RU2223566C1 - Multi-position switch using the principle of electrocapillarity - Google Patents

Abstract

FIELD: applicable for switching of low-current signals. SUBSTANCE: the multi-position switch has a closed duct filled with liquid electrolyte in one part, and in the other - by non-conductive liquid insoluble in electrolyte and non-reacting with it. Breaks of the signal conductors are positioned equidistantly in the part of the duct filled with non-conductive liquid, and drops of mercury are positioned along the duct at a distance one from another between the breaks of the signal conductors used for closing them. In the part of the duct that is filled with electrolyte provision is made for expansions at a distance equal to the distance between the breaks of the signal conductors, and a drop of mercury used as a propeller. An electrode insulated from electrolyte is available under each area of duct expansion. EFFECT: reduced time of switching and power consumption with alternate closing of the signal conductors. 3 dwg

Description

 The invention relates to multi-position electric switches and can be used to switch low-current signals in sound technology, communication technology, as well as in electronic devices operating at high radiation background, for example, in devices at nuclear power plants and spacecraft.

 Known micromechanical relay with thermally controlled microdroplets of mercury [1]. The relay is made on a silicon substrate and contains two cavities with nickel heaters placed in them and a channel with a diameter of 6-25 microns connecting these cavities. The signal conductor passes perpendicular to the channel and is divided inside it. Inside the channel, next to the rupture of the signal conductor, a drop of mercury is placed. The channel and cavities are filled with deionized water, and the entire device is sealed with a glass plate. When a voltage is applied to one of the heaters in the cavity where it is located, the liquid boils and a vapor bubble forms in its volume. The liquid pushed by the bubble moves a drop of mercury to break the signal conductor, which closes in this way. The electric power supplied to the heater required for bubble formation is about 100 mW [1, 2], and the device switching time is about 10 ms [2].

 The disadvantage of a micromechanical relay with a thermally controlled microdroplet of mercury [1] is that relatively large energy costs are required for switching. A significant drawback is the fact that to maintain the relay in the on state requires a constant supply of electricity. Another disadvantage is that the switching time of such a relay is an order of magnitude longer than the switching time of a conventional and MEMS relay with solid-state contacts [2]. In addition, the specified relay is difficult to make multi-position, for example, for alternately closing several signal conductors.

 The aim of the invention is the creation of a multi-position electric switch with a short switching time, low power consumption for switching and not requiring power supply to maintain its condition.

 This goal is achieved by using a closed channel in which the breaks of several signal conductors are located equidistantly, using several drops of mercury placed in the channel in the volume of non-conductive liquid at a distance from each other, a multiple of the distance between the breaks of the signal conductors, using these drops to close the signal conductors electrocapillary mercury exposure to another drop of mercury located in another part of the channel in the electrolyte volume, as well as the presence of this part of the channel extensions with a pitch equal to the distance between the signal conductors breaks.

 The device of the proposed multi-position electric switch is illustrated in FIG. 1 and 2. Here 1 is a substrate (for example, glass or quartz), 2 is a closed channel, 3 are parts of the signal conductors, 4 are contact drops of mercury, 5 is an electrocapillary moving drop of mercury (droplet mover), 6 are electrodes isolated from the electrolyte, which serve to creating an electrocapillary effect, 7 - non-conductive liquid, insoluble in the electrolyte and not reacting with it, 8 - electrolyte. Figure 1 corresponds to the case of a switch with one contact drop, one drop-mover and four signal conductors.

The proposed multi-position electric switch operates as follows. A potential difference is applied to two adjacent electrodes, above one of which a droplet mover, so that the positive potential is on this electrode. Under the action of electrocapillary forces, the droplet mover moves to the neighboring electrode with a negative potential [3], involving the entire volume of liquid in the channel into motion. Since mercury does not wet the walls of the channel (the contact angle in the mercury / glass system is about θ = 130-150 ^o [4], and in the mercury / quartz system it is 145 ^o [1]), the Laplacian pressure her to the wider part of the channel. Under the influence of this pressure, the droplet mover occupies a stable position in the next channel expansion, FIG. 3. In this case, contact drops of mercury occupy new positions, closing other signal conductors. Thus, electrical signals are switched. The next switching is performed by applying a voltage of the corresponding polarity to the same or other adjacent electrodes.

 Since the dropping mover occupies stable positions in the channel expansions under the influence of Laplace pressure, the states of the switch are automatically fixed, that is, energy supply is not required to maintain them.

For a square channel, the indicated pressure is P _l = 4σcosθ (1 / d ₂ -1 / d ₁ ), where σ = 466 mN / m is the surface tension of mercury [1], θ≈140 ^o , d ₁ and d ₂ are less and a large channel width in cross sections of three phase substrate / mercury / liquid boundaries relating to opposite ends of the droplet. For a channel with typical dimensions d ₁ = 10 μm [1] and d ₂ = 11 μm, we obtain a pressure P _l = 13 kPa, that is, a significant value. This pressure with the channel cross-sectional area S = d ₁ ² = 10 ^-10 m ² will correspond to the Laplace force
F _l = P • S = 13 • 10 ³ Pa • 10 ^-10 m ² = 13 • 10 ^-7 N.

The obtained value of the Laplace force is comparable with the inertia force F _i acting on d ₁ • d ₁ • d ₁ drop of mercury when accelerating gravity g≈10 m / s ² and mercury density ρ = 13.6 • 10 ³ kg / m ³ [ 5]. This force is defined as F _i = m • g = ρ • d $\genfrac{}{}{0ex}{}{\text{3}}{\text{1}}$ • g = 13.6 • 10 ^-11 H, where m is the mass of the drop. Thus, F _l / F _i ≈10 ⁴ , that is, the drop will be stably held in the channel extensions when the acceleration switch is acted upon up to 10 ⁴ g.

Since the surface tension of mercury is large, the Laplace pressure caused by the curvature of the surface of the droplets will press them to the walls of the channel and prevent the electrolyte and non-conductive fluid from flowing from one part of their volume to another. This pressure for a square channel with a width of 10 μm is P = (4σ | cosθ |) / d ₁ = 143 kPa.

The switching time of the proposed device can be estimated from the experimentally known velocity of a mercury drop in a closed channel with a cross section of 250 • 20 μm, which is about 100 mm / s with a potential difference between 3 V electrodes and a current consumption of 10 μA [3]. Then, by a distance of the order of the channel width, which is close to 10 μm [1], the drop will shift in 0.1 ms. This time is an order of magnitude less than the switching time of MEMS, relays with solid state contacts [2] and is comparable with the time of switching conventional relays with solid state contacts [2]. In this case, the energy consumption for switching will be 3 V • 10 μA • 0.1 ms = 3 • 10 ^-9 J, that is, a negligible amount compared to the relay [1], which is 100 mWM • 10 ms = 10 ^-3 J. An increase in the potential difference between the electrodes leads to a directly proportional increase in the droplet velocity [3]. Therefore, it is possible to achieve at least an order of magnitude shorter switching time.

 Thus, the proposed multi-position electric switch has the following advantages: due to the fact that the movement of contact drops of mercury is carried out by electrocapillary action on a single drop of mercury (droplet mover), which under the influence of Laplace pressure occupies stable positions in the channel extensions, the device has a short switching time , consumes little energy to switch and does not require energy supply to maintain its state.

LITERATURE
1. A micromechanical relay with a thermally-driven mercury micro-drop. J. Simon, S. Safer and C.-J. Kim. Proc. IEEE Micro Electro Mechanical Systems Workshop, San Diego, USA, Feb. 1996, pp. 515-520. (URL: http //: cjmems.seas. Ucla.edu/papers/Simon_MEMS96.pdf).

 2. Mercury contact micromechanical relays. J. Kim, J. Simon, S. Safer and C. -J. Kim. Proc. 46th Annual Int. Relay Conf., Oak Brook, II, Apr. 1998, pp. 19-1-19-8. (URL: http //: cjmems.seas.ucla.edu/papers/Jw_relay98.pdf).

 3. Microactuation by continuous electrowetting phenomenon and silicon deep RIE process. J. Lee, C.-J. Kim. ASME Int. Mechanical Engineering Congress and Exposition, Anahein, CA. Nov. 1998, pp. 475-480. (URL: http: // cjmems. Seas.ucla.edu/papers/Jung_imece98.pdf).

 4. Adamson A. Physical chemistry of surfaces. - M.: Mir, 1979.

 5. Tables of physical quantities. Directory. Ed. Acad. I.K. Kikoina. - M.: Atomizdat, 1976.

Claims (1)

A multi-position electric switch, characterized in that there is a closed channel filled with a liquid electrolyte and a non-conductive liquid, insoluble in the electrolyte and not reacting with it, in the part of the channel filled with a non-conductive liquid there are equidistant gaps of several signal conductors, and at a distance multiple of the distance between the gaps of the signal conductors conductors, there are droplets of mercury that close certain breaks in the signal conductors, in the part of the channel filled with electrolyte there are extensions, one of which is the mercury drop-mover under each expansion channel is isolated from the electrolyte electrode, and switching is performed by moving droplet electrocapillary propulsor next channel expansion by applying a potential difference of two neighboring electrodes.

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