A sachet includes a first wing made of a flexible material and having a first perimeter region circumscribing a first central region; a second wing made of the flexible material; a hinge connecting the first and second wings along a common boundary; an adhesive material applied to the perimeter region on the first wing; a first electrically conducting electrode formed on the first wing within the central region of the perimeter region; a second electrically conducting electrode formed on the second wing in a region that is opposed to and in alignment with the first contact area on the first wing; an array of contact pads formed on at least one of the first and second wings; first and second conducting traces electrically connecting first and second groups of one or more contact pads among the array of contact pads to the first and second electrodes, respectively.