Peter Vanveerdeghem

Compact Personal Distributed Wearable Exposimeter

A compact wearable personal distributed exposimeter (PDE) is proposed, sensing the power density of incident radio frequency (RF) fields on the body of a human. In contrast to current commercial exposimeters, our PDE, being composed of multiple compact personal wearable RF exposimeter sensor modules, minimizes uncertainties caused by the proximity of the body, the specific antenna used, and the exact position of the exposimeter. For unobtrusive deployment inside a jacket, each individual exposimeter sensor module is specifically implemented on the feedplane of a textile patch antenna. The new wearable sensor modules high-resolution logarithmic detector logs RF signal levels. Next, on-board flash memory records minimum, maximum, and average exposure data over a time span of more than two weeks, at a one-second sample period. Sample-level synchronization of each individual exposimeter sensor module enables combining of measurements collected by different nodes. The system is first calibrated in an anechoic chamber, and then compared with a commercially available single-unit exposimeter. Next, the PDE is validated in realistic conditions, by measuring the average RF power density on a human during a walk in an urban environment and comparing the results to spectrum analyzer measurements with a calibrated antenna.

Synchronous Wearable Wireless Body Sensor Network Composed of Autonomous Textile Nodes

A novel, fully-autonomous, wearable, wireless sensor network is presented, where each flexible textile node performs cooperative synchronous acquisition and distributed event detection. Computationally efficient situational-awareness algorithms are implemented on the low-power microcontroller present on each flexible node. The detected events are wirelessly transmitted to a base station, directly, as well as forwarded by other on-body nodes. For each node, a dual-polarized textile patch antenna serves as a platform for the flexible electronic circuitry. Therefore, the system is particularly suitable for comfortable and unobtrusive integration into garments. In the meantime, polarization diversity can be exploited to improve the reliability and energy-efficiency of the wireless transmission. Extensive experiments in realistic conditions have demonstrated that this new autonomous, body-centric, textile-antenna, wireless sensor network is able to correctly detect different operating conditions of a firefighter during an intervention. By relying on four network nodes integrated into the protective garment, this functionality is implemented locally, on the body, and in real time. In addition, the received sensor data are reliably transferred to a central access point at the command post, for more detailed and more comprehensive real-time visualization. This information provides coordinators and commanders with situational awareness of the entire rescue operation. A statistical analysis of measured on-body node-to-node, as well as off-body person-to-person channels is included, confirming the reliability of the communication system.

Whole-Body Averaged Specific Absorption Rate Estimation Using a Personal, Distributed Exposimeter

For the first time, a body area network (BAN) is used to construct a personal, distributed exposimeter (PDE), which can measure the whole-body averaged specific absorption rate (SAR_wb) in real life, together with the incident power density (S_inc). The BAN consists of four textile antennas with integrated radio frequency receiver nodes tuned to the Global System for Mobile Communications (GSM) 900 downlink band. Calibration measurements at 942.5 MHz, using a human subject, are performed in an anechoic chamber. These are combined with numerical simulations to estimate both SAR_wb and Sinc from the averaged received power on the PDE. The PDE has 50% prediction intervals of 3 dB on Sinc and 3.3 dB on the SAR_wb, caused by the presence of the human body, whereas the best single textile antenna in our measurements exhibits PI₅₀s of 7.1 dB on S_inc and 5 dB on SAR_wb. Measurements using the PDE are carried out in Ghent, Belgium, during which a median S_inc = 47 μW/m² and SAR_wb = 0.25 μW/kg are measured.

A Personal, Distributed Exposimeter: Procedure for Design, Calibration, Validation, and Application.

This paper describes, for the first time, the procedure for the full design, calibration, uncertainty analysis, and practical application of a personal, distributed exposimeter (PDE) for the detection of personal exposure in the Global System for Mobile Communications (GSM) downlink (DL) band around 900 MHz (GSM 900 DL). The PDE is a sensor that consists of several body-worn antennas. The on-body location of these antennas is investigated using numerical simulations and calibration measurements in an anechoic chamber. The calibration measurements and the simulations result in a design (or on-body setup) of the PDE. This is used for validation measurements and indoor radio frequency (RF) exposure measurements in Ghent, Belgium. The main achievements of this paper are: first, the demonstration, using both measurements and simulations, that a PDE consisting of multiple on-body textile antennas will have a lower measurement uncertainty for personal RF exposure than existing on-body sensors; second, a validation of the PDE, which proves that the device correctly estimates the incident power densities; and third, a demonstration of the usability of the PDE for real exposure assessment measurements. To this aim, the validated PDE is used for indoor measurements in a residential building in Ghent, Belgium, which yield an average incident power density of 0.018 mW/m².

Energy-efficient off-body communication nodes with receive diversity

Off-body wireless communication applications range from fall-detection systems for the elderly to monitoring networks for rescue workers. Further development of practical body-worn systems requires compact, low-cost and low-power battery-powered equipment. A versatile wearable network node offering all these features, including a powerful microcontroller for data processing and additional memory for local data logging was designed and implemented. The node allows receive diversity, mitigating the negative impact of fading, which is typically present in indoor propagation environments. Channel measurements are performed for an indoor Non Line-of-Sight communication between two nodes. Mobile-to-base-station as well as mobile-to-mobile links are considered. A statistical analysis of the performance determines outage probability with and without receiver diversity for both link types, showing a significant diversity gain in all cases. Correlation properties, level crossing rate and average fade duration are also determined.

Wireless power transfer in a body-centric setup: Recent advances and remaining challenges

In the recent past, wireless power transfer (WPT) has attracted a lot of research interest as enabling technology for wireless sensors networks, within the context of the Internet of Things, and to finally achieve fully autonomous electronic devices. A setup where wirelessly powered electronic devices are deployed on the human body is both very appealing and very challenging. Indeed, autonomous sensors that are unobtrusively integrated into the wearers jacket may monitor body parameters and the users environment while remaining invisible to the mobile user as well as to other persons in his/her proximity. Unfortunately, the body-centric environment is one of the hardest configurations to implement such a wireless transfer, given the movement of the wearers and the potential health hazards associated to the exposure to radiofrequency (RF) fields.