A carotid Doppler machine uses what change in frequency or wavelength of a wave for an observer who is moving relative to the wave source?
Carotid Doppler machine A carotid Doppler machine is a device which can be used to measure blood flow velocities within the cervical carotid arteries, as well as the vertebral arteries and sometimes the subclavian arteries by means of non-invasive ultrasonic scanning in which the Doppler effect is utilized. This can be useful for estimating the effects of atherosclerotic disease on the lumen in late stages; specifically the level of compromise in blood flow caused by reduction in arterial lumen diameter.
Circulator A circulator is a passive non-reciprocal three- or four-port device, in which a microwave or radio frequency signal entering any port is transmitted to the next port in rotation (only). A "port" in this context is a point where an external waveguide or transmission line (such as a microstrip line or a coaxial cable), connects to the device. For a three-port circulator, a signal applied to port 1 only comes out of port 2; a signal applied to port 2 only comes out of port 3; a signal applied to port 3 only comes out of port 1, so to within a phase-factor, the scattering matrix for an ideal three-port circulator is