ASTI Mono Crystaline Ferrite
Fabrication techniques for ferrite video heads have been pioneered by
equipment manufacturers. However, performance has been limited by the
properties of the ferrite head material itself. Problems with excessive
hardness, brittleness and abrasiveness have affected both head life and
tape wear. In addition, magnetic shortcomings result in excessive high-frequency
loss, and degradation in signal noise ratio. But a new approach to growing
manganese-zinc ferrite in a single-crystal form using a carefully controlled
oxidizing atmosphere and high temperatures results in a very dense and
highly homogenous basic material. It is superior in both mechanical properties
and has been found to be the best material yet devised for the fabrication
of video heads.
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Magnetic/Electrical Properties
When compared with ferrite heads manufactured by earlier techniques,
the ASTI heads show superior performance in the following areas:
Initial permeability is higher than 1200 at 1 MHz and 700 at 5MHZ.
A specific coercivity of less than 0.05 Oersted.
Saturation flux density above 4,500 Gauss.
These factors contribute to wider frequency response, lower noise, and
better signal to noise ratio.
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Mechanical Properties
ASTI monochrystaline ferrite ingots are characterized by high density
and extreme hardness, more than 650 HV (Vickers). They are also very
uniform in crystaline structure and virtually free of lattice defects.
Crystal orientation accuracy is controlled with great precision, holding
major crystal axes to within ±1o. This and other factors facilitate
slicing and cutting operations. The basic material is ready cut and shaped
with the proper equipment. The results are high yield, excellent wear
characteristics and long, trouble-free life.
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Precision Machining and Assembly
ASTI video head assemblies are machined to the highest standards and
microscopic assembly techniques are applied to ensure exact replacements
for most half-inch machines. Top electrical performance is assures by
the outstanding characteristics of ASTI video heads.
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Gap Thickness and Track Width
A highly refined glass bonding technique used in head fabrication permits
head-gap thickness in the range of 0.3 to 0.8 microns ±0.05 microns.
(0.55 microns is wavelength of green light!) And since many of the newer
VCR's employ extremely narrow track widths an entirely new process has
been developed to machine the gap area to provide track widths as low
as 20 microns. And azimith accuracy is maintained with-in 4 minuets of
arc.
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Glass Filling
To protect the delicate head gap area the material removed to establish
track width is filled and sealed with a specially developed glass. It
bonds the gap area, prevents wear and greatly reduces failure due to
fracture. The material used in this process came out of basic research
to find a material that matches managanese-zinc ferrite in terms of bonding
and temperature effects.
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Head Asemblies, Electrical Performance
When compared with head assemblies made by other manufacturers, ASTI's
are held to tighter tolerences. Basic specifications in terms of playback
sensitivity, optimum record current, inductance, impedance and moice
factor are held to the narrowest limits attianable.
Install ASTI video heads with confidence for long-term customer satisfaction.
Specifications
Characteristics of Magnanese-Zinc Monocrystal Ferrite
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Properties Symbol Unit 801 703
1. Initial permeability µo (at 0.01 MHz) >1200 >5000
µo (at 1 MHz) >1000 1200
µo (at 5 MHz) >800 >150
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2. Saturation flux
density B10 (Gauss) >3300 >4500
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3. Coercive force Hc (Oersted) <0.05 <0.05
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4. Loss factor Tan ð/µo (at 0.1 MHz) <2 x 10-5 <8 x 10-5
Tan ð/µo (at 1 MHz) <1 x 10-4 <3 x 10-4
Tan ð/µo (at 5 MHz) <7 x 10-4 <2 x 10-4
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5. Resistivity (Ohm-cm0 >0.5 >0.1
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6. Curie temperature Tc (C) >100 >200
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7. Victers hardness Hv >650 >650
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8. Thermal expansion coefficent (x106 deg. -7) 9-10 9-10
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