Feasibility of Second Harmonic Imaging in Active Sonar: Measurements and Simulations

Tissue harmonic imaging is a new ultrasound imaging technique which uses the harmonic components generated by non-linear acoustic propagation through human tissues to form an image. Several factors affect tissue harmonic imaging image quality. First, strong suppression of the fundamental frequency is necessary to allow the full dynamic range of the harmonic signals to appear. Second, the harmonic components should be enhanced when they are much weaker than the fundamental frequency. In this research, based on tissue harmonic imaging, a new technique for enhancing the ultrasound imaging is presented. We first theoretically prove obtaining and enhancing the fourth harmonic and suppressing the fundamental frequency, second and third harmonics, and then after simulation of the theory by MATLAB 7·1 software, we show that our method can enhance the ultrasound image quality.

Second harmonic imaging: Good reverberations

The performance of tissue imaging is improved by tissue harmonic imaging (THI) to expand and enhance the range and level of clinical diagnosis for many diseases. The separation based on High-pass filtering (S_HPF) is a commonly used method for extracting harmonic components from ultrasonic echo signals. However, the cut-off frequency, order and algorithm to realize a high-pass filter have a great influence on the separation accuracy of harmonic signals. In present study, a novel separation method (S_CEEMDAN) based on the complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) algorithm is proposed for adaptively separating harmonic components from ultrasonic echo signals. First, we calculate the ensemble size of CEEMDAN adaptively based on the added noise level, and draw a sum of intrinsic mode functions (IMFs) from the ultrasonic echo signals by CEEMDAN. Then, the spectrum of each IMF is computed and evaluated, and the IMFs containing both fundamental and harmonic components are further decomposed by using the CEEMDAN algorithm. This separation process is end until all of IMFs have been divided into either fundamental or harmonic categories. Finally, the corresponding fundamental and harmonic echo signals are yielded by accumulating separately these two categories. In experiments, simulated ultrasonic echo signals with a center frequency of 3.5MHz are separated by the proposed S_CEEMDAN method, and the results are compared with those processed by S_HPF. The edge of the harmonic image by S_CEEMDAN marginally better defined than S_HPF. The indices for the harmonic signals separated by S_CEEMDAN and S_HPF, respectively, are as follows: the center frequencies of 6.66 MHz and 6.65 MHz, 3 dB bandwidths of 1.04 MHz and 1.05 MHz, 6 dB bandwidths of 1.59 MHz and 1.55 MHz, signal-to-noise ratios (SNRs) of 14.00 and 13.63, and image contrasts of 7.01 and 7.06. In conclusion, due to good adaptive characteristics, and lower reconstruction errors, the proposed S_CEEMD method is superior to S_HPF in the performance of spectral accuracy and harmonic imaging. This method could be potentially alternative to the current method for the ultrasonic harmonic separation.

This paper presents a 94 GHz band high-efficiency rectifier MMIC using a GaAs Schottky diode. The diode used here is a commercial Schottky diode with a cutoff frequency of 3 THz. The proposed circuit employs a single shunt topology, and consists of a DC block, an input matching circuit, the diode, and a band stop filter. In the input matching circuit, an open stub is connected at a quarter-wave length of the fundamental frequency far from the diode cathode end. That configuration effectively improves the diode performances. The band stop filter at the DC output side consists of radial stubs to suppress fundamental and second harmonic frequency signals and a high-frequency cutoff inductor. To optimize their respective phases, the filter effectively returns the fundamental and second harmonic signals to a diode. The proposed rectifier MMIC achieves an RF-DC conversion efficiency of 49.7% at an input power of 15 dBm 94 GHz.

Nonlinear propagation creates additional high-frequency components in the ultrasound wave (called harmonics) as the wave is transmitted through tissue. When nonlinear propagation occurs, reflectors along the beam path generate echoes with both the fundamental and harmonic frequencies. Tissue harmonic imaging (THI) uses two methods, frequency band filtering and pulse phase inversion, to isolate the second harmonic frequency in the detected echo so that an image of harmonic reflection can be formed. The technique of THI is discussed with illustrative examples. Advantages and limitations of THI are presented.

In this paper, a quadruple-push oscillator is proposed for the first time. The quadruple-push oscillator consists of four identical sub-circuits and a microstrip ring resonator. By using the ring resonator as common resonator, the four identical sub-circuits oscillate in the same fundamental frequency f/sub 0/, and the fundamental oscillating signal of each sub-circuit has a phase difference of 90/spl deg/, 180/spl deg/ and 270/spl deg/ to that of the others. Therefore, the undesired fundamental signals (f/sub 0/), the second harmonic signals (2f/sub 0/), the third harmonic signals (3f/sub 0/) and so on can be suppressed in principle and the desired fourth harmonic signal (4f/sub 0/) is obtained when all the signals are combined. A Ka-band quadruple-push oscillator was designed and fabricated. The measured output power of the desired fourth harmonic signal (4f/sub 0/) was +1.67 dBm at the frequency of 35.8 GHz. The measured suppression of the undesired signals of the fundamental signal (f/sub 0/), the second harmonic signal (2f/sub 0/), the third harmonic signal (3f/sub 0/) and the fifth harmonic signal (5f/sub 0/) were -18.0 dBc, -17.9 dBc, -17.8 dBc and -35.5 dBc, respectively. The measured phase noise performance at 35.8 GHz was -104.0 dBc/Hz at an offset frequency of 1 MHz.

This paper reports a novel voltage and current waveform measurement system suitable for large-signal transistor and power amplifier characterization and optimization. This technique is original in its use of a double six-port (SP) reflectometer as a homodyne vector network analyzer, which is calibrated in magnitude and phase by means of a reference multiharmonic signal generator, to measure the waveforms at the output terminal of the device. An active branch load-pull setup is used to control the source impedance at the fundamental frequency, and the load impedance at the fundamental, second, and third harmonic frequencies. The capability of the proposed SP reflectometer-based configuration is demonstrated experimentally, by measuring the voltage and current waveforms of a GaAs metal-semiconductor field-effect transistor that is biased in class AB and tuned for maximum efficiency. To assess the level of accuracy of the proposed method, the same waveforms were also measured using a microwave-transition-analyzer-based system. A comparison of the results shows that the proposed SP reflectometer setup obtains results accurate enough for power amplifier characterization with lower equipment cost.

A method for fast simulation of nonlinear wave propagation has been developed. It is based on quasi-linear approximation. By using the angular spectrum method, the contribution from an arbitrarily plane was found by back propagation of the wave field from the focal plane, squaring the field, and forward propagation of the result to the observation plane. In the spatial/time Fourier-domain, propagation is performed by a complex exponential factor, whereas the square operation corresponds to a 3D convolution. It turned out that the integration along the ultrasound beam could be solved analytically. The computation in the Fourier-domain was then reduced to a triple-integral. The resulting second harmonic wave in the observation plane was found by (3D) inverse FFT. A simulation program has been implemented in Matlab, using a laptop PC with 1.2 GHz Pentium III processor. Applied to a phased array transducer the simulation time was less than 5 minutes. The implementation of the algorithm was verified by measurements. We observed satisfactory accordance between simulations and measurements.

<p>Harmonic tremor, ground vibrations captured by seismometers oscillating in different frequencies, has been widely identified as a result of distinct physical processes. In volcanic areas, the physical processes to explain the gliding spectral lines are usually identified preceding/accompanying eruptions. Less is known about harmonic tremor that occurs in active volcanic areas but does not end in an eruption.</p><p> </p><p>In this study we analyse a harmonic tremor signal with a spectral behaviour that, to our knowledge, has not previously been observed. We observed the harmonic signal in the vertical component spectrogram of 22 out of the 24 broad-band seismometers placed around and within Torfajökull caldera, in Iceland. The discovery was made while estimating a tomographic image of the volcano using a network of seismometers operating for nearly 3 months in summer 2005. a function of frequency and time, the detected harmonic signal has a parabola structure (or a ‘V’ shape) with a fundamental frequency and a few overtones exhibiting higher energy. The fundamental mode glides upward from frequencies below 1Hz up to and above 25 Hz and can take up to 10h from the minimum to the maximum achieved frequency. A few low and high-frequency tremors also occurred during the gliding of the harmonic signal.</p><p> </p><p>In an exploratory phase, we ruled out phenomena of anthropogenic (drilling, helicopters) and natural non-volcanic origins (colliding ice structures, tidal, magnetic field, rain, wind, aurora) due to the time and frequency characteristics of the signal. We then analyzed the temporal and spatial distribution of the harmonic tremors (signal of interest). Automatic detection was leading to a large number of false positives and true negatives, therefore we performed a manual classification of daily spectrograms to detect the ‘V’ shaped signal. We select the events where the high amplitude spectra were reaching below 2 Hz. The occurrence and strength of the harmonic signal are variable in time and space. The spatial density of signal occurrence does not correlate with the location of the source of subsidence we estimate from InSAR; the detected subsidence of ~13 mm/year is confined to the caldera outline while the harmonic events were registered mostly at seismometers outside the volcano caldera. The detected signal does correlate well with areas of low topography and identified low-velocity S-wave anomalies from the derived ambient noise seismic tomography model using the same seismic network. While the correlation with low topography may indicate preferred water paths, the low S-wave velocity anomalies may indicate the presence of a heat source, leading to a water-magma interaction hypothesis. Finally, we tested for the hypothesis of a resonance set up in magmatic conduits after magma-water interaction and changes in speed flow through conduits assuming the geometries of dykes, tubes and cracks.</p>

This paper presents a method to detect weak harmonic signal embedded in chaotic noise. Using different correlation characteristic of harmonic and chaotic signal ,we can transform the sample signal to a new data sequence which has new harmonic . The new harmonic frequency is m times of the original harmonic and beyond the center bandwidth of noise. Then use wavelet packet decomposition to analysis the energy distribution of harmonic and chaotic signals and extract the component which the harmonic energy concentrated on, In the end, a multiple signal classification (MUSIC) algorithm is employed to estimate harmonic frequencies . The method suit for the complex background noise (strong chaotic noise and gaussian noise).

Synthetic aperture imaging of contact acoustic nonlinearity to visualize the closing interfaces using tone-burst ultrasonic waves

Dual-frequency tissue harmonic suppression using phase-coded pulse sequence: Proof of concept using a phantom

The processes of formation of technical channels of leakage of confidential information on objects of information activity by methods of high-frequency imposition, physical essence of process of formation of dangerous signals by modulation of probing high-frequency signal by acoustic signals, conditions of formation of basic and auxiliary technical means and systems of dangerous signals are considered. As a basis for improvement, a method of blocking information interception channels by high-frequency imposition is used, in which target active noise protection signals are introduced into the medium used to supply probing oscillations, aimed at destroying informative parameters of dangerous signal with different types of carrier modulation. It is proposed to form a set of protective signals for the destruction of informative parameters of dangerous signals both on the fundamental frequency and on the combinational harmonics of the probing signal, which provides more effective protection of confidential information from interception. The parameters of effective noise protection signals, capable of destroying the informative parameters of dangerous signals of high-frequency imposition on the fundamental frequency and combinational harmonics of the probing signal, have been determined by mathematical and simulation modelling. Basic recommendations for the formation of protective signals are formulated.

In the previous papers, the authors proposed an active periodic noise control system using the filtered-x adaptive notch filter with a minimum amount of calculation. In this work, a method of improving for active noise control performance is presented for an application with multiple reference signals. Four-cylinder diesel engine noise inside cars contains fundamental and high-order harmonic frequencies. We apply active noise control for the five fundamental harmonic frequencies of diesel engine noise. When other order frequencies with amplitudes larger than those of the controlled frequencies are contained in the noise, the noise reduction effect is reduced because of interference with these frequencies in the adaptive notch filter. We solve this problem by adopting the spectrum-shaping method. This method consists of dividing the bandwidth of interest into low- and high-frequency regions using band-pass filters. This method is useful for suppressing coupling with harmonic-order frequencies and makes the control performance much better.

The bandwidth covered by contemporary communication technologies has reached over an octave. But most existing power amplifier (PA) configurations cannot meet this requirement while at the same time maintaining a high efficiency. Therefore, a novel structure for bandwidth enhancement at a high efficiency level is proposed together with the systematic design methodology in this article. The difficulty lies in the overlap of the fundamental and harmonic frequencies. On this issue, the extended continuous Class-B/J mode can extend the impedance of the second harmonic to a resistive-reactive and relax design requirements for overlapping design space of fundamental and second harmonic frequencies. Specifically, the presented innovative circuit structure uses the multiple frequencies matching method to manipulate four fundamental and the corresponding second harmonics frequency points simultaneously, which can further effectively expand the bandwidth on the basis of the extended continuous Class-B/J PA. To verify the validity of the proposed theory, a gallium nitride multioctave PA is designed, implemented, and measured. Measured results show a fractional bandwidth of 148.4% from 0.4 to 2.7 GHz, with drain efficiency of 63%-78%, saturated output power greater than 39 dBm, and large signal gain larger than 9 dB. For the single carrier WCDMA signal with a channel bandwidth of 3.84 MHz and a peak to average power ratio of 6 dB, the adjacent channel power ratio of −47.5 to −35 dBc and −42.8 to −31.5 dBc at an average output power of 33 and 36 dBm separately are achieved over the whole frequency band.