An active device array substrate and its fabricating method are provided. In particular, these improvements would mitigate or prevent focalized restenosis at the ends of the device. When the reference mark passes a photointerrupter, the photointerrupter detects the rotating position of the polygon mirror. For example, power can be drawn more slowly from the power adapter system. Embodiments of a transmission housing and bell housing are adapted to house components of an IVT and, in some embodiments, to cooperate with other components of the IVT to support operation andor functionality of the IVT. An echo profile is generated and then processed to determine the temporal position of the echo pulse on a temporal axis.