| 摘要 |
PURPOSE:To obtain an optimal characteristics over the whole depth region by providing a constitution wherein a variable attenuation element is connected in series or in parallel with an inductor. CONSTITUTION:In a circuit of an apparatus, an ultrasonic oscillator 15 is connected in series with an inductor 20, a PIN diode 23 and a condenser 30 for passing high frequency, and a bias electric current control circuit 3 is connected therewith and a direct current flowing into the PIN diode 23 is controlled by means of a bias resistance 22 and a bias electric current control circuit 3. A high frequency electric current IAC and a direct current IDC are energized in the PIN diode and when used under a condition of IAC<IDC, the value of a resistance of the PIN diode 23 is predominantly determined by the direct current IDC and the sharpness and the band of the resonance system can be made variable by the value of the direct current IDC. As the result, when a reflective wave in a shallow region is received, it is possible to make Q small and to keep high resolution and when a reflective wave in a deep region is received, it is possible to make Q large and to improve sensitivity and it is thereby possible to obtain an optimum image quality over the whole depth range. |
