| 摘要 |
An ultrasonic system and method for examining the structure of a subject body is disclosed. The system includes an improved ultrasonic transducer and power circuitry for electrically stimulating the transducer to produce an incident ultrasonic energy beam along a path extending into the subject. The incident beam produces echoes within the subject, some of which propagate back toward the transducer. The transducer, in response to received echoes, produces electrical signals bearing information about the structure of the subject. The system further includes circuitry for processing the electrical signals and a display apparatus responsive to the processed electrical signals for producing a visual display of subject structure. The transducer includes a concavo-convex piezoelectric emitter for producing ultrasonic energy having a dominant frequency, an acoustical impedance matching transformer and a coupling element. The impedance matching transformer includes a concavo-convex portion of material having a radius of curvature similar to that of the emitter, and being nested in contact with the emitter. The transformer has a uniform thickness equal to one-fourth of the wave length of the dominant ultrasonic frequency within the transformer. The characteristic acoustic impedance of the transformer material is approximately the geometric mean of the characteristic acoustic impedance of the emitter and the subject. The coupling element is made of material having acoustic characteristics similar to that of the subject body and is acoustically couplable between the impedance matching transformer and the subject surface, having a generally flat surface for contacting the subject.
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