Acoustic microscopy acoustic microscope (CSAM), and C-mode scanning acoustic microscope (C-SAM). More recently acoustic microscopes based around picosecond ultrasonics systems have demonstrated acoustic imaging in cells using sub-optical wavelengths working with ultrasonic frequencies into the multi-GHz. Since the vast majority of acoustic microscopes in use today are C-SAM type instruments, this discussion will be limited to these instruments. Ultrasound is broadly defined as any sound having a frequency above 20 kHz, which is approximately the highest frequency that can be detected by the human ear. However, the acoustic microscopes emit ultrasound ranging from 5 MHz to beyond 400 MHz so that micrometre
North American Regional Broadcasting Agreement and "Clear Channel" frequencies. The only provision the FRC made addressing international concerns was that six frequencies — 690, 730, 840, 910, 960, and 1030 — were designated for exclusive Canadian use. On May 5, 1932, through an exchange of letters, the U.S. and Canada informally endorsed and expanded the 1928 standards, including recognition of Canadian use of 540 kHz. During the 1930s, Canada also began using 1510 kHz, while in 1934 the U.S. authorized two experimental high-fidelity stations on each of 1530 and 1550 kHz. By 1939, Cuban stations existed on frequencies as high as 1600 kHz. As other