Puzzling Low-Temperature Behavior of the Van Der Waals Friction Force between Metallic Plates in Relative Motion

This paper presents the results of calculating the van der Waals friction force (dissipative fluctuation-electromagnetic force) between metallic (Au) plates in relative motion at temperatures close to 1 K. The stopping tangential force arises between moving plates along with the usual Casimir force of attraction, which has been routinely measured with high precision over the past two decades. At room temperatures, the former force is 10 orders of magnitude less than the latter, but at temperatures T<50 K, friction increases sharply. The calculations have been carried out in the framework of the Levin-Polevoi-Rytov fluctuation electromagnetic theory. For metallic plates with perfect crystal lattices and without defects, van der Waals friction force is shown to increase with decreasing temperature as T-4. In the presence of residual resistance ρ0 of the metal, a plateau is formed on the temperature dependence of the friction force at T→0 with a height proportional to ρ0-0.8. Another important finding is the weak force-distance dependence ~a-q (with q<1). The absolute values of the friction forces are achievable for measurements in AFM-based experiments.

Causes of Removal of metallic hardware employed in oral and maxillofacial surgery - A cross sectional survey.

Objective: This study was conducted to evaluate the causes of removal of titanium bone plates used routinely in maxillofacial region. Study Design: Cross Sectional Survey. Setting: Department of Oral & Maxillofacial Surgery, Armed Forces Institute of Dentistry (AFID). Period: January 2016 to June 2018. Material & Methods: A total of 60 patients previously operated in maxillofacial surgery department with open reduction and internal fixation with tru-dynamic titanium plating system in Operation Theater, who reported with complaints due to metallic hardware were included in the study. Data was collected regarding age, gender, time between plate insertion and removal, cause and site of plate removal was also recorded for each patient. Data was analyzed using SPSS 23.0 version. Results: During the study period, 60 patients underwent titanium plate removal out of which 34 were male and 26 were females. Most common cause of plate removal was infection followed by non-union. Majority of plates (43.3%) were removed within 6 to 12 months of insertion. Mandible was found to be the most common site of plate removal (60%). Gender was significantly associated with causes while age was associated with cause, site and duration of removing the metallic plates (P-Value, < 0.05). Conclusion: Removal of symptomatic titanium plates is likely to occur within first year of insertion. Infection was identified as the most common cause for removing the metallic plates.

Radiation Pattern Reconfigurable Antenna for IoT Devices

Based on the characteristic mode theory, a versatile radiation pattern reconfigurable antenna is proposed. The analysis starts from two parallel metallic plates with the same and different dimensions. By means of two PIN diodes, the size of one of the parallel metallic plates can be modified and consequently the behavior of the radiation pattern can be switched between bidirectional and unidirectional radiation patterns. Moreover, a SPDT switch is used to adjust the frequency and match the input impedance. The reconfigurable antenna prototype has been assembled and tested, and a good agreement between simulated and measured results is obtained at 2.5 GHz band which fits the IoT applications.

A MIMO Antenna with Enhanced Gain using Metasurface

This paper proposes a new metasurface to improve gain for dipole antenna. The antenna includes two sets of two elements (1 x 2), the integrated J shaped baluns, five metasurface cells (each metasurface cell consists of 5 periodic metallic plates printed on a thin low-cost FR4 substrate) for four antenna elements and the antenna is supplied by two T-junction power dividers. The metasurface is designed to operate as reflection surface. The antenna is designed based on RT5880 and witnesses an overall size of 140 x 37 x 35.075 mm3 (2.7λ x 0.71λ x 0.67λ at 5.8 GHz), an isolation of approximately 28 dB, a peak gain of 9.5 dBi, and a radiation efficiency of 84%.

A note on the cavitation phenomenon in metallic plates perforated by sharp-nosed rigid projectiles

We explore the perforation process of metallic plates impacted by rigid sharp-nosed projectiles at high velocities. In particular, we are looking at the diameters of the penetration hole in the plates through a series of 2D numerical simulations, in order to check for the occurrence of cavitation in finite-thickness plates. This phenomenon has not been observed by previous workers and we were looking for its effect on the perforation process. Our simulations show that for every projectile/plate pair there is a certain impact velocity which marks the onset of cavitation. These threshold velocities depend on the normalized thickness of the plates, as well as on their effective strength. Our simulations are supported by the results from perforation tests on plates made of a low strength lead-antimony alloy. The main conclusion from our work is that analytical models for plate perforation should take into account the cavitation phenomenon, especially for high velocity impacts.