Wireless signal transmission through non-metallic pipes with transmission gain

We study the propagation of electromagnetic waves through non-metallic pipes with diameters D of the order of the wavelength λ. Comparative measurements in clean straight pipes reveal transmission gains relative to free-space propagation, for values D/λ ≈ 5-10, which amount up to 25 dB. The wave-guiding effect depends on the boundary conditions, and is partially suppressed under conditions typical of sewerage pipes, which are soiled, wet, and rough. We present a phenomenological model that accounts for the multiple reflections along the propagation path, and find satisfactory agreement with experimental data. Based on our empirical studies, which extend knowledge available in literature, we aim at maximizing the achievable range of wireless signal transmission for pipe-cleaning devices with real-time inspection capability by proper choice of carrier frequency and antenna design.