Microwave energy transfer component for electrosurgical apparatus

Patent metadata

Field	Value
Publication number	US-11759256-B2
Application number	US-201816328662-A
Country	US
Kind code	B2
Filing date	Feb 7, 2018
Priority date	Feb 13, 2017
Publication date	Sep 19, 2023
Grant date	Sep 19, 2023

Abstract

A microstrip impedance transformer that permits efficient (i.e. low loss) coupling of a microwave feed line (e.g. a conventional 50Ω coaxial cable) to an instrument cable, where the instrument cable has a lower impedance (e.g. in the range 12 to 14Ω) and includes an internal passageway. The microstrip impedance transformer is configured to perform impedance matching between the microwave feed line and the instrument cable in a manner that does not adversely affect a separate feed, e.g. for delivering fluid, into the internal passageway.

First claim

The invention claimed is:

1. An electrosurgical apparatus comprising:
a microwave feed line for carrying microwave electromagnetic (EM) energy having a frequency from an electrosurgical generator;
an instrument cable for insertion into a patient's body to a treatment site, the instrument cable comprising:
a coaxial transmission line for conveying the microwave EM energy, and
an internal passageway for providing access to the treatment site; and

a junction formed between a distal end of the microwave feed line and a proximal end of the instrument cable, wherein the junction is configured to transfer the microwave EM energy directly between the distal end of the microwave feed line and the proximal end of the instrument cable,
wherein the microwave feed line has a first impedance at the frequency of the microwave EM energy,
wherein the instrument cable has a second impedance at the frequency of the microwave EM energy, the second impedance being lower than the first impedance, and
wherein the junction comprises:
a microstrip impedance transformer configured to match the first impedance and the second impedance, the microstrip impedance transformer being directly connected to the distal end of the microwave feed line and the proximal end of the instrument cable; and
a hollow conduit in fluid communication with the internal passageway for conveying fluid to the treatment site.

2. An electrosurgical apparatus according to claim 1 , wherein the microstrip impedance transformer comprises:
a planar dielectric substrate having an upper surface and a lower surface on opposite sides thereof,
a ground conductor layer on the lower surface; and
a microstrip conductor layer on the upper surface,
wherein the microstrip conductor layer is set back from the periphery of the upper surface.

3. An electrosurgical apparatus according to claim 2 , wherein the microstrip conductor layer comprises a proximal microstrip track portion having a first width (W 1 ) and a distal microstrip track portion having a second width (W 2 ), wherein the second width is greater than the first width (W 2 >W 1 ).

4. An electrosurgical apparatus according to claim 3 , wherein an electrical length of the distal microstrip track portion is an odd multiple of a quarter wavelength of the microwave EM energy conveyed by the quarter wave microstrip impedance transformer.

5. An electrosurgical apparatus according to claim 3 , wherein the second width is selected to make a characteristic impedance Z 0 of the distal microstrip track portion satisfy the equation:
Z 0 =√{square root over ( Z in −Z L )}

where Z in is an impedance of distal microstrip track portion and Z L is an impedance of the instrument cable at the frequency of the microwave EM energy.

6. An electrosurgical apparatus according to claim 3 , wherein the first width is selected to make a characteristic impedance of the distal microstrip track portion equal to the impedance of the microwave feed line at the frequency of the microwave EM energy.

7. An electrosurgical apparatus according claim 3 , wherein the coaxial transmission line comprises an inner conductor, an outer conductor and a dielectric material separating the inner conductor from the outer conductor, and wherein, at a proximal end of the coaxial transmission line, the inner conductor extends proximally from the dielectric material and outer conductor to overlie the distal microstrip track portion, and the dielectric material extends proximally from a proximal end of the outer conductor to overlie a gap between the microstrip conductor layer and a distal edge of the planar dielectric substrate.

8. An electrosurgical apparatus according to claim 7 , wherein the outer conductor is electrically connected to the ground conductor layer.

9. An electrosurgical apparatus according to claim 3 , wherein the microwave feed line comprises a coaxial cable having an inner conductor electrically connected to the proximal microstrip track portion and an outer conductor electrically connected to the ground conductor layer.

10. An electrosurgical apparatus according to claim 2 , wherein the hollow conduit is mounted on the microstrip conductor layer.

11. An electrosurgical apparatus according to claim 10 , wherein the hollow conduit is a tube that curves away from the planar dielectric substrate as it extends away from the instrument cable.

12. An electrosurgical apparatus according to claim 2 , wherein the microwave feed line and the instrument cable are secured to the planar dielectric substrate at the junction.

13. An electrosurgical apparatus according to claim 12 , wherein the microwave feed line and the instrument cable are secured to the planar dielectric substrate via conductive attachment elements that provide an electrical connection to the ground conductor layer.

14. An electrosurgical apparatus according to claim 1 , wherein the junction comprises a conductive shield housing that surrounds the quarter wave microstrip impedance transformer.

15. An electrosurgical apparatus according to claim 14 , wherein the shield housing acts as a Faraday cage to confine EM fields emitted at the junction.

16. An electrosurgical apparatus according to claim 14 , wherein the hollow conduit extends through an aperture in the shield housing.

17. An electrosurgical apparatus according to claim 14 , wherein the microwave feed line and the instrument cable are secured to the quarter wave microstrip impedance transformer via the shield housing.

18. An electrosurgical apparatus according to claim 1 , wherein the internal passageway is within the inner conductor of the coaxial transmission line.

19. An electrosurgical apparatus according to claim 1 , wherein the second impedance is 12 to 14Ω.

20. An electrosurgical apparatus according to claim 1 , wherein the frequency of the microwave EM energy is a stable fixed frequency selected from 5.8 GHz, 14.5 GHz, 24 GHz and 31 GHz.

Assignees

• Creo Medical Ltd

Inventors

• Hancock Christopher Paul
• White Malcolm
• Preston Shaun

Classifications

• A61B18/1815 Primary

  using microwaves · CPC title

• A61B2018/1823

  Generators therefor · CPC title

• A61B2018/1892

  Details of electrical isolations of the antenna · CPC title

• H01P5/08

  for linking dissimilar lines or devices (H01P1/16, H01P5/04 take precedence; linking lines of the same kind but with different dimensions H01P5/02) · CPC title

• A61B2018/00178

  Electrical connectors · CPC title