Abstract
Microwave technology plays a more important role in modern industrial sensing applications. Pushed by the significant progress in monolithic microwave integrated circuit technology over the past decades, complex sensing systems operating in the microwave and even millimeter-wave range are available for reasonable costs combined with exquisite performance. In the context of industrial sensing, this stimulates new approaches for metrology based on microwave technology. An old measurement principle nearly forgotten over the years has recently gained more and more attention in both academia and industry: the six-port interferometer. This paper reviews the basic concept, investigates promising applications in remote, as well as contact-based sensing and compares the system with state-of-the-art metrology. The significant advantages will be discussed just as the limitations of the six-port architecture. Particular attention will be paid to impairment effects and non-ideal behavior, as well as compensation and linearization concepts. It will be shown that in application fields, like remote distance sensing, precise alignment measurements, as well as interferometrically-evaluated mechanical strain analysis, the six-port architecture delivers extraordinary measurement results combined with high measurement data update rates for reasonable system costs. This makes the six-port architecture a promising candidate for industrial metrology.
Highlights
Industry and manufacturing technology is experiencing a revolution these days
A portion S1 of the oscillator signal is coupled by a radar coupler, e.g., a quadrature hybrid, to one input port of the six-port as a phase reference; the rest of S local oscillator (LO) is transmitted to an antenna and radiated
Instead of calculating a time-consuming fast Fourier transform (FFT) on an embedded device, the sensor’s response signal is processed already in the analog domain based on the concept of instantaneous frequency measurement [50]: by using a delay line of known length, the challenge of a precise frequency determination is mapped to a phase measurement that can be quickly evaluated by the six-port network
Summary
Industry and manufacturing technology is experiencing a revolution these days. The demand for products with a high degree of individuality leading to a huge variety of configurations is increasing more and more. The vision is to change from automated production towards intelligent production by adding cyber physical functionality to the process steps, i.e., the complete manufacturing process will be self-organizing and flexibly adaptive to the current conditions In this context, the digitalization of all production processes interacting and exchanging information among each other, as well as with the work pieces is self-evident. Precise remote metrology for the context sensitive and adaptive control of the robot is essential In this framework, remote and contact-free sensing of distances, angles or motions plays a key role and pushes new sensing approaches, which complement existing sensor technologies to cover all potential measurement tasks arising from the mentioned vision.
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