We recently published some Bryn Celli Ddu project results in the Antiquity Journal. The results come from an electrical resistance tomography (ERT) survey of the Bryn Celli Ddu mound and its immediate surroundings.
ERT is based upon the principles of resistivity, producing transects of varying depths. We surveyed half the monument, with transects at parallel 2m intervals. The results can be seen online on the Antiquity website.