Microwave oven leakage detector and method of using same to test door seal leakage

• US 4,354,153 A
• Filed: 11/19/1979
• Issued: 10/12/1982
• Est. Priority Date: 11/19/1979
• Status: Expired due to Term

• Current Assignee: Amana Refrigeration, Inc. (Whirlpool Corporation)
• Original Assignee: Litton Systems Incorporated (Northrop Grumman Corporation)
• Inventors: Lentz, Ronald R.
• Primary Examiner(s): Karlsen, Ernest F.
• Application Number:
  US06/095,690
• Time in Patent Office: 1,058 Days
• Field of Search: 324/95, 324/106, 324/72, 343/703, 343/771, 343/853, 219/10.55 R, 219/10.55 D, 219/10.55 M, 455/67, 340/600
• US Class Current: 324/95
• CPC Class Codes: G01R 21/01 in circuits having distributed constants G01R21/04, G01R21/07, G01R21/09, G01R21/12 take precedence
• CPC Class Codes: H05B 6/6432 Aspects relating to testing or detecting leakage in a microwave heating apparatus
• CPC Class Codes: H05B 6/763 Microwave radiation seals for doors

Abstract

A stationary microwave leakage detector and method for testing microwave ovens for the maximum power density of microwaves leaking through the oven'"'"'s door seals. The leakage detector is composed of an array of antennae arranged in a line generally circumscribing the circumference of the door at a fixed distance therefrom. The antennae are spaced apart a predetermined maximum distance thus insuring that a given antennae will sense at least a portion of the narrowest possible beam of microwaves emitting from the periphery of the door. Furthermore, the spacing and arrangement of the array vis-a-vis the oven door insure that the minimum power density observed by an antenna is a known ratio of the maximum power density of a narrowest beam possibly incident thereon, thus providing a means to guarantee from the measured power density levels that there are no microwaves leaking from the oven under test greater than a certain maximum power density. Alternately, the antennae are spaced such that the sum of any two adjacent antennae will be equal to or greater than the maximum power density of a narrowest beam possibly incident upon one of them. This antenna spacing provides a stationary method for testing microwave ovens for the maximum power density of microwaves leaking through the oven'"'"'s door seals.

Claims

1. A method for determining the maximum possible power density of microwave leakage from a microwave oven in the region of the microwave oven door comprising the steps of:

(A) arranging a plurality of microwave sensitive antennae in a linear array, said array having a configuration corresponding to at least one edge of the circumference of said oven door, each of said antennae being spaced from each adjacent antenna a predetermined spacing distance, said spacing distance being equal to or less than the beamwidth corresponding to the highest mode of standing wave resonant energy in the oven whereby the narrowest beam of energy leaking from any aperture along said door edge of an oven being tested will be sensed by at least one of said antennae;

(B) positioning an oven to be tested adjacent to said array by;

i. paralleling said oven door edge at a predetermined distance to said array, and

ii. orienting said oven door edge to said array at a predetermined angle relative to the direction of maximum energy propagation from said oven door edge;

(C) measuring the microwave power density sensed by each antenna, and

(D) determining from said measurements the maximum possible power density of leakage at any point along said array.

2. The method of claim 1 wherein step (B) includes positioning said oven a predetermined test distance from said array and wherein said predetermined spacing distance is less than the shortest distance between the minima on a power density contour map of microwave leakage beams leaking from a fully energized oven at said predetermined test distance and angle, where the beamwidth of said microwave leakage beams is determined principally by the highest mode of resonant energy inside the oven cavity.

3. The method of claim 2 wherein step (D) includes:

i. predetermining a minimum power density greater than any of the local minima in the power density contour map so as to be measurable by at least one of said antennae when measuring a microwave leakage beam of energy corresponding to a half wavelength of the highest mode of standing wave resonant energy in the oven,

ii. determining the highest power density measured by any antenna, and

iii. determining the maximum possible power density of microwave leakage by assuming said highest power density measured is taken from an antenna sensing said predetermined minimum power density of said microwave leakage, the result being the maximum power density possible at any point along said array.

4. The method of claim 2 wherein said predetermined spacing distance is the distance between the peak power density and the closest minima of said narrowest microwave leakage beam at said predetermined test distance and angle;

and wherein step D. includes;

summing the power density sensed by each pair of adjacent antennae; and

determining the highest of said sums, the result being the maximum possible power density at any point along said array.

5. The method of claim 3 wherein step D. includes providing a fault indication when said maximum possible power density has exceeded a predetermined microwave power density leakage level.

6. The method of claim 3 further including placing a predetermined test load in the oven before performing step C.

7. The method of claim 1 or claim 2 or claim 3 or claim 5 or claim 6 wherein step C. is performed a predetermined length of time and an average power density is determined before performing step D.

8. The method of claim 7 wherein there are further included the steps of

(E) mounting one or more ovens to be tested upon an assembly line;

(F) moving said one or more ovens to be tested one at a time to a test station;

(G) turning on to full power an oven present at said test station before performing step C;

(H) moving said oven present at said test station away therefrom at the completion of step D; and

(I) repeating steps F through H until there are no more ovens on said assembly line to be tested.

9. The method of claim 8 further including recording the identity of the oven tested and the results of step D. before performing step I.

10. The method of claims 1 or 2 or 3 or 5 or 6 further including recording the identity of the oven tested and recording the results of step D.

25. The invention of claim 1 or claim 11 or claim 18 or claim 19 wherein each of said antennae include crossed dipoles.

11. A microwave oven door seal power density leakage detector for detecting power density of a beam of microwaves leaking through a seal along the perimeter of the oven door, said microwave leakage beam having a direction of maximum power density propagation, said leakage detector comprising:

a plurality of microwave sensitive antennae, arranged in alignment with a segment of the perimeter of said door in a linear array and spaced therefrom a predetermined test distance at a predetermined test angle relative to said direction of maximum power density propagation, each of said antennae spaced from each adjacent antenna a spacing distance equal to or less than a beamwidth due to the highest mode of standing wave resonant energy in the oven emittable along said perimeter segment such that the narrowest beam of said microwave leakage will be sensed by at least one of said antennae; and

measuring means for measuring the power density sensed by each of said antennae.

12. The leakage detector of claim 11 wherein said spacing distance between adjacent antennae is predetermined such that the power density of said narrowest beam as measured by one of said adjacent antennae is at least a predetermined ratio relative to the maximum power of said narrowest beam.

13. The leakage detector of claim 11 wherein said spacing distance comprises the distance between a maximum and a closest minimum of the power density of any microwave leakage beam emitted along said perimeter segment at said predetermined test distance and angle such that the sum of the power densities measured from any two adjacent of said antennae is equal to or greater than said maximum power density of said narrowest beam.

14. The leakage detector of claim 11 wherein said spacing distance is less than the shortest distance between the minima of said narrowest beam of emissions along the line of said linear array.

15. The invention of claim 11 wherein said measuring means include commutator means for sequentially sampling the power density sensed by each of said antennae.

16. The invention of claim 11 or claim 12 further including means responsive to said measuring means for determining whenever a predetermined power density level has been exceeded by any measured power density.

17. The invention of claim 12 or claim 13 including means responsive to said measuring means for determining whether a predetermined power density level has been exceeded by said maximum possible power density of said narrowest microwave leakage beam as determined from the measurements from each of said antennae.

18. A cavity rf oscillator rf leakage detector for detecting the rf leakage from a substantially linear aperture therein, the rf energy oscillating therein having a predetermined substantially monochromatic frequency, and said cavity having a predetermined structure, said leakage detector comprising:

a plurality of rf sensitive antennae, arranged in a linear array corresponding to said linear aperture and spaced therefrom a predetermined distance at a predetermined angle relative to the direction of maximum power density propagation from said aperture, each of said antennae spaced from each adjacent of said antennae a spacing distance such that the narrowest beam of rf emitting from said aperture comprised of two minimum and one maximum spatially displaced power density points will be sensed by at least of one said antennae at a power level no less than a predetermined ratio relative to the maximum power density of said beam.

19. A rf leakage detector for detecting rf leakage from one or more substantially linear apertures in a cavity rf oscillator containing a predetermined bandwidth of rf energy, said cavity having predetermined structure such that only a predetermined set of resonance modes can oscillate therein and cause beam emission therefrom, said leakage detector comprising:

one or more linear arrays of antennae, a corresponding one for each of said apertures, each array having a plurality of antennae arranged in a line corresponding to the line of the corresponding aperture, each antenna spaced a predetermined distance from said corresponding aperture at a predetermined angle relative to the direction of maximum energy propagation therefrom, each antenna further spaced from each adjacent antenna a spacing distance such that every beam of rf energy comprising at least two minimum and one maximum spatially displaced power density points radiating from said corresponding aperture must be sensed by at least one of said antennae at no less than a predetermined minimum power density level relative to that beam'"'"'s maximum power density level along the line of said array.

20. The leakage detector of claim 19 wherein said spacing distance is further defined such that when the narrowest of beams comprised of at least two minimum and one maximum power density points due to a standing wave mode of resonant energy in said cavity is sensed by a given antenna at said predetermined minimum power density level, said narrowest beam must also be sensed by an adjacent of said antennae at the same predetermined minimum power density level.

21. The leakage detector of claim 19 wherein said spacing distance is further defined such that when the narrowest beam of rf energy is sensed by a given antenna at less than its maximum power density, said narrowest beam must also be sensed by an adjacent of said antennae at a power density level no less than the maximum power density of said narrowest beam at the line of said array minus the power density sensed by said given antenna.

22. The leakage detector of claim 19 or 20 or 21 wherein said apertures include waveguide structures having two open ends, one end coupled to said cavity, the other end being substantially linear in shape, and wherein each corresponding linear antenna array is arranged to correspond to said other end.

23. The leakage detector of claim 22 further including measuring means responsive to the power density sensed by each antenna of said one or more linear antenna arrays for determining the maximum power density possible at any point along each linear array.

24. The leakage detector of claim 23 further including means responsive to said measuring means for determining the maximum possible power density emitting from said cavity through any of said one or more linear apertures.