Window Material And Color; Coatings And Scratch Resistance - Newland EM50S-10 Integration Manual

Window Material and Color

Window material must be clear. Use only cell-cast plastics or optical glass. PMMA, ADC and chemically tempered glass are
recommended. Window material selected for the engine should meet or exceed the specifications specified in Table 2-4.
• PMMA (Cell-cast acrylic): When fabricated by cell-casting, has very good optical quality and low initial cost, but surface
must be protected from the environment due to its susceptibility to attack by chemcials, mechanical stresses, and UV
light. Reasonably good impact resistance. This material can be laser-cut into odd shapes and ultrasonically welded.
• ADC (CR-39): A thermal-setting plastic produced by the cell-casting process. Excellent chemical and environmental
resistance. Quite good surface hardness, and therefore does not have to be hard-coated. Reasonably good impact
resistance. This material cannot be ultrasonically welded.
• Chemically tempered glass: Glass is a hard material which provides excellent scratch and abrasion resistance. But
unannealed glass is brittle. Increased flexibility strength with minimal optical distortion requires chemical tempering.
Glass is hard to be cut into odd shapes and cannot be ultrasonically welded.
Table 2-4
Specification
Spectral Transmittance
Thickness
Wavefront Distortion
Clear Aperture
Surface Quality
Pay extra attention to the wavefront distortion when using plastic materials. Plastic materials are not recommended for
tilted windows; colored windows are not recommended if the engine is used to scan barcodes on moving objects.

Coatings and Scratch Resistance

Scratch on the window can greatly reduce the performance of the EM50S. It is suggested to use recessed window or apply
abrasion resistant coatings to window surface.
The following introduces two commonly-used types of coatings:
• Anti-reflection coatings: Anti-reflection (AR) coatings can be applied to window surfaces to reduce reflected light from
the window back into the engine. But they are expensive and have poor abrasion/scratch resistance.
• Polysiloxane coatings: Polysiloxane coatings can be applied to plastic surfaces to increase the surfaces' abrasion and
scratch resistance.
Both tempered glass and plastic windows can be AR coated. However, it is easier and more cost-effective to put an AR
coating on the glass than on the plastic.
Description
≥
90%
0.8-2.0mm
PV maximum: 0.2λ
RMS maximum: 0.04λ
1.0mm to edges
60-20 scratch/dig
14