Electro-optic cell with transverse electric field

This disclosure is directed to an electro-optic cell construction of the type which employs a layer of minute dipole particles in a suspension carried between two transparent sheets for use as an electro-optic light controlling device such as a shutter, or the like. In combination with the dipole particle containing fluid chamber are optically transparent piezoelectric transformer elements for causing a transverse electric field in the fluid chamber to increase the speed of response of the shutter action.

BACKGROUND AND SUMMARY OF THE INVENTION 
This invention relates to electro-optic shutters employing a suspension of 
dipole rod-like particles oriented for light transmission or rejection by 
an electric field. The term electro-optic shutter is intended to include 
more generally electro-optic cells useful for variable density filters, 
light choppers, displays, controllable polarizers and the like. 
Electro-optic fluid shutters have found a place in the art and 
representative are various Marks U.S Pat. Nos. 3,848,964, 3,527,525, RE 
28,211, 3,512,876, 3,341,274, 3,257,903. Often discussed in these 
references is the problem of response time: although the dipole particles 
respond rapidly to an applied field and are oriented to provide a 
transparent window, the opaquing of the window tends to be slow by 
comparison since the dipole rods must move into random orientations by 
Brownian motion. Several of the references, for example, U.S. Pat. No. 
3,848,964, describe forced disorientation by multi-electrode structure in 
the cell to which voltage pulses are applied generating a transverse 
electric field to provide a uniform positive disorientation of the 
dipoles. A limitation of this approach is that the transmittance of the 
panel depends on the proportion of the area taken up by the electrode 
lines as compared to the space between the lines. If the lines are far 
apart, the applied voltage to the conductors must be high to attain the 
necessary transverse field strength to move the dipoles. As the lines are 
moved closer together, the transmittance decreases. 
In the present invention, the transverse electric field in the fluid 
shutter is provided by optically transparent piezoelectric transformer 
elements. A relatively low voltage such as 100 volts can be used to 
energize the piezoelectric voltage step-up transformer which then provides 
a combination of transverse electric field and motion to rapidly reduce 
the longitudinal alignment of the dipoles and the second transmitter of 
the cell.

DESCRIPTION 
Referring now to the drawings wherein like numerals are used in each of the 
Figures, there is shown generally at 10 an electro-optic cell having upper 
and lower transparent plates 12 and 14, the transparent plates comprising 
substrates 16 and 18, respectively, such as glass, and transparent 
electrodes 20 and 22. Edge member 24 is sealed to the plates 12 and 14 to 
complete the cell chamber. Within the chamber is a fluid 26, such as VARAD 
fluid, having in suspension dipole particles, and also two piezoelectric 
transformer elements 28 and 30. 
Element 28, and also element 30, is a single- or polycrystalline 
ferroelectric piezoelectric and optically transparent material such as 
quartz, barium titanate, lithium niobate, Rochelle salt, ammonium 
dihydrogen phosphate (ADP) or lanthanum modified lead-zirconate titanate 
(PLZT) of various compositions. It is operated as a piezoelectric voltage 
step-up transformer. The operation of a piezoelectric transformer of this 
general type using PZT is taught, for example, in the Berlincourt U.S. 
Pat. No. 3,562,792. In one successful embodiment of my invention involving 
PLZT, the optically transparent element 28 is approximately 4 cm long by 2 
cm wide and has a thickness of one millimeter. The resonant frequency is 
.perspectiveto. 40 kilohertz. The piezoelectric body has different 
portions polarized differently. A portion of the body at both ends in the 
area of the electrodes may be polarized transversely while the extended 
central portion of the body is polarized longitudinally. The 
longitudinally polarized portion is the high voltage secondary of the 
transformer and may provide a voltage gain of 10 to 200 times. In the 
sample described, it was about 100 times. Thus, if the primary electrodes 
are energized with about 100 volts, the voltage in the central area of the 
body with respect to the ends will be about 10,000 volts. The field 
generated by this high voltage and the associated transformer motion (40 
kHz vibration) are sufficient to quickly eliminate the longitudinal 
alignment of the dipoles which are nearby the transformer element. 
Electrical contact is made to the transformer at metal film electrodes 32, 
34, 36, and 38. To energize the transformer an alternating voltage V is 
connected across electrodes 32 and 34 and across 36 and 38. The voltage 
step-up transformer action results in a high voltage being generated in 
the central section of the element. Piezoelectric transformer element 30 
is mounted at right angles to element 28, the two elements operating as 
polarizers when energized. 
The mounting means (not shown in FIGS. 1 and 2) of the piezoelectric 
transformers in the chamber may be a foam rubber mounting and the foam 
rubber mounting may or may not be located at a displacement node of the 
transformer depending on whether the transformer is driven at a 
fundamental or higher harmonic. 
When the dipole particles are free to move within the chamber, they respond 
to Brownian motion and become randomized so that the shutter is opaque. 
When a voltage V.sub.c is applied to electrodes 20 and 22 imposing an 
electric field in the cell, the dipole particles become aligned with their 
long direction parallel to the electric field (the Z direction) and normal 
to the plates 12 and 14. The shutter then becomes transparent and 
transmits light from a suitable light source 40 through the shutter to a 
light detecting means 42. When the voltage V.sub.c is removed, the 
orientation of the dipole particles will again become randomized but as 
has been discussed above, the time interval for this to occur is longer 
than desired. In the present invention, when V.sub.c is removed, V is 
applied to energize the piezoelectric transformers 28 and 30. The 
resulting high voltages generated are effective to align dipoles in X and 
Y directions. As soon as the PLZT element 28 begins to vibrate, 
piezoelectric effects generate an electric field, E.sub.y, and the 
particles of the fluid adjacent element 28 will align themselves in the 
y-direction. Similarly, element 30 begins to vibrate and the piezoelectric 
effects generate an electric field E.sub.x, and the dipole particles in 
the fluid adjacent element 30 will align themselves in the x direction. 
This provides a rapid opaquing of the shutter.