SPD SmartGlass uses a patented film that contains rod-like particles suspended in billions of encapsulated cells (liquid droplets) that are uniformly distributed throughout the film as shown.  Each of the cells contains many smaller rod-shaped particles.  With no applied voltage, the particles are randomly oriented and block light. When a voltage is applied, the particles align with the electric field and allow light though.  By varying the applied voltage, one can vary the tint of the glass from clear to dark, and any shade between.

SPD is a film-based technology, meaning that the rotating particles are trapped inside a dual layer of a glass lamination.  Inside is a dual layer of plastic film that consists of two layers of plastic with an emulsion dielectric between them.  By including conducting layers we get a classical parallel-plate capacitor. As discussed in basic electric theory, a parallel-plate capacitor has a uniform electric field. For this reason, SPD film has a uniform response throughout the film.  In other words, you do not get the unwanted iris effect, so common in Electro chromatic devices.

Figure 1 Cross section of SPD smart film

The physical mechanism behind SPD is similar to what occurs inside the dielectric of a capacitor, where the atoms are polarized by the electric field.  In an SPD, rod-shaped particles are polarized which forces their long axes to align with the electric field.  This produces a venetian-blind effect which allows light pass through the spaces between them.  When no voltage is applied, the particles are randomly oriented and block light, similar to closing venetian blinds.  The small blue dots in the above figure are liquid cells trapped inside a solid.  Each of these cells contains a liquid that is full of many rod-shaped SPD particles.  To understand the venetian blind effect better, look at the Fig. 2:

Figure 2 (a) Dark state (b) Clear state

With no voltage applied as shown on the left, the particles inside the cell are in disarray.  In this state no light can pass through the SPD device.  When voltage is applied it sets up an electric field.  This polarizes the SPD particles and forces them to align vertically.  As a result light can pass through the SmartGlass.  By varying the voltage one can set the dark state (on the left); the clear state (on the right) or any shade in between.

Electrical Characteristics (Electric Glass)

• SPD SmartGlass Requires ac voltage for normal operation
• SPD SmartGlass has no memory: If you turn off the applied voltage, the glass will default to the dark state
• The cycle lifetime of an SPD smart window is defined as the number of times you can cycle it between its clear and dark states without noticeable degradation of its control over light transmission. SPD SmartGlass has a cycle lifetime greater than 1,000,000, which implies no problems will ever be encountered with cycle lifetime.
• The operating temperature range is -20⁰c to +70⁰c.

For external use SmartGlass International recommends that windows be made in double or triple glazed unit format.  The use of the following configuration will help to either retain or reduce heat as required offering maximum U values and user comfort.

SPD Double Glazed units (DGU) are comprised of

• Low-E coated glass layer
• Laminated SPD-Smart^TM Glass
• Argon gas filled in chamber

We recommend at least this configuration to achieve the highest possible thermal, acoustic, and safety performance possible.  The following performance characteristics can be achieved using SPD DGU.

*Values are nominal (+/-5%) and are dependent on the glass configurations used. SmartGlass International reserves the right to amend information without prior notice.