Active microwave cavity for electron paramagnetic resonance (EPR) apparatus

• US 4,674,513 A
• Filed: 10/04/1985
• Issued: 06/23/1987
• Est. Priority Date: 10/04/1985
• Status: Expired due to Fees

• Current Assignee: Louis J. Jasper Jr
• Original Assignee: Louis J. Jasper Jr
• Inventors: Jasper, Louis J. Jr.
• Primary Examiner(s): Howell, Kyle L.
• Assistant Examiner(s): Smith, Ruth S.
• Application Number:
  US06/783,992
• Time in Patent Office: 627 Days
• Field of Search: 128/653, 128/804, 324/316, 330/44
• US Class Current: 600/430
• CPC Class Codes: A61B 6/107 Protection against radiation, e.g. shielding
• CPC Class Codes: G01R 33/345 of waveguide type G01R33/343 takes precedence
• CPC Class Codes: G01R 33/60 using electron paramagnetic resonance G01R33/24, G01R33/62 take precedence

Abstract

This disclosure relates to a microwave amplifier (22) having an active X-Band microwave cavity (33) for use in electron paramagnetic resonance (EPR) measurements on large, lossy, irradiated, samples such as a human finger. The amplifier comprises an input section (31), a drift section (32) and an output section (33) which is the aforementioned active microwave cavity. An electron beam is used to input RF energy into the cavity. The input and output section have small helical couplers (34) for coupling RF energy onto and off of the electron beam. The RF wave is essentially "trapped" in the cavity because of the non-reciprocal nature of the electron beam medium and because the guide (i.e., drift section) at the input to the cavity has dimensions such that the frequency of the RF microwave energy is below the guides lower cut-off frequency. Also, a frequency "locking" effect occurs in the output cavity. The input frequency can be varied from 1-2% yet the output frequency does not change. The active microwave cavity has a cylindrically shaped window (41) located at the back-end of the cavity which extends inward towards the region of high RF fields inside the cavity. A large, lossy, irradiated sample such as a finger can be inserted into or behind this window and analyzed for radiation damage.

Claims

1. A microwave amplifier for use in electron paramagnetic resonance (EPR) measurement apparatus comprising an input section, a drift section, and an active microwave cavity forming an output section, means for inputting an axial electron beam into said microwave amplifier, a pair of small helical couplers mounted in the input and output sections, respectively, for coupling RF microwave energy onto and off of the electron beam, said drift section having dimensions such that the frequency of the microwave energy is below the lower cut-off frequency of the drift section, said output cavity being insensitive to small input frequency changes, and a cylindrically-shaped window located at the back-end of the cavity and extending inward towards the region of high RF fields inside the active cavity.

2. A microwave amplifier as defined in claim 1 including driver means for generating the RF microwave energy, and means for coupling the RF microwave energy from said driver means to the helical coupler in said input section.

3. A microwave amplifier as defined in claim 2 wherein said driver means is a solid-state device which operates at a predetermined frequency in the X-Band.

4. A microwave amplifier as defined in claims 3 including means for establishing a phase velocity of the RF wave on the electron beam in the same direction as the drift velocity of the electron beam.

5. A microwave amplifier as defined in claim 4 wherein said window is adapted to receive a large, lossy, irradiated sample such as a human finger, said microwave amplifier being maintained under vacuum.

6. A microwave amplifier as defined in claim 5 wherein the input, drift, and output sections are cylindrical.

7. A microwave amplifier for use in electron paramagnetic resonance (EPR) measurement apparatus comprising an input section, a drift or intermediate section, and an active X-Band microwave cavity forming an output section, said microwave amplifier having an electron gun for producing an electron beam, means for establishing an axial travel of said electron beam in the input and drift sections of said microwave amplifier, a pair of small helical couplers mounted in the input and output sections, respectively, for coupling microwave energy onto and off of the electron beam, solid stae RF driver means for generating RF microwave energy, means for coupling said RF microwave energy from said driver means to the helical coupler in said input section, said driver means operating at a predetermined frequency in the X-Band, said drift section having dimensions such that the frequency of the RF microwave energy is below the lower cut-off frequency of the drift section, said output cavity being insensitive to small input frequency changes, means for establishing a phase velocity of the RF wave on the electron beam in the same direction as the drift velocity of the electron beam so as to transport energy from the input to output sections, and a cylindrically-shaped window made of a material that permits RF energy to pass through it, said window being located at the back-end of the cavity and extending inward towards the region of high RF fields inside the active cavity, said window being adapted to receive a large, lossy, irradiated sample such as a human finger.

8. A microwave amplifier as defined in claim 7 including dc inner block means coupled to the helical coupler in the output section of the microwave amplifier for blocking dc current collected on the helical coupler due to electron beam interception.