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Finite-Difference Modeling of Micromachine for Use in Gastrointestinal Endoscopy Mingyuan Gao, Chengzhi Hu, Zhenzhi Chen, Sheng Liu∗ , Member, IEEE, and Honghai Zhang
Abstract—An on-going research project is to develop a micromachine driven actively and wirelessly by external magnetic field. The micromachine has great potential for being used in medical fields such as gastrointestinal endoscopy. The ultimate goal is to develop a control mechanism capable of moving the wireless endoscope through the human’s gastrointestinal tract in any direction with minimum level of harm to human body. This paper establishes fluid dynamics model suitable for micromachine’s movement in intestinal tract, simulates pressure distributions of micromachine’s surface, and further calculates driving and load torques. Based on the fluid simulation results, parameters for generating appropriate rotating magnetic field can be calculated. This fluid dynamics simulation method provides a novel approach to analyze biomedical micromachine’s mechanical properties under external electromagnetic equipment. Index Terms—Biomedical equipment, finite-difference methods, gastrointestinal endoscopy, micromachine, rotating magnetic field.
I. INTRODUCTION APSULE endoscopy is an examination of the gastrointestinal track using a wireless capsule endoscope that contains digital camera, application-specified integrated circuit (ASIC) transmitter, antenna, illuminating LED-assisted imaging, and battery. Capsule endoscope with the size of a normal pill can be easily swallowed by patients of various ages. It takes pictures throughout the gastrointestinal tract by sending images to an external recorder, and thus, provides useful information for clinic diagnosis of gastrointestinal tract diseases [1]. However, recent products of capsule endoscope still have some problems: 1) no external guidance control system; 2) time and money consuming; and 3) unable to conduct on-time treatments such as drug delivery and body tissue collection. The movement of the capsule depends solely on the peristalsis system. Therefore, it takes around 6–8 h for an examination, and
C
Manuscript received April 14, 2009; revised May 24, 2009. First published July 17, 2009; current version published September 16, 2009. This work was supported by the National High Technology Research and Development Program of China under Ministry of Science and Technology (863 Program) (no. 2008AA04Z313). The work of M. Gao and C. Hu was supported by the Graduate Innovation Foundation Program from the Huazhong University of Science and Technology (no. HF0601108100). Asterisk indicates corresponding author. M. Gao, C. Hu, and Z. Chen are with the School of Mechanical Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China (e-mail:
[email protected];
[email protected];
[email protected]). ∗ S. Liu is with the School of Mechanical Science and Engineering, and Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China (e-mail:
[email protected]). H. Zhang is with the School of Mechanical Science and Engineering, and Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China (e-mail:
[email protected]). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TBME.2009.2026635
doctors cannot perform a pinpoint analysis once an irregular vision has been found. In addition, a camera in capsule takes thousands of photos in every part of the tract to prevent the possibility of missing an important picture. Therefore, hours of time are needed for doctors to organize and analyze a large number of images, still with a 60%–70% rate of success in diagnostics. All of these drawbacks render capsule endoscopy extremely high in cost, but extremely inefficient in terms of time spent and resources used [2]–[4]. With the development of microelectromechanical systems (MEMSs) technology, research and progress on a self-propelled capsule endoscope have been the topic of interests for several years [5]–[7]. A wide variety of active and wireless control mechanisms have been developed for self-propelled endoscopic capsule such as shape memory alloy (SMA) actuator, spiraltype micromachine, magnetic navigation, motor-legged robot, and hydraulic manipulator [8]–[13]. Ishiyama et al. in Tohoku University proposed one type of micromachine for capsule endoscopy [14]. Their micromachine was composed of a capsule dummy, an inside permanent magnet, and a spiral structure. The micromachine was rotated and propelled wirelessly by applying an external rotational magnetic field. They used 3-D finite-volume method for analyzing the swimming properties of a spiral-type magnetic micromachine, and calculated its swimming velocity, drag, and load torque [15]. In this paper, we theoretically analyzed the swimming properties of a spiral-type magnetic micromachine using the theories of fluid dynamics lubrication and the finite-difference methods. We also simulated rotating magnetic field and obtained optimal controlling parameters. We examined this analysis method, and compared our calculation result with the results from existing publications. II. METHODS A. Fluid Dynamics Model We use theories of hydrodynamic lubrication to analyze micromachine’s movement in the intestinal tract. For the model development, following assumptions are made: 1) the fluids in the tube are incompressible viscous fluids; 2) effects of anterior and posterior end of the machine is neglected; 3) active and passive deformation of the wall of intestinal tract is not considered; and 4) there is no inclination of the machine relative to the tube axis. Based on these assumptions, fluid dynamics model for micromachine’s motion in intestinal tract is established, as shown in Fig. 1. The micromachine, whose radius is r, rotates with the angular velocity ω, whereas intestinal tract with radius of R still holds relative to the selected coordinate. According to the
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Fig. 1.
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 56, NO. 10, OCTOBER 2009
Fluid dynamics models of capsule endoscope.
Fig. 3.
Illustration of rotating magnetic field’s generation.
Fig. 2. Illustration of micromachine driven by external magnetic field (redrawn based on [17]).
basic theory of lubrication, a thin film will form between micromachine’s surface and intestinal tract’s inner wall. Pressure will also be established on part of capsule’s surface, whose distributions are determined by the rotating direction and geometric profiles. Due to the pressure difference between the front and back of the spiral blade, the capsule endoscope will travel in a forward or backward direction in terms of the rotating direction, as shown in Fig. 2. But, we should know that it is appropriate to use lubrication theory when the distance between the wall and the machine surface is small, relative to the diameters of tube. According to capsule size and the intestinal specimen of pig shown in [16], the actual scales of film thickness is about 0–0.9 mm, which is far less than the scales of diameters of intestinal tract (8–12 mm). Surface roughness is another important factor that needs to be considered; however, the quantitative values of surface roughness of intestinal tract are still unavailable. We assume that the scales of surface roughness are far less than the scales of diameters in the intestinal tract for developing the following model.
Fig. 4. Illustration of guidance mechanism for micromachine in gastrointestinal tract.
a radial direction will be driven under external rotating magnetic field, and will move in the normal direction of rotating magnetic field plane [17]. Fig. 4 shows the guidance mechanism for the micromachine in the gastrointestinal tract. By changing normal direction of rotating magnetic field, we can control micromachine’s movement in any direction. C. Reynolds Equation and Electromagnetic Equation Compressible fluid’s lubrication problem is governed by Reynolds equations [18] ∂ ρh3 ∂p ∂ ρh3 ∂p + ∂x 12η ∂x ∂z 12η ∂z =U
B. Generation of Rotating Magnetic Field Fig. 3 illustrates the mechanism for generating rotating magnetic field. Two groups of Helmholtz coils (circular or quadrate) are set in an axial orthogonal position and stimulated by two way of sinusoidal current with π/2 phase difference. Then, we can obtain a rotating magnetic field plane, whose normal vector is perpendicular to both axes of two coils groups. The micromachine with an inside permanent magnet magnetized in
∂(ρh) ∂(ρh) ∂(ρh) +V + ∂x ∂z ∂t
(1)
where U = (u1 + u2 )/2 is the velocity in x-direction, V = (v1 + v2 )/2 is the velocity in z-direction, p is the pressure, η is the absolute viscosity, ρ is the fluid density, and h is the film thickness h = h0 [1 + ε cos (θ − θ0 )] + hg
(2)
where h0 is the radial gap between intestinal tract’s inner wall and micromachine’s outside surface and ε = e/h0 is the relative
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GAO et al.: FINITE-DIFFERENCE MODELING OF MICROMACHINE FOR USE IN GASTROINTESTINAL ENDOSCOPY
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eccentricity, where e is the eccentric distance, θ0 is the attitude angle, and hg is the groove depth. Vector form of Reynolds equations can be written as follows: 3 ρh ∂(ρh) → − ∇p = ∇(ρh U ) + . (3) ∇ 12η ∂t For incompressible fluid lubrication, the governing equation is
∇
h3 ∇p 12η
Fig. 5.
∂(h) → − = ∇(h U ) + . ∂t
(4)
Based on the Maxwell’s equations, we can obtain the following equations for transient analysis of rotating magnetic field [19]: σ
∂A −1 + ∇(µ−1 0 µr ∇A) = j ∂t nA = 0
(5) (6)
where µ0 is the permeability of vacuum, µr is the relative permeability, σ is the electric conductivity, A is the vector potential, n is the normal vector of solution boundary, and j denotes the externally applied current density. The Reynolds equation suitable for solving spiral-type micromachine can be written as ∂ ρh3 ∂p ∂ ρh3 ∂p + ∂x η ∂x ∂z η ∂z = 6U cos φ
∂(ρh) ∂(ρh) + 6U sin φ . ∂x ∂z
(7)
Reynolds boundary conditions are given as p=0
∂p = 0. ∂n
(8)
Define relevant dimensionless variables as follow, denoting them by an overbar: h h= (h0 = H − R − hg ) h0 x cos φ (r = R or r = R + hg ) θ= r z z= d p=
h20 cos φ p ηrU
2π d sin φ cos φ = cos φ n R 2πR S tan φ cos φ d = P cos φ = cos φ = n n δ=
Illustration of spiral parameters.
Fig. 5. The parameters used in our calculation are p = 6.6 mm, R = 1 mm, b = 0.2 mm, hg = 0.2 mm, h2 = 1 mm, and n = 1, 2, and 4. The length of the capsule is 15 mm. Substitute these variables into (7), the resulting dimensionless Reynolds equation is 3 3 h ∂p h ∂p 1 ∂ cos φ ∂h sin φ 1 ∂h ∂ + 2 = + . ∂θ 12 ∂θ δ ∂z 12 ∂z 2 ∂θ 2 δ ∂z (15) We suppose h is independent of z, and can obtain the following equation: 3h2
∂h ∂p ∂2 p 1 ∂2 p ∂h + h3 2 + 2 h3 2 = 6 cos φ . ∂θ ∂θ ∂θ δ ∂z ∂θ
Friction force in x and z direction can be written as follows [20], [21]: h ∂p ηU cos φ − Fx = dxdz (17) 2 ∂x h h ∂p ηU sin φ − dxdz. (18) Fz = 2 ∂z h Define dimensionless variables as follows, denoting them by an overbar: Fx =
h0 Fx LηrU
(19)
Fz =
h0 Fz . LηrU
(20)
(9) (10) (11) (12)
(16)
The resulting dimensionless equations of friction force are 1 h ∂p 1 − Fx = (21) dθdz 2 ∂θ cos φ h h ∂p 1 1 1 sin φ − Fz = (22) dθdz. 2 ∂z δ cos φ h cos φ
(13) (14)
where U is the circumferential velocity of micromachine, d is the vertical distance between two screw threads, hg is the groove depth, H is the inner radius of intestinal tract, P is the pitch of screw thread, S is the lead of screw thread, n is the number of leads, R is the radius of cylinder, and φ is the lead angle. Key parameters for spiral-type micromachine are shown in
D. Finite-Difference Method Our finite-difference technique divides the flow field into equally spaced nodes, as shown in Fig. 6. To economize on the use of parentheses of functional notation, subscripts i and j denote the position of an arbitrary, equally spaced node, and pi,j denotes the value of the pressure function at that node [22] pi,j = p(θ0 + i∆θ, z0 + j∆z).
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(23)
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Fig. 6.
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Definition sketch for capsule’s 2-D finite-difference grid. Fig. 8.
Visualization of the solved fluid field.
III. RESULTS AND DISCUSSION
Fig. 7.
Flow chart of fluid dynamics calculation.
An algebraic approximation for the derivative is ∂p 1 ≈ (pi+1,j − pi,j ) ∂θ ∆θ ∂2 p 1 ≈ (pi+1,j − 2pi,j + pi−1,j ). ∂θ2 ∆θ2
(24) (25)
In a similar manner, we can derive the equivalent difference expressions for the z direction as follows: ∂p 1 ≈ (pi,j +1 − pi,j ) ∂z ∆z ∂2 p 1 ≈ (pi,j +1 − 2pi,j + pi,j −1 ). 2 ∂z ∆z 2
(26) (27)
The finite-difference algorithm for calculating fluid dynamics properties was programmed. Fig. 7 shows the flow chart of fluid dynamics calculation. First, we input geometry and physics parameters such as radius, length, pitch, film depth, density, absolute viscosity, etc. Grid is generated, and initial value and boundary condition are input. Furthermore, we use iterative computation methods to calculate finite-difference equation, and then, judge the level of relative error. Once relative error satisfies the tolerance requirement, fluid dynamics parameters such as friction, drag, and load are output for subsequent analysis.
The intestinal mucus is known as non-Newtonian fluid; however, previous studies have revealed that assuming the fluid as Newtonian is appropriate for numerical calculation of intestinal tract [23]. In order to compare our calculation values with experimental results under similar fluid parameters, we used one type of liquid with absolute viscosity η = 100 Pa·s and density ρ = 985 kg/m3 , which is analogous to liquid with kinematic viscosity ν = 105 mm2 ·s and density ρ = 967 kg/m3 used in [15]. Fig. 8 is a visualization of the solved flow field. The arrows show the velocity of the fluid, and the background color shows the distribution of pressure. The inner line shows the profile of the micromachine. When the micromachine rotates in a clockwise direction, there is a pressure difference between two sides of the spiral blade. The load can be calculated by integrating pressure on micromachine’s surface. The drag and the load torque are calculated from the axial and tangential component of the viscous force acting on the micromachine’s surface, respectively. Fig. 9 shows the relation between the frequency and the swimming velocity of the micromachine. In this figure, the solid line plots the numerical calculation result. We use three types of spiral blades with number of spiral lines 1, 2, and 4, respectively. The swimming velocity increases in proportion to the frequency, and the 4 line spiral-blade micromachine has a greater swimming velocity than those of 1- and 2-line spiral blade. The order of magnitude of numerical calculation result is similar to the experimental results in [15]. Fig. 10 shows the relation between the frequency and the drag. The main contribution to the drag is the viscous force in the z direction generated on the micromachine’s surface (including cylinder and spiral blade). We use three types of spiral blades with number of spiral lines 1, 2, and 4, respectively. As a result of analysis, drag increases in proportion to the frequency, and the 4-line spiral-blade micromachine has a greater drag than those of 1- and 2-line spiral blades. We cannot discuss whether the calculated values of drag are exact or not. However, the order of magnitude in our calculation result is same with that of Ishiyama et al.’s calculation under similar fluid parameters [15].
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GAO et al.: FINITE-DIFFERENCE MODELING OF MICROMACHINE FOR USE IN GASTROINTESTINAL ENDOSCOPY
Fig. 9.
Fig. 10.
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Relation between frequency and velocity. Fig. 11.
Relation between frequency and load torque.
Fig. 12.
Relation between input current density and magnetic flux density.
Relation between frequency and drag.
Fig. 11 shows the relation between the frequency and the load torque. We use three types of spiral blades with a number of spiral lines 1, 2, and 4, respectively. As a result of the analysis, load torque increases in proportion to the frequency. It is found that the load torque of 4-line spiral blade is larger than those of the 1- and 2-line spiral blade. Since the velocity and load torque are much larger for 4-line spiral blade than those of 1 and 2 line spirals, it is clear that in order to swim micromachine at a faster speed with same frequency, multiple lines of spiral blade are needed, and therefore, greater driving force needs to be generated to overcome the load torque. We cannot discuss whether the calculate values of load torque are exact or not. However, the order of magnitude in our calculation result is same with that of Ishiyama et al.’s calculation under similar fluid parameters [15]. However, the value of locomotion velocity does not match with the experimental results very well; they are only similar from the view of order of magnitude. This may be because, effects of anterior and posterior ends of the micromachine are neglected, which may have certain contributions to reduce the frictional resistance, and thus, raise the locomotion velocity. In order to estimate the actual locomotion velocity of the micromachine moving inside the body, effects of anterior and posterior ends of the machine, active and passive deformation of the wall of intestinal tract, and inclination of the machine relative to the tube axis should be considered.
Fig. 12 shows the relation between input current density and corresponding magnetic flux density with different sizes of quadrate Helmholtz coils (510 mm in length and 225 mm2 in area of cross section, and 430 mm in length and 225 mm2 in area of cross section, respectively). In order to generate a rotating magnetic field, the magnitude of magnetic flux density for two groups of Helmholtz coils must be equivalent. As the figure mentioned before illustrates, when the magnitude of magnetic flux density required for driving capsule has been determined as B1 , the input current density for two groups of Helmholtz coils should be set to J1 and J2 , respectively. Fig. 13 shows the relation between driving torque and magnetic flux intensity with remanence 10 000 G, 5000 G, and 2000 G, respectively. The size of permanent magnet used in the calculation is Φ2 mm × 20 mm; the driving torque of micromachine depends on the magnetic flux density, the level of remanence, and the volume of permanent magnet. As the figure illustrates, the driving torque increases in proportion to the magnetic intensity, and thus, we can obtain required driving force by increasing magnetic density. Fig. 14 illustrates the profile of magnetic flux density in radial and axial directions, respectively. The magnitude of magnetic flux density varies with the differences of coordinate in axial and radial directions, and a high degree of uniformity is achieved
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Fig. 13.
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Driving torque as a function of magnetic intensity.
in the central region (−0.1–0.1 m). Two groups of quadrateHelmholtz coils are used to generate required magnetic field. The parameters of group1 are 510 mm in length and 225 mm2 in the area of cross section. The parameters of group2 are 430 mm in length and 225 mm2 in the area of cross section. Fig. 14 shows calculation results of group2. The magnetic flux density increases in proportion to the input current density J0 . When the value of J0 is set to 5 × 106 A/m2 , the magnitude of magnetic intensity in uniform area is approximately equal to 35.2 G, which is sufficient to drive the capsule endoscope moving in the intestinal tract. Fig. 15 shows the relationship between driving torque as a function of magnetic intensity and load torque as a function of frequency, and this figure is useful for determining control parameters of micromachine. The values of fluid density and absolute viscosity are supposed to be 985 kg/m3 and 100 Pa·s, respectively. Once the frequency f of capsule is determined by external magnetic equipment, the load torque can be obtained according to circle plot line, as shown before. In order to overcome the load torque, the magnitude of magnetic intensity must be adjusted to an appropriate value for generating enough driving force torque T , which can be obtained in terms of triangle plot line. In this figure, B is the threshold value of magnetic flux density. Therefore, this result shows that it is suitable to analyze micromachine’s locomotion in intestinal tract by using theories of fluid dynamics lubrication.
Fig. 14. Profile of magnetic flux density in (a) radial direction and (b) axial direction.
IV. SUMMARY Theories of fluid dynamics lubrication and finite-difference method had been used to analyze and calculate micromachine’s fluid dynamics properties in gastrointestinal tract. This numerical method was able to calculate the velocity, pressure distribution, and load torque of the micromachine. In addition, we simulated rotating magnetic field and calculated driving torque of the micromachine. By taking both fluid and electromagnetic field into consideration, we obtain optimal electromagnetic parameters for controlling micromachine. The order of magnitude of calculation results was same with that of existed publications under similar fluid parameters; it proved that the present method
Fig. 15.
Relation between driving torque and load torque.
was suitable for engineering analysis of micromachine for use in gastrointestinal endoscopy under external magnetic equipment. REFERENCES [1] G. Iddan, G. Meron, A. Glukhovsky, and P. Swain, “Wireless capsule endoscopy,” Nature, vol. 405, pp. 417–417, 2000. [2] K. Sandrasegaran, D. D. T. Maglinte, S. G. Jennings, and M. V. Chiorean, “Capsule endoscopy and imaging tests in the elective investigation of small bowel disease,” Clin. Radiol., vol. 63, pp. 712–723, Jun. 2008.
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GAO et al.: FINITE-DIFFERENCE MODELING OF MICROMACHINE FOR USE IN GASTROINTESTINAL ENDOSCOPY
[3] M. Hadithi, G. D. N. Heine, M. Jacobs, A. A. von Bodegraven, and C. J. J. Mulder, “A prospective study comparing video capsule endoscopy with double-balloon enteroscopy in patients with obscure gastrointestinal bleeding,” Amer. J. Gastroenterol., vol. 101, pp. 52–57, Jan. 2006. [4] D. Christodoulou, G. Haber, U. Beejay, S. J. Tang, S. Zanati, R. Petroniene, M. Cirocco, P. Kortan, G. Kandel, A. Tatsioni, E. Tsianos, and N. Marcon, “Reproducibility of wireless capsule endoscopy in the investigation of chronic obscure gastrointestinal bleeding,” Can. J. Gastroenterol., vol. 21, pp. 707–714, Nov. 2007. [5] J. Daveson and M. Appleyard, “Future perspectives of small bowel capsule endoscopy,” in Proc. 10th Endosc. Forum Jpn., 2008, pp. 262–270. [6] M. Delvaux and G. Gay, “Capsule endoscopy: Technique and indications,” Best Pract. Res. Clin. Gastroenterol., vol. 22, pp. 813–837, 2008. [7] D. K. Iakovidis, S. Tsevas, D. Maroulis, and A. Polydorou, “Unsupervised summarisation of capsule endoscopy video,” in Proc. 4th Int. IEEE Conf. Intell. Syst., 2008, pp. 140–145. [8] B. Kim, S. Lee, J. H. Park, and J. O. Park, “Design and fabrication of a locomotive mechanism for capsule-type endoscopes using shape memory alloys (SMAs),” IEEE/ASME Trans. Mechatronics, vol. 10, no. 1, pp. 77– 86, Feb. 2005. [9] K. Ishiyama, K. I. Arai, M. Sendoh, and A. Yamazaki, “Spiral-type micromachine for medical applications,” in Proc. Int. Symp. Micromechatron. Human Sci., 2000, pp. 65–69. [10] I. Kassim, W. S. Ng, G. Feng, and S. J. Phee, “Review of locomotion techniques for robotic colonoscopy,” in Proc. 20th IEEE Int. Conf. Robot. Autom. (ICRA), 2003, pp. 1086–1091. [11] F. Carpi, S. Galbiati, and A. Carpi, “Controlled navigation of endoscopic capsules: Concept and preliminary experimental investigations,” IEEE Trans. Biomed. Eng., vol. 54, no. 11, pp. 2028–2036, Nov. 2007. [12] M. Quirini, A. Menciassi, S. Scapellato, C. Stefanini, and P. Dario, “Design and fabrication of a motor legged capsule for the active exploration of the gastrointestinal tract,” IEEE/ASME Trans. Mechatronics, vol. 13, no. 2, pp. 169–179, Apr. 2008. [13] J. Peirs, D. Reynaerts, and H. Van, “Design of miniature parallel manipulators for integration in a self-propelling endoscope,” in Proc. Eurosens. XIII Meeting, 1999, pp. 409–417. [14] K. Ishiyama, M. Sendoh, A. Yamazaki, and K. I. Aral, “Swimming micro-machine driven by magnetic torque,” Physical, vol. A-91, no. 1–2, pp. 141–144, Jun. 2001. [15] A. Yamazaki, M. Sendoh, K. Ishiyama, K. I. Arai, and T. Hayase, “Threedimensional analysis of swimming properties of the spiral-type magnetic micro-machine,” Sens. Actuators, vol. A-105, pp. 103–108, 2003. [16] N. K. Baek, I. H. Sung, and D. E. Kim, “Frictional resistance characteristics of a capsule inside the intestine for microendoscope design,” in Proc. Inst. Mech. Eng. H, J. Eng. Med., vol. 218, pp. 193–201, May 2004. [17] M. Sendoh, K. Ishiyama, and K.-I. Arai, “Fabrication of magnetic actuator for use in a capsule endoscope,” IEEE Trans. Magn., vol. 39, no. 5, pp. 3232–3234, Sep. 2003. [18] B. J. Hamrock, Fundamentals of Fluid Film Lubrication. New York: McGraw-Hill, 1994, pp. 141–165. [19] R. P. Feynman, R. B. Leighton, and M. Sands, The Feynman Lectures on Physics, vol. 2. Reading, MA: Addison-Wesley, 1964, ch. 14. [20] X. F. Ma, Y. S. Zhou, and B. Chen, “Theoretical analysis and experimental research on a medical micro-robot,” (in Chinese), Chin. J. Mech. Eng., vol. 40, no. 7, pp. 124–127, Jul. 2004. [21] J. K. Wu, X. N. Ma, and Y. Y. Huang, “Parameter comparison calculations for oil film stability of grooved liquid-lubricated journal bearing,” (in Chinese), Trans. Tribol., vol. 19, no. 1, pp. 56–60, Mar. 1999. [22] F. M. White, Fluid Mechanics, 4th ed. New York: McGraw-Hill, 1999, pp. 540–543. [23] R. L. Powell, E. F. Aharonson, and W. H. Schwarz, “Rheological behavior of normal tracheobronchial mucus of canines,” J. Appl. Physiol., vol. 37, pp. 447–451, 1974.
Mingyuan Gao was born in Yinchuan, China, in 1985. He received the B.S. degree in mechanical design and manufacturing in 2008 from Huazhong University of Science and Technology, Wuhan, China, where he is currently working toward the Master’s degree. His current research interests include biomedical equipment, biomechanical modeling, and microsystems packaging.
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Chengzhi Hu received the B.S. degree in measuring and control technology, and instrumentation in 2008 from Huazhong University of Science and Technology, Wuhan, China, where he is currently working toward the Master’s degree in micromanufacturing technology. His current research interests include simulation and analysis of electromagnetics, structure design and fluid dynamics modeling, microsystems packaging technology, and active control of gastrointestinal endoscopy.
Zhenzhi Chen was born in China in 1985. He received the Bachelor’s degree in mechanical science and engineering from Harbin Institute of Technology, Harbin, China, in 2008. He is currently working toward the M.S. degree at the Institute of Microsystems, Huazhong University of Science and Technology, Wuhan, China. His current research interests include design and modeling for self-propelled robotic endoscopy system.
Sheng Liu (M’93) received the B.S. and M.S. degrees from Nanjing University of Aeronautics and Astronautics, Nanjing, China, in 1983 and 1986, respectively, and the Ph.D. degree from Stanford University, Stanford, CA, in 1992. During August 1995, he was an Assistant Professor of mechanical engineering at Wayne State University, Detroit, MI. In 1992, he joined Florida Institute of Technology as an Assistant Professor of mechanical and aerospace engineering. He is currently with the School of Mechanical Science and Engineering, and Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, China. His current research interests include microsystems/nanoelectromechanical systems, LED design and manufacturing, system packaging and integration, reliability, smart materials and composites, and mechanics of materials and structures. Dr. Liu is a member of the American Institute of Aeronautics and Astronautics (AIAA), the American Society of Mechanical Engineers (ASME), the American Society for Testing and Materials (ASTM), the Integrated Systems Health Management, and the Society for the Advancement of Material and Process Engineering (SAMPE).
Honghai Zhang received the Ph.D. degree in mechanical manufacturing engineering from Huazhong University of Science and Technology (HUST), Wuhan, China, in 1988. He is currently a Professor in the School of Mechanical Science and Engineering, and Wuhan National Laboratory for Optoelectronics, HUST. His current research interests include micro-/ nanomanufacturing technology, including nanoimprinting, microelectromechanical system devices, and microjetting. He has developed a number of micromanufacturing equipments, such as multifunctionally metrological scanning probe microscopy, nanoimprinting equipment, microjetting platform, and equipment for measurement and control of surface microcharacteristics in precision process.
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