With the rapid development of MEMS technology, endoscopy has made significant research achievements, particularly in the human gastrointestinal tract wireless capsule endoscopy is medical electronic Endoscope System of a major breakthrough [1-4].
Around capsule endoscopy, more and more research is being carried out. But there is also wireless endoscopic capsule, 2004 of the European technical report pointed out that the movement and posture control functions is the need to resolve the problem, including motion control and positioning problem [5], and in order to ensure that diagnosis and treatment process in motion and the orientation of the validity of these micro health capsule in the body of the space position in real-time positioning position detection becomes extremely important. In vivo micro device's location technology, traditional methods generally used ultrasound imaging, nuclear medicine imaging and modeling techniques such as position [6], but these positioning method there was costly, complex, on the human body easily lead to radiation and unable to meet the dynamic position for long periods of time. Many scholars on the device and positioning system for the study of the magnetic orientation of simplified model and the corresponding dynamic tracing technology [7-9].In order to better meet the magnet used in vivo measurement of micro-capsules accurate positioning, in this article the authors designed a three-axis HMC1021 HMC1022 and Magnetoresistive sensor module, with two-stage amplifier circuit magnification, the data acquisition device to the capsule space magnetic field strength more acquisition of positioning system.
The system incorporates more higher sensitivity of Magnetoresistive sensor module, reasonable arrangement of the sensor module groups, with higher detection sensitivity is high and the advantages of large measurement range.2. capsule orientation detection principle
Magnetic positioning is to use the Magnetoresistive sensor Hall-effect, which is under permanent magnet with its magnetic moment of the change of the direction and distance in space field formation of magnetic field distribution of specific rules.
Accordingly, by detecting changes in a specific field parameters, we can measure the magnet in space location changes, and determine its exact location in space [9].In the human body, the capsule can be regarded as rigid bodies.
At the same time, in order to position the Magnetoresistive sensor modules, placed in a capsule internal cylindrical permanent magnet. As shown in Figure 1, capsule in the space of posture can consist of any point inside the capsule permanent magnet magnetic moment and cylindrical coordinate system is formed by two horns, which are the coordinates of the center point of the capsule, the direction for capsule magnetic moment and the angle of the column coordinates, the origin of the coordinate space.When the capsules in cylindrical magnet size much less than its to magnetic sensor distance r, magnets can be simplified into a magnetic dipole, you can directly write the capsules in Magnetoresistive sensor module of magnetic induction [10]:
Type in the capsule of the magnetic moment of vector, vector for capsule space position and coordinates, Magnetoresistive sensor module position vector and coordinates, Magnetoresistive sensor module position relative to the capsule vectors.
As the size of the magnetic moment of capsules, which is arranged in the space of three axis Magnetoresistive sensor module coordinates, its axis coincides with the global coordinate system. From-(1) indicative amount, coordinates known then experiment various magnetic field component, if the requirements out five unknown quantity, then at least two of the three axis Magnetoresistive sensor module.3. system hardware design
This system consists of 4 sets of 3-axis magnetic sensor module (built-in set/reset circuit), amplifier and a data acquisition system consists of three parts.
3.1 Magnetoresistive sensor module
Figure 2 shows the design of the HMC1022 and HMC1021 mutually perpendicular installation consisting of three axis Magnetoresistive sensor module, built-in set/reset circuit, used for measuring capsule internal bar magnet in the space of magnetic flux density, of which, measured in both directions HMC1022 (axis) (i.e., formulas (3)), and a direction measurement HMC1021 (axis) of the magnetic flux density (i.e., formulas (3)).
HMC1022 and HMC1021 respectively double shaft and single Magnetoresistive sensor, which in addition to the measurement of magnetic flux density varying number of axes, have the same technical parameters. HMC1022 and integrate reset bit HMC1021/reset, you can reduce the temperature drift effect, linear error and because of the presence of high magnetic field causes the output signal loss [11].3.2 amplifier
As the distance increases, the distribution of the permanent magnet magnetic field attenuation quickly.
In view of the permanent magnet magnetic field strength decreases with distance variation, in experiments, using the typical AD620 amplifier, meet data acquisition card resolution precision is greater than the output resolution Magnetoresistive sensor accuracy requirements, through computational experiments in 1000 times magnification.3.3 data acquisition
Use PCI-1716 data acquisition card will amplifier output signal acquisition and access to computer processing and analysis.
Use LABVIEW virtual instruments graphical software programming, sampling the analog signal, A/D conversion functionality.4. test procedure
As Figure 4 shows the test step process diagrams.
Figure 4 test steps process diagram
Experiment with the following procedures:
(1) sensor coordinates when initializing the experiment will be four groups of three axis Magnetoresistive sensor module space coordinates fixed and documented (that is, the formula (1)), pending acquisition completed into the formula (1) processing for calculation.
(2) move each time capsule to the appropriate location and fixed, the record of capsules and the Group Magnetoresistive sensor module distance and Magnetoresistive sensor module integrated set/reset circuit to increase the sensitivity of the sensor.
(3) set/reset Magnetoresistive sensor module output effective field strength voltage, voltage amplifier and then after acquisition, fed into the computer analysis and processing, in accordance with the preceding formula (1) to calculate and steps (1) the actual record distance for comparative analysis.
5. experiment and result analysis
In the experiment, the four Magnetoresistive sensor module is placed in the faces of experimental aircraft (0.3mx0.3mx0.2m) of four top corners, as shown in Figure 3, the initial coordinates of the point fixed:,.
In the acquisition process, the capsule magnetic moment of reorientation and axis are consistent, Magnetoresistive sensor module placement plane the capsules in a straight line from point every 3cm orientation once and gradually move to the point, four Magnetoresistive sensor module after each position in turn-collecting data. As shown in Figure 5, Magnetoresistive sensor module A measured magnetic field strength is declining, Magnetoresistive sensor module B, and C magnetic trend gradually close, Magnetoresistive sensor module D measured magnetic field strength slowly rise. The experimental data and calculations-control, find the error in ± 10% range. Note This article design Magnetoresistive sensor module group to more accurately gauge the capsules in motion of the magnetic flux density.At the same time for capsule three to positioning and attitude, continuous 10 times the results of the calculation.
Select the position and orientation point for (0.15, 0.15, 0,, 0) and (0.15, 0.15, 0,, 0). Figure 6 to pose points (0.15, 0.15, 0,, 0) calculation results, visible in the diagram, the calculation of coordinates x, y are 0.15 fluctuations, error in ± 3%, and axis coordinate value and two values of the results is ideal, not marked. Figure 7 to pose points (0.15, 0.15, 0,, 0) the results of the calculation, this time capsule magnetic moment direction and axis angle is 30. From the coordinate values fluctuate in the figure, the error to a 7%, and the angle with the axis coordinates error of 5%, the other two parameters of the calculation result is very satisfactory.The above measurement and calculation results indicated that designs location detection system to be able to more accurately gauge the capsules in motion of the magnetic induction, resulting in accurate positioning a capsule of spatial position and orientation.
At the same time it should be noted that when the capsules in 4 groups Magnetoresistive sensor module measuring area Central, its calculation accuracy is high.6. conclusions
In this article, the authors presented a study on the location of the new experimental system, the use of high-sensitivity Magnetoresistive sensor module on micro-capsule space magnetic induction acquisition.
Theory and experiments have proved that can detect the permanent magnet magnetic field distribution in space to achieve on micro endoscopic capsule positioning. Through the analysis of the results of the experiment has proved that the positioning system for capsule in motion of the space position and direction of the position with high accuracy, can be effectively applied to micro endoscopic capsule in the body of the positioning, significantly improves the accuracy of clinical disease diagnosis.The author has used the innovation: the high sensitivity of three axis vertical Magnetoresistive sensor module, combined with zoom and acquisition circuits on the capsule space magnetic field detection, achieve accurate positioning.
This system than ever before, more accurate detection range, up to 20-30cm.Reference documents
[1] Iddan G, Meron G, Glukhovsky A, et al. Wireless Capsule Endoscopy.
Nature. 2000, 405 (6785):417 [2]http://www.microsystem.re.kr/ [3]http://www.cqjs.net/. [4]http://www.rfnorika.com/ [5]DARIO.P, DILLMAN.R. EURON-Techology Roadmaps.E.R.R network, Editor. April 23,2004, pages: 6-22. [6] Golden, et al. Apparatus and method for locating a medical tube in the body of a patient. US patent 5622169. [7] Hou Wensheng, Cheng Xiaolin Cheng Lin Pang, Peng Xiaoyan, Wu Xudong. in vivo micro appliance simplified model of magnetic orientation of. Instrumentation journal .2005, 26 (9): 895-897. [8] Hou Wensheng, Cheng Xiaolin Cheng Lin Pang, Peng Xiaoyan, Wu Xudong. based on the magnetic orientation of alimentary drug delivery device dynamic tracing technology of Beijing biomedical engineering .2005, 24 (1); 36-38. [9], Xu. Permanent magnet synchronous motor with vector control of magnetic orientation of DSP. Micro-computer information .2006, 5 (2): 171-172. [10] Fogel, L., Owens, A., Walsh, M. Artificial intelligence through simulated evolution. New York: Wiley, 1966 [11]http://www.hollywell.com.Author: Zhao Rui, male, born in 1979, the Han, master 's, mainly engaged in research on micro-electro-mechanical system design.
Email：zenzhaorui@sohu.comTutorial introduction: Huang Ping
, Male, born in 1957, the Han, Professor, mainly engaged in Tribology and micro electro mechanical system.
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