Oliver Lauer

Combining near‐ and far‐field exposure for an organ‐specific and whole‐body RF‐EMF proxy for epidemiological research: A reference case

A framework for the combination of near-field (NF) and far-field (FF) radio frequency electromagnetic exposure sources to the average organ and whole-body specific absorption rates (SARs) is presented. As a reference case, values based on numerically derived SARs for whole-body and individual organs and tissues are combined with realistic exposure data, which have been collected using personal exposure meters during the Swiss Qualifex study. The framework presented can be applied to any study region where exposure data is collected by appropriate measurement equipment. Based on results derived from the data for the region of Basel, Switzerland, the relative importance of NF and FF sources to the personal exposure is examined for three different study groups. The results show that a 24-h whole-body averaged exposure of a typical mobile phone user is dominated by the use of his or her own mobile phone when a Global System for Mobile Communications (GSM) 900 or GSM 1800 phone is used. If only Universal Mobile Telecommunications System (UMTS) phones are used, the user would experience a lower exposure level on average caused by the lower average output power of UMTS phones. Data presented clearly indicate the necessity of collecting band-selective exposure data in epidemiological studies related to electromagnetic fields.

Measurement setup and protocol for characterizing and testing radio frequency personal exposure meters

Body-worn radiofrequency electromagnetic field (RF-EMF) personal exposure meters (PEMs) have been increasingly used for exposure assessment in epidemiological research. However, little research on the measurement accuracy of these devices is available. In this article a novel measurement setup and a measurement protocol are presented for characterizing and testing PEMs. The whole setup and procedure is tested using two EME SPY 120 devices. The performance of the PEM was analyzed for absolute measurements in an anechoic chamber. Modulated signals representing the different services as real signals generated by appropriate testers were used. Measurement results were evaluated with respect to a root mean square detector. We found that measurement accuracy depends strongly on the carrier frequency and also on the number of occupied time slots for Time Division Multiple Access (TDMA)-based services. Thus, correction factors can only be derived if the distribution of the network configuration over the measurement time for all measurement points is available. As a result of the simplicity of the measurement setup and the straightforward measurement protocol, the possibility of fast validation leads to a higher accuracy in the characterization and testing of PEMs.

Characterization of the electromagnetic environment in a hospital

The electromagnetic environment in a hospital is characterized in order to evaluate the conditions for failsafe operation of critical electronic equipment. Field strengths within the University Hospital Zurich were measured at more than 60 different locations in the frequency range from 9 kHz up to 10 GHz. To account for variations in both, time and location, dasiastationary short termpsila and dasiastationary long termpsila measurements over 24 h were carried out. The measurement uncertainty of the measurement equipment, calibration and measurement procedure is assessed. Measurement results are evaluated with respect to given immunity levels (EMC) and in-band interferences (EMI). The ISM band features a noise power density of -32 dBm/MHz while for ultra wide band (UWB) there are different sub-bands with a maximum noise power density of less than -81 dBm/MHz. This suggests that communication in the UWB band requires significantly lower power levels than communication in the ISM band for equal dynamic ranges of the radio links.

Interference characterization and UWB channel measurements for wireless intensive care patient monitoring

The electromagnetic environment in a hospital is characterized by means of a measurement campaign. This serves as a basis for the evaluation of best-suited future technologies to be used for wireless patient monitoring, where highest quality of service is required for sensors recording vital data. Results show that the UWB band features equal dynamic ranges as the ISM band but allows operation at a significantly lower power level, which is crucial for Body Area Networks where low power consumption is highly required. Furthermore UWB channel measurements are done in order to specify main propagation paths for scenarios with a volunteer in a bed. Multi-path propagation with reflections at the ceiling and the bedside monitor could be identified as main propagation paths beside the Line-of-Sight link. The impact of these propagation paths on the system performance were evaluated in system simulations using a non-coherent UWB system.

Using impulse Radio UWB for medical monitoring sensor networks: a performance evaluation

A compact testbed for real-time UWB performance evaluation in terms of un-coded bit-error rate is presented. Both the transmitter and the receiver are realized in form of a small PCB. This testbed represents a very versatile tool for the evaluation of IR-UWB as physical layer for various wireless technologies. It operates in the frequency range from 3.1-5.0 GHz with a maximum data rate of 10 MBit/s. Several measurements involving the influence of the human body are performed in a laboratory room in order to get a realistic picture of the performance and reliability that can be expected using IR-UWB for body area networks. In this paper the focus is set on medical monitoring applications. A body area sensor network was emulated and showed good connectivity for all tested scenarios. At a data rate of 10 Mbit/s the measured bit-error rate was better than 10-5 for every node operating in the network.

Poster: A novel measurement system for environmental exposure monitoring

The realization of a prototype for a novel band-selective personal exposure assessment system is presented. The new system combines three features that are crucial for Non-Ionising-Radiation (NIR) monitoring, namely the measurement of power levels of selected near field sources, e.g. internal Wi-Fi module, field levels of far field sources and global position measurements. For this, it uses the features of a common smartphone by an additional software application and an external exposimeter module. The system can be either used for environmental monitoring of field levels or used in future epidemiological studies. Such an approach has the potential for huge NIR studies, featuring representative results with a higher measurement accuracy and an increased functionality compared to current systems.

Calibration measurement setup for band-selective personal exposure meters

In this paper a calibration measurement setup for band-selective personal exposure meters is presented. The equipment and the methods of the measurement procedure are described together with the uncertainty assessment of the measurement equipment, the calibration and the measurement procedure. The average measurement error for the reference measurement is ± 0.32 dB, while the expanded uncertainty with a confidence interval of 95% is calculated to 2.5 dB. Furthermore a straight forward calibration method is described and tested using the EME SPY 120 device from Antenessa. Up to seven different measurements must be performed for a full characterization of personal exposure meters. The presented measurement setup leads to a higher accuracy of the calibration and the achieved results will allow for an improved exposure assessment in experimental and epidemiological studies.

Specification of the ADC interface for an interference robust UWB impulse radio

In this paper, the Analog to Digital Converter interface of a pulse based UWB system operating in the presence of strong interferer is specified. The minimum number of quantization bits is determined for interfering signals caused either by in-band or out-of-band service signals and for different front-end realizations. While for an undisturbed UWB communication link 4 quantization bits are sufficient, up to 14 bits are necessary for an UWB short range communication distance from 3–15 meters for a ‘worst-case’ interference scenario. Results show that a non-linear Analog to Digital Converter approach can significantly reduce the number of required bits from 14 to 8 bits. Fast Fourier Transformation processing methods have also been investigated in terms of processing load and influence on receiver sensitivity. We show that, with a moderate 32-points Fast Fourier Transformation resolution that enables simple serial processing, we can implement efficient interference notch filtering with negligible Bit Error Rate degradation of less than 0.5 dB at a Bit Error Rate of 10−3.

Poster: Impulse radio UWB testbed for indoor and sensor network applications

A compact testbed for real-time Ultra-Wideband (UWB) wireless system performance evaluation in terms of un-coded bit-error rate is presented. Both the transmitter and the receiver are realized in form of a small PCB. The system operates in the frequency range from 3.1--5.0 GHz with a maximum data rate of 10 MBit/s. By means of two examples this poster illustrates possible applications of the testbed. In the first measurement presented in the poster, the performance of different UWB antennas is compared. In the second example, measurements involving the influence of the human body are performed in order to evaluate the real-world performance of Impulse radio UWB (IR-UWB) communication systems for body area and sensor network applications.

Front-End linearity and filter requirements for interference robust UWB systems

This paper presents the requirements on the preselect-filter for UWB applications for different Front-End linearities and interference scenarios. A procedure to calculate the minimum out of band attenuation was developed in order to achieve a high system performance in presence of interferer. A filter diagram is proposed for a robust UWB communication. Results show which UWB-bands are affected by narrow-band systems and how the receiver linearity can be traded off against preselect-filter requirements. The frequency band between 7.7 and 8.2 GHz could be identified as less influenced by intermodulation products. Therefore this band is highly recommended for communication of sensitive data.