Previous studies demonstrated the feasibility of using 100-microns inner diameter planar spiral inductors (microcoils) as detectors in 1H nuclear magnetic resonance (NMR) microspectroscopy. However, high-resolution NMR applications were not possible due to poor spectral resolution and low signal-to-noise ratio (SNR). These limitations in performance have now been largely overcome by using a nonconductive liquid fluorocarbon (FC-43) to minimize the effects of susceptibility mismatch between materials, and by carefully optimizing the microcoil geometry for maximum SNR. In this study, liquid samples were loaded into a fused silica capillary (75-microns inner diameter, 147-microns outer diameter). The capillary was positioned 50 microns above a 3.5-turn microcoil so that approximately 1 nL of the sample was present in the sensitive region of the microcoil. The microcoil was fabricated on a gallium arsenide substrate with an inner diameter of 60 microns, an outer diameter of 200 microns, trace width of 10 microns, trace spacing of 10 microns, and trace height of 3 microns. At 5.9 T (250 MHz) in 1H-NMR microspectroscopy experiments using a spectral width of 1 kHz, 4096 sampled data points, and a recovery delay of 1 s, a SNR of 25 (per acquisition) and a spectral linewidth of less than 2 Hz were obtained from a sample of water. These results demonstrate that planar microcoils can be used for high-resolution NMR microspectroscopy. Such coils may also be suitable for localized NMR studies at the cellular level and as detectors in capillary electrophoresis or microbore liquid chromatography.
The automatic identification system (AIS) signal is of particular interest to the defense and security community because of its capability to identify and classify ships in U.S. waters. Placing an AIS receiver on a satellite provides a low cost solution to enhance security over a wide region. This paper describes the development of an AIS burst-acquisition receiver on a software radio consisting of a field programmable gate array (FPGA) and general purpose processor (GPP). A simple hybrid 1-bit/2-bit differential receiver can be easily implemented on such a software radio platform, and is sufficient to reliably demodulate collision free bursts in a space-borne signal environment.
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