particular embodiments of the present disclosure will be described herein below with reference to the accompanying drawings . in the following description , well - known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail . fig1 shows a microwave ablation system 10 that includes a microwave antenna assembly 12 coupled to a microwave generator 14 via a flexible coaxial cable 16 . the microwave antenna assembly 12 may be a dipole antenna of 1 . 6 cm in length . in order to ablate small tumors , microwave antenna assembly 12 has a short radiating section ( srs ). the microwave antenna assembly 12 is capable of reducing the antenna length to one - quarter of the wavelength length required , effectively using half the length of the half wave length dipole antenna . the generator 14 is configured to provide microwave energy at an operational frequency from about 500 mhz to about 5000 mhz . antenna assembly 12 is generally comprised of radiating portion 18 , which may be connected by feedline 20 ( or shaft ) to the cable 16 . more specifically , the antenna assembly 12 is coupled to the cable 16 through a connection hub 22 . the connection hub 22 also includes an outlet fluid port 30 and an inlet fluid port 32 defined therein that are in fluid communication with a coolant jacket 38 and flow channel 13 ( see fig4 ). the coolant jacket 38 encloses a proximal portion 42 and the feedline 20 allowing coolant fluid from the ports 30 and 32 to be supplied and circulated around a portion of the antenna assembly 12 . the ports 30 and 32 also include inner lumens defined therein ( not shown ) that are in fluid communication with the flow channel 13 . the ports 30 and 32 are coupled to a supply pump 34 that is , in turn , coupled to a supply tank 36 . the supply tank 36 stores the coolant fluid and maintains the fluid at a predetermined temperature . in one embodiment , the supply tank 36 may include a coolant unit which cools the returning liquid from the antenna assembly 12 . in another embodiment , the coolant fluid may be a gas and / or a mixture of fluid and gas . assembly 12 also includes a tip 48 having a tapered end 24 that terminates , in one embodiment , at a pointed end 26 to allow for insertion into tissue with minimal resistance at a distal end of the radiating portion 18 . in those cases where the radiating portion 18 is inserted into a pre - existing opening , tip 48 may be rounded or flat . fig2 illustrates the radiating portion 18 of the antenna assembly 12 having an unbalanced dipole antenna 40 . the dipole antenna 40 includes a proximal portion 42 and a distal portion 44 interconnected by an injection molded seal 46 . the distal portion 44 and the proximal portion 42 are of different , unequal lengths so that the dipole antenna 40 is unbalanced . in one embodiment , the distal portion 44 may be longer than the proximal portion 42 . in one embodiment , in which the feedline 20 is formed from a coaxial cable , the outer conductor 56 and the inner insulator 52 may be sliced off to reveal the inner conductor 50 , as shown in fig5 . the dipole antenna 40 is coupled to the feedline 20 that electrically connects antenna assembly 12 to the generator 14 ( fig1 ). the assembly 12 includes a coolant jacket 38 coupled to a fluid seal 8 ( see fig4 ), which in turn is coupled to an injection molded seal 46 . the coolant jacket 38 may be formed from a medical grade metal . the injection molded seal 46 may be made of a high strength polyimide resin . the polyimide resin may be vespel ® sold by dupont of wilmington , del . in one embodiment , the injection molded seal 46 is fabricated by injecting a polyimide material into an inflow slot 9 a to an outflow slot 9 b of the distal portion 44 . as shown in fig3 , the injection molded seal 46 is disposed in - between a distal radiating section 44 and the ceramic layer 2 . the ceramic layer may be made of alumina ceramic . the injection molded seal 46 bonds the distal portion 44 and the ceramic layer 2 to the proximal portion 42 while providing mechanical strength to the distal portion 44 . as shown in fig3 - 4 , the feedline 20 includes an inner conductor 50 ( e . g ., wire ) surrounded by an inner insulator 52 , which is then surrounded by an outer conductor 56 ( e . g ., cylindrical conducting sheath ). the inner and outer conductors 50 , 56 may be constructed of copper , gold , stainless steel or other conductive metals with similar conductivity values . the metals may be plated with other materials , e . g ., other conductive materials , to improve their properties , e . g ., to improve conductivity or decrease energy loss , etc . in one embodiment , the inner insulator layer 52 is formed from a fluoropolymer , such as tetrafluorethylene , perfluorpropylene , and the like , and has a thickness of about 0 . 011 - 0 . 013 inches . in one embodiment , the feedline 20 may be formed from a coaxial semi - rigid or flexible cable having a wire with a 0 . 047 ″ outer diameter rated for 50 ohms . the inner insulator 52 may have a dielectric constant from about 1 to 10 . overlaying the outer conductor 56 is a flow channel 13 that cools the majority of the proximal portion 42 . the flow channel 13 is in fluid communication with fluid ports 30 , 32 . a polyimide inflow sleeve 15 is disposed in the flow channel 13 to create an inflow channel 17 a and an outflow channel i 7 b for the coolant . the abundance of cooling fluid from the concentric in - flow design of the polyimide inflow sleeve 15 in the flow channel 13 acts as a lossy material to absorb the microwave energy as well as to cool the feedline 20 for percutaneous use . in another embodiment , the fluid seal 8 may also be formed from solid wire machined component or a cylindrical conductor filled with solder . the fluid seal 8 is thereafter coupled to the outer conductor 56 ( joint e ), as shown in fig3 - 4 . this may be accomplished by soldering the fluid seal 8 to the outer conductor 56 , such as by melting the solder of the fluid seal 8 and inserting the outer conductor 56 therein . the distal portion 44 includes a conductive member 45 that may be formed from any type of conductive material , such as metals ( e . g ., copper , stainless steel , tin , and various alloys thereof ). the distal portion 44 may have a solid structure and may be formed from solid wire ( e . g ., 10 awg ). in another embodiment , the distal portion 44 may be formed from a hollow sleeve of an outer conductor of coaxial cable or another cylindrical conductor . the cylindrical conductor may then be filled with solder to convert the cylinder into a solid shaft . more specifically , the solder may be heated to a temperature sufficient to liquefy the solder within the cylindrical conductor ( e . g ., 500 ° f . ), thereby creating a solid shaft . as shown in fig2 and 3 , the distal portion 44 is coupled to the tip 48 , which may be formed from a variety of heat - resistant materials suitable for penetrating tissue , such as metals ( e . g ., stainless steel ) and various thermoplastic materials , such as poletherimide , polyimide thermoplastic resins , an example of which is ultem ® sold by general electric co . of fairfield , conn . the tip 48 may be machined from various stock rods to obtain a desired shape . the tip 48 may be attached to the distal portion 44 using various adhesives , such as epoxy seal . if the tip 48 is metal , the tip 48 may be soldered to the distal portion 44 or may be machined as one continuous component . fig6 is an exploded view of the microwave antenna assembly 12 . the microwave antenna assembly 12 includes a proximal portion 42 and a distal portion 44 . the proximal portion 42 may include an inner conductor 50 , an inner insulator layer 52 , and an outer conductor 56 . the proximal portion 42 may also include a flow channel 13 defined therein ( not shown ) that includes an inflow channel 17 a and an outflow channel 17 b that are separated by a polyimide inflow tube 15 . the polyimide inflow tube 15 ( not shown ) may be inserted into a pocket of a fluid seal 8 to cool the proximal portion 42 . the distal portion 44 includes an inner conductor 50 , a distal radiating section 51 , an injection molded seal 46 , and a ceramic layer 2 . fig7 a - 7c are enlarged cross - sectional views of sections a - a , b - b , and c - c of the microwave antenna assembly of fig4 . fig7 a illustrates a cross section at section a - a . section a - a illustrates from the inside towards the outer surface , an inner conductor 50 , insulator 52 , outer conductor 56 , flow channel 13 ( specifically inflow channel 17 a ), polyimide inflow tube 15 , flow channel 13 ( specifically outflow channel 17 b ), and coolant jacket 38 . fig7 b illustrates a cross section at section b - b . section b - b illustrates from the inside towards the outer surface , an inner conductor 50 , insulator 52 , outer conductor 56 , flow channel 13 ( specifically inflow channel 17 a ), polyimide inflow tube 15 , flow channel 13 ( specifically outflow channel 17 b ), fluid seal 8 , and coolant jacket 38 . fig7 c illustrates a cross section taken at section c - c of the distal portion . section c - c illustrates from the inside towards the outer surface , an inner conductor 50 , insulator 52 , an injection molded seal 46 , and a ceramic layer 2 . referring back to fig2 - 4 , the microwave antenna assembly 12 may be manufactured in various steps . a coaxial cable that includes the inner conductor 50 , insulator layer 52 , and outer conductor 56 may be manufactured and assembled as one component . the outer conductor 56 may be soldered to the fluid seal 8 , for example at joint e , to provide the electrical joint , if needed . the coolant jacket 38 may be bonded , threaded , laser welded , soldered or crimped to the fluid seal 8 at joint d . the coolant jacket 38 and the fluid seal 8 may be assembled as one component . the polyimide inflow tube 15 may be configurable to slide into a pocket of the fluid seal 8 . the inner conductor 50 is configured to slide inside a hole of the distal portion 44 . the distal portion 44 is affixed to a distal end of the inner conductor 50 by laser welding , soldering or crimping at joint f . the coaxial cable , coolant jacket 38 , proximal portion 42 , ceramic layer 2 , and distal portion 44 are placed into an injection mold cavity . fig8 is a schematic diagram of a mold according to the present disclosure . the mold 53 is used to inject a high strength polyimide material in - between the inner conductor 50 and the ceramic layer 2 . the mold 53 includes mold halves 111 a and 111 b . mold halves 111 a and 111 b include portions / cavities to receive coaxial cable , coolant jacket 38 , fluid seal 8 , ceramic layer 2 , and trocar tip 48 . mold halves 111 a and 111 b also include an inflow slot 9 a and an outflow slot 9 b . the mold halves 111 a and 111 b are clamped tightly together and heated polyimide is injected into the inflow slot 9 a until the heated polyimide fills into outflow slot 9 b defined therein . the polyimide flows into a cavity to form a uniform layer of polyimide layer along the distal portion 44 . the polyimide material bonds the distal portion 44 and the ceramic layer to the proximal portion while providing mechanical strength to the distal portion . in another embodiment , the mold 53 does not include a cavity for the trocar tip 48 . in such an embodiment , when the injection molding process is complete , the antenna assembly 12 is finished by installing the trocar tip 48 . fig9 illustrates various shapes and forms of a trocar tip 48 installed onto a sheath 38 , namely a stainless steel tip 48 a and a dielectric tip 48 b . both tips 48 a and 48 b include insertion bases 51 a and 51 b having an external diameter that is smaller than diameter of the tips 48 a and 49 allowing for easier insertion into a sheath 38 . the configuration also provides for a better seal between the tip 48 and the sheath 38 . in another embodiment , the sheath 38 and tip 48 c maybe threaded so as to attach to each other . therefore , the tip 48 c may be tightly screwed into the sheath 38 . the described embodiments of the present disclosure are intended to be illustrative rather than restrictive , and are not intended to represent every embodiment of the present disclosure . various modifications and variations can be made without departing from the spirit or scope of the disclosure as set forth in the following claims both literally and in equivalents recognized in law .
a method of fabricating a microwave antenna assembly is disclosed . the fabrication method includes providing a proximal portion having an inner conductor and an outer conductor , the inner conductor extending at least partially therein . the method further includes providing a distal portion disposed distally of the proximal portion , with the inner conductor extending at least partially therein . a high strength material may be injected from an inflow slot to an outflow slot of the distal portion such that the material is disposed in - between the inner conductor and a ceramic layer . the material bonds the distal portion and the ceramic layer to the proximal portion while providing mechanical strength to the distal portion .