Components Of Different Frequencies Research Articles

722 超音波干渉による仮想音源の生成に関する研究(振動と音源,OS-5 サイレント工学,総合テーマ「伝統を,未来へ!」)

In this study, a virtual sound production system is developed where the difference frequency component appears as the secondary audible sound at a point of interference locally by the nonlinear interaction of two independently radiated ultrasounds while they travel directionally and intersect each other. The design of high-directive ultrasonic radiator, followed by the investigation of virtual sound production performance has been done theoretically as well as experimentally.

Highly sensitive coherent detection of terahertz waves at room temperature using a parametric process

We report the experimental results of coherent detection of narrow-linewidth nanosecond terahertz radiation at room temperature using frequency conversion in a nonlinear MgO:LiNbO3 crystal. Mixing the terahertz radiation with a near-infrared intense pump pulse results in the excitation and amplification of the difference-frequency component, which is detected with an InGaAs-based photodiode. We demonstrate this method in a fast and very sensitive terahertz wave detector. The detector is capable of capturing the temporal profile of terahertz pulses with nanosecond resolution, and is at least one order more sensitive than a typical liquid-He-cooled Si bolometer for detecting nanosecond pulsed terahertz wave beams.

A New Contrast Echo Imaging Method Using Crossed Beams of Two Ultrasonic Frequencies

We propose a novel contrast echo imaging method using crossed beams of two different ultrasonic frequencies as an ultrasound method of diagnostic cancer, which we call the crossed beam contrast echo (CBCE) method. The sum or difference frequency components that are derived from the nonlinear oscillation of the microbubbles driven by dual-frequency ultrasound are used in the CBCE method. The blood flow information can only be obtained in the area of the crossed beams, because no sum or difference frequency components are generated by the propagation of biological soft tissues except in the crossed beam area. We discussed the driving conditions under which the sum frequency component is most efficiently generated, and experimentally confirmed the area in which the sum frequency component is generated. As a result, the sum frequency component was larger than the other harmonic components when its frequency was equal to the resonance frequency of the microbubbles. It was confirmed that the area in which the large sum frequency component is generated was equal to the crossing area of the two beams.

Dual chopped photoreflectance spectroscopy for nondestructive characterization of semiconductors and semiconductor nanostructures

Photoreflectance (PR) spectroscopy unaffected by photoluminescence and light scattering has been developed for performing precise characterization of the electronic band structure of semiconductors and semiconductor nanostructures. Dual chopping of both the pump and probe lights eliminates the unexpected components included in the signal when detecting the sum frequency or difference frequency component by using a lock-in detection system. The obtained PR signal contains no background and is considered to be an ideal electromodulated reflectance.

Bandwidth and gain of optical parametric chirped pulse amplification pumped by non-monochromatic light

Laser pulse was decomposed into components of different frequencies using Fourier transform, and the numerical calculation model was built up for coupled equations of optical parametric amplification pumped by non-monochromatic light. Effects of non-monochromatic light on small signal gain, large signal gain and gain bandwidth of optical parametric amplification were investigated. Though non-monochromatic pump light decreases the gain of optical parametric process, it can improve the gain bandwidth. The larger the bandwidth of the pump light, the wider the gain bandwidth. Reasons for parametric gain decrease and gain bandwidth improvement were analyzed with respect to the phase mismatch and the parametric bandwidth.

A semiempirical theory of a one-layer cellular sound-absorbing lining with a perforated face panel

On the basis of the known approximate theories and the recent experimental data, a semiempirical theory of a resonance-type one-layer cellular sound-absorbing lining is developed. Approximate formulas are obtained for calculating the effective normal impedance with allowance for the geometric parameters of the sound-absorbing lining, the high sound-pressure levels, the presence of an entraining flow, and the nonlinear interaction of sound components of different frequencies within a given one-third-octave spectrum of noise. The results of numerical calculations by approximate formulas are compared with experiments and with the experimental and theoretical data reported by other authors. The proposed theory is found to agree well with experimental data.

On the leading nonlinear correction to gravity-wave dynamics

The principal nonlinear correction to the dynamics of gravity waves on an irrotational fluid is traditionally derived as a non-resonant perturbation solution to the Stokes expansion. When the problem is reformulated in the Hamiltonian description and limited to moderately collimated random waves over infinite depth, the perturbation term assumes a very simple and descriptive form. The sum-frequency component for the surface height is just a bilinear product of the height with the associated scalar strain, and the accompanying term in the potential is half the time derivative of the squared linear height. This solution is exact in one surface dimension and remains quite accurate for long-crested waves in two dimensions, with an error small to second order in the angular spread of constituent wave vectors. It is a natural generalization for random, disordered wave ensembles of the second-order Stokes solution, and its effect is to sharpen the random crests and to flatten the troughs. For wave sets of narrow relative bandwidth the difference-frequency component consists of a negligible elevation term and a non-negligible potential term whose gradient is the surface value of the volume return flow balancing the quadratic wave transport of fluid.

Speckle reduction of echographic image by transmitting ultrasonic waves of double peak spectrum

Speckle noise of ultrasonic echography is a major issue. To reduce the speckle noise a method of summation after logarithmic compression of higher order harmonic images is proposed. The feasibility is confirmed by the phantom experiments using a mechanical scanner system equipped with a bi‐layered structure transducer of PZT and PVDF. The dynamic range of harmonic components higher than the third, however, is not enough for effective speckle reduction. In this study a method of using difference and sum frequency components as well as harmonic components by transmitting pulsed waves of double peak spectrum is proposed. To compare the dynamic range of those components the numerical simulation of transmitting the ultrasonic waves of 2 and 6 MHz and those of 2 and 8 MHz in absorbing media is carried out. An attenuation coefficient of 1.0 dB/cm/MHz is assumed. As a result, complex beam patterns are formed due to degeneration between second harmonic and difference frequency components of 4 MHz in the former case. In the latter case three focal beam patterns of 4‐, 6‐, and 8‐MHz components within 40 dB in dynamic range are formed. Consequently this method has the potential to apply for the biological tissues. [Work supported by a Grant‐in‐Aid for Scientific Research.]

Large signal analysis of wideband non-linear amplifiers with sum and difference frequency injection

Large signal analysis of a wideband non-linear amplifier excited by a multisinusoidal signal is presented. The special cases of two equal-amplitude sinusoids and their injected harmonics, sum- and difference-frequency components are considered in detail and the results are compared, whenever possible, with previously published simulation and experimental results.

Correspondence of Low Mean Shear and High Harmonic Content in the Porcine Iliac Arteries

Temporal variations in shear stress have been suggested to affect endothelial cell biology. To better quantify the range of dynamic shear forces that occur in vivo, the frequency content of shear variations that occur naturally over a cardiac cycle in the iliac arteries was determined. Computational fluid dynamic calculations were performed in six iliac arteries from three juvenile swine. Fourier analysis of the time-varying shear stress computed at the arterial wall was performed to determine the prevalence of shear forces occurring at higher frequencies in these arteries. While most of each artery experienced shear forces predominantly at the frequency of the heart rate, the frequency spectra at certain regions were dominated by shear forces at higher frequencies. Regions whose frequency spectra were dominated by higher harmonics generally experienced lower mean shear stress. The negative correlation between shear and dominant harmonic was significant (p=0.002). Since lesion development typically occurs in regions experiencing low time-average shear stress, this result suggests that the frequency content of the shear exposure may also be a contributing factor in lesion development. A better understanding of the vascular response to shear components of different frequencies might help rationalize the notion of "disturbed flow" as a hemodynamic entity.

Direct measurement of the intrinsic RC roll-off in a radio frequency single electron transistor operated as a microwave mixer

By operating the radio frequency single electron transistor (rf-SET) as a mixer we present measurements in which the RC roll-off of the tunnel junctions is observed at high frequencies. Our technique makes use of the nonlinear rf-SET transconductance to mix high frequency gate signals and produce difference-frequency components that fall within the bandwidth of the rf-SET. At gate frequencies >15GHz the induced charge on the rf-SET island is altered on time scales faster than the inverse tunnel rate, preventing mixer operation. We suggest the possibility of utilizing this technique to sense high frequency signals beyond the usual rf-SET bandwidth.

A multitime circuit formulation for closely spaced frequencies

Verifying circuits with two or more closely-spaced driving frequencies is important in RF and wireless communications, for example, in the design of down-conversion mixers. Existing steady-state calculation methods, like harmonic balance, rely on Fourier series expansions to find the difference-frequency components typically of interest. Time-domain methods are, however, better suited for circuits with strong nonlinearities such as switching. Towards this end, we present a purely time-domain method for direct computation of difference tones in closely-spaced multitone problems. Our approach is based on multiple artificial time scales for decoupling the tones driving the circuit. Our method relies on a novel multitime reformulation that expresses circuit equations directly in terms of time-scales corresponding to difference tones. We apply the new technique to an RF-CMOS mixer to predict baseband bit-streams and down-conversion gain and distortion, in two orders of magnitude less CPU time than traditional time-stepping simulation. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005.

Terahertz plasma wave resonance of two-dimensional electrons in InGaP∕InGaAs∕GaAs high-electron-mobility transistors

We have observed the frequency dependence of the plasma resonant intensity in the terahertz range for a short gate-length InGaP∕InGaAs∕GaAs pseudomorphic high-electron-mobility transistor. The plasma resonance excitation was performed by means of interband photoexcitation using the difference-frequency component of a photomixed laser beam. Under sufficient density of two-dimensional (2D) conduction electrons (>1012cm−2) and a moderate modulation index (the ratio of the density of photoexcited electrons to the initial density of the 2D electrons) we clearly observed the plasma-resonant peaks at 1.9 and 5.8THz corresponding to the fundamental and third-harmonic resonance at room temperature, which is in good agreement with theory.

Finite amplitude waves in isotropic elastic waveguides with arbitrary constant cross-sectional area

Harmonic generation in homogeneous, isotropic, stress-free elastic waveguides with arbitrary constant cross-sectional area is investigated theoretically. Perturbation and modal analysis are used to obtain solutions of the nonlinear equation of motion for harmonic generation. Conditions for internal resonance are quantified. There are no restrictions on the modes or frequencies of the primary waves. Calculations for second-harmonic and difference-frequency components are presented for cylindrical rods and shells.

Finite-amplitude waves in isotropic elastic plates

The propagation of finite-amplitude waves in a homogeneous, isotropic, stress-free elastic plate is investigated theoretically. Geometric and weak material non-linearities are included, and perturbation is used to obtain solutions of the non-linear equations of motion for harmonic generation in the waveguide. Solutions for the second-harmonic, sum, and difference-frequency components are obtained via modal decomposition. Ordinary differential equations for the modal amplitudes in the expansion of the second-order solution are obtained using a reciprocity relation. There are no restrictions on the modes or frequencies of the primary waves. Two conditions for internal resonance are quantified: phase matching, and transfer of power from the primary to the secondary wave.

Experimental evaluation of force frequency shifting for low-frequency vibration excitation

A novel approach known as force frequency shifting (FFS) has been previously proposed for low-frequency (less that 1 Hz) vibration excitation. The technique requires a time-varying forcing function to be applied in a spatially varying fashion. The non-linear dynamic response produces excitation forces and moments at sum and difference frequencies of the force (i.e. f z ) and translational motion (i.e. f x ) frequencies. It is the difference frequency component (i.e. f z − f x ) that produces the desired low-frequency excitation. The purpose of this paper is to examine the fundamental behaviour of the FFS concept in depth and explore the feasibility of the method for structural excitation of large-scale systems with low natural frequencies. First, a set of tests was performed on a laboratory prototype to quantify the character of the excitation output. The prototype system was instrumented at component interfaces allowing reaction forces to be measured and compared to analytical model results. The tests show that the model frequency predictions were very accurate. Force and moment amplitude predictions were nominally within 5% of the experimental values. However, some amplitude comparisons showed larger errors and can be attributed to a number of identified modelling and experimental issues. Next, a full-scale FFS prototype was used to perform vibration tests on a large test structure (inertial vibration isolation platform). The results from two tests were compared: (1) a traditional modal analysis using an impact excitation and (2) an operating deflection shapes analysis using the FSS as the excitation. The comparison was excellent demonstrating the potential for the FFS technology to be used for modal testing of large structures.

Observation of Nonlinear Effects in Ocean Surface Wave Frequency Spectra

Abstract Nonlinearity and directionality of an evolving open-ocean surface wave field are investigated under increasing wind forcing. In addition to the frequency wave elevation spectrum, the frequency wave slope spectrum, the bicoherence of the wave elevation time series, and the peak wavenumber at a given frequency estimated by the maximum likelihood method are examined. As the wave field matures, an increasing portion of the high-frequency components of the wave elevation spectrum becomes phase correlated with the dominant wave component. This observation clearly suggests that the contribution to the frequency spectrum from the higher harmonics generated by steep dominant waves becomes increasingly important relative to the contribution from free waves that propagate at their own phase speed predicted by the dispersion relation. The observation therefore invalidates the common assumption that an ocean surface wave spectrum is a superposition of linear surface wave components of different frequencies. I...

Analysis and reproduction of a signal's periodic components by means of an extended block-adaptive fourier analyzer

This paper presents some results of developing a signal analyzer for performing spectral analysis and simultaneous reproduction/filtering of the input signal's periodic components of different (in general, not harmonically related) frequencies and waveforms/spectra. The proposed analyzer accomplishes this task by applying adaptive recursive Fourier analysis.

Ultrasonic diagnostic imaging system transmitter for sum and difference frequency imaging

An ultrasonic diagnostic imaging system is described for performing nonlinear echo signal imaging with intermodulation product (sum or difference frequency) components. The system includes a digital transmitter which develops digital waveforms for two frequencies of a transmit beam. The digital waveforms are combined, converted to analog waveforms, and applied as transmit signals to the elements of a transducer array. In an alternate embodiment, a library of digital, multifrequency waveforms is maintained, from which a desired digital waveform is selected, converted to an analog waveform, and applied as transmit signals to the elements of a transducer array.

Ultrasonic diagnostic imaging of nonlinearly intermodulated and harmonic frequency components

An ultrasonic diagnostic imaging system and method are described for performing nonlinear echo signal imaging with harmonic and intermodulation product (sum or difference frequency) components. Both the harmonic and the intermodulation products are produced by nonlinear effects of tissue or contrast agents and both are advantageously separated from the fundamental transmit components of the echo signals by pulse inversion processing. The use of both nonlinear components can improve the signal to noise ratio of the ultrasonic images, and the two types of components can be blended or used in different regions of an image to offset the effects of depth dependent attenuation.