Process and instrument for moisture measurement

• US 6,407,555 B2
• Filed: 02/26/2001
• Issued: 06/18/2002
• Est. Priority Date: 06/09/1997
• Status: Expired due to Term

• Current Assignee: University of PUNE (Government of Maharashtra)
• Original Assignee: National Research Development Corporation
• Inventors: Karekar, Ravi Narhar, Aiyer, Rohini Chandrashekhar, Abegaonkar, Mahesh Pandurang, Joshi, Kalpana Keshav
• Primary Examiner(s): Le, N.
• Assistant Examiner(s): Kerveros, James
• Application Number:
  US09/791,633
• Publication Number:
  US 20010030543A1
• Time in Patent Office: 477 Days
• Field of Search: 324/636, 324/63, 324/640, 324/643
• US Class Current: 324/636
• CPC Class Codes: G01N 27/221 by investigating the dielectric properties using microwaves G01N22/00; measuring loss factors or dielectric constants per se G01R27/26
• CPC Class Codes: G01N 33/025 Fruits or vegetables

Abstract

An instrument and process for measuring moisture content of an article. A microstrip resonator receives a signal from a microwave sweep oscillator. A holder holds the article wherein the article under test is placed over a substrate of the resonator and covers the resonator and provides orientation to the article under test in a desired direction to the sample. A detector receives transmitted as well as reflected signals from a resonator sensor for measurement of Q factor and frequency shift of the resonator. The moisture content of the article is determined by the change in effective permittivity of a cross-section of the miscorstrip.

Claims

1. An instrument for measurement of moisture content of an article selected from the group consisting essentially of grains, pulverised samples, fruits, nuts, dry fruits, and industrial and food products, comprising:

a microwave sweep oscillator,

microstrip resonator receiving signal from the microwave sweep oscillator;

a holder for holding the article wherein the article under test is placed over the substrate of the resonator, covering the resonator and providing orientation to the article under test in a desired direction to the sample; and

a detector receiving transmitted as well as reflected signal from a resonator sensor for measurement of frequency of the resonator,

wherein the moisture content of the article is determined by the change in effective permittivity of a cross-section of the microstrip by formula;

$\frac{f_o^2}{f_s^2}=\frac{{\mathrm{\epsilon <br><br>}}_{\mathrm{eff}<br><br>\text{\hspace{1em}<br><br>}<br><br>s}}{{\mathrm{\epsilon <br><br>}}_{\mathrm{eff}<br><br>\text{\hspace{1em}<br><br>}<br><br>o}}$

and wherein the change in effective permittivity is calibrated against moisture with electromagnetic software.

2. A process for measurement of moisture content of an article comprising the steps of measuring resonant frequency and quality factor of a microwave microstrip resonator, and calculating a shift in the resonant frequency caused by change in effective permittivity, caused by the presence of moist material under test, wherein the moisture content of the article is determined by the change in effective permittivity of a cross-section of the microstrip by formula:

$\frac{f_o^2}{f_s^2}=\frac{{\mathrm{\epsilon <br><br>}}_{\mathrm{eff}<br><br>\text{\hspace{1em}<br><br>}<br><br>s}}{{\mathrm{\epsilon <br><br>}}_{\mathrm{eff}<br><br>\text{\hspace{1em}<br><br>}<br><br>o}}$

and wherein the change in effective permittivity is celebrated against moisture.

3. The process of claim 2, wherein effective permittivity is calibrated against moisture using electromagnetic software.

4. The process of claim 2, wherein effective permittivity is calibrated against moisture using a dedicated microcontroller.

5. An instrument for measurement of moisture content of an article selected from the group consisting essentially of grains, pulverized samples, fruits, nut, dry fruits, and industrial and food products, comprising:

a pulse generator;

a multilayer microstrip integrated hybrid circuit connected to the pulse generator through a coaxial cable;

an article under test placed over a substrate of the integrated hybrid circuit covering the substrate;

a time domain reflectometer detecting and measuring delay between an input pulse and a reflected pulse; and

means for calibrating effective permittivity measured against moisture content of the sample.

6. The instrument of claim 5, wherein the multilayer microstrip integrated hybrid circuit is a microstrip with dielectric overlay.

7. The instrument of claim 5, wherein the multilayer microstrip integrated hybrid circuit is an asymmetric inhomogeneous Stripline.

8. The instrument of claim 5, wherein the multilayer microstrip integrated hybrid circuit is a coplanar waveguide with dielectric overlay.

9. The instrument of claim 5, wherein the means for calibrating effective permittivity is a microcontroller.

10. The instrument of claim 5, wherein the means for calibrating effective permittivity is a computer with on-line electromagnetic software.

11. The instrument of claim 5, wherein the instrument further comprises a spacer block placed over the sample for putting pressure on the sample.

12. The instrument of claim 5, wherein the substrate is selected from a group consisting of glass, ceramic, polymer and semiconductor substrate.

13. The instrument of claim 5, wherein the article under test placed over the substrate of the integrated hybrid circuit partially covers the substrate.

14. The instrument of claim 5, wherein the article under test placed over the substrate of the integrated hybrid circuit fully covers the substrate.

15. The instrument of claim 5, wherein the article under test placed over the substrate of the integrated hybrid circuit covers the substrate and protrudes beyond the substrate.