Two-dimensional patterns for optical alignment.
Two-dimensional patterns that have properties suited for optical alignment have been constructed from one-dimensional binary Barker codes. Applications include automated alignment of masks with patterns in photolithography.
Signal-to-Noise and Resolution Enhancement in Ion Mobility Spectrometry Using Correlation Gating Techniques: Barker Codes
Ion mobility spectroscopy (IMS) is a technology that is ideally suited for the detection of very low levels of analyte due to its extreme sensitivity and ability to speciate. Detection of common military and industrial explosives using IMS is an ideal application, since IMS can be tailored to be sensitive to compounds that form negative ions such as nitrate-laden explosives. However, realization of a miniaturized IMS-based detection system for explosives has been hampered by limitations in resolution of miniaturized IMS tubes and by the need to preconcentrate explosive samples and then rapidly desorb them creating a transient chemical concentration. We have demonstrated a new gating and data processing technique that takes advantage of pulse compression approaches developed for modern radar systems for decreasing granularity in target identification. We will show that closely spaced peaks can be isolated by adding discriminating codes to the gating signal. We will then employ matched filtering for the received ion current signal greatly improving instrument performance. This scheme is most advantageous to small geometry IMS drift cells that suffer from lack of resolution due to their small size but would improve sensitivity and peak location uncertainty in any geometry IMS tube. Specifically, we have demonstrated a 13 fold increase in signal-to-noise ratio and have effectively decreased the uncertainty in the location of the signal peak by a factor of 4.4 using a 13-bit Barker coding pattern to operate our IMS gating.
Structural properties of pseudorandom arrays and volumes and their related sequences
The structure of two-and three-dimensional pseudorandom arrays produced by the folding of binary and multiple-valued m-sequences is investigated. This procedure is shown to be related to the process of sequence sampling, and this enables the recursions corresponding to the rows and columns of the arrays to be related to that of the parent m-sequence. These recursions then determine the nature of symmetries which may be apparent in the arrays. It is also demonstrated that pseudorandom volumes can be constructed by folding any one of the three related two-dimensional arrays. The structure of arrays derived from twin-prime pseudorandom sequences is also investigated. Tables of the available binary and multiple-valued PRAs and PRVs are appended.