Capacitance humidity sensor
First Claim
1. A humidity sensor element comprising:
- a thin, flexible film consisting essentially of a dielectric, water-absorbing first polymer having a dielectric constant which varies substantially linearly as a function of relative humidity,a pair of thin, water-permeable conductive layers disposed on opposite sides of said film and integrally bonded thereto, said conductive layers each consisting of a second polymer containing sulfur and having electrically conductive particles distributed therein, which conductive particles are effective to render said layers electrically conductive.
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Abstract
A capacitance humidity sensor according to the invention has a film core which is in contact with a pair of polymeric conductive layers bonded to opposite faces of the core. The core is made of a polymeric material having a dielectric constant which varies substantially linearly with humidity, such as a polyimide or polyparabanic acid. The conductive layers are made of a polymeric material, at least a portion of which includes sulfur atoms in the backbone chain and having conductive particles, such as carbon particles, dispersed therein. Such conductive layers provide superior performance and corrosion resistance in comparison to the metal films employed in the prior art and in comparison to cellulosic polymers containing conductive particles.
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Citations
20 Claims
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1. A humidity sensor element comprising:
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a thin, flexible film consisting essentially of a dielectric, water-absorbing first polymer having a dielectric constant which varies substantially linearly as a function of relative humidity, a pair of thin, water-permeable conductive layers disposed on opposite sides of said film and integrally bonded thereto, said conductive layers each consisting of a second polymer containing sulfur and having electrically conductive particles distributed therein, which conductive particles are effective to render said layers electrically conductive. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method for making a humidity sensor element, comprising:
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(a) the step of disposing a piece of a thin, flexible film made of a dielectric, water absorbing first polymer having a dielectric constant which varies as a function of relative humidity on a holder; (b) the step of applying a stencil over the film; (c) screen printing the film through the stencil with a liquid composition comprising an electrically non-conductive second polymer containing sulfur, electrically conductive particles and a solvent; (d) the step of drying the liquid composition under conditions effective to form a water-permeable, first conductive layer on one side of the film and integrally bonded thereto, which conductive layer has a shape corresponding to the stencil; and (e) repeating steps b-d to form a second conductive layer on the face of the film opposite the first conductive layer. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification