Conductive liquid-based latching switch device

Details Conductive liquid-based latching switch device Conductive liquid-based latching switch device

2002-02-21

2004-04-06

Donovan, Lincoln (Department: 2832)

Electricity: magnetically operated switches, magnets, and electr

Electromagnetically actuated switches

Utilizing conductive liquid

C200S182000

Reexamination Certificate

active

06717495

ABSTRACT:

BACKGROUND OF THE INVENTION
Switch devices based on conductive liquids have been known since the 19th century. Recently, electrically-controlled, highly-miniaturized conductive liquid-based switches have been proposed. Such switches can be fabricated in a semiconductor substrate, and therefore can be integrated with other electrical devices fabricated in the substrate. Such switches have the advantage that they provide a substantially higher isolation between the control signal and the switched circuit than switch devices based on semiconductor devices.
Published Japanese Patent Application No. S47-21645 discloses an example of a switch device for electrically switching solid electrodes by means of a conductive liquid. In this switch device, a conductive liquid such as mercury is movably disposed inside a cylinder. The switch device is designed so that the conductive liquid is moved to one side by a pressure differential in a gas provided on both sides of the conductive liquid. When the conductive liquid moves, it touches electrodes that extend into the interior of the cylinder and forms an electrical connection between the electrodes. A drawback to this structure, however, is that the electrical connection characteristics of the switch device deteriorate as a result of the surfaces of the electrodes being modified over time by intermittent contact with the conductive liquid.
U.S. Pat. No. 6,323,447, assigned to the assignees of this disclosure and, for the United States, incorporated herein by reference, discloses a switch device that solves the above-mentioned problem. In this switch device, the electrical path is selectively changed from a connected state to a disconnected state by a conductive liquid such as mercury. However, the electrodes remain in constant contact with the conductive liquid, and the connected or disconnected state of the electrical path is determined by whether the conductive liquid exists as a single entity (connected state) or is separated into two discontinuous entities (disconnected state). This eliminates the problem of poor connections that was a disadvantage of the switch device disclosed in published Japanese Patent Application No. S47-21645.
The switch device described in U.S. Pat. No. 6,323,447 is composed of an elongate passage filled with a conductive liquid and having electrodes located at its ends, a first cavity filled with non-conductive fluid and connected to approximately the mid-point of the passage by a single channel, a second cavity filled with non-conductive fluid and connected to near the ends of the passage by two channels. A heater is located in each cavity.
The heater in the first cavity is activated to switch the switch device to its OFF state. Heat generated by the heater causes the non-conductive fluid in the cavity to expand. The excess volume of the non-conductive fluid passes though the single channel to the passage where it forms a gap in the conductive liquid. The gap filled with the non-conductive fluid electrically insulates the electrodes from one another. The conductive liquid displaced by the non-conductive fluid enters the channels at the ends of the passage.
The heater in the second cavity is activated to switch the switch device to its ON state. Heat generated by the heater causes the non-conductive fluid in the cavity to expand. The excess volume of the non-conductive fluid passes though the two channels to displace the conductive liquid from the channels. The conductive liquid returning to the passage displaces the non-conductive fluid from the gap and the conductive liquid returns to its continuous state. In this state, the conductive liquid electrically connects the electrodes.
Some embodiments of the switch device described in U.S. Pat. No. 6,323,447 include latching structures located in the channels connecting the cavities to the passage. The latching structures hold the switch device in the switching state to which it has been switched after the respective heater has been de-energized. The latching structures require the conductive liquid to enter the channels, which have somewhat smaller cross-sectional dimensions than the passage. This increases both the energy required to operate the switch and the time required to change the switching state of the switch.
Moreover, the latching structures may provide inadequate latching reliability for some applications. A substantial amount of the conductive liquid connects each latching structure to the respective surface of the conductive liquid. The conductive liquid connecting the latching structure to the surface is not fully bounded. A stimulus, such as vibration or a temperature change, can therefore cause the form of the conductive liquid to change to one that changes the switching state of the switch device.
Published International Patent Application No. WO 01/46975, assigned to the assignees of this disclosure and, for the United States, incorporated herein by reference, discloses a switch device in which the conductive liquid is confined to the passage. This decreases both the energy required to operate the switch and the time required to change the switching state of the switch compared with the switch device shown disclosed in U.S. Pat. No. 6,323,447.
FIGS. 1A and 1B
show an example 10 of the conductive liquid-based switch device disclosed in published International Patent Application No. WO 01/46975. Switch device
10
is composed of elongate passage
12
, chambers
14
and
16
, channels
18
and
20
, non-conductive fluid
22
and
24
, conductive liquid
26
, electrodes
31
and
32
and heaters
50
and
52
. Electrodes
30
,
31
and
32
are disposed along the length of passage
12
. Conductive liquid
26
is located in the passage and has a volume less than that of the passage so that the conductive liquid only partially fills the passage. The conductive liquid therefore exists as a number of conductive liquid portions
40
,
41
and
42
.
Channel
18
extends from cavity
14
to passage
12
. Channel
20
extends from cavity
16
to the passage. The channels are offset from one another along the length of the passage and are located between electrode
30
and electrode
31
and between electrode
31
and electrode
32
, respectively. Cavities
14
and
16
and channels
18
and
20
are filled with non-conductive fluid
22
and
24
, respectively. Heaters
50
and
52
are located in cavities
14
and
16
, respectively, for regulating the internal pressure of the non-conductive fluid in the cavities. Channels
18
and
20
transfer the non-conductive fluid in cavities
14
and
16
, respectively, to and from passage
12
.
The switching operation of switch device
10
is as follows. In the initial switching state shown in
FIG. 1A
, heater
50
is energized and heater
52
is not energized. Conductive liquid portions
41
and
42
are joined together to form conductive liquid portion
41
,
42
. Conductive liquid portion
41
,
42
is separated from conductive liquid portion
40
by non-conductive fluid
22
. Thus, conductive liquid portion
41
,
42
electrically connects electrode
31
to electrode
32
, but non-conductive fluid
22
between conductive liquid portion
41
,
42
and conductive liquid portion
40
electrically insulates electrode
30
from electrode
31
.
Switch device
10
switches to the switching state shown in
FIG. 1B
when heater
50
is de-energized and heater
52
is energized. Heat generated by heater
52
causes non-conductive fluid
24
in cavity
16
to expand. Non-conductive fluid
24
passes through channel
20
and enters passage
12
. In the passage, non-conductive fluid
24
forms a gap in conductive liquid portion
41
,
42
(FIG.
1
A). The gap separates conductive liquid portion
41
,
42
into non-contiguous conductive liquid portions
41
and
42
. Separation of conductive liquid portion
41
,
42
into conductive liquid portions
41
and
42
expels non-conductive fluid
22
from the gap between conductive liquid portions
40
and
41
. This allows conductive liquid portions
40
and
41
to unite to

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