{"id":1188,"date":"2015-06-18T06:04:28","date_gmt":"2015-06-18T06:04:28","guid":{"rendered":"http:\/\/biomedpharmajournal.org\/?p=1188"},"modified":"2020-04-25T03:08:10","modified_gmt":"2020-04-25T03:08:10","slug":"development-of-draft-design-for-magnet-control-system-of-wireless-endoscopic-capsule","status":"publish","type":"post","link":"https:\/\/biomedpharmajournal.org\/staging\/vol8no1\/development-of-draft-design-for-magnet-control-system-of-wireless-endoscopic-capsule\/","title":{"rendered":"Development of Draft Design for Magnet Control System of Wireless Endoscopic Capsule"},"content":{"rendered":"

Introduction<\/strong><\/p>\n

At present, a lot of attentionis paid to control systems of wireless endoscopic capsules, because they help to stop the capsule in the exact part of the digestive system for more detailed examination. There are different approaches to control, for example, in [1] expandable capsule is described made of the electroactive polymer, which changes its size when electric current is applied.\u00a0 But control systems are often built on the basis of magnet field usage.<\/p>\n

Magnet systems for wireless endoscopic capsules control are described in many patent claims (descriptions) and scientific articles. For example, Sun et al. describe multi-applications of a magnet configuration in actuating wireless capsule endoscope [2]. Lien et al. propose a capsule endoscope magnetic control system [3]. Wakefield tells about magnetically propelled capsule endoscopy provides for the medical examination and treatment of the gastrointestinal tract, reproductive tract, trachea, lungs, vascular system or any accessible body cavity [4]. Kim et al. present a modified magnetic capsule endoscope that can be fixed inside the stomach and to monitor the gastric motility [5].<\/p>\n

The described methods differ from the one, described in this article. The developed solution helps to provide more accurate and quick magnet field change (in this case magnetic field distribution can be stable and can guarantee, that the capsule will move in the required direction and with the necessary speed), system fault tolerance increases.<\/p>\n

Control system development should be based on the results of detailed numerical modeling and prototype creation, which helps to check modeling results, to work in practice developed approaches to issue resolution and form general technical specifications for the system.<\/p>\n

Materials and Methods<\/strong><\/p>\n

To evaluate sample coil parameters it is necessary to estimate, which fields and field gradients are required for creation of efforts and moments, which can move and spin the coil.For this purpose preliminary analytical estimations were made. To solve the issue at first it is necessary to make some resistance to motion of the capsule to simulate the movement within intestine. At second, on the first stage it is convenient to compensate gravity to take into account only the interaction between the magnet field and the environmental resistance. That is why on this stage it is more preferable to put the capsule with some thick liquid, like glycerin. Thus, to evaluate the necessary power for capsule movement it was considered that is can be compared with thick friction force within the liquid [6]:<\/p>\n

Ffr<\/sub>= 3\u03c0d\u03bd\u03b7 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 (1)<\/p>\n

where d is a capsule diameter equal to 0.012 m, movement speed (\u03bd) equals10 mm\/sec (this speed is enough to move through 4-5 m tract for a reasonable amount of time), \u03b7 \u2013 dynamical liquid viscosity.<\/p>\n

Means, for glycerin with viscosity 1480* Pa*secat a temperature of 20\u00b0\u0421 the friction force will be:<\/p>\n

Ffr<\/sub>= 3*3.14*0.012(m)*0.01(m\/sec)*1480* (Pa*sec) = 1.67* \u041d = 0.167 g.wt<\/p>\n

Let us assume that some threshold value of force is equal to 0.2 g.wt.To determine the limit spin moment produced by the magnet field, let us evaluate the moment of a couple for friction force, evaluate the moment of a couple for friction forceaffecting the capsule, which is spinning around the axis perpendicular to the symmetry axis:<\/p>\n

Nfr<\/sub>= 2*Ffr<\/sub>*L\/2=3\u03c0d\u03bd\u03b7*L\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 (2)<\/p>\n

where L is the length of the capsule, thus:<\/p>\n

Nfr<\/sub> = 0.167(g.wt)*3(sm) = 0.5 g.wt*sm.<\/p>\n

Now for the evaluated limit values of force and moment let us calculate the coils parameters. Consider that the working volume, where the capsule will be places, is a cube 200 mm on a side. Because it was necessary to preliminary evaluate the coils parameters, we assume a coil with one circular turn with the current.<\/p>\n

Field of circular turn axis depends on the distance from the turn center [7]:<\/p>\n

\"Formula\"<\/p>\n

 <\/p>\n

Let us make a diagram of this dependence for the case, when the coil is recorded. In Fig. 1 the dependence of coefficient before\u00a0\u03bc0<\/sub>I\/R2\u00a0<\/sup>from the distance along Z axis between the coils in coil radius units; one turn is powered with current and is situated in -1 coordinate of coil radius.<\/p>\n\n\n\n
\u00a0\"Figure<\/td>\n\u00a0Figure 1<\/strong><\/p>\n

Click here to View figure<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/p>\n

To determine power characteristics of the coil it is necessary to take into consideration the least force influencing a dipole. This force is influencing the dipole placed in the furthest dot from the \u201cpulling\u201d coil with the least gradient on the distance of two coil radiuses. Zero gradient in the center of the turn was not taken into consideration, because this dot is knowingly placed outside of the working area.<\/sup><\/p>\n

Further magnetic moment for the magnet was determined. The magnet placed inside the capsule will be considered in approximation of the magnet dipole with the magnet moment and will be calculated according to the formula:<\/p>\n

\"Formula\"<\/p>\n

where\u00a0Br<\/em> is a remanent magnetic induction of the N38 magnet equal to 1.25 T, and V is the magnet\u2019s volume, therefore the magnet moment equals:<\/p>\n

\"Formula\"<\/p>\n

Let us put the force expression, which affects the dipole and is situated on the symmetry axis in the center of the system and in the center of the opposite turn without power (z = 2R) depending on the number of ampere-turns and turn radius:<\/p>\n

\"Formula\"<\/p>\n

 <\/p>\n

Results<\/strong><\/p>\n

Consider next several coil systems: two systems made from the copper hollow tube 6.35 mm in diameter, two systems made from copper wires 1 mm in diameter and two systems made from the copper wire 2 mm in diameter.<\/p>\n

    \n
  1. Copper hollow tube. Characteristics:<\/li>\n<\/ol>\n