Thermally switched reflective optical shutter

• US 8,755,105 B2
• Filed: 12/05/2011
• Issued: 06/17/2014
• Est. Priority Date: 07/11/2007
• Status: Active Grant

• Current Assignee: Ravenbrick, LLC
• Original Assignee: Ravenbrick, LLC
• Inventors: Powers, Richard M., McCarthy, Wil
• Primary Examiner(s): Spector, David N
• Application Number:
  US13/311,212
• Publication Number:
  US 20120140311A1
• Time in Patent Office: 925 Days
• Field of Search: 251/713, 257/14, 349/16, 349/163, 359/227, 359/265, 359/275, 359/288
• US Class Current: 359/288
• CPC Class Codes: E06B 2009/2464 featuring transparency control by applying voltage, e.g. LCD, electrochromic panels
• CPC Class Codes: E06B 9/24 Screens or other constructions affording protection against light, especially against sunshine; Similar screens for privacy or appearance; Slat blindsoperating, guiding or securing devices or arrangements for roll-type closures E06B9/56; free-hanging flexible screens A47H23/00
• CPC Class Codes: G02B 27/28 for polarising used in stereoscopes G02B30/25
• CPC Class Codes: G02F 1/0136 for the control of polarisation, e.g. state of polarisation [SOP] control, polarisation scrambling, TE-TM mode conversion or separation G02F1/0353 takes precedence
• CPC Class Codes: G02F 1/0139 Polarisation scrambling devices; Depolarisers
• CPC Class Codes: G02F 1/0147 based on thermo-optic effects G02F1/132 takes precedence
• CPC Class Codes: G02F 1/132 Thermal activation of liquid crystals exhibiting a thermo-optic effect
• CPC Class Codes: G02F 1/133514 Colour filters
• CPC Class Codes: G02F 1/133533 Colour selective polarisers G02F1/1347 takes precedence
• CPC Class Codes: G02F 1/133536 Reflective polarizers G02F1/13362 takes precedence
• CPC Class Codes: G02F 1/133538 with spatial distribution of the polarisation direction

Abstract

The thermally switched reflective optical shutter is a self-regulating “switchable mirror” device that reflects up to 100% of incident radiant energy above a threshold temperature, and reflects up to 50% of incident radiant energy below a threshold temperature. Control over the flow of radiant energy occurs independently of the thermal conductivity or insulating value of the device, and may or may not preserve the image and color properties of incoming visible light. The device can be used as a construction material to efficiently regulate the internal temperature and illumination of buildings, vehicles, and other structures without the need for an external power supply or operator signals. The device can be tailored to transmit sufficient visible light to see through in both the transparent and reflective states, while still providing significant control over the total energy transmission across the device.

Claims

1. A device for regulating the reflection of incident radiant energy to control an internal temperature of a building, a vehicle, or other structure comprising

a first reflective polarizer;

a second polarizer; and

a twisted nematic, thermotropic liquid crystal positioned between the first reflective polarizer and the second polarizer that is directly responsive to environmental temperature to rotate a polarity of the incident radiant energy from a polarity of the first reflective polarizer to a polarity of the second polarizer when in a twisted nematic state;

wherein

when below a threshold temperature the liquid crystal is in the twisted nematic state; and

when above the threshold temperature the liquid crystal is in an isotropic state and has no rotational effect on the polarity of the incident radiant energy.

2. The device of claim 1, wherein the threshold temperature is at or around room temperature.

3. The device of claim 1, wherein the threshold temperature is between 16.5 degrees C. and 29.0 degrees C.

4. The device of claim 1, wherein

above the threshold temperature up to 100% of incident light is reflected by the device, and

below the threshold temperature up to 50% of incident light is reflected by the device.

5. The device of claim 1, wherein

at a first temperature a first percentage of the incident radiant energy is reflected from the device and a second percentage of the incident radiant energy is transmitted through the device;

and

at a second temperature a third percentage of the incident radiant energy is reflected from the device and a fourth percentage of the incident radiant energy is transmitted through the device.

6. The device of claim 1, wherein the second polarizer is an absorptive polarizer.

7. The device of claim 1, wherein either or both of the first reflective polarizer or the second polarizer are a diffuse reflective polarizer.

8. The device of claim 1, wherein either or both of the first reflective polarizer or the second polarizer are a polarity-rotating polarizer.

9. The device of claim 1, wherein the first reflective polarizer and the second polarizer each define transparent areas to allow transmission of radiant energy through the device.

10. The device of claim 1 further comprising an electrotropic control system to place the thermotropic liquid crystal in the twisted nematic state outside of the threshold temperature.

11. The device of claim 1, wherein the thermotropic liquid crystal further comprises an additive in a mixture with the thermotropic liquid crystal to affect optical properties of the thermotropic liquid crystal, a speed of transition between physical states of the thermotropic liquid crystal, or both.

12. The device of claim 1 further comprising

a first pane of glass;

a second pane of glass parallel to and spaced apart from the first pane of glass, wherein

the first reflective polarizer, the thermotropic liquid crystal, and the second polarizer are positioned between the first and second panes of glass;

the first reflective polarizer is adhered to a surface of the first pane of glass opposite the second pane of glass.

13. The device of claim 1, wherein the device is in a form of a flexible film.

14. The device of claim 1, wherein the second polarizer is a reflective polarizer.

15. The device of claim 14, wherein

the first reflective polarizer reflects up to 50% of the incident radiant energy and transmits a majority of non-reflected radiant energy;

and

the second polarizer reflects up to 100% of the radiant energy transmitted by the first reflective polarizer when the thermotropic liquid crystal is above the threshold temperature and transmits up to 100% of the radiant energy transmitted by the first reflective polarizer when the thermotropic polarizer is below the threshold temperature.

16. The device of claim 1, wherein either or both of the first reflective polarizer or the second polarizer are a thermotropic reflective polarizer.

17. The device of claim 16, wherein above the threshold temperature down to 0% of the incident radiant energy is transmitted by the device, and below the threshold temperature up to 100% of the incident radiant energy is transmitted by the device.

18. The device of claim 13, wherein the second polarizer is spaced apart from the second pane of glass.

19. The device of claim 1, wherein the first reflective polarizer and the second polarizer are oriented with respect to each other such that a difference in alignment of polarity between the first reflective polarizer and the second polarizer is 90 degrees.