Electrochromic film/Polymer-dispersed LCs

[rpbarry58]

All of the electrochromic film I have seen for sale operates on the principle that when electricity is applied, the film becomes clear, and I understand why that is...but is there an electrochromic film on the market which operates in the opposite way?  Is there a film which remains clear or semi-clear until electricity is applied, after which the film becomes opaque?

[studiot]

Would a Kerr cell do you?

https://www.google.co.uk/search?source=hp&ei=tYajXdHUBYvIwQKSlL7AAw&q=kerr+cell&oq=kerr+cell&gs_l=psy-ab.3..0l8.196.2072..2706...0.0..1.748.3248.2-1j0j2j2j1......0....1..gws-wiz.......0i131.IRR3KjHGLV0&ved=0ahUKEwiRg-Oxh5rlAhULZFAKHRKKDzgQ4dUDCAc&uact=5

[rpbarry58]

Thank you for your reply.

What I am looking for is essentially the same effect offered by standard electrochromic film, but with it's functionality completely in reverse...we are trying to develop a vehicular license plate frame for a security/executive protection application where a film could be applied to the clear molded lens used in a license plate frame...which would remain clear in it's unpowered state, but once 12V is applied from from the vehicle's electrical system, the film would become opaque and essentially obfuscate the plate number of the vehicle in the event of an emergency situation.

As the technology currently exists, the film remains opaque until electricity is applied.  Meaning that, were it applied to a license plate frame it would require the vehicle's electrical system to be constantly powering the film to allow the lens to remain clear in the event that the vehicle was parked with the engine off, for example.  This would present an unacceptable drain on the vehicle's battery.

[Sensei]

If you would merge two layers of polarization filters. One with e.g. p-polarization, and second one made by material which is able to rotate polarization vector due to applied electric or magnetic field, in such a way that will be opposite axis e.g. s-polarized. They working together would be creating opaque (black) material on demand.

 

https://en.wikipedia.org/wiki/Pockels_effect

"Pockels cells are used in a variety of scientific and technical applications. A Pockels cell, combined with a polarizer, can be used for switching between no optical rotation and 90° rotation creates a fast shutter capable of "opening" and "closing" in nanoseconds. The same technique can be used to impress information on the beam by modulating the rotation between 0° and 90°; the exiting beam's intensity, when viewed through the polarizer, contains an amplitude-modulated signal. This modulated signal can be used for time-resolved electric field measurements when a crystal is exposed to an unknown electric field.[2][3]"

 

 

[studiot]

51 minutes ago, rpbarry58 said:

Thank you for your reply.

What I am looking for is essentially the same effect offered by standard electrochromic film, but with it's functionality completely in reverse...we are trying to develop a vehicular license plate frame for a security/executive protection application where a film could be applied to the clear molded lens used in a license plate frame...which would remain clear in it's unpowered state, but once 12V is applied from from the vehicle's electrical system, the film would become opaque and essentially obfuscate the plate number of the vehicle in the event of an emergency situation.

As the technology currently exists, the film remains opaque until electricity is applied.  Meaning that, were it applied to a license plate frame it would require the vehicle's electrical system to be constantly powering the film to allow the lens to remain clear in the event that the vehicle was parked with the engine off, for example.  This would present an unacceptable drain on the vehicle's battery.

 

Whilst I can think of many legal applications of your film, such a device would be illegal in the UK and no doubt the US and many other places.

 

Interestingly you are asking a similar question to the one I asked decades ago (not here).

Electronic devices that had a control electrode to switch on or increase current or voltage go back to the 1920s (Valves, thyratrons, thyristors, fets, transistors etc)

Although corresponding switch off devices were invented in the early 1960s they were not made practical until the 1990s. (GTO devices)

 

[rpbarry58]

This type of device would certainly be construed as illegal in several countries...however,, I purchase and sell equipment designed for diplomatic/executive protection and security in Eastern European as well as Middle Eastern countries....radio signal jammers, caltrop dispensers, run-flat tires, etc.  Legality is not always of paramount concern in the development of my products.

[Strange]

On 10/13/2019 at 9:09 PM, rpbarry58 said:

All of the electrochromic film I have seen for sale operates on the principle that when electricity is applied, the film becomes clear, and I understand why that is...but is there an electrochromic film on the market which operates in the opposite way?  Is there a film which remains clear or semi-clear until electricity is applied, after which the film becomes opaque?

That does not seem to be the case: "As the color change is persistent and energy need only be applied to affect a change"

The alternative would be to use LCD technology. Whether the LCD is transparent or opaque with no voltage applied depends on the relative alignments of the front and back polarisers. Also, even when a voltage is applied, minimal current is drawn (which is one of the major benefits of the technology). I assume this is also true of electrochromic materials.