In a radiotelephone, a channel estimator receives a time division multiple access information signal including a synchronous codeword, formed of a first subset of seven sequential symbols followed by a second subset of seven sequential symbols, followed by a data sequence formed of multiple sequential symbols. The technique involves the incremental application of precise and measured quantities of corona charge, QC, onto the dielectric surface followed by determination of the contact potential difference, VCPD, as the material structure response. The access slot has a first open end positioned at the fastener opening and a second open end offset from the fastener opening.