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.
Large scale (i.e. <10 m) and small scale (i.e. 1 � 1� 1 cm) measurements and characterization of a scattered wireless channel with different antenna polarizations and configurations in the underground mine galleries at 60 GHz are addressed. Results show that the rough surface scattering and the gallery dimensions affect the path loss (PL) exponent and it becomes smaller than the free space. Vertically polarized antennas give a lower value of the PL exponent and root mean square (RMS) delay spread compared to the horizontal one. The small scale 3D measurement results show that the power loss of around 1-5 dB within a small scale cubical area. Results also show that the channel is less time dispersive in a wider gallery and observed a higher value of the RMS delay spread compared to a smaller gallery. The statistical results of the small scale multipath amplitude fading provide a better fit with the Rician distribution. The effects such as scattering, polarization, antenna radiation patterns, and waveguide which caused increase and decrease of the value of PL exponent and delay spread are also analysed. Results revealed that a directional narrow beam dualpolarized antenna configuration might be a good candidate in this environment.
| INTRODUCTIONNowadays, short-range wireless communications offer huge possibilities to provide seamless multimedia services. Recently, the 60 GHz band has generated significant interest because of its high data rate (i.e. >1 Gbps) capability within a short-range communication in indoor environments [1]. However, the utility of wireless communications is also essential for safety and productivity particularly in an underground mine environment [2,3]. Besides the multimedia services (voice, video, and data), wireless communications are used for geolocalization of miners and equipment, speedy rescue operation of trapped miners under debris etc. In the mining industry, the well-known Through The Earth communication systems are used for vehicle tracking, monitoring, and controlling. Other systems such as radio-frequency identification, Zigbee, wireless sensor networks, and Wi-Fi systems are also convenient to use in underground mine. The use of the Internet of Things and This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
In this paper, we are interested in evaluating the capacity of an underground mine channel in the millimeter wave band. Using a vector network analyzer (VNA) and three carefully chosen antennas, one omni and two horn antennas, we performed measurements at 40 m and 70 m levels in the CANMET mine located in Val-d'Or, Canada. This mine has tunnels with a width varying between 2.5 and 4 m and a height varying between 3 and 4 m. Our work uses data for propagation in an underground mine obtained using a different setup from what was used previously. With both uniform and optimal power spectrum allocation (UPSA, OPSA) at the transmitter side, we have computed the capacity of the channel based on the measurements. By using optimal power allocation, we take into account the fading characteristics of the channel. The results prove that the capacity gain depends on the multipath characteristics. Also, they show the pertinence of the optimal power spectrum allocation for this type of channel.
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