Showing papers by "Bart Nauwelaers published in 2015"

A Visible Light Positioning system using Frequency Division Multiple Access with square waves

Abstract: In this paper, a Visible Light Positioning (VLP) system using Frequency Division Multiple Access (FDMA) with square waves is presented. For the multiple access technology, the properties of square waves in the frequency domain is exploited. Neighboring LEDs will use multiples of the ground frequency of the first LED where the receiver performs a Fast Fourier Transform (FFT) and retrieves the Received Signal Strength (RSS) for every LED. In order to facilitate implementation, the LEDs are transmitting pilot tones in a non-synchronized way to the receiver, and thus requiring no backbone network. The positioning algorithm uses the RSS to perform triangulation and finds the position by taking the least square fit. Practical results show that this VLP system has position errors smaller then 10 cm when an photodiode is used which has a Field Of View (FOV) of 70°. Simulation results show that when a photodiode with a FOV of 90° is applied, the position error can drop to a few centimeter within the entire test bench surface. The key advantage of the system is the use of unsynchronized low bandwidth transmitters, leading to an easy implementation using current high efficiency LED drivers.

Sensitivity Analysis of Broadband On-Wafer Dielectric Spectroscopy of Yeast Cell Suspensions up to 110 GHz

Abstract: This letter presents broadband on-wafer dielectric spectroscopy of baker's yeast cell suspensions up to 110 GHz. A detailed analysis of the sensitivities to measurement repeatability and uncertainties in the multi-step de-embedding procedure is performed. The Cole-Cole dispersion parameters of the cell suspensions are obtained from measured complex permittivity data between 0.5 and 110 GHz. Our analysis shows that the measured complex permittivity per frequency is most sensitive to length uncertainties of the test fixture, while the relaxation time in the Cole-Cole model is most sensitive to measurement repeatability.

Microwave heater at 20 GHz for nanoliter scale digital microfluidics

Abstract: This paper proposes an optimized microwave heater at 20 GHz for nanoliter scale liquid samples in digital microfluidics. The developed measurement setup allows translating of the reflection coefficient of the heater to the temperature change of the water droplet via the temperature dependency of the liquid permittivity, thus avoiding a contact-based temperature measurement. Measurements have been carried out on pure water samples of 500 nL at power levels of 20 and 23 dBm at the probe tips. The measured data agrees very well with multiphysics simulation data. Heating performance has been characterized and high temperature gradients of 30 deg. C per second have been measured.

SPICE analysis of RL and RC snubber circuits for synchronous buck DC-DC converters

Abstract: Operation of a 1.3-MHz, 12-to-1.2 V, 20-A synchronous buck converter is analyzed by SPICE simulations. Special attention is given to two resonances formed by the capacitance of FETs in the off-state and the total inductance of the input decoupling network. The resonances are the main source of the broadband electromagnetic (EM) interference. Two most common circuit level methods for reducing the EM interference, an RL snubber circuit and an RC snubber circuit, are analyzed and compared in terms of their impact on the radiation characteristics, efficiency and reliability of the analyzed synchronous buck converter.

Performance simulations of a 2.4 GHz indoor angle of arrival system for multipath components

Abstract: Multipath propagation is generally considered as an inconvenience in indoor radio frequency positioning systems, causing a degradation of localization accuracy. However, it is possible to exploit spatial information of reflected signals in a multipath assisted indoor positioning system, based on angle of arrival estimation. In order to assess the accuracy of the estimated angles and optimize system parameters, a simulation tool was developed. The tool simulates indoor line-of-sight signals and specular reflections of a 2.4 GHz signal, impinging on an antenna array. With this simulator, the performance of the MVDR, Beamscan, root MUSIC and ESPRIT algorithms for angle of arrival estimation is compared. Other investigated parameters include the position of the array in a square or rectangular room, the number of antennas, the number of signal decorrelation operations and the number of angles of arrival to be estimated. For each configuration, the spatial distribution of angular errors was evaluated, facilitating the design and dimensioning of an accurate indoor angle of arrival system.

Capacitive micromachined ultrasonic transducers for acoustic manipulation

Abstract: This paper presents for the first time the single-beam acoustic manipulation of micro-particles using capacitive micromachined ultrasonic transducers (cMUTs). We demonstrate polydimethylsiloxane (PDMS) micro-particles trapping in water using a 1.8 MHz hexagonal cMUT annular array as test vehicle. FEM simulations show that PDMS particles can be trapped on the center axis of a single cMUT cell relying solely on natural focusing. Experimental results confirm these findings. To our best knowledge, it is the first time to realize a single-beam acoustic trapping of micro-particles using three-dimensional confinement. Besides, it establishes cMUTs as good candidates for acoustic manipulation offering large potential for highly miniaturized and complex acoustic tweezers.

Influence of MAI in a CDMA VLP system

Abstract: In this paper, we study a Visible Light Positioning (VLP) system using Code Division Multiple Access (CDMA). In order to facilitate implementation, the LEDs are transmitting data in a non-synchronized way to the receiver requiring no backbone network. The positioning algorithm uses the received optical power calculated from the auto- correlation peak value. Because of the asynchronous system Multiple Access Interference (MAI), random interference with the auto- correlation peak, will occur and cause position errors. Practical results show that a CDMA VLP system can have position errors smaller then 40 cm and not be influenced by synchronization problems due to MAI. The positioning error and synchronization aren't only determined by the MAI but also the receiver Field Of View (FOV) is an important parameter. Depending on the CDMA code, the LEDs still have 97% of the illumination functionality compared when there is no communication.

A test bench for a VLP system using CDMA as Multiple Access Technology

Abstract: In this paper, we present a test bench for a Visible Light Positioning (VLP) system using Code Division Multiple Access (CDMA). A VLP system should be easy and low cost to install in existing infrastructures meaning there is no backbone network between the LEDs. CDMA can therefore be used as multiple access technology, with the challenging observation that the LEDs are transmitting data in a non-synchronized way to the receiver. Because the VLP system uses the received optical power for the positioning algorithm, Multiple Access Interference (MAI) can introduce errors. For the evaluation of the influence of MAI a test bench was developed where different CDMA codes are used in a VLP system. From practical measurements it is demonstrated that our approach leads to position errors smaller than 20 cm, making the system suitable for indoor Location Based Services (LBS).

Micromechanical ring resonators with a 2D phononic crystal support for mechanical robustness and providing mask misalignment tolerance

Abstract: This paper reports on the design of ring-type electrostatically transduced bulk acoustic wave resonators designed for increased shock and vibration resistance. This was achieved through a 2D Phononic Crystal (PnC) support. The PnC is designed to operate in its bandgap so that it acts as a non-propagating medium, hereby achieving simultaneously a mechanically strong and acoustically well-confined support. We manufactured SiGe-resonators at 137.8MHz with a Q-factor of around 17,000. Another feature of this design is the process tolerance of the Q-factor (within 5%) and the resonance frequency towards mask misalignment (<7µm) for the center support.

Radiation of input decoupling network typically used in switching DC-DC converters

Abstract: Radiation characteristics of an input decoupling network for switching DC-DC converters are analyzed by a set of electromagnetic (EM) simulations. Input decoupling network is a part of a DC-DC converter with a dominant contribution to its radiated emissions. The impact of geometrical parameters of an input decoupling network such as the dimensions of metal plates on a printed circuit board (PCB), thickness of a PCB, number of layers, number of vias and radius of vias on the maximum radiated fields is analyzed. Design guidelines for minimizing radiated emissions of an input decoupling network for switching DC-DC converters are summarized.

Study of broadband propagation characteristic of quasi-fractal phononic crystal for enhanced sensing applications

Abstract: This paper reports on bulk acoustic wave (BAW) resonators with quasi-fractal perforations for increased sensitivity in bio-sensing applications and on the broadband transmission line (TL) model of such resonators. Fractal perforations are implemented in BAW resonators to increase their surface area-to-volume ratio and to thereby enhance the sensitivity. We found that a further improvement is expected at higher resonance frequencies for the quasi-fractal phononic crystal (PnC) we have designed. This particular PnC has local resonances entailing strongly dispersive effective acoustic properties. Therefore, we have modeled the device implementing this PnC as a broadband dispersive transmission line (TL) to account for all the essential modes of longitudinal resonance. Our measurements, in very good agreement with this model, confirm the existence of the propagation mode in the PnC with enhanced projected sensitivity.

Extraction of small-signal model parameters of Si/SiGe heterojunction bipolar transistor using least squares support vector machines

Abstract: A novel straightforward methodology for extracting bias-dependent small-signal equivalent circuit model parameters (SSECMPs) of silicon/silicon–germanium heterojunction bipolar transistors is presented. The inverse mapping between SSECMPs and scattering (S) parameters is established and fitted using simulated data of the SSECM. Since the problem has large input space, S-parameters at many frequency points, the least squares support vector machines concept is used as regression technique. Physical SSECMPs values are obtained using the proposed methodology. Moreover, an excellent agreement is noted between the S-parameters measurements and their simulated counterpart using the extracted SSECMPs in the frequency range from 40 MHz to 40 GHz at different bias conditions.

Indoor Localization System Based on Correlation of MVDR Spatial Spectra

Abstract: Indoor angle of arrival localization systems generally require the setup of multiple antenna arrays at fixed positions. They rely on line-of-sight connections for the localization of a mobile node. This paper presents a solution that consists of a single antenna array. By using the Minimum Variance Distortionless Response algorithm for angle of arrival estimation, a spatial spectrum is calculated from antenna array measurements. This spatial spectrum is correlated with a reference set of spatial spectra, resulting in an estimated position. The reference data set is not acquired with labour-intensive fingerprinting techniques, but with a ray tracing algorithm. The proposed system is evaluated in simulations to investigate the influence of Non-Line-Of-Sight (NLOS) connections and interfering multipath components. Results for various configurations show that reasonable performance in NLOS conditions is achievable.

Optimized shape of a parametric designed HF loop antenna

Abstract: The design of loop antennas is no longer limited to circular and square shapes. Adapting the shape of the antenna to its environment is needed to increase the reliability of the application, especially when we have to place the antenna in an atypical environment or orientation. We will evaluate an HF loop antenna which differs in shape from commercially available antennas. This work demonstrates how the knowledge of the designer and the use of an optimization tool can create an antenna shape with specific goals. The optimization tool combines MATLAB® and CST EM Studio®. The dedicated antenna shape is implemented in a practical environment, e.g., a metallic drawer for medication storage. The results of the simulations are presented and are verified experimentally. These measurements confirm the simulation results, leading to the realisation of a very reliable, dedicated RFID solution with an atypical antenna shape.

Radiation characteristics of small loop antenna above perforated finite image plane

Abstract: Radiation characteristics of a loop antenna, small compared to the wavelength and placed centrally above a perforated finite image plane, are presented. Holes in the image plane typically occur in a multilayer printed circuit boards (PCBs) when vias pass through the second layer which serves as a reflector. A 3D finite element method (FEM) electromagnetic (EM) simulation of a System-in-Package (SiP) synchronous buck converter shows a significant impact of the holes on the characteristics of the converter. A parametric analysis of the impact of the number and radius of holes on the radiated characteristics and on the inductance of a small loop antenna above perforated image plane is performed by 3D FEM EM simulations. Guidelines for a design of multilayer PCBs for magnetically driven sources, such as DC-DC converters, are deduced.