Abstract
The Doppler effect has well-established applications in astronomy, medicine, radar and metrology. Recently, a number of experimental demonstrations of the inverse Doppler effect have begun to appear. However, the inverse Doppler effect has never been observed on an electronically reconfigurable system with an external electromagnetic wave source at radio frequencies (RF) in experiment. Here we demonstrate an experimental observation of the inverse Doppler shift on an electronically reconfigurable RF metamaterial structure, which can exhibit anomalous dispersion, normal dispersion or a stop band, depending on an applied bias voltage. Either inverse or normal Doppler shift is realized by injecting an external RF signal into the electronically reconfigurable metamaterial, on which an electronically controllable moving reflective boundary is formed. The effective velocity of this boundary and the resulting frequency shift can be tuned over a wide range by a digital switching circuit. This work is expected to open up possibilities in applying the inverse Doppler effect in wireless communications, radar and satellite navigation.
Highlights
The Doppler effect has well-established applications in astronomy, medicine, radar and metrology
The inverse Doppler effect was observed experimentally at optical and acoustic frequencies[14,21], and was observed when magnons reflected from a moving solid object and magnonic crystal in the gigahertz frequency range[22,23]. This has motivated us to explore an experimental observation of the inverse Doppler effect with an external radio frequencies (RF) source on an electronically reconfigurable composite right-left handed transmission line (CRLH TL), which was originally proposed by Eleftheriades and Carloz et al as a convenient 1-D metamaterial structure[24,25,26,27]
The dispersion characteristic of the metamaterial, a CRLH transmission line unit, loaded with varactors, inductors and capacitors, can be tuned to provide a right-handed passband, band gap or left-handed passband by controlling the bias voltages. By this means an electronically controllable moving reflective boundary between the passband and band gap regions can be formed on the CRLH transmission line by the reflective boundary controller
Summary
The Doppler effect has well-established applications in astronomy, medicine, radar and metrology. This has motivated us to explore an experimental observation of the inverse Doppler effect with an external RF source on an electronically reconfigurable composite right-left handed transmission line (CRLH TL), which was originally proposed by Eleftheriades and Carloz et al as a convenient 1-D metamaterial structure[24,25,26,27] By loading such a transmission line with the varactors[28], we have further extended its reconfigurability, by arranging that the dispersion characteristics of each line section can be controlled electronically through a digital switching circuit (later referred to as a reflective boundary controller). Either the inverse Doppler effect or the normal Doppler effect (both frequency up-shifted and down-shifted) can be realized by applying a suitable switching mode of the controlling voltage on this CRLH transmission line
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
