Acoustic wave H.sub.2 O phase-change sensor capable of self-cleaning and distinguishing air, water, dew, frost and ice

• US 5,051,645 A
• Filed: 01/30/1990
• Issued: 09/24/1991
• Est. Priority Date: 01/30/1990
• Status: Expired due to Fees

• Current Assignee: Johnson Service Company
• Original Assignee: Johnson Service Company
• Inventors: Sanfelippo, Thomas S., Brace, John G.
• Primary Examiner(s): Budd, Mark O.
• Assistant Examiner(s): Dougherty, Thomas M.
• Application Number:
  US07/472,125
• Time in Patent Office: 602 Days
• Field of Search: 310/313 D, 310/313 R, 340/580-582, 340/602-604, 73/579, 333/152, 333/153
• US Class Current: 310/313.00D
• CPC Class Codes: G01N 2291/0251 Solidification, icing, curing composites, polymerisation
• CPC Class Codes: G01N 2291/0423 Surface waves, e.g. Rayleigh waves, Love waves
• CPC Class Codes: G01N 29/022 Fluid sensors based on microsensors, e.g. quartz crystal-microbalance [QCM], surface acoustic wave [SAW] devices, tuning forks, cantilevers, flexural plate wave [FPW] devices microdevices per se B81B

Abstract

A surface-acoustic-wave (SAW) H₂ O phase-change sensor capable of distinguishing air, water, dew, frost and ice. The sensor can also distinguish various frost thicknesses. The sensor has a size allowing batch fabrication of the chips, and allowing the device to fit in small spaces such as between fins of an evaporator. The sensor is fabricated on a strong piezoelectric substrate with a short acoustic path length. The SAW phase-change sensor experiences large changes in insertion loss and impedance upon deposition of water in various phases. The sensor has a hydrophobic surface treatment covering the SAW sensor surface, and if placed in a vertical position will self-clean during a refrigeration defrost cycle.

Claims

1. A surface acoustic wave H₂ O phase-change sensor comprising:

(a) a piezoelectric substrate;

(b) metallization patterns fabricated on said piezoelectric substrate to form an input interdigitated transducer and an output interdigitated transducer;

(c) electrical connectors connected to said metallization patterns;

(d) a hydrophobic surface treatment covering said metallization patterns to form a sensing surface; and

(e) means for detecting and discriminating between at least water, frost and ice on said sensing surface, said means including said piezoelectric substrate configured to have a thickness to acoustical wavelength ration of 9 or higher.

2. A surface acoustic wave H₂ O phase-change sensor as defined by claim 1 wherein said piezoelectric substrate is composed of lithium niobate cut with substantially 128 degree Y rotation.

3. A surface acoustic wave H₂ O phase-change sensor as defined by claim 1 wherein said interdigitated transducers are oriented for substantially X-propagation of surface acoustic waves.

4. A surface acoustic wave H₂ O phase-change sensor as defined by claim 1 wherein said metallization patterns are composed of RF-diode sputtered Cr/Au.

5. A surface acoustic wave H₂ O phase-change sensor as defined by claim 1 wherein said input interdigitated transducer has 10 finger pairs, said output interdigitated transducer has 30 finger pairs, and said unput interdigitated transducer to said output interdigitated transducer center-to-center spacing is substantially 30 acoustical wavelengths.

6. A surface acoustic wave H₂ O phase-change sensor as defined by claim 1 wherein said thermally conductive package is composed substantially of gold-plated nickel.

7. A surface acoustic wave H₂ O phase-change sensor as defined by claim 1 wherein said hydrophobic surface treatment is a polysiloxane derivatizer.

8. A surface acoustic wave H₂ O phase-change sensor as defined by claim 1 wherein said sensor operates at about 75 MHz.

9. A surface acoustic wave H₂ O phase-change sensor as recited in claim 1, further comprising:

(f) a thermally conductive package; and

(g) means for thermally coupling said thermally conductive package to said piezoelectric substrate.

10. A surface acoustic wave H₂ O phase-change sensor as recited in claim 9, wherein said thermally coupling means comprises a thermally conductive adhesive attaching said thermally conductive package to said piezoelectric substrate.

11. A method of detecting H₂ O phase changes comprising the steps of:

(a) exposing a surface acoustic wave device with a hydrophobic sensing surface so that various H₂ O phases form on said hydrophobic sensing surface;

(b) measuring an electrical parameter from said surface acoustic wave device; and

(c) determining from said electrical parameter whether said various H₂ O phases are air, water, frost, dew, or ice.

12. A method of detecting H₂ O phase changes as defined by claim 11 wherein said electrical parameter is insertion loss.

13. A method of detecting H₂ O phase changes as defined by claim 11 wherein said electrical parameter is radiation conductance.

14. A method of detecting H₂ O phase changes as defined by claim 11 further comprising the step of determining from said electrical parameter a thickness of said various H₂ O phases formed on said hydrophobic sensing surface.

15. A method of detecting H₂ O phase changes as defined by claim 11 further comprising the step of orienting said hydrophobic sensing surface so that gravity will remove water from said hydrophobic sensing surface.

16. A surface acoustic wave H₂ O phase-change sensor comprising:

(a) a piezoelectric substrate;

(b) metallization patterns fabricated on said piezoelectric substrate to form an input interdigitated transducer and an output interdigitated transducer;

(c) electrical connectors connected to said metallization patterns;

(d) a hydrophobic surface treatment covering said metallization patterns to form a sensing surface; and

(e) means for detecting and discriminating between at least air, water, frost, dew and ice on said sensing surface, said means including said piezoelectric substrate configured to have a thickness to acoustical wavelength ratio of 9 or higher.

17. A surface acoustic wave H₂ O phase-change sensor as recited in claim 16, further comprising:

(f) a thermally conductive package;

(g) means for thermally coupling said thermally conductive package to said piezoelectric substrate.

18. A surface acoustic wave H₂ O phase-change sensor comprising:

(a) a piezoelectric substrate;

(b) metallization patterns fabricated on said piezoelectric substrate to form an input interdigitated transducer and an output interdigitated transducer;

(c) electrical connectors connected to said metallization patterns;

(d) a thermally conductive package;

(e) means for thermally coupling said thermally conductive package to said piezoelectric substrate; and

(f) a hydrophobic surface treatment covering said metallization patterns to form a sensing surface;

(g) said piezoelectric substrate having a thickness to acoustical wavelength ratio of 9 or higher.

19. A surface acoustic wave H₂ O phase-change sensor as recited in claim 18, further comprising:

(h) a thermally conductive package;

(i) means for thermally coupling said thermally conductive package to said piezoelectric substrate.

20. A method of detecting H₂ O phase changes comprising the steps of:

(a) providing an interdigitated piezoelectric surface acoustic wave device with a hydrophobic surface treatment, said acoustic wave device having a thickness to acoustical wavelength ratio of 9 or higher;

(b) exposing the treated surface of the acoustic wave device so that various H₂ O phases form on the treated surface;

(c) measuring an electrical parameter from said surface acoustic wave device; and

(d) determining from said electrical parameter whether said various H₂ O phases are water, frost or ice.

21. The method as recited in claim 20 further comprising the steps of:

(e) thermally and mechanically coupling said surface acoustic wave device to a thermally conductive package so that said treated surface is exposed; and

(f) positioning the thermally conductive package to a component of a system desired to be monitored.

22. The method as recited in claim 20 further comprising the step of determining from said electrical parameter whether said various H₂ O phases are air, water, dew, frost or ice.