System theoretic modeling of high-density digital magnetic recording

This work is a system theoretic approach to modeling the recording process in high-density, digital, longitudinal magnetic recording systems. Observable properties of the system are discussed. The practice of inferential measurement of track average magnetization using phenomenological forms is discussed. It is shown that unless the total effective separation distance between head and medium is known, there will always exist an uncertainty in the length of the magnetic transition when inferential determinations of it are made. By using direct observations of the magnetic transition and a new measurement technique involving blind deconvolution it is possible to determine the depth of the dead layer in ferrite heads. The measurement of efficiency in ferrite heads is also discussed. It is shown that head efficiency may be determined from vector impedance measurements of the head if the permeability vs. frequency characteristics of the head material are known. Head efficiency measurements prove that head efficiency is relatively insensitive to frequency out to at least 10 MHz using commercial Mn-Zn ferrites.