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M I C R O V A L V E S

Tensile Stress Predetermined Micro-check Valve

Micro Systems Lab. in AJOU UNIVERSITY

Fig. 1. The structure of the micro valve.

Fabrication of a Two-way Pressure Reculation Micro Valve with the Anti-siphon Effect
S. W. Lee, H. J. Yoon, and S. S. Yang

ABSTRACT
  This paper presents the fabrication and test of an implantable two-way pressure regulation micro valve with the anti-siphon effect for the hydrocephalus patients. Hydrocephalus is a disease of the ventricular enlargement due to abnormal accumulation of cerebrospinal fluid (CSF). The CSF shunt system to be used to treat Hydrocephalus drains cerebrospinal fluid from the brain to the abdominal cavity [1]. The conventional CSF shunt system consists of a passive shunt valve, a ventricular catheter and a distal catheter. However, it is too complex and expensive. We developed the adaptive micro valve to be applied to hydrocephalus patients by using micromachining technology.
  Figure 2 shows the principle of the micro valve. The micro valve has an initial opening pressure attributed to the tensile stress in the silicone rubber membrane extended by the valve seat. The opening pressure exists in both cases of the forward flow and the backward flow. The opening and closing pressures in both directions of the two-way valve are determined by the valve structure and dimension. If the membrane tensile stress due to the inlet pressure is smaller than the built-in tensile stress in the membrane, the valve closes. When the inlet pressure is larger than the opening pressure, the valve opens. If the outlet pressure is negative and large enough, the valve closes, which is the anti-siphon effect.
  The structure of the micro valve is shown in Figure 1. The upper substrate has a silicone rubber membrane and the lower substrate consists of an inlet with a valve seat and a micro channel.
Each substrate is fabricated by the anisotropic etching with TMAH and the silicone rubber coating. Figure 4 shows the photograph of the fabricated micro valve. The size of the micro valve is 7.8 mm ´ 5.8 mm ´ 0.8 mm and the height of the valve sheet is 190 ± 20 ㎛. The width and the height of the micro channel are 300 ㎛ and 20 ㎛, respectively. The sizes of the membrane and the inlet are 4200 ㎛ and 800 ㎛, respectively.
However, the flow rate decreases as the outlet pressure decreases below the critical negative pressure. Finally, the valve closes when the negative inlet pressure is large enough. This result proves the anti-siphon effect of the valve. On the bases of this result, more researches are needed for the improvement of the valve quality by optimizing the valve structures.

Fig. 2. The principle of the electromagnetic flowmeter.


Fig. 3. The photograph of the fabricated micro valve.	Fig. 4. Von-mises stress profiles.


Fig. 5. Velocity profiles of forward flow.	Fig. 6. Velocity profiles of reverse flow.

KOREAN ABSTRACT

Micro Systems Lab. in AJOU UNIVERSITY

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