Differential uncloneable variability-based cryptography techniques are provided. A microphone whose input level has continued to be above a threshold value for not shorter than a predetermined time period is detected, based on input signals from dispersedly arranged microphones. A second conductive strip is positioned on the insulating layer and connected to a second bus bar. A related method for testing the PS2 interface is also provided. The first sequence may include additional RF refocusing pulses that, when coupled with movement of the NMR measurement apparatus or sample, may also be used to substantially saturate the first region.