Microwave amplifier for electrosurgical instruments

Abstract

Various embodiments provide a microwave amplifier for an electrosurgical instrument. The microwave amplifier includes a cable assembly, a proximal delivery section, and a distal amplifier section. The proximal delivery section is connected to a proximal end of the cable assembly, the proximal delivery section including a DC source configured to deliver a DC signal through the cable assembly and a microwave source configured to deliver a microwave signal through the cable assembly. The distal amplifier section is connected to the distal end of the cable assembly, the distal amplifier section including a power amplifier configured to receive a microwave signal as an input signal to be amplified. The distal amplifier section is configured to apply the DC signal as a drain voltage across the power amplifier. The power amplifier also has an output connectable to deliver the amplified microwave signal to a structure configured to deliver microwave energy to biological tissue. Another embodiment provides an electrosurgical instrument including the microwave amplifier.

Description

[Technical field]

[0001] The present invention relates to an electrosurgical device in which microwave frequency energy is used to treat living tissue, for example to effect ablation or hemostasis (i.e., to seal ruptured blood vessels by promoting blood clotting), and which may also be used as part of a surgical device that also provides radio frequency energy, for example to cut tissue. [Background technology]

[0002] Electromagnetic (EM) energy, particularly microwave and radio frequency (RF) energy, has been found to be useful in electrosurgery due to its ability to cut, coagulate, and ablate body tissue. Generally, devices for delivering EM energy to body tissue include a generator with an EM energy source and an electrosurgical instrument connected to the generator to deliver energy to the tissue. Conventional electrosurgical instruments are often designed to be inserted percutaneously into the patient's body. However, it can be difficult to place the instrument percutaneously inside the body, for example, when the target site is in a moving lung or a thin-walled portion of the gastrointestinal (GI) tract. Other electrosurgical instruments can be delivered to the target site by a surgical scope device (e.g., an endoscope) that can pass through internal body passages such as the airway or the lumen of the esophagus or colon. This allows for less invasive treatments, thereby reducing patient mortality and intraoperative and postoperative complication rates.

[0003] Tissue ablation using microwave EM energy is based on the fact that biological tissue is composed primarily of water. Human soft organ tissues typically have a water content of 70%-80%. Water molecules have a permanent electric dipole moment, meaning that there is a charge imbalance in the molecule. This charge imbalance causes the molecule to move in response to the force generated by the application of a time-varying electric field, rotating to align its electric dipole moment with the polarity of the applied electric field. At microwave frequencies, the molecules rapidly vibrate, resulting in frictional heating, which results in the dissipation of the electric field energy in the form of heat. This is known as dielectric heating.

[0004] This principle is utilized in microwave ablation therapy, in which the application of a localized electromagnetic field at microwave frequencies rapidly heats water molecules in targeted tissue, resulting in tissue coagulation and cell death. It is known to use microwave emitting probes to treat various conditions in the lungs and other organs. For example, in the lungs, microwave radiation can be used to treat asthma and to ablate tumors or lesions.

[0005] Surgical resection is a method of removing a portion of an organ from the human or animal body. Such organs may contain a large number of blood vessels. When tissue is cut (divided or transected), tiny blood vessels called arterioles are damaged or ruptured. Initial bleeding is followed by a clotting cascade in which blood is converted into a clot in an attempt to plug the bleeding point. During surgery, it is desirable for the patient to lose as little blood as possible, and therefore various devices have been developed in an attempt to provide a bleeding-free cut. In the case of endoscopic procedures, it is undesirable for bleeding to occur, or for bleeding not to be addressed as soon as possible or in an appropriate manner, as blood flow may obstruct the operator's view, which may force the procedure to be terminated and another method, e.g., laparotomy, used instead.

[0006] Electrosurgical generators are common in hospital operating rooms for use in open and laparoscopic procedures, and increasingly in endoscopy laboratories. In endoscopic procedures, electrosurgical accessories are typically inserted through lumens in the endoscope. When contrasted with comparable access channels for laparoscopic procedures, such lumens are relatively narrow in diameter and longer in length. For bariatric patients, surgical accessories may measure 300 mm from handle to RF tip, whereas the equivalent distance for a laparoscope may exceed 2500 mm.

[0007] Instead of a sharp blade, it is known to use radio frequency (RF) energy to cut biological tissue. The method of cutting using RF energy works on the principle that as an electric current passes through the tissue matrix (aided by the ionic content of the cells and intercellular electrolytes), heat is generated due to the impedance to the flow of electrons across the tissue. When an RF voltage is applied to the tissue matrix, sufficient heat is generated within the cells to vaporize the water in the tissue. As a result of this increased desiccation, the tissue adjacent to the cutting pole of the RF blade loses direct contact with the blade, especially adjacent to the RF emission area of ​​the instrument (referred to herein as the RF blade) which has the highest current density in the entire current path through the tissue. The applied voltage is then generated across almost the entire gap, and as a result, this gap ionizes and a plasma is formed. The plasma has a very high volume resistivity compared to the tissue. This differentiation is important because it focuses the applied energy in the plasma that has completed the electrical circuit between the cutting pole of the RF blade and the tissue. Any volatile material that enters the plasma at a sufficiently slow speed will be vaporized and thus recognized as a plasma cutting through the tissue.

[0008] GB2486343 discloses a control system for an electrosurgical device that delivers both RF and microwave energy to treat biological tissue, where an energy delivery profile of both the RF and microwave energy delivered to the probe is set based on sampled voltage and current information of the RF energy delivered to the probe, and sampled forward and reflected power information of the microwave energy delivered to and from the probe. Summary of the Invention [Means for solving the problem]

[0009] Most generally, the invention provides a microwave amplifier as part of an electrosurgical instrument mounted at the distal end of a flexible cable assembly, e.g., a cable assembly suitable for insertion through a patient's body and possibly through an instrument channel of a surgical scope device, e.g., an endoscope, bronchoscope, or the like, to a treatment site. The cable assembly may provide a common path for low power microwave signals and DC signals. The microwave amplifier includes a power amplifier arranged to amplify a low power microwave input to a power level suitable for treatment. In one example, the cable assembly may carry both a primary DC signal for providing a drain voltage for the power amplifier and a secondary DC signal for providing a bias voltage for the power amplifier. In another example, the microwave amplifier includes circuitry at the distal end that derives drain and gate voltages for the power amplifier from a single DC signal.

[0010] Both arrangements can be contrasted with conventional structures in which microwave energy at a power level suitable for enabling treatment is generated proximally and then transmitted by a cable assembly. The present arrangement avoids the undesirable cable losses that may occur in previous arrangements. This can be illustrated with an example. If 10 W of power is required for the instrument and there is a loss of 10 dB along the length of the cable, a conventional system would require an input power of 100 W. In such a system, 90 W of power is lost along the cable, so the proximal amplifier must be able to achieve an output power of 100 W or more. In contrast, by using an amplifier with a gain of 10 dB at the distal end, the device of the present invention can achieve an output of 10 W if the power of the microwave signal received at the distal part is 1 W. With a cable loss of 10 dB, this requires a power of 10 W at the proximal end of the microwave signal. Thus, the loss along the cable in this scenario (9 W) is an order of magnitude less than in the conventional arrangement.

[0011] According to the present invention, there is provided a microwave amplification apparatus for an electrosurgical instrument, comprising a cable assembly, a proximal delivery section connected to a proximal end of the cable assembly, the proximal delivery section comprising a DC source configured to deliver a DC signal through the cable assembly and a microwave source configured to deliver a microwave signal through the cable assembly, and a distal amplifier section connected to a distal end of the cable assembly, the distal amplifier section comprising a power amplifier configured to receive a microwave signal as an input signal to be amplified, the distal amplifier section configured to apply the DC signal as a drain voltage across the power amplifier, the power amplifier having an output connectable to deliver the amplified microwave signal to a structure configured to deliver microwave energy to biological tissue. In the apparatus, the DC signal is manipulated to enable operation of the power amplifier at the distal end of the cable assembly. Thus, the apparatus operates without transmitting a high power microwave signal through the cable assembly.

[0012] The device may include a gate voltage extraction module configured to extract a bias voltage from the DC signal and apply it to the gate of the power amplifier. The gate voltage extraction module may be in the distal amplification section or the proximal delivery section. When in the proximal delivery section, the DC signal may include two separate components: a primary DC signal corresponding to the drain voltage of the power amplifier and a secondary DC signal corresponding to the bias voltage of the power amplifier. The separate components may be conveyed by independent transmission lines in the cable assembly.

[0013] The cable assembly may include a coaxial transmission line with an inner conductor separated from an outer conductor by a dielectric material. The microwave signal may be transmitted by the coaxial transmission line. Advantageously, the DC signal may be transmitted through the inner conductor, whereby a common transmission line structure is used to transmit both the microwave signal and the DC signal. In another example, the DC signal may be transmitted by a separate transmission line within the cable assembly. If the DC signal has two components, one component (e.g., a secondary DC signal) may be transmitted on the inner conductor of the coaxial transmission line, and the other component is transmitted on a separate transmission line.

[0014] The microwave signal may be coupled to the coaxial transmission line through a capacitor to prevent the DC signal from leaking back to the microwave source. The DC source may include a low pass filter to prevent the microwave signal from leaking back into the DC source.

[0015] The output of the power amplifier may include a capacitor configured to couple the amplified microwave signal to the structure, the capacitor acting as a DC isolator to prevent DC signals from being transmitted to the structure for delivering microwave energy to the living tissue, i.e., the capacitor may protect the patient from the DC signals.

[0016] The gate voltage extraction module may include a DC-DC converter configured to down-convert a voltage of the DC signal to generate the bias voltage. For example, the DC-DC converter may include a step-down converter.

[0017] In one embodiment, the gate voltage extraction module may be configured to extract a pair of bias voltages from the DC signal. The pair of bias voltages may include a first bias voltage corresponding to a non-conducting state of the power amplifier and a second bias voltage corresponding to a conducting state of the power amplifier. For example, the gate voltage extraction module may comprise a pair of step-down converters connected in parallel, the pair of step-down converters comprising a first step-down converter for generating the first bias voltage and a second step-down converter for generating the second bias voltage. The apparatus may further comprise a gate control module configured to selectively apply the first bias voltage or the second bias voltage to the gate of the power amplifier. For example, the gate control module may be configured to apply the first bias voltage as a default condition (to ensure that the power amplifier is non-conducting and therefore does not provide any gain to the input signal) and can override this condition to apply the second bias voltage in certain circumstances (i.e., when treatment of tissue is sought). For example, the gate control module may comprise a switch arranged to selectively apply a first bias voltage or a second bias voltage to the gate of the power amplifier. The distal amplifier may comprise a voltage rail arranged to adopt an operating voltage provided by a DC signal. The switch may be configured to select the second bias voltage upon application of the operating voltage to the voltage rail. In other words, the switch is operably connected to the voltage rail, and the actuation of the switch depends on the voltage of the voltage rail. When the voltage of the voltage rail is below a threshold (indicating, for example, the absence of a DC signal), the switch adopts a default position and the power amplifier is in a non-conducting state.

[0018] The gate control module may further comprise a delay circuit arranged to introduce a time lag between applying the operating voltage to the voltage rail and actuating the switch to select the second bias voltage.

[0019] The gate extraction voltage module may be configured to provide both the first and second bias voltages with opposite polarity to the drain voltage. In one example, the drain voltage is 28 V, the first bias voltage is −6 V, and the second bias voltage is −2 V. In this example, the second bias voltage is chosen to be just before the transition to a conductive state in the power amplifier's characteristics.

[0020] The microwave signal may have a power of 1 W or less at the proximal end of the cable assembly, while the amplified microwave signal may have a power of 5 W or more, such as 10 W or more.

[0021] The distal amplifier module may include an isolation structure to protect components that process DC signals from microwave signals. For example, the distal amplifier module may include a low pass filter connected between the gate voltage extraction module and the gate of the power amplifier. The low pass filter may be fabricated on a microstrip transmission line. The low pass filter may include a pair of quarter wavelength stubs each having a length of ((2n-1)λ) / 4, the pair of quarter wavelength stubs may include a first quarter wavelength stub located at a distance of nλ / 2 from the gate of the power amplifier and a second quarter wavelength stub spaced a distance nλ / 2 from the first quarter wavelength stub, where λ is the wavelength of the microwave signal and n is an integer equal to or greater than 1.

[0022] The distal amplifier section includes a voltage rail arranged to adopt an operating voltage provided by a DC signal, the voltage rail being connected by a first connection line to a distal end of the cable assembly to receive the DC signal, and the voltage rail being connected by a second connection line to the drain of the power amplifier to provide a drain voltage. The voltage rail can be protected from the microwave signal in a manner similar to the gate voltage extraction module by appropriately arranging a low pass filter. For example, there may be a proximal low pass filter on the first connection line and a distal low pass filter on the second connection line. The proximal low pass filter includes a pair of quarter wavelength stubs each having a length of ((2n-1)λ) / 4, the pair of quarter wavelength stubs including a first quarter wavelength stub located at a distance of nλ / 2 from a connection point between the first connection line and the cable assembly, and a second quarter wavelength stub spaced a distance nλ / 2 from the first quarter wavelength stub, where λ is the wavelength of the microwave signal, and n is an integer equal to or greater than 1. The distal low pass filter comprises a pair of quarter wavelength stubs each having a length of ((2n-1)λ) / 4, the pair of quarter wavelength stubs comprising a first quarter wavelength stub located at a distance nλ / 2 from the drain of the power amplifier and a second quarter wavelength stub spaced a distance nλ / 2 from the first quarter wavelength stub, where λ is the wavelength of the microwave signal and n is an integer greater than or equal to 1.

[0023] In another aspect, an electrosurgical instrument is provided that includes a microwave amplifier arrangement as described above and a radiating tip connected to an output of a power amplifier, the radiating tip comprising an antenna configured to radiate the amplified microwave signal to biological tissue. Any suitable antenna structure can be used. For example, the radiating tip can have a coaxial structure in which an inner conductor extends beyond a distal end of an outer conductor to form an antenna. Alternatively, the radiating tip can have a planar structure including a planar piece of insulating dielectric material having layers of metallization on opposing surfaces. The layers of metallization can be configured to operate as an antenna.

[0024] The microwave amplifier and emitting tip may be dimensioned to be insertable through an instrument channel of a surgical scope device.

[0025] The emitting tip can be configured to receive an additional input, for example, radio frequency energy. The emitting tip can include a means for delivering a fluid to the treatment site (e.g., a needle, etc.).

[0026] As used herein, the term "inner" means radially closer to the center (e.g., axis) of the instrument channel and / or coaxial cable, and the term "outer" means radially farther from the center (axis) of the instrument channel and / or coaxial cable.

[0027] As used herein, the term "conductive" means electrically conductive, unless the context indicates otherwise.

[0028] As used herein, the terms "proximal" and "distal" refer to the ends of an elongate instrument. In use, the proximal end is closer to a generator for providing RF and / or microwave energy, while the distal end is farther from the generator.

[0029] As used herein, "microwave" may be used broadly to refer to a frequency range of 400 MHz to 100 GHz, but preferably refers to the range of 1 GHz to 60 GHz. Preferred spot frequencies of microwave EM energy include 915 MHz, 2.45 GHz, 3.3 GHz, 5.8 GHz, 10 GHz, 14.5 GHz, and 24 GHz. 5.8 GHz may be preferred. Devices may provide energy at more than one of these microwave frequencies.

[0030] The term "radio frequency" or "RF" may be used to indicate frequencies between 300 kHz and 400 MHz.

[0031] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. [Brief description of the drawings]

[0032] [Figure 1] 1 is an overall schematic system diagram of an electrosurgical device to aid in understanding the present invention; [Diagram 2] FIG. 1 is an exploded view of the distal end of an electrosurgical instrument in which the present invention may be used. [Diagram 3] FIG. 2 is a schematic diagram of a microwave generation module based on a distal instrument, an embodiment of the present invention. [Figure 4] FIG. 1 is a schematic diagram of components for delivering DC power and low power microwave energy to a proximal end of a coaxial transmission line. [Diagram 5] FIG. 1 is a schematic circuit diagram illustrating a distal microwave amplifier module for an embodiment of the present invention. [Figure 6] FIG. 13 is a schematic diagram of a distal instrument based microwave generation module, another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Further options and examples Background - Electrosurgery Device 1 is a schematic diagram of an electrosurgical device 400 as disclosed in GB2486343, which is useful for understanding the present invention. The device comprises an RF channel and a microwave channel. The RF channel includes components for generating and controlling an RF frequency electromagnetic signal at a power level suitable for treating (e.g., cutting or desiccation) biological tissue. The microwave channel includes components for generating and controlling a microwave frequency electromagnetic signal at a power level suitable for treating (e.g., coagulation or ablation) biological tissue. As will be explained in more detail below, the present invention provides a means for supplying microwave energy which can replace the microwave channel of the device.

[0034] The microwave channel comprises a microwave frequency source 402 followed by a power splitter 424 (e.g., a 3 dB power splitter) that splits the signal from the source 402 into two. One branch from the power splitter 424 forms the microwave channel. This microwave channel is controlled by a control signal V 10 and a variable attenuator 404 controlled by a controller 406 via a control signal V 11 4. The microwave channel includes a power control module comprising a signal modulator 408 controlled by the controller 406 via a power control signal V , and an amplifier module comprising a drive amplifier 410 and a power amplifier 412 for generating forward microwave EM radiation for delivery from the probe 420 at a power level suitable for treatment. After the amplifier module, the microwave channel continues to a microwave signal coupling module (forming part of a microwave signal detector). The microwave signal coupling module comprises a circulator 416 connected to deliver microwave EM energy from a frequency source to the probe along a path between its first and second ports, a forward coupler 414 at a first port of the circulator 416, and a reflective directional coupler 418 at a third port of the circulator 416. The microwave EM energy from the third port is absorbed in a power dump load 422 after passing through the reflective directional coupler. The microwave signal coupling module also controls a control signal V , for connecting either the forward coupled signal or the reflective coupled signal to a heterodyne receiver for detection. 12 The switch 415 is actuated by the controller 406 via

[0035] The other branch from the power splitter 424 forms the measurement channel. The measurement channel is configured to provide a low power signal from the probe, as it bypasses the amplification train on the microwave channel. The control signal V 13A primary channel selection switch 426, controlled by the controller 406 via , is operable to select a signal from either the microwave channel or the measurement channel to provide to the probe. A high pass filter 427 is connected between the primary channel selection switch 426 and the probe 420 to protect the microwave signal generator from low frequency RF signals.

[0036] The measurement channel includes components arranged to detect the phase and magnitude of the power reflected from the probe, which may provide information about the material, e.g., biological tissue, at the distal end of the probe. The measurement channel includes a circulator 428 connected to provide microwave EM energy from the source 402 to the probe along a path between its first and second ports. The reflected signal returning from the probe is directed to a third port of the circulator 428. The circulator 428 is used to separate the forward and reflected signals to facilitate accurate measurement. However, because the circulator does not completely separate its first and third ports, i.e., some of the forward signal may leak into the third port and interfere with the reflected signal, a carrier cancellation circuit may be used to inject some of the forward signal (from the forward coupler 430) back into the signal emerging from the third port (via the injection coupler 432). The carrier cancellation circuit includes a phase adjuster 434 that ensures that the injected portion is 180 degrees out of phase with any signal leaking from the first port to the third port in order to cancel that signal. The carrier cancellation circuit also includes a signal attenuator 436 that ensures that the magnitude of the injected portion is the same as any leaking signals.

[0037] To compensate for drift in the forward signal, a forward coupler 438 is provided on the measurement channel. The combined output of the forward coupler 438 and the reflected signal from the third port of the circulator 428 are connected to respective input terminals of a switch 440. The switch 440 is controlled by a control signal V 14 The control circuit 406 operates the control circuit 406 via the

[0038] The output of switch 440 (i.e., the output from the measurement channel) and the output of switch 415 (i.e., the output from the microwave channel) are connected to respective input terminals of a secondary channel selection switch 442. This secondary channel selection switch 442 operates in conjunction with the primary channel selection switch to control signal V to ensure that the measurement channel output is connected to the heterodyne receiver when the measurement channel is energizing the probe, and that the measurement channel output is connected to the heterodyne receiver when the microwave channel is energizing the probe. 15 The controller 406 can operate via

[0039] A heterodyne receiver is used to extract phase and magnitude information from the signal output by the secondary channel selection switch 442. Although a single heterodyne receiver is shown in this system, a double heterodyne receiver (including two local oscillators and a mixer) may be used if desired, which mixes down the source frequency twice before the signal enters the controller. The heterodyne receiver includes a local oscillator 444 and a mixer 448 for mixing down the signal output by the secondary channel selection switch 442. The frequency of the local oscillator signal is selected so that the output from the mixer 448 is at an intermediate frequency suitable for receipt by the controller 406. Bandpass filters 446, 450 are provided to protect the local oscillator 444 and the controller 406 from high frequency microwave signals.

[0040] The controller 406 receives the output of the heterodyne receiver and determines (e.g., extracts) from the output information indicative of the phase and magnitude of the forward and / or reflected signals on the microwave channel or the measurement channel. This information can be used to control the delivery of high power microwave EM radiation on the microwave channel or high power RF EM radiation on the RF channel. A user can interact with the controller 406 via a user interface 452.

[0041] The RF channel shown in Figure 1 is connected to the control signal V 16 The RF signal generator includes an RF frequency source 454 connected to a gate driver 456 controlled by the controller 406 via a gate driver 456. The gate driver 456 provides an operating signal to an RF amplifier 458 in a half-bridge arrangement, the drain voltage of which is controllable by a variable DC power supply 460. An output transformer 462 transfers the generated RF signal onto a line for supply to the probe 420. A low pass, band pass, band reject or notch filter 464 is connected onto the line to protect the RF signal generator from high frequency microwave signals.

[0042] A current transformer 466 is connected on the RF channel to measure the current delivered to the tissue load. A voltage divider 468 (which may be taken from the output transformer) is used to measure the voltage. The output signals from the voltage divider 468 and current transformer 466 (i.e., voltage outputs indicative of voltage and current) are conditioned by respective buffer amplifiers 470, 472 and voltage clamping Zener diodes 474, 476, 478, 480 before being connected directly to the controller 406 (shown as signals B and C in FIG. 1).

[0043] To obtain phase information, the voltage and current signals (B and C) are also connected to a phase comparator 482 (e.g., an EXOR gate). The output voltage of this phase comparator 482 is integrated by an RC circuit 484 to produce a voltage output (shown as A in FIG. 1) that is proportional to the phase difference between the voltage and current waveforms. This voltage output (signal A) is connected directly to the controller 406.

[0044] The microwave / measurement channel and the RF channel are connected to a signal combiner 114, which transmits both types of signals separately or simultaneously to a probe 420 through a cable assembly 116. The signals are delivered (e.g., radiated) from the probe 420 to the patient's biological tissue. The cable assembly 116 may be insertable through the entire length of an instrument (working) channel of a surgical scope device (not shown). The probe 420 may be shaped to pass through the instrument channel of the surgical scope device and protrude (e.g., into the patient's body) at the distal end of the tube of the endoscope. The probe 420 may include an active tip for delivering RF EM and / or microwave EM energy to the biological tissue and a retractable hypodermic needle for delivering fluid. These combined technologies provide a unique solution for cutting and destroying unwanted tissue and the ability to seal blood vessels around the target area.

[0045] At the junction of the microwave channel and the signal coupler 114, a waveguide isolator (not shown) may be provided. The waveguide isolator may be configured to perform three functions: (i) to allow the passage of very high microwave power (e.g., more than 10 W); (ii) to block the passage of RF power; and (iii) to provide a high withstand voltage (e.g., more than 10 kV). Also, a capacitive structure (also called a DC break) may be provided at (e.g., inside) or adjacent to the waveguide isolator. The purpose of the capacitive structure is to reduce capacitive coupling across the isolation barrier.

[0046] Background - Electrosurgical Instruments 2 shows an exploded view of an exemplary probe 214 (sometimes referred to as a distal end assembly or instrument tip) that is an electrosurgical instrument to which the present invention may be applied. The probe 214 is attached to the distal end of an outer cannula tube 216 of a flexible shaft that corresponds, for example, to the cable assembly 116 described above with reference to FIG. 1. The cannula tube 216 forms a flexible sleeve that defines a lumen for conveying fluid to the instrument tip, which is fixed at its distal end. To provide a torque transmission function, the outer cannula tube 216 is formed of a braided tube that includes, for example, a braided wire (e.g., stainless steel) wrap attached between a radially inner polymer layer and a radially outer polymer layer, which may be, for example, Pebax®.

[0047] The outer cannula tube 216 is connected at its distal end to a non-braided tubular section 218, which may be a flexible conduit. The tubular section 218 may be formed from any suitable polymeric material, such as Pebax®. The tubular section 218 may have an axial length (i.e., along the shaft axis) of 1 mm or more. This may ensure that a safe distance is introduced between the end of the braid and the proximal end of the distal tip assembly 214 to avoid the risk of the braid heating as a result of capacitive conductance during use of microwave energy. This arrangement may also prevent the two plates of a planar transmission line or the two conductors in a coaxial transmission line from shorting out or connecting to each other.

[0048] The tubular portion 218 may also be referred to as a "soft tip" 218. The soft tip 218 may in some instances be an additional length of polymer tubing bonded to the distal end of the sleeve or cannula tube 216. The bond may be made using any suitable adhesive, such as epoxy. A support tube 217 may be attached over the junction between the tubular portion 218 and the cannula tube 216 to reinforce the junction by providing additional mechanical strength. The support tube 217 may be a short section of polymer tubing within which both the tubular portion 218 and the cannula tube 216 are secured, for example by gluing. The support tube 217 may be flexible and / or may have a length selected to ensure that it does not adversely affect the flexibility of the shaft.

[0049] The junction of tubular portion 218, cannula tube 216, and support tube 217 may also be encased in a heat shrink sleeve (not shown) to provide additional structural strength to the distal end of the shaft.

[0050] The braid within the cannula tube 216 allows torque applied to the proximal end of the shaft to be translated into rotational motion of the instrument tip.

[0051] The distal end of tubular portion 218 is configured to fit over a corresponding proximal portion 220 of a protective shell 222. Protective shell 222 is formed from a rigid material that has low friction with living tissue, such as stainless steel. Shell 222 is preferably formed from a metallic material, but may also be formed from a non-metallic material, such as ceramic. The shell may be formed from: - fastening the distal end assembly 214 to the cannula tube 216; providing a protective underside to an active tip structure that delivers energy to surrounding biological tissue; -Providing a housing and support frame that protects the retractable needle; and - configured to perform several functions for positioning the active tip structure relative to the coaxial cable during assembly and subsequent use.

[0052] The portions of the structure of shell 222 that perform these functions are described in more detail below.

[0053] In an embodiment of the invention, the protective shell 222 is further configured to house distal components of a microwave generation circuit (also referred to herein as a distal microwave generation module), as will be described in more detail with reference to Figures 3-5.

[0054] The distal tip assembly 214 includes an active tip 224, which is a planar piece of dielectric material 221 (e.g., alumina) having conductive layers (e.g., layers of metallization) on its upper and lower surfaces. Each of the conductive layers is electrically connected to a respective one of an inner conductor 228 and an outer conductor 226 of a coaxial cable 142 carried by a cannula tube 216. At the distal end of the coaxial cable 142, its outer sheath is removed to expose a length of the outer conductor 226. The inner conductor 228 of the coaxial cable extends beyond the distal end of the outer conductor 226. As described below, the coaxial cable 142 and the active tip 224 are attached to one another such that a protruding portion of the inner conductor 228 overlies a first conductive layer of the active tip, while the outer conductor 226 is electrically connected to a second conductive layer through a protective shell 222. The first conductive layer is separated from the outer conductor 226 and the second conductive layer is separated from the inner conductor 228 .

[0055] The conductive layer may be formed from a high melting point conductor, such as W or Ti. However, in one example, to facilitate the use of solder in the electrical connection between the inner and outer conductors of the coaxial cable 142 and the active tip 224, a lower melting point conductor may be deposited on the conductive layer in the proximal region where the electrical connection is made. This lower melting point conductor may be silver (Ag) or gold (Au).

[0056] The distal end of the active tip 224 is curved to avoid presenting sharp corners inside the patient.

[0057] The outer conductor 226 is electrically connected to a lower conductive layer on the underside of the active tip 224 through the protective shell 222. The proximal end of the protective shell 222 is formed with a U-shaped channel 248 for receiving and supporting the distal end of the coaxial feed cable 142. The distal end assembly is configured such that the exposed portion of the outer conductor 226 fits within the U-shaped channel 248. A conductive element 230, such as a sleeve or collar, is used to crimp the exposed portion of the outer conductor 226. The compression caused by the crimping means that the coaxial cable deforms in the area received by the protective shell 222. For example, the exposed portion of the outer conductor 226 of the coaxial cable may have an elliptical cross-section so that it abuts against the sides of the U-shaped channel 248 to form a stable electrical contact. That is, the crimped outer conductor 226 may be held by the shell via an interference fit.

[0058] To complete the electrical connection between the outer conductor 226 and the lower conductive layer 229 on the active tip 224, the protective shell 222 is electrically coupled to the lower conductive layer, for example by soldering (see, for example, FIG. 5). In this embodiment, a solder preform 231 is provided for this purpose. The solder preform 231 is shaped to be received within a recess 249 formed in the upper surface of the protective shell 222. In this example, the recess 49 is rectangular and the solder preform 231 has a corresponding shape, but any suitable shape can be used. The recess 249 is set back from the edge of the protective shell to ensure that the solder is only between the lower surface of the active tip 224 and the protective shell 222, i.e., does not flow to the side edges of the active tip 224. When assembled, the solder preform 231 can match the area on the lower surface of the active tip 224 that is coated with the low melting point conductor (e.g., gold) described above. To facilitate the soldering process, a suitable flex (not shown) may be provided along with the solder preform when the components are assembled. The soldering process itself may be induction soldering. The effect of induction soldering may be limited to the area of ​​the active tip 224 and protective shell 222 on the solder preform 231.

[0059] The above configuration is advantageous because the protective shell 222 holds (i) the active tip 224, (ii) the solder preform 231, and (iii) the coaxial cable 142 all in a fixed spatial relationship that ensures accurate and repeatable assembly.

[0060] In an embodiment of the present invention, the connection between the distal portion of the coaxial cable 142 and the active tip 224 may be made through a distal microwave generation module, as described in more detail below.

[0061] The distal tip assembly further comprises a needle guide 232 that is retained within a recess formed in the underside of the protective shell 222. The needle guide 232 is a hollow tube (e.g., a ferrule), for example made of polyimide, in which a hypodermic needle 234 is slidably mounted. The needle 234 is in fluid communication with the interior volume of the cannula tube 216 for receiving and delivering fluid contained therein to the treatment site.

[0062] After the distal tip assembly 214 is assembled, it may be secured within the distal end of the tubular portion 218 by an interference fit and adhesive (e.g., epoxy). The adhesive may also form a plug for the distal end of the tubular portion 218 to provide a fluid tight seal, which results in the only exit for fluids introduced at the interface joint being through the needle 234. Similarly, the joint (e.g., soldered joint) between the inner conductor 228 and the top conductive layer 227 may have a protective cover 251 (see FIG. 5 ), which may be formed from a suitable adhesive (e.g., epoxy). The protective cover 251 may strengthen the connection between the protective shell 222 and the active tip 224, while also forming an end plug of the tubular portion 218, i.e., a fluid tight seal, which results in the only exit for fluids introduced at the interface joint being through the needle 234.

[0063] In use, the active tip 224 is in intimate contact with the patient. The needle 234 can be extended beyond the distal end of the active tip 224 and retracted to a position back inside the guide tube 232 through control of a sliding mechanism on the interface joint that acts on a control wire 235 to deploy and retract the needle 234. In its extended position, the needle is used to inject fluids for the purposes of localized distension and / or marking of tissue. A conductive layer on the active tip 224 forms a bipolar electrode for delivery of RF and / or microwave electromagnetic energy.

[0064] The needle guide 232 extends back inside and proximally of the distal assembly to provide increased creepage clearance, thereby ensuring that RF / microwave activation occurs only over the distal tip region of the active tip 224.

[0065] Instrumental microwave amplification 3 shows an embodiment of a microwave generator 300 according to the present invention. The microwave generator 300 has a proximal delivery section 302 and a distal amplifier section 304 separated by a flexible cable assembly 306. The cable assembly 306 may correspond to the cable assembly 116 described above with respect to FIG.

[0066] The proximal delivery section 302 functions to deliver both DC power and the microwave signal 310 to the cable assembly 306. The cable assembly 306 comprises a coaxial transmission line for delivering the microwave signal 310 to the distal amplifier section 304. The cable assembly 306 may include a separate elongated conductor (e.g., a wire) for delivering the DC power to the distal amplifier section 304. However, the DC power may be advantageously delivered on the inner conductor of the coaxial transmission line that carries the microwave signal 310.

[0067] The proximal delivery section 302 includes a DC power generator 316 for generating DC power. The DC power generator 316 has a voltage V DD The input signal may output a DC signal having the following characteristics:

[0068] The proximal delivery section 302 includes a microwave signal generator 314 arranged to generate a microwave signal 310, which is described below with reference to Figure 4. The microwave signal 310 from the microwave signal generator 314 is coupled to the coaxial transmission line via a capacitor 312, which acts as a DC isolation barrier to prevent a DC signal from a DC power generator 316 from leaking into the microwave signal generator 314.

[0069] The microwave signal 310 from the microwave generator 314 may have a power level less than the power level required to treat (e.g., ablate or coagulate) biological tissue. For example, the microwave signal 310 output from the microwave generator 314 may have a power level of 10 W or less. If the cable assembly exhibits a loss of 10 dB along its length, this means that the power of the microwave signal 322 at the distal end is 1 W. Thus, if the power amplifier 320 exhibits a gain of 10 dB, the power available for treatment is 10 W.

[0070] Transmitting a low power microwave signal from the microwave signal generator means that less power is lost during transmission through the cable assembly 306. This avoids or reduces heating of the cable assembly 306 due to microwave losses, and therefore avoids the risk of inadvertent heating of tissue along the path of the cable assembly.

[0071] The distal amplifier section 304 functions to amplify the microwave signal 310 received from the cable assembly 306 to a power level suitable for treatment. Once the amplified microwave signal 318 is output by the distal amplifier section 304, it is coupled via a capacitor 319 to an instrument tip 308, such as the active tip 224 described above, from where it is delivered (e.g., radiated or otherwise emitted) to biological tissue at the treatment site. The capacitor 319 acts as a DC barrier between the instrument tip 308 and the distal amplifier section 304, preventing the DC signal from reaching the instrument tip.

[0072] The distal amplifier section 304 includes a power amplifier 320, such as a power MOSFET, that receives as an input a microwave signal 322 output from the coaxial transmission line. The input to the power amplifier 320 is protected from DC signals in the cable assembly 306 by a capacitor 324.

[0073] The distal amplifier section 304 is arranged to separate DC power from the microwave signal and apply it across the power amplifier 320. The distal amplifier section 304 separates the DC signal (V DD ) is applied to the power amplifier 320. The microwave signal 322 may be blocked from the voltage rail 326 by a filtering array 328, which may comprise a pair of quarter wavelength stubs, as described in more detail below. Similarly, a filtering array 330 may be disposed at the connection between the voltage rail 326 and the power amplifier 320 to prevent microwave energy from leaking out of the power amplifier 320 onto the voltage rail 326.

[0074] The distal amplifier 304 is connected to a bias voltage V GG from the DC signal. The gate voltage extraction module 332 may include a DC-DC converter that down-converts the DC signal voltage to a level suitable for the power amplifier 320.

[0075] The distal amplifier section 304 may further comprise a gate control module 334 for controlling application of a gate voltage to the power amplifier 320. As described in more detail below, the gate control module 334 may operate to switch between two bias voltage states corresponding to an on (conducting) state and an off (non-conducting) state, respectively, of the power amplifier 320. The gate control module 334 may operate to introduce a time delay between application of a DC signal across the power amplifier 320 (i.e., as its drain voltage) and application of a bias voltage to turn on the power amplifier 320, to ensure smooth initialization of the amplification process.

[0076] A filtering arrangement 336 may be disposed at the connection between the gate control module 334 and the gate of the power amplifier 320 to prevent microwave energy from leaking from the power amplifier 320 to the gate control module 334 .

[0077] The detailed structures of the gate voltage extraction module 332 and the gate control module 334 will be described later with reference to FIG.

[0078] In use, the microwave generator 300 thus performs amplification of a low power input microwave signal to a power level suitable for treatment. The amplified power level can be an order of magnitude or more higher than the input power level, for example 10 W or more. This configuration results in very little power loss along the cable assembly 306, thereby reducing the risk of inadvertent heating of tissue along the path taken by the cable assembly 306.

[0079] The distal amplifier section 304 may be located within the distal tip assembly 214 shown in FIGURE 2. For example, the distal amplifier section 304 may be disposed between the proximal end of the active tip section 224 and the distal end of the coaxial cable 142. The protective shell 222 may have a substrate (e.g., a PCB, etc.) mounted thereon to support the components of the distal amplifier section 304, or may be a substrate (e.g., a PCB, etc.).

[0080] Figure 4 is a schematic diagram of an example of a proximal launch section 302 where microwave and DC signals are launched at the proximal end of a coaxial transmission line 370. Features in common with Figure 3 are numbered the same and will not be described again. The coaxial transmission line 370 comprises an inner conductor 372 separated from an outer conductor 376 by a dielectric material 374. The coaxial transmission line 370 may be, for example, a Sucoform cable manufactured by Huber+Suhner.

[0081] FIG. 4 shows the components for microwave signal generator 314. In this example, microwave signal generator 314 includes a microwave frequency source 378 followed by a variable attenuator 380, which may be controlled by a controller (not shown) via a control signal in a manner similar to the system shown in FIG. 1. The output of variable attenuator 380 is input to a signal modulator 382, ​​which may be controlled by the controller, for example to apply a pulsed waveform to the microwave signal. The output from the signal modulator is input to a drive amplifier 384 to generate a microwave signal at a desired power level for transmission to the distal amplifier. The microwave signal is coupled to coaxial transmission line 370 via capacitor 312.

[0082] The DC power generator 316 comprises a voltage source 386 connected to apply a DC voltage to the inner conductor 372 of the coaxial transmission line 370. The voltage source 386 may be a switched mode power supply or may use a battery to make the device portable. The connection may be a portion of or may include a microstrip transmission line 388 to which a low pass filter 390 is provided to prevent back transmission of the microwave signal to the voltage source 386. The low pass filter 390 comprises a pair of quarter wavelength stubs 392, 394 on the microstrip transmission line 388. The first stub 392 is located half a wavelength (i.e., nλ / 2) away from the connection point 396 to the inner conductor 372 of the coaxial transmission line 370, where λ is the wavelength of the microwave signal on the microwave transmission line 388 and n is an integer equal to or greater than 1. This ensures that the base of the first quarter wavelength (i.e., ((2n-1)λ) / 4) stub 392 is shorted and therefore the other end of the quarter wavelength stub 392 is open circuited. The second quarter wavelength stub 394 is spaced a half wavelength (i.e., nλ / 2) distance from the first stub.

[0083] The DC power generator 316 further comprises a set of capacitors 387 shunt-connected to the transmission line carrying the DC signal to eliminate other unwanted AC elements on the DC signal path.

[0084] 5 is a schematic circuit diagram showing a distal microwave amplifier module 304 for an embodiment of the present invention. Features in common with previous figures are given the same reference numbers and will not be described again.

[0085] In this example, the distal end of the cable assembly 306 is connected to the distal microwave amplifier module 304. The cable assembly 306 may include the coaxial transmission line 370 described above that carries both the microwave signal and the DC signal. The distal microwave amplifier module 304 splits the microwave signal from the DC signal using a filter. The DC signal travels to the DC rail 326 via a first connection line 502 that has a low pass filter comprising a pair of quarter wavelength stubs 328 positioned to block the passage of the microwave signal.

[0086] The pair of stubs 328 may be fabricated on a microstrip transmission line. The first stub is placed a half wavelength (i.e., nλ / 2) away from the connection point to the inner conductor of the coaxial transmission line, where λ is the wavelength of the microwave signal on the microwave transmission line, and n is an integer equal to or greater than 1. This ensures that the base of the first quarter wavelength (i.e., ((2n-1)λ) / 4) stub is in a short circuit and therefore the other end of the quarter wavelength stub is in an open circuit state. The second quarter wavelength stub is spaced a half wavelength (i.e., nλ / 2) away from the first stub.

[0087] Meanwhile, the microwave signal travels along connection line 504 to power amplifier 320 where it becomes the input signal to be amplified. Connection line 504 may be a microstrip transmission line or the like. Connection line 504 includes capacitor 324 to which the microwave signal is coupled but which blocks DC signals. Capacitor 324 thus isolates power amplifier 320 from any DC components transmitted from coaxial transmission line 370 in cable assembly 306.

[0088] A connection line 506 connects the voltage rail 326 to the power amplifier 320 to apply a DC signal voltage across the power amplifier 320 (i.e., as a drain supply). A pair of quarter wavelength stubs 330 are arranged as a low pass filter to prevent microwave energy from leaking out of the power amplifier 320 on the connection line 506. The pair of stubs 330 may be arranged in a similar manner as the stubs 328, but with respect to the connection point between the connection line 506 and the power amplifier 320.

[0089] The connection line 506 further comprises a set of capacitors 508 shunt-connected to the connection line carrying the DC signal to remove other unwanted AC components on the DC signal path.

[0090] The connecting line 506 further comprises an inductor 510 connected in series between the power amplifier 320 and the voltage rail 326. This inductance further reduces leakage of AC signals to the voltage rail 326.

[0091] Each of the above mentioned connecting lines can be implemented as a suitable transmission line for carrying DC or microwave signals as required, such as a microstrip line on a flexible substrate that can be packed into a compact configuration.

[0092] In this embodiment, the distal microwave amplifier module 304 receives a bias voltage V for the power amplifier from a voltage rail 326. GGThe voltage rail 326 may be a relatively high voltage, e.g., 28V or a similar voltage, while the bias voltage for the power amplifier 320 may need to be an order of magnitude lower. To obtain the bias voltage, the distal microwave amplification module 304 includes a gate voltage extraction module 332. The gate voltage extraction module 332 functions as a DC-DC converter, and in this embodiment is implemented as a pair of parallel step-down converters 512, 514, each of which is configured to output a different voltage, allowing the bias voltage to be switched between two different states.

[0093] Each buck converter 512, 514 is connected to the voltage rail 326 to provide an input voltage. The capacitance and inductance values ​​in each buck converter 512, 514 are selected to convert the input voltage to a desired output voltage. The output voltage can be selected based on the operating characteristics of the power amplifier. In this example, the buck converters 512, 514 are configured to generate a negative output voltage by using diodes to control the appropriate current flow direction in each converter. This means that the output voltage (bias voltage) can be set close to the characteristic point where the power amplifier is conductive.

[0094] For example, the first buck converter 512 may be configured to output a bias voltage in the non-conducting portion of the power amplifier characteristic, e.g., −6 V. The second buck converter 514 may be configured to output a bias voltage in the conducting portion of the power amplifier characteristic, preferably just after the transition to the conducting state, e.g., −2 V.

[0095] The outputs from the pair of buck converters 512, 514 are connected to respective input poles of a switch 516 which forms part of the gate control module 334. The output of the switch 516 is connected to a connection line 518 which is connected to the connection line 504 for providing a bias voltage from the gate voltage extraction module 332 to the gate of the power amplifier 320.

[0096] A pair of quarter wavelength stubs 336 are positioned as a low pass filter to prevent microwave energy from leaking out of power amplifier 320 on connection line 518. The pair of stubs 336 may be positioned in a similar manner as stub 328, but with respect to the connection point between connection line 518 and connection line 504.

[0097] The connection line 518 further comprises a set of capacitors 520 shunt-connected to the connection line 518 carrying the bias voltage to eliminate other unwanted AC components on the bias voltage signal path.

[0098] The gate control module 334 operates to apply the required bias voltage to the gate of the power amplifier 320. Thus, the gate control module 334 effectively operates to selectively activate the power amplifier 320. In this example, the gate control module 334 functions to control a switch 516 that selects the buck converter 512, 514 to provide the bias voltage to the power amplifier 320. The switch 516 may be controlled by an inductor 522 that is energized upon application of a DC signal to the voltage rail 326. Thus, the switch 516 can adopt a default (e.g., off) configuration when the inductor 522 is not energized. In this configuration, the switch 516 connects the buck converter at a non-conducting voltage level (e.g., −6V) to the power amplifier. When the inductor 522 is energized, the switch adopts an activated (e.g., on) configuration and the buck converter at a conducting voltage level (e.g., −2V) is connected to the power amplifier.

[0099] In this embodiment, the gate control module 334 includes a "soft start" circuit 524 for the power amplifier 320, which acts to delay the switch state change by smoothly increasing the voltage applied to the inductor 522. The advantage of this configuration is that it allows the drain voltage across the power amplifier 320 to reach a steady state before a bias voltage is applied to activate the power amplifier. The "soft start" circuit 524 is implemented using a comparator 526 that generates an output to the inductor 522 based on the difference between a varying first input from an RC circuit 528 and a fixed input from a voltage divider circuit 530.

[0100] 6 is a schematic diagram showing another example of a microwave amplification device 550 according to an embodiment of the present invention. Features common to those in FIG. 3 are given the same reference numerals and will not be described again.

[0101] The apparatus 550 of Figure 6 differs from that of Figure 3 in that the gate voltage is generated at the proximal end and transferred as a secondary DC signal through the cable assembly 306. Thus, the DC power generator 316 of this example generates a DC signal (voltage V DD 6. In this example, the cable assembly includes a dedicated transmission line 371 for the DC signal. In the proximal portion 304, the distal end of the transmission line 371 is coupled to the drain of the power amplifier 320 via a low pass filter 330, which may be of the type described above. The dedicated transmission line 371 may be connected directly to the drain via a low pass filter or may be connected via a voltage rail 326 as shown in FIG. 6.

[0102] The DC power generator 316 may also include a means for generating a bias voltage for the power amplifier. In some examples, the bias voltage may be generated using a separate DC source, for example operating at a lower voltage than the DC source 386 for the drain voltage. However, in the embodiment shown in FIG. 6, the proximal portion 302 is provided with a gate voltage extraction module 332 to derive the bias voltage from the same DC source as the drain voltage. The gate voltage extraction module 332 may be configured to operate in the same manner as described above. The proximal portion 302 may also include a gate control module 334 for controlling the bias voltage supplied to the cable assembly 306.

[0103] In this example, the bias voltage is transmitted to the distal portion through the inner conductor of a coaxial transmission line 370 in the cable assembly 306. The coaxial transmission line 370 is also used to transmit the microwave signal 310 from the microwave signal generator 314.

[0104] In some examples, a dedicated line 371 for the DC signal may be an additional conductive layer formed around the outer conductor of the coaxial transmission line 370 and separated therefrom by an insulating layer, effectively forming, for example, a signal triaxial cable. In this example, it may be desirable to include a low pass filter in the distal portion 304 at the point where the DC signal is separated from the coaxial transmission line 370 to avoid the microwave signal leaking onto the voltage rail 326.

Claims

1. 1. A microwave amplifier device for an electrosurgical instrument, comprising: A cable assembly; a proximal delivery section connected to a proximal end of the cable assembly, the proximal delivery section comprising: a DC source configured to send a DC signal through the cable assembly; a microwave source configured to transmit a microwave signal through the cable assembly; the proximal delivery portion comprising: a distal amplifier connected to a distal end of the cable assembly, the distal amplifier comprising a power amplifier configured to receive the microwave signal as an input signal to be amplified, the distal amplifier configured to apply the DC signal as a drain voltage across the power amplifier; a gate voltage extraction module configured to extract a bias voltage from the DC signal and apply it to a gate of the power amplifier; the power amplifier having an output connectable to provide an amplified microwave signal to a structure configured to deliver microwave energy to biological tissue; The microwave amplification apparatus, wherein the distal amplifier section and the gate voltage extraction module are sized for insertion through an instrument channel of a surgical scope apparatus.

2. 2. The microwave amplification apparatus of claim 1, wherein the gate voltage extraction module comprises a DC-DC converter configured to down-convert a voltage of the DC signal to generate the bias voltage.

3. The microwave amplifier of claim 2 , wherein the DC-DC converter comprises a step-down converter.

4. The microwave amplifier device according to any one of claims 1 to 3, wherein the gate voltage extraction module is configured to extract a pair of bias voltages from the DC signal, the pair of bias voltages including a first bias voltage corresponding to a non-conducting state of the power amplifier and a second bias voltage corresponding to a conducting state of the power amplifier.

5. 5. The microwave amplification apparatus of claim 4, wherein the gate voltage extraction module comprises a pair of step-down converters connected in parallel, the pair of step-down converters comprising a first step-down converter for generating the first bias voltage and a second step-down converter for generating the second bias voltage.

6. 6. The microwave amplification apparatus of claim 4, further comprising a gate control module configured to selectively apply the first bias voltage or the second bias voltage to the gate of the power amplifier.

7. 7. The microwave amplification apparatus of claim 6, wherein the gate control module comprises a switch arranged to selectively apply the first bias voltage or the second bias voltage to the gate of the power amplifier.

8. 8. The microwave amplification apparatus of claim 7, wherein the distal amplifier section comprises a voltage rail arranged to adopt an operating voltage provided by the DC signal, and the switch is configured to select the second bias voltage upon application of the operating voltage to the voltage rail.

9. 9. The microwave amplification apparatus of claim 8, wherein the gate control module further comprises a delay circuit arranged to introduce a time lag between application of the operating voltage to the voltage rail and actuation of the switch to select the second bias voltage.

10. The microwave amplifying device according to any one of claims 4 to 9, wherein the first bias voltage and the second bias voltage both have polarities opposite to that of the drain voltage.

11. The microwave amplification device according to any one of claims 1 to 10, wherein the gate voltage extraction module is in the distal amplification section.

12. 12. The microwave amplification apparatus of claim 11, further comprising a low pass filter connected between the gate voltage extraction module and the gate of the power amplifier.

13. 13. The microwave amplification apparatus of claim 12, wherein the low pass filter comprises a pair of quarter wavelength stubs each having a length of ((2n-1)λ) / 4, the pair of quarter wavelength stubs comprising a first quarter wavelength stub located a distance nλ / 2 from the gate of the power amplifier and a second quarter wavelength stub spaced a distance nλ / 2 from the first quarter wavelength stub, where λ is the wavelength of the microwave signal and n is an integer greater than or equal to 1.

14. 11. The microwave amplification apparatus of claim 1, wherein the gate voltage extraction module is in the proximal delivery section and the DC signal includes a bias voltage transmitted by the cable assembly to the distal amplification section.

15. 15. The microwave amplification apparatus of claim 1, wherein the cable assembly comprises a coaxial transmission line having an inner conductor separated from an outer conductor by a dielectric material, the microwave signal being transmitted by the coaxial transmission line and the DC signal being transmitted through the inner conductor.

16. 16. The microwave amplification apparatus of claim 15, wherein the microwave signal is coupled to the coaxial transmission line through a capacitor.

17. 17. A microwave amplification apparatus according to any preceding claim, wherein the output of the power amplifier includes a capacitor configured to couple the amplified microwave signal to the structure.

18. A microwave amplification apparatus according to any preceding claim, wherein the microwave signal has a power of 10 W or less at the proximal end of the cable assembly.

19. 19. The microwave amplification apparatus of any one of claims 1 to 18, wherein the distal amplifier section comprises a voltage rail arranged to adopt an operating voltage provided by the DC signal, the voltage rail being connected by a first connection line to a distal end of the cable assembly to receive the DC signal, and the voltage rail being connected by a second connection line to a drain of the power amplifier to provide the drain voltage.

20. 20. The microwave amplification device of claim 19, further comprising a proximal low pass filter in the first connecting line and a distal low pass filter in the second connecting line.

21. 21. The microwave amplification apparatus of claim 20, wherein the proximal low pass filter comprises a pair of quarter wavelength stubs each having a length of ((2n-1)λ) / 4, the pair of quarter wavelength stubs comprising a first quarter wavelength stub located at a distance of nλ / 2 from a connection point between the first connection line and the cable assembly, and a second quarter wavelength stub spaced a distance nλ / 2 from the first quarter wavelength stub, where λ is the wavelength of the microwave signal, and n is an integer equal to or greater than 1.

22. 22. The microwave amplification device of claim 20 or 21, wherein the distal low pass filter comprises a pair of quarter wavelength stubs each having a length of ((2n-1)λ) / 4, the pair of quarter wavelength stubs comprising a first quarter wavelength stub located at a distance of nλ / 2 from the drain of the power amplifier and a second quarter wavelength stub spaced a distance nλ / 2 from the first quarter wavelength stub, where λ is the wavelength of the microwave signal and n is an integer equal to or greater than 1.

23. A microwave amplifier according to any one of claims 1 to 22, a radiating tip connected to the output of the power amplifier, the radiating tip comprising an antenna configured to radiate the amplified microwave signal into biological tissue.

24. 24. The electrosurgical instrument of claim 23, wherein the microwave amplifier and the radiating tip are dimensioned for insertion through an instrument channel of a surgical scope device.

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