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). <EOS>