Pulse echo-overlap technique

In this work, we measured ultrasonic velocity and absorption in furan and cyclohexane mixtures over a range from 60 to 700 MHz using high-resolution Bragg reflection technique. Also used cooperatively were Brillouin scattering and pulse-echo-overlap techniques. In this binary system, small amount of cyclohexane increases substantially the relaxation frequency of furan. 

Overlap of lines can make analysis difficult when several nuclei contribute in the one-dimensional (ID) two- and three-pulse ESEEM spectra. Eollowing the development in NMR, methods to simplify the analysis involving two-dimensional (2D) techniques have therefore been designed. The Hyperfine Sublevel Correlation Spectroscopy, or HYSCORE method proposed in 1986 [14] is at present the most commonly used 2D ESEEM technique. The HYSCORE experiment has been applied successfully to study single crystals, but is more often applied to orienta-tionally disordered systems. It is a four-pulse experiment (Fig. 2.23(a)) with a k pulse inserted between the second and the third k/2 pulse of the three-pulse stimulated echo sequence. This causes a mixing of the signals due to the two nuclear transitions with m.s = Vi of an 5 = Vi species. For a particular nucleus two lines appear at (v , V ) and (V ", v ) in the 2D spectrum as shown most clearly in the contour map (d) of Fig. 2.23. The lines of a nucleus with a nuclear Zeeman frequency... 

Another version of the multiple echo technique (172,173) that has been used to make very accurate sound speed measurements in pol5miers makes use of a single transducer bonded directly to the specimen (110). Pulses are reflected from the opposite face and return as echoes to the front face. By adjusting the pulse repetition rate, an echo from a later pulse can be made to overlap a multiple echo from an earlier pulse. When the repetition rate is adjusted to obtain an in-phase condition, constructive interference will result in a maximum amplitude in the superimposed signals. A value of sound speed accurate to 0.05% can be obtained by observing several repetition rates that 5deld an in-phase condition at the transducer resonant frequency and by repeating the measurements at some other frequency, eg, 10% below resonance, and on other specimens that differ only in thickness. 

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