Important Frequency Bands Research Articles

UHF and X Band Electro-Magnetic Shielding of Advanced Devices by Some Polymer–Composites

Electro-magnetic interference (EMI) affects delicate electronic devices and living beings. Composites of a polymeric binder with fine metallic turnings (copper and brass), powders of conducting inorganic compounds (suitably fired cadmium oxide), ferroelectric powders (BaTiO3 and orthorhombic PbNb2O6), and with their combinations have been prepared as cloth-like sheets, and characterized in a Vector Network Analyzer (VNA) with respect to EMI shielding and reflection capabilities. Input power (Pin) for the EMI shield (above-mentioned test materials), the reflected power (Prefl) and the transmitted power (Pout) have been measured by the VNA as a function of EM wave frequency in two technically important frequency bands - in 700 MHz to 3 GHz part of the ultra-high frequency (UHF) band and in the X-band, covering 8 to 12 GHz. From the measured data, Shielding Effectiveness in dB unit = 10 log (Pout / Pin) and Reflection Effectiveness in dB = 10 log (Prefl / Pin) have been calculated and studied for all the samples, with the results presented and discussed. In particular, our substitution of expensive metal powders by fine metallic turnings, available as waste from mechanical workshops, reduces the cost of polymer-metal composites substantially, retaining high shielding i.e. low transmission (down to -33dB in 08 to 12 GHz range).

Spectrum measurement modelling and prediction based on wavelets

In this study, a new spectrum measurement modelling method is proposed for several important frequency bands by using the Daubechies wavelets. On the basis of this method, spectrum measurement prediction is also proposed by using regression. Unlike most previous works that model or predict the occupancy rate of the frequency band of interest, this study models and predicts the power measurements directly to remove the dependence of the model on the challenging detection threshold and also to provide more comprehensive descriptions of the licenced user signals for performance improvement in cognitive radios (CRs). Numerical results show that the new spectrum models have acceptable accuracies. They also show that the proposed spectrum measurement prediction method tracks the trend of the true values well. Therefore, these results are very useful in CR designs.

Design of recursive variable digital filters with theoretically guaranteed stability

ABSTRACTStability is one of the most concerned issues in designing a recursive variable digital filter (VDF). This is because the coefficients of a recursive VDF constantly vary in the tuning process, and updating the coefficients may incur instability. Thus, an appropriate measure needs to be taken for ensuring its stability. This paper presents a new coefficient transformation (CT) method for transforming the coefficients of a recursive transfer-function denominator into a set of new coefficients. From the viewpoint of conventional constant-coefficient filter (constant filter) design, the new coefficients can take arbitrary values without incurring instability. For designing a stable VDF, we apply this CT to the variable case and approximate each transformed coefficient as a distinct polynomial in the tuning parameter. Thus, we can change the filter coefficients by changing the value of the tuning parameter, and thus tune the magnitude response. Thanks to the proposed CT, updating the filter coefficients will never incur instability. This is the core part of the CT-based design approach. In this paper, we utilise a weighting function to ignore the transition-band errors and thus enhance the design accuracy of important frequency bands (passband and stopband). Moreover, the polynomials use different degrees so as to reduce the VDF complexity. Two design examples (lowpass VDF and bandpass VDF) are provided for verifying the design accuracy and checking the stability.

Optimized broadband and dual-band printed slot antennas for future millimeter wave mobile communication

In this paper, a broadband and a dual-band printed slot antennas for the future millimeter wave mobile network communication are proposed. The antennas are designed for Ka-band frequency of operation. The basic antenna design consists of a circular radiating patch that is placed non-concentrically inside a circular slot etched off the ground plane. Matching between a radiating patch and the 50Ω microstrip line is manipulated through a proximity-feed technique. The simulated antenna prototype – I and prototype – II are fabricated and successfully measured. The results indicate that the proposed antenna prototype – I yields the broadband impedance bandwidth >20GHz (from 20 to >40GHz) define by S11<−10dB that covers two important millimeter wave frequency bands (28/38GHz). To reduce the interference between the different applications operating around these frequency bands, the L-shaped slot is etched off in prototype – II feedline to create a notched band of 30–35GHz. The measured results show that the designed antenna has dual-band at 28 and 38GHz with a band notched at 33GHz. The low profile/cost broadband antenna (prototype – I) and dual-band antenna (prototype – II) has the measured gain upto 5.30dBi and 5.6dBi with the estimated radiation efficiency of 93% and 94%, respectively. The simulations are performed using industry-standard software CST MWS and HFSS. The measurements are in a good match with the simulated results.

A Compact Multiband Hybrid Fractal Antenna for Multistandard Mobile Wireless Applications

This paper presents a compact Multiband hybrid fractal antenna designed for mobile wireless applications it has planar structure and suitable for mobile applications at low cost. The proposed antenna structure is obtained by integrating a Koch curve and Minkowski curve. It exhibits multiband behavior, acceptable values of return loss, VSWR and gain in-spite of its compact size and less complexity. The proposed antenna design has been examined up to 2nd iteration of the new fractal geometry. The simulated results exhibited seven bands of operation covering some important frequency bands like GPS (L1 = 1227.60 MHz), bluetooth (2.41---2.49 GHz) of ISM band, WLAN 802.11 a/b (5.15---5.35 GHz) and other bands covers applications like mobile/fixed satellite and aeronautical navigation (3.876---4.375, 6.6188---7.0045, 7.9698---8.3373 and 9.1648---9.6214 GHz). Proposed antenna is designed by using scripting method of HFSS using MATLAB.

4 K high frequency pulse tube cryocooler used for terahertz space application

Terahertz (THz) frequency region, defined from 0.1 to 10 THz, is an important frequency band for radio astronomy and atmospheric science. As NbN Superconductor-Insulator-Superconductor (SIS) mixers used for terahertz detection, which are studied by the Purple Mountain Observatory (PMO), Chinese Academy of Sciences (CAS), work at 8-10 K, and require condition of micro vibrations, its astronomical observation in aerospace is limited by suitable refrigeration method. 4 K high frequency pulse tube cryocooler developed by Key Laboratory of Space Energy Conversion Technologies (SECT), Technical Institute of Physics and Chemistry (TIPC), CAS, offers an opportunity for the application of SIS mixers. This article introduces the progress of the two-stage high frequency pulse tube cryocooler researched by TIPC. The cryocooler has reached a no load temperature of 4.5 K which is the lowest temperature for this kind of cryocooler reported so far. The successful coupling between the THz component and the high frequency pulse tube cryocooler lays a solid foundation for space detection in the terahertz band.

High-accuracy interpolator design with reduced first-order derivative constraints

In this article, we propose a new frequency-domain weighted-least-squares method for designing high-accuracy interpolator (interpolation kernel) that reduces the number of the first-order derivative continuity constraints. By reducing the number of the first-order derivative constraints, we can increase the degree of freedom in the design, and thus have more flexibility to get more accurate design results. The interpolator consists of 6 piecewise polynomials of the third degree (cubic), and it is performed in the frequency-domain through minimising the weighted integrated-squared-error of the spectrum (frequency response). The weighting function is adjusted so as to ignore some insignificant frequency bands and put more emphasis on the important frequency bands. By imposing the continuity constraints on the interpolator itself as well as the reduced first-order derivative constraints at the contacting points, we get three free parameters of the interpolator. These three parameters are then optimised in such a way that the weighted integrated-squared-error of the frequency response is minimised. We will utilise a narrow-band example to demonstrate the performance improvement over other existing interpolators.

Automatic sleep staging using empirical mode decomposition, discrete wavelet transform, time-domain, and nonlinear dynamics features of heart rate variability signals

The conventional method for sleep staging is to analyze polysomnograms (PSGs) recorded in a sleep lab. The electroencephalogram (EEG) is one of the most important signals in PSGs but recording and analysis of this signal presents a number of technical challenges, especially at home. Instead, electrocardiograms (ECGs) are much easier to record and may offer an attractive alternative for home sleep monitoring. The heart rate variability (HRV) signal proves suitable for automatic sleep staging. Thirty PSGs from the Sleep Heart Health Study (SHHS) database were used. Three feature sets were extracted from 5- and 0.5-min HRV segments: time-domain features, nonlinear-dynamics features and time–frequency features. The latter was achieved by using empirical mode decomposition (EMD) and discrete wavelet transform (DWT) methods. Normalized energies in important frequency bands of HRV signals were computed using time–frequency methods. ANOVA and t-test were used for statistical evaluations. Automatic sleep staging was based on HRV signal features. The ANOVA followed by a post hoc Bonferroni was used for individual feature assessment. Most features were beneficial for sleep staging. A t-test was used to compare the means of extracted features in 5- and 0.5-min HRV segments. The results showed that the extracted features means were statistically similar for a small number of features. A separability measure showed that time–frequency features, especially EMD features, had larger separation than others. There was not a sizable difference in separability of linear features between 5- and 0.5-min HRV segments but separability of nonlinear features, especially EMD features, decreased in 0.5-min HRV segments. HRV signal features were classified by linear discriminant (LD) and quadratic discriminant (QD) methods. Classification results based on features from 5-min segments surpassed those obtained from 0.5-min segments. The best result was obtained from features using 5-min HRV segments classified by the LD classifier. A combination of linear/nonlinear features from HRV signals is effective in automatic sleep staging. Moreover, time–frequency features are more informative than others. In addition, a separability measure and classification results showed that HRV signal features, especially nonlinear features, extracted from 5-min segments are more discriminative than those from 0.5-min segments in automatic sleep staging.

Intelligent acoustic rotor speed estimation for an autonomous helicopter

Acoustic sensing to gather information about a machine can be highly beneficial, but processing the data can be difficult. In this work, a variety of methodologies have been studied to extract rotor speed information from the sound signature of an autonomous helicopter, with no a-priori knowledge of its underlying acoustic properties.The autonomous helicopter has two main rotors that are mostly identical. In order to identify the rotors’ speeds individually, a comparative evaluation has been made of learning methods with input selection, reduction and aggregation methods. The resulting estimators have been tested on unseen training data as well as in actual free-flight tests.The best results were found by using a genetic algorithm to identify the important frequency bands, a centroid method to aggregate the bands, and a neural-network estimator of the rotor speeds. This approach succeeded in estimating individual rotor speeds of an autonomous helicopter without being distracted by the other, mainly identical, rotor. These results were achieved using standard, low-cost hardware, and a learning approach that did not require any a-priori knowledge about the system's acoustic properties.

A Low-Power ECoG/EEG Processing IC With Integrated Multiband Energy Extractor

Electrocorticography (ECoG) implants have recently demonstrated promising results towards potential use in brain-computer interfaces (BCIs). Spectral changes in ECoG signals can provide insight on functional mapping of sensorimotor cortex. We present a 6.4 μ W electrocorticography (ECoG)/electroencephalography (EEG) processing integrated circuit (EPIC) with 0.46 μ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> noise floor intended for emerging brain-computer interface (BCI) applications. This chip conditions the signal and simultaneously extracts energy in four fully programmable frequency bands. Functionality is demonstrated by tuning the four bands to important frequency bands used by ECoG/EEG applications: α (8-12 Hz), β (18-26 Hz), low-γ (30-50 Hz), and γ (70-100 Hz). Measured results from in vivo ECoG recording from the primary motor cortex of an awake monkey are presented.

Application of atmospheric absorption models for aircraft enroute noise.

Propagation of aircraft enroute noise for flights above 18 000 ft above ground level (AGL) (5.49 km AGL) is important for estimating noise impact in U.S. National Parks and other quiet areas. One key to the accurate estimation of noise impact is atmospheric absorption. In our atmosphere, it turns out that the absorption coefficient is dependent on altitude as well as frequency. The altitude dependent parameters include mean pressure, temperature, and relative humidity as well as the concentration of molecular species. This altitude effect can be important for certain frequency bands, and this point will be emphasized in this paper. In addition, an improved atmospheric absorption model for high altitudes of Sutherland and Bass [J. Acoust. Soc. Am. 115, 1012–1032 (2004)] shows slightly different values of atmospheric absorption in important frequency bands for aviation noise at altitude compared to the typical ANSI Standard S1.26-1995 (R 2009). For certain situations, the updated atmospheric absorption coefficient could produce different enroute noise predictions on the ground. [Work supported by FAA/NASA/Transport-Canada PARTNER Center of Excellence.]

Localised coastal habitats have distinct underwater sound signatures

There is evidence that ambient underwater sound is used by some pelagic larval reef fishes and decapods as a guide to direct them toward coastal areas. It would be advantageous to these organisms if they were also able to use sound to remotely identify suitable settlement habitats. However, it is unknown whether different coastal habitats produce different sounds that would be capable of providing distinctive cues for larvae. This study identified marked differences in the char- acteristics of ambient underwater sound at 3 distinct types of coastal habitat: a macroalgal-dominated reef, a sea urchin-dominated reef, and a sandy beach. The sea urchin-dominated reef habitat pro- duced sound that was significantly more intense overall in a biologically important frequency band (800 to 2500 Hz), compared with that from macroalgal-dominated reefs and beach habitats. The sound produced by snapping shrimp also exhibited marked differences among habitat types, with the sea urchin-dominated reef having significantly more snaps than the macroalgal-dominated reef or beach habitat. Many of the differences in the sound produced by the 2 reef habitats became more apparent at dusk compared with noon. This study provides evidence that there are significant differ- ences in the spectral and temporal composition of ambient sound associated with different coastal habitat types over relatively short spatial scales. An acoustic cue that conveys both directional and habitat quality information that is transmitted considerable distances offshore would have the poten- tial to be of immense value to the pelagic larval stage of a coastal organism attempting to remotely locate a suitable habitat in which to settle.

Uncovering Gamma in Visual Tasks

Gamma is an important frequency band of the electroencephalogram (EEG), but its study has been impaired by problems with artefacts. This paper focuses on the artefacts caused by contraction of the extra-ocular muscles at the start of a saccade, which produces spurious gamma oscillations in the EEG. An algorithm was written and tested which detects and reduces the effect of this artefact. It involves novel adaptations of standard regression techniques which have traditionally been used to reduce blink artefacts, so as to render them applicable to the gamma band ocular artefact. Before the algorithm can be applied any power-line noise must be removed by noise cancellation and not notch filtering. The sharp, broadband gamma peak at around 200 ms was substantially reduced by the algorithm in all three subjects tested. However, there may be lower amplitude, task related, modulations in gamma which are uncovered when the artefact is reduced. The amplitude of the artefact had its largest positive value at the most anterior electrodes and its largest negative value at midline central and parietal electrodes, and these two sets of locations also showed the greatest reductions in gamma band magnitude after application of the algorithm. This study demonstrates the feasibility of reducing the saccade linked gamma band artefact.

A novel LTCC miniaturized dualband balun

In this letter, a novel low temperature cofired ceramic (LTCC) miniaturized dualband balun using a tapered line structure has been presented. The key concept for our dualband solution is by employing tapered line structures in the conventional Marchand baluns. In our new design, we have demonstrated the tapered line structure can shift the periodic operation frequency to a desired frequency band. A sample balun design has been presented. The novel LTCC dualband balun has been simulated and verified by measurement. The measured results exhibit that the proposed balun can easily cover the important radio frequency bands at 2.4GHz, 5.25GHz, and 5.85GHz.

Assessment of potential noise-induced hearing loss with commercial “Karaoke” noise

A study was conducted to assess the noise levels of popular Karaoke environments in Korea and the degree of potential noise-induced hearing loss due to commercial Karaoke noise. Using 18 subjects with normal hearing, a two-way, mixed-factors experimental design was used with two independent variables of “noise source” (no-singer, one-singer, and two-singer conditions) and “music type” (Trot, Ballad, and Rock music). For each experimental condition, average sound pressure levels and maximum sound pressure levels were measured. For assessing amount of temporary hearing threshold shift as a measure of potential hearing loss index, pure-tone audiometry was applied for measuring subjects’ hearing threshold levels of both ears before and after 100 min exposure to Karaoke noise. Questionnaires from 155 actual Karaoke users were also obtained to evaluate realistic user subjective perception on the Karaoke environment. Results showed that noise levels of typical Karaoke singing environments were higher than 95 dBA, with maximum noise levels often exceeded the US OSHA's non-permissible 115 dBA level. Further statistical analysis of hearing threshold shift revealed that up to 8 dB of significant hearing loss was found at the most important human hearing frequency band, centered at 4000 Hz, after about less than 2 h of Karaoke noise exposure, indicating that Karaoke facilities may pose a serious threat to noise-induced hearing loss. Along with some ergonomic/safety issues, practical hearing protection strategies are suggested and discussed. Relevance to industry Since noise levels from popular commercial Karaoke facilities are found to be potentially dangerous, the Karaoke-related industries, of supporting a big consumer market of entertainment, need to provide safer environments to protect naive users from potential hearing loss. Providing better design of Karaoke facilities with some ergonomic intervention strategies (such as proper sound absorptive treatment in Karaoke rooms, displaying warning signs of potential hearing loss, and setting up an upper safety volume limit in the Karaoke machine, etc.) may help those industries not only contribute for consumer protection but also develop better market with strong ethical and legal support in the future.

Edge-based subband VQ techniques for images and video

A key issue in subband coding is the efficient compression of the less informative but perceptually important upper frequency bands of the decomposed image. A new approach capable of effectively encoding the upper-bands is described. An intra-band vector quantization (VQ) technique is employed for compression of the base-band while the upper frequency bands are encoded by a hierarchical inter-band VQ method. The proposed inter-band vector quantization scheme exploits the redundancies that exist between pels of significant perceptual importance across the upper frequency bands of the same resolution. Such pels are observed to be at or around the edge-locations, displaying similar discontinuity behavior across the subbands. Therefore, an edge-detector is applied on the reconstructed base-band to extract the edge locations, and as a result no overhead information is transmitted to identify the position of these pels in the upper-bands. Furthermore, a residual subband, being the difference between the original base-band of each layer and its encoded version, is incorporated in the proposed inter-band VQ model. Thus, the proposed interband VQ scheme is simply the vector quantization of pixels across the upper-bands together with their corresponding residual band. Compression results are presented for both digital images and video sequences which demonstrate high subjective visual qualities.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An auditory fovea in the barn owl cochlea

The distribution of frequencies along the basilar papilla of the barn owl (Tyto alba) was studied by labelling small groups of primary auditory neurones of defined frequency response and tracing them to their peripheral innervation sites. The exact location of marked neurones was determined in cochlear wholemounts with the aid of a special surface preparation technique. The average basilar papilla length (in fixed, embedded specimens) was 10.74 mm. The resulting frequency map shows the basic vertebrate pattern with the lowest frequencies represented apically and increasingly higher frequencies mapped at progressively more basal locations. However, the length of basilar papilla devoted to different frequency ranges, i.e. the space per octave, varies dramatically in the barn owl. The lower frequencies (up to 2 kHz) show values between about 0.35 and 1 mm/octave, which are roughly equivalent to values reported for other birds. Above that, the space increases enormously, the highest octave (5–10 kHz) covering about 6 mm, or more than half of the length of the basilar papilla. Such an overrepresentation of a narrow, behaviourally very important frequency band is also seen in some bats, where it has been termed an acoustic or auditory fovea.

Mean circulation and variability on the eastern Canadian continental shelf

The circulation and variability on eastern Canadian continental shelves is reviewed with emphasis on horizontal and vertical structure in the water column. Mean and seasonal currents, sheared by stratification and friction, generally follow bathymetry and are driven primarily by surface wind stress and buoyancy fluxes. In certain near-resonant embayments, nonlinear interactions of the tide also make significant contributions to the mean and low-frequency currents. Direct forcing of low-frequency shelf circulation by offshore currents and pressure fields is of lesser importance according to recent observations and models. At higher frequencies, the wintertime response to atmospheric forcing occurs in three important frequency bands: surface wave (periods of 2–20 s), inertial (17–22 h) and synoptic or subtidal (2–10 days). Most of the subtidal energy in the subsurface pressure (SSP) field is attributable to direct local forcing by alongshore wind and to remote forcing by coastal-trapped waves (CTW). The subtidal current variability is less coherent with these sources primarily because of small scale circulations created by vortex stretching, topographic steering and scattering by the rugged shelf bathymetry. Bottom friction and scattering control the ratio of locally and remotely forced subtidal energy as a function of position on the shelf. Intermittent inertial currents in stratified shelf waters, often associated with mesoscale atmospheric forcing, exhibit a 180° phase change across the pycnocline and are inhibited near the coast. Surface waves generated by storm winds are strongly dissipated in shallow water, where they enhance bottom stresses that: (1) balance the surface wind stress; and (2) may contribute to the damping of inertial waves. Specific examples of these phenomena are drawn from observations on the Scotian Shelf and in the Gulf of Maine.

Vibrational fluctuations of the hydrogen bonds around a nucleation defect of melting in poly(dG)-poly(dC).

Vibrational fluctuations of the hydrogen bonds around a nucleation defect of strand-separation melting of a DNA polymer, poly(dG)-poly(dC) (dG denotes repeating guanine bases on one strand and dC the repeating cytosine bases on the other strand), are analyzed at 293 and 340 K using a modified self-consistent phonon theory with a complex Green's function. At 293 K the helix is very stable and the important frequency band for fluctuation is the band between 60 and 120 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. This is the same important band as that for the fluctuation of the hydrogen bonds which are far from the defect. At 340 K, near the temperature at which the hydrogen-bond instability in the neighboring cells to the defect occurs, there are two important frequency bands. One is the band between 60 and 120 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ which is essential for the fluctuation of the bond near the major groove. A second band is the band under 20 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ which is critical for the fluctuation of the bond near the minor groove. We also explain the directional effects around the defect when the instability of the bonds begins to occur based on the roles of the particular phonons.

LONGSHORE VARIABILITY OF WAVE RUN-UP ON NATURAL BEACHES

The longshore variability of wave run-up from a natural beach is examined using data from a large field experiment at the Field Research Facility in Duck, North Carolina, in October, 1982. Two particular runs were selected for intensive analysis. These were chosen to represent a dissipative and a reflective surf zone condition, so have I ribarren numbers 0.97 and 1.81 respectively. The dissipative data run showed much more uniform statistics in the longshore than did the reflective run. Also, the dissipative run was dominated by the infragravity band energy while the reflective run was dominated by the incident band. Selection of several important frequency bands for frequency-domain EOF analysis showed that the lower frequency peaks appeared to be associated with leaky modes (very long longshore wavelengths) and the pier had little influence. On the other hand, higher frequencies were clearly influenced by the pier in both amplitude and phase. An interesting subharmonic peak from the reflective run appeared to be a low (but not zero) mode standing edge wave. A new technique,time exposure photography, is introduced. It allows the quick determination of longshore variability such as would be produced by a dominant standing edge wave. It can also be used to image offshore bathymetry and sand bar systems.