What is Electrophoretic Smartglass?

Electrophoretic smart glass tints rapidly between transparent and opaque using minimal power consumption, and offers on-demand light control for buildings and transportation.

Introduction

This article introduces electrophoretic smart glass, which changes tint through the movement of ink particles operating under an electric field.

This technology is synonymous with ‘electrophoretic ink’ or ‘e-ink’.

For a high-level primer on smart glass in general, please check out our article on the basics of smart glass.

Let’s first look at the key benefits of e-ink technology:-

Benefits of E-Ink

  • 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), which reduces cabling cost and weight
  • In some cases, photovoltaic solar cells can directly power this technology
  • Excellent colour rendering
  • Very good contrast ratio and low haze

Limitations

  • In some cases, use of transparent conductors may reduce the switching speed 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 non-conducting medium under the application of an electric field.

‘Electrophoretic ink’ forms the basis for ‘electronic paper’ (e-paper) based readers, which are an important application area, but 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 a thin transparent plastic sheet containing millions of randomly-dispersed polyethylene beads. One face is black, and the other white. The result is flexible and viewable from wide angles. It is also possible to write to it over thousands of cycles. 

Each face carries an 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.

  • Under an electric field the beads rotate such that the white face points upwards and the ‘pixel’ looks white.
  • When we reverse the electric field, the black face of each bead reorients itself, turning the pixel black.

How Electrophoretic Technology Works

More recently, we have observed electrophoretic technology applied to smartglass in construction and in transportation. Other examples include consumer wearables, dynamic paint and retail smart labels.

The diagram below shows the basic operation of a ‘cell’ of electrophoretic ink, and relates specifically to smart windows. 

Implementations for other use cases vary in design, but the principle remains the same wherein charged particles migrate, altering the optical properties of the glass.

Electrophoretic smartglass

  • Under application of a voltage, the ink particles (typ. 60 – 200 nm in size) migrate to locations under the electrodes, hidden from view. Light can then pass through to a reflective panel underneath.
  • When we reverse the voltage, the ink particles disperse randomly, thus absorbing and blocking incident light.

Microencapsulated Electrophoretics

The ink particles find themselves in a low-viscosity fluid inside a container (called a microcapsule). From this, 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.

Whereas MIT Media Lab originally created the technology, E Ink corporation now develops and sells it as a series of products.

Electrophoretic Smart Glass

One implementation of electrophoretic technology in smart glass is by eLstar Dynamics, as described in their patent.

The patent describes a low voltage applied across a short vertical gap which results in fast switching times.

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 general 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 a rechargeable battery in the frame that is charged 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 fast dynamic tinting of building facades using a cost- and energy-efficient variation of the core technology.

The large dynamic range of their windows (0% VLT to 70% VLT) enables applications in display cases for retailers and museums, as privacy partitions in banks, and as smartglass windows and doors for healthcare.

eLstar’s technology promises low cost and is backed by enormous manufacturing capacity, with maximum dimensions up to 2940 x 3370 mm, and low power operation, which is ideal for automotive, architectural and other specialty markets.

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. 

This is thanks to a low power consumption requiring activation only when changing state.

This can have major benefits for Internet-of-Things (IoT) smart wearables, IoT traffic lights and electric vehicles that require longer battery life.

Electrophoretic technologies offer advantages over LCD and OLED displays such as wider viewing angles, higher contrast ratios and sunlight readability.

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

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