专业英语论文

Optical Fluorescence and Its application to blood

glucose monitor

Pan Yongfeng

(Wuhan University of Technology, Wuhan, China, xhyzjiji@126.com)

Abstract—Blood glucose monitor system is designed with the core of photonic crystal fiber (PCF) and technology of small—invasive photoelectric. According to the principle that different blood glucose concentration absorbs different light, optical modulation is controlled by MSP430．Light is emited to the blood samples through transmission of three probe fiber—optic

sensor. The reflected light is inputed to MSP430 after

photoelectric conversion. Blood glucose concentration is calculated after A/D conversion. The system has characteristics of easy— operation, low energy. Keywords—photonic crystal fiber(PCF); small—invasive; blood glucose I. INTRODUCTION W

ith the rapid development of science and technology,

optical fiber has increasingly expanded in the medical, communications, electronics and electricity, and other fields. It is becoming the basis of promising materials. In practice, however, the optical fiber, as a transmission medium to wire will inevitably need to be bended. When traditional optical fibers are of bending, bending loss will affect the signal transmission properties and sensitivity. Photonic crystal fiber (photonic crystal fiber, PCF) is a new type of optical fiber, which is formed by a single medium, clad in two-dimensional photonic crystals structure. It is different from the traditional optical fiber because of its small bending loss, Optical fiber features stable etc. Based on this, the blood glucose monitor system use PCF as optical waveguide materials and designe the three probe beam PCF sensor to monitor blood glucose. The system has high precision, low cost, good portability. II. DESIGN PRINCIPLES

A. Measuring principle

The glucose in the blood will be oxidated and finally turn

into delta-gluconolactone by GOD, when the blood sample

drops into the test paper which contains oxidase for the

oxidation of glucose. This substance reacts with peroxidase in

the reagent, and then will generate a light-absorbing material.

We place the paper in the reflective intensity modulation type

fiber optic sensor in the optical path, as shown in figure 1. The

whole sensor system includes a light source, optical fiber, optical fiber and optical detectors. The light emitted by light source reach the surface of blood sample through the filter and transmitting fiber. Due to material suction light modulation,

reflected light with blood sugar information will be received by

receiving optical fiber, finally turned into electrical signals by the photoelectric receiver converts. When the power of light source and optical fiber probe and the distance between the reflective surfaces remain unchanged, the receiving optical fiber receives a certain wavelength of light intensity and the wavelength of incident light intensity is the ratio of the

corresponding relationship with blood sugar levels. According to the light intensity of the signal, the blood glucose concentration can be calculated. But the main drawback of this kind of optical fiber sensor is measurement error caused by light source, optical power changes when light excitation is not

stable. In addition, the different reflectivity of the reflector

surface and light transmission loss in the optical fiber should also cause measurement error. Therefore, to put forward three

probe fiber optic sensor compensation measuring method can

eliminate the influence of all kinds of unstable factors in the

measuring environment. Figure 1. Reflective intensity modulation type fiber optic sensor B. Three probe compensating optical fiber bundle sensors measurement principle Traditional reflective intensity modulation type fiber optic sensor using a single optical fiber transmitting and receiving

the light energy is very weak. Moreover, in the design of wiring, because of the warped shape change the geometry of the symmetry of the fiber and the relative refractive index of fiber core and cladding, which affect the lateral distribution of the optical fiber mode field, and destroy the total reflection of light waves along the optical fiber transmission conditions, lead to light leaked to the packet layer and outer layer medium. Therefore, this design is composed of three probe of optical fiber sensor including PCF which use to send and receive light and the additional reference light path, as shown in figure 2. Figure 2. Three probe optical fiber bundle sensors

Ordinary single mode optical fiber loss theory of improvements can be applied to PCF, gaussian beams transmit along the optical fiber, the relationship between light intensity and bend loss coefficient and length is

P(z)?P(0)exp(?az)

(1)

a in the formula is bend loss coefficient, and

?2exp(?4Ra??Ae?3?V2W3)8PWWR2 (2)

??V2?Win the formula,

??2sin2?c/2, V???sin?c,

W???2??2c1, ?is the radius of optical fiber core, R

is bend radius, introduce a parameter V???2??2c1,

under

the

condition

of large mode field, use ??2?neff/??2?ns/?, when the optical fiber bending

radius R is greater than optical fiber core radius, formula (2) can be written as

a?1A2??1?2?V?3e?86?PnF?22R???

(3) s??6?ns?????F(x)?x?1/2exp(?x)

(4)

in the formula, ns is refractive index of SiO2, Aeis

coefficient of electric field in the packet layer, P is power of base membrane, ?is distance of mesopores in the packet layer. In type (3), V/A increases with air filling ratio (d/A), and F(x) is a monotone decreasing function. It turns out that bend loss decreases with the filling ratio, and increase with bending radius. Therefore, we can draw the conclusion: in the case of inevitable bending, we can offset optical fiber bending loss via improving air filling ratios, the bending resistability of PCF will be stronger with the increase of optical fiber filling ratio. It is recommended that the light spot of reference light and measurement light on the sample should be consistent, so that reference light can play a role of reference. Therefore, the optical fiber sensing probe adopt the concentric circles structure, two paths for launching optical fiber bundle work as inner circle with the uniform distribution random permutation, the outer ring works as the receiving fiber bundle. In the case of enough quantity of measurement optical fiber and reference optical fiber, the spot area produced by exposuring to the object with two wavelengths of light. In actual production process measurement and reference fiber bundle are used 4000 each optical fiber glass strand. As a result, it can approximate thought that measuring light and reference light are the same light path, the structure is shown in figure 3. According to spectrum analysis theory, the light of 635nm wavelength cannot be absorbed by effective light-absorbing substance in the blood, it only related to other light-absorbing factors. So it

can be used as reference wavelength. The light in 700nm wavelength is not only associated with light suction material concentration, but also associated with other light-absorbing factors expect this material’s influence. Therefore, the light emitted by emitting diode D1 and D2 with the same intensity and two separate wavelengths, 635nm and 700nm, import into optical fiber, respectively after reflection by the D3, and then get their intensity which can reflects the level of the blood glucose concentration through the spectral components and filter to isolate different wavelengths of light. This kind of optical fiber probe that is arranged closely with the same fiber size and optical path is easy to make ribbon. It can automatically compensate light source intensity and reflectivity and the influence of environmental factors such as changes on the measurement accuracy.

Figure 3. Cross-section of fiber probe

II.

HAREWARE DESIGN

A. System design

Monitoring device consists of CPU, three probe fiber bundle sensor, amplified circuit, LCD, keyboard, type Y splitter, alarm parts, filter, etc. , as shown in figure 4. Its working process is: the program stored in CPU will control the LED driver circuit to produce a 10 kHz reference wavelength and a measurement wavelength by CPU’s IO port. Measuring light and reference light irradiate on the blood sample through the three probe optical fiber bundle sensors. And the reflective light import Y type coupler. After passing filter, two beams of light at different wavelengths will respectively go into the logarithmic amplification and differential amplification, and then input to the CPU to achieve A/D conversion and data analysis, finally return the result on the LCD.

KeyboardLight source1logarithmic CPUPCF amplificationLight sensorslogarithmic LEDsource2amplificationfilterdifferential amplification Figure 4. Structure device

B. Photoelectric converting and amplifying circuit design According to theoretical analysis, it’s necessary to turn the blood glucose concentration measurement into light intensity ratio measurement. After photoelectric conversion, it turns to measure current ratio. Therefore, to obtain the current ratio needs the logarithmic amplifier and differential amplification.

LOG114 amplifier from TI which has two road 2 independent of differential amplifier and a internal reference voltage of 2.5V can meet the needs of the testing. It is dedicated to he detection of the photodiode signal optical fiber cable output. There is no need other circuits. It also supports to detect 8 orders of magnitude. The dynamic range is 100pA ~ 10mA. It has high speed, high accuracy etc. advantages. It is very suitable for light control system, thereby, it can avoid quadratic error brought by the composed of discrete element in the circuit.

III. SOFTWARE DESIGN

Software structure is mainly composed of main program and interrupt functions and display program modules and program flow is shown in figure 5.

StartInitialize End of RAM, LEDsampling?NKey Ypress?Stop pulse, Ydata analysisGenerate pulseEnable Value interruptionoverflow?Y Interrupt?NAlarmNYRead and Display save dataresults

Figure 5. Program flow IV. EXPERIMENTAL RESULTS

We use this system to collect the blood samples after lunch and dinner, the sampling data are shown in Table 1. After data fitting, we will make comparison between fitting curve and curve measured by blood giucose monitoring system, as shown on Figure 6.

Table 1. Sampled data between lunch and dinner Blood Blood glucose glucose concentration Output Output (mgdL?1Voltage concentration ) (mgdL?1Voltage ) 82 1.3926 118 2.7575 93 1.8326 1220 2.8505 101 2.1812 132 3.1579 109 2.5132 138 3.3446 115 2.6537 140 3.3986 3.53V/eg2.5atloV tuptu2O1.518090100110120130140Blood Glucose Concentration/mg*dL-1Figure 6. Experimental results

ACKNOWLEDGMENT

I would like to thank particularly my lab colleagues for their advice throughout this research, and my master for his help with some mathematical aspects and optical aspects of this paper.

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