Antenna assemblies for medical applications

1. A device for directing energy to a target volume of tissue, comprising:

a helical antenna assembly that includes a helical antenna radiating section, wherein the helical antenna radiating section includes a helical antenna element; and

a sleeve member disposed coaxially about the helical antenna element,

wherein the helical antenna assembly is configured to operate in at least a first mode of operation where the helical antenna element radiates energy at a first wavelength for directing energy into a first portion of the target volume of tissue and a second mode of operation where the helical antenna element radiates energy at a second wavelength for directing energy into a second portion of the target volume of tissue,

wherein the sleeve member is formed of a ferroelectric dielectric material having a variable dielectric constant, the ferroelectric dielectric material of the sleeve member configured to vary the wavelength of the energy radiated by the helical antenna element between the first and second modes of operation, and

wherein the helical antenna assembly is configured to vary the dielectric constant of the sleeve member through the application of a DC voltage field to the ferroelectric dielectric material of the sleeve member.

2. The device of claim 1 , wherein, when the device operates in the first mode of operation, the helical antenna element radiates energy in a plane perpendicular to a longitudinal axis of the helical antenna element.

3. The device of claim 2 , wherein, when the device operates in the second mode of operation, the helical antenna element radiates energy along the longitudinal axis of the helical antenna element.

4. The device of claim 1 , wherein the sleeve member is disposed coaxially about substantially the entire length of the helical antenna element.

5. The device of claim 1 , wherein the helical antenna element is formed of a shape-memory alloy element.

6. The device of claim 5 , wherein the shape-memory alloy element is at least one of a copper-zinc-aluminum-nickel alloy, a copper-aluminum-nickel alloy, and a nickel-titanium (NiTi) alloy.

7. The device of claim 1 , wherein the helical antenna radiating section further includes a shell encircling the sleeve member.

8. The device of claim 7 , wherein the shell is formed of a conductive material.

9. The device of claim 8 , wherein the shell is slideably moveable along the periphery of the sleeve member between a first position, in which an outer diametrical wall of the sleeve member is entirely covered by the shell, and a second position, in which a portion of the outer diametrical wall of the sleeve member is exposed.

10. The device of claim 9 , wherein, when the device operates in the first mode of operation, the shell is positioned in the second position.

11. The device of claim 9 , wherein, when the device operates in the second mode of operation, the shell is positioned in one of the first position and the second position.

12. The device of claim 7 , wherein the shell is configured to apply a DC voltage field to the ferroelectric dielectric material of the sleeve member to vary the dielectric constant of the sleeve member.

13. The device of claim 1 , wherein the helical antenna radiating section further includes a dielectric core located at the interior of the helical antenna element coaxially with the helical antenna element.

14. The device of claim 13 , wherein the dielectric core is formed of a ferroelectric dielectric material.

15. The device of claim 13 , wherein the dielectric properties of the sleeve member and the dielectric core are substantially the same.

16. The device of claim 1 , wherein a circumference of the helical antenna element is about 0.8 to about 1.2 of the first wavelength and less than about 0.4 of the second wavelength.

17. The device of claim 1 , wherein the first portion of the target volume of tissue is located substantially adjacent the helical antenna assembly.

18. The device of claim 1 , wherein the second portion of the target volume of tissue located distal of the helical antenna assembly.

19. A method for directing energy to a target volume of tissue, comprising the steps of:

positioning a helical antenna assembly for the delivery of energy to a target volume of tissue, the helical antenna assembly including a helical antenna element and a sleeve member disposed coaxially about the helical antenna element, the sleeve member formed of a ferroelectric dielectric material having a variable dielectric constant;

operating the helical antenna assembly in a first mode of operation radiating energy at a first wavelength to perform a first procedure on a first portion of the target volume of tissue, the first portion located substantially adjacent to a longitudinal portion of the helical antenna assembly; and

operating the helical antenna assembly in a second mode of operation radiating energy at a second wavelength to perform a second procedure on a second portion of the target volume of tissue, the second portion located distal to an end portion of the helical antenna assembly,

wherein the wavelength of the energy radiated by the helical antenna assembly is varied between the first and second modes of operation by varying the dielectric constant of the sleeve member, the dielectric constant of the sleeve member being varied by the application of a DC voltage field to the ferroelectric dielectric material.