Showing papers by "Pedro Silva Girao published in 2010"

Theory and Developments in an Unobtrusive Cardiovascular System Representation: Ballistocardiography

Abstract: Due to recent technological improvements, namely in the field of piezoelectric sensors, ballistocardiography – an almost forgotten physiological measurement – is now being object of a renewed scientific interest. Transcending the initial purposes of its development, ballistocardiography has revealed itself to be a useful informative signal about the cardiovascular system status, since it is a non-intrusive technique which is able to assess the body’s vibrations due to its cardiac, and respiratory physiological signatures. Apart from representing the outcome of the electrical stimulus to the myocardium – which may be obtained by electrocardiography – the ballistocardiograph has additional advantages, as it can be embedded in objects of common use, such as a bed or a chair. Moreover, it enables measurements without the presence of medical staff, factor which avoids the stress caused by medical examinations and reduces the patient’s involuntary psychophysiological responses. Given these attributes, and the crescent number of systems developed in recent years, it is therefore pertinent to revise all the information available on the ballistocardiogram’s physiological interpretation, its typical waveform information, its features and distortions, as well as the state of the art in device implementations.

Physiological Parameters Measurement Based on Wheelchair Embedded Sensors and Advanced Signal Processing

Abstract: This paper presents a multisensing system with wireless communication capabilities embedded on a smart wheelchair that can measure physiological parameters such as heart rate and respiratory rate in an unobtrusive way. Ballistocardiography (BCG) sensors and a three-axis inertial microelectromechanical system accelerometer are embedded on the seat or in the backrest of the wheelchair and the acquired data are transmitted by Wi-Fi to a laptop computer for advanced data processing and logging. In addition, a 3-D accelerometer with ZigBee communication capability is used to extract information about the user's posture. Considering the static and dynamic use of the wheelchair, an extended set of measurements for different utilization scenarios was analyzed. An important part of this paper is focused on BCG noise and artifacts removal and heart rate and respiratory rate accurate estimation from BCG signal using wavelet-based filtering and independent component analysis algorithms. A study on wavelet-based filtering considering different types of mother wavelets and different levels of decomposition was also carried out. In the future, other signals will also be acquired to improve the system capabilities and flexibility.

Cross-Correlation and Sine-Fitting Techniques for High-Resolution Ultrasonic Ranging

Abstract: This paper presents a combination of two techniques for high-resolution ultrasonic distance measurements in air. The first is the cross correlation between transmitted and received signals to determine the time of flight (TOF), and the second is sine fitting of other transmitted and received signals to determine the phase shift (PS) between them. Sine fitting can estimate the PS with very high accuracy. The result of this synergy is a very accurate distance measurement. For example, the final uncertainty is less than 100 for distances up to 1200 mm.

Microwave FMCW Doppler radar implementation for in-house pervasive health care system

Abstract: In recent years, the research in the area of ubiquitous healthcare has intensified. There are many technological advances regarding the development of unobtrusive sensors for cardiac and respiratory activity, but the current scenario is still far away from an everyday life fulfilled with ubiquitous healthcare systems. In this paper, it is described the usage of 24GHz microwave FMCW (frequency modulated continuous wave) Doppler radar (MDR) as one of the main components of a pervasive biomedical system that is part of an assistive environment for the people with less mobility or people with long term health condition. As parts of the present work, in this paper are mentioned the design and implementation of an assistive environment based on a MDR sensor, an experimental study concerning the microwave Doppler radar characteristics and remote sensing of heart rate and breath rate, based on acquisition and processing of the signals delivered by the used radar.

Implementation of compressed sensing in telecardiology sensor networks

Abstract: Mobile solutions for patient cardiac monitoring are viewed with growing interest, and improvements on current implementations are frequently reported, with wireless, and in particular, wearable devices promising to achieve ubiquity. However, due to unavoidable power consumption limitations, the amount of data acquired, processed, and transmitted needs to be diminished, which is counterproductive, regarding the quality of the information produced. Compressed sensing implementation in wireless sensor networks (WSNs) promises to bring gains not only in power savings to the devices, but also with minor impact in signal quality. Several cardiac signals have a sparse representation in some wavelet transformations. The compressed sensing paradigm states that signals can be recovered from a few projections into another basis, incoherent with the first. This paper evaluates the compressed sensing paradigm impact in a cardiac monitoring WSN, discussing the implications in data reliability, energy management, and the improvements accomplished by in-network processing.

Non-Intrusive Device for Real-Time Circulatory System Assessment with Advanced Signal Processing Capabilities

Abstract: This paper presents a device that uses three cardiography signals to characterize several important parameters of a subject’s circulatory system. Using electrocardiogram, finger photoplethysmogram, and ballistocardiogram, three heart rate estimates are acquired from beat-to-beat time interval extraction. Furthermore, pre-ejection period, pulse transit time (PTT), and pulse arrival time (PAT) are computed, and their long-term evolution is analyzed. The system estimates heart rate variability (HRV) and blood pressure variability (BPV) from the heart rate and PAT time series, to infer the activity of the cardiac autonomic system. The software component of the device evaluates the frequency content of HRV and BPV, and also their fractal dimension and entropy, thus providing a detailed analysis of the time series’ regularity and complexity evolution, to allow personalized subject evaluation.

A new approach for real time fault diagnosis in induction motors based on vibration measurement

Abstract: Condition monitoring is used to increase machinery availability and machinery performance, reducing consequential damage, increasing machine life, reducing spare parts inventories, and reducing breakdown maintenance. An efficient real time vibration measurement and analysis instruments is capable of providing warning and predicting faults at early stages. In this paper, a new methodology for the implementation of vibration measurement and analysis instruments in real time based on circuit architecture mapped from a MATLAB/Simulink model is presented. In this study, signal processing applications such as FIR filters and fast Fourier transform are treated as systems, which are implemented in hardware using a system generator toolbox, which translates a Simulink model in a hardware description language - HDL for FPGA implementations.

Unobtrusive and Non-invasive Sensing Solutions for On-Line Physiological Parameters Monitoring

Abstract: Demographic developments, social changes, and the rising costs of health and social care due to people with chronic disease, people with mobility limitations and elderly population make necessary to rethink care delivery. A practical way to improve care and cut healthcare costs is to develop integrated electronic health (e-health) solutions that permit monitoring of physiological parameters and motor activities of the users in their homes.

Automatic wavelet detrending benefits to the analysis of cardiac signals acquired in a moving wheelchair

Abstract: Biomedical signals are customarily overlaid with interferences and noise, furthermore, baseline wandering is another significant drawback to their accurate interpretation, especially if the implementation platform is a wheelchair. The nonlinear processes which generate the physiologic signals, and the disturbances, regularly exclude, or limit, the usage of classical linear techniques, hence, among other options, wavelets have been used to decompose the signals. Unobtrusively acquired signals are prone to have important baseline fluctuations, namely contactless impedance plethysmogram, and ballistocardiogram, therefore making them apposite to detrending. Sensing hardware was embedded in a wheelchair to acquire these signals, given the valuable information provided about the cardiovascular system of the monitored subject. This work also reports the improvements achieved by automatic wavelet detrending application in the real-time processing of these signals. Although significant baseline wavering is acquired, important enhancements are swiftly computed without noteworthy error.

Online heart rate estimation in unstable ballistocardiographic records

Abstract: When recording the pressure oscillations of a seated subject two distinct effects are assessed, ample vibrations due to the person's movement, and periodic oscillations of small amplitude due to cardiopulmonary activity, expressed by the ballistocardiogram (BCG). Embedding a pressure sensor in a chair's back or seat allows unobtrusive monitoring of the BCG. However, inconspicuously acquired signals are affected by numerous artifacts, often generated by the subject's forgetfulness, and posture changes due to lack of constrains. Moreover, the signal changes considerably its shape from person to person, and when the seating posture, or conversely, sensor position, is different. For real-time continuous monitoring, it is still to be found a method which, without introducing significant delays, can deal with such volatility. Thus, tailored calibration of peak detectors and other algorithms is recurrent, and even so, the neighboring samples of artifacts are possibly untreatable. This work evaluates the advantages of Empirical Mode Decomposition, as well as a coarser demodulation approach of the BCG signal, as dependable methods to allow real-time heart rate estimation on unstable BCG records. An analysis of the Fourier transform of the demodulated signals is the method used to provide and compare robustness of heart rate estimates.

Stationary wavelet transform and principal component analysis application on capacitive electrocardiography

Abstract: The gradual aging and the prevalence of cardiac pathologies in society has motivated an increase in research of homecare technologies. Capacitive sensing of the electrocardiogram (ECG) allows unobtrusively monitoring of the most well-known physiological signal. However, this measurement process is relentlessly superimposed with interferences and noise, namely movement artifacts which nearly erase the signal. This work presents a system implementing a new data processing technique, based on stationary wavelet transform together with principal component analysis. This approach is successful, as it is able to characterize motion artifacts, and to improve the quality of the ECG acquired without the subject's knowledge.

Improving celerity of heavy metals measurements

Abstract: This paper presents a low cost measurement system to identify heavy metals dissolved in water and to evaluate their concentrations. Two main objectives of the proposed measurement system must be underlined, both related with measurement celerity. The first one improves measurement celerity by reducing the requested time to remove dissolved oxygen contained in the water sample. The second one proposes a flexible voltammetry voltage scan that improves measurement celerity using a fast voltage scan that identifies the heavy metals dissolved in the solution with higher concentrations and then a slower voltage scan is performed around the voltammogram current peaks associated with the heavy metals with higher concentrations.

Fixed-Point Implementation of Infinite Impulse Response Notch Filters

Abstract: Many studies have been developed aiming to improve di gital filters realizations, recurring to intricate structures and analyzing probabilistically the errors behavior. The work presented in this paper analyzes the feasibility of fixed-point implementation of classical infinite impulse re sponse notch filters: Butterworth, Chebyshev I and II, and elliptic. To scrutinize the deformations suffered for distinct design specifications, it is assessed: the effect of the quality factor and normalized cut-off frequency, in the number of significant bits nece ssary to represent the filter's coefficients. The implications brought to FP GA implementation are also verified. The work focuses especially on the implementation of power line notch filters used to improve the signal-to- noise ratio in biomedical signals. The results obtain ed, when quantizing the digital notch filters, show that by applying second-order sections decomposition, low-ord er digital filters may be designed using only part of double precision capabilities. High-order notch filters with harsh design constraints are implementable using double precision, but only in second-order sections. Thus, it is revealed that to optimiz e computation time in real-time applications, an optimal digital notch filter im plementation platform should have variable arithmetic precision. Considering these implementation constraints, utmost operation performance is finally estimated when implementing digital notch filters in Xilinx Virtex-5 field-programmable gate arrays. The influence of several design specifications, e. g. type, and order, in the filter's behavior was evaluat ed, namely in regard to order, type, input and coefficient number of bits, quality factor and cut-off frequency. Finally the implications and potential applications of such results are discussed. Ke ywords: digital filter implementation, digital filter word length effects, notch digital filters.

Automated and remote operated system for spectrum monitoring and control in Portugal

Abstract: In this paper the authors describe the Portuguese system set-up by the national authority in charge of monitoring, control and manage the electromagnetic spectrum to fulfill the mission legally assigned to it. The system is a distributed one composed of four nodes — monitoring and control centers (MCCs) — and the paper describes system's evolution from a set of manual, local operated centers to a fully integrated, automated system whose nodes can be remotely operated.

Non-Volatile Memory Interface Protocols for Smart Sensor Networks and Mobile Devices

Abstract: Data acquisition, storage and transmission are mandatory requirements for different applications in the area of smart sensors and sensor networks. Different architectures and scenarios can be considered. Thus for smart sensors architectures (Frank, 2002) based on the IEEE1451.X standard (IEEE, 2007) the acquired data can be processed at the smart sensor level using data of the so-called standard template TEDS (Honeywell, 2009) stored in a non-volatile memory (Brewer & Gill, 2008). The autoidentification of the smart sensor (Yurish & Gomes, 2003) unit from a sensor network is based on the Basic TEDS that also represents part of the stored information. Considering smart sensor architectures (Song & Lee, 2008), the communication between the sensor processing unit (e.g. microcontroller) and one or multiple non-volatile memory units (e.g. Flash EEPROM memory units) is done using different communication protocols, such as SPI, I2C, 1-wire (Kalinsky & Kalinsky, 2002); (Paret & Fenger, 1997); (Linke, 2008). These protocols are thus frequently used in smart sensor implementations (IEEE, 2004)(Ramos et al., 2004). As the name implies, smart sensors networks are networks of smart sensors, that is, of devices that have an inbuilt ability to sense information, process the information and send selected information to an external receiver (including to other sensors). A "smart sensor" is a transducer (or actuator) that provides functions beyond what is necessary to generate a correct representation of a sensed or controlled quantity. This means that such nodes require memory capabilities to store data temporarily or permanently. In an increasingly number of applications, the nodes are required to change their spatial position (mobile nodes), which leads to wireless networks. The sensor network nodes data management and advanced data processing are carried out by a host unit characterized by high data processing capabilities, non-volatile data storage capabilities and data communication capabilities. One kind of solutions that materialize the host unit is mobile devices (e.g. phones and PDAs) with special operating systems (e.g. WindowsCE, Symbian, BalckBerry OS) and internal and extended data storage memory capabilities (CF card memory, SD card memory). Specific protocols, CompactFlash and Secure-Digital (Compact Flash, 2009) (SD Association, 2009) are associated with memory card interfaces that are used to perform the communication between the host unit processor and the memory units. In wireless sensors networks, special attention is granted to the memory read/write operations 10

Analog to Digital Conversion Methods for Smart Sensing Systems

Abstract: The new capabilities of smart sensing systems namely, adaptability, reconfiguration, lowenergy consumption and cost, between others, require a wisely selection of the methods that are use to perform analog to digital conversion. It is very important to optimize the trade-offs between, resolution, accuracy, conversion rate, and energy consumption, between others, and above all to adapt dynamically the conversion parameters for different signals characteristics and applications’ purposes. Establishing the best trade-offs are even more important when signals to be digitized have different signal-to-noise ratios (S/N) ratios, different requirements of measuring accuracy and acquisition rate, their characteristics are time-variant and above all if they are sharing the same digitalization device. Very low resolution or conversion rate of data acquisition (DAQs) systems are generally not compliant with measurement systems’ requirements since signal information is lost without any possible recovery procedure. Otherwise, if resolution or data acquisition rate are excessively high that means the sampling rate is much higher than its minimum value (Nyquist rate), the excessive amplitude and time resolutions provided by A/D conversion or frequency-to-digital conversion (FDC) does not improve measurements system’s performance. Moreover, the excessive resolution or data acquisition rate implies an increase of hardware and software complexity, data processing load and a higher implementation cost, without any benefits. So, for any A/D or FDC conversion method the best trade-off between different conversion characteristics must be established considering applications’ purposes. For example, in wireless sensing and actuating networks (WSAN) energy wastes are particularly important because a wrong choice of conversion method can affect deeply measurement system autonomy. Whenever possible, classical A/D conversion methods are being replaced by discrete A/D conversion methods that are supported by low cost microcontroller (C) (Microchip, 2010) connected to a few external resistive or capacitive components. This solution takes full advantage of Cs benefits, namely specific hardware and software capabilities and it provides a conversion rate that can be higher that several hundreds of kHz that is sufficient 24

Performance evaluation of a Web-Service-based DMCS

Abstract: The paper describes a set of experiments conducted on a service-oriented middleware infrastructure in order to evaluate its performance and applicability in the context of Distributed Measurement and Control Systems (DMCS). The infrastructure, entirely based on Web Services, was built using the Windows Communication Foundation (WCF), a software package released by Microsoft to develop distributed applications. The experiments were performed on a real plant equipped with all the instrumentation needed to run control loops for pressure, level, flow and temperature, quantities widely found in the process industry. The work focus on measuring the time delays associated with control loops and remote calls. The methodology of each experiment is described, results are presented and conclusions are drawn.