The technology for mechanically compensating Lorentz Force detuning in superconducting RF cavities has already been developed at DESY. One technique is based on commercial piezoelectric actuators and was successfully demonstrated on TESLA cavities [1]. Piezo actuators for fast tuners can operate in a frequency range up to several kHz; however, it is very important to maintain a constant static force (preload) on the piezo actuator in the range of 10 to 50% of its specified blocking force. Determining the preload force during cool-down, warm-up, or re-tuning of the cavity is difficult without instrumentation, and exceeding the specified range can permanently damage the piezo stack. A technique based on strain gauge technology for superconducting magnets has been applied to fast tuners for monitoring the preload on the piezoelectric assembly. The design and testing of piezo actuator preload sensor technology is discussed. Results from measurements of preload sensors installed on the tuner of the Capture Cavity II (CCII)[2] tested at FNAL are presented. These results include measurements during cool-down, warmup, and cavity tuning along with dynamic Lorentz force compensation.
The 60 GHz frequency band is identified as a suitable band for Gbps speed wireless communication in an Underground mine due to its high antenna directivity and high signal attenuation. However, the rough mine surface and the 5 mm wavelength may produce rich scattering phenomenon of multipath signals. To characterize the channel and more insight into the scattering, the angular dispersion measurements are conducted in different mine gallery depths and dimensions. The scattering is analyzed by the angle of arrivals of the incoming paths at the receiver, which is characterized by the statistical parameters of the multipath shape factors. The results of the multipath shape factor are explained and show that at around 3 m link distance, the incoming paths are mostly in two or three directions within a resolution angle of around between ±30 • and ±40 • . The statistical distribution of the multipath angle of arrivals follows a Gaussian probability distribution. The results also show that the angular spreads of multipath are proportional to the gallery dimensions and inversely proportional to the link distances.INDEX TERMS 60 GHz wideband channel measurements, underground mine, angle of arrivals, scattering.
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