GB2458329A

GB2458329A - Applicator for plasma sterilisation of body cavities

Info

Publication number: GB2458329A
Application number: GB0804885A
Authority: GB
Inventors: Christopher Paul Hancock
Original assignee: Microoncology Ltd
Current assignee: Creo Medical Ltd
Priority date: 2008-03-15
Filing date: 2008-03-15
Publication date: 2009-09-16
Anticipated expiration: 2028-03-15
Also published as: GB0804885D0; GB2458329B

Abstract

The applicator is suitable for killing or reducing bacteria or viruses contained inside the human body, and may also be used externally. The applicator comprises an integrated cable assembly carrying both microwave RF energy and gas to an antenna structure which creates a plasma. The applicator and antenna may be integrated and so be suitable for direct insertion through natural orifices of the human body, or endoscopically. The cable assembly comprises a microwave connector 340, a first tube 304 made from a dielectric material and coated on the inside and the outside with metallic coatings 308, 309 and with a hollow channel 301 transporting gas to the antenna. The first tube also forms a coaxial waveguide for feeding microwave energy to the antenna. This first tube may be located in a second tube 303 with spacers 302 providing a second channel 307 for extracting gas. The antenna may comprise a first 310, 330 and second 320,330 impedance transformers producing an electric field capable of producing a plasma suitable for sterilisation.

Description

MANOEUVRABLE FLEXIBLE ANTENNAE AND SYSTEMS

FOR PRODUCING CONTROLLABLE ATMOSPHERIC

PLASMA FOR KILLING OR REDUCING BACTERIA

AND/OR VIRUSES MANIFESTED INSIDE NATURAL

ORIFICES WITHIN THE HUMAN BODY OR OTHER

REGIONS

FIELD OF THE INVENTION

The current invention is concerned with integrated flexible cable assemblies that may be used to transport microwave energy and gas (or a mixture of gases), antenna structures, and instrumentation, that may be used to kill or reduce bacteria or viruses contained inside natural orifices within the human body, other regions associated with the human body, or regions external to the human body.

Sterilisation is an act or process that destroys or eliminates all forms of life, especially micro-organisms. During the process of plasma sterilisation, active agents are produced. These active agents are high intensity ultraviolet photons and free radicals, which are atoms or assemblies of atoms with chemically unpaired electrons. An attractive feature of plasma sterilisation is that it is possible to achieve sterilisation at relatively low temperatures, such as body temperature. Plasma sterilisation also has the benefit that it is safe to the operator and the patient.

Low temperature atmospheric pressure plasmas may be used to replace conventional sterilisation methods and offer clear advantage over existing means of sterilisation in terms of their non-toxic nature, instant treatment effects, and the ability to produce the plasma at a range of energy levels and in a range of different forms.

This invention introduces structures that may be used to transport microwave energy and gas into the body (or elsewhere) for generation of biologically useful plasma inside natural orifices (or elsewhere), and introduces the instrumentation required to prevent a build up of pressure within the natural orifice (or other region of the body or external to the body that may be of interest) by returning the residual gas that is not used for plasma generation back into a reservoir. This feature of the invention is also beneficial in terms of enabling unused gas to be recycled and not lost into the atmosphere.

The current invention makes use of modulated controllable non-ionising microwave radiation and an inert gas, or a mixture of inert gases, to produce atmospheric plasma (or conducting gas). The invention may use a mixture of inert gases, i.e. 5% air and 95% helium.

This invention makes use of controlled microwave energy sources and a single gas (or a mixture of gases) to produce plasma that is suitable for treating a range of bacteria or viruses contained within the human body. The system described here is not limited for use inside the human body, i.e. it may also be used to sterilise instruments or used in other external applications.

This invention may be used to significantly reduce levels of bacteria without whipping it out completely. There are advantages of using the invention in this way. For other applications, it may be appropriate to arrange the system or equipment in such a manner that enables the bacteria or viruses to be totally destroyed.

The treatment system introduced here makes use of non-ionising radiation generated using a source oscillator to produce a low power RF or microwave frequency signal, and a power amplifier comprising of an arrangement of RF or microwave transistors to amplify the low power signal to a level that is high enough to enable an electric field to be produced which is required to strike the plasma using an inert gas (or mixture of inert gases) found to be suitable for the particular application. The invention makes use of solid state power amplifiers, but this invention is not limited to using this particular technology to amplify the low power signal.

The invention makes use of at least one signal modulator and a means of controllably adjusting the microwave power level.

In this specification the frequency spectrum used is between 400MHZ and 100 GHz. Specific frequencies that have been considered are: 900MHz, 2.45GHZ, 3.3GHZ, 5.2GHZ, 10GHz, 14.5GHz and 24GHZ.

One or both of the modulation frequencies may be contained within the range from 0.1Hz up to 10MHz, and the duty cycle from less than i% to ioo% duty cycle. More specifically, the frequency may be from 10Hz to iooKHz and the duty cycle may be between io% and 25%. Interesting results have been obtained using frequencies of between 100Hz and 1KHz, and a duty cycle of 20%.

The microwave frequency may be adjusted to enable the energy delivered by the plasma to be optimised, for example, during initial pilot studies on this work, an antenna structure or applicator that was designed to operate at 900MHz, but was found to produce plasma most efficiently when the frequency was adjusted to 866MHz.

Either resonant structures or voltage transformers may be used to generate the electric field required to strike the plasma. The plasma may also be struck using an arrangement that uses a voltage transformer with suitable switching devices, i.e. a boost converter, to create a voltage high enough to strike the plasma, i.e. a voltage greater than iooV.

Co-axial or waveguide arrangements may be used as the applicators to create the plasma. Quarter wave (or an odd number thereof) impedance transformers may be realised in co-axial or waveguide systems and the specific structure used is determined by the specific application and the environment in which it is desired to generate the plasma, i.e. over an external surface or inside a body cavity.

This invention draws heavily on miniature applicator or antenna arrangements, and feed structures that enable the microwave power and the gas (or mixture of gases) to be transported along a single flexible assembly. In particular, this invention makes use of a first section of a co-axial microwave cable assembly to enable the gas to be fed into the applicator to enable plasma of appropriate nature to be generated, and a second section of the same co-axial microwave cable assembly to enable the gas to be withdrawn from the structure for the purpose of preventing pressure build up within the cavity or the natural orifice where the applicator is inserted.

It may be necessary to suck the gas back along the applicator and the cable to ensure that pressure cannot build up within the cavity. It may also be desirable to use this arrangement to re-circulate a portion of the gas rather than loosing the returned gas into the atmosphere. This also helps preserve valuable sources of natural gases that may become short in supply in the future.

It may be necessary to include a reservoir to store the returned gas to enable it to be effectively used again to create the treatment plasma. It may also be necessary to include a number of one way valves in the system in order to ensure that the gas flow is in the desired direction within the system.

Applications relating to sexually transmitted diseases: The current invention may be used to selectively reduce or kill bacteria or viral diseases that exist in an environment located inside the human body and one particularly useful application for this feature is to treat a number of sexually transmitted diseases. In these applications it is required to insert the applicator inside various natural orifices contained within the human body, e.g. the vagina, the rectum, penis, or the mouth, where the plasma may be used to significantly reduce, or completely destroy, the bacteria caused by the disease. In such an application it is possible for pressure to build up within the body cavity, and it is highly undesirable for this pressure, caused by the gas (or gas mixture), to build up since this may lead to damage being caused to the organ of interest, therefore, some form of exhaust or extraction system is required. This invention may be particularly suitable for treating Chiamydia or Gonorrhoea where it is preferable to completely destroy or kill the cells. In this application, the treatment solution may overcome drawbacks of currently used antibiotic treatments where the disease has become resistant to various antibiotic treatments that have been developed by leading drug companies.

Sexually transmitted diseases (STDs) or sexually transmitted infections (STIs) are diseases that can be transmitted through body contact during sex. They are caused by viruses, bacteria, and parasites. There are at least 25 different STDs and they are caused by many different types of bacteria and viruses. They all have one common feature and this is that they are spread by sexual contact through the vagina, the mouth or the anus.

The most common STDs are as follows: 1. Chlamydia; 2. Gonorrhoea; 3. Genital herpes (Herpes genitalis); 4. Genital warts; 5. Syphilis.

Chiamydia is the most common and fastest spreading STD in the United Kingdom. This disease stems from a bacterium known as Chlamydia trachomatis.

Symptoms normally appear approximately 7 to 21 days after infection and tend to differ for men, women, and children. This disease can damage the reproductive organs.

Gonorrhoea is caused by Neisseria gonorrhoea bacteria that grows and multiplies quickly in moist, warm areas of the body such as the cervix, urethra, mouth, or rectum. In women, the cervix is the most common site of infection. However, it can also be spread in the uterus and fallopian tubes. Gonorrhoea is most commonly spread during genital contact, but can also be passed from the genitals of one partner to the throat of another during oral sex. Gonorrhoea of the rectum can occur in people who practice anal intercourse.

Genital herpes is a highly contagious viral infection caused by the herpes simplex virus. It principally infects the skin and mucous membranes of the genitals and rectum, but can also appear in areas such as the mouth. It is transmitted primarily through physical and sexual contact.

Genital warts or condylomata acuminate are caused by the human papilloma virus. In women, the human papilloma virus can lead to changes in the cervix and to the development of cervical cancer.

Syphilis is a dangerous and life threatening bacterial disease. After infection, bacteria are transported through the body, via the bloodstream, and this adversely affects the vital organs such as the heart, brain, nervous system and spine.

For treatment of some of these diseases it is necessary to completely destroy the bacteria, whereas for others it may be highly desirable to significantly reduce the levels of bacteria rather than completely wiping it out due to the fact that this may destroy the body's natural flora.

Embodiments of the current invention may include applicators that can be inserted inside the vagina, the mouth, or the anus. These applicators may be of diameter such that they can be inserted into the orifice without causing pain or discomfort to the patient. The system can be set-up to enable controlled plasma plumes to be emitted at the distal end of the applicators and the plasma may be used to destroy or reduce the bacteria. In this particular application, the temperature of the plasma will not exceed body temperature to ensure that no tissue damage can be caused by excessive heating of the tissue. In this application, the plasma may be produced using a combination of helium or argon with compressed air or oxygen. The microwave power level, modulation frequency, duty cycle, and gas flow rate are controlled to enable the plasma to be optimised to create the most desirable clinical effect.

Other clinical applications: The invention may also be used to treat gum diseases or kill bacteria residing inside the mouth.

The invention may be used to treat ulcers or sores, wounds or other tissue structures that may contain bacteria. This feature may be particularly useful for people that are otherwise hospitalised. If the bacteria can be removed from an ulcer then the ulcer may begin to heal and the patient may be able to go home to their family where they can be looked after (this would not be possible if the bacteria remained in the ulcer).

The invention may also be used to sterilise wound beds or remove bacteria from artificial skin prior to skin grafts taking place.

The invention may be used in outpatient surgeries where cuts have become infected by bacteria and need to be cleaned prior to dressing or stitching in order to prevent the wound from getting further infected or from causing gangrene to set in, which may lead to amputation.

The invention may be used to destroy viruses in the back of the throat and, in doing so, replace the use of antibiotics for treating throat infections.

The invention may be used to clean inserts that have been placed inside the human body, or sterilise medical equipment or devices prior to them being used inside the human body. The equipment described in this invention may be inserted through key-hole surgery into the body to clean various regions of the body that are not easily accessible.

The controlled plasma generation and specific applicators considered for use in the current invention may also be used to destroy the MSRA, or the \TRSA, or the C. Duff, bacterium by introducing the plasma into the body using non-invasive or minimally invasive techniques and suitable antenna structures. The current invention may also be used to disinfect' those with a high risk of attracting MSRA, for example, patients or nurses, by exposing certain regions of the body, for example, the throat, the hands or the nose, to focussed high frequency microwave energy for short durations of time.

The current invention may be used to remove bacteria from inserts or devices that have already been placed inside the human body, for example pins or inserts used to repair fractures, pacemakers or heart valves by inserting the integrated cable assembly and the applicator to the site where the insert or device is located through key hole surgery and then using the plasma produced by the instrumentation described in this document, and associated UK applications, to kill the bacteria.

The current invention may be used to destroy bacteria that exists within any region of the body that is infected where the site is accessible through key hole or minimally invasive surgery, for example, where a surgical procedure has taken place and some bacteria has been left behind. This new method of killing the bacteria in situ to deal with the infection offers significant advantage over the alternative, which may involve opening the patient up again to disinfect the region where infection has occurred.

ESSENTIAL FEATURES

The integrated cable assembly used to transport gas in at least one direction (preferably, two directions), the plasma generating applicator (or antenna), and the controlled microwave power/gas control system (the instrumentation) form this basis of the current invention and unique features from these elements will be identified and form the essential features of this patent.

This invention makes use of the fact that for effective propagation of electromagnetic fields at microwave frequencies the wall thicknesses of the conductors involved in the field propagation is limited to a small fraction of the overall conductor thicknesses, i.e. only a small fraction of the outer wall of the inner conductor and the inner wall of the outer are required to enable the microwave fields to propagate unimpaired, thus, the inner of the inner conductor and the outer of the outer conductor may be used for purposes other than to transport the electromagnetic energy.

It is proposed that the inner of the inner conductor be used to transport gas (or a mixture of gases) from the gas cylinder (source) into the applicator, and for the outer of the outer conductor be used to transport the residual gas from the applicator back into the gas cylinder (or into an external reservoir for recycling or re-circulating back along the cable assembly to produce more plasma). The current invention is not limited to this arrangement, i.e. the gas may be transported from the cylinder to the applicator along the outer of the outer conductor of the co-axial arrangement, etc. In order to keep the wall thicknesses to a minimum, it is preferable to use high conductivity conductors when constructing the co-axial assembly, i.e. it is preferable to use silver, copper, or gold when fabricating the inner and outer conductors.

Accordingly, a first aspect of the current invention is an arrangement that allows microwave power and a suitable gas (or mixture of gases), to be transported simultaneously along an integrated structure that can be inserted inside a range of natural orifices within the human or animal body. In the aforementioned arrangement, the microwave power is transported using a co-axial waveguide, that is able to support the propagation of a transverse electromagnetic (TEM) wave, and the gas (or gas mixture) is transported using either a channel formed by the centre of the centre conductor of the co-axial waveguide and/or a channel formed between the outer metallic wall of the waveguide and the inner wall of a jacket or protective layer. In this arrangement, the idea of limited conductor thickness required for the microwave field to propagate is used to enable the centre conductor to be used as a conduit for the gas. For example, if a solid conductor to be used was 2mm diameter then only a fraction of this solid wire or rod is required for the propagation of the microwave field.

A second aspect of the current invention is where the co-axial waveguide or transmission line arrangement for the microwave field to propagate is formed using a tube of flexible low loss dielectric material, where the centre section of the tube is bored out or extruded to form a channel for a gas to flow, and the inner and outer walls of the tube are coated with a metallic layer, the thickness of which is between i to io skin depths at the frequency of interest, to form the metallic walls for the electromagnetic field to propagate. As an example a solid PTFE material may be used as the dielectric, where the loss factor is between o.oooi and 0.0008 at a frequency of 2.45GHZ. The electrical properties of the dielectric material and the thickness of the ratio between the inner diameter of the outer conductive layer and the outer diameter of the inner conductive layer are chosen such that the characteristic impedance of the transmission line is a commonly used value, for example, 50fl or 75f1. It is necessary for the electrical and mechanical properties of the dielectric material to be homogeneous along the length of the material in order to minimise discontinuities along the transmission line that may lead to reflections and power loss along the cable.

A third aspect of the current invention is a similar arrangement described for the first aspect, but where the co-axial waveguide is replaced with a single conductor waveguide, for example, a flexible or flexible/twistable rectangular or cylindrical waveguide. In this instance, the gas may travel along the open cavity. It may be preferable to separate the cavity into longitudinal sections, where a first section is used to transport the gas from the source to the applicator, and a second section is used to transport the residual gas from the applicator back along the waveguide to the gas source. An alternative to using the centre of the waveguide to transport the gas, is to use a region or channel formed between the outer wall of the waveguide and an insulating jacket. This may be preferable since the gas flow inside the cavity may affect the electromagnetic fields propagating inside the waveguide. Due to the fact that the gas flow will be inconsistent and the gases used may vary, it may not be a good idea to transport the gas in the region where the fields are set up as this will cause the propagation medium to be inhomogeneous. If it is chosen to use the centre cavity of a waveguide to transport the gas then it may be preferable to load the waveguide with a dielectric or magnetic material in order to reduce the affect caused by having the cavity filled with gas. In this arrangement, the loading material would need to allow the gas to flow, i.e. it may contain a number of holes or may only partially fill the waveguide cavity. In this arrangement, a number of different modes may be set up in the waveguide, for example, it may be preferable to set up the dominant TE01 mode if a rectangular guide is used, or the dominant TE11 mode if a circular guide is used. These modes are known as dominant modes due to the fact that they define the lowest frequency that can propagate in the guide. Other higher order modes will be set up inside the guide when higher frequencies are launched into the same guide.

A fourth aspect of the invention is a structure that comprises of the integrated cable assembly that enables the microwave power and gas to be delivered using a single structure that is integrated itself with the plasma applicator or antenna. In this arrangement, the gas is fed directly into the applicator from a channel provided by either the hollow centre conductor and/or the channel formed between the outer wall of the second conductor and the insulating jacket. Either of the two channels may also be used to transport excess gas back from the applicator to the gas supply or reservoir. The applicator comprises of a hollow co-axial or waveguide structure for the gas and the microwave energy to combine.

The structure is arranged in such as manner that the microwave energy produces a high enough electric field to enable the gas to be turned into plasma or a conducting gas. The integrated structure may contain a single or plurality of impedance transformers to enable the voltage at the end of the cable to be multiplied or increased to a high enough level to enable the plasma to be struck.

The impedance transformers may be quarter wave transformers or any odd multiple of a quarter of the wavelength at the frequency of operation. The integrated applicator may be produced such that it has the same physical diameter as the integrated microwave/gas cable assembly. The structure may be arranged in such a manner that the hollow centre conductor carrying the gas feeds straight into the first impedance transformer contained within the applicator. Such an arrangement is shown in figure 3.

A fifth aspect of the invention is the gas control system, which enables excess gas to be returned by sucking it back along the antenna and the cable assembly, back to the supply. The gas control system also enables the gas fed into the antenna to create the plasma to be controlled in terms of pressure or flow rate. The gas control system may contain a reservoir to enable the excess plasma to be stored prior to being pumped back into the antenna to produce more plasma. The gas control system may also contain a gas combiner or mixer to enable the returned gas to be mixed with the gas supply (from a cylinder or a gas generating system).

The gas control system may also contain an arrangement of pumps to enable the gas to be sucked from the antenna, or pumped into the gas combiner, or pumped into the antenna. The gas control system may also contain an arrangement of gas flow valves to ensure that the gas flows in the desired direction only. The gas control system may also contain a flow switch, whose operation may be governed by signals obtained from a microprocessor, DSP unit or other suitable digital or analogue signal processing arrangement. The flow switch may be a solenoid arrangement where an applied magnetic field controls the position of the valve or the level of valve opening. The gas control system may also contain a flow rate adjuster and monitor, whose operation may be governed by signals obtained from a microprocessor, DSP unit or other suitable digital or analogue signal processing arrangement. The gas control system will also contain an arrangement of pipes or tubes that may be made from a plastic or metallic material. The gas control system may contain at least one gas cylinder or a gas generator.

The control system is also responsible for monitoring the remaining level of gas inside the cylinder Cs), the amount of gas inside the applicator, the flow rate, and the pressure.

A sixth aspect of the current invention is a means of synchronising the microwave energy with the gas flow to ensure that the microwave energy is only present when the antenna or applicator is filled with gas to enable the desired plasma to be struck and maintained. A microprocessor or digital signal processor is used to perform the timing functions to ensure that the microwave power and the gas are turned on and off at the correct times. Correct synchronisation ensured that gas is not wasted and that the microwave energy produced by the microwave generator is not reflected back along the antenna to the generator. The latter event is undesirable as it will cause applicator and cable heating, and also may lead to unnecessary stress on these and other components within the system.

Monitors will be included to indicate when excess microwave power is being reflected back along the cable and/or the gas flow rate varies from the demanded value.

DESCRIPTION

Features of the current invention are now explained in the detailed description of examples of the invention given below with reference to the accompanying drawings, in which: Figure 1: Shows an arrangement for the gas flow control system connected to an integrated cable assembly that enables microwave power to be transported to the applicator and returned back along same channel, and for gas supply to be introduced into the applicator and excess gas returned along a second channel to prevent pressure build up when the applicator is inserted inside a closed system or a natural orifice and to enable the unused gas to be recycled; Figure: Shows an arrangement for the controlled microwave power generator and the gas control system. This arrangement includes a system to enable the microwave energy to be matched into the impedance presented by the applicator in order to ensure that the plasma is struck and maintained in an efficient manner; Figure: Provides a detailed diagram of an integrated cable assembly and applicator where the plasma is produced. In this arrangement, the cable assembly is an integrated assembly itself that comprises of a co-axial arrangement formed from two tubes. The first tube is a relatively thick walled tube made from a flexible dielectric material and is coated with a layer of metal on both the inner and outer walls of said tube. The second tube is a relatively thin walled tube made from a flexible material. The first tube is suspended inside the second tube using spacers that may be made from a low loss dielectric material and allow gas to flow along said the channel formed between the outer wall of first tube and the inner wall of second tube. The integrated applicator comprises of two impedance transformers, a means of feeding gas from centre channel of first tube into applicator, and a means of extracting excess gas from applicator along channel formed between the outer wall of first tube and the inner wall of second tube; Figure 4 (a): Shows the cross section through the combined microwave power and gas feed assembly, where the channel formed by the hollow centre conductor is used to transport the gas from the source into the applicator; Figure 4 (b): Shows the cross section through the combined microwave power and gas feed assembly, where the channel formed by the hollow centre conductor, and the channel formed between outer wall of the second conductor that forms the co-axial cable to transport the microwave power and the inner wall of the sheath are used to transport the gas from the source into the applicator; Figure 4 Cc) shows the cross section through the combined microwave power and gas feed assembly, where the channel formed between outer wall of the second conductor, used to transport microwave energy, and the inner wall of the outer sheath is used to transport the gas from the gas supply (not shown here) into the applicator or antenna.

Figure 4 (d): Shows the cross section through the combined microwave power and gas feed assembly, where the channel formed by the hollow centre conductor is used to transport the gas from the gas supply into the applicator, and the channel formed between outer wall of the second conductor that forms the co-axial cable to transport the microwave power and the inner wall of the sheath (or outer covering) is used to return the excess gas in the applicator back to the gas supply for reuse; Figure 4 (e): Shows the cross section through the combined microwave power and gas feed assembly, where the channel formed by the hollow centre conductor is used to return the excess gas in the applicator back to the gas supply for reuse, and the channel formed between outer wall of the second conductor that forms the co-axial cable to transport the microwave power and the inner wall of the sheath (or outer covering) is used to transport the gas from the gas supply into the applicator; Figure: Shows an arrangement where the gas is fed into the antenna using two separate tubes that are combined at the source. In this arrangement, the microwave power and gas are supplied to the applicator using two separate conduits and both the microwave power and the gas enter the applicator at the proximal end of the applicator in the same direction as the applicator. The applicator shown in figure is comprised of two impedance transformers and an insert at the distal end; Figure 6: Shows a similar arrangement given in figure 5 where the applicator and cable assembly is inserted into the body through the month and the plasma produced at the distal end of the applicator is used to treat an internal organ; Figure: Shows the full block diagram for the plasma generation system consisting of a modulated solid state microwave source, a mixture of compressed air and a second gas, a tuning filter, control instrumentation, a user interface, and an antenna structure containing two voltage transformers.

Arrangements for the integrated cable assembly that can transport both microwave power and a suitable gas (or mixture), suitable applicators where the plasma is formed, and the control system to generate the controllable microwave power and gas mixture will now be described.

In order to enable the microwave power and the gas supply to be transported to the applicator where bacteria contained within small orifices is to be destroyed; it may be preferable for the co-axial cable that supplies the microwave power and the tube that supplies the gas (or gas mixture) to be integrated into one single assembly. The limited depth of penetration of microwave energy at the frequencies of interest for implementing the current invention may be utilised to enable the two conductors that form the co-axial cable assembly to be used to transport the gas supply into the applicator. In a particular arrangement where it is necessary to return the gas back along the cable assembly into a reservoir or back into the gas supply in order to prevent pressure build up in the cavity or natural orifice where the applicator is inserted, it may be desirable to use one of the conductors to act as a channel to transport the gas back. The two channels that are available for transporting gas to the applicator and/or for transporting gas back from the applicator to the gas supply or reservoir are the inner section of the inner conductor, and the outer section of the outer conductor.

Consideration for using inner of inner conductor and outer of outer conductor of co-axial feed cable for transporting the gas: For a solid conductor, the current concentrates on the outer surface. For this reason, when skin depth is shallow, the solid conductor can be replaced by a hollow tube with no loss in performance.

Skin depth can be calculated using either equation i or equation 2, given below: 6V(2/(wpO)) (i) = V(p/(f /1)) (2) Where: = skin depth in metres (m) = radian frequency in Hertz (Hz) u = conductivity in siemens (S or mho/m) p = resistivity in ohms metres (fl m) 1= frequency in Hertz (Hz) p = permeability of free space in Henry per metre (H/rn) = 411 * 10-7 H/rn = constant p1 or 3.1415927 Table i provides values of skin depth at spot frequencies of 1GHz and 10GHz for commonly used conductive materials.

This table illustrates the benefit of using high microwave frequencies when it is desirable to keep the metallization thickness to a minimum, for example, in co-axial arrangements where a hollow centre conductor and an outer conductor with minimal wall thickness are desirable to enable these regions of the assemblies to be used for purposes other than transporting microwave energy to produce the sterilisation or treatment plasma.

Chemical Bulk Resistivity Skin Depth Skin Depth Symbol @20C Material (.cm = �=)1Om) 1 GHz (pm) 10 GHz (pm) Aluminium Al 2.65 2.59 0.819 Beryllium Be 3.3 2.89 0.914 Brass Cu7o/Zn3o 7 4.21 1.33 Bronze Cu89/Snhl 15 6.16 1.95 Copper Cu 1.69 2.07 0.654 Gold Au 2.2 2.36 0.747 Graphite C 783.7 446 14.1 Nickel Ni 6.9 4.18 1.32 Silver Ag 1.63 2.03 0.643 Table 1: Skin depth for a range of materials at iGHz and ioGHz The percentage of power transferred as a function of material thickness can be described by equation 3 given below: %P= (1_e-x/os) *100% (3) Where: -x = thickness of the layer of metallization in metres (m) %P percentage of the power flowing in given thickness of metallization in watts (W) For example, equation 3 predicts that for a thickness of metallization of six skin depths, 99.75% of the power will be transported.

For structures considered to be useful here, three materials that may be used are silver (Ag), copper (Cu), and aluminium (Al).

If the frequency of choice for generating microwave plasma is 2.45GHZ, the skin depth where 67% of the microwave field is concentrated, and the thickness of material required for 99.75% of the microwave field to be transported for three materials that have been considered for this work is given if Table 2.

Material Depth for 67% of Field to Depth for 99.75% of Field Propagate (Urn) to Propagate (Urn) Silver (Ag) 1.30 7.80 Copper (Cu) 1.32 7.92 Aluminium (Al) 1.66 9.96 Table 2: Depths of Penetration at 2.45GHZ for three considered materials It can be seen from Table 2 that the required thickness for the walls of the centre and outer conductors is less than bUm for the three materials of choice, therefore, taking into account the need to provide a level of rigidity for the conductors, it is feasible to use a thickness of around ten times this value, i.e. 0.1mm.

The characteristic impedance (Z0) of the microwave cable assembly can be described by equation 4 given below (also refer to figures i and 3): 138/\/Cri log10 k/f = Z0 [f'] (4) Where: Cr1 is the relative permittivity of first dielectric material (dimensionless) k is the inner diameter of the outer conductor (in metres) f is the outer diameter of the first inner conductor (in metres) If one assumes that the characteristic impedance of the microwave cable assembly of interest is 50C1, and the maximum outside diameter of the integrated cable assemble that can be tolerated to enable the assembly to be inserted inside a natural orifice is iomm (see Figs. 1 & 3 -dimension d), then a practical cable assembly design may be as follows: 1. Assume that the co-axial transmission line is formed by coating a first tube of low loss dielectric material with a first layer of metallization on the inside wall, and a second layer of metallization on the outer wall; 2. Also assume that a second tube is used to provide the second channel for the gas to flow along and that the first tube is suspended inside said second tube using a plurality of thin disks containing holes or perforations placed at regular intervals along the length of the transmission line structure; 3. If we also assume that the metallization thickness on the inner surface and the outer surface of the tube is o.imm (see Figs. 1 and 3 -dimensions bande); 4. And the diameter of the hole inside the first tube is 2mm (see Figs. iand 3 -dimension fl, the channel available for gas to flow along is (2mm -2 x 0.1mm) = 1.8 mm (see Figs. 1 and 3-dimension c); 5. Also if the outer diameter of the first tube is 6mm (see Figs. 1 and 3 -dimension k), the dielectric constant of the material used to form the 50i) transmission line using the tube may then be calculated as follows: Cr = (138/50 Log10 6/2)2 1.317 6. The material of choice for the dielectric material may be a low loss PTFE or Nylon; 7. Since the layer of metallization attached to the outside of the tube is o.imm, the overall diameter of the co-axial structure is 6mm + 2 x 0.1mm = 6.2 mm (see Figs. 1 and 3 -dimension L); 8. If the wall thickness of the second tube is o.3mm and the outside diameter of the second tube is iomm (overall outside diameter), then the channel available for the gas to be returned along is mm -0.3mm -3.imm = 1.6mm (see Figs. 1 and 3 -dimension a).

There are a number of possible arrangements that make use of the hollow centre conductor and/or the hollow outer conductor for feeding the gas into the applicator and returning the gas from the applicator, these are: 1. Gas fed through hollow section of centre conductor only; 2. Gas fed through hollow section of outer conductor only; 3. Gas fed through hollow section of centre and hollow section of outer conductors; 4. Gas fed through hollow section of centre conductor and returned through hollow section of outer conductor; 5. Gas fed through hollow section of outer conductor and returned through hollow section of centre conductor.

These five arrangements are shown in figures a to e respectively.

In the instance whereby the outer of the outer conductor is to be used then it will be necessary to provide a means of support for the outer channel. This may be provided by use of spacers placed along the length of the cable. These spacers may be made from any material as long so it doesn't react with the gas since said spacers are transparent to the microwave field and their sole purpose is to prevent the outer jacket or wall of the outer conductor from collapsing. The spacers must allow gas to flow along the structure, thus they could be made from dielectric disks with a number of holes or a web type structure. Possible materials that may be used are PTFE, Nylon, rubber or PEEK. Metallic materials may also be used.

One of the requirements for the structure is that it is flexible and can be manipulated or guided whilst inside the patient.

The outer of the outer jacket may be made from a flexible plastic or rubber material as long as it does not allow the gas being passed along the length of the tube to escape. It may also be desirable for the jacket material to be biocompatible, since this will be a requirement when the integrated structure is inserted inside the human body through a natural orifice. It is preferable for said jacket material to be able to withstand sterilisation either using the ethylene oxide (EtO) or gamma irradiation process. The fact that only a thin layer of metallization is required to form the outer conductor therefore offers advantage in terms of enhanced flexibility of the structure.

It is also possible to form the co-axial cable using a tube consisting of a low loss dielectric material with a thin layer of metallization on the inner and outer walls to allow a TEM field or wave to propagate along the length of the transmission cable. In this arrangement, the thickness of the dielectric layer is such that a transmission line of impedance equal to 5O1 is formed (the transmission line impedance is not limited to being 5O2, e.g. it may be 25, 75fl or 15O). In this instance, both the inner and outer walls of the dielectric tube may be coated with a layer of metallization with a thickness as given in Table 2. This construction offers advantage in terms of enabling a flexible structure to be produced that can support both the microwave energy and the gas necessary to produce biologically useful plasma when mixed together inside the applicator. This arrangement also offers advantage in terms of enabling the gas to be fed into and extracted from the applicator since the feed or extraction pipes are in the same direction as the microwave feed, i.e. longitudinal to the length of the applicator. This enables the cable assembly and applicator to be inserted into natural orifices or small cavities within the human or animal body with ease and allows orifices of small diameter to be accessed.

The current invention is not limited to using co-axial cable assemblies and co-axial applicators. As an alternative, waveguide assemblies may be used, where flexible or flexible/twistable waveguide is used to transport both the microwave power and the gas to and from the applicator. It may be preferable to fill, or partially fill, the waveguide structures with a dielectric or magnetic material in order to reduce the size (diameter or width/height) of the waveguide structure in order to enable the waveguide cable and the antenna or applicator to be fitted inside a region of the body. In these arrangements, no centre conductor is required and impedance transformations maybe realised by changing the height or diameter of the waveguide or by varying the dielectric or magnetic constants (relative permittivity and relative permeability) of the loading or filling material.

Quarter wavelength transformers may be implemented by using longitudinal sections that have a loaded or unloaded electrical length that is equal to a quarter wavelength (or an odd multiple thereotTj at the frequency of operation. In the instance whereby loading or filling material is used, it is necessary for the material to contain holes along its length to enable the gas to be transported along the waveguide and into the applicator and to allow it to be returned where the device is to be used in a closed environment or inserted into a cavity within the human body. It may be preferable to use sections of material to load the waveguide or form the impedance transformations which do not totally fill the waveguide section in order to allow the gas to flow in one or both directions within the waveguide. An advantage of using waveguide assemblies is that the frequency of operation may be higher since the insertion loss along waveguide is less than that associated with co-axial cable assemblies. The power handling of waveguide is also higher than that of co-axial cable, thus it is possible to produce plasma of higher energy, which may be desirable for use in certain clinical applications.

Figure 1 gives an arrangement for a gas flow control system connected to the integrated cable assembly that forms a part of the current invention. The integrated cable assembly shown here enables forward going microwave power to be transferred to the applicator and any reflected returned microwave power to be transferred back along same cable to the generator where measurements may be taken. The integrated cable assembly also enables the same cable to be used to enable the gas to be introduced into the applicator along a first channel and for excess gas to be returned along a second channel to prevent pressure build up when the applicator is inserted inside a closed system or a natural orifice, and also to enable the unused gas to be recycled. Cable assembly 200/470 shown in figure 1 enables gas to be fed along transfer tube 305 into a hollow section or channel 301 of centre conductor 309 into an applicator comprising of parts 310, 320 and 330 (not shown here). The first section of centre conductor 309 is shown as a solid conductor 311, and this is connected to the centre conductor of microwave connector 340, which is connected to microwave generator 2000 to provide the microwave power necessary to produce the electromagnetic field to generate the plasma inside applicator 310, 320, 330. In the arrangement shown in figure 1, any excess gas is returned from applicator 310, 320, 330, along a channel formed between the inner wall of outer jacket 303 (this may be made from an insulating or conducting material) and the outer wall of outer conductor 308. The gas leaving cable assembly 200/470 is fed into transfer tube 306 and transferred back into the gas control system. A plurality of spacers 302 are inserted along the length of the cable assembly between outer jacket 303 and the outer wall of outer conductor 308 to ensure that the channel is kept opened along its length in order to allow gas to flow. This invention is not limited to using the hollow section of the inner conductor to transfer gas from the gas supply to the applicator and the channel formed between outer jacket 303 and the outer wall of outer conductor 308 to transfer gas back to the gas supply, i.e. the two feed pipes or transfer tubes may be interchanged.

The overall integrated cable assembly comprises of an outer jacket 303, which may comprise of a metallic or insulating material, a plurality of spacers 302 to enable a channel 307 to be formed between 303 and layer of metallization 308 that forms the outer conductor of the microwave transmission line. It is preferable for said spacers to be made from an insulating material, for example, nylon, PTFE or Teflon. Spacers 302 should allow gas to flow along the channel, i.e. they may contain a plurality of holes or perforations. A feed pipe 306 is attached to the wall of 303 to allow gas to be injected into or extracted from the system. The section of the cable assembly that enables the microwave field to propagate from the generator to the applicator comprises of a dielectric material 304, which is preferably a low loss material that allows the microwave energy to propagate with a minimum amount of insertion loss (for example, low density PTFE may be used), a first layer of metallization 309, and a second layer of metallization 308. It is preferable for said layers of metallization to be materials with a high conductivity, for example, silver, copper or gold. The first section of cable assembly 200/470 uses a solid section of metallization 309 (denoted here as 311) up until the point where feed pipe 305 is attached. Said solid section 311 enables the centre conductor of microwave connector 340 to be attached. The remaining section of metallization 309 comprises of a thin layer of metallization attached to the inner wall of a hollow tube formed in dielectric material 304. This hollow section is denoted as 301 and forms a channel to enable gas to be injected into the applicator or removed from the applicator. The impedance of the microwave cable assembly formed by this structure is described formally by equation 4 above, where an analysis of the dimensions associated with the overall integrated assembly is also given. Details of the use of the skin effect at microwave frequencies to enable a solid centre conductor to be replaced by a thin layer of metallization, where said metallization may be applied to the inner wall of the dielectric material, and where only a thin coating of metallization is required on the outer surface of said dielectric material 304 to complete the transmission line structure is also provided with this analysis and so this

description has not been repeated here.

The gas control system consists of gas extraction pipe 306, which is used to transport the excess gas back into the system. The distal end of pipe 306 is connected to an inlet to pump 426, whose purpose is to enable the excess gas to be sucked back from applicator along channel 307 and pipe 306 into reservoir 425. The flow or pumping rate at which pump 426 operates is determined by a control signal provided from a microprocessor or DSP unit within the controllable microwave generator and control system 2000. Said control signal controls the speed of the motor within the pump, which determines amount of gas that can be sucked back into gas reservoir 425. The outlet from pump 426 is connected to a one way valve 420, whose purpose is to ensure that the gas slows in one direction only, i.e. it flows into gas reservoir 425. The purpose of gas reservoir 425 is to store or hold the excess gas that has been collected from the applicator. The outlet from reservoir 425 is connected to second one way valve 419, whose purpose is to ensure that gas only flows in one direction; in this case, it flows from the reservoir into the inlet port of second pump 427. The purpose of second pump 427 is to suck gas from reservoir 425 to enable it to be transported back into the applicator to enable more plasma to be produced. The flow or pumping rate at which pump 427 operates is determined by a control signal provided from a microprocessor or DSP unit within the controllable microwave generator and control system 2000. Said control signal controls the speed of the motor within the pump, which determines amount of gas that can be sucked out of gas reservoir 425 back into the plasma producing applicator. The outlet from pump 427 is connected to third and fourth one way valves 418, 416 whose purpose is to ensure that gas only flows in one direction; in this case, to ensure that it flows from the outlet port of pump 427 to the inlet port of gas combiner 422. The purpose of gas combiner 422 is to combine the recycled gas with the gas provided from gas cylinder 410. The gas flow from cylinder 410 is controlled using an adjustable valve 411, which may be controlled either by mechanical or electrical means; in this arrangement, a mechanical means is chosen. Gauges 412 and 413 are shown connected to valve 411. The purpose of these gauges is to provide a means of indicating the gas pressure. One way valve 414 is connected between the output of gas cylinder 410 and the input of adjustable valve 411 to ensure that the gas flow is in one direction. A further one way valve 415 is inserted between the output of one way valve 411 and one of the inlet ports of gas combiner 422 for the purpose of ensuring that gas is not directed back into the gas cylinder 410 via adjustable valve 411. The outlet port from gas combiner 422 is connected to a further one way valve 417, whose purpose is to ensure that the gas flows in one direction, i.e. towards the applicator. The operation of gas combiner 422 may be controlled by a control signal provided from a microprocessor or DSP unit within the controllable microwave generator and control system 2000.

The outlet from one way valve 417 is connected to the inlet port of flow adjust controller 423, whose purpose is to enable the rate of flow of the gas into the applicator to be controlled by electronic means. The operation of the flow adjust controller 423 is determined by a control signal provided from a microprocessor or DSP unit within the controllable microwave generator and control system 2000. The output from flow adjust controller 423 is connected to a further one way valve 421, whose purpose is to ensure that the gas flows in one direction only, i.e. towards the applicator. The outlet from One way valve 421 is connected to the inlet port of flow switch 424, whose purpose is to control the gas flow going towards the applicator. It may be possible to use flow adjust controller 421 to perform this operation as well as to adjust the amount of gas flowing in the system. If this is the case, then flow switch 424 may be omitted from the system without loss in functionality. Some or all of One way valves: 420, 419, 418, 416, 415, 414, 417 and 421 may also be omitted without loss in functionality. The operation of the flow switch 424 is determined by a control signal provided by a microprocessor or DSP unit within the controllable microwave generator and control system 2000. The outlet port from flow switch 424 is connected to gas feed pipe 305, whose function is to transfer the gas from the gas controlling system contained within the instrumentation into the applicator or cable assembly 200/470.

Figure 1 also shows the controllable microwave generator and control system 2000 and user interface 150. The operation, together with a full description of the components contained within these units, is fully addressed in the descriptions given below that refer to figures 2 and 7.

Figure 2 provides a more detailed arrangement of the controlled microwave power generator 2000 and the gas control system 410, 450. The arrangement given here includes a system to enable the microwave energy used to strike and maintain the plasma to be matched into the impedance presented by the applicator in order to ensure that the plasma is struck and maintained in an efficient manner. The impedance to strike the plasma will be high, but, once it has been established and the conducting gas is formed, it will be reduced.

Therefore, it may be advantageous to perform automatic matching when the plasma changes impedance. The impedance may change when the plasma plume is coupled to a biological surface, or the temperature within the applicator increases, or the gas flow rate changes, thus the ability to automatically match into the changing impedance load will ensure that the microwave to plasma energy conversion is optimised in terms of conversion efficiency. This may be beneficial in terms of being able to accurately quantify the amount of energy delivered into tissue. The controlled microwave power and matching circuit 2000 comprises of stable frequency sources 10, which may provide a main carrier frequency and a reference frequency. The frequency sources are locked to a temperature compensated crystal reference 1.5, which provides the required frequency stability and accuracy, i.e. between ippm and o.lppm. One output from the stable frequency sources 10 enters the power level controller 20, where it is used to provide the main carrier frequency for the system, and the other outputs from stable frequency source enter the heterodyne detector/receiver unit 120, where they are used to provide local oscillator signals to enable the carrier frequency to be mixed down to a frequency whereby phase and/or magnitude information can be extracted and used to control the tuning network to enable the microwave energy to be efficiently matched into the plasma. On the main signal path, the power level controller 20 is used to control the level of microwave power fed into the applicator or antenna strUcture 300 to create the plasma.

Power level controller 20 attenuates the signal produced by one of the stable frequency sources 10 in accordance with the state (o or 1, oV or 5V) of the control signals produced by microprocessor 140 or digital signal processor 145 (these control lines are not shown here). The output from power level controller 20 is fed into pulse (or modulation) switch 30, whose function is to enable the microwave energy to be delivered into antenna 300 in a pulsed or other non continuous wave (CW) format. It may be possible and desirable to use power level controller 20 to provide the function of pulse switch o; this will be dependent upon the pulse rise/fall times and width requirements. The output from pulse switch 30 is connected to the input of semiconductor power amplifier 500, whose function is to amplify the signal provided by one of the stable frequency sources contained within 10 to a level that enables plasma to be struck and maintained. The level of microwave power produced by amplifier 500 is one of the main factors that determine the amount of plasma energy produced at the output of antenna 300 and used to destroy bacteria. Amplifier 500 is protected, in terms of reflected power being able to get back into the output transistors and causing damage, by use of protection circulator 50 and power dump load 51.

When the microwave power is not impedance matched to the plasma, or the tuning network ioo is arranged such that a mismatch occurs, then the microwave power will be reflected back towards the output of the amplifier; this reflected power is directed into and absorbed by power dump load 51 using microwave circulator 50. The output from circulator 50 is fed into the input of forward/reflected power monitor 60/70, whose function is to measure a portion of the forward going and reflected power at this point in the line-up. The signals from forward/reflected power monitor 60/70 are fed into receiver 120, where magnitude and/or phase information is extracted and used to control the operation of tuning network ioo and/or the operation of the power level controller 20 used in the power control loop. The output from forward/reflected power monitor 60/70 is fed into the input of tuning network ioo, whose function is to match the output power produced by amplifier 500 with the impedance seen at the antenna 300. The automatic control of tuning network 100 based on forward and reflected information gathered from the coupled ports of directional couplers 60/70, 80/90 allows the microwave energy to be efficiently converted into plasma energy. In the diagram shown in figure 2, three tuning stubs or rods are used as the tuning elements and these are positioned inside a waveguide tuner and the position of the rods is controlled by an electromechanical actuator 101, and PID controller 102, which is driven by signals produced by signal processor 145; these signals are determined by the mathematical manipulation of the magnitude and/or phase information supplied by receiver 120. This invention is not limited to using this tuning arrangement, i.e. power varactor diodes or PIN diodes may be used. The output from tuning network 100 is fed into the input port of second forward/reflected power monitor 80/90, whose function is similar to that of first forward/reflected power monitor 60/70. It may be possible and desirable to use second forward/reflected power monitor 80/90 only to provide the necessary magnitude and/or phase information to control the operation of tuning network 100. The output from forward/reflected power monitor 80/90 is connected to a microwave cable assembly 200, whose purpose is to transport microwave energy from the generator 2000 into the antenna 300, where the plasma is produced. It is desirable for microwave cable assembly 200 to be a low loss assembly in order to ensure that as much as possible of the microwave power produced by amplifier 500 is delivered into antenna 300. The output of cable assembly 200 is connected to the input of antenna 300, whose purpose is to convert the microwave power and the gas (or mixture of gases) at its input ports into clinically useful plasma. The gas (or mixture of gases) is supplied by gas source 410, and the flow of gas into antenna 300 is controlled using valve 450, whose operation is determined by signals produced by microprocessor 140.

Microprocessor 140 and digital signal processor 145 are used to control the operation of the system and to accept information from and send information to the user interface 150. User interface i.o is used to allow the user to input control information into the system and to display useful output information to the user.

Full details of components that may be used to implement this system are given

in the description relating to figure 7 below.

Figure 3 shows a detailed diagram of an integrated microwave cable assembly and antenna or applicator where the plasma is produced. In this arrangement, the integrated gas microwave cable assembly forms a part of another integrated assembly and comprises of a co-axial arrangement formed using two tubes. The first tube 304 is a relatively thick walled tube made from a flexible dielectric material and is coated with a layer of metal on both the inner 309 and outer 308 walls of said tube. The second tube 303 is a relatively thin walled tube made from a flexible material. The first tube 304 is suspended inside the second tube 303 using spacers 302 that may be made from a metallic or dielectric material and must allow gas to flow within and along the channel formed between the outer wall of first tube 308 and the inner wall of second tube 303. The integrated applicator comprises of two impedance transformers 310, 320, a means of feeding gas from centre channel of first tube into applicator via feed pipe 305, and a means of extracting excess gas from applicator along channel formed between the outer wall of first tube and the inner wall of second tube via feed pipe 306. The first section of the inner channel used to feed gas into the applicator 311 is solid to enable the centre pin within microwave connector 34o to be electrically connected to the new microwave cable assembly. Said input microwave connector may be any connector suitable for carrying microwave power up to 6ooW CW at the frequency of interest, e.g. SMA or N-type connectors may be used. The centre 301 of the inner conductor 309 used to form the co-axial microwave cable assembly is hollow due to the fact that the microwave field produced at the frequency of interest only requires a small amount of wall thickness to enable the field to efficiently propagate along the cable or waveguide, thus the centre part or section 301 of centre conductor 309 is transparent to the microwave field (this is a main feature of the current invention and, as such, has already been addressed in detail in this description). The same criteria applies to outer conductor 308, where it is only the inner layer that is attached to first tube 304 that plays an important part in the microwave field or wave propagation along the waveguiding channel. First tube 304 should preferably be made from a low loss dielectric material, e.g. low density PTFE, in order to ensure that the power loss along the structure (the insertion loss) is minimised. The integrated applicator or antenna is formed inside second tube 303 and forms an integral part of the cable assembly. This feature is particularly useful when the applicator is to be inserted inside a natural orifice of small diameter, i.e. less than 6mm, or where the device is to be used endoscopically. The integrated antenna shown in figure 3 consists of two quarter wave impedance transformer sections. The first section is a low impedance section whose impedance is determined by the ratio of the diameter of centre conductor 310 (g) and the diameter of outer conductor 330 (i). Said outer conductor 330 is an extension of outer conductor 308 within the integrated microwave cable assembly used to transport the microwave energy from the generator 2000 to the applicator. Both ends of first conductor 310 that forms a part of the applicator are tapered in order to prevent an abrupt step change in impedance occurring where the relatively higher impedance (nominally 50(1) co-axial feed line enters the first low impedance section of the applicator (nominally less than 10(1), and where the other end of the low impedance first section joins the input end of the second high impedance transformer (nominally greater than ioo(1). A gradual change in impedance at these junctions is desirable since this will minimise the level of reflection at the two junctions. It may be desirable for the taper to be of angle 450* The gas (or gas mixture) contained within channel 301 is fed into the applicator through a hole, groove, or channel made in centre conductor 310. The second transformer section is a high impedance section whose impedance is determined by the ratio of the diameter of centre conductor 320 (h) and the diameter of outer conductor 330 (i). It is desirable for the distal tip of centre conductor 320 to be sharp and pointed in order to maximise the electric field produced at this point. It is also desirable for the material used to form centre conductor 320 to be a material that is able to withstand high temperature without change of physical form or characteristic, e.g. tungsten.

Figure 4 (a) shows a cross section through the combined microwave power and gas feed assembly, where the channel 301 formed by the hollow centre conductor 310 is used to transport the gas from the gas source 410 (not shown here) into the applicator (also not shown). The gas is fed into channel 301, produced by making centre conductor 310 hollow, using feed pipe 305, which is preferably made from a dielectric material similar to that used to separate inner conductor 310 from outer conductor 330 in order to minimise discontinuities or reflections caused by use of a dissimilar material. The dielectric material 304 should be a low loss material at the frequency of operation and should provide a level of flexibility for the cable assembly, e.g. low density PTFE or polyurethane. Both the inner and outer conductors 310, 330 should be good conductors of electricity, e.g. silver, copper or gold, and their thickness e' may be limited to less than 10 skin depths at the frequency of operation without affecting the microwave field in anyway(this is addressed in detail above). The characteristic impedance of the cable assembly is determined by the ratio of the inner diameter of the outer conductor 330 (k) divided by the outer diameter of the inner conductor 310 (f + 2e), and the relative permittivity of di&ectric material 304. Equation 4 given above may be used to formally calculate the characteristic impedance of the microwave cable formed using this construction.

Figure 4 (b) shows the cross section through the combined microwave power and gas feed assembly, where the channel 301 formed by the hollow centre conductor 310, and the channel 307 formed between outer wall of the second conductor 330 that forms the co-axial cable, used to transport the microwave power, and the inner wall of the sheath 303 are used to transport the gas from the source 410 (not shown here) into the applicator (not shown here). In this arrangement, the gas is fed into the channels 301, 307 using feed pipe 305, which is preferably made from a dielectric material. Channel 307 formed between outer wall of the second conductor 330 and the inner wall of sheath 303 is supported using a plurality of spacers 302, which are preferably made from a material that will support the channel without it collapsing or closing to prevent gas flow when bent or twisted. Spacers 302 must enable gas to flow along channel 307, thus said spacers should contain a plurality of suitable holes or perforations. The characteristic impedance of the microwave cable assembly is determined by the ratio of the inner diameter of the outer conductor 330 divided by the outer diameter of the inner conductor 310, and the relative permittivity of dielectric material 304. Equation 4 given above may be used to formally calculate the characteristic impedance of this assembly. The material used to form outer sheath 303 may be a metallic or non-metallic material. It is preferable for said material to be a plastic or rubber material in order to help ensure the overall flexibility of the assembly to enable it to be manipulated by clinicians or other users.

Figure 4 (c) shows the cross section through the combined microwave power and gas feed assembly, where the channel 307 formed between outer wall of the second conductor and inner wall of sheath 303 is used to transport the gas from the gas supply 410 (not shown here) into the applicator or antenna. In this arrangement, inner conductor 310, which forms a part of the microwave energy delivery channel, is a solid conductor, i.e. it is not used to form a channel for the transportation of the gas. The gas is fed into channel 307 using feed pipe 305, which is preferably made from a dielectric material. Channel 307 formed between outer wall of the second conductor 330 and the inner wall of sheath 303 is supported using a plurality of spacers 302, which are preferably made from a material that will support the channel without it collapsing or closing to prevent or inhibit gas flow. Spacers 302 must enable gas to flow along channel 307, thus said spacers should contain a plurality of holes or perforations. The characteristic impedance of the microwave cable assembly is determined by the ratio of the inner diameter of the outer conductor 330 within microwave energy delivery assembly divided by the outer diameter of the inner conductor 310, and the relative permittivity of dielectric material 304 that separates the two conductors.

Equation 4, given above, may be used to formally calculate the characteristic impedance of this part of the assembly. The material used to form outer sheath 303 may be a metallic or non-metallic material. It is preferable for said material to be a plastic or rubber material in order to help ensure the overall flexibility of the assembly.

Figure 4 (d) shows the cross section through the combined microwave power and gas feed assembly, where the channel 301 formed by the hollow centre conductor 310 is used to transport the gas from gas supply 410 (not shown here) into the applicator where the plasma is produced, and the channel 307 formed between outer wall of the second conductor 330, that forms the co-axial cable to transport the microwave power, and the inner wall of sheath 303 (or outer covering) is used to return the excess gas inside the applicator back to the gas supply for reuse. The gas is fed into the channel 301 using feed pipe 305, which is preferably made from a dielectric material similar to that used to separate inner conductor 310 from outer conductor 330 used to enable the microwave field to be set up.

The dielectric material 304 should be a low loss material at the frequency of operation and should provide a level of flexibility for the cable assembly, e.g. low density PTFE or polyurethane. In the arrangements presented in the current invention a TEM field will be set-up between conductors 310, 330, inside dielectric material 304. Feed pipe 305 is fed into dielectric material 304 and used to carry gas 307. Said pipe is sealed or isolated from second channel to prevent the gas flows becoming mixed. Both the inner and outer conductors 310, 330 should be good conductors of electricity, e.g. silver, copper or gold, and their thickness may be limited to less than 10 skin depths at the frequency of operation without affecting the microwave field that is set up, inside dielectric material 304 in any way (this is addressed in detail above). The characteristic impedance of the cable assembly is determined by the ratio of the inner diameter of the outer conductor 330 divided by the outer diameter of the inner conductor 310, and the relative permittivity of dielectric material 304. Equation 4 may be used to formally calculate the characteristic impedance. Channel 307 formed between outer wall of the second conductor 330 and the inner wall of sheath 303 is supported using a plurality of spacers 302, which are preferably made from a material that will support the channel without it collapsing or closing and preventing or inhibiting gas flow within the channel. Spacers 302 must enable gas to flow along channel 307, thus said spacers should contain a plurality of holes or perforations. The gas is extracted from channel 307 using extraction pipe or tube 306, which is fed into the gas reservoir 425 (not shown here) for re-use.

The ability to remove or extract gas from the system also prevents gas pressure from building up when the applicator is inserted inside the human body, e.g. when inserted into a human orifice which has a small diameter and the applicator is tight to the wall of the orifice.

Figure 4 (e) shows an arrangement similar to that shown in figure 4 Cd), but where the gas is extracted through extraction pipe 305 using channel 301 formed by making centre conductor 330 hollow, and the gas is fed into the system through feed pipe 306 using channel 305 formed between outer jacket or sheath 303 and second conductor 310 that provide the outer conductor for the microwave transmission line, where a plurality of spacers 302 are used to support the channel without it collapsing or closing and preventing or inhibiting gas flow along the channel. Spacers 302 must enable gas to flow along channel 307, thus said spacers should contain a plurality of holes or perforations.

Figure 5 shows an arrangement where the gas is fed into the antenna using two separate tubes 470 that are shown here to be combined at the source. In an alternative embodiment of this arrangement, the tubes may be separated where a first tube is used to supply the gas (or gas mixture) and a second tube is used to extract the gas from the system to relieve pressure build up and/or to recycle the gas. The microwave power is fed into a microwave cable assembly 200 using a suitable microwave connector 210. In this arrangement, the microwave power and gas are supplied to the applicator using two separate conduits and both microwave power and gas enter the applicator at the proximal end of the applicator in the same direction as the applicator. The microwave power produced at the distal end of microwave cable assembly 200 is connected to the proximal end of the applicator using a suitable microwave connector arrangement 340; this may comprise of an N-female attached to the distal end of the microwave cable assembly 200 and an N-male attached to the proximal end of the applicator or the like. The applicator is comprised of two impedance transformer sections 310, 320. An insert 360 is included at the distal end of the structure. Said insert may be a dielectric rod, which may be used to help focus the plasma. The dielectric rod may be omitted without loss of plasma, but the beam may be more spread out. The gas 350 is set up within the applicator and is combined with the microwave power produced by generator 2000 (not shown here) to generate a plasma iooo that emanates from the distal end of the applicator. This plasma is clinically useful and may be used for sterilisation purposes to destroy bacteria.

Figure 6 shows a similar arrangement to that given in figure 5 where the applicator 300 (comprising of parts: 310, 320, 330), together with cable assembly and gas supply pipes 470 (combined here as 4000) are inserted into a region of the patients body 4010 through the mouth 4020, and the plasma produced at the distal end of the applicator 1000 is used to treat or sterilise the organ of interest 4040. This assembly may also be inserted through the nose 4030 or any other natural orifice contained within the human body. The integrated assembly described here may also be inserted percutaneously or endoscopically into the human body.

The overall system diagram for a plasma sterilisation system is given in figure 7.

Most of the components shown in figure 7 are depicted and described as the controllable microwave generator and control system' sub-system 2000 in figure 1, and is also shown in less detail in figure 2. This arrangement has already been disclosed in our previous patent application GB0721714.7, filed on 6th November 2007, where claims have not yet been filed, but it is intended to file claims against certain unique aspects of this system. Therefore, this overall system arrangement has been captured here for completeness. The source of microwave energy 10 is preferably a low power microwave source oscillator, i.e. able to produce power levels from greater than -iodBm to less than 2OdBm, that produces a well controlled single frequency, but where this single frequency may be adjustable over a narrow band of frequencies, i.e. has a centre frequency of 900MHz that is adjustable between 850MHZ and 950 MHz. The source oscillator io may be a voltage controlled oscillator (VCO), a dielectric resonator oscillator (DRO), a gunn diode oscillator or a similar device that is capable of producing a controllable low power microwave signal. A frequency synthesiser that comprises of a plurality of VCOs or DROs may also be used.

The output from the frequency oscillator in is connected to the input port of a power level controller 20, whose function is to enable the level of the signal produced by frequency oscillator io to be adjusted over a range that is suitable to enable the plasma to be struck and then enable the plasma energy to be adjusted.

The power level controller 20 may be a PIN diode attenuator that may be a reflective or absorptive type. The output from the power level controller 20 is connected to the input of a first modulator 30, whose function is to switch the microwave power produced at the output of power controller 20 on and off using a signal produced by microprocessor 140 to enable the output microwave power produced at the output of power amplifier 500 to be in a pulsed format rather than a continuous wave format. The ability to control the switching action of first modulator 30 enables the pulse on time, the pulse off time and the pulse format to be controlled. This enables the ratio between the on and off times (the duty cycle) and the frequency (the inverse of the sum of the on time and the off time) to be determined. The modulation may not necessarily be periodic, i.e. it may consist of a train of pulses with various duty cycles and frequencies. The ability to control the pulse on and off times in this manner provides an additional means of controlling the energy produced by the plasma.

The output from first modulator 30 is fed into the input of the power amplifier 500. Power amplifier 500 is preferably a semiconductor based amplifier whose function is to amplif' the power level at the output of first modulator 30 to a level that is sufficient to enable a plasma to be struck and to enable enough energy to be delivered into the plasma for the plasma to produce a useful clinical affect in terms of reducing or killing bacteria or viruses. Power amplifier 500 may comprise of a plurality of stages, i.e. driver stage, pre-amplifier stage and high power stage. The amplifier may use following semiconductor devices, i.e. high frequency bipolar junction transistors (BJTs), heterostructure bipolar transistors (HBTs), metal oxide semiconductor field effect transistors (MOSFETs), or metal semiconductor transistors (MESFETs). In terms of the semiconductor materials that may be used, of particular interest are gallium arsenide (GaAs) and gallium nitride (GuN). For example, a recently reported single-ended amplifier using small packaged GaN FETs has demonstrated a record output power at 2.14GHz.

This amplifier consisted of a paralleled 48 mm gate periphery FET die, delivering a peak saturated output power of 371 W with a linear gain of 11.2 dB at a drain voltage of 45 V. The output power density is said to be twice as high as that of the existing over 300 W GaAs FET amplifiers.

GaN FETs offer higher efficiency (microwave power/DC power) than GaAs FETs.

This feature is of particular interest when developing a plasma system that is capable of providing high power microwave energy since the heating effects caused by DC power losses are significantly reduced, which increases the portability of the system and minimises thermal design issues that need to be overcome when developing the system.

It is desirable to be able to switch the main device power supplies (drain supply in FETs and the collector supply in BJTs) completely off during periods when it is not required to produce microwave power, i.e. when the switch contact of first modulator 30 is in the off position. A second modulator 130 may be employed to perform this function. Said second modulator 130 may comprise of a plurality of lower frequency power MOSFET or BJT switches that enable the DC power supplies to be connected to the high frequency power BJTs or PETs only when it is required to generate microwave power for the production of plasma. The operation of the lower frequency power devices that form second modulator 130 can be controlled by varying the gate voltage or base current of the power FETS or power BJTs respectively. The control signals are provided by microprocessor and the signals used to control the operation of second modulator 130 may be synchronised to the control signal used to control the operation of first modulator 30. Second modulator 130 will have a slower response time than that of first modulator 30, therefore, it may be desirable to modulate or pulse using first modulator 30 inside a window when second modulator 130 is enabled or switched on. For example, second modulator 130 may be switched on for a time slot of looms and off for a time slot of 1 second; during the on period, first modulator 30 may produce 50 pulses with an on time of ims and an off time of ims. First modulator 30 and second modulator 130 enable the energy produced by the plasma to be controlled to ensure that the temperature of the plasma and the plasma energy is controlled to enable optimal clinical effects in terms of killing or the reduction of bacteria and/or viruses.

The output from microwave power amplifier 500 is fed into the input port of microwave power circulator or power isolator 50, whose function is to ensure that high levels of reflected microwave power, due to impedance mismatches at antenna 300 or anywhere else in the path between the antenna 300 and the input port to first forward power coupler 60, i.e. 200, 90, 80, 100, and 70, cannot damage the output stage of power amplifier 500. In the arrangement shown in figure 1, a o11 power dump load 51 is shown connected to the third port of microwave power circulator 50. Any power that does get reflected back along the aforementioned path between antenna 300 and first coupler 6o will be absorbed by said power dump load 51.

Port 2 (the output port) of said microwave power circulator 50 is connected to the main line input port of first forward power directional coupler 60, whose function is to sample a portion of the forward going power produced by power amplifier 500. This information may be used to control the level of microwave power produced by power amplifier 500 to ensure that the demanded power level is the same as the delivered (actual) power level, i.e. this information may be used in a feedback control loop to automatically adjust the input power going into the amplifier to compensate for output power drift caused by heating or ageing of microwave components used in the line-up. The information provided by first forward going directional coupler 60 may also be used in the tuning algorithm to control the position of the stubs used in the stub tuning network (or tuning filter) ioo. The main line output from first forward power directional coupler 6o is connected to the main line input port of first reflected power directional coupler 70, whose function is to sample a portion of the reflected power that comes back from the input port of tuning filter 100 due to an impedance mismatch caused either by the position of the tuning elements or the impedance set-up inside the tuning filter or the impedance set up by antenna 300 in accordance with the state of the plasma, and the impedance transformations 330-310/330-320 set up inside the applicator. The information provided by first reflected power directional coupler 70 may also be used in the tuning algorithm to control the position of the stubs used in the stub tuning network (or tuning filter) 100. This information may also be used to as a part of a safety mechanism to detect the condition of the microwave components used in the line-up.

The main line output from first reflected power directional coupler 70 is connect to the input port of tuning filter 100, whose function is to set-up a condition that will enable the impedance of applicator 300 to be such that the plasma can be struck and then maintained. The condition for the plasma to be struck is a high voltage (high impedance) condition and that for it to be maintained is a high current (low impedance) condition. The tuning filter 100 may be a stub tuner that contains a single or a plurality of tuning rods or stubs, or may be an arrangement of power varactor or PIN diodes, where the bias voltage is changed to enable the capacitance to be varied. This capacitance variation is used to enable the tuned conditions to be set-up based on the requirements associated with clinical applications for the plasma.

In the system shown in figure 1, a stub adjuster unit 110 is included; this is for a mechanical tuning mechanism where tuning rods are moved in and out of a cavity, for example, a waveguide cavity. Three tuning stubs are shown here, but this invention is not limited to the use of three, i.e. one, two, or four may be used.

Three stubs may be preferable due to the fact that this arrangement will enable any impedance from an open circuit to a short circuit to be set-up inside the tuning cavity, thus it is guaranteed that it will be possible to set-up the high and low impedance conditions. The signals used to control the stub adjuster comes from microprocessor 140, and these signals may be based on the signals produced by detection unit 120 in accordance with the information available at the coupled ports of directional couplers 6o, 70, 80, and 90. The control signals provided to stub adjuster 110 may also be in the form of two fixed signal formats; a first to create a known high impedance condition that is used to strike the plasma, and a second to create a known low impedance condition to maintain the plasma. The dynamic adjustment of the tuning stubs may also be used to optimise and control the plasma energy.

It should be noted that a PID controller could be used between microprocessor and stub adjuster iio to control the response of the electromechanical stub adjuster no. Alternatively, the PID control functions may be handled by microprocessor 14o. A further alternative is to replace the mechanical tuning system with a power PIN or varactor diode arrangement, whereby the bias voltage applied to the diodes is used to adjust the depletion layer within the diodes to produce a capacitance variation.

The output port of the tuning filter is connected to the main line input of second forward power directional coupler 80, whose function is to sample a portion of the forward going power coming out of tuning filter ioo. This information may be combined with the information produced by the coupled port of first forward power coupler 6o (or used independently) to control the level of microwave power produced by power amplifier 500 to ensure that the delivered power level is the same as the demanded power level, i.e. this information may be used in a feedback control loop to automatically adjust the input power going into the amplifier to compensate for output power drift caused by heating, ageing of microwave components used in the line-up, or changes in the characteristics of tuning filter 100. It may also compensate for mismatches occurring between the amplifier and the distal end of the applicator. The information provided by second forward going directional coupler 8o may also be used in the tuning algorithm to control the position of the stubs used in the stub tuning network (or tuning filter) 100. The main line output from second forward power directional coupler 8o is connected to the main line input port of second reflected power directional coupler 90, whose function is to sample a portion of the reflected power that comes back from microwave cable assembly 200 due to an impedance mismatch caused the impedance of antenna 300 (310, 320, 330, 340, 350) that varies in accordance with the state of the plasma, and the impedance transformation sections 330-310 and 330-320. The information provided by second reflected power directional coupler 90 may also be used in the tuning algorithm to control the position of the stubs used in the stub tuning network (or tuning filter) 100. This information may also be used as a part of a safety mechanism to detect the condition of the microwave components used in the line-up, i.e. used to detect a break in the line-up or any defect that may occur between the output of the amplifier and the distal end of the applicators.

The main line output from second reflected power directional coupler 90 is connected to the proximal end of microwave cable assembly 200, whose function is to transport microwave energy used to strike and maintain the plasma from the controllable microwave generator (io, 20, 30, 500, 130, 50, 51, 6o, 70, 80, 100, 110, So, 90, 140 and 150) to antenna 300. Microwave assembly 200, may take the form of a co-axial cable designed to support propagation of microwave energy at the frequency of interest, or any other structure that produces a minimal amount of loss in power between the output of the generator and the distal end of the applicator, for example, a flexible or a flexible/twistable waveguide.

The distal end of microwave cable assembly 200 is connected to the proximal end of antenna 300, whose function is to take in the microwave energy and the gas (or gas mixture) into the device to produce plasma that is suitable for reducing or destroying bacteria or a range of viruses. The antenna shown in figure i comprises of a first impedance transformer 310-330, a second impedance transformer 320-330, a microwave input connector 340, and a means of coupling the pipe or tube that supplies the gas mixture 470 into 300.

The sampled forward and reflected power levels (or signals) available at the coupled ports of directional couplers 60, 70, 80, and 90 are fed into detection unit 120, whose function is to enable either amplitude or amplitude/phase information to be available at microprocessor 140, where this amplitude or amplitude/phase information is extracted and used to control tuning filter ioo.

The information from the coupled ports of directional couplers 60, 70, 80, and may be routed to detection unit 120 using a four pole single throw switch, which may be a PIN (reflective or absorptive) or a co-axial switch, and whose operation is controlled by signals produced by microprocessor 140 to enable one detector to be used to process the information produced by the four couplers. In an alternative embodiment, four detectors may be used.

The detection unit 120 may take the form of a diode detector, a homodyne detector or a heterodyne detector. The diode detector may take the form of a tunnel diode, a Schottky diode or any other diode that can be operated at the frequency of interest to provide amplitude or magnitude information relating to the forward and reflected power levels at directional couplers 6o, 70, 8o, or 90.

The homodyne detector may take the form of a microwave mixer and a local oscillator that operates at the same frequency as the signal produced by microwave oscillator 10 to enable base band information to be extracted. The heterodyne detector may take the form of at least one microwave frequency mixer and at least one local oscillator. In this configuration the local oscillator frequency (ies) is/are different from that of microwave oscillator io. This arrangement may also contain band pass and low pass filters to filter out signals at unwanted frequencies contained within the intermediate frequency signal (IF) produced at the output of the microwave frequency mixer(s) and to remove signals produced at the local oscillator frequency (ies) or at the main microwave oscillator frequency in when they occur within the microwave line-up in locations where they are unwanted.

Microprocessor unit 140 is used to control the operation of the plasma generation system. It is responsible for controlling the operation of the following components used in the system: power level controller 20, first modulator 30, second modulator 130, gas mixer 400, flow switches 430-440, flow adjust controllers 450-460, compressed air generator 420, stub adjuster iio, and the user interface 150. It also reads the signals produced by detection unit 120 and uses this information to calculate the adjustments required by the tuning stubs via stub adjuster no. Microprocessor unit 140 also determines the mixture of gas required, the gas pressure, and the flow rate based on the required application. It is necessary to determine when to introduce the gas mixture into the antenna in relation to the microwave energy. It is desirable to ensure that the applicator is filled with gas prior to introducing the microwave energy in order to ensure that the plasma is struck as soon as the microwave source is activated. It is also desirable to ensure that the correct or optimal conditions are set up inside the stub tuner prior to the microwave source being activated. An example of a sequence of events may be as follows: 1. Set stubs into a position where a known high impedance will be produced at the distal end of second conductor of second impedance transformer 320; 2. Determine the gas flow rate, the gas mixture, the gas pressure, and the pulsing sequence required to produce optimal plasma for the particular application; 3. Determine the level of microwave power and the modulation (or waveform) format required to produce optimal plasma for the particular application; 4. Introduce the gas mixture into the applicator; 5. After a period of time when it is assured that the applicator is full of gas introduce the microwave energy into the applicator.

When the system is being operated in pulse mode, it may be desirable to stop the gas flow during the time that the microwave source is in the off' state and start it again just before switching the microwave energy back on again. For example, the microwave power may be delivered using a 10% duty cycle where the on time is ioms and the off time is 9oms. In this instance, it may be desirable to start the gas flow ms before the start of the microwave pulse and turn it off ms after the microwave pulse has been switched off, thus for each ioms of microwave energy the gas will flow for 2oms.

It may be desirable to stop the gas flow at the same time as turning the microwave power off since it will take a finite time for the gas to cease flowing.

It may also be necessary to initially start the gas flow for a longer period of time in order to be sure that the gas has reached the applicator and has had enough time to enable it to fill the inside of the applicator. The applicator may therefore include a gas sensor, which will provide a signal to the microprocessor.

A further function of microprocessor unit 140 is to activate alarms and handle safety features and system shut down procedures in the instance when a fault occurs. It may be necessary to use a second microprocessor unit or a similar device that can be used as a watchdog for ensuring that safety critical features are handled correctly.

Microprocessor unit 140 may take the form of a single board computer, a microcontroller (or PlC device) a single board computer and a PlC device (used as a watch dog), more than one single board computer, more than one PLC device, a digital signal processor, or any combination of these devices.

The user interlace 15o provides a means of allowing the user to control the system and to provide information to the uses regarding the status and operation of the system. The user interface may be in the form of a touch screen display, a flat LCD display and a set of membrane keys, or any other means of outputting and inputting user control information.

The sub-system responsible for the control of the gas mixture comprises of at least one gas cylinder 410 and/or a compressed air generator 420, a means of controlling the rate of flow of the gases 430,450, 440, 460, a means of mixing the gases together and a means of controlling the gas pressure. The rate of gas flow may be controlled using a flow valve with a flow controller in combination with a suitable flow switch, which may be a solenoid switch. In specific embodiments of the current invention, the flow switches 430, 440 may not be implemented and the flow adjustment may be implemented using only flow adjust controllers 450, 460. On the other hand, flow adjust controllers 450, 460 may be omitted and flow control may be implemented by mechanical adjustment of the valve connected to the particular gas cylinder 410 combined with electrical control of flow switch 430, 440. In the instance when a compressed air generator 420 is used, it may be possible to operate the system using only flow switch 440. Gas mixer 400 may be required where more than one type of gas is used and it is necessary to optimise the mixture or vary the mixture during operation in order to optimise the plasma produced by the applicator.

Gas mixer 400 may take the form of a pneumatic device which works by balancing pressures from the input gas supplies to ensure that the component gases are mixed at the same pressure regardless of their individual inlet pressures and flow rate. The gases may be combined in a chamber fed by variable orifices, which are set by the mixing control. The mixers may be factory set for the gases specified. For example, in a two gas system the mix control can be calibrated directly in proportionality 0 -ioo% -gasl/gas2. This single control sets up the required mix. In a three gas mixer, where there are two proportional regulators, the proportionality may be set with two controls to set the total mix.

Where the flow is intermittent, i.e. for pulsed operation, a special control valve may be required to ensure accurate feeding of a ballast tank. Built in alarms and sensors may be added to monitor the pressure conditions in the mixer to ensure correct mixing conditions.

The operation of the gas mixer 400, the flow switches 430, 440, the flow adjust controllers 450, 460, and the compressed air generator 420 is controlled using microprocessor io, and adjustment of these devices may take place using a closed loop feedback system where the adjustments are based on the feedback signals from detection unit 120. The adjustment may also be based on information picked up by a gas sensor contained in the applicator.

It has been found from practical experimentation that clinically useful plasma can be produced using a mixture of helium and compressed air.

Claims

CLAIMS1. A manoeuvrable applicator (or antenna arrangement) that can be inserted inside a natural orifice contained within the human or animal body to reduce or kill bacteria or viruses, where the applicator comprises of: a co-axial cable assembly that can deliver microwave power and supply of gas (or a mixture of gases) to a suitable antenna using a single assembly; and a co-axial antenna consisting of at least one impedance transformer to enable an electric field to be generated that is sufficient to enable a plasma to be produced that can be used to reduce or kill certain types of bacteria or viruses, wherein the coaxial cable assembly contains at least one hollow section that can be used to enable the gas to be transported into the antenna.
2. A system for reducing or killing bacteria or viruses contained within the human or animal body or external surfaces that uses microwave energy and at least one gas, where residual gas is recycled and the system comprises of: a controllable microwave power source; a controllable source of gas (or mixture of gases); an antenna or applicator that has microwave power and gas at its input and enables a suitable plasma to be produced at its output; a channel to transport the microwave power from the microwave source to the antenna or applicator; a channel to transport the gas (or mixture of gas) from the gas supply to the antenna or applicator; a channel to transport the residual gas back from the antenna or applicator to the gas supply or reservoir, wherein a pump, a one way valve, a reservoir arid a gas combiner may be included to draw the gas back along the channel to enable it to be reused in the plasma creating process; auser interface; a controller or signal processing and control unit, wherein the controller is used to determine the correct dosage of plasma necessary to destroy the bacteria, to synchronise the gas supply with the microwave source, to determine the correct microwave energy and gas flow rate required to enable the correct dosage of plasma to be generated at the distal end of the antenna, and to provide other control functions necessary to produce the required dosage of plasma to destroy bacteria.
3. A system according to claim 2, wherein an impedance matching network or matching filter is inserted between the output of the controllable microwave source and the input to the antenna (or applicator) to enable the plasma energy produced at the distal end of the antenna to be optimised in terms of enabling a high electric field to be produced (high impedance state) to allow plasma to be struck and then enabling the microwave energy to be matched into the impedance of the conducting gas plasma (lower impedance state).
4. A tube made from a dielectric material that forms a waveguide structure or a co-axial transmission line to enable microwave power to be propagated along its length, whereby the inner and outer walls of said tube are coated with a layer of metallic material that is a good conductor of electricity, e.g. silver, copper, or aluminium.
5. An arrangement according to claim 4, whereby the thickness of the layers of metallization on the inner and outer walls of the tube are between i and 10 skin depths at the microwave frequency of interest to allow for the microwave field to propagate inside the dielectric material between the two conductive layers, and where said thickness is between o.ipm and 1mm, or more preferably between ipm and 10pm.
6. As claimed in 5 whereby the microwave field set up inside the tube is atransverse electromagnetic field.
7. An arrangement according to claims 4 and 5, whereby the hollow centre of aforementioned tube is used as a channel to supply gas to the applicator or antenna, and the co-axial transmission line described in 4 is used to supply the microwave power to the applicator.
8. An arrangement according to claims 4 to 7, whereby said dielectric material used to form the co-axial cable is a flexible material to allow the overall structure to be easily manipulated when inserted inside the human or animal body.
9. An arrangement according to claims 4 to 7, whereby a second tube is inserted over the first tube to form an additional channel for gas to flow along.
10. An arrangement according to claim 9, whereby disks containing holes or an arrangement of webbing is used to suspend the first tube within the second tube to provide the necessary channel to enable the gas to flow along.
ii. An arrangement according to the above claims, wherein the inner section of the inner conductor or the outer section of the outer conductor of the co-axial cable assembly is hollow to provide a channel to enable the gas (or gas mixture) to be transported from the gas supply to the antenna where the plasma is produced.
12. An arrangement according to the above claims, wherein the inner section of the inner conductor and the outer section of the outer conductor of the co-axial cable assembly is hollow or not made of solid metal sections to enable the gas (or gas mixture) to be transported to the antenna where the plasma is produced.
13. An arrangement according to the above claims, wherein the inner section of the inner conductor is used to transport gas (or a mixture of gases) from the gas source to the antenna and the outer section of the outer conductor of the co-axial cable assembly is used to transport residual gas back to the gas source or a reservoir used to store the gas or to re-circulate it back to the antenna, wherein a pump is used to suck the gas from the applicator, along the outer section of the outer conductor contained within the microwave cable assembly.
14. An arrangement according to the above claims, wherein the outer section of the outer conductor is used to transport gas (or a mixture of gases) from the gas source to the antenna and the inner section of the inner conductor of the co-axial cable assembly is used to transport residual gas back to the gas source or a reservoir used to store the gas or to re-circulate it back to the antenna, wherein a pump is used to suck the gas from the applicator along the inner section of the inner conductor contained within the microwave cable assembly.
15. A co-axial antenna according to the above claims, wherein the impedance transformer(s) is (are) a single quarter wave transformer(s) or a transformer(s) made up of an odd number of quarter wavelengths at the frequency of interest.
16. A co-axial antenna according to the above claims, where an additional half wavelength transformer is added to the distal end of the applicator to increase the value of electric field produced at the distal end of the applicator.
17. Apparatus and method according to the above claims that may be used to reduce or kill bacteria contained on the surface of the human or animal body, or contained inside natural orifices within the human or animal body.
18. A manoeuvrable applicator (or antenna arrangement) that can be inserted inside a natural orifice contained within the human or animal body to reduce or kill bacteria or viruses, where the applicator comprises of: a waveguide cable assembly that can deliver microwave power and supply of gas (ora mixture of gases) to a suitable antenna using a single assembly; and a waveguide antenna consisting of at least one impedance transformer to enable an electric field to be generated that is sufficient to enable a plasma to be produced that can be used to reduce or kill certain types of bacteria or viruses, wherein the waveguide cable assembly contains one hollow section that can be used to enable the gas to be transported into the antenna.
19. An arrangement according to claim i8 whereby the waveguide cable assembly and/or the antenna is loaded with a dielectric or magnetic material in order to reduce the size of the assembly.
20. An arrangement whereby the integrated cable assembly and the antenna (applicator) are integrated to form a single item or unit, and the overall system comprises of: a co-axial arrangement formed from two tubes, where the first tube is a relatively thick walled tube made from a flexible dielectric material and is coated with a layer of metal on both the inner and outer walls of said tube, and the second tube is a relatively thin walled tube made from a flexible material, whereby the first tube is suspended inside the second tube using spacers that allow gas to flow along said the channel formed between the outer wall of first tube and the inner wall of second tube; an integrated antenna (applicator) that comprises of at least one impedance transformer, a means of feeding gas from centre channel of first tube into applicator, and a means of extracting excess gas from applicator along channel formed between the outer wall of first tube and the inner wall of second tube.
21. An arrangement according to claim 20, whereby the gas control system comprises of: a channel to transport the excess gas from the antenna (applicator) back to the supply system; a pump to enable excess gas to be returned to the source; a reservoir to contain or hold the returned gas; a second pump to pump the gas contained in the reservoir into a gas combiner arrangement; a gas combiner arrangement; at least one gas cylinder to provide the source of gas; a flow adjustment controller to enable the flow rate to be adjusted and, a channel to transport the gas from the gas source back to the antenna (applicator).
22. An arrangement according to claim 21, whereby a flow switch is included to provide an additional means of controlling the gas inside the antenna (applicator).
23. An arrangement according to claim 21, whereby the one way valves are included in the system to ensure that the gas travels in the desired direction within the system.
24. An arrangement according to claims 21 and 22 whereby the operation of the flow switch is synchronised with the microwave power source to ensure that the applicator is full of gas prior to the microwave source being activated, and that the gas supply is ceased as soon as the microwave source is switched off.
25. Apparatus according to any one of the aforementioned claims whereby the antenna is inserted into a natural orifice within the human or animal body.