SARA, Inc. has developed microphone arrays that are as effective at reducing flow noise as foam windscreens and
sufficiently rugged for tough battlefield environments. These flow noise reducing (FNR) sensors have a metal body
and are flat and conformally mounted so they can be attached to the roofs of land vehicles and are resistant to
scrapes from branches.
Flow noise at low Mach numbers is created by turbulent eddies moving with the fluid flow and inducing pressure
variations on microphones. Our FNR sensors average the pressure over the diameter (~20 cm) of their apertures,
reducing the noise created by all but the very largest eddies. This is in contrast to the acoustic wave which has
negligible variation over the aperture at the frequencies of interest (f less or equal than 400 Hz).
We have also post-processed the signals to further reduce the flow noise. Two microphones separated along the flow
direction exhibit highly correlated noise. The time shift of the correlation corresponds to the time for the eddies in
the flow to travel between the microphones. We have created linear microphone arrays parallel to the flow and have
reduced flow noise as much as 10 to 15 dB by subtracting time-shifted signals.
The "ColorDazl" is a device designed to be used for testing eye and sensor dazzling, at modest range, in a
package that can be carried, and with a projector that could be mounted to a lethal weapon (or if desired, to
another type of non-lethal device such as a "stinger"). The Tri-Laser Module (TLM) is a completely self
contained subsystem of the device containing functional 3 color (RGV) laser sources. The laser beams are
transmitted to the projector by an optical fiber. A 2" or larger diameter projector produces an eye-safe beam
throughout its range, yet one of sufficient Irradiance or Illuminance to potentially dazzle sensors, and the
unaided eye at ranges between 20' and 200' under night-time or twilight conditions.
The TLM is a single pulse laser source, which can be fired every few seconds, with computer controls which
keep it eye-safe at the exit aperture, and throughout the range. The output is adjustable with varying power
levels and varying pulse duration of the three colors, allowing a flickering output. The system is operated
from a LapTop computer which controls the total power, and pulse lengths of each individual laser, so that the
total power is below 500 mW, and the energy per pulse for all 3 beams is kept below 30 mJ per pulse. This
mode of operation ensures that the device is a Class 3b source as determined by ANSI Z136 classification, and
is therefore free from the limitations of Class 4 which include key lock, emission delay, audible warning, etc.
With simple refinements to the ColorDazl laser controller software and new projector and receiver
combinations currently being considered, a higher power dazzler could be designed in the near future that
will be effective and relatively safe under brighter ambient lighting and longer range conditions.