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The
Recording Physics and
Instrumentation group
innovates, designs,
and consults in the
technical fields of: |
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This
group, created in 1986,
has a long and established
track record with their
instrumentation for
the characterization
of hard disk drives,
winning awards for Outstanding
Corporate and Technical
Achievement, along with
numerous publications
and patents. |
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Electronically measuring
the Flying Height (FH)
of a Read/Write transducer
in situ in a disk drive
was one of the major innovations.
This FH measurement technique
is based on the Wallace
Spacing Loss relationship,
where the change in amplitude
of the measured read-back
signal harmonics directly
relate to the FH change
of the Read/Write transducer.
The relationship between
the read-back signal waveform,
the spectrum, and the
FH is shown in the animation.
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By
calculating the ratio
of the fundamental amplitude,
Va , and 3rd harmonic
amplitude, Vb, the FH
is derived from the following
expression: |
, where: , 
and d = the head-to-disk
spacing.
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This
Harmonic Ratio Flying
height (HRF) measurement
technique earned a Corporate
Award in 1992, and was
issued U.S. Patent 5130866.
A number of articles were
published reviewing the
theory and application
of various FH measurement
techniques and useful
"derivatives",
such as disk texturing,
slider lift-off dynamics,
etc..
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Stand-alone
measurement systems for
determining the FH and
its derivatives were built
and are now used in research
and development labs as
well as in manufacturing
lines. Since its inception,
the FH measurement systems
have continually improved
giving better performance
(higher precision, wider
frequency ranges and larger
SN ratios) at lower cost
for the end-user. The
current cost of a FH measurement
system is less than $5,000.
Contact
Dr. Klaas Klaassen for details (Ph:
408-927-2052) |
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The
instrumentation
and methodology
for measuring popcorn noise in inductive
recording heads is another example
of a Recording Physics and Instrumentation
group contribution to Hitachi's
business. This popcorn, or Barkausen,
noise is the result of delayed domain
wall relaxation immediately following
a write operation. The write field
drives the magnetic circuit of the
head into (partial) saturation,
from which it may decay via a number
of meta-stable magnetic states.
Each state change comes with a rapid
flux change producing voltage glitches
in the head coil which interfere
with the read process. This is brought
about by non-zero magnetostriction
and the cooling of the write current
heated coil and eddy current heated
magnetic circuit of the head. The
popcorn noise is measured during
repeated write/read cycles and statistics
are gathered on the voltage glitch
amplitude, area, and time after
write termination. Shown is the
"foot print" of a head
as a function of the write current
amplitude and pulse area. The associated
equipment was spun off to be made
by Xyratex (a UK company). |
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The
Transition Width Instability
Tester (TWIST) is another
major innovation. TWIST
characterizes the read-back
transducer/media by measuring
the isolated-pulse width
and compiling the statistical
data. Using TWIST, the
isolated-pulse width (t
) is measured at level
x, divided by the pulse
interval time (T), and
then translated to a voltage, 
Shown is the statistical
data from a TWIST measurement
with level x set at 50%
of the read-back peak
signal. |
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This
group has contributed
in advancing measurement
and instrumentation techniques
for many other facets
of the disk drive technology
such as:
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write-transducer
temperature measurements,
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electrostatic
charge generation measurement
in spindle motors with
ceramic ball bearings,
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time
domain reflectometry for
verification of interconnect
designs, |
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test-stand
read/write electronics,
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recording
head response statistics
measurements (see plot
above), etc.. |
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Since
many of the above measurements require
custom discrete/PCB circuit designs,
the RPI group is highly skilled in
analog circuit design, for signals
from DC up into the Gigahertz region.
This analog circuit design is also
critical to Hitachi's disk drive IC
circuit design; this group designs/consults
on the front-end Read/Write and Channel
IC modules. In this area this group
has many Outstanding Technical Achievement
Awards, patents and publications.
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This
group’s
effort, in analog circuit
designs, continues to
reveal new solutions in
utilizing today’s
and future technology,
such as distributed amplifiers,
SiGe and HEMT IC technology,
as well as solutions for
newer write transducers
and tunnel-junction read
transducers. The image
below shows the recent
exploration test-site
utilizing SiGe IC technology. |
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The RPI group’s
broad skill base is often
recruited for tackling
bottlenecks limiting the
disk drive performance.
Maintaining the users’
data integrity as well
as drive performance is
vital to a disk drive’s
product success. The RPI
group plays a vital roll
in combating performance
bottlenecks in the serial
data stream from the Channel
IC through the Back-end
Interconnect to the Read
Write IC through the Front-End
Interconnect and then
back through the Read/Write
Transducers and Disk Magnetics.
Maintaining the signal
fidelity through this
part of the system is
the heart-beat of a disk
drive.
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