Electrical resistors – Mechanically variable – Deformable
Patent
1984-08-08
1987-01-27
Goldberg, E. A.
Electrical resistors
Mechanically variable
Deformable
338 47, H01C 1010, H01C 1012
Patent
active
046397116
DESCRIPTION:
BRIEF SUMMARY
It has since long been known that the resistivity of an elastic body, consisting of rubber with an addition of carbon black, is changed when the body is deformed by tension or--which deformation pattern is normally used--by compression. The physical phenomenon causing the resistivity variation may in simple terms be described as follows. Rubber without any filling agent is electrically insulating, whereas carbon black particles are conductive. However, a rubber body containing carbon black may in its entirety become electrically conductive. This change may arise in consequence of two different mechanisms which may occur either separately or together. However, in the last-mentioned case, one of the two phenomena does as a rule dominate.
The one mechanism occurs upon a deformation of the rubber body causing compression within at least some portion thereof. In that portion the carbon black particles are brought so close to one another, in the limit case they are maintained pressed against each other, that continuous current paths are formed. If the deformation consists of compression only this type of state will prevail within all of the rubber body. This mechanism may occur independently of which type of carbon black the rubber contains.
In contrast thereto the second mechanism does only occur together with carbon blacks of the types forming structure. This means that the carbon black particles have the capacity of becoming interconnected to form long chains and networks which form current paths, thus making the material electrically conductive. If such a material is later on deformed, the carbon black chains are broken and the resistivity increases. That increased resistivity will remain during a certain time interval after the forces causing the deformation are no longer applied and the rubber body has resumed its original shape. Also, the current paths are successively regenerated but the just-mentioned delay means that a hysteresis effect will be present.
In both of the two cases above described an additional contribution to the conductivity increase may arise due to the so-called tunnel effect. This effect is present when the distance between the individual carbon black particles is extremely small, which means a distance of the order of magnitude of 10.sup.-9 meters The transition resistance will then be very small and electrons may move between the particles under the influence of fluctuating thermal energy.
It has since long been known that it is possible in signal transmitters to utilize the resistivity variations above described in the way that a rubber body, containing carbon black, is connected to a signal circuit and, when a signal shall be transmitted, deformed. However, the area of use of such known signal transmitters has been very limited, primarily due to the fact that the maximum obtainable relative change of the dimensions of the rubber body, when subjected to compression, is very small. Differently put this means that the interval within which the deformation occurs is so narrow that signal transmitters of this type cannot be used when the movement interval of the control member affecting the transmitter also is not correspondingly limited. In addition thereto, a rubber body under compression exerts relatively strong reactional forces on the control member which in certain applications is unsuitable or out of question, respectively. Third, the total resistance change obtainable is comparatively small.
The object of the invention is to provide a signal transmitter which in all respects above discussed is remarkably superior to the prior art transmitters. Consequently, its elastic body shall be capable of handling great amplitudes in the movement of the control member (which term has here been used in a functional, not in a limiting, sense). Further, it shall be possible to deform the body without having to subject it to large forces which in turn could generate correspondingly large reactional forces. Last but not least it shall have such a composition that the relative resistivity change
REFERENCES:
patent: 4163204 (1979-07-01), Sado et al.
patent: 4426884 (1984-01-01), Polchaninoff
patent: 4492949 (1985-01-01), Peterson et al.
Edholm Stig
Stenberg Bengt
Goldberg E. A.
Lateef Marvin M.
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