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BACKGROUND OF THE INVENTION
The present invention relates to a two-dimensional electric conductor
designed to function as an electric switch and enabling the formation of
an electric circuit comprising any number of electric switches located at
any point on a flat surface.
The two-dimensional electric conductor according to the present invention
is designed to solve the problem of closing an electric circuit by
applying given pressure at any point on a flat surface. Such performance
is frequently required in a number of technical applications, e.g. for
producing an electric signal for activating a relay, for example, and so
indicating that external pressure is being applied at any point on a
surface.
At present, this problem can only be solved approximately, by setting out a
number of separate switches having their terminals connected to conductors
on an electric line. Such a system, however, only enables control of a
limited number of points on the surface. What is more, the said electric
line is unreliable and involves the use of numerous switches and electric
conductors, connection of which is both time-consuming and expensive.
SUMMARY OF THE INVENTION
The aim of the present invention is to provide a two-dimensional electric
conductor designed to function as an electric switch, and to solve the
aforementioned problem without involving any of the aforementioned
drawbacks. With this aim in view, according to the present invention,
there is provided a two-dimensional electric conductor, characterised by
the fact that it comprises a first and second electric conducting element,
each in the form of a flat plate; and at least a third electric conducting
element, also in the form of a flat plate; the said first and second
electric conducting elements being arranged in such a manner that one
surface contacts a surface on the said third electric conducting element;
and a spacer element formed from electrically-insulating material being
arranged between the opposite surfaces of the said third element and at
least one of the said first and second elements, so as to at least
partially shield the said two surfaces; the structure of the material from
which the said third electric conducting element is formed comprising a
supporting matrix formed from flexible, electrically-insulating material
and particles of electrically-conductive material scattered in random,
substantially uniform manner inside cells on the said matrix; said cells
communicating at least partially with one another, and being at least
partially larger in size than the respective particles of
electrically-conductive material housed inside the same.
The structure of the said material from which the said third electric
conducting element is formed is as described in U.S. patent application
Ser. No. 07/145,612, filed Jan. 19, 1988, by the present Applicant and
entitled: "Electric resistor designed for use as an electric conducting
element in an electric circuit, and relative manufacturing process", to
which the reader is referred for further details. The entire disclosure of
U.S. patent application Ser. No. 07/145,612 is incorporated herein by
reference.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be described, by way of a nonlimiting example,
with reference to the accompanying drawings, in which:
FIG. 1 shows a cross section of a first embodiment of a two-dimensonal
electric conductor in accordance with the teachings of the present
invention;
FIG. 2 shows a larger-scale detail of the FIG. 1 section;
FIGS. 3 and 4 show cross sections of a second and third embodiment
respectively of the two-dimensional electric conductor according to the
present invention;
FIGS. 5 and 6 show two structural sections, to different scales, of a
portion of the resistor according to the present invention;
The graphs in FIGS. 7 to 10 show the variation in electrical resistance of
the resistor according to the present invention, as a function of the
pressure exerted on the resistor itself;
FIG. 11 shows a schematic diagram of a test circuit arrangement for
plotting the results shown in FIGS. 7 to 10; and
FIGS. 12 to 16 show schematic diagrams of the basic stages in the process
for producing the electric resistor according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
With reference to FIG. 1, the two-dimensional electric conductor according
to the present invention is substantially in the form of a flat plate, and
comprises a first and second electric conducting element 1 and 2, and at
least a third electric conducting element 3, each in the form of a flat
plate. In the FIG. 1 embodiment, provision is made for a pair of third
conducting elements 3a and 3b. The said conducting elements are arranged
one on top of the other, so as to form a structure in which upper surface
4 of element 3a contacts lower surface 5 of element 1, and lower surface 6
of element 3b contacts surface 7 of element 2. Between surfaces 8 and 9 of
elements 3a and 3b, there is provided a spacer element 10 formed from
electrically-insulating material; and on the outer surfaces of elements 1
and 2, there are provided layers of insulating material 12 and 13.
The material of the said third conducting element (3a and 3b in the FIG. 1
embodiment) presents a structure comprising a supporting matrix 14 (FIG.
2) formed from flexible, electrically-insulating material, and particles
15 of electrically-conductive material scattered in random, substantially
uniform manner inside cells in the said matrix. The said cells
communicate, at least partially, with one another, and are, at least
partially, larger than the respective particles of electrically-conductive
material housed inside the same, so as to define gaps 16 between the
surfaces of particles 15 and the said cells.
A material presenting the aforementioned structure is described in U.S.
patent application Ser. No. 07/145,612, filed Jan. 19, 1988, by the
present Applicant and entitled: "Electric resistor designed for use as an
electric conducting element in an electric circuit, and relative
manufacturing process."
As stated in the aforementioned Patent Application, the said material is
electrically conductive, and presents the favourable property of
increasing in electrical conductivity as increasing pressure is applied on
it. Such favourable performance is due to improved electrical conductivity
of chains of particles 15. In fact, as increasing pressure is applied on
the material, this improves the conductivity of chains of contacting
particles 15, while at the same time rendering conductive any chains of
non-contacting particles 15, when sufficient pressure is applied for
reducing or eliminating gaps 6 between the said non-contacting particles
15. Conducting elements 1 and 2 may be formed from wire mesh.
To enable a clearer understanding of the process according to which the
third conducting elements 3a and 3b are formed, a description will first
be given of the structure of the resistor so formed.
The structure of the resistor is as shown in FIGS. 5 and 6, which show
sections of a portion of the resistor enlarged a few hundred times.
The said resistor substantially comprises a supporting matrix 214, formed
from flexible, electrically insulating material, and particles 215 of
electrically conductive material arranged in substantially uniform manner
inside corresponding cells 230 on the said matrix 214. As in the
embodiment shown, the said particles preferably consist of granules of
electrically conductive material. As shown in the larger-scale section in
FIG. 6, at least some (e.g. 50 to 90%) of the said cells communicate with
one another, and in a number of cases, are exactly the same shape and size
as the granules contained inside. Other cells, on the other hand, are
slightly larger than the said granules, so as to form a minute gap 216
between at least part of the outer surface of the granule and the
corresponding inner surface portion of the respective cell.
The arrangement of cells 230, and therefore also of granules 215, inside
matrix 214 is entirely random. Though the advantages of the resistor
according to the present invention are obtainable even if only a few of
cells 230 communicate with one another, it is nevertheless preferable for
most of them to do so. For best results, the estimated percentage of
communicating cells is around 50-90%.
Though conducting granules 215 may be of any size, this conveniently ranges
between 10 and 250 microns. Likewise, granules 15 may be of any shape and,
in this case, are preferably irregular, as shown in FIGS. 5 and 6.
Matrix 214 may be formed from any type of electrically insulating material,
providing it is flexible enough to flex, when a given pressure is applied
on the resistor, and return to its original shape when such pressure is
released. Furthermore, the material used for the matrix must be capable of
assuming a first state, in which it is sufficiently liquid for it to be
injected into a granule structure statistically presenting each of the
said granules arranged at least partially contacting the adjacent granules
with which it defines a number of gaps; and a second state in which it is
both solid and flexible. The viscosity of the liquid material conveniently
ranges from 500 to 10,000 centipoise.
Matrix 214 may conveniently be formed from synthetic resin, preferably a
synthetic thermoplastic resin, which presents all the aforementioned
characteristics and is thus especially suitable for injection into a
granule structure of the aforementioned type.
Though the size of granules 215, which depends on the size of the resistor
being produced, is not a critical factor, the said granules are preferably
very small, ranging in size from 10 to 250 microns.
The conducting material used for the granules may be any type of metal,
e.g. iron, copper, or any type of metal alloy, or non-metal material, such
as graphite or carbon. The materials for matrix 214 and granules 215 may
thus be selected from a wide range of categories, providing they present
the characteristics already mentioned.
The material employed for matrix 214 which, as already stated, must be
flexible and insulating, is preferably, though not necessarily, so
precompressed inside matrix 214 itself as to exert sufficient pressure on
particles 215 to maintain contact between the same. It follows, therefore,
that each minute element of the said matrix 214 material is in a
sufficiently marked state of triaxial precompression as to exert on
adjacent elements, in particular particles 215, far greater stress, for
producing contact pressure between the surfaces of the said particles,
than if the said triaxial precompression were not provided for. As will be
made clearer later on, such a state of triaxial precompression is a direct
consequence of the process according to the present invention.
With the structure described and shown in FIGS. 5 and 6, the resistor
according to the present invention presents an extremely large number of
granules 215 of conducting material, which granules either contact one
another, or are separated from adjacent granules by extremely small gaps
216 which may be readily bridged when given pressure is applied on the
resistor. This results in the formation, inside the said structure, of a
number of electrical conductors, each consisting of a chain comprising an
extremely large number of granules 215, which are normally already
arranged contacting one another inside the said structure. Each of the
said chains may electrically connect end surfaces 50 and 60 on the
resistor directly, as shown by dotted line C1 in FIG. 5. Alternatively,
chains may be formed inside the resistor, as shown by dotted line C2 in
FIG. 5, in which the individual granules in the chain are partly arranged
contacting one another directly, and partly separated solely by gaps 216.
The granules in such chains may be brought into contact, as in the case of
chain C1, by subjecting surfaces 50 and 60 on the resistor to a given
pressure sufficient to flex the material of matrix 214 so bridge the said
gaps for bringing the adjacent granules separated by the same into direct
contact.
The process according to the present invention is as follows.
The first step is to prepare a homogeneous system comprising particles,
preferably granules, of a first electrically conductive material arranged
in substantially uniform manner inside a mass of a second liquid material
which, when solidified, is both electrically insulating and flexible. The
mass of the said second liquid material is then solidified to form a
supporting matrix for the granules. According to the present invention,
throughout solidification of the said second material, a given pressure is
applied on the system for the purpose of producing triaxial precompression
of the said second material when solidified. Such pressure, which is
maintained substantially constant throughout solidification, ranges from a
few tenths of a N/mm.sup.2 to a few N/mm.sup.2.
For forming the said homogeneous system, a granule structure is first
formed, which structure statistically presents each granule arranged at
least partially contacting the adjacent granules, with which it defines a
number of gaps which are then injected with the said second liquid
material. The said second material may be liquified by simply heating it
to a given temperature. For solidifying it, cooling is usually sufficient.
In the case of synthetic resins, however, these must be solidified by
means of curing.
The process according to the present invention may comprise the following
stages.
A first stage, in which a mass of electrically conductive granules 116 is
formed, for example, inside an appropriate vessel 115 (FIG. 12). For this
purpose, the granules, after being poured into the said vessel, are
vibrated so as to enable settling. The bottom of vessel 115 is
conveniently either porous or provided with holes for letting out the air
or gas trapped between the granules.
A second stage, as shown in FIG. 13, in which the mass of granules 116 is
compacted by subjecting it to a given pressure, e.g. by means of piston
117, applied in any appropriate manner on the upper surface of mass 116.
This produces a granule structure in which, statistically, at least part
of the surface of each granule is arranged contacting surface portions of
the adjacent granules, with gaps inbetween.
As shown in FIG. 13, piston 117 is conveniently provided with a tank 118
containing the said second material in liquid form; which liquid material
may be forced, e.g. by a second piston 119, through hole 120 into a
chamber 121 defined between the upper surface of granules 116 and the
lower surface of piston 117 as shown clearly in FIG. 14. The said second
liquid material in tank 118 is a material which may be solidified and,
when it is, is both insulating and flexible. In the event the said
material is liquified by heating, appropriate heating means (not shown)
are also provided for.
A third stage (FIGS. 14 and 15) in which piston 119 moves down and piston
117 up, so as to force a given amount of the said second liquid material
inside chamber 121 (FIG. 14). Piston 117 is then brought down for
producing a given pressure inside the liquid material in chamber 121 and
so forcing it to flow into the gaps between the granules in mass 116 and
form, with the said granules, the said homogeneous system. At the same
time, any air between the granules is expelled through the porous bottom
of vessel 115. The pressure produced by piston 117, at this stage, inside
the liquid material mainly depends on the size of the granules, the
viscosity of the liquid, the height of the granule mass being impregnated,
and required impregnating time.
Penetration of the liquid material inside the gaps in granule mass 116 has
been found to have no noticeable effect on the granule arrangement
produced in the compacting stage.
A fourth stage (FIG. 15) in which the homogeneous system of granules and
liquid material produced in the foregoing stage is substantially
solidified. This may be achieved by simply allowing the system to cool and
the said second liquid material to set. At this stage, changes may be
observed in the structure of the said second material due, for example, to
curing of the same.
It has been found necessary to dose the liquid material fed into chamber
121 prior to the injection stage, in such a manner as to ensure that it is
sufficient to impregnate only a large part of granule mass 116 leaving a
nonimpregnated layer 122 (e.g. of about 25%). In like manner, the liquid
material flowing inside the gaps between the granules is subjected solely
to atmospheric pressure through the porous bottom of vessel 115. The
granules, on the other hand, (be they impregnated or not), are subjected
to the pressure exerted by piston 117, as shown in FIG. 16. The said
pressure is applied evenly over all the contact points between adjacent
granules, and is what determines the specific electrical resistance of the
resulting material. That is to say, using the same type of granules and
liquid material, an increase in the said pressure results, within certain
limits, in a reduction of the specific electrical resistance of the
resulting material. The said pressure must be maintained constant until
the liquid material has set, and must be at least equal or greater than
the compacting pressure applied in stage 2 (FIG. 13).
Though the said pressure may be selected from within a very wide range,
convenient pressure values have been found to range from a few tenths of a
N/mm.sup.2 to a few N/mm.sup.2. For resistors prepared as described in the
following examples, the following pressures were selected:
Example 1 : 1.17 N/mm.sup.2
Example 2 : 0.62 N/mm.sup.2
Example 3 : 1.56 N/mm.sup.2
Example 4 : 2.35 N/mm.sup.2
Example 5 : 1.17 N/mm.sup.2
The mass of material so formed inside vessel 115 may be cut, using standard
mechanical methods, into any shape or size for producing the electric
resistor according to the present invention.
To those skilled in the art it will be clear that changes may be made to
both the resistor and the process as described and illustrated herein
without, however, departing from the scope of the present invention.
In particular, granules 215 arranged inside matrix 214 may be replaced by
particles of electrically conductive material of any shape or size, e.g.
short fibres.
For preparing the said homogeneous system comprising particles of a first
electrically conductive material distributed inside a mass of a second
liquid material which, when solidified, is both electrically insulating
and flexible, processing stages may be adopted other than those described
with reference to FIGS. 12 to 16.
The said homogeneous system, in fact, may be obtained by mixing the said
particles mechanically with the said second liquid material, using any
appropriate means for the purpose.
According to the aforementioned variation, throughout solidification of the
said second material, the said system is forced against a porous (or
punched) septum for letting out, through the said septum, at least part of
the said second liquid material. The pressure so produced may be
maintained until the said second material solidifies, so as to produce the
said triaxial precompression in the solidified said second material.
For achieving the said precompression, the said system may be spun
throughout solidification of the said second liquid material.
When incorporated in an electric circuit, performance of the resistor
according to the present invention is as follows.
If no external pressure is applied on the resistor, and end surfaces 50 and
60 are connected electrically via appropriate conductors, electric current
may be fed through the resistor as in any type of rheophore. The density
of the current feedable through the resistor has been found to be very
high, at times in the region of ten A/cm.sup.2. When idle, the resistance
of the resistor according to the present invention may, therefore, be low
enough to produce an electrical conductor capable of handling a high
current density, as required for supplying a circuit component or device.
A number of resistance values relative to resistors produced by
appropriately selecting the characteristics of the particles and the
material of matrix 214, and the parameters of the present process, are
shown in the Examples given later on.
Total resistance of the resistor so formed has been found to be constant,
and dependent solely on the structure of the resistor, in particular, the
number and size of communicating cells 230 in matrix 214, and the number
of gaps 216 separating adjacent granules 215.
By appropriately selecting the aforementioned parameters, some of which
depend on the process described, a resistor may be produced having a given
prearranged resistance. When pressure is applied perpendicularly to
surfaces 50 and 60, the electrical resistance measured perpendicularly to
the said surfaces is reduced in direct proportion to the amount of
pressure applied. FIGS. 7 to 10 show four resistance-pressure graphs by
way of examples and relative to four different types of resistors, the
characteristics of which will be discussed later on. As shown in the said
graphs, the fall in resistance as a function of pressure is a gradual
process represented by a curve usually presenting a steep initial portion.
Even very light pressure, such as might be applied manually, has been
found to produce a considerable fall in resistance. In the case of a
resistor having the resistance-pressure characteristics shown in FIG. 10,
starting resistance was reduced to less than one percent by simply
applying a pressure of around 1 N/mm.sup.2 (about 10 kg/cm.sup.2). With a
different structure and pressures of around 2 N/mm.sup.2 (about 20
kg/cm.sup.2), starting resistance may be reduced by 1/3 (as shown in the
FIG. 7 graph).
If the pressure applied on the resistor according to the present invention
is maintained constant (or zero pressure is applied), electrical
performance of the resistor has been found to conform with both Ohm's and
Joule's law. For application purposes, it is especially important to
prevent the heat generated inside the resistor (Joule effect) from
damaging the structure. This obviously entails knowing a good deal about
the thermal performance of the material from which the supporting matrix
is formed.
Assuming the resistor according to the present invention is capable of
withstanding an average maximum temperature of 50.degree. C., under normal
heat exchange conditions with an ambient air temperature of 20.degree. C.,
the density of the current feedable through the resistor ranges from 0.2
A/cm.sup.2 (Example 4) to 11 A/cm.sup.2 (Example 5) providing no external
pressure is applied.
In the presence of external pressure, such favourable performance of the
electric resistor according to the present invention is probably due to
improved electrical conductivity of granule chains such as C1 and C2 in
FIG. 5. In fact, as pressure increases, the conductivity of
contacting-granule chains (such as C1) increases due to improved
electrical contact between adjacent granules, both on account of the
pressure with which one granule is thrust against another, and the
increased contact area between adjacent granules. In addition to this,
granule chains such as C2, in which the adjacent granules are separated by
gaps 216, also become conductive when a given external pressure is applied
for bridging the gaps between adjacent pairs of otherwise non-conductive
granules.
Total electrical conductivity of the granule chains increases gradually
alongside increasing pressure by virtue of matrix 14 being formed from
flexible material, and by virtue of the said material being precompressed
triaxially. As a result, adjacent granules separated by gaps 216 are
gradually brought together, and the contact area of the granules already
contacting one another is increased gradually as flexing of the matrix
material increases. Each specific external pressure is obviously related
to a given resistor structure and a given total conducting capacity of the
same. When external pressure is released, the resistor returns to its
initial unflexed configuration and, therefore, also its initial resistance
rating.
In the said initial unflexed configuration, the electrical performance of
the material the resistor is made of has been found to be isotropic, in
the sense that the specific resistance of the material is in no way
affected by the direction in which it is measured. If, on the other hand,
the material the resistor according to the present invention is made of is
flexed by applying external pressure in a given direction, the specific
resistance of the material has been found to vary continuously in the said
direction, depending on the amount and direction of the flexing pressure
applied.
To illustrate the electrical performance of the resistor according to the
present invention, when subjected to varying external pressure, four
resistors featuring different structural parameters will now be examined
by way of examples.
A fifth example will also be examined in which the specific resistance of
the resistor according to the present invention is sufficiently low for it
to be considered a conductor.
EXAMPLE 1
A cylindrical resistor, 12.6 mm in diameter and 7.4 mm high was prepared,
as shown in FIGS. 12 to 16, using epoxy resin (VB-BO 15) for matrix 214.
Conducting granules 215 consisted of carbon powder ranging in size from 200
to 250 microns.
On resistors with granules of this sort, the matrix insulating material
injected between the granules occupies approximately 56.8% of the total
volume of the resistor. The resistor so formed was connected to the
electric circuit in FIG. 11 in which it is indicated by number 110. The
said circuit comprises a stabilized power unit 111 (with an output
voltage, in this case, of 4.5 V), a load resistor 112 (in this case, 10
ohm), and a digital voltmeter 113, connected as shown in FIG. 11. Resistor
110 was subjected to pressures ranging from 7.8.multidot.10.sup.-2
N/mm.sup.2 to 196.multidot.10.sup.-2 N/mm.sup.2.
Resistance was measured by measuring the difference in potential at the
terminals of resistor 112 using voltmeter 113, and plotted against
pressure as shown in the FIG. 7 graph. From a starting figure of 5.4 Ohm,
resistance gradually drops down to 1.78 Ohm as the said maximum pressure
is reached.
EXAMPLE 2
A cylindrical resistor, 12.6 mm in diameter and 7.2 mm high was prepared as
before using an alpha-cyanoacrylatebase resin for matrix 214 and carbon
granules ranging in size from 200 to 250 microns.
Once again, the resistor was connected to the FIG. 11 circuit, the
components of which presented the same parameters as in Example 1. The
relative resistance-pressure graph is shown in FIG. 8, which shows a
resistance drop from 16 to 5.25 Ohm between the same minimum and maximum
pressures as in Example 1.
EXAMPLE 3
A tubular resistor with an outside diameter of 12.6 mm, an inside diameter
of 3.5 mm, and 5.4 mm high was prepared as before, using epoxy resin
(VB-BO 15) for the matrix and iron granules ranging in size from 50 to 150
microns. On resistors with granules of this sort, the matrix insulating
material injected between the granules occupies approximately 55% of the
total volume of the resistor. Resistance was again measured as shown in
FIG. 11 using a 1000 Ohm load resistor 112 and 4.5 V power unit 111.
Pressure was adjusted gradually from 59.multidot.10.sup.-2 N/mm.sup.2 to
7.22 N/mm.sup.2 to give the graph shown in FIG. 9, which shows a
resistance drop from 1790 to 493 Ohm between minimum and maximum pressure.
EXAMPLE 4
A 2.4 mm high tubular resistor having the same section as in Example 3 was
prepared as before, using silicon resin for matrix 214 and iron granules
ranging in size from 50 to 150 microns.
Resistance was again measured on the FIG. 11 circuit, using a 100 Ohm load
resistor 112 and a 1.2 V power unit 111. Pressure was adjusted from
4.2.multidot.10.sup.-2 N/mm.sup.2 to 119.multidot.10.sup.-2 N/mm.sup.2 to
give the graph shown in FIG. 10 which shows a resistance drop from 1100 to
8.1 Ohm between minimum and maximum pressure.
EXAMPLE 5
A 3.4 mm high tubular resistor having the same section as in Example 4 was
prepared as before, using epoxy resin (VB-ST 29) for matrix 214 and tin
granules ranging in size from 50 to 200 microns.
Resistance, measured in the absence of external pressure between the two
bases of the tubular-section cylinder, was 0.08 Ohm. The specific
resistance of the resistor material, in this case, therefore works out at
0.27 Ohm.cm, which is low enough for the resistor to be considered a
conductor. Assuming heat (Joule effect) is dissipated by normal heat
exchange in air at a temperature of 20.degree. C., and the maximum
temperature withstandable by the resistor is 50.degree. C., the density of
the current feedable through this resistor is approximately 11 A/cm.sup.2.
Instead of a pair of conducting elements 3a and 3b formed from the said
material, the conductor in the FIG. 3 embodiment comprises only one such
element 17. The FIG. 3 embodiment presents the same conducting elements as
in the previous embodiment, which elements are indicated using the same
numbering system, and spacer element 10 is located between elements 17 and
2 as shown clearly in FIG. 3.
In the FIG. 4 embodiment, conducting elements 1 and 2 are formed in such a
manner as to define a number of strips arranged alternately and
substantially in the same plane, so as to present adjacent strips
pertaining to different elements. Spacer element 10 is located between the
said strips and the third conducting element which, in this case, is
numbered 18 and consists of a flexible pad 18a, formed from the same
conducting material as element 3 in the FIG. 1 embodiment, and a
conducting mesh 18b having no external electrical connections. Spacer
element 10 may, as in the previous case, be formed from a mesh of
insulating material.
The two-dimensional electric conductor according to the present invention
may be connected to an electric circuit comprising a current source, of
which terminals 19 are shown in the attached drawings, and a user device,
such as a relay 20.
The said circuit is formed so as to connect the said components to
conducting elements 1 and 2, as shown in the attached drawings. When so
arranged, and when no pressure is applied on the outer surfaces of the
two-dimensional electric conductor according to the present invention, the
said circuit is maintained open and current prevented from circulating
inside the same by virtue of spacer element 10, which separates the
surfaces of the conducting elements facing the respective surfaces of
spacer element 10 itself.
When, on the other hand, pressure is applied on a given portion 21 (FIG. 2)
of at least one of the outer surfaces of the conductor according to the
present invention, this produces localised flexing of the said portion of
the third conducting element (3a, 3b, 17 or 18), thus causing a surface of
the said conducting element to contact the respective surface of the
adjacent conducting element. Should both conducting elements 3a and 3b in
the FIG. 1 embodiment be flexed, this results in contact between portions
21 of surfaces 8 and 9 (FIG. 2), thus closing the electric circuit and
allowing current to circulate inside the same, for activating user device
20. As shown clearly in FIG. 2, closure of the circuit is made possible by
surfaces 8 and 9 contacting on the portion left exposed by spacer element
10.
The same applies also to the conductors in the FIG. 3 and 4 embodiments, in
the first of which, flexing of element 17 produces electrical contact
between element 17 and the underlying conducting element 2, and, in the
second, contact is established between two of the adjacent strips of
conducting elements 1 and 2.
In addition to conducting current, the two-dimensional electric conductor
according to the present invention clearly also provides for forming an
infinite number of electric switches, each of which may be activated by
pressure applied on any given point on the conductor itself. Furthermore,
by virtue of the material of the said third conducting element increasing
in conductivity alongside increasing pressure, the said pressure, in
addition to closing the said circuit, also provides for producing a signal
proportional to the amount of pressure applied.
To those skilled in the art it will be clear that changes may be made to
the embodiments described and illustrated herein without, however,
departing from the scope of the present invention.
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