| 摘要 |
A system is provided having a transmitting transducer for transmitting a burst of energy in response to an electrical drive waveform. The system includes a receiving transducer for generating an electrical signal in response to arrival of the transmitted burst of energy. A generator is provided for generating the electrical drive waveform, such generator generating such waveform to enable the receiving transducer to produce the electrical signal with at least one of the following characteristics: (a) a series of waves having an amplitude which increases, then decreases, and then increases again; (b) a series of groups of waves, such series having an initial group of waves of a period, T, followed by a transitional group having at least one wave with a period different from the period, T, followed by a succeeding group of waves having the period, T; or (c) a series of groups of waves, such series having an initial group of waves and a later group of waves, the later group of waves having a phase shift of 2pin relative to the initial group of waves, where n is a non-integer number. A detector is provided for detecting one of the characteristics of the electrical signal generated by the receiving transducer. The detector uniquely detects a specific point in the generated signal, such point being unambiguously identifiable because of the characteristic in the electrical signal generated by the receiving transducer.
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