NASA Technical Reports Server (NTRS) 20110016549: Controllable Sonar Lenses and Prisms Based on ERFs

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by  NASA Technical Reports Server (NTRS)

ide goes back into solution, releasing A research group in Norway has pro- home and industrial heating and cooling.
heat. A pump circulates the solution be- duced mechanically actuated carbon diox- This work was done by Jack A. Jones of Cal-
tween the generator and absorber. ide vapor-compression air conditioners for tech for NASA’s Jet Propulsion Labora-
Carbon dioxide can be an excellent automobiles and has shown those air con- tory. Further information is contained in a
refrigerant fluid for automobiles be- ditioners to be more efficient and poten- TSP (see page 1)
cause its critical temperature is only tially lighter than are comparable air con- This invention is owned by NASA, and a
about 88 °F (31 °C). Therefore, precool- ditioners based on a chlorofluorocarbon patent application has been filed. Inquiries
ing prior to expansion can take place refrigerant fluid. The champagne heat concerning nonexclusive or exclusive license
over a relatively wide supercritical tem- pump goes beyond the Norwegian re- for its commercial development should be ad-
perature range; in contrast, the com- search by replacing mechanical actuation dressed to the Patent Counsel, NASA Man-
mon refrigerant 134a must be con- with heat actuation. Potential applications agement Office–JPL; [phone]. Refer
densed at one specific temperature for a (other than automotive air conditioning) to NPO-19855.
given pressure. for the champagne heat pump include
Controllable Sonar Lenses and Prisms Based on ERFs
Compact devices without moving parts would focus and steer acoustic beams.
NASA’s Jet Propulsion Laboratory, Pasadena, California
Sonar-beam-steering devices of the pro- logical fluids (ERFs) between electrodes. of refraction of acoustic beams, thereby
posed type would contain no moving parts An ERF typically consists of dielectric steering the beams and, in the case of
and would be considerably smaller and less particles floating in a dielectric fluid. lenses, controlling focal lengths.
power-hungry, relative to conventional When an electric field is applied to the Figure 1 schematically illustrates a sonar
multiple-beam sonar arrays.The proposed fluid, the particles become grouped into assembly according to the proposal. A pla-
devices are under consideration for instal- fibrils aligned in rows, with a consequent nar array of acoustic transmitting/receiving
lation on future small autonomous under- increase in the viscosity of the fluid and transducers would both send out acoustic
water vehicles because the sizes and power a corresponding increase in the speed of signals to irradiate targets and, in the
demands of conventional multiple-beam sound in the fluid. The change in the acoustic analog of a retina, sense the spatial
arrays are excessive, and motors used in speed of sound increases with an in- pattern of return acoustic signals. The
single-beam mechanically scanned systems crease in the applied electric field. By transmitted and return signals would be
are also not reliable. thus varying the speed of sound, one collimated and focused, respectively, by use
The proposed devices would include a varies the acoustic index of refraction, of two acoustic lenses. The front acoustic
variety of electrically controllable acoustic analogously to varying the index of re- lens would be designed to contain an ERF
prisms, lenses, and prism/lens combina- fraction of an optical lens or prism. In in multiple compartments separated by
tions – both simple and compound. the proposed acoustic devices, this effect electrodes, rather than one compartment
These devices would contain electrorheo- would be exploited to control the angles between a single pair of outer electrodes, in
Rectangular Array of
Acoustic Transducers
Rear Acoustic Lens
Front Acoustic Triplet Lens
Acoustic Prism
Electrodes
Electrodes
Electrorheological Fluid
Between Electrodes
Figure 1. Electric Fields Would Be Appliedto electrorheological fluids between electrodes to vary the indices of refraction of the acoustic prism and lens,
thereby varying the beam direction and focal length, respectively.
NASA Tech Briefs, January 2004 27
order to reduce the magnitudes of the po- front of the front lens would also be con- be varied by modulating the potentials ap-
tentials needed to be applied to the elec- structed in layers, for the same reason. The plied to the prism electrodes in order to
trodes to vary the focal length of the lens index of refraction of the prism and, hence, steer the outgoing and incoming acoustic
through the required range. A prism in the angle of refraction of the beam, would beams.
The concept of ERF-filled compart-
ments separated by electrodes could be
generalized and modified to that of a
multicellular device comprising a rec-
tangular array of ERF-filled cells (see
Figure 2). Electrodes would be affixed
to both the row and the column walls
between cells, so that an electric field of
controlled magnitude and direction
could be applied to the ERF within each
cell. Lens shape (convex, concave, etc.)
can be varied by selectively activating in-
dividual cells.
This work was done by Yoseph Bar-Cohen,
Stewart Sherrit, Zensheu Chang, and Xiaoqi
Bao of NASA’s Jet Propulsion Labora-
tory; Iris Paustian and Joseph Lopes of
NSWC Coastal Systems Station; and Donald
Folds of Ultra-Acoustics, Inc. Further infor-
Figure 2.Cells in a Rectangular Arraywould be filled with an electrorheological fluid. Electrodes on
the walls between the cells would make it possible to apply electric fields to individual cells along mation is contained in a TSP (see page 1)
the row and column directions. NPO-30884
Measuring Gravitation Using Polarization Spectroscopy
Numbers of cold atoms could also be measured.
NASA’s Jet Propulsion Laboratory, Pasadena, California
A proposed method of measuring grav- gravitational acceleration from the phase be steered through a quarter-wave plate
itational acceleration would involve the measurements. oriented at 45°with respect to the origi-
application of polarization spectroscopy to The figure depicts the optical layout nal linear polarization. This quarter-wave
an ultracold, vertically moving cloud of of a version of an apparatus that would plate would transform the beam into a
atoms (an atomic fountain). A related pro- be used in the proposed method to mea- linearly polarized beam, the polarization
posed method involving measurements of sure the gravitational acceleration. (A direction of which would differ from that
absorption of light pulses like those used slightly different version would be used of the original laser light by an angle, φ,
in conventional atomic interferometry to measure a gradient in the gravita- that would depend on the velocity of the
would yield an estimate of the number of tional acceleration.) Also shown is a dia- atoms. A second polarizing beam splitter
atoms participating in the interferometric gram of the relevant energy levels of (PBS2), also oriented at 45°with respect
interaction. atoms of an element suitable for use in to the original polarization, would split
The basis of the first-mentioned pro- these methods: The element must be the beam into two parts that would go to
posed method is that the rotation of po- one that has a Λ-shaped energy-level two photodiodes (d1 and d2). The out-
larization of light is affected by the accel- scheme as depicted here. A linearly po- put currents of the two photodiodes
eration of atoms along the path of larized laser beam would impinge on a would be proportional to
propagation of the light. The rotation of first polarizing beam splitter (PBS1), (1/2)[P++ P-±2(P+P-)1/2sin(2φ)],
polarization is associated with a phase which would divide the beam into two where P+and P-denote the powers of the
shift: When an atom moving in a labora- beams of equal power. By use of quarter- two opposite circularly polarized beams.
tory reference interacts with an electro- wave plates, the two beams would be The sum of the two photocurrents would
magnetic wave, the energy levels of the given opposite circular polarizations. be proportional to the total output power,
atom are Doppler-shifted, relative to One of the two beams would be steered while the difference between them would
where they would be if the atom were sta- to propagate upward, the other to prop- give information on the polarization-rota-
tionary. The Doppler shift gives rise to agate downward along a vertical tube tion angle, φ.
changes in the detuning of the light from containing an ultracold cloud of the A lengthy mathematical derivation
the corresponding atomic transitions. atoms in question. that must be omitted here for the sake
This detuning, in turn, causes the electro- After propagating through the cloud, of brevity leads to an equation for de-
magnetic wave to undergo a phase shift the beams would be converted back to pendence of φon a number of variables
that can be measured by conventional linear polarizations by the same quarter- that include time (t) and the gravita-
means. One would infer the gravitational wave plates, then recombined in PBS1 to tional acceleration (g). The equation
acceleration and/or the gradient of the produce an output beam, which would could be used to infer g from the mea-
28 NASA Tech Briefs, January 2004