a new technique to improve the responsiveness of the sensor.

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TransducerA�[2]

A major component of this is the fiber optic sensors, light sources, optical detectors, and transducer. Transducer function change the shape of the signal from the style in the form of pressure due to respiration into angled optical fiber. The higher the intensity of breathing, then the greater the style press received by the transducer. It causes the larger micro-bending that occurs, and the greater the loss experienced by fiber optics. Loss optical fiber processed to find out the patient's breathing pattern.

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The working principle of the Sensor Micro[2] Bending (with changes)

Several parameters are taken into account in the design of transducer including high sawtooth, the distance between the sawtooth and other geometric measure affecting micro bending radius, as well as the number of teeth of sawtooth.

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Sawtooth Design [2]

The results obtained are the optical output intensity curve against time. Due to the nature of the respiratory cycle, the resulting graph is shaped. Various analyses performed, including analysis of the frequency spectrum. From here it can be known if there is a breathing disorder in patients. The rate of breathing is also known from the change of loss experienced by fiber optic sensors.

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Examples of experimental results and analysis of the spectrum of[2]
the source:

[1] V. b. Kalyani and v. Sharma, "Optical Sensors And Their Use In Medical Field" Journal of Management Engineering and Information Technology, vol. 3, no. 5, 2016.

[2]A�Hai-feng Hu, Si-jia Sun, Ri-qing, Zhao Yong, Lv and "Design and experiment of an optical fiber micro bend sensor for monitoring respiration" Sensors and Actuators A, vol. 251, pp. 126-133, 2016.

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