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
500 kHz for the use of 500 kHz first appeared in the second Berlin International Radiotelegraphic Convention, which was signed November 3, 1906, and became effective July 1, 1908. The second Service Regulation affixed to this Convention designated 500 kHz as one of the standard frequencies to be employed by shore stations, specifying that "Two wave lengths, one of 300 meters [1 Mc/s] and the other of 600 meters, are authorized for general public service. Every coastal station opened to such service shall use one or the other of these two wave lengths." (These regulations also specified that ship stations normally used