InSb薄膜ホール素子を用いたオーディオ用磁気再生ヘッド

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The Hall effect magnetic head (thereafter called as a Hall head) has long been investigated because it has the following potential advantages: (1) higher sensitivity in the low frequency range and (2) compactness in size. But the Hall heads so far reported seem to have two serious drawbacks: firstly much smaller signal to noise ratio, and secondly poor frequency responce. The authors therefore investigated a thin film Hall element with high signal to noise ratio, and more efficient magnetic core in order to offset the above-mentioned drawbacks to adopt a Hall head for audio use (an 8-track 4-channel type, Fig. 4). As a semiconducting material for the Hall element, we selected InSb thin film because it has a high signal to noise ratio even when it is prepared as a thin film. We found, moreover, that it is necessary for the InSb thin film to be microzone-melted on a ferrite substrate. After this treatment the current noise is reduced sufficiently. The thin film 2μm thick thus treated is formed into a K-shaped Hall element (Fig. 2). On this Hall element a ferrite pole-piece is fastened and the front end is ground and lapped to form a front gap type Hall head with the gap length of 3μm (Fig. 1). The shape of pole-piece is so designed as shown in the plane view (Fig. 2) and in the side view (Fig. 1) to be triangular in order to enhance flux density on the Hall element and to reduce contour effect. Between the Hall elements a shield plate is placed (Fig. 3) to avoid cross-talk. The output level and noise level between 40Hz and 10kHz of the Hall head thus manufactured are measured by a B & K level meter using a standard tape of Japan Industrial Standard (JIS) specification (20mMaxwell/mm at 400Hz, 9. 5cm/s). Moreover, the crosstalk, contour effect and transient characteristics are measured. During this measurement DC control current is passed through the Hall element at 12mA. The results obtained are as follows: (1) Output level: As shown in Fig. 5, the frequency spectrum of the Hall head is quite similar to that of the recorded level in the tape (shown by dotted line). This aspect is characteristic to the Hall head. The output level at 400Hz is 1. 5mV and larger than that of the coil head, 0. 9mV. (2) Frequency response and SN ratio: In case of the Hall head, equalization has to be carried out in order to enhance the output level in the high frequency range. The frequency spectra of both the output level and the noise level (output level from the signalless tape) of the Hall head are measured and compared with those of a typical coil head (Fig. 6). It is found that there is no difference in these heads and the signal to noise ratio between 40Hz and 10kHz is 54dB. (3) Contour effect: As the top end of the pole-piece (point A in Fig. 1) is designed never to touch the magnetic tape, an echo signal is reduced as shown in Fig. 7. Therefore, the contour effect is also reduced to ±2dB. (4) Cross-talk: A permalloy shield plate 0. 6mm thick is enough to reduce the crosstalk below -50dB at 80Hz. (5) Transient characteristics: The Hall head shows lower distortion than coil heads when triangular waveform is played back (Fig. 8) due to the fact that a Hall element has no reactance. (6) Temperature coefficient: When the Hall head is driven under constant voltage condition, the temperature coefficient of the output around room temperature is ±0. 5%/deg, or equal to that of electron mobility of InSb (Table 2).
社団法人日本音響学会の論文
1976-02-01

InSb薄膜ホール素子を用いたオーディオ用磁気再生ヘッド

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