Subharmonic Signal Research Articles

10-GHz SiGe BiCMOS Sub-Harmonic Gilbert Mixer Using the Fully Symmetrical and Time-Delay Compensated LO Cells

A 10-GHz sub-harmonic Gilbert mixer is demonstrated in this paper using the 0.35 μm SiGe BiCMOS technology. The time-delay when the sub-harmonic LO (Local Oscillator) stage generates sub-harmonic LO signals is compensated by using fully symmetrical multiplier pairs. High RF-to-IF isolation and sub-harmonic LO Gilbert cell with excellent frequency response can be achieved by the elimination of the time-delay. The SiGe BiCMOS sub-harmonic micromixer exhibits 17 dB conversion gain, -74 dB 2LO-to-RF isolation, IP1 dB of -20 dBm, and IIP3 of -10 dBm. The measured double sideband noise figure is 16 dB from 100-kHz to 100-MHz because the SiGe bipolar device has very low 1/f noise corner.

Methods and apparatus for subharmonic generation, stereo expansion and distortion

Methods and apparatus are disclosed that achieve sub-harmonic signal processing, stereo-width expansion, sub-woofer signal processing, and tube distortion emulation to achieve various desirable acoustic effects when used to modify an input signal containing, for example, music content.

V-Band GaAs pHEMT Cross-Coupled Sub-Harmonic Oscillator

A V-band cross-coupled sub-harmonic injection-locked oscillator has been designed and fabricated using 0.15-mum GaAs pHMET technology. Based on the known harmonic injecting circuit topology, this oscillator was designed by a differential output approach, a low-Q microstrip-line resonator, and a current mirror, which has a free-running oscillation frequency around 60GHz with a tuning range of 2.5GHz (from 57.8GHz to 60.3GHz). The maximum single-end output power is 3.8dBm with a dc dissipation of 225mW under a -3V supply voltage. Within the input matching network for second (30GHz) and fourth (15GHz) sub-harmonic signals injection, it demonstrates the maximum locking ranges close to 120MHz and 30MHz, respectively

Theoretical predictions of harmonic generation from submicron ultrasound contrast agents for nonlinear biomedical ultrasound imaging

Submicron ultrasound contrast agents have aroused attention for their significant promise in ultrasonic contrast/molecular imaging, targeted therapy and echo particle imaging velocimetry. However, nonlinear acoustic properties of submicron encapsulated gas bubbles for ultrasonic applications are still not clearly understood. In this paper, nonlinear acoustic emission characteristics from submicron bubbles were examined using a numerical study. The modified RP equation incorporating viscosity, acoustic radiation, thermal effects and encapsulated shell was used to study single bubble dynamics. Further, a size integration method, shown previously to be useful in prediction of backscatter spectra from groups of bubbles, was applied to analyse response from a bubble population. We show that bubbles with radii (200–500 nm) produce significant subharmonic and ultraharmonic components of the backscatter spectrum, while smaller bubbles (<200 nm) provide substantial second harmonic components. Additionally, nanoscale bubbles (<100 nm) produce very low backscatter amplitudes and thus may not be useful with the use of current ultrasound technology. Analysing optimal ultrasound driving pressures and bubbles size ranges for maximal subharmonic and ultraharmonic signals showed that sub and ultraharmonic mode nonlinear imaging methods may be potentially competitive for larger size bubbles (>200 nm) in providing proper contrast-to-tissue signal ratios.

A genetic based algorithm for measurement of power system disturbances

This paper introduces genetic algorithms (GA) as a powerful tool for monitoring and supervising power system disturbances generated due to dynamic performance of power systems. Monitoring power system disturbances involves monitoring fundamental voltage magnitude and its frequency as well as harmonic and sub-harmonic voltage magnitudes and their frequencies under different operating conditions for power quality evaluation purposes. The proposed method is based on genetic algorithms optimization technique. The method uses digital set of measurements for the voltage or current waveforms at power system bus to perform the estimation process digitally. The algorithm is tested using different simulated data to monitor power quality. Three different study cases are considered in this work. In the first part, the estimation of voltage flicker levels and its frequency is presented and discussed. In the second part, the frequency of a bus voltage signal that is contaminated with harmonics is estimated. The harmonic contents are also estimated in this case. In the third part, the analysis of a damped sub-harmonic signal is presented. Effects of number of samples, sampling frequency and the sample window size are studied. Effects of GA parameters and operators, such as population size, crossover, mutation probabilities and niching are also studied. Results are reported and discussed.

A model for the dynamics of gas bubbles in soft tissue

Understanding the behavior of cavitation bubbles driven by ultrasonic fields is an important problem in biomedical acoustics. Keller-Miksis equation, which can account for the large amplitude oscillations of bubbles, is rederived in this paper and combined with a viscoelastic model to account for the strain-stress relation. The viscoelastic model used in this study is the Voigt model. It is shown that only the viscous damping term in the original equation needs to be modified to account for the effect of elasticity. With experiment determined viscoelastic properties, the effects of elasticity on bubble oscillations are studied. Specifically, the inertial cavitation thresholds are determined using R(max)/R(0), and subharmonic signals from the emission of an oscillating bubble are estimated. The results show that the presence of the elasticity increases the threshold pressure for a bubble to oscillate inertially, and subharmonic signals may only be detectable in certain ranges of radius and pressure amplitude. These results should be easy to verify experimentally, and they may also be useful in cavitation detection and bubble-enhanced imaging.

Time and pressure dependence of acoustic signals radiated from microbubbles

Encapsulated microbubbles are considered to be microsensors for in vivo blood pressure measurements in the cardiovascular system. To study the potential of this method, we developed a simulation and an experimental set-up that relate various characteristics of radiated acoustic signals from the microbubbles to the varying ambient pressure. Both the simulation and the experiment show that the radiated pressure from microbubbles generates a significant subharmonic component, which is modulated by changes in the ambient pressure. A time-dependent decrease of the steady-state radii within a population of microbubbles causes a phase reversal phenomenon, which explains the observed time delay in the build-up of the subharmonic modulation response. Additionally, we identify a frequency-capturing effect that indicates the termination of the nonlinear behavior of the microbubbles. Our research suggests that these subharmonic signals can be used for in vivo blood pressure measurements and highlights some of the considerations that need to be addressed in developing such techniques. (E-mail: yanivg@tx.technion.ac.il)

Nonlinear dynamics of gas bubbles in viscoelastic media

Understanding the behavior of cavitation bubbles driven by ultrasonic fields is an important problem in biomedical acoustics. The Keller–Miksis equation for nonlinear bubble dynamics is combined with the Voigt model for viscoelastic media. Using experimentally determined values, the effects of elasticity on bubble oscillations are studied. Inertial cavitation thresholds are determined using Rmax/R0=2, and subharmonic emissions are also estimated. The elasticity increases the threshold pressure for inertial cavitation, and subharmonic signals are significant only in a certain region of radii and driving pressures at a given frequency. These results should prove useful in cavitation detection and bubble-enhanced imaging work.

In vivo pressure estimation using subharmonic contrast microbubble signals: proof of concept

Changes in ambient pressure affects the reflectivity of ultrasound contrast microbubbles leading to an excellent correlation between subharmonic signals and hydrostatic pressure. The aortas of two dogs were scanned with an experimental pulse-echo system to validate in vivo pressure estimation based on subharmonic microbubble signals. Results matched well with instantaneous pressure measurements (from 20-60 mmHg) obtained simultaneously with a pressure catheter (root mean square errors <27%).

Nonlinear dynamics of gas bubbles in soft tissue

Understanding the behavior of cavitation bubbles driven by ultrasonic fields is an important problem in biomedical acoustics. The previous studies are largely limited by availability of experimental data on soft tissue. To approach this problem, we combine the Keller-Miksis equation for nonlinear bubble dynamics with the linear Voigt model for viscoelastic media. Using experimentally determined values of viscoelastic properties of soft tissue as a guide, the effects of elasticity on bubble oscillations are studied. The inertial cavitation thresholds are determined using a criterion of Rmax/R0=2, and subharmonic emissions from an oscillating bubble are calculated. The results show that the presence of the elasticity increases the threshold pressure for inertial cavitation, and subharmonic signals only can be detected in a certain region of radii and driving pressures at a given frequency. These results should be useful in cavitation detection and bubble-enhanced imaging work. The model also could be used to determine values for the viscoelastic properties of soft tissue.

Subharmonic signal generation from contrast agents in simulated neovessels

Detection and measurement of blood flow in neovessels around a tumor can yield prognostic information about the tumor. Early detection and classification may help differentiate benign and malignant tumors; thus, improving patient management. This can be accomplished by injecting ultrasonic contrast agents and measuring the backscattered signals from them. Use of the subharmonic backscattered signals from these agents may be better than fundamental or second harmonic components because of the negligible subharmonics generated by the surrounding tissue. Preliminary results on the detection and measurement of subharmonic signal components up to 12 dB (at increasing pressures) from very small tubes (200 to 300 μm diameter) are reported, demonstrating the possibility and potential application of subharmonic imaging in detecting tumor angiogenesis. (E-mail: pshankar@coe.drexel.edu)

Optical phase locking among femtosecond subharmonic pulses.

We stabilized the relative carrier-envelope phase slip among the pump pulse and its subharmonic signal and idler pulses in a femtosecond optical parametric oscillator, resulting in long-term phasecoherence among the pulses. The stabilized beat signal corresponding to the relative carrier-envelope phase slip among subharmonic pulses had an accumulated phase error of 0.24 rad in the 1-mHz-1-MHz region. The fluctuation of the beat frequency measured by a 1-s-averaged counter was less than 1 mHz in a 1480-s measurement.

Phase-coherent multicolor femtosecond pulse generation

We achieved phase-coherent multicolor femtosecond pulse generation by optical phase locking among the pump and its subharmonic signal and idler pulses in an optical parametric oscillator. The ability for coherent superposition of the multicolor pulses is demonstrated in a time-domain measurement. Clear interferometric fringes between two sum-frequency pulses, corresponding to phase stability among the subharmonics, were observed with phase locking.

A dual-gate FET subharmonic injection-locked self-oscillating active integrated antenna for RF transmission

A planar subharmonic injection-locked GaAs dual-gate MESFET (DGMESFET) self-oscillating active integrated antenna (AIA) is presented for RF transmission. The oscillation is obtained with one gate of the DGMESFET at 2.052 GHz, and the stabilization of the oscillation is achieved by injecting a small subharmonic low-noise signal into the other gate of the DGMESFET. Phase noise was measured to be -98 dBc/Hz at the 10 KHz offset. The structure was shown to have the potential in performing triple functions of radiation, low noise oscillation and mixing (or modulation), a capability required for low cost wireless systems such as RFID tags and indoor positioning systems.

Unconditional temporal instability and self-pulse structuration in the phase-matched degenerate backward optical parametric oscillator

Stability analysis of the degenerate backward optical parametric oscillator in the phase-matching decay interaction, between a CW-pump and a sub-harmonic counter-propagating signal, proves that the inhomogeneous stationary solutions are always temporally unstable whatever the cavity length and pump power above threshold. The nonlinear dynamics exhibits self-pulse structuration of the backward signal with unlimited amplification and compression. Above a critical pulse steepening, dispersion saturates this singular behavior leading to strongly modulated solitary structures.

Direct optical injection locking of InP/InGaAs HPT oscillator ICs for microwave photonics and 40-Gbit/s-class, optoelectronic clock recovery

Presents fully monolithically integrated 10- and 39-GHz-band InP/InGaAs heterojunction phototransistor (HPT) oscillators that can be optically injection locked by directly illuminating the HPT. When optical signals are modulated by fundamental frequencies around free-running oscillations, the 10-GHz-band HPT oscillator integrated circuit (IC) achieves an ultra-wide locking range of 1401 MHz (relative bandwidth of 13.6%), and the 39-GHz-band HPT oscillator IC achieves a wide locking range of 768 MHz, which are records among the indirect and/or direct optical injection-locked oscillators reported to date. The 10-GHz-band HPT oscillator IC also achieves very wide locking ranges of 618 and 160 MHz for third and fifth subharmonic modulated optical signal injection, respectively, which is very useful for microwave photonics applications. Optoelectronic clock recovery for optical transmission systems was tested by using the 39-GHz-band HPT oscillator IC and a planar lightwave circuit Mach-Zehnder interferometer. A 38.8-GHz electrical clock signal was successfully extracted from 38.8-Gbit/s nonreturn-to-zero optical data streams.

Acoustic Nonlinear Behaviour of Microbubble Contrast Agent

We have investigated the nonlinear characteristics of a microbubblecontrast agent Sonazoid (Nycomed, Norway), including thesecond, third, 1/2-order, 3/2-order and 5/2-order harmonics. We havemeasured the 1/2-order subharmonic response to different transmissionsound pressures. We have found that subharmonic signals cannot begenerated until the acoustic pressure reaches a certain value, whichis the most different subharmonic from high harmonics. This result isfavourable for the further study of the subharmonic in the bubblyliquid. The 3/2-order ultraharmonic response to acoustic pressure wasalso measured.

Quantitative millimetre wavelength spectrometry at pressures approaching atmospheric: II. Determination of oxygen at atmospheric pressure

A millimetre wavelength (MMW) Fabry-Perot cavity spectrometer described in earlier work has been applied to the measurement of oxygen absorption at 60 GHz and atmospheric pressure in a gas matrix of nitrogen. The spectrometer has also been modified such that the MMW source is stabilised by a sub-harmonic microwave signal transmitted by an infrared carrier on a single mode telecommunications fibre optic. This is a step towards developing an instrument comprising minimal electronic components that can perform MMW spectrometry remotely. Oxygen determinations were achieved by monitoring the change in the quality factor ( Q) of a resonant Fabry-Perot cavity due to the presence of an absorbing sample. The MMW absorption of the sample was determined by incrementing the frequency modulation (FM) deviation of the source frequency scanning the cavity resonance profile. The response curve of absorption signal versus fraction of oxygen in nitrogen was found to be linear throughout the working range of 1–100% O 2 (v/v) in N 2 with a slope of (1.407±0.007)×10 −4 m −1 (% O 2) −1. The detection limit (3× standard deviation of the background) was found to be ∼0.8% (v/v). The MMW technique employed is advantageous since, unlike common MMW techniques, there is no vacuum requirement. Application of this method, to the monitoring of oxygen in gas mixtures of practical importance, is proposed. Values of the oxygen spectral absorption coefficients of lines between 55 and 60 GHz were measured at reduced pressure and found to be within ±2% of previous literature values. A pressure correction coefficient for O 2 absorption at 60 GHz in the 45–121 kPa range was obtained and found to be (1.354±0.014)×10 −4 m −1 kPa −1.

Macroscopic quantum fluctuations in noise-sustained optical patterns

We investigate quantum effects in pattern formation for a degenerate optical parametric oscillator with walk-off. This device has a convective regime in which macroscopic patterns are both initiated and sustained by quantum noise. Familiar methods based on linearization about a pseudoclassical field fail in this regime and new approaches are required. We employ a method in which the pump field is treated as a c-number variable but is driven by the c-number representation of the quantum subharmonic signal field. This allows us to include the effects of the fluctuations in the signal on the pump, which in turn act back on the signal. We find that the nonclassical effects, in the form of squeezing, survive just above the threshold of the convective regime. Further, above threshold, the macroscopic quantum noise suppresses these effects.

Method and system for pressure estimation using subharmonic signals from microbubble-based ultrasound contrast agents

Method and system for pressure estimation using subharmonic signals from microbubble-based ultrasound contrast agents