Sharp Filter Research Articles

A Compact and Sharp Rejection Ultra-Wideband Bandpass Filter Based on Short and Open Stub-Loaded Multiple Mode Resonators

A compact and high-rejection ultra-wideband (UWB) microstrip band-pass filter is proposed by using the multi-mode resonator (MMR) technique. The proposed MMR structure is realized by three open stubs-loaded and two short stubs-loaded and a high impedance microstrip line. Five modes, including two odd modes and three even modes could be designed within the UWB band. By resizing the dimensions of the stubs, the resonant modes of the MMR structure are arranged wider bandpass which the passband selectivity with this configuration significantly improved. By this configuration, the even modes can be flexibly controlled, while the odd modes remain the same. The proposed filter has a passband covers 4.1–10.6 GHz and its measured 3 dB fractional bandwidth is about 89%. In order to validate the performance of the proposed technique, the designed UWB band-pass filter is fabricated and the experimental verification is provided. A good agreement has been found between simulation and measurement’s results. To our knowledge, the size of the proposed UWB filter is small in comparison with known similar filters.

Simplified approach to low-frequency coherent anti-Stokes Raman spectroscopy using a sharp spectral edge filter.

Coherent anti-Stokes Raman scattering (CARS) has found wide applications in biomedical research. Compared with alternatives, single-beam CARS is especially attractive at low frequencies. Yet, currently existing schemes necessitate a relatively complicated setup to perform high-resolution spectroscopy. Here we show that the spectral sharp edge formed by an ultra-steep long-pass filter is sufficient for performing CARS spectroscopy, simplifying the system significantly. We compare the sensitivity of the presented methodology with available counterparts both theoretically and experimentally. Importantly, we show that this method, to the best of our knowledge, is the simplest and most suitable for vibrational imaging and spectroscopy in the very low-frequency regime (<200 cm-1).

Maximal quantum scattering by homogeneous spherical inclusions

Scattering of matter waves, present at multiple quantum setups, is required to be maximized in several applications from sensing and imaging to quantum switching and memory. The simplest case of a homogeneous spherical scatterer is rigorously solved and optimized with respect to its size, texture, and background by considering the effective quantum properties from a long directory of materials. In this context, several alternative layouts with maximal scattering efficiency are proposed, offering additional degrees of freedom in design without requirements for careful engineering of quantum texture. Many of the reported inclusions exhibit substantial selectivity in their scattering response, admitting them to operate as sharp filters for particle energies or sensitive detectors of electron beams.

Evaluation of image quality and radiation dose in kilovoltage cone beam computed tomography

This study was to evaluate the image quality and radiation dose of kV-CBCT when varying mAs and reconstruction filter. The radiation dosimetry (CBDIw) and quality control of kV-CBCT image were done. Routine protocols in head, thorax, and pelvis protocols were performed as a reference image. Then the images were acquired with varied mAs, the other parameters were fixed. Each technique was reconstructed with different filter. The image quality in terms of low contrast and high contrast resolution including CBDIw were compared. The result found that the variation of mAs with auto filter affected low contrast resolution, but slightly effect high contrast resolution. When mAs increased, low contrast detectability increased. Decreasing one step of mAs (16.67%) kept in acceptable image quality and reduced about 15% of CBDIw. The smooth filter improved the low contrast resolution, but it decreased the high contrast resolution. While the sharp or ultra-sharp filter improved the high contrast resolution. In conclusion, the changing of mAs affects the low contrast resolution and CBDIW. While the reconstruction filter changed the both of low and high contrast resolution, but no effect to CBDIw. To optimize the image quality and radiation dose of routine protocols, mAs can reduce one step-down.

Edge enhancement of IBP reconstruction by using sharp infinite symmetrical exponential filter

This study contributes to provide an enhancement technique for improving the Iterative Back Projection (IBP) Super Resolution technique by using the Sharp Infinite Symmetrical Filter (SISEF). Theoretically, the IBP technique operates as minimizer the error reconstruction iteratively until it refined the High Resolution (HR) image. However, due to iterative manner and lack of edge guidance during the back projection operation, this technique has suffered from produced the ringing artefact on the HR image appearances. Additionally, the IBP reconstruction also demands for large number iteration for accomplishing the prediction HR image. This problem arose when the IBP estimator tended to oscillate at the same solution frequently. In order to overcome these constraints, the SISEF is deployed as regulator to improve the IBP estimator with provides an accurate edge information for enhancing the edge image and reduce the ringing artefacts. Fortunately, highly precision of edge information provided by SISEF capable to reduce amount of estimation process repetition.

Large Eddy Simulation Requirements for the Flow over Periodic Hills

Large eddy simulations are carried out for flows in a channel with streamwise-periodic constrictions, a well-documented benchmark case to study turbulent flow separation from a curved surface. Resolution criteria such as wall units are restricted to attached flows and enhanced criteria, such as energy spectra or two-point correlations, are used to evaluate the effective scale separation in the present large eddy simulations. A detailed analysis of the separation above the hill crest and of the early shear layer development shows that the delicate flow details in this region may be hardly resolved on coarse grids already at Re = 10595, possibly leading to a non monotonic convergence with mesh refinement. The intricate coupling between numerical and modeling errors is studied by means of various discretization schemes and subgrid models. It is shown that numerical schemes maximizing the resolution capabilities are a key ingredient for obtaining high-quality solutions while using a reduced number of grid points. On this respect, the introduction of a sharp enough filter is an essential condition for separating accurately the resolved scales from the subfilter scales and for removing ill-resolved structures. The high-resolution approach is seen to provide solutions in very good overall agreement with the available experimental data for a range of Reynolds numbers (up to 37000) without need for significant grid refinement.

Optimal Design of Multiplier-Less Non-uniform Channel Filters with Successive Approximation of Vectors

Applications such as software-defined radio (SDR) receivers utilize channel filters to isolate the individual frequency bands of different communication standards present in a wideband input signal. Low complexity and sharp transition width are the two important design constraints of channel filters in SDR receivers. Frequency response masking (FRM) with the multiplier-less design is an effective approach for designing sharp filters with low complexity. This paper presents an optimal design for multiplier-less implementation of FRM-based non-uniform channel filters. In the proposed design, multiplier-less channel filters are realized basing upon decomposing their impulse response values in generalized bit planes. This decomposition is based on a vector successive approximation technique in which impulse responses are successively approximated using a dictionary of vectors. The resulting coefficients of channel filters belong to signed sums of powers of two form. The proposed channel filter designs are simulated using MATLAB R2017b, and the results have been compared with the existing ones in order to signify the effectiveness of the proposed design. The simulations show that the proposed channel filter design has low complexity (number of adders) and the design time is considerably low.

Substrate Integrated Plasmonic Waveguide for Microwave Bandpass Filter Applications

In this paper, we numerically and experimentally demonstrate a substrate integrated plasmonic waveguide (SIPW) concept and its application in microwave bandpass filters. This SIPW consists of double arrays of slots etched on the top and bottom metal layers of a substrate integrated waveguide (SIW) to support spoof surface plasmon polariton (SSPP) modes with low and high cutoff frequencies. The simulated results show that by tuning the parameters of the SIPW's unit cell, the dispersion characteristics can be engineered at will. Then, we propose a sharp roll-off microwave bandpass filter based on this SIPW. This filter has a passband from 7.5 to 13.0 GHz with high return loss and low insertion loss. Furthermore, to demonstrate the independent tuning of the passband of the filter, we also design two microwave bandpass filters with passbands of 9.2-13.0 GHz and 7.5-10.5 GHz by decreasing the distance between two rows of via holes and increasing the slot length, respectively. Finally, to experimentally validate the filter designs, we fabricate and measure three prototypes and find that the experimental results are in excellent agreement with the simulations. This SIPW concept may have extensive potential applications in the development of various plasmonic integrated functional devices and circuits.

Spectrum Assignment in Hardware-Constrained Cognitive Radio IoT Networks Under Varying Channel-Quality Conditions

ABSTRACT The integration of cognitive radio (CR) technology with future Internet-of-Things (IoT) architectures is expected to allow effective massive IoT deployment by providing huge spectrum opportunities to IoT devices. Several communication protocols have been proposed for CR networks while ignoring the adjacent channel interference (ACI) problem by assuming sharp filters at the transmit and receive chains of each CR device. However, in practice, such an assumption is not feasible for low-cost hardware-constrained CR-capable IoT (CR-IoT) devices. Specifically, when large number of CR-IoT devices are operating in the same vicinity, guardband channels (GBs) are needed to mitigate the ACI problem. Introducing GB constraint spectrum efficiency and protocol design. In this paper, we develop a channel assignment mechanism for hardware-constrained CR-IoT networks under time-varying channel conditions with GB-awareness. The objective of our assignment is to serve the largest possible number of CR-IoT devices by assigning the least number of idle channels to each device subject to rate demand and interference constraints. The proposed channel assignment in this paper is conducted on a per-block basis for the contending CR-IoT devices while considering the time-varying channel conditions for each CRIoT transmission over each idle channel such that spectrum efficiency is improved. Specifically, our channel assignment problem is formulated as a binary linear programming (BLP) problem, which is NP hard. Thus, we propose a polynomial-time solution using a sequential fixing algorithm that achieves a suboptimal solution. Simulation results demonstrate that our proposed assignment provides significant increase in the number of served IoT devices over existing assignment mechanisms.

55. A statistical method for assessing Low Contrast Detectability in CT: A phantom study using Filtered Back Projection and Iterative reconstructions

Purpose To calculate Low Contrast Detectability (LCD) curves using a statistical approach on CT images reconstructed with filtered back projection (FBP) and Iterative (IR) algorithms. Methods 25 axial images of a water phantom (25 cm diameter), scanned on a Somatom Definition Flash with different tube loads, were reconstructed with FBP and IR (IRIS) filters. A volume of 16 × 16 × 5 cm3 (VOI-BIG) was divided in many smaller contiguous squared ROI (ROI-lets) drawn in each axial slice and the standard deviations (SDX-m) of their mean CT values (X-m) were calculated for different dimensions. Threshold (Th) for the detectability of a low contrast object can be predicted, for an ideal observer, as Th = 3.29 ∗ SDX-m, assuming a normal distribution of X-m with a confidence level of 95% and Signal-Known-Exactly/Background Known Exactly conditions. LCD curves were obtained with this method by increasing the dimensions of the ROI-lets from 2 mm (4 pixel) to 25 mm (52 pixel) for smooth, medium-smooth and sharp FBP filters together with their corresponding iterative versions at different dose levels (CTDIvol range: 2.8–20.7 mGy). Contrast Gain (CG) was defined as the difference between 2 LCD thresholds for the same object size. Results Compared to FBP images, the noise in IR with CTDIvol = 6.9 mGy, calculated as pixel SD in the VOI-BIG, was reduced by 24%, 33% and 36% for smooth, medium-smooth and sharp filter respectively. This improvement in image quality resulted also in the LCD curves: an average CG of 0.4 HU and 2.3 HU was observed for smooth/medium and sharp filters for details dimension within 5 and 20 mm. When FBP-Smooth and IR-Medium/Smooth filters are compared, CG increase monotonically with dose reduction and object size. Conclusions Although the proposed method is valid for ideal observers only, it provides a simple but potentially attractive metric for image quality assessment and protocol optimization.

Filtered back projection revisited in low-kilovolt computed tomography angiography: sharp filter kernel enhances visualization of the artery of Adamkiewicz.

The reliability of assessment of the artery of Adamkiewicz before the aortic repair is highly dependent on the display of the continuity of this artery with the aorta, mainly around the vertebral pedicle, by computed tomography angiography (CTA). We hypothesized that the sharp filter kernel can improve visualization of this continuity of the vessel structure because of its edge enhancement and high-spatial resolution. This study was performed to compare the subjective and objective image quality of spinal CTA reconstructed with sharp and smooth filter kernels. We retrospectively reviewed 40 consecutive patients who had undergone 80-kV CTA to detect the artery of Adamkiewicz before aortic repair. We measured the CT number and the contrast-to-noise ratio of the anterior spinal artery to the spinal cord. Furthermore, the continuity of the artery of Adamkiewicz was evaluated using a 3-point scale (2 points, absolute; 0 points, undetectable). CTA with the sharp filter kernel showed a significantly higher CT number and contrast-to-noise ratio of the spinal artery than did CTA with the smooth filter kernel (P < .001 for both). Moreover, the sharp filter kernel showed a significantly higher continuity of the artery of Adamkiewicz with the aorta than did the smooth filter kernel (P < .001). The sharp filter kernel significantly improved the image quality in low-tube-voltage CTA for the assessment of the artery of Adamkiewicz. Thus, CTA with the sharp filter kernel can generate a high-confidence level in the evaluation of the artery of Adamkiewicz.

Interstitial lung diseases: Imaging contribution to diagnosis and elementary radiological lesions.

Interstitial pneumonias comprise a heterogeneous group of disorders in which a multidisciplinary approach is important for accuracy in diagnosis; indeed, one might say, even mandatory. The team of collaborators should include radiologists, because high resolution computed tomography (HRCT) of the thorax is the first, and most of times, the only imaging examination to be prescribed after chest X-ray. Elementary lesions of the interstitium can be accurately described with HRCT, inasmuch as lung windowing with sharp filtering in this technique reproduces the microscopic features of the lung. Guidance of bronchoalveolar lavage and biopsy procedures is also possible with HRCT.

Female Japanese quail visually differentiate testosterone-dependent male attractiveness for mating preferences

Biased mating due to female preferences towards certain traits in males is a major mechanism driving sexual selection, and may constitute an important evolutionary force in organisms with sexual reproduction. In birds, although the role of male ornamentation, plumage coloration, genetic dissimilarity, and body size have on mate selection by females have been examined extensively, few studies have clarified exactly how these characteristics affect female mate preferences. Here, we show that testosterone (T)-dependent male attractiveness enhances female preference for males of a polygamous species, the Japanese quail. A significant positive correlation between female mating preference and circulating T in the male was observed. The cheek feathers of attractive males contained higher levels of melanin and were more brightly colored. The ability of females to distinguish attractive males from other males was negated when the light source was covered with a sharp cut filter (cutoff; < 640 nm). When females were maintained under short-day conditions, the expression of retinal red-sensitive opsin decreased dramatically and they became insensitive to male attractiveness. Our results showed that female preference in quail is strongly stimulated by male feather coloration in a T-dependent manner and that female birds develop a keen sense for this coloration due to upregulation of retinal red-sensitive opsin under breeding conditions.

A compact and sharp ultra-wide bandpass filter by using short-stub-loaded rectangular ring and split ring resonators

ABSTRACTA compact and sharp-rejection ultra-wideband (UWB) microstrip bandpass filter (BPF) is presented. The proposed filter is constructed with multiple-mode resonator (MMR) and split ring resonator (SRR). Moreover, proposed structure consists of two doublets parallel coupling gaps at each side of a microstrip ring. In comparison with some other filters, this structure shows a significantly wider passband due to the introduction of a cross-coupling between the feed lines (input and output) which generate four pairs of attenuation zeros in the passband.In order to control the transmission zeros in the passband and adjust the transmission zeros near the lower edge of the filter, a short stub loaded on microstrip rectangular ring is used. Also, In order to sharpen the upper edge of the filter, the SRRs have been used in both side of the doublets parallel coupling gaps which leads to the addition of one extra transmission poles at the upper edge of the filter. Consequently, a compact five-zero and one-pole UWB BPF is designed which exhibits extremely sharp-rejection skirts around the target passband.The proposed filter has a passband covering 2.83–10.06 GHz and its measured 3 dB fractional bandwidth is about 112.5%. Furthermore, rejection level better than 20 dB in upper stop-band is extended to around 18 GHz. To our knowledge, the size of proposed UWB filter is more compact in comparison with known similar filters.

Monitoring of fetal heart rate using sharp transition FIR filter

Abstract We propose a novel technique which uses a linear phase sharp transition finite impulse response filter with reduction in band edge ripples due to Gibb’s phenomenon. This is accomplished by a slope matching technique. This design can be used for processing a wide variety of signals irrespective of their bandwidth. This paper includes the mathematical design analysis of the band pass filter with slope matching which used fetal frequency fiduciary edges to filter the raw abdominal ECG signals. Our filter design displayed a fairly good magnitude response in all passband, stopband and transition regions with very little computation time and thus is suitable for real time processing of numerous records at a time. The magnitude responses of our finite impulse response filter design was compared to Parks-McClellan algorithm. It was observed that our algorithm showed better results in the passband and stopband at lower filter orders. The peak passband in conventional finite impulse response designs is about 18% which is reduced to around 1.5% with the use of trigonometric functions in the proposed filter model combined with slope equalization technique. The QRS detector effectively extracts the fetal R-peaks to display the fetal heart rate variability which diagnoses the mother-fetus health status. The accuracy of the noninvasive fetal heart rate measurement using our technique is found to be impressive and matches closely with the fetal scalp records. The obtained results show that the sensitivity ranges from 88.36% to 100%, the positive predictive value ranging from 92.31% to 100% and an overall average accuracy recorded at 95.19%.

Low complexity reconfigurable channelizers using non-uniform filter banks

A Software Defined Radio (SDR) channelizer needs reconfigurable sharp filter banks with low implementation complexity. In this paper, the design of non-uniform Modified Discrete Fourier Transform filter bank (MDFT FB) is proposed to be used in SDR channelizer. The frequency response masking technique is used to design the prototype filter which gives sharp filters with lower hardware complexity, compared to the finite impulse response filters. The canonic signed digit (CSD) representation is used in the design, to convert the continuous filter coefficients into discrete coefficients. Multi-objective artificial bee colony algorithm is utilized to improve the performance degradation when the CSD represented filter coefficients are used. Further, the shift inclusive differential technique with common sub-expression elimination is used to reduce the number of adders. Xilinx ISE is used to verify the hardware requirement, for the implementation of the non-uniform MDFT FB. Hence low complexity reconfigurable SDR channelizers using non-uniform MDFT FB is proposed in this paper.

Is there a relationship between perceptual difficulties and auditory functioning at the periphery and the brainstem in children suspected with auditory processing disorder?

The test battery typically used for the diagnosis of auditory processing disorder (APD) is highly heterogeneous, with an emphasis on the central auditory nervous system. As such, the peripheral auditory system is typically only screened for the presence of an overt hearing loss. Our previous work suggested that children suspected of APD (sAPD) have atypically sharp cochlear tuning when measured using stimulus frequency otoacoustic emission (SFOAE) group delay. In the present work, we extend our previous findings and test the hypothesis that cochlear tuning influences auditory brainstem response (ABR) latencies. Our hypothesis is based on filter theory, which suggests that a sharper filter will take longer to build-up and ring longer. We predicted that sharper cochlear filters in sAPD should result in delayed ABR wave latencies and will be associated with poorer performance on speech perception tests. Preliminary data from 16 sAPD and 6 typically developing children show a positive correlation between cochlear tuning and ABR peak I latency. Cochlear tuning explains a significant proportion of the variance in ABR peak I latency (R2 = 0.25). Further behavioral results and implications for inclusion of auditory peripheral examination in APD tests will be discussed.

Unified FRM‐based complex modulated filter bank structure with low complexity

Software defined radios typically employ digital filter banks (FBs) for channelisation. Frequency response masking (FRM) approach is used to reduce the computational complexity of the complex modulated FB with narrow transition band. A unified FRM-based complex modulated FB structure is proposed to design sharp filters with arbitrary passband bandwidth. The proposed unified FRM-based complex modulated FB structure with low complexity is suitable for different even-stacked or odd-stacked, maximally decimated or non-maximally decimated structures. It also can be directly applied to high sampling rate systems. It is shown that the proposed unified FRM-based complex modulated FB structure can obtain the improvement of the computational complexity compared with the other methods.

Novel angular‐independent higher order band‐stop frequency selective surface for X‐band applications

A higher order miniaturised band-stop frequency selective surface (FSS) with angular stability performance for X-band applications is presented in this study. The miniaturisation has been achieved by incurving the arms of conventional cross dipole shape inside. The unit cell size of FSS is diminished up to 75% compared to cross dipole FSS operating at the same resonant frequencies. Moreover, the presented FSS is designed to exhibit stable angular performance for incident angles up to about 60° for TE- and TM-polarised waves. The maximum relative frequency deviation is 1.28% with respect to different angles of incidence. Although the designed FSS consists of two layers, higher order and sharp roll-off filter characteristics have been obtained. The simulation of the proposed FSS is performed with the CST MWS. To verify the simulation results, the presented FSS is measured and a good match between the experimental and simulation results are obtained.

Automatic Calcium Scoring in Low-Dose Chest CT Using Deep Neural Networks With Dilated Convolutions.

Heavy smokers undergoing screening with low-dose chest CT are affected by cardiovascular disease as much as by lung cancer. Low-dose chest CT scans acquired in screening enable quantification of atherosclerotic calcifications and thus enable identification of subjects at increased cardiovascular risk. This paper presents a method for automatic detection of coronary artery, thoracic aorta, and cardiac valve calcifications in low-dose chest CT using two consecutive convolutional neural networks. The first network identifies and labels potential calcifications according to their anatomical location and the second network identifies true calcifications among the detected candidates. This method was trained and evaluated on a set of 1744 CT scans from the National Lung Screening Trial. To determine whether any reconstruction or only images reconstructed with soft tissue filters can be used for calcification detection, we evaluated the method on soft and medium/sharp filter reconstructions separately. On soft filter reconstructions, the method achieved F1 scores of 0.89, 0.89, 0.67, and 0.55 for coronary artery, thoracic aorta, aortic valve, and mitral valve calcifications, respectively. On sharp filter reconstructions, the F1 scores were 0.84, 0.81, 0.64, and 0.66, respectively. Linearly weighted kappa coefficients for risk category assignment based on per subject coronary artery calcium were 0.91 and 0.90 for soft and sharp filter reconstructions, respectively. These results demonstrate that the presented method enables reliable automatic cardiovascular risk assessment in all low-dose chest CT scans acquired for lung cancer screening.