Using capacitors to regulate current in transducer arrays for applying tumor treating fields (TTFields)
Transducer arrays for applying alternating electric fields (e.g., tumor treating fields a.k.a. TTFields) to a subject's body typically include a plurality of capacitively coupled electrode elements. Often, certain electrode elements on a given array tend to run hotter than other electrode elements. For example, in many anatomical contexts, the corner elements of the transducer array tend to run hotter than the non-corner elements. The spread of operating temperatures between the electrode elements that tend to run hotter and the other electrode elements can be reduced by wiring a capacitor in series with those electrode elements that tend to run hotter (e.g., the corner elements).
1 . An apparatus for applying an alternating electric field to a living subject, the apparatus comprising:
a plurality of conductive regions, each of the conductive regions having a front face and a respective area, wherein the plurality of conductive regions includes a plurality of first conductive regions and at least one second conductive region;
a plurality of regions of dielectric material, each of which has (i) a respective front face and (ii) a respective rear face disposed against the front face of a corresponding one of the plurality of conductive regions;
a substrate configured to hold the front faces of the plurality of regions of dielectric material on or in the subject's body and support the plurality of conductive regions at respective positions;
a main conductor that is electrically connected to each second conductive region; and
a plurality of capacitors, each of which has a respective first terminal electrically connected to a respective one of the first conductive regions and a respective second terminal electrically connected to the main conductor.
2 . The apparatus of claim 1 , wherein the respective positions are distributed about a centroid, and wherein each of the first conductive regions is positioned more peripherally with respect to the centroid than each second conductive region.
3 . The apparatus of claim 2 , wherein the apparatus has at least four first conductive regions and at least five second conductive regions.
4 . The apparatus of claim 1 , wherein the apparatus has at least three first conductive regions and at least six second conductive regions, and
wherein the respective positions are distributed in a pattern such that each of the first conductive regions is positioned at a given single end of the pattern, and none of the second conductive regions are positioned at the given single end of the pattern.
5 . An apparatus for applying an alternating electric field to a living subject, the apparatus comprising:
a plurality of conductive regions, each of the conductive regions having a front face and a respective area, wherein the plurality of conductive regions includes a plurality of first conductive regions and at least one second conductive region;
a plurality of regions of dielectric material, each of which has (i) a respective front face and (ii) a respective rear face disposed against the front face of a corresponding one of the plurality of conductive regions;
a substrate configured to hold the front faces of the plurality of regions of dielectric material on or in the subject's body and support the plurality of conductive regions at respective positions; and
a plurality of first capacitors, each of which is electrically connected in series with a respective first conductive region.
6 . The apparatus of claim 5 , wherein the respective positions are distributed about a centroid, and wherein each of the first conductive regions is positioned more peripherally with respect to the centroid than each second conductive region.
7 . The apparatus of claim 6 , wherein the apparatus has at least four first conductive regions and at least five second conductive regions.
8 . The apparatus of claim 5 , wherein the apparatus has at least three first conductive regions and at least six second conductive regions, and
wherein the respective positions are distributed in a pattern such that each of the first conductive regions is positioned at a given single end of the pattern, and none of the second conductive regions are positioned at the given single end of the pattern.
9 . The apparatus of claim 5 , further comprising a plurality of electronically controllable switches, each of which is (a) electrically connected in parallel with a respective one of the first capacitors and (b) controllable by a respective electrical signal.
10 . The apparatus of claim 5 , wherein each of the plurality of first capacitors is a variable capacitor whose capacitance is controllable by a respective electrical signal.
11 . The apparatus of claim 5 , further comprising a connector having a plurality of pins, wherein the series connection between each of the plurality of first capacitors and the respective first conductive region passes through a respective pin of the connector.
12 . The apparatus of claim 5 , wherein the apparatus has at least four first conductive regions, at least five second conductive regions, and at least four first capacitors.
13 . The apparatus of claim 12 , further comprising at least four electronically controllable switches, each of which is (a) electrically connected in parallel with a respective one of the first capacitors and (b) controllable by a respective electrical signal.
14 . The apparatus of claim 12 , further comprising a connector having at least four pins, wherein the series connection between each of the at least four first capacitors and the respective first conductive region passes through a respective pin of the connector.
15 . The apparatus of claim 12 , further comprising at least five second capacitors, each of which is electrically connected in series with a respective second conductive region.
16 . The apparatus of claim 5 , further comprising:
a plurality of thermistors, each of which is (a) positioned in thermal contact with a respective first conductive region and (b) configured to generate a respective first signal in response to a detected temperature,
wherein each of the first capacitors is a variable capacitor having a respective capacitance-control input that receives a respective one of the first signals.