High Cutoff Frequency Research Articles

Improving surface EMG burst detection in infrahyoid muscles during swallowing using digital filters and discrete wavelet analysis

The visual inspection is a widely used method for evaluating the surface electromyographic signal (sEMG) during deglutition, a process highly dependent of the examiners expertise. It is desirable to have a less subjective and automated technique to improve the onset detection in swallowing related muscles, which have a low signal-to-noise ratio. In this work, we acquired sEMG measured in infrahyoid muscles with high baseline noise of ten healthy adults during water swallowing tasks. Two methods were applied to find the combination of cutoff frequencies that achieve the most accurate onset detection: discrete wavelet decomposition based method and fixed steps variations of low and high cutoff frequencies of a digital bandpass filter. Teager-Kaiser Energy operator, root mean square and simple threshold method were applied for both techniques. Results show a narrowing of the effective bandwidth vs. the literature recommended parameters for sEMG acquisition. Both level 3 decomposition with mother wavelet db4 and bandpass filter with cutoff frequencies between 130 and 180Hz were optimal for onset detection in infrahyoid muscles. The proposed methodologies recognized the onset time with predictive power above 0.95, that is similar to previous findings but in larger and more superficial muscles in limbs.

Numerical investigation on the effect of structure parameter of acoustic field rotator on its operating bandwidth

The theory about transformation acoustics is introduced to indicate that designing an acoustic field rotator, in reality, is feasible. Then, numerical research is conducted to investigate the effect of geometrical parameters on the high cut-off frequency, including the size of building block, the aspect ratio of building block, the size of acoustic field rotator, the external diameter of acoustic field rotator, and the internal diameter of acoustic field rotator. The results suggest that the sizes of building blocks of acoustic field rotators are inversely proportional to their high cut-off frequencies in the studied frequencies. The effect of the size of acoustic field rotator mainly lies in the size of building block instead of the number of the building block. There is a linear relationship between the aspect ratio of the building block and high cut-off frequency in the studied frequencies. In addition, the layer of building block has an effect on high cut-off frequency as well. The current numerical study is helpful to give a better guidance for designing the acoustic field rotator.

Neural representation of the self-heard biosonar click in bottlenose dolphins (Tursiops truncatus).

The neural representation of the dolphin broadband biosonar click was investigated by measuring auditory brainstem responses (ABRs) to "self-heard" clicks masked with noise bursts having various high-pass cutoff frequencies. Narrowband ABRs were obtained by sequentially subtracting responses obtained with noise having lower high-pass cutoff frequencies from those obtained with noise having higher cutoff frequencies. For comparison to the biosonar data, ABRs were also measured in a passive listening experiment, where external clicks and masking noise were presented to the dolphins and narrowband ABRs were again derived using the subtractive high-pass noise technique. The results showed little change in the peak latencies of the ABR to the self-heard click from 28 to 113 kHz; i.e., the high-frequency neural responses to the self-heard click were delayed relative to those of an external, spectrally "pink" click. The neural representation of the self-heard click is thus highly synchronous across the echolocation frequencies and does not strongly resemble that of a frequency modulated downsweep (i.e., decreasing-frequency chirp). Longer ABR latencies at higher frequencies are hypothesized to arise from spectral differences between self-heard clicks and external clicks, forward masking from previously emitted biosonar clicks, or neural inhibition accompanying the emission of clicks.

Detection of vibrations on windows and doors excited by a speaker using video cameras

Algorithms were developed and tested to estimate acoustic coupled vibrations on doors and windows in a small building using data from commercial video cameras. The building was excited with a speaker that emitted low frequency tones. Image processing based algorithms were developed to estimate the frequency, amplitude, and signal-to-interference-plus-noise ratio (SINR) of the tones. Sensors such as Laser Doppler Vibrometers (LVDs) and accelerometers are much more sensitive than video cameras for measuring small vibrations and have a higher cutoff frequency. However, video cameras are ubiquitous, passive, and can potentially monitor a large area. Their performance is limited by the target range due to increased pixel size and atmospheric turbulence, lighting conditions, the contrast of the object of interest and the sample rate of the camera. Given these limitations, there are still potential new applications and niches for using video cameras to remotely measure vibrations of objects.

The properties of two-dimensional fractal plasma photonic crystals with Thue-Morse sequence

In this paper, the properties of the acceptor modes and photonic band gaps (PBGs) of two-dimensional (2D) fractal plasma photonic crystals (PPCs) under a transverse-magnetic wave are theoretically studied by a modified plane wave expansion method. The density of states is calculated to elaborate the characteristics of the proposed 2D PPCs in which the dielectric cylinders are inserted in the plasma background according to the iteration rule of the Thue-Morse sequence with square lattices. The band structures of the proposed PPCs and 2D PPCs with a conventional square lattice are numerically determined to analyse the properties of PBGs and acceptor modes. The results illustrate that the performance is improved in the proposed PPCs compared to the 2D conventional PPCs with similar lattices. The larger PBGs and higher cutoff frequency are obtained when the Thue-Morse structure is introduced. The lowest edges of PBGs are flat, and they are originated from the Mie resonances. The acceptor modes can be considered as the quasi-localized states since the Thue-Morse sequence has the self-similarity and non-periodicity at the same time. The influences of configurational parameters on the properties of the proposed PPCs are studied in detail as well. The results demonstrate that the PBGs and acceptor modes can be easily tuned by changing those configurational parameters.

Enhanced performance in graphene RF transistors via advanced process integration

The state-of-the-art performance of a graphene radio-frequency (RF) field-effect transistor (FET) made of chemical vapor deposition (CVD) graphene is presented. The record high cut-off frequency as high as 380 GHz using CVD graphene was attributed to the implementation of advanced process integration. On the one hand, interface engineering has become critical in two-dimensional (2D) electronics since the charge transport of a 2D electron system like graphene is highly affected by the interface. The interface engineering was made for both the top and bottom of the graphene surface by implementing a non-polar material (1, 3, 5-trimethyl-1, 3, 5-trivinyl cyclotrisiloxane). In contrast to conventional polar materials, such as SiO2, the non-polar materials significantly reduce the surface optical phonon scattering in the graphene channel, leading to the enhanced RF performance of graphene FET. On the other hand, micro-scaled holes over the multilayer graphene and self-aligned structure also become a critical factor in minimizing the parasitic resistance that is inversely proportional to RF performance. As the growth technique of CVD graphene greatly advances, the advanced process integration scheme could bring graphene electronics one step further towards practical application.

Transport properties of graphene field effect transistors

Nowadays, integrated circuit design and manufacturing level is one of important symbols to evaluate the industrial development level of a country. Silicon-based metal oxide semiconductor field effect transistor has an important application in large-scale integrated circuit, and its special size has reached 14nm. However, further miniaturization in reaching the silicon physical limits of 10nm channel length. Graphene is one of the most promising materials to replace silicon. Due to its outstanding performance such as ultrafast carrier mobility, excellent mechanical strength and high transparency invisible light region, graphene is regarded as one of the vital next generation electronic materials. In recent years, the rapid development of the preparation technology of large area and high quality graphene has further promoted the research of new electronic devices based on graphene, which has attracted wide attention of researchers in the field of integrated circuit. Graphene field effect transistor has fast response rate and high cut-off frequency, whose feature size can continue to narrow. Therefore, the study of graphene field effect transistors has very important significance for the continuation of Moore’s law. Currently, SiO2 is generally used to the gate insulating layer of graphene field effect transistors. The dielectric constant value of SiO2 is lower, which leads to higher power consumption of the device. When the thickness of the SiO2 gate insulating layer is reduced to a certain degree, the device is easy to breakdown. However, when the semiconductor materials with high dielectric constant (Ta2O5, TiO2, Al2O3, etc.) as the gate insulating layer, the device can obtain higher mobility in the operating voltage as low as possible. This is an effective way to solve the high power consumption of the device. Although graphene field effect transistors have made some progress in the preparation and performance, the existing field effect transistors based on graphene have no obvious advantage in carrier mobility and current on/off ratio. Accordingly, the research of graphene field effect transistor will be the main direction of the field of integrated circuit in the future. In this paper, the graphene field effect transistors use ITO as the gate electrode, Ta2O5 as the gate insulating layer, graphene as the active layer, Ti/Au double-layer metal as the source/drain electrodes. The results of electrical properties measurements and analyses show that the graphene strip is in good ohm contact with source/drain electrodes. At room temperature, graphene field effect transistors exhibit an unique bipolar characteristic. The mobility for hole carrier is about 2272cm2/(Vs) and the current on/off ratio is about 6.2. The hysteresis phenomenon in the transfer characteristic curve is observed, which becomes more obvious with the increase of gate voltage. Meanwhile, the effect of the temperature on the characteristic of the graphene field effect transistor is studied. With the increase of temperature, the Dirac point voltage gradually shifts to zero point, and the hysteresis phenomenon becomes more and more obvious. The mobility for hole carrier and the current on/off ratio achieve optimum when the temperature is 75°C. The content and conclusions of above may provide a reference for further research of graphene field effect transistors.

SLD-MOSCNT: A new MOSCNT with step–linear doping profile in the source and drain regions

In this paper, a new structure, step–linear doping MOSCNT (SLD-MOSCNT), is proposed to improve the performance of basic MOSCNTs. The basic structure suffers from band to band tunneling (BTBT). We show that using SLD profile for source and drain regions increases the horizontal distance between valence and conduction bands at gate to source/drain junction which reduces BTBT probability. SLD performance is compared with other similar structures which have recently been proposed to reduce BTBT such as MOSCNT with lightly-doped drain and source (LDDS), and with double-light doping in source and drain regions (DLD). The obtained results using a nonequilibrium Green’s function (NEGF) method show that the SLD-MOSCNT has the lowest leakage current, power consumption and delay time, and the highest current ratio and voltage gain. The ambipolar conduction in the proposed structure is very low and can be neglected. In addition, these structures can improve short-channel effects. Also, the investigation of cutoff frequency of the different structures shows that the SLD has the highest cutoff frequency. Device performance has been investigated for gate length from 8 to 20 nm which demonstrates all discussions regarding the superiority of the proposed structure are also valid for different channel lengths. This improvement is more significant especially for channel length less than 12 nm. Therefore, the SLD can be considered as a candidate to be used in the applications with high speed and low power consumption.

Image Noise Analysis of a Large Ring PET Scanner

Image noise analysis of a large ring PET scanner “macro PET” performed using two different phantoms, namely a Jaszczak SPECT phantom and a uniform cylindrical phantom. In the present work, simple 2D filtered back projection was used to reconstruct all the images, and in almost all the cases a Hamming filter of cutoff frequency 0.4 and a 256 by 256 matrix with zoom factors from 1 to 4 were used in order to investigate the imaging capabilities of the new scanner and the influence of filter and cut-off frequency on the filtered back projected images. Results indicate that 11.1 mm cold rod in the Jaszczak phantom images can consistently be seen. The Coefficient of variation (CV) results for Hann and Hamming filters are very similar and increase approximately in linear fashion with higher cutoff frequency. The value of CV for the Parsen filter is lower than the value for Hann and Hamming filters. It concludes that all filters with low cut off-frequency (0.6) would suppress image noise but decrease contrast.

Research progress of graphene radio frequency devices

Graphene, the first realized two-dimensional material, has received much attention in electronic applications in recent years. With ultra-high carrier mobility and one atom thick structure, graphene becomes a promising semiconductor candidate for solving the problem of short channel effect in nanoscale metal-oxide-semiconductor field-effect transistor (MOSFET), and exploring its applications in radio frequency devices. How to develop the advantages of graphene transistor in radio frequency is an attractive research area. The first step is to obtain high quality graphene material. In this article we summarize the graphene growth methods commonly used in electronic field, including chemical vapor deposition on metal substrates and epitaxial method on wide bandgap semiconductor and insulator substrates. Another key factor to improve graphene transistor performance is to carefully design the device structure and process flow. Multi-finger gate and T-shaped gate are widely used in MOSFET. These two structures can significantly reduce gate resistance, and result in a better radio frequency performance. Inverted process is introduced for graphene FET fabrication, which is compatible with silicon-based back-end-of-line technology. It can reduce the damages to graphene during fabrication. Another improved self-aligned gate deposition process can lead to a good gate coupling and less parasitic parameters. These newly developed process play a prominent part in increasing the cut-off frequency and maximum oscillation frequency of graphene radio frequency devices. In addition, single crystal graphene is helpful in eliminating carriers scattering and improving the radio frequency properties of graphene transistor. So far, the highest cut-off frequency of graphene transistor reaches over 300 GHz by a few groups, but the maximum oscillation frequency remains low. Record-high maximum oscillation frequency is 200 GHz when gate length is 60 nm. Further improvement of maximum oscillation frequency needs to be tried out. Several graphene radio frequency circuits are also discussed in the paper. Some of the circuits have similar structures to silicon-based circuits, and others are designed based on the unique property of graphene transistor, like ambipolar transport properties. The new concept circuits have simpler structures than conventional circuits. With the rapid development of graphene growth and related integrating technology, the potential to use graphene in radio frequency field will be further increased.

Highly compact UWB bandpass filter based on composite right/left-handed transmission line and meander fractal like ring slot in ground

An ultra-wideband (UWB) highly compact bandpass filter with extremely high passband bandwidth is presented. The proposed structure is made using three-staged stepped-impedance lines and a composite right/left-handed transmission line (CRLH-TL) synthesized with meander fractal like ring slot in the ground and series capacitive gap in conductor strip. The capacitive gap in conductor strip and meander fractal like ring slot in the ground plane play major role for controlling the lower and higher cut-off frequencies. The equivalent circuit model of proposed filter is demonstrated and lumped parameters are extracted. A prototype is fabricated to experimentally validate the performance of proposed filter. The proposed UWB filter has extremely wide −10 dB return loss passband bandwidth from 3.14 to 18.26 GHz with relative bandwidth of 142% and insertion loss better than 0.5 dB. Also it achieves a wide upper-stopband from 19.7 to 24.4 GHz with insertion loss better than 13.0 dB, return loss <1.5 dB and sharpened rejection skirts outside the passband at both lower and upper frequency ends. Good agreement is found between simulated and measured results with measured group delay variation in the passband <0.65 ns.

CNTs and Graphene-Based Diodes for Microwave and Millimeter-Wave Circuits on Flexible Substrates

This paper presents the fabrication and characterization of carbon nanomaterials, i.e., carbon nanotubes (CNTs) and reduced graphene oxide (r-GO), based diodes on flexible substrates for high-frequency circuit applications. CNTs and graphene are good candidates as they possess excellent electronic and mechanical properties. For high-frequency circuits, diodes with lower parasitics and optimal impedance are required to achieve a high cutoff frequency and ease of impedance matching. Here, multiple CNTs are arranged in parallel to reduce the series resistance and to lower the impedance value, whereas 2-D graphene readily provides the desired impedance values. CNT and r-GO diodes with dissimilar metal contacts are fabricated using a novel process on high-frequency-compatible flexible substrates. The process utilizes an undercut and self-alignment approach that allows fabrication of submicrometer-size devices using an all-photolithographic process. The fabricated diodes demonstrate nonlinear current–voltage characteristics with current in the microampere range. Both types of diodes work efficiently as microwave rectifiers showing a near-ideal behavior with a rectification sensitivity of 4 V/W (18 GHz) and 33 V/W (22 GHz) for the CNT and r-GO, respectively. In addition, the results for r-GO-based frequency multiplication at fundamental frequencies ranging from 2 to 6 GHz and frequency mixing for 1.5 and 1.0 GHz are also presented.

Comparative study on noise characteristics of As and Sb‐based high electron mobility transistors

We study comparatively the RF and the noise characteristics for the In0.7Ga0.3As, InAs/AlSb and InSb high electron mobility transistors (HEMTs) by using the quantum corrected Monte Carlo (QC‐MC) simulation. The increase in the current fluctuation <Δ> with Vds is caused by the increase in the electron velocity variance (i.e., the electron heating); this indicates clearly that the low Vds operation is essential to lowering <Δ>. The smaller electron effective m* results in the larger and thus the larger <Δ>, yet it allows the low Vds operation through the higher μ. The InSb HEMT with the channel of the smallest m* overcomes the inherent nature of the larger <Δ> through the ability of the lower Vds operation along with the larger gm. Eventually, the InSb HEMT shows the smallest minimum noise figure NFmin of 0.31 dB with the associated gain Gass of 12.4 dB at 100 GHz and the highest cutoff frequency fT of 1.8 THz at Vds of 0.2 V. These results indicate the potential of the InSb HEMT for the ultra‐low power, ultra‐high frequency, and the ultra‐low noise transistor.

Discrete-Time Tool for Stability Analysis of DC Power Electronics-Based Cascaded Systems

DC distribution power systems are vulnerable to instability because of the destabilizing effect of converter-controlled constant power loads (CPLs) and input filters. Standard stability analysis tools based on averaging linearization techniques can be used only when the switching frequency of the converter is significantly higher than the cutoff frequency of the filter. However, dc distribution systems with a reduced size filter, and consequently a high cutoff frequency, are common in transportation applications. Conventional methods fail to detect instabilities in the system because they do not take into account the switching effect. To overcome this drawback, this paper proposes a discrete-time method to analyze the stability of dc distribution systems. This model is applied here to a dc power system with a CPL. The switching effects and the nonlinearities of the system model are taken into account with a simple discretization approach. The proposed method is able to predict the dynamic properties of the system, such as slow-scale and fast-scale instabilities. An active stabilizer is also included in the system model in order to extend the stability margin of the system. Finally, these observations are validated experimentally on a laboratory test bench.

Phase extraction using multi-directional moiré fringes for multi-lateral shearing interferometry

The multi-lateral shearing interferometers (multi-LSIs) are featured in the improved accuracy and noise resistance of wavefront reconstruction using phase differences in multiple directions. Nowadays the multidirectional phase differences are usually extracted from multi-LSIs’ interferogram using the fast Fourier transform (FFT) method, whose accuracy is limited by spectral leakage effect. To improve the measurement accuracy of multi-LSIs, a phase extraction method developed from moiré technique is proposed in this paper. Using virtual gratings with properly large carrier frequencies, the desired phase information in each of the multiple directions can be modulated into low-frequency domain of the corresponding moiré pattern with larger separations between unnecessary side lobes. In this way, low-pass filters with higher cut-off frequencies can be applied in moiré technique to reduce the inaccuracy induced by spectral leakage effect. Meanwhile, phase shifting method can be applied to extract phase information from a single fringe pattern with better noise resistance by easily introducing phase shifts in computer generated virtual gratings. Simulation results show that the proposed method has higher accuracy and better anti-noise performance than the FFT method when spectral leakage effect exists. To demonstrate accuracy of the proposed method, a null test experiment of the quadriwave LSI has been conducted and experimental results show that measurement accuracy of the quadriwave LSI can be significantly improved by substituting the FFT method with the proposed method in phase extraction process.

Thin-Film Single-Crystal Schottky Diodes for IR Detection and Beyond

Thin-film p-type Co–Si and n-type Cr–Si Schottky diodes have been fabricated, in which a thin silicon layer is sandwiched between the anode and the cathode of the diodes, in a vertical configuration. The thicknesses of the silicon are 70 and 40 nm, for Co–Si and Cr–Si diodes, respectively. The thin layer significantly reduces the series resistance and the vertical structure reduces the parasitic capacitances in the diode, resulting in a high cutoff frequency, 100 and 54 THz, for the Co–Si and Cr–Si diodes, respectively. The dc current–voltage measurements show that the ideality factor is $\sim 1.25$ . The small ideality factor is attributed to the use of crystalline silicon, enabled by the transfer method. This leads to a relatively high theoretical estimation of responsivity of the diodes in nonlinear detection/rectification. The high cutoff frequency and high responsivity make these diodes a suitable candidate for terahertz (THz) detection, in the range of infrared (IR) and beyond. Our fabrication method and device structure allow for a better integration of Schottky diodes with a strip antenna, which provides a better mechanical stability for practical THz and IR applications.

Place specificity of the click-evoked auditory brainstem response in the bottlenose dolphin (Tursiops truncatus).

Cochlear place specificity of the auditory brainstem response (ABR) was investigated in five bottlenose dolphins by measuring ABRs to broadband clicks presented simultaneously with masking noise having various high-pass cutoff frequencies. Click and noise stimuli were digitally compensated to account for the transmitting response of the piezoelectric transducers and any multipath propagation effects to achieve "white" or "pink" spectral characteristics. Narrowband evoked responses were derived by sequentially subtracting responses obtained with noise at lower high-pass cutoff frequencies from those obtained with noise having higher cutoff frequencies. The results revealed little contribution to the click-evoked brainstem response from frequency bands below 10 kHz and, in dolphins with full hearing bandwidth, the largest amplitude derived band evoked responses were obtained from the highest frequency bands. Narrowband latencies decreased with increasing frequency and were adequately fit with a power function exhibiting relatively large change in latency with frequency below ∼30 kHz and little change above ∼30 kHz. These data demonstrate that frequency bands below ∼10 kHz do not substantively contribute to the farfield ABR in the bottlenose dolphin when using place-specific approaches such as high-pass subtractive-masking techniques.

Enhancement of the Performance of TFET using Asymmetrical Oxide Spacers and Source Engineering

paper, some techniques to enhance the performance of the tunneling field effect transistor (TFET) devices are studied. Two proposed techniques, which could be used simultaneously to improve the performance of TFET, are presented. The first technique is using different oxide materials for the spacers over the drain and source. The second technique is to select a different material of the source other than Si. The study is based on the DC ID-VGS characteristics as well as the high frequency characteristics regarding the capacitance and cut-off frequency. It was found from this study, that it is advantageous to use different materials for the spacers. The materials chosen for this work are HfO2 as the spacer over the source and SiO2 over the drain. It is also shown that using Ge as a source material provides the best performance. The criterion of the choices presented in this paper is based on providing higher ON current and lower ambipolar current and higher cut-off frequency.

On the Challenges of SiGe HBTs in Advanced BiCMOS Technology Toward Half THz fMAX

Advanced BiCMOS technology is a cost-effective candidate for wide-range of applications, including Radar (automotive radars, high-speed industrial sensors), high-speed wireless and wireline communication, high-speed instrumentation, and mmWave THz imaging and sensing that require high performance SiGe HBTs with high cut-off frequencies fT and high maximum frequencies fMAX. Development of SiGe HBTs in BiCMOS technology with both high fT and fMAX faces significant challenges. Vertical scaling is employed to increase fT in advanced SiGe HBTs including reduction in base and collector thickness or by increasing the collector doping. All these approaches reduce the carrier transit times, but result in an increase in the base resistance and the collector-base capacitance, which degrade fMAX. To overcome these limits, lateral scaling is necessary to reduce the base resistance and the collector-base capacitance. Reduction in emitter width reduces the intrinsic base resistance and Ccb, self-aligned emitter-base integration schemes reduce the extrinsic base link resistance, and raised extrinsic base helps with lower Rb and Ccb. In short, these scaling rules and approaches would need to reduce both base resistance and collector-base capacitance simultaneously for improved fMAX and fT In this paper, results from two experimental studies are presented in a 90nm SiGe BiCMOS technology. Compared with the baseline, one experiment shows more reduction in collector-base capacitance, while the other shows more reduction in base resistance. Both experiments achieved 300GHz fT and met or exceeded the 360GHz fMAX goal of the technology. In addition to straight vertical and lateral scaling, a series of experiments employing other process techniques and structure innovation have also been studied and are reviewed in this paper, including millisecond anneal techniques, low temperature silicide and low temperature contact processes, and secondary trench isolation, achieving fT around 300GHz and fMAX toward half THz.

A low-noise widely tunable Gm-C filter with frequency calibration**Project supported by the National Natural Science Foundation of China (No. 61574045).

A fourth-order Gm-C Chebyshev low-pass filter is presented as channel selection filter for reconfigurable multi-mode wireless receivers. Low-noise technologies are proposed in optimizing the noise characteristics of both the Gm cells and the filter topology. A frequency tuning strategy is used by tuning both the transconductance of the Gm cells and the capacitance of the capacitor banks. To achieve accurate cut-off frequencies, an on-chip calibration circuit is presented to compensate for the frequency inaccuracy introduced by process variation. The filter is fabricated in a 0.13 μm CMOS process. It exhibits a wide programmable bandwidth from 322.5 kHz to 20 MHz. Measured results show that the filter has low input referred noise of and high out-of-band IIP3 of 16.2 dBm. It consumes 4.2 and 9.5 mW from a 1 V power supply at its lowest and highest cut-off frequencies respectively.