Sebastian Rickers

Leadless pacing using induction technology: impact of pulse shape and geometric factors on pacing efficiency

AIMS Leadless pacing can be done by transmitting energy by an alternating magnetic field from a subcutaneous transmitter unit (TU) to an endocardial receiver unit (RU). Safety and energy consumption are key issues that determine the clinical feasibility of this new technique. The aims of the study were (i) to evaluate the stimulation characteristics of the non-rectangular pacing pulses induced by the alternating magnetic field, (ii) to determine the extent and impact of RU movement caused by the beating heart, and (iii) to evaluate the influence of the relative position between TU and RU on pacing efficiency and energy consumption. METHODS AND RESULTS In the first step pacing efficiency and energy consumption for predefined positions were determined by bench testing. Subsequently, in a goat at five different ventricular sites (three in the right ventricle, two in the left ventricle) pacing thresholds using non-rectangular induction pulses were compared with conventional pulses. Relative position, defined by parallel distance, radial distance, and angulation between TU and RU, were determined in vivo by X-ray and an inclination angle measurement system. Bench testing showed that by magnetic induction for every alignment between TU and RU appropriate pulses can be produced up to a distance of 100 mm. In the animal experiment pacing thresholds were similar for non-rectangular pulses as compared with conventional pulse shapes. In all five positions with distances between 62 and 102 mm effective pacing was obtained in vivo. Variations in distance, displacement and angle caused by the beating heart did not cause loss of capture. At pacing threshold energy consumptions between 0.28 and 5.36 mJ were measured. Major determinants of energy consumption were distance and pacing threshold. CONCLUSION For any given RU position up to a distance of 100 mm reliable pacing using induction can be obtained. In anatomically crucial distances, up to 60 mm energy consumption is within a reasonable range.

Wireless Power Transfer H-Bridge design with serial resonance and varying supply voltage

In this manuscript the authors discuss the issues of designing and implementing an H-Bridge circuit with respect to small switching losses, minimal hardware afford and maximal flexibility of excitation and control. The H-Bridge is targeted for a biomedical Wireless Power Transfer (WPT) application, where the receiver (RX) is small compared to the transmitter (TX) and, thus, negligible. Resonance is applied on the TX side, while the input voltage to the H-Bridge is able to vary in the range of 3V to 28V depending on a flexible relation between the TX and RX. This causes effects to the design and the gate drivers of the H-Bridge. An H-Bridge design is proposed, which includes the use of an n-channel and p-channel Metal-Oxide Semiconductor Field-Effect Transistor (MOSFET) for a direct addressing of gates with a microcontroller (μC). In addition, the switching losses are lowered by the introduction of choke inductors and non-overlapping time delayed driving signals. Furthermore, the proposed solution has been verified, since significant advancements compared to state-of-the-art H-Bridge designs can be shown.

Java implementation of localization and tracking application based on HDR-UWB platform

In recent years extensive research was carried out in order to develop applications for the Ultra-Wideband (UWB) technology and to resolve the practical challenges in implementing an efficient UWB communication system utilizing the UWB impulse radio for precision localization. ToA (Time of Arrival) or TDoA (Time Difference of Arrival) of ranging frame are widely used because ToA and TDoA provide high accuracy due to the high time resolution with high bandwidth of IR-UWB (Impulse Radio - UWB) signal. HDR-UWB (High Data Rate -UWB) uses MB-OFDM (Multi Band - Orthogonal Frequency Division Multiplexing) to transmit signals, which can reach a data rate of 200 Mbit/s. In this paper a Java implementation of an active LT (Localization and Tracking) method based on a HDR-UWB platform is investigated. The hardware is composed of three UWB anchors, one UWB tag and one UWB location coordinator, which is connected to a PC (Personal Computer) or a PDA (Personal Digital Assistant). The Java program, which is hosted on the PC or PDA, is used to instruct the UWB coordinator to send and receive the UWB ranging frame and localize the tag. ToA is used as a ranging parameter in this work to measure the distance between the used UWB anchors and the UWB tag. The most important aspect is to reduce the jitter of ToA caused by CPU processing and the clock drift between UWB anchors and UWB tag. In this paper a 3-way ranging mechanism to minimize the clock drift is deployed. In addition the use of the JPCAP (Java Package for CAPturing) library in Java reduces the jitter of the ToA.

Multi data rate signaling based on IEEE 802.15.4

The IEEE 802.15.4 standard was brought up for the use in wireless personal area networks (WPANs) and is widely known as ZigBee. It employs spread spectrum techniques to obtain a robust transmission at comparatively low data rates of up to 250 kbit/s. In order to better match a certain transmission environment, different spreading factors could be used to obtain additional data rate modes. This approach appears to be a feasible extension to IEEE 802.15.4 allowing the coverage of a wider range of the signal to interference and noise ratio (SINR). However, a signaling scheme must be added to distinguish the additional modes from the native ZigBee mode. This scheme should also allow the operation of extended devices without interfering native ZigBee devices. Based on the structure of an IEEE 802.15.4 frame a method is presented that will allow extending the specified frame structure to a multi data rate system without interfering IEEE 802.15.4 compliant devices.

Receiver coil parameter optimization process for the efficiency of an implantable Inductive Power Transfer system

In order to develop a high power transmission efficiency for an Inductive Power Transfer (IPT) system especially the parameters of the receiver (RX) coil have to be analyzed in detail. This becomes essential, when the RX coil is part of a medical implant and dramatically limited in size. The parameters, which completely describe a coil, are its inductance and ohmic losses. Both values are just dependent on a few geometrical and material parameters, i.e. filling factor, diameter of the wire, outer radius, inner radius and length of the coil, as well as the length and the initial permeability of the utilized ferrite rod. This study shows that, the two latter parameters have both to be maximal to reach the highest efficiency of the system. The effect of the remaining parameters on the system efficiency in a predefined parameters range can be summarized as follows: optimal points for the inner and outer radius as well as for the length of the coil have been found, while for the filling factor an analytical expression has been found to show that it has to be maximized to get the best efficiency. Finally, the wire diameter that was found to be the most critical parameter can be optimized for a given set of parameters by calculating an optimal value for the ohmic losses of the RX coil.

Cooperative transmitter structure for improving efficiency in wireless power transfer

Wireless power transfer (WPT) is widely used in portable devices with the advantage of flexibility and conveniences. This paper aims to design a cube transmitter structure, which generates a spatially focused magnetic field providing effective power transfer. The phase shift in multiple coils has been optimized for maximum power transfer efficiency and free positioning in the charging spatial domain. The performance of out-phase multiple coil cube (OPMC) antenna has been compared to that of in-phase multiple coil cube (IPMC) transmitter and traditional single coil. Simulation results show that the OPMC is better and provides higher efficiency wherever the receiver is located inside the cubical region above the cube base.

Impact of frequency offsets on zero crossing demodulation based receivers

In practical communication systems, frequency offsets between transmitters and receivers cannot be avoided. Both transmitter and receiver require local clocks which are usually derived from independent crystal oscillators. Typical low-cost crystals show a relative frequency tolerance of 20 ppm. Though devices with less tolerance are available, they are too expensive for most mass market devices. It is rather desirable to attempt to estimate and correct the frequency offset at the receiver side, preferably in digital domain. For regular sampling based receivers, such algorithms can be considered well-known [1]. However, for irregular sampling schemes such as zero-crossing demodulation, neither the impact on the receiver performance nor ways of estimating and correcting frequency offsets are widely known. This manuscript is a first attempt to close this gap.

Postringing analysis of an inductive power transfer system to determine the coupling factor

Inductive Power Transfer (IPT) techniques are gaining more and more interest in wireless power systems. The knowledge of the coupling factor of transmitter (TX) and receiver (RX) coil is a crucial, but mostly during operation not available parameter for such systems. In this manuscript a novel method to determine the coupling factor by measuring the self-resonating frequency of the postringing signal in the TX is presented. The postringing signal occurs in bridge converter topologies, when the excitation is stopped. The cause of the postringing signal can be found in the free-wheeling diodes parallel to the MOSFETs that allow a current flow in the TX circuitry. The determination of the coupling factor with the postringing signal matches the results of benchmark methods, so that the properness of the novel method could be shown. Furthermore, the presented method has no additional hardware effort, since only a frequency measurement needs to be done. Thus, the measurements can be done on-the-fly during the application, so that the system can react on changes of the coupling factor.

Combined method for frequency error detection/correction in DAB-based systems

The digital audio broadcasting (DAB) standard has established the family of standards for efficient and reliable multimedia broadcasting. Based on OFDM technology the DAB standard provides high spectrum efficiency and reliable data transfer. Due to its limited channel bandwidth, DAB can be used for cognitive radio (CR) application in the TV whitespace bands. OFDM technique requires precise frequency for proper operation; at the same time the end-user equipment must have competitive price. This tradeoff is normally being solved by using carrier frequency offset (CFO) estimation and compensation blocks in the receiver path. This manuscript describes a combined algorithm for synchronization and CFO estimation for the DAB system. The method uses information about DAB synchronization channel and phase reference symbol (PRS).

DAB physical layer considerations for a reuse in cognitive radio systems

The digital audio broadcasting (DAB) standard allows high spectrum efficiency, high voice quality, energy saving transmission and additional non-audio services like video and data transmission. Especially the last aspect enables the reuse of the DAB physical layer (PHY) for cognitive radio (CR) systems This manuscript analyzes the performance of a DAB system with respect to the standardized forward error correction (FEC) in an additive white Gaussian noise (AWGN) scenario under perfect synchronization assumption. The FEC consists of a Reed-Solomon (RS) code, followed by a convolutional code. In addition, puncturing as part of the equal error protection profiles (EEPPs) in the MSC (Main Service Channel) is applied.