Remember Univac? Back in the days they used tubes filled with mercury to store data using ultrasonic soundwaves. I always loved the Idea. Its like storing the data in the future. In lack of mercury, i will use a PAL-delayline (once used to store a single analog scanlines color information for 64 microseconds) to store some digital data.
Its a simple process:
Data is amplitude-modulated onto a carrier of about 5Mhz and fed to the sending end of the delayline.
When the signal has travelled trough the delayline, it is picked up by the receiver, amplified, demodulated, retimed and fed back into the input.