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
Longwave ground-wave propagation suffers less attenuation due to limited ground conductivity at lower frequencies. Long-wave carrier frequencies are exact multiples of 9 kHz; ranging from 153 to 279 kHz, except for a French-language station, Europe #1 in Germany. This station kept correctly spaced channels spacing for 4 months—only 7 years ago, and all Mongolian transmitters are 2 kHz above the internationally recognized channels. Until the 1970s, some long-wave stations in northern and eastern Europe and the Soviet Union operated on frequencies as high as 433 kHz. Some radio broadcasters, for instance Droitwich transmitting station in the UK, derive their carrier frequencies