Frequently Ask Questions

  • What is the frequency range studied?

    • 70 GigaHertz(GHz) to 2 TeraHertz(THz)

  • What is the technique used to make a dry air environment?

    • For analyzing the effect of water vapor on the terahertz signal, by using plastic, a tunnel is created around the transmitter and receiver and dry air is blown into the tunnel continuously to get the 0% relative humidity.

  • What is a collimating lens?

    • A collimating lens is used for producing parallel rays of light. It consists of a curved lens with some type of light source at its focus which creates collimated beams. Collimated beam is light whose rays are parallel and in ideal situation won't disperse with distance.

    A perfect collimating lens will bring parallel beams to a focus at single point and will produce collimated beams from a point source at its focus.

  • How does lens focal length depend on wavelength?

    • 1/f(λ) = [n(λ) - 1][1/R1 - 1/R2]

    Where f is the lens' focal length, λ is wavelength, n is refractive index which describes how light propagates through the medium and depends on the λ, R1 and R2 are the radii of curvature of the two surfaces of the lens.

    Also, frequency of oscillation × wavelength = speed of light.

  • What is lens divergence in a collimating lens?

    • Due to diffraction, a perfectly collimated beam cannot be created and it always have divergence. In the collimated lens, beam divergence is the angular measure of the increase in beam diameter with distance from the transmitter lens.

  • How does lens divergence in a collimating lens relate to source size?

    • The divergence of the beam in collimated lens relates to source size and can be calculated as below:

    θ = l/f

    Here θ is the divergence angle, l is half of the source size, and f is the focal length of the lens.

  • What is the channel model?

    • In order to get Matlab code for channel model, please send an email to singh@cs.pdx.edu.