Switching of thermochromic and pressure sensitive films with surface acoustic waves

Apparatus for erasing thermochromic information displays comprising:

• a lithium niobate substrate;
• a vanadium oxide thin film deposited on the surface of said substrate, said film capable of undergoing marked increases in reflectance relative to surrounding areas of said film at any region thereof heated above the transition temperature of said film, the reflectance of said film exhibiting hysteresis with temperature at temperatures near said transition temperature;
• an acoustical transducer on the surface of said substrate containing at least one pair of electrodes spaced apart in substantially parallel relation for generating surface acoustic waves on the surface thereof;
• said film oriented on said substrate such that the internal strains in said film are polarized by surface acoustic waves;
• and
• an RF source connected to said electrodes for energizing said acoustical transducers.

In a thermochromic display for writing and erasing images the combination comprising:

• a piezoelectric substrate;
• a thermochromic recording film deposited on the surface of said substrate, said film undergoing markedly increased reflectance at any region thereof heated in excess of the transition temperature of the film, the reflectance of said film exhibiting hysteresis with temperature at temperatures near said transition temperature;
• a thermal energy source for selectively heating regions of said film in excess of the transition temperature to create high contrast images in said film;
• and
• means for generating high frequency surface acoustic waves in said film on said substrate, said waves having sufficient energy to counteract the strains in said film.

A solid state information display comprising:

• a piezoelectric substrate;
• a thin film of pressure sensitive material deposited on the surface of said substrate, said material capable of exhibiting markedly increased reflectance at any region thereof subjected to an external pressure in excess of a predetermined threshold pressure, the reflectance of said film exhibiting hysteresis such that the increased reflectance at any such region is substantially unchanged when said pressure is removed;
• first, second and third surface acoustic wave transducers disposed on the surface of said substrate and responsive to first, second and third signals for causing deformations in said substrate to generate surface acoustic waves on the surface thereof and in said film;
• said waves creating regions of pressure in said film such that the regions where any two of said first, second or third waves intersect, the pressure at said regions is always less than said threshold pressure and the pressure at any point where all three of said waves intersect is in excess of said threshold pressure thereby causing an increase in reflectance in the film at said point;
• generating means for supplying first, second and third input signals to said first, second and third transducers;
• and
• timing means connected between said generating means and said first, second and third transducers for supplying an RF signal to each of said transducers at a preselected time.

A method for creating high resolution images at predetermined locations on a pressure sensitive film, capable of switching from a lower to higher reflectance at regions of switching from a lower to higher reflectance at regions thereof subjected to pressures in excess of a predetermined threshold pressure, comprising the steps of:

• generating a first acoustic surface wave train in said film of a first pressure at a first preselected time;
• generating a second acoustical surface wave in said film of a second pressure in a direction perpendicular to said first wave at a second preselected time;
• generating a third acoustic surface wave in said film of a third pressure in a direction substantially opposite to said second wave at a third preselected time;
• said first, second and third pressures selected such that a point of intersection of said first, second and third waves will be subjected to a resulting pressure in excess of said threshold pressure to switch the film at said point to a higher reflectance and any regions where any two of said first, second and third waves intersect will experience a pressure less than said threshold pressure;
• and
• selecting said first, second and third times to switch a preselected point on said film to a higher reflectance.

A method for selectively erasing images formed in pressure sensitive films which undergo increased reflectance at regions thereof when subjected to pressure in excess of a predetermined threshold pressure, comprising the steps of:

• generating a first acoustic surface wave in said film of a first pressure opposite in effect to the internal strains of said film in a first direction at a first preselected time;
• generating a second acoustical surface wave in said film of a second pressure opposite in effect to the internal strains of said film in a second direction substantially perpendicular to said first direction at a second preselected time;
• generating a third acoustic surface wave in said film exerting a third pressure opposite in effect to the internal strains of said film in a third direction substantially opposite to said second direction and perpendicular to said first direction at a third preselected time;
• and
• said first, second and third pressures selected such that a point of intersection of said first, second and third waves will subject said point to a pressure sufficient to counterbalance the induced strain at said point and any regions where any two of said waves intersect will not experience sufficient strain to counteract said internal strain.