Figure 1.1: Principles of Operation
"...the acoustic ultrasound signal from the scanner is converted
into a radio frequency (RF) electrical signal by means of an input
transducer attached to the ESI phantom. The signal is then split into
two signals shifted in phase by (p)/2 radians.
Each RF signal is then electronically mixed with an audio frequency signal in a device known as a balanced `modulator' or `mixer', which performs the mathematical operation of multiplication. The audio frequency signals, as might be expected, are also (p)/2 radians out of phase with each other. "
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