Fukashi Kobayashi

Magnetic tape duplication by contact printing at short wavelengths

Magnetic tape duplication by the contact printing method was first developed in 1949, but there were still many difficulties in the way of successful duplication at short wavelength signals of a few micrometers. The bifilar tape winding system has been newly developed for successful duplication of signals as short as 2 μm. The optimum strength of the transfer field for maximum output of the duplicated slave tape is exactly the same value even at very short wavelengths. The optimum coercivity of the master tape is about two and half times that of the slave tape. The decrease of the recorded master tape at 2-μm wavelength is within 2 dB for the first duplication with no further decrease after more than hundreds duplications. This system is applied to a video tape duplicator and can transfer automatically a 1-hour program within 2 minutes. The duplicated picture quality is almost undiscernible from the master. This system is also adaptable to the duplication of audio, digital, and any other magnetic tapes or sheet information.

MAGNETIC TAPE DUPLICATION BY CONTACT PRINTING

The magnetic tape recorder was developed by V. Paulsen in 1898, and magnetic recording techniques are now used very widely in our life. One of the biggest features of magnetic recording was that which permitted recording and reproduction easily, reliably and simultaneously on an inexpensive and erasable recording medium. And, since 1950, magnetic tape recorders have been used for prerecording tapes. In order to duplicate many audio tapes economically, ten slave tape recorders, for instance, are connected to a master tape recorder, which is of higher quality than that of the slaves, and master and slave tape speeds are increased as much as 16 or 32 times normal tape speed. Thus, tape production rate is increased 160 to 320 times. The upper limit of the audible frequency is 20 kHz, at best, and so the highest recording frequency of the duplication signal is 640 kHz. If the normal recording speed is 3% inches per second (i.p.s.), for instance, 32 times the recording speed for duplication is 120 i.p.s. which is the highest speed of a conventional instrumentation tape recorder, and the recording frequency is only the medium band of IRIGS specifications. High-speed duplication of audio tape is, therefore, performed by current magnetic recording techniques. The major uses of audio magnetic tape are prerecorded music as well as oral digests of journals or other institutional information. When it comes to video recording on a magnetic tape, video tape recorders (VTR) with one or two rotary heads dominate nonprofessional applications, while four rotary head models are mostly used for professional use. The upper video recording frequency range is approximately 10 MHz, which is almost the upper limit of conventional magnetic head materials. The relative head-to-tape speed is 10 to 40 mlsec. which is supposed to be the limitation of relative speed by conventional mechanical scanning methods. Such being the case, if the duplication speed increases as for audio tape duplication, very big efforts will be required even to increase two times the production rate of video tape duplication. At present, it is accomplished by so-called “brute force,” where, by simply connecting one master VTR to one or more slave V T R s , the duplication of the program is made in real time. The duplication efficiency is determined by the number of slave tape VTR’s. So far, the duplication of video tapes has been limited to broadcasting and institutional use, and the number of tapes duplicated from one program has been few. We are, however, now approaching an era of diversity. People in the past who were content to see relatively few television programs are now demanding programs in more variety and, at times, at their own convenience. These trends give every indication that they will increase more in the future.

Theoretical analysis of contact printing on magnetic tape

The magnetization process in contact printing is considered to be the same process as an ideal anhysteretic magnetization process. In the anhysteretic magnetization process a self-demagnetization effect by an internal field is an important factor, especially at short wavelength. Therefore, the internal field effect should be evaluated dynamically depending on the instantaneous strength of the diminishing bias field. It was shown that such an anhysteretic magnetization process including the internal field effect can be represented as a first-order feedback system in an automatic control theory. Thus the numerical analyzing method for the anhysteretic magnetization was established, and excellent coincidence between the numerically computed result and the experimental result in the contact printing was obtained. Consequently the distribution patterns of the magnetization and the internal field in the duplicated tape was computed.

Super-narrow track MR head

A magnetoresistive (MR) head produces high output. A stripe type MR head, however, has poor wave-length response due to its stripe width loss and has limitation in reducing track width due to its configuration. A new MR head, therefore, is proposed here to obtain extremely narrow track width. This head can achieve very high areal density and has no wear problems, since having flux guide cores.

A study of the thermal transfer process

The thermal transfer process takes place at high temperatures, and the temperature which freezes the magnetization is distributed in some wide range depending upon the signal field strength, but most magnetization is frozen between 115°C and 120°C. The time constant of the changing magnetization and demagnetization field from frozen magnetization are very significant in the thermal transfer process. Because of the demagnetization field, thermoremanent magnetization becomes small and is limited to only the tape surface. The computed magnetization pattern of the slave tape indicates that the transfer characteristics of thermoremanent magnetization are similar to that of the anhysteretic method. In the thermoremanent magnetization process the magnetization recovers about 3 times the high temperature magnitude when it is cooled to room temperature. Consequently, a high output can be obtained by thermoremanent magnetization.

Theoretical Investigation of Ideal Anhysteretic Magnetization Including Internal Field Effect

磁化過程中における反磁界の作用を考慮に入れた理想磁化機構の理論的検討を行なった.解析方法としては, セルフコンシステント磁化機構の考え方にもとづき, フィードバックモデルによる解法, 固定磁化に着目した解法, プライザッハ分布図を用いた計算機シミュレーションによる解法について検討した.この結果, 反磁界係数の増大とともに磁化曲線の勾配は大幅に減少し, 同時に信号磁界に対する線形動作領域が増大することが定量的に示された.