Abstract
We present the principle of a terahertz-wave radar and its proof-of-concept experimental verification. The radar is based on a 522 GHz resonant-tunneling-diode oscillator, whose terahertz output power can be easily modulated by superimposing the modulation signal on its bias voltage. By using one modulation frequency and measuring the time delay of the returning signal, a relative measurement of the propagation distance is possible; adding a second modulation frequency removes the ambiguity stemming from the periodicity of the modulation sine wave and allows an absolute distance measurement. We verified this measurement method experimentally and obtained a submillimeter precision, as predicted by theory.
Highlights
The terahertz radiation, defined as electromagnetic waves with frequencies roughly between0.1 and 10 THz, has already started solving real-life problems in fields such as security, safety, and product inspection
It only requires a DC bias voltage in the order of 1 V and consumes less than 100 mA to produce a coherent, continuous terahertz wave with a frequency determined by its fabrication parameters and with an output power currently just below the milliwatt order [4,5]
This structure shows a resonance peak in its current–voltage (I–V) curve, beyond which there is an interval of negative differential conductance (NDC)
Summary
The terahertz radiation, defined as electromagnetic waves with frequencies roughly between. While in research environments size, complexity, energy consumption, and equipment price are lesser problems, for a commercially successful application of the terahertz waves it is often critical that systems are compact, economic, robust, and inexpensive In this context, the resonant-tunneling diode (RTD) is a terahertz-wave source on a chip [3], with a size much below one cubic millimeter, working at room temperature, and as such is expected to find its way in future terahertz applications. In a product inspection scenario, for instance, three-dimensional measurement of the target may reveal whether or not dents, swellings, or other deformations in a surface are within specifications For such cases, a terahertz-wave radar functionality is useful. In the the first first step, step, phase phase delays delays measured measured at at two two modulation modulation frequencies frequencies are are used used to to determine a rough, but absolute, value of the propagation time difference.
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