A transducer apparatus for delivering tumor treating fields to a subject's body, the transducer apparatus comprising: an array of electrodes, the array configured to be positioned over the subject's body with a front face of the array facing the subject's body, the array comprising electrode elements (204; 302A; 302B; 302C; 302D; 402A-F; 502A-F; 502A -D; 602A-F; 602A -F; 602A -F; 602A -D; 602A -C; 702A; 702B; 702C; 702D -D; 702E -E; 702F -F; 702G -G; 702H -H; 702I -I) positioned in existing electrode positions (708A; 708B; 708C; 708D -D; 708E -E; 708F -F; 708G -G; 708H -H; 7081 -1) arranged around a centroid (440; 640; 640; 706A; 706B; 706C; 706D; 706E; 706F; 706G; 706H; 7061) of the array; characterized by: an anisotropic material layer (310E; 452; 572; 672; 672; 672; 672) electrically coupled to the array and located on a front side of the front face of the array; and at least one void space (404A-F; 504A-F; 504A -D; 604A-F; 604A -F; 604A -F; 604A -D; 604A -C; 704A; 704B; 704C; 704D -D; 704E -E; 704F -F; 704G -G; 704H -H; 704I -I) in the array capable of enclosing an areal footprint equivalent to at least a portion of an areal footprint of at least one existing electrode position (708A; 708B; 708C; 708D -D; 708E -E; 708F -F; 708G -G; 708H -H; 708I -I), and superimposable on at least a portion of at least one existing electrode position (708A; 708B; 708C; 708D -D; 708E -E; 708F -F; 708G -G; 708H -H; 708I -I) by rotation of the array around the centroid (440; 640; 640; 706A; 706B; 706C; 706D; 706E; 706F; 706G; 706H; 7061). an array of electrodes, the array configured to be positioned over the subject's body with a front face of the array facing the subject's body, the array comprising electrode elements (204; 302A; 302B; 302C; 302D; 402A-F; 502A-F; 502A -D; 602A-F; 602A -F; 602A -F; 602A -D; 602A -C; 702A; 702B; 702C; 702D -D; 702E -E; 702F -F; 702G -G; 702H -H; 702I -I) positioned in existing electrode positions (708A; 708B; 708C; 708D -D; 708E -E; 708F -F; 708G -G; 708H -H; 7081 -1) arranged around a centroid (440; 640; 640; 706A; 706B; 706C; 706D; 706E; 706F; 706G; 706H; 7061) of the array; characterized by: an anisotropic material layer (310E; 452; 572; 672; 672; 672; 672) electrically coupled to the array and located on a front side of the front face of the array; and at least one void space (404A-F; 504A-F; 504A -D; 604A-F; 604A -F; 604A -F; 604A -D; 604A -C; 704A; 704B; 704C; 704D -D; 704E -E; 704F -F; 704G -G; 704H -H; 704I -I) in the array capable of enclosing an areal footprint equivalent to at least a portion of an areal footprint of at least one existing electrode position (708A; 708B; 708C; 708D -D; 708E -E; 708F -F; 708G -G; 708H -H; 708I -I), and superimposable on at least a portion of at least one existing electrode position (708A; 708B; 708C; 708D -D; 708E -E; 708F -F; 708G -G; 708H -H; 708I -I) by rotation of the array around the centroid (440; 640; 640; 706A; 706B; 706C; 706D; 706E; 706F; 706G; 706H; 7061). an anisotropic material layer (310E; 452; 572; 672; 672; 672; 672) electrically coupled to the array and located on a front side of the front face of the array; and at least one void space (404A-F; 504A-F; 504A -D; 604A-F; 604A -F; 604A -F; 604A -D; 604A -C; 704A; 704B; 704C; 704D -D; 704E -E; 704F -F; 704G -G; 704H -H; 704I -I) in the array capable of enclosing an areal footprint equivalent to at least a portion of an areal footprint of at least one existing electrode position (708A; 708B; 708C; 708D -D; 708E -E; 708F -F; 708G -G; 708H -H; 708I -I), and superimposable on at least a portion of at least one existing electrode position (708A; 708B; 708C; 708D -D; 708E -E; 708F -F; 708G -G; 708H -H; 708I -I) by rotation of the array around the centroid (440; 640; 640; 706A; 706B; 706C; 706D; 706E; 706F; 706G; 706H; 7061).