Spiral configuration of electrodes and dielectric material for sensing an environmental property

• US 4,858,063 A
• Filed: 12/31/1987
• Issued: 08/15/1989
• Est. Priority Date: 12/31/1987
• Status: Expired due to Fees

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Stephens, James B., Laue, Eric G.
• Primary Examiner(s): GRIFFIN, DONALD
• Application Number:
  US07/140,295
• Time in Patent Office: 593 Days
• Field of Search: 427/79, 29/25.42, 73/336.5, 338/35, 338/34, 174/36, 174/115, 361/286
• US Class Current: 361/286
• CPC Class Codes: G01N 27/225 by using hygroscopic materials

Abstract

A reliable moisture-indicating capactive sensor is provided with wire electrodes at least one of which includes a coating of moisture-absorbing dielectric material by spirally twisting the wire electrodes about each other, thereby establishing a pair of electrodes in contact with opposite surfaces of a layer of dielectric material, and assuring consistent contact of each electrode with the dielectric material despite changes in environmental conditions.

Claims

1. A spiral sensor comprising

first and second elongated electrodes, and

a layer of dielectric material surrounding each of said elongated electrodes separately, said dielectric material having electrical properties that vary with a characteristic of the environment, and

at least one bare wire,

said elongated electrodes separately surrounded by dielectric material being spirally twisted, each one about the other, to form a pair of multiturn electrodes spiraled with said bare wire, each elongated electrode tightly engaging said dielectric material, said dielectric material being distributed throughout the length of said spiral sensor, whereby said electrodes and dielectric material surrounding each electrode are urged into constant contact with each other and said bare wire.

2. A sensor comprising first and second elongated electrodes, each of said electrodes being in the form of a wire, a layer of dielectric material provided as a separate film surrounding each of said wire electrodes, said dielectric material having electrical properties that vary with a characteristic of the environment, and including at least one bare wire, said wire electrodes and said bare wire being spirally twisted together about each other to form a pair of multiturn spiraled electrodes, each tightly engaging said dielectric material, said dielectric material being distributed throughout the length of said spiral sensor, whereby said wire electrodes with surrounding dielectric material are urged into constant contact.

3. A sensor comprising first and second elongated electrodes, each of said electrodes being in the form of a wire, a layer of dielectric material provided as a separate film surrounding each of said wire electrodes, said dielectric material having electrical properties that vary with a characteristic of the environment, and including a pair of bare wires, said wire electrodes and bare wires being spirally twisted together about each other with said bare wires separated from each other by wire electrodes having a surrounding film of dielectric material to form a pair of multiturn spiraled electrodes, each tightly engaging said dielectric material, said dielectric material being distributed throughout the length of said spiral sensor, whereby said wire electrodes with surrounding dielectric material are urged into constant contact.

4. A sensor comprising

a pair of electrically conductive wires,

a film of moisture absorbing dielectric material whose dielectric coefficient varies as a function of moisture absorbed, said film being disposed about each of said wires to form two film-enclosed wire electrodes,

said two film-enclosed wire electrodes being spirally twisted about each other to elastically deform said wire electrodes into a pair of tightly engaged multiturn spirals, and

including at least one bare wire twisted together with said wire electrodes, said bare wire being in contact with the dielectric film of both of said wire electrodes throughout the length of said multiturn spirals.