People-Sensing Spatial Characteristics of RF Sensor Networks

An "RF sensor" network can monitor RSS values on links in the network and perform device-free localization, i.e., locating a person or object moving in the area in which the network is deployed. This paper provides a statistical model for the RSS variance as a function of the person's position w.r.t. the transmitter (TX) and receiver (RX). We show that the ensemble mean of the RSS variance has an approximately linear relationship with the expected total affected power (ETAP). We then use analysis to derive approximate expressions for the ETAP as a function of the person's position, for both scattering and reflection. Counterintuitively, we show that reflection, not scattering, causes the RSS variance contours to be shaped like Cassini ovals. Experimental tests reported here and in past literature are shown to validate the analysis

Joint Ultra-wideband and Signal Strength-based Through-building Tracking for Tactical Operations

Accurate device free localization (DFL) based on received signal strength (RSS) measurements requires placement of radio transceivers on all sides of the target area. Accuracy degrades dramatically if sensors do not surround the area. However, law enforcement officers sometimes face situations where it is not possible or practical to place sensors on all sides of the target room or building. For example, for an armed subject barricaded in a motel room, police may be able to place sensors in adjacent rooms, but not in front of the room, where the subject would see them. In this paper, we show that using two ultra-wideband (UWB) impulse radios, in addition to multiple RSS sensors, improves the localization accuracy, particularly on the axis where no sensors are placed (which we call the x-axis). We introduce three methods for combining the RSS and UWB data. By using UWB radios together with RSS sensors, it is still possible to localize a person through walls even when the devices are placed only on two sides of the target area. Including the data from the UWB radios can reduce the localization area of uncertainty by more than 60%.Comment: 9 pages, conference submissio

Dial It In: Rotating RF Sensors to Enhance Radio Tomography

A radio tomographic imaging (RTI) system uses the received signal strength (RSS) measured by RF sensors in a static wireless network to localize people in the deployment area, without having them to carry or wear an electronic device. This paper addresses the fact that small-scale changes in the position and orientation of the antenna of each RF sensor can dramatically affect imaging and localization performance of an RTI system. However, the best placement for a sensor is unknown at the time of deployment. Improving performance in a deployed RTI system requires the deployer to iteratively "guess-and-retest", i.e., pick a sensor to move and then re-run a calibration experiment to determine if the localization performance had improved or degraded. We present an RTI system of servo-nodes, RF sensors equipped with servo motors which autonomously "dial it in", i.e., change position and orientation to optimize the RSS on links of the network. By doing so, the localization accuracy of the RTI system is quickly improved, without requiring any calibration experiment from the deployer. Experiments conducted in three indoor environments demonstrate that the servo-nodes system reduces localization error on average by 32% compared to a standard RTI system composed of static RF sensors.Comment: 9 page

Cytotoxicity Of Orthodontic Temporary Anchorage Devices In Vitro

Introduction: Cytotoxicity is a major concern in the clinical application of dental materials including Temporary Anchorage Devices (TADs). The purpose of this study was to test the cytotoxicity of four of the commercially available brands of TADs (Aarhus, American Orthodontics; Dual top, RMO; Vector TAS, ORMCO; Unitek TAD, 3M UNITEK). Materials and Methods: Twenty-four (six from each brand) TADs were individually incubated in complete cell culture medium and shaken at a rate of 1.5 rpm at 37ºC for 30 days to generate the conditioned medium (CM). To test the cytotoxicity, human periodontal ligament fibroblasts (hPDLF) were exposed to the CM for 24 hours. As endpoints, morphological changes were observed along with cell death and damage which were quantified by MTT and LDH assays, followed by statistical analysis of oneway ANOVA with Bonferroni adjustment. Results: No morphological changes were found in any of the four types of TADs compared to the control cells. LDH assay showed that none of the tested TADs caused significant cell death after CM treatment in contrast to the positive control (P \u3e 0.05). No significant intragroup differences were found between any of the four brands of TADs (P \u3e 0.05). MTT assay showed similar results as for the LDH assay, except for a marginally significant increase of MTT release found in the TADs from 3M UNITEK compared to the negative control (P = 0.047). Conclusions: According to the ISO10993:5 standards, none of the tested TADs exhibited statistically significant cytotoxicity, suggesting their safe clinical application