Environmental sensor

• US 20070273394A1
• Filed: 06/07/2004
• Published: 11/29/2007
• Est. Priority Date: 06/06/2003
• Status: Abandoned Application

• Current Assignee: M.B.T.L. Limited
• Original Assignee: M.B.T.L. Limited
• Inventors: Tanner, Philip, Johnson, Peter, Suzuki, Takeharu, Adamec, Richard, Thiel, David, Beadle, Peter
• Application Number:
  US10/558,695
• Publication Number:
  US 20070273394A1
• Time in Patent Office: Days
• US Class Current: 324/664
• CPC Class Codes: A01G 25/167 Control by humidity of the soil itself or of devices simulating soil or of the atmosphere; Soil humidity sensors
• CPC Class Codes: G01D 21/02 Measuring two or more variables by means not covered by a single other subclass
• CPC Class Codes: G01F 1/6845 Micromachined devices
• CPC Class Codes: G01F 1/692 Thin-film arrangements
• CPC Class Codes: G01N 27/223 for determining moisture content, e.g. humidity rain detectors on vehicle windows B60S1/0825
• CPC Class Codes: G01N 33/246 for water content
• CPC Class Codes: G01P 13/02 Indicating direction only, e.g. by weather vane
• CPC Class Codes: G01P 5/12 using variation of resistance of a heated conductor

Abstract

Multi functional sensors are described. A silicon based sensor utilizes metal layers arranged as resistors around a central pair if resistors separated by a humidity sensitive polymer with one of the central resistors being a heater. This enables temperature humidity wind speed and direction to be measured. In another embodiment an array of resistors is printed onto a flexible substrate to form the basis of an array of sensors. A soil moisture sensor, which is also useful as a leaf wetness sensor, incorporates a novel self calibrating capacitive sensor structure. The flexible substrate is rolled into a stake that can be inserted in the soil so that below ground sensors measure soil moisture and above ground sensors measure temperature, light, humidity, wind speed and direction.

Claims

1. A sensor array for horticultural and agricultural use which includes

a) a substrate

b) at least one sensor selected from temperature, humidity, light, wind and leaf wetness sensors printed or mounted on said substrate

c) capacitive moisture sensors printed on said substrate at a location remote from said at least one sensor

d) support electronics for the sensors a) and b) mounted and/or printed on said substrate

e) an antenna printed on said substrate.

2. A capacitive sensor which may be used for measuring soil moisture or leaf wetness, which includes at least one pair of sensor pads one of each pair consisting of a conductor covered by a dielectric layer and the other of each pair consisting of a conductor covered by the same dielectric layer with a top conducting layer.

3. A soil moisture sensor consisting of

a) a body portion for insertion into the soil

b) a surface on said body portion adapted to contact with the soil

c) a plurality of sensor locations on said surface interconnected by conductive layers

d) each sensor includes a conductive layer on said surface and a dielectric layer on said conductive layer

e) a pair of sensors are used to determine the upper and lower capacitance values

f) an electronic support circuit which sends an interrogation pulse to each sensor and records the return signal.

4. An environmental sensor which includes

a) a substrate comprising silicon coated front and back with a dielectric layer

b) a first metal layer on said substrate

c) a water vapour sensitive polymer layer on said first metal layer

d) a second metal layer on said water vapour sensitive polymer to define a capacitive humidity sensor

e) an insulating layer over said second metal layer

f) a plurality of symmetrically placed resistors on said insulating layer to define an airflow sensor in combination with a heating element.

5. An environmental sensor as claimed in claim 4 which also includes an etch pit in the silicon beneath the sensor layers that forms a thermally isolated membrane.

6. An environmental sensor as claimed in claim 4 in which the dielectric layer is silicon nitride or silicon oxynitride.