Microwave frequency sensor utilizing a single resonant cavity to provide simultaneous measurements of a plurality of physical properties

• US 3,927,369 A
• Filed: 01/31/1973
• Issued: 12/16/1975
• Est. Priority Date: 01/31/1973
• Status: Expired due to Term

• Current Assignee: Lee D. Philipp, Thomas R. Billeter
• Original Assignee: Lee D. Philipp, Thomas R. Billeter
• Inventors: Billeter, Thomas R., Philipp, Lee D.
• Primary Examiner(s): Krawczewicz, Stanley T.
• Application Number:
  US05/328,220
• Time in Patent Office: 1,049 Days
• Field of Search: 324/58.5C,58C
• US Class Current: 324/642
• CPC Class Codes: G01K 5/52 with electrical conversion means for final indication
• CPC Class Codes: G01L 11/04 by acoustic means
• CPC Class Codes: G01R 27/04 in circuits having distributed constants , e.g. having very long conductors or involving high frequencies
• CPC Class Codes: G21C 17/10 Structural combination of fuel element, control rod, reactor core, or moderator structure with sensitive instruments, e.g. for measuring radioactivity, strain
• CPC Class Codes: Y02E 30/30 Nuclear fission reactors

Abstract

A multiple property measurement microwave sensor and associated instrumentation are described employing a single hollow cavity resonating at a plurality of frequency modes to provide simultaneous measurements of a corresponding plurality of parameters. The sensor is specifically suited to operate in caustic, hostile environments, such as are found in fast breeder reactors, but is applicable to other environments as well. Pressure variations are sensed by the movement or deflection of a portion of one wall of the resonant microwave cavity. The movement or deflection results in a variation in the effective cavity length along the axis of an incident energy wave employed to excite multiple resonant frequency modes and thus, in a variation of the resonant frequency of the pressure dependent modes. Temperature changes cause the cavity size, and thus, the resonant frequency of the temperature dependent modes to vary. Both physical properties can be continuously monitored simultaneously as each relates to a distinct mode of cavity resonance. In one embodiment, a pressure feedback loop is employed to minimize deflection and plastic strain on the movable wall portion. Alternate modes of operation employ degenerate resonant frequency modes to resonate the cavity, thus minimizing the bandwidth of the incident energy necessary to excite the cavity to resonance and the bandwidth of the detection instrumentation employed to monitor reflected energy.

Claims

1. Apparatus for providing the simultaneous measurement of a plurality of physical properties of a given environment including:

a high frequency electromagnetic energy source capable of transmitting energy having a frequency varying within a given range of frequencies;

cavity resonator means comprising a single hollow member having a wall section responsive to one of the physical properties to be measured to move in a manner to change the effective dimension of the hollow cavity along a prescribed axis, said resonator means being designed to have a plurality of coexisting resonant frequency modes, within the given range of frequencies, corresponding to the plurality of physical properties being measured, said resonant frequency modes being respectively dependent upon a unique combination or permutation and collectively dependent on all of the properties being measured;

means for communicating said energy from said source to said cavity to excite said cavity to resonate at said plurality of resonant frequency modes, said comMunication means further transmitting any reflected energy resulting thereby; and

detection means responsive to said reflected energy to provide respective outputs each representative of one of the plurality of properties measured.

2. The apparatus of claim 1 wherein the movable wall section of the cavity resonator comprises a piston and a portion of the remaining interior of the cavity is designed to form the walls of a piston cylinder to accommodate movement of the piston in response to a variation in the one of the physical properties to be measured.

3. The apparatus of claim 1 wherein the movable wall section comprises a deflectable member.

4. The apparatus of claim 3 wherein the deflectable member comprises a bellows.

5. The apparatus of claim 3 wherein the deflectable member comprises a diaphragm.

6. The apparatus of claim 1 wherein said cavity is adapted to be isolated from and disposed within the environment measured.

7. The apparatus of claim 1 wherein said resonant frequency modes are degenerate modes having a coincident resonant frequency at the ambient state of the environment measured.

8. The apparatus of claim 7 wherein the physical properties to be measured are temperature and pressure and the degenerate modes employed are TE201 and TM002 .

9. The apparatus of claim 1 wherein said communication means comprises:

a waveguide communicably coupling the energy transmitted from said source to said cavity;

means coupled to said source and responsive thereto to provide an output representative of the frequency of the energy transmitted thereby; and

means responsive to the energy reflected by said cavity to provide an output representative of the resonant frequencies thereof.

10. The apparatus of claim 1 wherein said detection means comprises:

means responsive to the resonant frequencies of said cavity to provide an output representative of one of the physical properties being measured; and

means for providing a representation of a comparison between the resonant frequencies of said cavity with the resonant frequencies of said source and responsive to provide an output representative of a second of the physical properties being measured..

11. The apparatus of claim 1 wherein said cavity forms a pressure tight chamber and including a pressure feedback loop responsive to the environmental pressure external to said wall section to balance the pressure within said chamber to the pressure external of said wall section, said pressure feedback loop having a slower response time than said detection means.

12. A method for providing the simultaneouos measurement of a plurality of physical properties of a given environment comprising the steps of:

exciting a single resonant hollow cavity with a high frequency electromagnetic energy wave varying in frequencies within a given range of frequencies to resonate the cavity at plurality of coexisting frequency modes corresponding to the plurality of physical properties being measured, the cavity having a wall section responsive to one of the physical properties to be measured to move in a manner to change the effective dimension of the hollow cavity along a prescribed axis of the incident exciting energy wave, the resonant frequency modes being respectively dependent upon a unique combination or permutation and collectively dependent on all of the properties being measured;

exposing an exterior portion of the cavity including the movable wall section to the environment measured;

monitoring the reflected energy emanating from said cavity to provide an output representative of the resonant frequencies of the cavity; and

detecting variations in the resonant frequencies of the cavity to provide respective outputs each representative of one of the plurality of properties measured.

13. The method of claim 12 including the steps of disposing the cavity within and isolating the cavity from the environment being measured.

14. THe method of claim 12 whwerein said exciting step excites the cavity to resonate at a plurality of degenerate frequency modes.

15. The method of claim 12 wherein said detecting step comprises the steps of monitoring any relative and absolute shift in the resonant frequency modes of the reflected energy from the cavity to provide respective outputs representative of the properties being measured.

16. The method of claim 12 including the step of adjusting the pressure of the cavity to balance the pressure external to the wall section thereof subsequent to a predesigned time delay after an external pressure change.