What is Electrophoretic Smartglass?

Electrophoretic smartglass changes tint between transparent and opaque with minimal power consumption and offers on-demand light control for IoT consumer devices, buildings, vehicles and smart city infrastructure.

Benefits

  • Adaptive, on-demand
  • Facilitates controlled daylighting (reducing artificial lighting costs)
  • Reduces air-conditioning costs
  • Provides visual comfort
  • Neutral colouration
  • Fast switching time (typically a few seconds)
  • High visible light transmittance (VLT) of around 50%-70% when activated
  • Low VLT when switched off, providing after-hours security and privacy
  • Only consumes current when switching state (ideal for IoT devices)
  • Blocks ultraviolet (UV) which reduces colour fading of artworks and interior furnishings
  • Low voltage operation (typ. 5 – 15Vdc)
  • Can be driven directly from photovoltaic solar cells (without requiring an inverter)
  • Excellent colour rendering
  • Very good contrast ratio and low haze

Limitations

  • Limited market availability at the time of writing (March 2024)
  • Switching speed reduces with increased glass dimensions
  • When used in display devices, not suitable for showing video animations (since constant updates reduce the power efficiency of the ink)

Terminology

Phoresis: derives from the Greek word meaning “to carry.” 

Electro-phoresis: involves the migration of charged particles in a conducting medium under the application of an electric field.

‘Electrophoretic ink’ is synonymous with ‘electronic ink’ (e-ink), which forms the basis for ‘electronic paper’ (e-paper) based e-readers, which are an important application area, but as you will see below, not the only one.

Applications

Present-day electrophoretic technologies have applications in:-

  • consumer wearables
    • mobile phones, smart spectacles, smart jewellery
  • smart windows 
    • auto-tinting skylights, building facades, privacy doors
  • automotive displays
    • heads-up displays, road traffic information
  • display signage 
    • supermarket shelf labels, road signage
  • smart cards
    • authentication, fraud alerts

Origins

To understand the origins of electrophoretic technology, we need to look at the work done in the 1970s by Xerox Palo Alto Research Center (PARC), creators of an electronic ink technology called Gyricon.

Gyricon is essentially a thin transparent plastic sheet containing millions of randomly-dispersed polyethylene beads with one face coloured black, and the other white. The result is flexible, viewable from wide angles, and can be written (and re-written) thousands of times. 

Each face carries an opposite electrical charge (one positive, the other negative) due to additives doped into the materials.

Gyricon electrophoretic ink

Gyricon rotating beads (Attribution: Eugeni.Pulido, CC BY-SA 3.0, via Wikimedia Commons)

The Gyricon beads sit in an oil-filled cavity, allowing them to rotate freely.

  • When an electric field is applied to the sheet, the beads rotate in the direction of the applied electric field, such that the white face points upwards and the ‘pixel’ looks white.
  • When the electric field is reversed, the black face of each bead reorients itself to face upwards, turning that ‘pixel’ black.

Technology

More recently, electrophoretic technology has been applied to smartglass in construction and transportation, as well as in consumer wearables, dynamic paint and retail smart labels.

The basic operation of a ‘cell’ of electrophoretic ink can be visualised as below, and is taken from the specific use case for smart windows in buildings. 

Implementations for other use cases vary in design, but the principle remains the same where charged ink particles migrate under an electric field, changing the optical properties of the glass.

Electrophoretic smartglass

 

  • When a voltage is applied to the electrodes, the ink particles (typ. 60 – 200 nm in size) migrate to locations under the electrodes, and are thus hidden from view, allowing light to pass through to a reflective panel placed underneath.
  • When the applied voltage is reversed, the ink particles disperse randomly, thus absorbing and blocking incident light.

How This Works

The ink particles are held in a low-viscosity fluid inside a container (called a microcapsule), from which we get the term ‘microencapsulated electrophoretic display’ based on work done at the MIT Media Lab.

This work featured on the cover of the prestigious Nature magazine in 1998.

This microencapsulated electrophoretic display is now commercialised by E Ink corporation, which was founded by MIT Media Lab researchers.

According to one implementation of electrophoretic smart glass by eLstar Dynamics in the Netherlands, and appearing in their patent, the voltage applied to an electrophoretic display is typically between 5 – 15Vdc.

The electric field is applied across a short vertical gap which results in a strong field density, resulting in rapid particle flow and fast switching times.

The electrodes are normally composed of indium tin oxide, a common transparent conductor (used also in SPD and PDLC smartglass).

Each pixel is controlled by a thin-film transistor in an active matrix configuration (where each pixel is addressable by its row and column).

The width, shape and separation distance of the electrodes dictates optical properties such as haze since light is diffracted through the areas between the electrodes, creating a rainbow effect.

The vertical distance between electrodes is around 20 um which makes the device less sensitive to imperfections in the materials used, producing fewer production issues, and better stability in both optical states.

Each individual pixel can be addressed independently by controlling the electric field presented to the upper electrodes, which means that each pixel can be made transparent or dark.

E Ink feature an excellent overview of the technology:-

Champions

Present-day electrophoretic technology is being championed by the following firms, listed in alphabetical order:-

Crown Electrokinetics

Crown Electrokinetics offers a fascinating ‘smart window insert’, featuring their DynamicTint™ electrokinetic (as they call it) technology, which is essentially the same as electrophoretic technology. 

This is a smartglass panel which can be mechanically inserted over the interior of an existing window frame and is powered by photovoltaic (solar) cells placed on the exterior face. 

This strikes us as an excellent low-cost alternative to replacing entire building facades, and with the added benefit of removing the cabling that would normally be required to power the smartglass.

For more information, see crownek.com

E Ink

Surely the market leader in this space, E Ink practically invented this sector and are responsible for bringing several types of electrophoretic display technology to the market.

Some versions are based on a single ink, others feature multiple inks in the same encapsulation, bringing not only black & white but also full colour images on a paper-like background.

A recent application can be found in this BMW Nostokana car exterior which features art written in electrophoretic ink as a dynamic automotive cladding.  Check out the details in this press release.

Ideal for commercial fleets of vehicles, we can imagine this being used for vehicle identification, branding and even on-the-road messaging for law enforcement vehicles.

For more information, see eink.com.

eLstar Dynamics

A young and exciting hi-tech startup based in the Netherlands, eLstar Dynamics have incorporated electrophoretic ink inside glass to enable dynamic tinting of building facades using this cost- and energy efficient technology.

Due to the large dynamic range of tint, this smart window technology offers from 0% VLT up to 70% VLT, enabling further applications in interior display cases for retailers and museums, privacy partitions in banks, and as smartglass doors for healthcare.

For more information, see elstar-dynamics.com

Plastic Logic

Plastic Logic, based in Germany and Hong Kong is a manufacturer of flexible, glass-free electrophoretic displays (EPDs), used in signage, smart cards, smart wearables and mobile devices.

For more information, see plasticlogic.com

Remarkable

Possibly the most exciting electrophoretic product on the market, this Norwegian company has revolutionised the tablet with a stunning digital productivity tool that feels like real paper.

For more information, see remarkable.com

Suppliers

If you are looking for manufacturers, distributors or installers of electrophoretic smart glass, look no further than our parameterised search.

The screenshot below shows that we have some companies listed already, which can be filtered down if you specify product attributes, such as minimum transmittance, U-value or haze:

Search Electrophoretic Suppliers

If you press the ‘Show Results’ button, this will produce a list of companies, which you can contact by posting a request on the Smartglass World Marketplace.

Search result for electrophoretic smartglass suppliers

Outlook

As pointed out in the “Electrophoretic E-paper Display Global Market Analysis Report”, the prospects for this technology are bright, thanks to the low power consumption of this technology which only requires activation when changing state.

This can have major benefits for Internet-of-Things (IoT) smart wearables, smart city infrastructure such as IoT traffic lights and electric vehicles that need to preserve battery life.

Electrophoretic technologies offer advantages over LCD and OLED displays including wider viewing angles, higher contrast ratios, sunlight readability and not requiring continuous backlighting.

Currently, research is underway to embed photovoltaic layers as a sustainable energy source to directly power electrophoretic devices.

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