PhanTOm project Dental haptics Training System

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Visual Display

One of the dentist requirements is to have 3D stereo vision. This allows the tools to be position much more quickly and more accurate depth perception. Traditional red/blue eye image filter is not an option in this project due to the importance of colour. Using CRT monitor alongside with shutter glasses is a possible solution, but the limited availability of CRT and the eye tiredness caused by such system make it very difficult. Other option such as Head Mounted Display (HMD) is also not feasible as the current viewing angle and resolution is limited. Currently, the only options are to use multi-projector system or LCD 3D display. Both of these technology are based on either linear polarization or circular polarization.
      1. Polarization

Polarization is an electromagnetic wave property that describes the orientation and direction of the electric field oscillation. Absorptive or beam split polarizer is used to allow light to be polarized in certain way. Polaroid film and elongated silver nano-particles are the most common materials of adsorptive polarizer, which includes application such as LCD and 3D polarized glasses. Circular and linear polarizations are the two main polarization techniques used in nowadays LCD or projector based 3D display.
        1. Linear and Circular Polarization

When the electromagnetic wave is linearly polarized, the vector of the electric field oscillation is happening along a straight line. The two most commonly used linear polarizations are horizontal and vertical. They are very widely used in LCD display. There are other common directions of linear polarization such as 45 and 135 degrees.

Figure 5. Creating a circular polarization from single linear polarixzation using birefringent materials.

Circular polarization works very differently with linearly polarization. Circular polarization consists of 2 linearly polarized waves; both waves are 90 degree out of phase with each other and have equal amplitudes and wavelength. The direction of the electric field oscillate of one wave is perpendicular to the other wave. The resulting electric wave is a helix shape along the wave propagation [3]. For example, one horizontal linear wave and one 90 degree out of phase vertical linear wave together creates a circular polarised wave (Figure 5). Due to the wave propagation, the wave can either be a lead or lag wave with respect to other one. This makes circular polarization to be either clockwise or anti-clockwise.

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