referring now to fig1 , one embodiment of the present invention is a handpiece 10 with a handpiece assembly 12 . handpiece assembly 12 includes a handpiece housing 14 and a cooling fluidic medium valve member 16 . an electrode assembly 18 is coupled to handpiece housing 14 . electrode assembly 18 has a least one rf electrode 20 that is capacitively coupled to a skin surface when at least a portion of rf electrode 20 is in contact with the skin surface . without limiting the scope of the present invention , rf electrode 20 can have a thickness in the range of 0 . 010 to 1 . 0 mm . handpiece 10 provides a more uniform thermal effect in tissue at a selected depth , while preventing or minimizing thermal damage to the skin surface and other non - target tissue . handpiece 10 is coupled to an rf generator . rf electrode 20 can be operated either in mono - polar or bi - polar modes . handpiece 10 is configured to reduce , or preferably eliminate edge effects and hot spots . the result is an improved aesthetic result / clinical outcome with an elimination / reduction in adverse effects and healing time . a fluid delivery member 22 is coupled to cooling fluidic medium valve member 16 . fluid delivery member 22 and cooling fluidic medium valve member 16 collectively form a cooling fluidic medium dispensing assembly . fluid delivery member 16 is configured to provide an atomizing delivery of a cooling fluidic medium to rf electrode 20 . the atomizing delivery is a mist or fine spray . a phase transition , from liquid to gas , of the cooling fluidic medium occurs when it hits the surface of rf electrode 20 . the transition from liquid to gas creates the cooling . if the transition before the cooling fluidic medium hits rf electrode 20 the cooling of rf electrode 20 will not be as effective . in one embodiment , the cooling fluidic medium is a cryogenic spray , commercially available from honeywell , morristown , n . j . a specific example of a suitable cryogenic spray is r134a 2 , available from refron , inc ., 38 - 18 33 rd st , long island city , n . y . 11101 . the use of a cryogenic cooling fluidic medium provides the capability to use a number of different types of algorithms for skin treatment . for example , the cryogenic cooling fluidic medium can be applied milliseconds before and after the delivery of rf energy to the desired tissue . this is achieved with the use of cooling fluidic medium valve member 16 coupled to a cryogen supply , including but not limited to a compressed gas canister . in various embodiments , cooling fluidic medium valve member 16 can be coupled to a computer control system and / or manually controlled by the physician by means of a foot switch or similar device . a key advantage of providing a spray , or atomization , of cryogenic cooling fluidic medium is the availability to implement rapid on and off control . cryogenic cooling fluidic medium allows more precise temporal control of the cooling process . this is because cooling only occurs when the refrigerant is sprayed and is in an evaporative state , the latter being a very fast short - lived event . thus , cooling ceases rapidly after the cryogenic cooling fluidic medium is stopped . the overall effect is to confer very precise time on - off control of cryogenic cooling fluidic medium . referring now to fig2 , fluid delivery member 22 can be positioned in handpiece housing 14 or electrode assembly 18 . fluid delivery member 22 is configured to controllably deliver a cooling fluidic medium to a back surface 24 of rf electrode 20 and maintain back surface 24 at a desired temperature . the cooling fluidic medium evaporatively cools rf electrode 20 and maintains a substantially uniform temperature of front surface 26 of rf electrode 20 . front surface 26 can be sufficiently flexible and conformable to the skin , but still have sufficient strength and / or structure to provide good thermal coupling when pressed against the skin surface . rf electrode 20 then conductively cools a skin surface that is adjacent to a front surface 26 of rf electrode 20 . suitable fluidic media include a variety of refrigerants such as r134a and freon . fluid delivery member 22 is configured to controllably deliver the cooling fluidic medium to back surface 24 at substantially any orientation of front surface 26 relative to a direction of gravity . a geometry and positioning of fluid delivery member 22 are selected to provide a substantially uniform distribution of cooling fluidic medium on back surface 24 . the delivery of the cooling fluidic medium can be by spray of droplets or fine mist , flooding back surface 24 , and the like . cooling occurs at the interface of the cooling fluidic medium with atmosphere , which is where evaporation occurs . if there is a thick layer of fluid on back surface 24 the heat removed from the treated skin will need to pass through the thick layer of cooling fluidic medium , increasing thermal resistance . to maximize cooling rates , it is desirable to apply a very thin layer of cooling fluidic medium . if rf electrode 20 is not horizontal , and if there is a thick layer of cooling fluidic medium , or if there are large drops of cooling fluidic medium on back surface 24 , the cooling fluidic medium can run down the surface of rf electrode 20 and pool at one edge or corner , causing uneven cooling . therefore , it is desirable to apply a thin layer of cooling fluidic medium with a fine spray . in various embodiments , rf electrode 20 , as illustrated in fig3 , has a conductive portion 28 and a dielectric portion 30 . conductive portion 28 can be a metal including but not limited to copper , gold , silver , aluminum and the like . dielectric portion 30 can be made of a variety of different materials including but not limited to polyimide , and the like . other dielectric materials include but are not limited to silicon , sapphire , diamond , zirconium - toughened alumina ( zta ), alumina and the like . dielectric portion 30 can be positioned around at least a portion , or the entirety of a periphery of conductive portion 28 . suitable materials for a dielectric portion 30 include , but are not limited to , teflon ® and the like , silicon nitride , polysilanes , polysilazanes , polyimides , kapton and other polymers , antenna dielectrics and other dielectric materials well known in the art . in another embodiment , rf electrode 20 is made of a composite material , including but not limited to gold - plated copper , copper - polyimide , silicon / silicon - nitride and the like . dielectric portion 30 creates an increased impedance to the flow of electrical current through rf electrode 20 . this increased impedance causes current to travel a path straight down through conductive portion 28 to the skin surface . electric field edge effects , caused by a concentration of current flowing out of the edges of rf electrode 20 , are reduced . dielectric portion 30 produces a more uniform impedance through rf electrode 20 and causes a more uniform current to flow through conductive portion 28 . the resulting effect minimizes or even eliminates , edge effects around the edges of rf electrode 20 . in one embodiment , conductive portion 28 adheres to dielectric portion 30 which can be substrate with a thickness , by way of example and without limitation , of about 0 . 001 ″. this embodiment is similar to a standard flex circuit board material commercially available in the electronics industry . in this embodiment , dielectric portion 30 is in contact with the tissue , the skin , and conductive portion 28 is separated from the skin . the thickness of the dielectric portion 30 can be decreased by growing conductive portion 28 on dielectric portion 30 using a variety of techniques , including but not limited to , sputtering , electro deposition , chemical vapor deposition , plasma deposition and other deposition techniques known in the art . additionally , these same processes can be used to deposit dielectric portion 30 onto conductive portion 28 . in one embodiment dielectric portion 30 is an oxide layer which can be grown on conductive portion 28 . an oxide layer has a low thermal resistance and improves the cooling efficiency of the skin compared with many other dielectrics such as polymers . fluid delivery member 22 has an inlet 32 and an outlet 34 . outlet 34 can have a smaller cross - sectional area than a cross - sectional area of inlet 32 . in one embodiment , fluid delivery member 22 is a nozzle 36 . cooling fluidic medium valve member 16 can be configured to provide a pulsed delivery of the cooling fluidic medium . pulsing the delivery of cooling fluidic medium is a simple way to control the rate of cooling fluidic medium application . in one embodiment , cooling fluidic medium valve member 16 is a solenoid valve . an example of a suitable solenoid valve is a solenoid pinch valve manufactured by the n - research corporation , west caldwell , n . j . if the fluid is pressurized , then opening of the valve results in fluid flow . if the fluid is maintained at a constant pressure , then the flow rate is constant and a simple open / close solenoid valve can be used , the effective flow rate being determined by the pulse duty cycle . a higher duty cycle , close to 100 % increases cooling , while a lower duty cycle , closer to 0 %, reduces cooling . the duty cycle can be achieved by turning on the valve for a short duration of time at a set frequency . the duration of the open time can be 1 to 50 milliseconds or longer . the frequency of pulsing can be 1 to 50 hz or faster . alternatively , cooling fluidic medium flow rate can be controlled by a metering valve or controllable - rate pump such as a peristaltic pump . one advantage of pulsing is that it is easy to control using simple electronics and control algorithms . electrode assembly 18 is sufficiently sealed so that the cooling fluidic medium does not leak from back surface 24 onto a skin surface in contact with a front surface of rf electrode 20 . this helps provide an even energy delivery through the skin surface . in one embodiment , electrode assembly 18 , and more specifically rf electrode 20 , has a geometry that creates a reservoir at back surface 24 to hold and gather cooling fluidic medium that has collected at back surface 24 . back surface 24 can be formed with “ hospital corners ” to create this reservoir . optionally , electrode assembly 18 includes a vent 38 that permits vaporized cooling fluidic medium to escape from electrode assembly 18 . this reduces the chance of cooling fluidic medium collecting at back surface 24 . this can occur when cooling fluidic medium is delivered to back surface 24 in vapor form and then , following cooling of back surface 24 , the vapor condenses to a liquid . vent 38 prevents pressure from building up in electrode assembly 18 . vent 38 can be a pressure relief valve that is vented to the atmosphere or a vent line . when the cooling fluidic medium comes into contact with rf electrode 20 and evaporates , the resulting gas pressurizes the inside of electrode assembly 18 . this can cause rf electrode 20 to partially inflate and bow out from front surface 26 . the inflated rf electrode 20 can enhance the thermal contact with the skin and also result in some degree of conformance of rf electrode 20 to the skin surface . an electronic controller can be provided . the electronic controller sends a signal to open vent 38 when a programmed pressure has been reached . various leads 40 are coupled to rf electrode 20 . one or more thermal sensors 42 are coupled to rf electrode . suitable thermal sensors 42 include but are not limited to thermocouples , thermistors , infrared photo - emitters and a thermally sensitive diode . in one embodiment , a thermal sensor 42 is positioned at each corner of rf electrode 20 . a sufficient number of thermal sensors 42 are provided in order to acquire sufficient thermal data of the skin surface . thermal sensors 42 are electrically isolated from rf electrode 20 . thermal sensors 42 measure temperature and can provide feedback for monitoring temperature of rf electrode 20 and / or the tissue during treatment . thermal sensors 42 can be thermistors , thermocouples , thermally sensitive diodes , capacitors , inductors or other devices for measuring temperature . preferably , thermal sensors 42 provide electronic feedback to a microprocessor of the rf generator coupled to rf electrode 20 in order to facilitate control of the treatment . the measurements from thermal sensors 42 can be used to help control the rate of application of cooling fluidic medium . for example , the cooling control algorithm can be used to apply cooling fluidic medium to rf electrode 20 at a high flow rate until the temperature fell below a target temperature , and then slow down or stop . a pid , or proportional - integral - differential , algorithm can be used to precisely control rf electrode 20 temperature to a predetermined value . thermal sensors 42 can be positioned placed on back surface 24 of rf electrode 20 away from the tissue . this configuration is preferable ideal for controlling the temperature of the rf electrode 20 . alternatively , thermal sensors 42 can be positioned on front surface 26 of rf electrode 10 in direct contact with the tissue . this embodiment can be more suitable for monitoring tissue temperature . algorithms are utilized with thermal sensors 42 to calculate a temperature profile of the treated tissue . thermal sensors 42 can be used to develop a temperature profile of the skin which is then used for process control purposes to assure that the proper amounts of heating and cooling are delivered to achieve a desired elevated deep tissue temperature while maintaining skin tissue layers below a threshold temperature and avoid thermal injury . the physician can use the measured temperature profile to assure that he stays within the boundary of an ideal / average profile for a given type of treatment . thermal sensors 42 can be used for additional purposes . when the temperature of thermal sensors 42 is monitored it is possible to detect when rf electrode 20 is in contact with the skin surface . this can be achieved by detecting a direct change in temperature when skin contact is made or examining the rate of change of temperature which is affected by contact with the skin . similarly , if there is more than one thermal sensor 42 , the thermal sensors 42 can be used to detect whether a portion of rf electrode 20 is lifted or out of contact with skin . this can be important because the current density ( amperes per unit area ) delivered to the skin can vary if the contact area changes . in particular , if part of the surface of rf electrode 20 is not in contact with the skin , the resulting current density is higher than expected . referring now to fig4 , a force sensor 44 is also coupled to electrode assembly 18 . force sensor 44 detects an amount of force applied by electrode assembly 18 , via the physician , against an applied skin surface . force sensor 44 zeros out gravity effects of the weight of electrode assembly 18 in any orientation of front surface 26 of rf electrode 20 relative to a direction of gravity . additionally , force sensor 44 provides an indication when rf electrode 20 is in contact with a skin surface . force sensor 44 also provides a signal indicating that a force applied by rf electrode 20 to a contacted skin surface is , ( i ) below a minimum threshold or ( ii ) above a maximum threshold . an activation button 46 is used in conjunction with the force sensor . just prior to activating rf electrode 20 , the physician holds handpiece 10 in position just off the surface of the skin . the orientation of handpiece 10 can be any angle relative to the angle of gravity . to arm handpiece 10 , the physician can press activation button 46 which tares force sensor 44 , by setting it to read zero . this cancels the force due to gravity in that particular treatment orientation . this method allows consistent force application of rf electrode 20 to the skin surface regardless of the angle of handpiece 10 relative to the direction of gravity . rf electrode 20 can be a flex circuit , which can include trace components . additionally , thermal sensor 42 and force sensor 44 can be part of the flex circuit . further , the flex circuit can include a dielectric that forms a part of rf electrode 20 . electrode assembly 18 can be moveable positioned within handpiece housing 12 . in one embodiment , electrode assembly 18 is slideably moveable along a longitudinal axis of handpiece housing 12 . electrode assembly 18 can be rotatably mounted in handpiece housing 12 . additionally , rf electrode 20 can be rotatably positioned in electrode assembly 18 . electrode assembly 18 can be removably coupled to handpiece housing 12 as a disposable or non - disposable insert 52 , see fig5 . for purposes of this disclosure , electrode assembly 18 is the same as insert 52 . once movably mounted to handpiece housing 12 , insert 52 can be coupled to handpiece housing 12 via force sensor 44 . force sensor 44 can be of the type that is capable of measuring both compressive and tensile forces . in other embodiments , force sensor 44 only measures compressive forces , or only measures tensile forces . insert 52 can be spring - loaded with a spring 48 . in one embodiment , spring 48 biases rf electrode 20 in a direction toward handpiece housing 12 . this pre - loads force sensor 44 and keeps insert 52 pressed against force sensor 44 . the pre - load force is tared when activation button 46 is pressed just prior to application of rf electrode 20 to the skin surface . a shroud 50 is optionally coupled to handpiece 10 . shroud 50 serves to keep the user from touching insert 52 during use which can cause erroneous force readings . a non - volatile memory 54 can be included with insert 52 . additionally , non - volatile memory can be included with handpiece housing 12 . non - volatile memory 54 can be an eprom and the like . additionally , a second non - volatile memory 56 can be included in handpiece housing 12 for purposes of storing handpiece 10 information such as but not limited to , handpiece model number or version , handpiece software version , number of rf applications that handpiece 10 has delivered , expiration date and manufacture date . handpiece housing 12 can also contain a microprocessor 58 for purposes of acquiring and analyzing data from various sensors on handpiece housing 12 or insert 52 including but not limited to thermal sensors 42 , force sensors 44 , fluid pressure gauges , switches , buttons and the like . microprocessor 58 can also control components on handpiece 10 including but not limited to lights , leds , valves , pumps or other electronic components . microprocessor 58 can also communicate data to a microprocessor of the rf generator . non - volatile memory 54 can store a variety of data that can facilitate control and operation of handpiece 10 and its associated system including but not limited to , ( i ) controlling the amount of current delivered by rf electrode 20 , ( ii ) controlling the duty cycle of the fluid delivery member 22 , ( iii ) controlling the energy delivery duration time of the rf electrode 20 , ( iv ) controlling the temperature of rf electrode 20 relative to a target temperature , ( v ) providing a maximum number of firings of rf electrode 20 , ( vi ) providing a maximum allowed voltage that is deliverable by rf electrode 20 , ( vii ) providing a history of rf electrode 20 use , ( viii ) providing a controllable duty cycle to fluid delivery member 22 for the delivery of the cooling fluidic medium to back surface 24 of rf electrode 20 , ( ix ) providing a controllable delivery rate of cooling fluidic medium delivered from fluid delivery member 22 to back surface 24 , and the like . handpiece 10 can be used to deliver thermal energy to modify tissue including , but not limited to , collagen containing tissue , in the epidermal , dermal and subcutaneous tissue layers , including adipose tissue . the modification of the tissue includes modifying a physical feature of the tissue , a structure of the tissue or a physical property of the tissue . the modification can be achieved by delivering sufficient energy to cause collagen shrinkage , and / or a wound healing response including the deposition of new or nascent collagen . handpiece 10 can be utilized for performing a number of treatments of the skin and underlying tissue including but not limited to , ( i ) dermal remodeling and tightening , ( ii ) wrinkle reduction , ( iii ) elastosis reduction , ( iv ) sebaceous gland removal / deactivation , ( v ) hair follicle removal , ( vi ) adipose tissue remodeling / removal , ( vii ) spider vein removal , and the like . in various embodiments , handpiece 10 can be utilized in a variety of treatment processes , including but not limited to , ( i ) pre - cooling , before the delivery of energy to the tissue has begun , ( ii ) an on phase or energy delivery phase in conjunction with cooling and ( iii ) post cooling after the delivery of energy to tissue has stopped . handpiece 10 can be used to pre - cool the surface layers of the target tissue so that when rf electrode 20 is in contact with the tissue , or prior to turning on the rf energy source , the superficial layers of the target tissue are already cooled . when rf energy source is turned on or delivery of rf to the tissue otherwise begins , resulting in heating of the tissues , the tissue that has been cooled is protected from thermal effects including thermal damage . the tissue that has not been cooled will warm up to therapeutic temperatures resulting in the desired therapeutic effect . pre - cooling gives time for the thermal effects of cooling to propagate down into the tissue . more specifically , pre - cooling allows the achievement of a desired tissue depth thermal profile , with a minimum desired temperature being achieved at a selectable depth . the amount or duration of pre - cooling can be used to select the depth of the protected zone of untreated tissue . longer durations of pre - cooling produce a deeper protected zone and hence a deeper level in tissue for the start of the treatment zone . the opposite is true for shorter periods of pre - cooling . the temperature of front surface 26 of rf electrode 20 also affects the temperature profile . the colder the temperature of front surface 26 , the faster and deeper the cooling , and vice verse . post - cooling can be important because it prevents and / or reduces heat delivered to the deeper layers from conducting upward and heating the more superficial layers possibly to therapeutic or damaging temperature range even though external energy delivery to the tissue has ceased . in order to prevent this and related thermal phenomena , it can be desirable to maintain cooling of the treatment surface for a period of time after application of the rf energy has ceased . in various embodiments , varying amounts of post cooling can be combined with real - time cooling and / or pre - cooling . in various embodiments , handpiece 10 can be used in a varied number of pulse on - off type cooling sequences and algorithms may be employed . in one embodiment , the treatment algorithm provides for pre - cooling of the tissue by starting a spray of cryogenic cooling fluidic medium , followed by a short pulse of rf energy into the tissue . in this embodiment , the spray of cryogenic cooling fluidic medium continues while the rf energy is delivered , and is stopping shortly thereafter , e . g . on the order of milliseconds . this or another treatment sequence can be repeated again . thus in various embodiments , the treatment sequence can include a pulsed sequence of cooling on , heat , cooling off , cooling on , heat , cool off , and with cooling and heating durations on orders of tens of milliseconds . in these embodiments , every time the surface of the tissue of the skin is cooled , heat is removed from the skin surface . cryogenic cooling fluidic medium spray duration , and intervals between sprays , can be in the tens of milliseconds ranges , which allows surface cooling while still delivering the desired thermal effect into the deeper target tissue . in various embodiments , the target tissue zone for therapy , also called therapeutic zone or thermal effect zone , can be at a tissue depth from approximately 100 μm beneath the surface of the skin down to as deep as 10 millimeters , depending upon the type of treatment . for treatments involving collagen contraction , it can be desirable to cool both the epidermis and the superficial layers of the dermis of the skin that lies beneath the epidermis , to a cooled depth range between 100 μm and two millimeters . different treatment algorithms can incorporate different amounts of pre - cooling , heating and post cooling phases in order to produce a desired tissue effect at a desired depth . various duty cycles , on and off times , of cooling and heating are utilized depending on the type of treatment . the cooling and heating duty cycles can be controlled and dynamically varied by an electronic control system known in the art . specifically the control system can be used to control cooling fluidic medium valve member 16 and the rf power source . the foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description . it is not intended to be exhaustive or to limit the invention to the precise forms disclosed . obviously , many modifications and variations will be apparent to practitioners skilled in this art . it is intended that the scope of the invention be defined by the following claims and their equivalents .
apparatus for transcutaneously treating tissue beneath a skin surface using radiofrequency energy . the apparatus includes an electrode assembly supported by a handpiece . the electrode assembly includes an electrode configured to transfer the radiofrequency energy through the skin surface to the tissue . a force sensor , which is located in the handpiece , is configured to detect an amount of force applied by the electrode against the skin surface .