A cw rf signal is split into two channels. One of them is pulsed and sent to the sample sitting in the cryostat and magnetic field. LiNbO3 transducers are attached to the end faces of the sample. The signal, traveling through the sample as a sound wave, is time delayed and attenuated. It is reconverted back into an electrical signal, and mixed with the cw in the first channel and phase detected. From the two components (0o and 90o) the phase change and attenuation in the sample is computed.
We mixed rf signal from the receiving transducer with cw signal at frequency (f + 12.5MHz). The signal at IF=12.5MHz was stored using a high sampling rate digitizer - a GaGe-CS 1250 oscilloscope card with a sample rate equal to 50 MHz; the phase shift and attenuation were later calculated using software written expressly for this purpose.
Updated 11/30/'04 MSW