電子走査式超音波診断装置用探触子の素子配列

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Since it takes about several seconds to obtain an image pattern in mechanical scan ultrasonodiagnostic tomography, high speed electronical scanning is required to obtain image patterns of moving human organs like a heart. Since the high speed sector scan system designed by J. C. Somer required many electrical circuits connected to each of many transducer elements, the system should be complicated and expensive. We planned to use a small number of transducer elements. However, the reduction in number of elements caused an enlargement of side lobes. In order to suppress the side lobes, the signal processing technique was employed to process the output signals of the receiver. In this paper is described a designing method of an array transducer for electronic sector scan ultrasonic tomography. An array transducer which was designed by this method was produced and its directivity was measured. When each element of the array transducer arranged with an equal interval of d is excited with a suitable delay time, large lobes which equal to main lobe in amplitude should appear at every angle θ satisfing Eq. (3). However, with the maximum interval d_<max> satisfing Eq. (4), these large lobes disappear within ±90°. Then, the overall sensitivity in the direction φ, the deflected angle of the main lobe, decreases due to the directivity of each element. Accordingly, if this sensitivity reduction at the maximum deflection angle φ_<max> is allowed down to α, the width of each element 2B is limitted by Eq. (6). The farfield directivity of the array is given by Eq. (2). Therefore, by designing the transmitter and receiver suitably, overall directivity of the transducer shown in Fig. 6 is given by Eq. (7). When the second zero angle in D_1(θ) equals to the first zero angle in D_2(θ) or 2Md equals to Nd/2, both of the first and the second side lobes in D(θ) become considerably small. Employing the signal processing technique as shown in Fig. 7 to process the output signals from the receiver, the width of the main lobe is narrowed and the side lobes decrease. In this case, the first zero angle θ_<f0> of the overall directivity is given by Eq. (9). We designed the array transducer by the above method on the specifications that the receiver consists of 4 elements, width of the main lobe is ±1 cm at a distance of 10cm from the array, every side lobe smaller than -20dB of main lobe and maximum deflected angle is ±45°. The calculated directivity of the designed array transducer are shown in Figs. 11 and 12, where frequency is 1. 5MHz and α is 0. 7. Figure 8 shows the construction of the transducer consisting of PZT bars of 1mm in thickness, 0. 4mm in width ans 15mm in length. Block diagram of the measuring system is shown in Fig. 9. Figure 10 shows the overall directivity of one element. Figures 11 and 12 show the overall directivity of the arry transducer when the deflected angle φ are 0° and 45° respectively. As a result of the measurement, the transducer had a main lobe with 13° in angular width and side lobes with the lebel less then -20dB in amplitude, when the signal processing technique is employed to process the output signals from the receiver.
社団法人日本音響学会の論文
1974-06-01

電子走査式超音波診断装置用探触子の素子配列

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