Random signal systems are used in radars, but very seldom in medical and materials ultrasonic applications. Yet, compared with conventional techniques which use the same peak power, pseudo-random signal correlation techniques can easily improve the signal-to-noise ratio by a thousand or more times without sacrificing spatial resolution. To overcome the limitations imposed by the high ratio of peak power to average power, we developed a technique by which the echo energy is integrated with respect to time. As in radar systems, we used a sinusoidal signal which was phase-modulated by the pseudo-random binary code. This approach simplified our apparatus compared to those techniques using noise signals.
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