Patent Description:
Each transducer array <NUM>-<NUM> is configured as a set of capacitively coupled electrode elements E (e.g., a set of <NUM> electrode elements, each of which is about <NUM> in diameter) that are interconnected via flex wires. Each electrode element includes a ceramic disk that is sandwiched between a layer of an electrically conductive medical gel and an adhesive tape. When placing the arrays on the patient, the medical gel adheres to the contours of the patient's skin and ensures good electric contact of the device with the body. The adhesive tape holds the entire array in place on the patient as the patient goes about their daily activities.

The amplitude of the alternating current that is delivered via the transducer arrays is controlled so that skin temperature (as measured on the skin below the transducer arrays) does not exceed a safety threshold of <NUM>° C. The temperature measurements on the patient's skin are obtained using thermistors T placed beneath some of the disks of the transducer arrays. In the existing Optune® system, each array includes <NUM> thermistors, with one thermistor positioned beneath a respective disk in the array. (Note that most arrays include more than <NUM> disks, in which case the temperature measurements are only performed beneath a sub-set of the disks within the array).

The AC signal generator <NUM> obtains temperature measurements from all <NUM> thermistors (<NUM> arrays × <NUM> thermistors per array). The controller in the AC signal generator uses the temperature measurements to control the current to be delivered via each pair of arrays in order to maintain temperatures below <NUM>° C on the patient's skin. The current itself is delivered to each array via an additional wire (i.e., one wire <NUM> for each of the arrays <NUM>-<NUM>) that runs from the AC signal generator <NUM> to each array.

<CIT> discloses an electrode for applying electric fields to a body part of a subject, comprising a plurality of ceramic elements arranged in an array.

<CIT> discloses an insulated electrode system for delivering a plurality of tumor treating fields, which includes an array of electrode elements which are each independently electrically accessible.

<CIT> discloses a non-invasive electric brain stimulation system, comprising an electrode array which includes a plurality of co-centric or semi-co-centric electrodes.

<CIT>shows another apparatus for applying TTFields with an alternating current (AC) signal generator, a plurality of arrays of electrode elements configured for placement against a subject's body and temperature sensors in the respective arrays.

One aspect of the invention is directed to an apparatus for applying an alternating electric field to a subject's body according to claim <NUM>.

Although the prior art approach described above in connection with <FIG> is very effective for delivering TTFields to a tumor, the effectiveness of the treatment will drop if good electrical contact is not maintained between each of the elements in the four transducer arrays <NUM>-<NUM> and the person's body. This can happen, for example, if the hydrogel beneath one or more elements of the transducer arrays dries out over time, or due to hair growth beneath one or more of the elements.

Assume, for example, in a prior art system with <NUM> electrode elements E in each of the transducer arrays <NUM>-<NUM>, that the hydrogel beneath a single electrode element E on the front transducer array <NUM> has dried out; and that enough hydrogel is present beneath (a) all the other electrode elements E of that transducer array <NUM>, and (b) all the electrode elements E of the other transducer arrays <NUM>-<NUM>. In this situation, the resistance between the single electrode element E and the person's body will be higher than the resistance between any of the other electrode elements and the person's body. And this increase in resistance will cause the temperature of the single electrode element E to rise more than the other electrode elements.

In this situation, the prior art AC signal generator <NUM> must limit the current that is applied to the front/back pair of transducer arrays <NUM>, <NUM> in order to keep the temperature of the single electrode element E on the front array <NUM> below <NUM>°, even though the temperature at all the remaining electrode elements E on the front and back transducer arrays <NUM>, <NUM> may be well below <NUM>° C. And this decrease in current causes a corresponding decrease in the strength of the electric field at the tumor.

The embodiments described herein can be used to minimize or eliminate the decrease in current that is coupled into the person's body, and thereby minimize or eliminate the decrease in strength of the electric field at the tumor. This may be accomplished by alternately switching the current on and off for each individual electrode element that begins to approach <NUM>° in order to reduce the average current for those electrode elements, without affecting the current that passes through the remaining electrode elements (which are not approaching <NUM>°).

Assume, for example, a situation in which <NUM> mA of current is passing through a transducer array that includes <NUM> electrode elements, and only a single one of those electrode elements begins to approach <NUM>°. Assume further that a <NUM>% reduction of current through the single electrode element would be necessary to keep the temperature at that single electrode element below <NUM>°. Instead of achieving this <NUM>% reduction in current by cutting the current through the entire transducer array from <NUM> mA to <NUM> mA (as in the prior art), the embodiments described herein can cut the average current through the single electrode element by <NUM>% by switching the current through that single electrode element on and off with a <NUM>% duty cycle, while leaving the current on full-time for all the remaining electrode elements. Note that the switching rate must be sufficiently fast so that the instantaneous temperature at the single electrode element never exceeds <NUM>°, in view of the thermal inertia of the electrode elements. For example, a <NUM>% duty cycle could be achieved by switching the current on for <NUM> and switching the current off for <NUM>. In some preferred embodiments, the period of switching the current on and off is less than <NUM>.

When this approach is used, the current through the remaining <NUM> electrode elements can remain unchanged (i.e., <NUM> mA per electrode element), and only the current through the single electrode element is reduced to an average of <NUM> mA. The average net total current through the transducer array will then be <NUM> mA (i.e., <NUM>×<NUM> + <NUM>), which means that significantly more current can be coupled into the person's body without exceeding <NUM>° at any of the electrode elements.

The system may even be configured to increase the current through the remaining nine electrode elements in order to compensate for the reduction in current through the single electrode element. For example, the current through the remaining nine electrode elements could be increased to <NUM> mA per electrode element (e.g., by sending a request to the AC voltage generator to increase the voltage by <NUM>%). If this solution is implemented, the average net total current through the entire transducer array would be (<NUM> electrodes × <NUM> mA + <NUM> electrode × <NUM> mA × <NUM> duty cycle) = <NUM> mA, which is extremely close to the original <NUM> mA of current.

If, at some subsequent time (or even at the same time), the temperature at a second electrode element begins to approach <NUM>°, a similar technique (i.e. a reduction in the duty cycle from <NUM>% to something less than <NUM>%) may be used to prevent the temperature at the second electrode element from exceeding <NUM>°.

In some embodiments, this technique may be used to individually customize the duty cycle at each of the electrode elements in order to maximize the current that flows through each of those electrode elements while keeping the temperature at each of those elements below <NUM>°. Optionally, instead of taking remedial action to reduce the duty cycle only when the temperature at a given electrode element begins to approach <NUM>°, the system may be configured to proactively set the duty cycle at each of the electrode elements in a given transducer array individually so as to equalize the temperature across all of the electrode elements in the array. For example, the system could be configured to individually set the duty cycle at each electrode element so as to maintain a temperature that hovers around <NUM>° at each of the electrode elements. Optionally, the system may be configured to send a request to the AC voltage generator to increase or decrease the voltage as required in order to achieve this result.

This approach can be used to ensure that each and every electrode element will carry the maximum average current possible (without exceeding <NUM>°), which will provide an increased field strength in the tumor and a corresponding improvement in the treatment.

<FIG> depicts a first design that periodically switches the current on and off for each individual electrode element that begins to approach <NUM> °. The AC signal generator <NUM> has two outputs (OUT1 and OUT2), each of which has two terminals. The AC signal generator <NUM> generates an AC signal (e.g. a <NUM> sine wave) between the two terminals of each of those outputs in an alternating sequence (e.g., activating OUT1 for <NUM> sec. , then activating OUT2 for one sec. , in an alternating sequence). A pair of conductors <NUM> are connected to the two terminals of OUT1, and each of those conductors <NUM> goes to a respective one of the left and right transducer assemblies <NUM>, <NUM>. A second pair of conductors <NUM> are connected to the two terminals of OUT2 and each of those conductors <NUM> goes to a respective one of the front and back transducer assemblies (not shown). The construction and operation of the front and back transducer assemblies is similar to the construction of the left and right transducer assemblies <NUM>, <NUM> depicted in <FIG>.

Each of the transducer assemblies <NUM>, <NUM> includes a plurality of electrode elements <NUM>. In some preferred designs, each of these electrode elements <NUM> is a capacitively coupled electrode element that is similar to the prior art electrode elements used in the Optune® system. However, in this <FIG> design, instead of wiring all of the electrode elements <NUM> in parallel, an electrically controlled switch (S) <NUM> is wired in series with each electrode element (E) <NUM>, and all of these S+E combinations <NUM>+<NUM> are wired in parallel. Each of the switches <NUM> is configured to switch on or off independently of other switches based on a state of a respective control input that arrives from the digital output of the respective controller <NUM>. When a given one of the switches <NUM> is on (in response to a first state of the respective control input), current can flow between the electrical conductor <NUM> and the respective electrode element <NUM>. Conversely, when a given one of the switches <NUM> is off (in response to a second state of the respective control input), current cannot flow between the electrical conductor <NUM> and the respective electrode element <NUM>.

In some preferred designs, each of the capacitively coupled electrode elements <NUM> is disc-shaped (e.g., with a <NUM> diameter) and has a dielectric layer on one side. The transducer assembly <NUM>, <NUM> holds the electrode elements <NUM> against the subject's body with the dielectric layer of the electrode elements facing the subject body. Preferably, a layer of hydrogel is disposed between the dielectric layer of the electrode elements and the subject's body when the transducer assembly <NUM>, <NUM> is placed against the subject's body so it can hold the electrode elements <NUM> against a subject's body.

In some preferred designs, each of the capacitively coupled electrode elements <NUM> comprises a conductive plate with a flat face, and the dielectric layer is disposed on the flat face of the conductive plate. In some preferred designs, all of the capacitively coupled electrode elements are held in place by a support structure. Optionally, this support structure may comprise a layer of foam. In some preferred designs, the electrical connection to each of the electrode elements <NUM> comprises a trace on a flex circuit.

Each of the transducer assemblies <NUM>, <NUM> also includes a temperature sensor <NUM> (e.g., a thermistor) positioned at each of the electrode elements <NUM> so that each temperature sensor <NUM> can sense the temperature of a respective electrode element <NUM>. Each of the temperature sensors <NUM> generates a signal indicative of the temperature at (e.g., beneath) the respective electrode element <NUM>. The signals from the temperature sensors <NUM> are provided to the analog front and of the respective controller <NUM>.

In designs where thermistors are used as the temperature sensors <NUM>, temperature readings may be obtained by routing a known current through each thermistor and measuring the voltage that appears across each thermistor. In some designs, thermistor-based temperature measurements may be implemented using a bidirectional analog multiplexer to select each of the thermistors in turn, with a current source that generates a known current (e.g., <NUM>µA) positioned behind the multiplexer, so that the known current will be routed into whichever thermistor is selected by the analog multiplexer at any given instant. The known current will cause a voltage to appear across the selected thermistor, and the temperature of the selected thermistor can be determined by measuring this voltage. The controller <NUM> runs a program that selects each of the thermistors in turn and measures the voltage that appears across each of the thermistors (which is indicative of the temperature at the selected thermistor) in turn. An example of suitable hardware and procedures that may be used to obtain temperature readings from each of the thermistors is described in <CIT>.

In some preferred designs, the controller <NUM> may be implemented using a single-chip microcontroller or Programmable System on Chip (PSoC) with a built in analog front end and multiplexer. Suitable part numbers for this purpose include the CY8C4124LQI-<NUM>. In alternative designs, other microcontrollers may be used with either built-in or discrete analog front ends and multiplexers, as will be apparent to persons skilled in the relevant arts.

In alternative designs, not shown, an alternative approach (e.g., the conventional voltage divider approach) for interfacing with the thermistors may be used in place of the constant current approach described above. In other alternative designs, a different type of temperature sensor may be used in place of the thermistors described above. Examples include thermocouples, RIDs, and integrated circuit temperature sensors such as the Analog Devices AD590 and the Texas Instruments LM135. Of course, when any of these alternative temperature sensors is used, appropriate modifications to the circuit (which will be apparent to persons skilled in the relevant arts) will be required.

In some designs, the controller <NUM> is programmed to keep the temperature at all of the electrode elements below a safety threshold (e.g., below <NUM>° C) using intelligence that is built into each transducer assembly <NUM>. This may be accomplished, for example, by programming the controller <NUM> to start out by setting its digital output so that each of the switches <NUM> is continuously on (i.e., with a <NUM>% duty cycle). Then, based on signals arriving via the controller <NUM> analog front end, the controller <NUM> determines whether the temperature at each of the electrode elements exceeds an upper threshold (e.g. <NUM>° C) that is below the safety threshold. When the controller <NUM> detects this condition, the controller <NUM> reduces the duty cycle for the corresponding switch <NUM> by toggling the corresponding digital output at the desired duty cycle. This will interrupt the current to the corresponding electrode element <NUM> at the same duty cycle, thereby reducing the average current at the specific electrode elements <NUM> whose temperature exceeds that upper threshold. The level of reduction in current is determined by the duty cycle. For example, using a <NUM>% duty cycle will cut the current by half; and using a <NUM>% duty cycle will cut the current by <NUM>%.

Notably, this procedure only interrupts the current to specific ones of the electrode elements <NUM> on the transducer assembly <NUM>, and does not interrupt the current to the remaining electrode elements <NUM> on that transducer assembly <NUM>. This provides a very significant advantage over the prior art, because it eliminates or reduces the need to cut the current that is being routed through the electrode elements when only a small number of those electrode elements are getting hot.

A numeric example will be useful to illustrate this point. Assume, in the <FIG> design, that the left and right transducer assemblies <NUM>, <NUM> are positioned on the left and right sides of a subject's head, respectively; that all of the switches <NUM> in the transducer assemblies <NUM>, <NUM> are in the ON state with a <NUM>% duty cycle; and that the AC signal generator <NUM> is initially outputting <NUM> mA of current into the conductors <NUM>. An AC voltage will appear between the electrode elements <NUM> of the left transducer assembly <NUM> and the electrode elements <NUM> of the right transducer assembly <NUM>, and the <NUM> mA AC current will be capacitively coupled through the electrode elements <NUM> through the subject's head. The controller <NUM> in each of the transducer assemblies <NUM>, <NUM> monitors the temperature at each of the electrode elements <NUM> in that transducer assembly by inputting signals from each of the temperature sensors <NUM> via the analog front end of the controller <NUM>. Now assume that the temperature at a given one of the electrode elements <NUM> in the transducer assembly <NUM> has risen to <NUM>° C. This condition will be reported to the controller <NUM> in the transducer assembly <NUM> via a signal from the corresponding temperature sensor <NUM>. When the controller <NUM> recognizes that the temperature of the given electrode element <NUM> has risen to <NUM>° C, the controller <NUM> will toggle the control signal that goes to the corresponding switch <NUM> at the desired duty cycle in order to periodically interrupt the current to the given electrode element <NUM> and maintain a lower average current.

This stands in sharp contrast with the prior art devices which had to decrease the current that flows through ALL of the electrode elements as soon as the temperature at even a single one of the electrode elements <NUM> approached <NUM>° C.

Note that if the duty cycle at only one of the remaining electrode elements <NUM> is being reduced, it may be possible to maintain the original <NUM> mA current (and enjoy the advantages that arise from using the full current). However, if the duty cycle at a large enough number of the electrode elements <NUM> is being reduced, the original <NUM> mA current may have to be dropped. To accomplish this, the controller <NUM> can send a request to the AC signal generator <NUM> via the UART in the controller <NUM>. When the AC signal generator <NUM> receives this request, the AC signal generator <NUM> will reduce the output current at its corresponding output OUT1.

Optionally, the duty cycle that is selected by the controller <NUM> may be controlled based on the speed at which the given electrode element <NUM> heats up after current is applied to the given electrode element <NUM> (as measured via the temperature sensors <NUM> and the analog front end of the controller <NUM>). More specifically, if the controller <NUM> recognizes that a given electrode element <NUM> is heating up twice as fast as expected, the controller <NUM> can select a duty cycle of <NUM>% for that electrode element. Similarly, if the controller <NUM> recognizes that a given electrode element <NUM> is heating up <NUM>% faster than expected, the controller <NUM> can select a duty cycle of <NUM>% for that electrode element.

In other designs, instead of deterministically cutting the average current by reducing the duty cycle, the controller <NUM> can reduce the average current at a given electrode element <NUM> based on real-time temperature measurements by turning off the current to the given electrode element <NUM> and waiting until temperature measured using the temperature sensors <NUM> drops below a second temperature threshold (e.g., below <NUM>° C). Once the temperature drops below this second temperature threshold, the controller <NUM> can restore the current to the given electrode element <NUM>. This may be accomplished, for example, by controlling the state of the control input to the switch <NUM> that was previously turned off so that the switch <NUM> reverts to the ON state, which will allow current to flow between the electrical conductor and the respective electrode element <NUM>. In these designs, the current to a given electrode element <NUM> may be repeatedly switched off and on based on real-time temperature measurements in order to keep the temperature at the given electrode element <NUM> below the safety threshold.

In the <FIG> design, each of the transducer assemblies <NUM>, <NUM> is connected to the AC signal generator <NUM> via a respective cable. Notably only <NUM> conductors are required in each of the cables that run between the transducer assembly and the AC signal generator <NUM> (i.e., Vcc, data, and ground for implementing serial data communication, plus one additional conductor <NUM> for the AC current TTFields signal).

Note that in <FIG>, each transducer assembly <NUM>, <NUM> includes nine electrode elements <NUM>, nine switches <NUM>, and nine temperature sensors <NUM>. But in alternative designs, each transducer assembly <NUM>, <NUM> can include a different number (e.g., between <NUM> and <NUM>) of electrode elements <NUM> and a corresponding number of switches and temperature sensors.

<FIG> is a schematic representation of one mechanical layout that may be used for any given one of the left/right transducer assemblies <NUM>, <NUM> depicted in <FIG>, or the front/back transducer assemblies <NUM>, <NUM> (not shown in <FIG>) that are connected to the second output OUT2 of the AC signal generator <NUM> depicted in <FIG>. In this design, each transducer assembly <NUM>-<NUM> includes a plurality of capacitively coupled electrode elements <NUM> that are mounted on a support <NUM>. The electrode elements <NUM> are configured for placement against the subject's body (preferably with a layer of hydrogel disposed on the surface of the electrode elements <NUM> that face the subject's body), and the support <NUM> holds the plurality of electrode elements <NUM> against the subject's body so that the dielectric layer of the electrode elements <NUM> faces the subject's body. The support <NUM> is preferably flexible and may be made of a material such as cloth or a dense medical foam. An adhesive layer may be used to affix the support <NUM> to the person's body. The temperature sensors <NUM> are positioned so that they can sense the temperature at each of the electrode elements <NUM>. For example, each of the temperature sensors <NUM> may be positioned adjacent to and/or beneath a corresponding one of the electrode elements <NUM>. In some designs, each of the electrode elements <NUM> has a small hole in its center, and the temperature sensors <NUM> are positioned in that small hole. Note that although only two electrode elements <NUM> and corresponding switches <NUM> and temperature sensors <NUM> are depicted in <FIG>, a larger number (e.g., between <NUM> and <NUM>) of each of those components is preferably used. This is denoted by the nomenclature E1. Sn, and T1. Tn in <FIG> for the electrode elements, switches, and temperature sensors, respectively.

A module <NUM> is mounted (either directly or through intervening components) to the support <NUM>. The module <NUM> includes the controller <NUM> and the switches <NUM>. Optionally, the module <NUM> can connect to the support <NUM> using an electrical connector <NUM>, in which case one half of the connector <NUM> is provided on the module <NUM>, and the mating half of the connector <NUM> is provided on the support <NUM>. When both halves of the connector <NUM> are mated, signals from thermistors <NUM> will travel through wiring on the support <NUM> (e.g., flex circuit wiring), through the connector <NUM>, and into the controller <NUM> on the module <NUM>. In addition, the AC current signal from the output side of each of the switches <NUM> travels through the connector <NUM> and through wiring on the support <NUM> (e.g., flex circuit wiring) to each of the electrode elements <NUM>.

Including the optional connector <NUM> provides an advantage over designs that do not include that connector because the array of electrode elements <NUM> are preferably sterilized before use. Sterilization is ordinarily performed using either radiation or gas. Since radiation can interfere with electronics, assemblies in which the electronics cannot be disconnected from the array of electrode elements <NUM> can only be sterilized with gas. On the other hand, if the electronic components <NUM>, <NUM> can be disconnected from the array of electrode elements <NUM> via the connector <NUM> (as it is in <FIG>), the electronics can be plugged in after sterilization. This permits sterilization of the array of electrode elements <NUM> to be performed using either gas or radiation without risk of damage to the sensitive electronic components <NUM>, <NUM>.

As noted above, only <NUM> conductors are required in each of the cables that run between each of the transducer assemblies <NUM>-<NUM> and the AC signal generator <NUM> (i.e., Vcc, data, and ground for implementing serial data communication, plus one additional conductor <NUM> for the AC current TTFields signal). In some preferred designs, the connection between the transducer assembly <NUM>-<NUM> and the AC signal generator (shown in <FIG>) is connectorized using, for example, an electrical connector <NUM>.

In the designs described above, the decision to adjust the duty cycle or turn off one or more of the switches <NUM> in a given transducer assembly <NUM>, <NUM> in order to reduce the average current to one or more of the electrode elements <NUM> is made locally in each transducer assembly <NUM>, <NUM> by the controller <NUM> within that transducer assembly <NUM>, <NUM>. But in alternative designs, the decision to adjust the duty cycle or turn off one or more of the switches <NUM> may be made by the AC signal generator <NUM> (or another remote device e.g., a central hub disposed between the AC signal generator <NUM> and each of the transducer assemblies <NUM>, <NUM>). In these designs, the controller <NUM> in each of the transducer assemblies <NUM>, <NUM> obtains the temperature readings from each of the temperature sensors <NUM> in the respective transducer assembly and transmits those temperature readings to the AC signal generator <NUM> via the UART of the controller <NUM>. The AC signal generator <NUM> decides which, if any, of the switches require a duty cycle adjustment or should be turned off based on the temperature readings that it received, and transmits a corresponding command to the corresponding controller <NUM> in the corresponding transducer assembly <NUM>, <NUM>. When the controller <NUM> receives this command from the AC signal generator <NUM>, the controller <NUM> responds by setting its digital output to a state that will switch off the corresponding switch <NUM> at the appropriate times, in order to carry out the command that was issued by the AC signal generator <NUM>. In these designs, the AC signal generator <NUM> can also be programmed to reduce its output current if a reduction in current is necessary to keep the temperature at each of the electrode elements <NUM> below the safety threshold.

In these designs, the controller <NUM> may be programmed to operate as a slave to a master controller located in the AC signal generator <NUM>. In these designs, the controller <NUM> starts out in a quiescent state, where all it does is monitor incoming commands from the master controller that arrive via the UART. Examples of commands that can arrive from the master controller include a "collect temperature data" command, a "send temperature data" command, and a "set switches" command. When the controller <NUM> recognizes that a "collect temperature data" command has arrived, the controller <NUM> will obtain temperature readings from each of the temperature sensors <NUM> and store the result in a buffer. When the controller <NUM> recognizes that a "send temperature data" command has arrived, the controller <NUM> will execute a procedure that transmits the previously collected temperature readings from the buffer to the AC signal generator <NUM> via the UART <NUM>. And when the controller <NUM> recognizes that a "set switches" command has arrived, the controller <NUM> will execute a procedure to output appropriate voltages on its digital output in order to set each of the switches <NUM> to a desired state (i.e., either ON, OFF, or switching between on and off at a commanded duty cycle) based on data that arrives from the AC signal generator <NUM>.

In the designs described above, a single controller <NUM> is used in each of the transducer assemblies <NUM>, <NUM> to control the switches <NUM> in that assembly and also to obtain temperature measurements from each of the temperature sensors <NUM> in that assembly. In alternative designs, instead of using a single controller <NUM> to control the switches <NUM> and to obtain the temperature measurements, those two tasks may be divided between two controllers, one of which is only used to control the switches <NUM>, and the other of which is used to obtain the temperature measurements from each of the temperature sensors <NUM> (e.g., using any of the approaches described above). In these designs, these two controllers may communicate directly with each other, and/or the AC signal generator <NUM>.

In other alternative designs (not shown), temperature measurement does not rely on a local controller that is positioned in the vicinity of the electrode elements <NUM>. Instead, wires run from each of the temperature sensors <NUM> back to the AC signal generator <NUM> (or to a central hub disposed between the AC signal generator <NUM> and each of the transducer assemblies <NUM>, <NUM>), and the AC signal generator uses signals that arrive via these wires to determine the temperature at each of the temperature sensors <NUM>. Note, however, that in these designs, the cables that run to the transducer arrays will require a larger number of conductors, which may reduce the flexibility of the cables and increase the cumbersomeness of the cables.

In the <FIG> and <FIG> designs described above, the number of temperature sensors <NUM> matches the number of electrode elements <NUM>, and each temperature sensor <NUM> is dedicated to sensing the temperature at a single one of the electrode elements <NUM>. <FIG> depicts an alternative configuration that groups the electrode elements into n sets, and uses a single temperature sensor to measure the temperature for each of these n sets. In some preferred embodiments, n is between <NUM> and <NUM>.

For this to work, the electrode elements within any given set must be adjacent to each other. In the embodiment illustrated in <FIG>, each set includes an inner disc-shaped electrode element <NUM> that is similar to the electrode elements described above in connection with <FIG>, plus an additional outer ring-shaped electrode element <NUM>' that surrounds the inner disc-shaped electrode element <NUM> and is concentric thereto. The temperature sensor <NUM> is positioned in the center of the inner disc-shaped electrode element <NUM>. Each electrode element <NUM>, <NUM>' has its own individual switch <NUM>, <NUM>' that enables the controller <NUM> to switch the current on or off. In alternative embodiments (not shown) additional concentric ring-shaped electrode elements may be added to each set. In other alternative embodiments (not shown) instead of arranging all of the electrode elements in any given set in concentric rings, the electrode elements in each set may be laid out next to each other (e.g. using electrode elements that are arranged like the slices of a pie, and positioning the temperature sensor in the center of the pie). In these alternative embodiments, each electrode element will have its own individual switch that enables the controller <NUM> to switch the current on or off individually.

The <FIG> embodiment can be operated to achieve the same results described above in connection with <FIG> and <FIG> by programming the controller <NUM> to always switch the current to all of the electrode elements <NUM>, <NUM>' in any given set on or off together. But this embodiment also provides additional flexibility. More specifically, if the controller <NUM> determines, based on a signal from one of the temperature sensors <NUM>, that a hot region exists in a given transducer assembly, the controller in this embodiment has the option to reduce the current at that hot region by deactivating some but not all of the electrode elements that correspond to the hot region. Assume, for example, that the signal from the first temperature sensor <NUM> (T1) beneath the first set of electrodes <NUM>, <NUM>' (E1/E1') reveals that the temperature beneath that set of electrodes has risen above <NUM>° C. The controller <NUM> in this <FIG> embodiment has the option to reduce the current in that region by issuing a command to turn off only some of the corresponding switches. This could be accomplished, for example by turning off the switch S1 that feeds the inner element E1, and leaving the switch S1' that feeds the outer element E1' on. Alternatively, the same result could also be accomplished by turning off the switch S1' that feeds the outer element E1', and leaving the switch S1 that feeds the inner element E1 on.

Optionally, the duty cycle for each of the individual electrode elements within any given set of electrodes elements in the <FIG> embodiment may be adjusted individually to obtain additional control over the average current that is coupled in through any region, as described above in connection with <FIG> and <FIG>.

Note that although only two sets of electrode elements <NUM>, <NUM>' and corresponding switches <NUM>, <NUM>' and temperature sensors <NUM>, <NUM>' are depicted in <FIG>, a larger number (e.g., between <NUM> and <NUM>) of sets of those components is preferably used. This is denoted by the nomenclature E1. Tn and T1'. Tn' in <FIG> for the electrode elements, switches, and temperature sensors, respectively.

<FIG> is a schematic diagram of a circuit that is suitable for implementing the switches <NUM>, <NUM>' in the designs of <FIG> and <FIG> and the embodiment of <FIG> described above. The circuit includes two field effect transistors <NUM>, <NUM> wired in series, which is a configuration that can pass current in either direction. One example of a suitable FET for this circuit is the BSC320N20NSE. (Note that the diodes depicted in <FIG> are inherently included within the FETs <NUM>, <NUM> themselves. ) The series combination of the two FETs <NUM>, <NUM> will either conduct or block the flow of electricity, depending on the state of the control input that arrives from one of the digital outputs of the controller <NUM> described above. When the series combination is conducting, current can flow between the shared conductor <NUM> and the respective electrode element <NUM>, <NUM>'. On the other hand, when the series combination of FETs <NUM>, <NUM> is not conducting, current will not flow between the shared conductor <NUM> and the respective electrode element <NUM>, <NUM>'.

Optionally, a current sensing circuit <NUM> may be positioned in series with the switch <NUM>, <NUM>'. The current sensing circuit <NUM> may be implemented using any of a variety of conventional approaches that will be apparent to persons skilled in the relevant arts. When the current sensing circuit <NUM> is included, it generates an output that is representative of the current, and this output is reported back to the controller <NUM> (shown in <FIG>). The controller <NUM> can then use this information to determine whether the measured current is as expected and take appropriate action if necessary. For example, if an overcurrent condition is detected, the controller <NUM> can turn off the corresponding switch. Of course, where the current sensing circuit <NUM> is omitted, it should be replaced with the wire (or other conductor) so that the current can flow between the shared conductor <NUM> and the top leg of the upper FET <NUM>.

In the illustrated embodiment, the current sensing circuit <NUM> is positioned between the shared conductor <NUM> and the top leg of the upper FET <NUM>. But in alternative embodiments, the current sensing circuit may be positioned between the bottom leg of the lower FET <NUM> and the respective electrode element <NUM>, <NUM>'. And in other alternative embodiments (not shown), the current sensing circuit may be integrated within the circuitry of the switch itself.

Claim 1:
An apparatus for applying an alternating electric field to a subject's body, the apparatus comprising:
a plurality of sets of at least two electrode elements (<NUM>, <NUM>');
a support (<NUM>) configured to hold the sets of electrode elements (<NUM>, <NUM>') so that the electrode elements (<NUM>, <NUM>') can be positioned in contact with the subject's body;
a plurality of temperature sensors (<NUM>), wherein each of the sets of electrode elements (<NUM>, <NUM>') has a single temperature sensor (<NUM>) positioned to sense a temperature at the respective one of the sets of electrode elements (<NUM>, <NUM>') and generate a respective signal indicative of the sensed temperature;
an electrical conductor;
a plurality of electrically-controlled switches (<NUM>, <NUM>'), wherein each of the switches (<NUM>, <NUM>') is configured, depending on a state of a respective control input, either to allow current to flow between the electrical conductor and respective ones of the electrode elements (<NUM>, <NUM>') in each of the sets of electrode elements (<NUM>, <NUM>') or prevent current from flowing between the electrical conductor and the respective ones of the electrode elements (<NUM>, <NUM>') in each of the sets of electrode elements (<NUM>, <NUM>'); and
a controller (<NUM>) configured to control the state of the control input of each of the switches (<NUM>, <NUM>') in each of the sets of electrode elements (<NUM>, <NUM>') based on the signal indicative of the sensed temperature generated by the respective temperature sensor (<NUM>) in the respective set of electrode elements (<NUM>, <NUM>');
wherein the electrode elements (<NUM>, <NUM>') within each of the sets of electrode elements (<NUM>, <NUM>') are arranged (i) concentrically, with the respective temperature sensor (<NUM>) at the inner electrode element (<NUM>), or (ii) radially next to each other in the form of slices of a pie, with the respective temperature sensor (<NUM>) at the center of the electrode elements (<NUM>, <NUM>').