Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
The
first level of isolation
is the sensor enclosure shock mounts.
These mounts
consist of four commercial elastomeric pads.
The enclosure weighs about 100
lbs, including
the internal batteries.
Weight per mount, resonant frequency, spring rate,
static deflection,
and isolation efficiency entered into the selection.
The enclosure/mount resonance frequency
is no more than 10 Hz to ensure reasonable isolation of rotating machinery components at 30
Hz.
The next level of isolation
is the sensor suspension system, which
is a spring-mass
type with a much lower resonance frequency than the enclosure.
The sensor
is attached to a
bob weight that
is suspended from the top of the enclosure via a spring.
The weight
is about
2 lbs; the spring rate was selected to provide a resonance frequency of about 2 Hz.
This
provides an additional isolation factor of about 12 dB
(6 dB/octave)
at the enclosure
resonance frequency assumed to be about 10 Hz.
Beyond 10 Hz, the overall isolation
is the
sum of the two (12 dB/octave).
Extension springs are not characterized for torsional spring rate; however,
a check
of nearly identical size torsion and extension springs does yield an estimate. For the metallic
spring selected above, the torsional spring constant
is about 0.1 lb-ft/radian.
Assuming that
the sensor weight
is a 2-lb lead sphere, the rotational moment of inertia
is about
1.0 x 10-4
lb-ft-sec2
, which implies that the rotational harmonic frequency
is around 5 Hz.
Isolation from low-frequency vibrations (such as those induced by footsteps and
vehicle road “rumble”)
is not easy to provide.
In this case, the assumption
is that the energy
below 10 Hz
(the electrical signal lower frequency cutoff point)
will not be so large that
it
masks the noise that will be visible above 10 Hz.
As mentioned earlier an extra vibration
isolation element was added to eliminate some specific ambient artifacts.
2.
Acoustic Vibration
Just as for mechanical vibration, acoustic energy can easily cause the PZT sensor
to produce noise signals
if the sounds are allowed to impinge upon the PZT element directly.
Since this
is the case,
it would seem obvious that the PZT sensors should be
heavily isolated, perhaps by being encased in lead or other sound deadening material.
This
approach could not be followed since
it was considered a necessity that the participant be in
visual contact with the sensors.
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
As the participants gain confidence in interacting with the apparatus,
it
is
contemplated that more restrictions can be introduced.
For the present experiment however,
we believe that we were successful in controlling acoustic artifact through the following steps:
•
Isolation of the sensors in a hard,
steel enclosure that reflects
higher frequency sounds.
•
Isolation of the entire sensor enclosure in another room (Condition
III).
•
Tape recording of
all Condition
III sessions.
The
final step of rejecting any acoustic correlated events was added as a measure
of extra caution.
Qualitative experimentation demonstrated that,
in Condition
III,
a
substantial amount of noise and movement was required to trigger an artifact from inside the
participant’s room.
However, we could not quantitatively measure the audible sound pressure
level and frequencies necessary to generate an artifact at the time of the experiment.
Consequently, the use of the tape recorder to reject any events correlated with room noise
appeared an appropriately conservative measure.
A small amount of conformal coat elastomeric rubber was also applied as a
sound-absorbing skin. In addition, the external silver-paint coat (which serves for EMI
protection)
serves in a small way as an acoustic reflector at the highest frequencies.
Proof of the efficacy of all these measures may be found in the control
trials and
testing.
During the course of the testing, we duplicated
all the normal ambient noises
occurring outside the room
(i.e., doors slamming, people talking,
etc.).
None of these was
correlated with any artifact production.
3.
Heat-Induced Variations
All of the elements that make up the analog portion of the sensor hardware are
sensitive to heat in various ways.
The sensor
is the most critical because
its physical size
(mass)
is very small, which means that the thermal time constant
is low also.
Hence, any
thermal input such as an infrared ’’pulse”
(from the subject’s hand moving past the viewing
window) may induce a response in the sensor
if the pulse has significant spectral energy above
the system high-pass
filter response of 10 Hz.
Because IR
is long-wave energy,
it penetrates many materials and
is difficult to
shield.
The only direct protection
is the
silver paint applied to the outside of the sensor over
the rubber coating.
However, the shielded window of the enclosure
is covered by an
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
anti-reflective coating that reduces the 1R transmission.
A test of waving one’s hand in front
of the sealed enclosure does not produce any IR artifact.
Further IR isolation was provided
by the isolation of participant and sensor in Condition
III
(see Figure
5).
4.
Electro-Magnetic Isolation
Because the entire sensor system
is electronic,
it must be shielded from both
electric and magnetic
field influences.
No high-voltage or large-current devices are near the
sensor enclosure, and
all electrical devices within 100
feet meet the FCC minimum
requirements for RFI emission suppression.
The primary danger from stray fields
(field-to-cable coupling outside our shielded enclosure)
is eliminated entirely by using fiber
optics cables to carry the signal to the external hardware.
The primary shield against EM signals which might affect the PZTs
is the basic
sensor enclosure, which
is a standard industrial NEMA
steel RFI-specified box.
According
to the manufacturer’s data book,
this box provides up to 95 dB of magnetic-field shielding
from
14 kFIz up to
1 MHz, and over 100 dB of shielding for electric fields from 14 kHz up
to at least 450 MHz.
These levels of performance are degraded
if any openings are made in
the steel case.
The viewing window in the front of the box
is of a special EMI/RFI material
(metallized and containing an embedded metal mesh).
The manufacturer’s specification for
the shielding effectiveness (SE)
for electric
fields
is about 80 dB up to 10 MHz.
The SE for
magnetic
fields varies from about 10 dB
at 100 kHz to about 45 dB
at
10 MHz.
Clearly, low
frequency magnetic
fields directly in front of the window could be a problem.
However, the
PZT
is a capacitive element, not resistive and, therefore, should be relatively insensitive to
such
fields.
In future studies,
as the participants gain confidence, we should be able to use an
unmodified windowless enclosure.
Power resides inside the box in the form of chemical
batteries, and the only other holes through the shell are two
1 /4-inch openings for the
fiber-optic cables.
A straightforward calculation can demonstrate that signals must be greater
than about 10 GHz to propagate through these openings.
Because of internally generated EM
fields (from the dc to dc convertors and the
fiber-optic driver electronics), the sensor and preamplifier are totally enclosed within a
metallic shield.
This shield
is a combination of the lead bob weight or the silver-paint coat;
neither of which afford any magnetic shielding.
Because
all interconnect wires are shielded
coaxial or multiconductor cables, they are relatively immune to extraneous
fields. A
single-point common “ground” was used to minimize “ground loop currents” and the
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
associated signal noise voltages.
The critical low-noise preamplifier
is powered from batteries
only.
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
IV CONCLUSIONS
Five individuals designated by researchers from JFK University have participated in a
series of RA experiments conducted
at SRI.
Each participant was asked to influence one of a
pair of piezoelectric strain gauges, operating in differential mode, to produce an event above a
predetermined threshold.
Altogether, the
five participants contributed 20 sessions, each
lasting approximately 90 minutes.
The
last
8 sessions were conducted in Condition
III,
in
which the sensor enclosure was located in a locked room adjacent to the participant s area.
At that point the participant was approximately 3 meters from the sensor pair.
Under those
conditions, one of the participants produced a total of
1 1 events above threshold.
Those
events, the largest of which was 33 mV, were distributed into three separate effort periods
over two sessions on different days.
Known sources of artifacts
(electromagnetic, acoustic, mechanical, and infra-red) were
considered and, wherever possible,
controlled, minimized, or measured.
However, some
potential but unlikely sources of artifact such as cosmic rays and low-frequency magnetic
fields were excluded from consideration in this
initial series of experiments.
The preliminary and pilot nature of these sessions cannot be stressed too strongly,
especially since
all possible sources of artifact have not been excluded.
Nonetheless, our
conclusion at this time
is that sufficient data have been collected to warrant further
investigation,
Future studies will heavily emphasize further shielding, detection of rare events that may
produce
artifacts, possible testing of the apparatus against standard EMI specifications such as
MIL STD-4 6 lb or TEMPEST, and detection of subaudible acoustic
artifact production.
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
Appendix A
STRAIN GAUGE REMOTE ACTION SCREENING DEVICE
by
Steven M. Ohriner
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
General Description:
The purpose of the RA screening device (SD)
is to
facilitate selecting the subjects
exhibiting RA
ability.
The individuals selected using the SD are to be subsequently tested and
trained using the RA laboratory instrument.
Shielding against artifact, although of concern,
is not the principal design consideration
for the SD.
So that a large number of subjects can be easily screened, the SD
is portable
and
fairly rugged when packed into
its two typewriter-size carrying cases.
It
is quickly and
easily assembled on a table or desk top.
The SD consists of two parts:
a strain gauge sensor and preamplifier assembly and
a processing and display unit.
The strain gauge sensor and preamplifier assembly are
suspended from a stand to provide some degree of mechanical isolation.
Miniature coaxial
cables connect the sensor assembly to the desktop display unit.
The display unit contains the
processing and display hardware and the batteries that supply the entire system.
The front
panel of the display unit has a
digital volt meter (DVM)
that displays voltage in millivolts, and
a twenty-element linear LED bar graph that shows the voltage graphically on a 0-to-2-volt
scale.
Headphone jacks, volume controls, battery test pushbuttons and remote handset jack
are located on the right side panel.
Strain Gauge Sensor and Preamplifier:
The strain gauge sensor
is an aluminum strip
(3 inches x 3/4 inches x .016 inches)
on which two Omega Y series
foil strain gauges have been mounted.
These strain gauges
have a coefficient of thermal expansion matched to aluminum.
The gauges are mounted side
by side and oriented parallel to the long (3-inch)
axis.
The aluminum
strip
is anchored to a
shielded aluminum enclosure
(1 inch x 3 inches x 5 inches) that houses the preamplifier
circuitry.
A small coaxial cable connects each of the two gauges to the bridge and
preamplifier circuitry located inside the shielded enclosure.
These cables were kept short
(2
inches) to minimize sensitivity to electromagnetic
fields.
The two gauges are connected in serial to make up one leg of the bridge. The three other
legs are made up of 240-Ohm resistors.
The bridge output
is ac-coupled to a Burr Brown
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
INA-110 instrumentation amplifier.
The INA-110 has a common mode rejection (CMR) of
106 dB and
is configured for the maximum gain of 500 using precision trimmed internal
resistors.
In addition to providing gain, the INA-110 converts the
differential signal from the
bridge to a single ended signal.
An additional gain of 100
is applied by a TL064 operational
amplifier followed by a unity gain buffer to serve as a line driver.
Thus, the sensor
preamplifier applies an overall gain of 50,000.
At room temperature, the thermal noise of a 240-fi resistor
is 2 nV\/Hz.
The noise
voltage of the INA-110
is 10 nV Hz.
Clearly, the noise voltage of the instrumentation
amplifier
is a factor of five greater than the thermal noise of the sensor.
System tests showed
that the noise floor
is limited, not by the INA-110 but by the sensor environment
(mechanical vibrations and audio noise).
A high-pass
filter with a 100-msec, time constant, and a low-pass
filter with a 0.1-msec
time constant preceed the instrumentation amplifier. The high-pass
filter rejects artifacts that
are caused by differences in expansion coefficients between the aluminum strip and the strain
gauge due to variations in room temperature.
The low-pass
filter rejects noise as well as
pulses shorter than 0.1 msec.
The resonant frequency of the aluminum
strip
is approximately
20 Hz.
Exciting the sensor strip mechanically with a pulse narrower than 0.1 msec (which
is
the low-pass
filter bandwidth)
will produce a response with an envelope at the resonant
frequency of the
strip or 20 Hz.
This
is within the bandwidth of the low-pass
filter.
The circuitry described above
is that for the signal channel.
There
is also a control
channel.
The control channel
is identical to the signal channel with this exception:
the two
strain gauges are replaced by two 240-fl resistors.
Elements of one channel are located in
close proximity to those of the other channel so that any signals induced by local
electromagnetic (EM)
fields disturb each channel equally.
The two resistors used in place of
the strain gauges are mounted next to the strain gauges on the aluminum
strip.
Batteries provide the power to drive the sensor circuitry in the processing and display
unit.
An 8-volt regulator in the sensor enclosure
is used to derive the bridge voltage.
By
connecting the two strain gauges in series, the voltage across them
is kept to only 4
volts, well
below the 9 volt maximum specified.
Processing And Display Unit:
The function of the processing and display unit
is to take the sensor outputs from the
preamplifiers and feed them back to the operator in real time. The amplified signals from the
sensor preamplifiers enter the processing and display unit and are again amplified by a factor
of three for an overall gain of 150,000.
After amplification, the signals are injected into a
low-pass
filter 660 Hz with a rolloff of 12 dB per octave.
To complete the signal processing,
a
full wave rectification and peak hold are done on each channel.
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
The signal processing functions described above are realized by two identical channels of
hardware:
one for the signal channel, and one for control. From this point on the hardware
is shared between the two channels.
The operator chooses the desired channel with a
pushbutton toggle switch.
There are three forms of feedback:
two visual and one audio.
A DVM displays the
voltage held by the peak hold circuit of the selected channel, while
a twenty-element LED
bar display shows the voltage in a bar graph fashion.
The selected peak hold output
is
simultaneously converted to an audio tone
(using a V to F converter), which
is played into
two sets of headphones:
one for the subject and one for the operator.
Individual volume
controls are provided.
The threshold for the tone can be
is adjusted via an internal resistor.
Once above this threshold, the frequency of the tone increases linearly with the peak held
voltage.
The two peak holds
(signal and control)
are reset by a single pushbutton.
Both the
“reset” and the “channel select” pushbuttons are mounted on a small hand-held cylinder
connected to the processing and display unit by a 12-foot cord.
The screening device
is powered by three different batteries. A 9-volt alkaline battery
with a lifetime of 6 months powers the DVM.
The negative 12
is supplied by two
12-volt
smoke alarm batteries connected in parallel.
These provide 25 hours of continuous operation.
A 12-volt 2.6-amp hour rechargeable gel
cell supplies the +12 and +5
volts. A
fully charged
battery will provide
10 to 20 hours of operation depending on LED usage. A battery test
pushbutton and a battery select switch (+12 or -12 volt)
display the selected battery voltage
on the front panel DVM.
The DVM
is equipped with a “low battery”
indicator for the 9-volt
alkaline
cell that powers
it.
Performance:
Testing in the Geoscience And Engineering Center demonstrated that with the high
degree of sensitivity built into the electronics, noise tended to be a problem.
By reducing the
low pass
filter bandwith to 660 Hz, thermal noise
at the output
is theoretically reduced to
200 mV.
With a 2-volt full-scale voltage,
this poses some obvious problems.
Fortunately
because random thermal noise
will be present on both channels, the control channel can
provide a baseline to which the signal channel may be compared. With the SD on a table in
our laboratory, which
is not a particularly quiet environment readings as high as 300 mV were
recorded. We believe these signals were produced by the ventillation system and ambient
noise.
Aside from thermal noise, there
is of course mechanical vibration of the table on which
the sensor stand rests as well as acoustic noise.
The sensitivity of the screening device
is such
that air currents, particularly those normal to the aluminum
strip surface, produce measurable
strain. These effects can be minimized by training the operators prior to subject testing.
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
The effect of electromagnetic
fields on the screening device proves to be minimal.
Keeping the connections between the gauges and preamplifiers short, the use of coaxial cable,
and shielding the sensor circuitry in
its enclosure, together provide good electromagnetic
isolation.
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
Appendix B
ENGINEERING CONSIDERATIONS AND CONSTRUCTION DETAILS OF A
PIEZOELECTRIC SENSOR SYSTEM
By
Philip B. Bentley
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6
Approved For Release 2001/03/07
: CIA-RDP96-00789R002200100001-6