Integrated ferroelectric millimeter-wave phase shifters with a periodic structure

Integrated phase shifters with a periodic structure that includes BaSrTiO₃ ferroelectric varactors parallel-and series-connected to the transmission line are investigated theoretically and experimentally. The phase shifters are designed for the frequency range 26–32 GHz. The dispersion characteristics and insertion losses in the transmission line of the phase shifters are analyzed with regard to the dependence of the capacitance and loss tangent of the varactors on control voltage and temperature. It is shown that parasitic amplitude modulation in the phase shifters can be suppressed if the connection scheme of the varactors takes into account the voltage dependence of the their loss tangent. In the phase shifters with series-connected varactors, the temperature dependence of the phase shift is much weaker than in those with parallel-connected varactors.     

The effect of carrier level on tuning in amplitude-modulation masking

The effect of carrier level on tuning in modulation masking was investigated for noise and tonal carriers. Bandwidths of the modulation filters, estimated from the masked detection thresholds using an envelope power spectrum model, were independent of level for the noise carrier but seemed to decrease with increasing level for the tonal carrier. However, the apparently sharper tuning could be explained by increased modulation sensitivity and modulation dynamic range with increasing level rather than improved modulation-frequency selectivity. Consistent with this interpretation, the addition of a high-pass noise with a level adjusted to maintain the same threshold for the detection of the signal modulation for each carrier level used eliminated the effect of level on tuning. Overall, modulation filters estimated from psychophysical data do not depend on level in contrast to the modulation transfer functions obtained from neural recordings in the inferior colliculus in physiological studies. The results highlight differences between the characteristics of modulation processing obtained from neural data and perception. The discrepancies indicate the need for further investigation into physiological correlates of tuning in modulation processing.     

An analysis of quasi-frequency-modulated noise and random-sideband noise as comparisons for amplitude-modulated noise

Experiments were performed to determine under what conditions quasi-frequency-modulated (QFM) noise and random-sideband noise are suitable comparisons for AM noise in measuring a temporal modulation transfer function (TMTF). Thresholds were measured for discrimination of QFM from random-sideband noise and AM from QFM noise as a function of sideband separation. In the first experiment, the upper spectral edge of the noise stimuli was at 2400 Hz and the bandwidth was 1600 Hz. For sideband separations up to 256 Hz, at threshold sideband levels for discriminating AM from QFM noise, QFM was indiscriminable from random-sideband noise. For the largest sideband separation used (512 Hz), listeners may have used within-stimulus envelope correlation in the QFM noise to discriminate it from the random-sideband noise. Results when stimulus bandwidth was varied suggest that listeners were able to use this cue when the carrier was wider than a critical band, and the sideband separation approached the carrier bandwidth. Within-stimulus envelope correlation was also present in AM noise, and thus QFM noise was a suitable comparison because it made this cue unusable and forced listeners to use across-stimulus envelope differences. When the carrier bandwidth was less than a critical band or was wideband, QFM noise and random-sideband noise were equally suitable comparisons for AM noise. When discrimination thresholds for QFM and random-sideband noise were converted to modulation depth and modulation frequency, they were nearly identical to those for discrimination of AM from QFM noise, suggesting that listeners were using amplitude modulation cues in both cases.     

Implanted silicon varactor for TV tuner

Ion implanted silicon planar varactor diodes of large capacitance variation ratio have been developed for UHF/VHF TV tuner circuits. The ratio of the capacitance variation achieved at 3 V to 25 V is between 6 and 7 with devices exhibiting low leakage and a required breakdown voltage of 30 V. Ion implantation has been used to introduce phosphorus into n-type silicon in the predeposition cycle. The device fabrication is completed using conventional diffusion techniques which also include thermal annealing. The fabrication process involves a minimum number of processing steps to produce low-cost devices. These diodes were used in a VHF TV tuner to obtain gain between 18 and 32 db in different bands, indicating high values of the quality factor of the varactors.     

Noise improves modulation detection by cochlear implant listeners at moderate carrier levels

Envelope detection and processing are very important for cochlear implant (CI) listeners, who must rely on obtaining significant amounts of acoustic information from the time-varying envelopes of stimuli. In previous work, Chatterjee and Robert [JARO 2(2), 159-171 (2001)] reported on a stochastic-resonance-type effect in modulation detection by CI listeners: optimum levels of noise in the envelope enhanced modulation detection under certain conditions, particularly when the carrier level was low. The results of that study suggested that a low carrier level was sufficient to evoke the observed stochastic resonance effect, but did not clarify whether a low carrier level was necessary to evoke the effect. Modulation thresholds in CI listeners generally decrease with increasing carrier level. The experiments in this study were designed to investigate whether the observed noise-induced enhancement is related to the low carrier level per se, or to the poor modulation sensitivity that accompanies it. This was done by keeping the carrier amplitude fixed at a moderate level and increasing modulation frequency so that modulation sensitivity could be reduced without lowering carrier level. The results suggest that modulation sensitivity, not carrier level, is the primary factor determining the effect of the noise.     

Design of a varactor-tunable metamaterial absorber

In this paper, we design a varactor-tunable metamaterial absorber （MA）. The tunable MA is based on a mushroom-type high impedance surface （HIS）, in which varactors are loaded between adjacent metal patches to adjust the capacitance and tune the resonance frequency, the primary ground plane is etched as the bias network to bias all of the varactors in parallel, and another ultra-thin grounded film is attached to the bottom. Its absorption characteristics are realized for electrically dielectric loss. The simulated values of a sample indicate that a tunable frequency range from 2.85 GHz to 2.22 GHz is achieved by adjusting the varactor capacitance from 0.1 pF to 2.0 pF, and better than 0.97 absorbance is realized; in addition, the tunable frequency range is expanded from 4.12 GHz to 1.70 GHz after optimization.     

Parametric oscillator based on a single-layer resonant metamaterial

We perform numerical simulations demonstrating parametric generation and oscillation processes in a single-layer of metamaterial composed of split ring resonators (SRRs). In general, a parametric resonance is achieved by introducing a time-modulation of one of the energy-storing parameters of a resonant system. An individual SRR is a resonant system that can be modeled as an RLC-circuit inductively coupled to an applied time-varying magnetic field. The relatively simple circuit model can be employed to establish the range of parameters providing the growth of parametric oscillations within the SRR medium. We relate the numerically predicted circuit parameters that ensure the buildup of parametric oscillations to those parameters expected to be available in a modified SRR medium, in which lumped element varactors integrated into the SRRs are used as modulable capacitance elements.     

New approaches to lifetime-resolved luminescence imaging

An overview of recent developments in time-resolved imaging technology is presented. A directly modulated CCD imaging device has been developed which is suitable for frequency-domain phosphorescence measurements up to more than 400 kHz. This has been used with a recently-developed blue/UV LED source to implement a low-noise, solid-state phosphorescence/fluorescence imaging system suitable for macroscopic and microscopic imaging. For shorter lifetimes a range of new light sources has become available with higher light output and/or higher frequency modulation performance. Acoustooptic tunable filters have also been investigated as optical “light gates” both for modulation of excitation and for time-resolved imaging, and the limits of performance of these devices are discussed.     

Nonlinear TLM modelling of high-frequency varactor multipliers and halverstm

A numerical modelling procedure in the time-domain of microstrip circuits containing non-linear devices such as varactor multipliers and halvers ^tm , is described. The two-dimensional Transmission Line Matrix (TLM) method has been extended to model elements with voltage-dependent capacitance (varactors). Waveforms and spectra computed with the TLM model compare well with measured results.     

Factors affecting the loudness of modulated sounds.

Loudness matches were obtained between unmodulated carriers and carriers that were amplitude modulated either periodically (rates between 2 and 32 Hz, modulation sinusoidal either on a linear amplitude scale or on a dB scale; the latter is called dB modulation) or with the envelope of the speech of a single talker. The carrier was a 4-kHz sinusoid, white noise, or speech-shaped noise. Both normally hearing subjects and subjects with cochlear hearing loss were tested. Results were expressed as the root-mean-square (rms) level of the modulated carrier minus the level of the unmodulated carrier at the point of equal loudness. If this difference is positive, this indicates that the modulated carrier has a higher rms level at the point of equal loudness. For normally hearing subjects, the results show: (1) For a 4000-Hz sinusoidal carrier, the difference was slightly positive (averaging about 0.7 dB). There was no significant effect of modulation rate or level over the range 20-80 dB SL. (2) For a speech-shaped noise or white noise carrier, the difference was close to zero, although for large modulation depths it tended to be negative. There was no clear effect of level (over the range 35-75 dB SPL) or modulation rate. For the hearing-impaired subjects, the differences were small, but tended to be slightly negative for both the 4000-Hz carrier and the noise carriers, when the modulation rate was above 2 Hz. Again, there was no clear effect of overall level. However, for dB modulation, the differences became more negative with increasing modulation depth. For modulation rates in the range 4-32 Hz, the results could be fitted reasonably well using the assumption that the loudness of modulated sounds is based on the rms value of the time-varying intensity of the response of the basilar membrane (taking into account the compression that occurs in the normal cochlea). The implications of the results for the fitting of multi-band compression hearing aids and for the design of loudness meters are discussed.     

A comparison of steady-state evoked potentials to modulated tones in awake and sleeping humans.

Steady-state evoked potential responses were measured to binaural amplitude-modulated (AM) and combined amplitude- and frequency-modulated (AM/FM) tones. For awake subjects, AM/FM tones produced larger amplitude responses than did AM tones. Awake and sleeping responses to 30-dB HL AM/FM tones were compared. Response amplitudes were lower during sleep and the extent to which they differed from awake amplitudes was dependent on both carrier and modulation frequencies. Background EEG noise at the stimulus modulation frequency was also reduced during sleep and varied with modulation frequency. A detection efficiency function was used to indicate the modulation frequencies likely to be most suitable for electrical estimation of behavioral threshold. In awake subjects, for all carrier frequencies tested, detection efficiency was highest at a modulation frequency of 45 Hz. In sleeping subjects, the modulation frequency regions of highest efficiency varied with carrier frequency. For carrier frequencies of 250 Hz, 500 Hz, and 1 kHz, the highest efficiencies were found in two modulation frequency regions centered on 45 and 90 Hz. For 2 and 4 kHz, the highest efficiencies were at modulation frequencies above 70 Hz. Sleep stage affected both response amplitude and background EEG noise in a manner that depended on modulation frequency. The results of this study suggest that, for sleeping subjects, modulation frequencies above 70 Hz may be best when using steady-state potentials for hearing threshold estimation.     

基于FPGA的跳频通信系统开发

为了提高通信的抗干扰和保密性,对跳频通信进行了研究,通过分析跳频通信的实现方式,提出基于FPGA的跳频通信系统实现方案。该方案中发端信号采用QPSK调制,接收端采用超外差接收以达到减少噪声和提高接收灵敏度的效果,接收端跳频同步采用等待自同步的跳频捕获和基于延迟锁相环的跳频跟踪。测试结果表明所设计的跳频通信系统可以正确实现跳频通信。与传统跳频通信实现方案相比,该方案具有灵活性强、开发周期短、开发费用低等优点。     

Modulation detection for amplitude-modulated bone-conducted sounds with sinusoidal carriers in the high- and ultrasonic-frequency range

Ultrasonic vibration generates a sensation of sound via bone-conduction. This phenomenon is called bone-conducted ultrasonic (BCU) hearing. Complex sounds can also be perceived by amplitude-modulating a BCU stimulus (AM-BCU). The influence of the modulation frequency on the sensitivity to detecting amplitude modulation of sinusoidal carriers of 10, 20, and 30 kHz was examined to clarify the characteristics of the perception of amplitude modulation over the sonic or audio-frequency range and the ultrasonic range. In addition, the detection sensitivity for single-sideband modulation for a 20 kHz carrier was measured. Temporal modulation transfer functions (TMTFs) obtained at each carrier frequency suggest that the auditory system has the ability to process timing information in the envelopes of AM-BCUs at lower modulation frequencies, as is the case with audio-frequency sounds. The possible influence of peripheral filtering on the shape of the TMTF at higher frequencies was examined.     

A Novel Coherent Multilevel Combined Phase and Polarization Shift Keying Modulation in Twisted Fibers

This article proposes a novel coherent multilevel modulation model that exploits polarization and phase of the field. This model is based on the possibility of coherent systems to use all the four degrees of freedom of the electromagnetic field. The proposed scheme is able, by applying a suitable twisting process to the optical fiber, to physically confine the polarization and the phase of the transmitted field within the phase sphere. In this way, with the same performances of existing systems, the receiver is considerably simplified because there is no longer need of birefringence tracking circuits.     

Phase-Measuring Algorithms to Suppress Spatially Nonuniform Phase Modulation in a Two-Beam Interferometer

Phase modulation of presently used phase-shifting interferometers is assumed to be spatially uniform across the observing aperture. However, calibration errors or the configuration of an interferometer can cause a spatial nonuniformity in the phase modulation. Spatial nonuniformity causes a significant error in the measured phase when the phase modulator has nonlinear sensitivity. An even-order nonlinearity in the phase modulation in particular contributes to the errors. Lowest-order errors can be suppressed by adding a new symmetry to the sampling functions of the phase-shifting algorithm, however the algorithm suffers from large random noise. The random noise is shown to be decreased substantially by applying one more sampled frame to the algorithm. We derive new seven-sample and eight-sample algorithms that can compensate for a nonuniform phase shift and has much less random noise than the previous algorithm we proposed.     

Intrinsic envelope fluctuations and modulation-detection thresholds for narrow-band noise carriers

A model is presented which calculates the intrinsic envelope power of a bandpass noise carrier within the passband of a hypothetical modulation filter tuned to a specific modulation frequency. Model predictions are compared to experimentally obtained amplitude modulation (AM) detection thresholds. In experiment 1, thresholds for modulation rates of 5, 25, and 100 Hz imposed on a bandpass Gaussian noise carrier with a fixed upper cutoff frequency of 6 kHz and a bandwidth in the range from 1 to 6000 Hz were obtained. In experiment 2, three noises with different spectra of the intrinsic fluctuations served as the carrier: Gaussian noise, multiplied noise, and low-noise noise. In each case, the carrier was spectrally centered at 5 kHz and had a bandwidth of 50 Hz. The AM detection thresholds were obtained for modulation frequencies of 10, 20, 30, 50, 70, and 100 Hz. The intrinsic envelope power of the carrier at the output of the modulation filter tuned to the signal modulation frequency appears to provide a good estimate for AM detection threshold. The results are compared with predictions on the basis of the more complex auditory processing model by Dau et al.     

Amplitude modulation of underwater noise produced by seagoing vessels

Data obtained from the processing of records of underwater noise produced by seagoing vessels are used to refine the model of the noise amplitude modulation caused by the rotation of the propeller shaft and ship roll and pitch in a seaway. Specifically, the width of the frequency band of the modulation process, the value of the modulation coefficient, and the distribution of the magnitude and phase of the modulation coefficient over the carrier frequency spectrum are investigated.     

Automatic tuned MRI RF coil for multinuclear imaging of small animals at 3T

We have developed an MRI RF coil whose tuning can be adjusted automatically between 120 and 128 MHz for sequential spectroscopic imaging of hydrogen and fluorine nuclei at field strength 3 T. Variable capacitance (varactor) diodes were placed on each rung of an eight-leg low-pass birdcage coil to change the tuning frequency of the coil. The diode junction capacitance can be controlled by the amount of applied reverse bias voltage. Impedance matching was also done automatically by another pair of varactor diodes to obtain the maximum SNR at each frequency. The same bias voltage was applied to the tuning varactors on all rungs to avoid perturbations in the coil. A network analyzer was used to monitor matching and tuning of the coil. A Pentium PC controlled the analyzer through the GPIB bus. A code written in LABVIEW was used to communicate with the network analyzer and adjust the bias voltages of the varactors via D/A converters. Serially programmed D/A converter devices were used to apply the bias voltages to the varactors. Isolation amplifiers were used together with RF choke inductors to provide isolation between the RF coil and the DC bias lines. We acquired proton and fluorine images sequentially from a multicompartment phantom using the designed coil. Good matching and tuning were obtained at both resonance frequencies. The tuning and matching of the coil were changed from one resonance frequency to the other within 60 s.     

PN9000相位噪声测试系统扩频方法研究

在航天测控领域,相位噪声指标已成为系统性能的限制性因素,精确测量载波的相位噪声显得尤为重要;PN9000相位噪声测试系统可直接应用于相位噪声测试,具备测试灵敏度高、系统稳定、测试快速等优点;随着航天测控领域所用频率的不断提高,针对PN9000相位噪声测试系统基本配置的频率范围已无法满足测试需求的问题,为满足PN9000相位噪声测试系统扩频需求,文中提出基于相位检波器法(基本型)和基于中频相位检波器法两种扩频方法,并对两种方法进行原理分析和实验验证;根据实验结果,两种方法均能有效实现扩频功能,但在系统本底相位噪声及经费使用方面各有不同特点;文中提供的方法及实验数据,对PN9000相位噪声测试系统扩频升级及配件选购等具有很好的借鉴作用。     

Second-order temporal modulation transfer functions

Detection thresholds were measured for a sinusoidal modulation applied to the modulation depth of a sinusoidally amplitude-modulated (SAM) white noise carrier as a function of the frequency of the modulation applied to the modulation depth (referred to as f'm). The SAM noise acted therefore as a "carrier" stimulus of frequency fm, and sinusoidal modulation of the SAM-noise modulation depth generated two additional components in the modulation spectrum: fm-f'm and fm+f'm. The tracking variable was the modulation depth of the sinusoidal variation applied to the "carrier" modulation depth. The resulting "second-order" temporal modulation transfer functions (TMTFs) measured on four listeners for "carrier" modulation frequencies fm of 16, 64, and 256 Hz display a low-pass segment followed by a plateau. This indicates that sensitivity to fluctuations in the strength of amplitude modulation is best for fluctuation rates f'm below about 2-4 Hz when using broadband noise carriers. Measurements of masked modulation detection thresholds for the lower and upper modulation sideband suggest that this capacity is possibly related to the detection of a beat in the sound's temporal envelope. The results appear qualitatively consistent with the predictions of an envelope detector model consisting of a low-pass filtering stage followed by a decision stage. Unlike listeners' performance, a modulation filterbank model using Q values > or = 2 should predict that second-order modulation detection thresholds should decrease at high values of f'm due to the spectral resolution of the modulation sidebands (in the modulation domain). This suggests that, if such modulation filters do exist, their selectivity is poor. In the latter case, the Q value of modulation filters would have to be less than 2. This estimate of modulation filter selectivity is consistent with the results of a previous study using a modulation-masking paradigm [S. D. Ewert and T. Dau, J. Acoust. Soc. Am. 108, 1181-1196 (2000)].