Electronic Filter Research Articles

The origin of Korotkoff sounds and the accuracy of auscultatory blood pressure measurements

This study explores the hypothesis that the sharper, high frequency Korotkoff sounds come from resonant motion of the arterial wall, which begins after the artery transitions from a buckled state to an expanding state. The motions of one mass, two nonlinear springs, and one damper, driven by transmural pressure under the cuff, are used to model and compute the Korotkoff sounds according to principles of classical Newtonian physics. The natural resonance of this spring-mass-damper system provides a concise, yet rigorous, explanation for the origin of Korotkoff sounds. Fundamentally, wall stretching in expansion requires more force than wall bending in buckling. At cuff pressures between systolic and diastolic arterial pressure, audible vibrations (> 40 Hz) occur during early expansion of the artery wall beyond its zero pressure radius after the outward moving mass of tissue experiences sudden deceleration, caused by the discontinuity in stiffness between bucked and expanded states. The idealized spring-mass-damper model faithfully reproduces the time-domain waveforms of actual Korotkoff sounds in humans. Appearance of arterial sounds occurs at or just above the level of systolic pressure. Disappearance of arterial sounds occurs at or just above the level of diastolic pressure. Muffling of the sounds is explained by increased resistance of the artery to collapse, caused by downstream venous engorgement. A simple analytical model can define the physical origin of Korotkoff sounds, suggesting improved mechanical or electronic filters for their selective detection and confirming the disappearance of the Korotkoff sounds as the optimal diastolic end point.

Analysis of improvement in performance and design parameters for enhancing resolution in an atmospheric scanning electron microscope.

The scanning electron microscope is used in various fields to go beyond diffraction limits of the optical microscope. However, the electron pathway should be conducted in a vacuum so as not to scatter electrons. The pretreatment of the sample is needed for use in the vacuum. To directly observe large and fully hydrophilic samples without pretreatment, the atmospheric scanning electron microscope (ASEM) is needed. We developed an electron filter unit and an electron detector unit for implementation of the ASEM. The key of the electron filter unit is that electrons are transmitted while air molecules remain untransmitted through the unit. The electron detector unit collected the backscattered electrons. We conducted experiments using the selected materials with Havar foil, carbon film and SiN film.

Progress Towards Commercial Solid Hydrogen Storage Systems

Cella Energy has developed an ammonia borane-poly(ethylene oxide) solid hydrogen storage fuel that is being demonstrated as a lightweight high-performance replacement for batteries in a number of premium markets such as powering unmanned aerial vehicles. Cella’s technology will be suitable for the high energy requirements of “green/electric aircraft” replacing carbon fuels for powering on-board systems with a safety factor that exceeds the capability of compressed hydrogen. Development of a viable hydrogen storage system will overcome a critical barrier for the widespread commercialization of hydrogen and fuel cells technologies, an emerging renewable, clean energy industry with potential for growth in stationary, portable, and transportation areas. One of the most promising approaches to achieve high energy density system goals is to store hydrogen as a solid chemical hydride and release the hydrogen thermally, ideally between 80-150°C. The process by which the solid hydrogen fuel will be used is conceptually easy: the fuel is packaged as discrete “pellets” that are in contact with an ignition element such as a heater, insulated, and packed into a cartridge-type container. Combined with the appropriate electronic controls and filters, this is a hydrogen storage fuel system. Several challenges impact the success of these systems significantly. Simply put, in addition to hydrogen, all solid hydrogen fuels release some quantity of toxic impurities on heating, and many fuels expand rapidly and considerably while releasing a large quantity of heat, which imparts mechanical stress on packaging, among other issues. In addition, some volatiles are able to oligomerize in the gas phase, which means that if not trapped before leaving the hydrogen fuel cartridge then there is high probability of clogging fuel lines to the fuel cell based energy conversion system, as well as contamination of the fuel cell stack. This presentation will present an overview of Cella’s efforts to develop solid hydrogen fuel systems, as well as active R&D efforts to understand and optimize solid hydrogen material properties for safe storage and dehydrogenation when fuel is needed.

Advances in the Endoscopic Assessment of Inflammatory Bowel Diseases: Cooperation between Endoscopic and Pathologic Evaluations.

Endoscopic assessment has a crucial role in the management of inflammatory bowel disease (IBD). It is particularly useful for the assessment of IBD disease extension, severity, and neoplasia surveillance. Recent advances in endoscopic imaging techniques have been revolutionized over the past decades, progressing from conventional white light endoscopy to novel endoscopic techniques using molecular probes or electronic filter technologies. These new technologies allow for visualization of the mucosa in detail and monitor for inflammation/dysplasia at the cellular or sub-cellular level. These techniques may enable us to alter the IBD surveillance paradigm from four quadrant random biopsy to targeted biopsy and diagnosis. High definition endoscopy and dye-based chromoendoscopy can improve the detection rate of dysplasia and evaluate inflammatory changes with better visualization. Dye-less chromoendoscopy, including narrow band imaging, iScan, and autofluorescence imaging can also enhance surveillance in comparison to white light endoscopy with optical or electronic filter technologies. Moreover, confocal laser endomicroscopy or endocytoscopy have can achieve real-time histology evaluation in vivo and have greater accuracy in comparison with histology. These new technologies could be combined with standard endoscopy or further histologic confirmation in patients with IBD. This review offers an evidence-based overview of new endoscopic techniques in patients with IBD.

Tunable optoelectronic oscillator incorporating an all-optical microwave photonic filter

A tunable optoelectronic oscillator (OEO), which employs an all-optical microwave photonic filter (MPF) consisting of two laser sources (LD1 and LD2), an optical coupler (OC, 50:50), a Mach-Zehnder modulator (MZM), and a chirped fiber Bragg grating, is proposed. Because the central frequency of the all-optical MPF can be shifted by changing the wavelength spacing between the two laser sources, the frequency tunability of the OEO can be realized by incorporating such an all-optical MPF into an optical domain dual-loop OEO without any electronic microwave filters. A detailed theoretical analysis is presented and the results are confirmed by an experiment. A microwave signal with a frequency-tuning range from 4.057 to 8.595 GHz is generated. The phase noise, the long-term stability, and the side-mode suppression performance of the generated microwave signal are also investigated.

Low-power, chip-based stimulated Brillouin scattering microwave photonic filter with ultrahigh selectivity

Highly selective and reconfigurable microwave filters are of great importance in radio-frequency signal processing. Microwave photonic (MWP) filters are of particular interest, as they offer flexible reconfiguration and an order of magnitude higher frequency tuning range than electronic filters. However, all MWP filters to date have been limited by trade-offs between key parameters such as tuning range, resolution, and suppression. This problem is exacerbated in the case of integrated MWP filters, blocking the path to compact, high-performance filters. Here we show the first chip-based MWP bandstop filter with ultrahigh suppression, high resolution in the megahertz range, and 0–30 GHz frequency tuning. This record performance was achieved using an ultralow Brillouin gain from a compact photonic chip and a novel approach of optical resonance-assisted RF signal cancellation. The results point to new ways of creating energy-efficient and reconfigurable integrated MWP signal processors for wireless communications and defence applications.

Benchmark Data on a Linear Time- and Parameter-varying system

This article describes benchmark data for time- and parameter varying systems, from measurements conducted at the ELEC department, Vrije Universiteit Brussel. The system is an electronic bandpass filter, the resonance frequency of which can be varied in a controlled fashion. The signal that controls the resonance frequency is provided (and can be interpreted as a scheduling variable), along with the measured input and output signals, and the signals stored into the arbitrary waveform generator. The system is suitably modelled as a Linear Parameter Varying system, or as a Linear Time-Varying system if the scheduling variable is not used. The measurements are conducted in a low-noise environment, allowing for a Signal-to-Noise-Ratio of more than 60 dB. The system is mainly linear in its input-output relation, although some nonlinear effects are visible. The data includes different typical excitation scenarios, including band-limited noise, randomphase multisines with sparse excited frequencies, piecewise constant scheduling, and slow, medium and fast varying scheduling. The data sets are available at the IFAC TC1.1 repository: http://tc.ifac-control.org/1/1/Data%20Repository.

Improved Thermoelectric Performance of Silver Nanoparticles‐Dispersed Bi2Te3 Composites Deriving from Hierarchical Two‐Phased Heterostructure

A practical and feasible bottom‐up chemistry approach is demonstrated to dramatically enhance thermoelectric properties of the Bi2Te3 matrix by means of exotically introducing silver nanoparticles (AgNPs) for constructing thermoelectric composites with the hierarchical two‐phased heterostructure. By regulating the content of AgNPs and fine‐tuning the architecture of nanostructured thermoelectric materials, more heat‐carrying phonons covering the broad phonon mean free path distribution range can be scattered. The results show that the uniformly dispersed AgNPs not only effectively suppress the growth of Bi2Te3 grains, but also introduce nanoscale precipitates and form new interfaces with the Bi2Te3 matrix, resulting in a hierarchical two‐phased heterostructure, which causes intense scattering of phonons with multiscale mean free paths, and therefore significantly reduce the lattice thermal conductivity. Meanwhile, the improved power factor is maintained due to low‐energy electron filtering and excellent electrical transport property of Ag itself. Consequently, the maximum ZT is amazingly found to be enhanced by 304% arising from the hierarchical heterostructure when the AgNPs content reaches 2.0 vol%. This study offers an easily scalable and low‐cost route to construct a wide range of multiscale hierarchically heterostructured bulk composites with significant enhancement of thermoelectric performance.

The electrocardiogram as an electronic filter and why ac circuits are important for pre-health physics students

We present a general physics laboratory exercise that centres around the use of the electrocardiogram sensor as an application of circuits and electronic signal filtering. Although these topics are commonly taught in the general physics classroom, many students consider topics such as alternating current as unrelated to their future professions. This exercise provides the motivation for life science and pre-health majors to learn concepts such as voltage, resistance, alternating and direct current, RLC circuits, as well as signal and noise, in an introductory undergraduate physics lab.

Roles of epsilon-near-zero (ENZ) and mu-near-zero (MNZ) materials in optical metatronic circuit networks.

The concept of metamaterial-inspired nanocircuits, dubbed metatronics, was introduced in [Science 317, 1698 (2007); Phys. Rev. Lett. 95, 095504 (2005)]. It was suggested how optical lumped elements (nanoelements) can be made using subwavelength plasmonic or non-plasmonic particles. As a result, the optical metatronic equivalents of a number of electronic circuits, such as frequency mixers and filters, were suggested. In this work we further expand the concept of electronic lumped element networks into optical metatronic circuits and suggest a conceptual model applicable to various metatronic passive networks. In particular, we differentiate between the series and parallel networks using epsilon-near-zero (ENZ) and mu-near-zero (MNZ) materials. We employ layered structures with subwavelength thicknesses for the nanoelements as the building blocks of collections of metatronic networks. Furthermore, we explore how by choosing the non-zero constitutive parameters of the materials with specific dispersions, either Drude or Lorentzian dispersion with suitable parameters, capacitive and inductive responses can be achieved in both series and parallel networks. Next, we proceed with the one-to-one analogy between electronic circuits and optical metatronic filter layered networks and justify our analogies by comparing the frequency response of the two paradigms. Finally, we examine the material dispersion of near-zero relative permittivity as well as other physically important material considerations such as losses.

High-Q filters with complete transports using quasiperiodic rings with spin-orbit interaction

A high Q filter with complete transports is achieved using a quasiperiodic Thue-Morse array of mesoscopic rings with spin-orbit interaction. As the generation order of the Thue-Morse array increases, not only does the Q factor of the resonance peak increase exponentially, but the number of sharp resonance peaks also increases. The maximum Q factor for the electronic filter of a Thue-Morse array is much greater than that in a periodic array, for the same number of the rings.

Artificial intelligence methods in diagnostics of analog systems

Abstract The paper presents the state of the art and advancement of artificial intelligence methods in analog systems diagnostics. Firstly, the diagnostic domain is introduced and its problems explained. Then, computational intelligence approaches usable for fault detection and identification are reviewed. Particular groups of methods are presented in detail, explaining their usefulness and drawbacks. Examples, such as the induction motor or the electronic filter, are provided to show the applicability of the presented approaches for monitoring the state of analog objects from engineering domains. The discussion section reviews the presented approaches, their future prospects and problems to be solved.

Power Budget Improved Symmetric 40-Gb/s Long Reach Stacked WDM-OFDM-PON System Based on Single Tunable Optical Filter

We propose a stacked wavelength-division-multiplexed orthogonal-frequency-division-multiplexed passive optical network (WDM-OFDM-PON) system that is capable of transmitting 10-Gb/s per wavelength downstream OFDM signals and directly modulated upstream on-off keying (OOK) signals up to 100 km without any repeater. In this scheme, we use our specially designed electronic controlled liquid tunable optical filter to simultaneously select downstream signals and process upstream signal chirp. By experiment, we demonstrate this bidirectional transmission system and achieve error-free transmission performance over different fiber distances. A power budget of 35.6 dB for 25-km fiber transmission is obtained to support 1 : 512 splitting ratios. Through 100-km fiber transmission, a 34.4-dB optical power budget with a nonrepeater is also achieved. Moreover, the effects of various system parameters such as filter profile and downstream signals' launched power, are also investigated in detail by simulation and experiment for improving system performance.

Spatial and Temporal Overview of Research in Pediatric and Congenital Cardiology: Trends and Global Challenges

Available information on the global distribution of research output in pediatric cardiology (PC) is sparse. This study took a bibliometric approach to characterize research output, assess the level of competition, describe the geographic distribution of the leading research centers in the field, and investigate determinants of research output. In addition, the study characterized the journals publishing PC research and identified temporal trends in research interest over time. Publications presenting original research in PC between 1995 and 2011 were identified. A total of 9,410 relevant articles were identified based on a PubMed search followed by subsequent electronic filtering and manual review. A dramatic increase in PC publications was seen during the study period (from 309 in 1995 to 1,075 in 2011). This was accompanied by an increase in impact factors and an overproportional rise in PC contributions relative to the general PubMed trend. Research in PC was shown to be highly competitive and becoming increasingly so (Herfindahl-Hirschman index of 1.64%). Research output correlated with gross domestic product, national levels of corruption, education, urbanization, geography, and presence of national centers of excellence. The data presented in this report allow benchmarking of different cities and countries and provide insights into the potential determinants of high-quality publications and the spectrum of publishing journals. The report also highlights the central role of subspecialty journals and shows that PC research output is related to national wealth, surrogates of appropriate use of resources, an adequate workforce, and education. Additionally, it emphasizes the potential beneficial effects of establishing centers of excellence in the field.

Novel diagnostic and therapeutic techniques for surveillance of dysplasia in patients with inflammatory bowel disease.

The risk for developing dysplasia and colorectal cancer in patients with longstanding inflammatory bowel disease (IBD) involving the colon is well documented. Random biopsies during white-light, standard-definition colonoscopy (33 to 50 biopsies) with or without dye spraying chromoendoscopy has been the recommended strategy in North America to detect dysplastic lesions in IBD. However, there are several limitations to this approach including poor physician adherence, poor sensitivity, increased procedure time and considerable cost. The new generation of high-definition endoscopes with electronic filter technology provide an opportunity to visualize colonic mucosal and vascular patterns in minute detail, and to identify subtle flat, multifocal, polypoid and pseudopolypoid neoplastic and non-neoplastic lesions. The application of these new technologies in IBD is slowly being adopted in clinical practice. In addition, the advent of confocal laser endomicroscopy provides an opportunity to explore real-time histology, thus redefining the understanding and characterization of the lesions in IBD. There is emerging evidence that serrated adenomas are also associated with longstanding IBD colitis and may be recognized as another important contributing factor to colorectal cancer development. The circumscribed neoplastic lesions can be treated using endoscopic therapeutic management such as mucosal resection or, especially, endoscopic submucosal dissection. This may replace panproctocolectomy in selected patients. The authors review the potential of these techniques to transform endoscopic diagnosis and therapeutic management of dysplasia in IBD.

Low‐mobility‐pass filter between atmospheric pressure chemical ionization and electrospray ionization sources and a single quadrupole mass spectrometer: computational models and measurements

Mixtures of ions produced in sources at atmospheric pressure, including chemical ionization (APCI) and electrospray ionization (ESI) can be simplified at or near ambient pressure using ion mobility based filters. A low-mobility-pass filter (LMPF) based on a simple mechanical design and simple electronic control was designed, modeled and tested with vapors of 2-hexadecanone in an APCI source and with spray of peptide solutions in an ESI source. The LMPF geometry was planar and small (4 mm wide × 13 mm long) and electric control was through a symmetric waveform in low kHz with amplitude between 0 and 10 V. Computational models established idealized performance for transmission efficiency of ions of several reduced mobility coefficients over the range of amplitudes and were matched by computed values from ion abundances in mass spectra. The filter exhibited a broad response function, equivalent to a Bode Plot in electronic filters, suggesting that ion filtering could be done in blocks ~50 m/z units wide. The benefit of this concept is that discrimination against ions of high mobility is controlled by only a single parameter: waveform amplitude at fixed frequency. The effective removal of high mobility ions, those of low mass-to-charge, can be beneficial for applications with ion-trap-based mass spectrometers to remove excessive levels of solvent or matrix ions.

I-SCAN targeted versus random biopsies in Barrett's oesophagus

The accuracy and effectiveness of targeted oesophageal biopsies in Barrett's oesophagus to detect dysplasia using new magnification techniques are unknown. Aim of this study was to investigate whether the combined use of acetic acid, magnification and electronic filters allows the same accuracy as the four-quadrant random biopsies pattern; pathologist interobserver agreement both in low grade and high grade dysplasia was also assessed. Fifty-four consecutive patients newly diagnosed with Barrett's oesophagus were enrolled in a prospective study from a single endoscopy unit. Biopsies were evaluated by the local pathologist and by an expert pathologist from another pathology unit. Dysplasia detection rate and interobserver agreement for the histologic diagnosis of dysplasia. The use of acetic acid, magnification and electronic filters showed an unacceptably low dysplasia detection rate by the two pathologists (9.2% and 5.5% for targeted biopsies, respectively). The interobserver agreement for low grade dysplasia between pathologists was low (Cohen's K weighted=0.45). In an average setting, the standard four-quadrant method should still be preferred, along with the implementation of a routine second evaluation by an expert pathologist.

Spin-polarized currents in the tunnel contact of a normal conductor and a two-dimensional topological insulator

The spin filtering of electrons tunneling from the edge states of a two-dimensional topological insulator into a normal conductor under a magnetic field (external or induced due to proximity to a magnetic insulator) is studied. Calculations are performed for a tunnel contact of finite length between the topological insulator and an electronic multimode quantum strip. It is shown that the flow of tunneling electrons is split in the strip, so that spin-polarized currents arise in its left and right branches. These currents can be effectively controlled by the contact voltage and the chemical potential of the system. The presence of a magnetic field, which splits the spin subbands of the electron spectrum in the strip, gives rise to switching of the spin current between the strip branches.

An Optoelectronic Oscillator Based on Carrier-Suppression-Effect-Free Single Bandpass Microwave Photonic Filter

A novel optoelectronic oscillator based on a single bandpass microwave photonic filter (MPF) without any electronic microwave filter is proposed and experimentally demonstrated. The MPF, which is composed by a broadband optical source, an inline interferometer based on a variable optical delay line (VODL), an intensity modulator, and a dispersive element, serves as an oscillating mode selector. The oscillation frequency can be tuned by changing the differential time delay via the VODL. Due to the non-carrier-suppression effect of the selector, the oscillator can generate transmission-null-free microwave signal with widely tunable frequency range. An experiment is performed, and a tunable frequency range of 6.8 GHz is achieved. The generated microwave signal at ~ 6.5 GHz ( ~ 1.06 GHz) exhibits a good phase noise performance about -95 dBc/Hz ( -110 dBc/Hz) at an offset of 10 kHz.

A novel optoelectronic oscillator based on all optical signal processing

A novel dual-loop optoelectronic oscillator (OEO), which is constructed based on all optical signal processing, is proposed and analyzed. By inserting an erbium-doped fiber amplifier (EDFA) and a fiber Bragg grating (FBG) on the optical domain, the amplification and filter are implemented in the OEO loop. The performance of the OEO is improved without any electronic filter or electronic amplifier. A theoretical analysis is performed, and the generated microwave signal exhibits good performance with phase noise lower than −120 dBc/Hz at 10 kHz and a high side-mode suppression ratio (SMSR).