Directional microwave applicator and methods
Inventors
Fink, Patrick W. • Lin, Greg Y. • Chu, Andrew W. • Dobbins, Justin A. • Arndt, G. Dickey • Ngo, Phong H.
Assignees
National Aeronautics and Space Administration NASA
Publication Number
US-7410485-B1
Publication Date
2008-08-12
Expiration Date
2025-01-14
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Abstract
A miniature microwave antenna is disclosed which may be utilized for biomedical applications such as, for example, radiation induced hyperthermia through catheter systems. One feature of the antenna is that it possesses azimuthal directionality despite its small size. This directionality permits targeting of certain tissues while limiting thermal exposure of adjacent tissue. One embodiment has an outer diameter of about 0.095″ (2.4 mm) but the design permits for smaller diameters.
Core Innovation
The invention provides a miniature directional microwave antenna suitable for biomedical applications such as radiation induced hyperthermia through catheter systems. The antenna is designed to possess azimuthal directionality despite its small size, permitting targeting of specific tissues while limiting thermal exposure to adjacent tissue. One embodiment has an outer diameter of about 0.095 inches (2.4 mm), but the design allows for smaller diameters.
The antenna comprises an elongate structure with a substantially non-radiating portion functioning as a waveguide with defined waveguide gaps, and a radiating portion comprising an antenna conductor and antenna elements defining an antenna gap continuous with the waveguide gap. The antenna gap width is greater than the waveguide gap width, creating azimuthal directionality of radiation. The waveguide conductors and antenna elements are mounted on or closely adjacent to the surface of the elongate structure, which is preferably rounded and non-conductive. An impedance matching section is provided between the non-radiating and radiating portions to ensure efficient power transfer.
The problem being solved is that conventional microwave antennas for medical applications often lack directionality due to space constraints within catheters or syringes, resulting in symmetric radiation that may undesirably heat healthy tissues adjacent to damaged tissues. Larger antennas capable of directionality cannot fit within small diameter catheters. Prior art attempts include expandable antennas limited to regions with sufficient interior space. The invention addresses the need for a small diameter antenna that provides azimuthal directionality to focus microwave energy effectively within confined spaces such as catheters or syringes.
Claims Coverage
The patent contains one independent claim covering a miniature microwave applicator with multiple inventive features related to its structural and functional aspects.
Miniature microwave applicator structure with waveguide and radiating portions
The applicator comprises an elongate structure with a substantially non-radiating portion containing a waveguide mounted on or closely adjacent to the surface, defining at least one waveguide gap, and a radiating portion containing an antenna conductor and one or more antenna elements mounted on or closely adjacent to the surface. The antenna gap is continuous with the waveguide gap and has a width greater than that of the waveguide gap.
Impedance matching section with variable gap width
An impedance matching section is positioned between the substantially non-radiating portion and the radiating portion, where the impedance matching gap width varies along its length to ensure smooth transition and minimize impedance mismatch.
Waveguide conductors continuity and configuration
The waveguide includes a center conductor and substantially continuous second and third conductors extending along the non-radiating and into the radiating portions, where the second and third conductors are electrically shorted to effectively provide a single conductor. These conductors decrease in width within the radiating portion.
Electrical connection with coaxial cable
The apparatus includes a coaxial cable electrically connected to the substantially non-radiating portion, where the coaxial cable inner conductor is either shorted or electromagnetically coupled to the waveguide center conductor, and the coaxial sheath is connected to the ground conductors completing the ground path.
Radiating portion design for azimuthal microwave radiation
The antenna conductor of the radiating portion is spaced sufficiently from the antenna elements so that it acts as a microwave radiator, with the antenna elements being substantially arc-shaped in cross-section to direct the microwave energy predominately in an azimuthal direction relative to the antenna conductor.
Radiating portion length for resonance or traveling wave operation
The radiating portion is characterized by a length that results in it being substantially resonant over a predetermined operating frequency band, preferably at the first resonance or designed such that energy reflected at the end of the radiating portion is substantially radiated or absorbed by surrounding biological material before returning to the waveguide portion.
The independent claim covers a miniature microwave applicator with a novel combination of structural features including a waveguide and radiating antenna with variable gap widths, impedance matching, specific conductor arrangements, connections to coaxial cables, azimuthal radiation capability, and controlled radiating section length to optimize directional microwave delivery in biomedical contexts.
Stated Advantages
Provides azimuthal directionality of microwave radiation despite the antenna's miniature size, allowing targeted heating within small confined spaces like catheters or syringes.
Limits thermal exposure to adjacent healthy tissue by directing microwave energy preferentially toward targeted damaged tissue.
Enables integration within very small diameter devices, e.g., about 0.095 inches diameter or smaller, suitable for minimally invasive biomedical procedures.
Includes impedance matching features and structural design that minimize power reflection and maximize power delivered into biological tissue.
Allows internal passage for cooling fluids or other functions without compromising antenna operation due to conductor positioning.
Documented Applications
Microwave angioplasty system for treatment of vascular tissues.
Microwave-based hyperthermia treatment system to replace or supplement vertebroplasty.
Microwave treatment system for prostate tumors requiring directional heating within small confines.
Biological sterilization applications in difficult to access regions.
Miniaturized antenna use in catheters, syringes, or cannulas for insertion into biological tissue.
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