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Ultra-wideband (UWB) communications have gained popularity in recent years for being able to provide distance measurements and localization with high accuracy, which can enhance the capabilities of devices in the Internet of Things (IoT). Since energy efficiency is of utmost concern in such applications, in this work we evaluate the power and energy consumption, distance measurements, and localization performance of two types of UWB physical interfaces (PHYs), which use either a low- or high-rate pulse repetition (LRP and HRP, respectively). The evaluation is done through measurements acquired in identical conditions, which is crucial in order to have a fair comparison between the devices. The LRP devices that we tested have the same ranging and localization performance, but ten times (10x) lower power consumption, 6x lower energy consumption per distance measurement, and at least 8x higher coverage than the HRP devices. Therefore, UWB LRP devices can offer high-accuracy ranging and localization even to ultra-low-power devices in the IoT. We performed measurements in typical LOS and NLOS scenarios and propose theoretical models for the distance errors obtained in these situations. The models can be used to simulate realistic building deployments and we illustrate such an example. This paper, therefore, provides a comprehensive overview of the energy demands, ranging characteristics, and localization performance of state-of-the-art UWB devices., Comment: Accepted at the IEEE Internet of Things Journal (IoT-J)

The charge doped into a semiconductor in a field effect transistor (FET) is generally confined to the interface of the semiconductor. A planar step at the interface causes a potential drop due to the strong electric field of the FET, which in turn is screened by the doped carriers. We analyze the dipolar electronic structure of a single step in the Thomas-Fermi approximation and find that the transmission coefficient through the step is exponentially suppressed by the electric field and the induced carrier density as well as by the step height. In addition, the field enhancement at the step edge can facilitate the electric breakthrough of the insulating layer. We suggest that these two effects may lead to severe problems when engineering FET devices with very high doping. On the other hand steps can give rise to interesting physics in superconducting FETs by forming weak links and potentially creating atomic size Josephson junctions., Comment: 6 pages, 4 figures, submitted to J. Appl. Phys

We investigate the possibility of doping C60 crystals by applying a strong electric field. For an accurate description of a C60 field-effect device we introduce a multipole expansion of the field, the response of the C60 molecules, and the Stark splitting of the molecular levels. The relevant response coefficients and splittings are calculated ab initio for several high symmetry orientations. Using a group theoretic analysis we extend these results to arbitrary orientations of the C60 molecules with respect to the external field. We find that, surprisingly, for the highest occupied (HOMO) and the lowest unoccupied molecular orbital (LUMO), respectively, the two leading multipole components lift the degeneracy of the molecular level in the same way. Moreover the relative signs of the splittings turn out to be such that the splittings add up when the external field induces charge into the respective level. That means that when charge carriers are put into a level, its electronic structure is strongly modified. Therefore, in general, in C60 field-effect devices charge is not simply put into otherwise unchanged bands, so already because of this their physics should be quite different from that of the alkali-doped fullerenes., Comment: 14 pages, 13 figures, submitted to PRB