Harmonic Signature Research Articles

Tracing Back the Pressure-impact Zone of the CO2 Geological Storage through a Cyclic Injection Strategy

Industrial-scale CO2 injection into deep aquifers might induce far-field pressure perturbations on the basin scale, potentially impacting other underground uses present within the same aquifer formation. In the present paper, we investigate an approach to trace back the area of elevated pressure induced by CO2 storage operations through an injection strategy in a cyclic manner over time. In this manner, the CO2 injection-induced pressure field is characterized by a low magnitude harmonic signature very specific to the considered CO2 storage, the frequency being chosen as different to naturally fluctuating phenomena or other anthropogenic underground activities. We rely on the combination of de-trending and FFT technique to detect the harmonic pattern associated the CO2 storage injections. We apply the methodology on synthetic pressure signal numerically generated using a typical injection scenario in the Paris basin case. On this basis, we discuss how trace back the CO2 storage site causing the pressure impact, in particular regarding the existing sources of noise.

Engineering superficial zone features in tissue engineered cartilage

A major challenge in cartilage tissue engineering is the need to recreate the native tissue's anisotropic extracellular matrix structure. This anisotropy has important mechanical and biological consequences and could be crucial for integrative repair. Here, we report that hydrodynamic conditions that mimic the motion-induced flow fields in between the articular surfaces in the synovial joint induce the formation of a distinct superficial layer in tissue engineered cartilage hydrogels, with enhanced production of cartilage matrix proteoglycan and Type II collagen. Moreover, the flow stimulation at the surface induces the production of the surface zone protein Proteoglycan 4 (aka PRG4 or lubricin). Analysis of second harmonic generation signature of collagen in this superficial layer reveals a highly aligned fibrillar matrix that resembles the alignment pattern in native tissue's surface zone, suggesting that mimicking synovial fluid flow at the cartilage surface in hydrodynamic bioreactors could be key to creating engineered cartilage with superficial zone features.

Classification of Military Ground Vehicles Using Time Domain Harmonics' Amplitudes

In the context of the United Nations peacekeeping operations, we developed an energy-efficient method for the detection and classification of military vehicles using a group of wireless sensors. The method is adequate for low-power unattended sensors which perform sensing, feature extraction, and classification in a standalone scenario. Harmonics' amplitudes approximating the harmonic signature of the time domain acoustic signal captured by wireless sensor nodes are estimated for vehicle discrimination. The computational complexity for the time domain features extracted from ground vehicles' acoustic signals is lower than their equivalent spectral features. Classification is performed using a multilayer feedforward neural network, where discrimination between vehicles depends on their acoustic signature irrespective of their speed or location. Evaluation of the time domain method, through processing of an acoustic data set for heavyweight and lightweight military ground vehicles with comparison to spectral features, shows that time domain harmonics' amplitudes are simpler to obtain and provide the reliability of the spectral features in both the detection and false alarm rate.

Extraction of small boat harmonic signatures from passive sonar

This paper investigates the extraction of acoustic signatures from small boats using a passive sonar system. Noise radiated from a small boats consists of broadband noise and harmonically related tones that correspond to engine and propeller specifications. A signal processing method to automatically extract the harmonic structure of noise radiated from small boats is developed. The Harmonic Extraction and Analysis Tool (HEAT) estimates the instantaneous fundamental frequency of the harmonic tones, refines the fundamental frequency estimate using a Kalman filter, and automatically extracts the amplitudes of the harmonic tonals to generate a harmonic signature for the boat. Results are presented that show the HEAT algorithms ability to extract these signatures.

The twisted higher harmonic signature for foliations

We prove that the higher harmonic signature of an even dimensional oriented Riemannian foliation $F$ of a compact Riemannian manifold $M$ with coefficients in a leafwise $U(p, q)$-flat complex bundle is a leafwise homotopy invariant. We also prove the leafwise homotopy invariance of the twisted higher Betti classes. Consequences for the Novikov conjecture for foliations and for groups are investigated.

Brightness temperature of synchronic exoplanets measured by infrared photometry from the ground: Method and perspective

We explore a method to measure the temperature at the surface of “hot Jupiter” type exoplanets by relative photometry in the infrared at around 10 μm in N spectral band. The method is described and validated by numerical simulations. Thermal radiation from an exoplanet and its parent star are analysed. Geometrical configurations of extra-solar planet rotating synchronously around parent star are explored for a feasibility study of the detection. A Jupiter size planet in orbit at 0.025 astronomical unit from Sun-like parent star should have a harmonic signature of up to 0.2% in amplitude with a period of the planets orbital duration. Such a signature is difficult to detect when making absolute measurements, but by differential methods of analyses, and using a radiative transfer model to take into account background sky contribution of the Earth’s atmosphere, this relative accuracy can be reached. Some results of simulations of observation are also presented.

User-controllable mesh segmentation using shape harmonic signature

Due to different shape modeling applications, partitioning a given complex 3D mesh model into some patches or meaningful subparts is one of the fundamental problems in digital geometry processing. By using the high-dimensional mean-shift clustering scheme in shape signature space, a new method is proposed which can generate user-specified segmentation results automatically for different applications. The shape signature is composed of mesh geometric attributes and its spectral harmonics. The latter one can reflect mesh frequency spectrum information. The low frequency components are essential for semantics-oriented segmentation, while the high frequency components are important for purely geometry-oriented segmentation. The effects of the proposed method are demonstrated by several examples.

Acoustic classification of battlefield vehicles based on their seismic detection.

Identification of battlefield vehicles using a wireless sensor network is an event driven application that requires simple detection and energy efficient classification. Seismic and acoustic sensors have the capability to detect and track targets in a passive non-line-of-sight manner. The proposed approach uses seismic emissions for event detection and acoustic emissions for classification of detected events. Seismic detection using unpowered geophones achieves minimal energy for wakeup and event detection in addition to elimination of wind and background noise events. Time domain extracted features from the acoustic emission of vehicles are very efficient in battlefield vehicle discrimination preserving the coupled harmonic signature for both tracked and wheeled vehicles. We propose a simple energy efficient time domain detection and classification scheme that enables the sensor node to perform detection, feature extraction, and classification. Classification of acoustic features is performed using a multilayer feedforward neural network. The proposed approach shows that selective time domain acoustic features surpass equivalent spectral features. Evaluation of the proposed approach using recorded data shows an average classification rate (single node and single event) that exceeds 83% and an average false alarm rate of 16% (over both tracked and wheeled vehicles).

Broadband seismic measurements of degassing activity associated with lava effusion at Popocatépetl Volcano, Mexico

From November 1999 through July 2000, a broadband seismic experiment was carried out at Popocatépetl Volcano to record seismic activity over a wide period range (0.04–100 s). We present an overview of the seismicity recorded during this experiment and discuss results of analyses of long-period (LP) and very-long-period (VLP) seismic signals recorded at stations nearest to the crater over a four-month interval December 1999–March 2000. Three families of LP signals (Types-I, II, and III) are identified based on distinctive waveform features observed periods shorter than 1 s, periods longer than 15 s, and within the period range 0.5–2.5 s. Type-I LP events have impulsive first arrivals and exhibit a characteristic harmonic wave train with dominant periods in the 1.4–1.9 s range during the first 10 s of signal. These events are also associated with a remarkable VLP wavelet with period near 30 s. Type-II LP events represent pairs of events occurring in rapid succession and whose signatures are superimposed. These are typically marked by slowly emergent first arrivals and by a characteristic VLP wave train with dominant period near 30 s, made of two successive wavelets whose shapes are quasi-identical to those of the VLP wavelets associated with Type-I events. Type-III LP events represent the most energetic signals observed during our experiment. These have an emergent first arrival and display a harmonic signature with dominant period near 1.1 s. They are dominated by periods in the 0.25–0.35 s band and contain no significant energy at periods longer than 15 s. Hypocentral locations of the three types of LP events obtained from phase picks point to shallow seismic sources clustered at depths shallower than 2 km below the crater floor. Observed variations in volcanic eruptive activity correlate with defined LP families. Most of the observed seismicity consists of Type-I events that occur in association with 1–3-min-long degassing bursts (“exhalations”). Eruptive activity increased in intensity in February, coinciding with an increasing occurrence of Type-II LP events. Type-III events were first observed at the end of February and during March, in coincidence with the formation of a new lava dome. Vulcanian eruptions occurred in April and May. These events typically exhibit broadband signatures extending over the full period range of the sensors and lasting 30–80 min.

Loudspeaker defect analysis using ultrasonic harmonic characterization

This study presents the results of an ongoing investigation of defect detection in transducers. Loudspeaker assembly faults, such as a rubbing voice coil, bent frame, loose spider, etc., have traditionally been detected using experienced human listeners at the end of a production line, or through the use of low‐order harmonics for total harmonic distortion measurement. The findings of Thompson et al. [‘‘Higher‐order harmonic signature analysis for loudspeaker defect detection,’’ J. Acoust. Soc. Am. 114, 2400 (2003)] described a new method wherein the total energy of high‐order harmonics groups (10th through the 20th, or 31st through the 40th), were measured and analyzed. This approach demonstrated the ability to delineate distinct signatures that correlated to the root cause of audible rub and buzz distortions. This paper presents the results of a follow‐up study using equipment that collected harmonic data up to 100 kHz. Results are presented for ten 5‐in. midrange loudspeakers, in which trends for specific acoustic signatures were correlated to known defects. The use of a computer‐based electroacoustic measurement and analysis system using frequencies that are inaudible but beneficial for analysis of defects are discussed. [Work supported by Listen Inc., Boston, MA.]

Higher-order harmonic signature analysis for loudspeaker defect detection

Loudspeaker assembly faults, such as a rubbing voice coil, bent frame, loose spider, etc., have traditionally been detected using experienced human listeners at the end of a production line. Previous attempts to develop production measurement systems for on-line testing typically analyze only low-order harmonics for the primary purpose of measuring total harmonic distortion (THD), and thus are not specifically designed to detect defective rub, buzz, and ticking sounds. This paper describes a new method wherein the total energy of high-order harmonics groups, for example, 10th through the 20th or 31st through the 40th, are measured and analyzed. By grouping high-order harmonics and resolving their respective total energies, distinct signatures can be obtained that correlate to the root cause of audible rub and buzz distortions [Temme (2000)]. The paper discusses loudspeakers tested with specific defects, as well as results of a computer-based electroacoustic measurement and analysis system used for detection.

A Wireless, Passive, Magnetically-soft Harmonic Sensor for Monitoring Sodium Hypochlorite Concentrations in Water

A wireless, passive, remote-query sensor for monitoring sodium hypochlorite (bleach) solutions is reported. The sensor is comprised of a magnetically-soft ferromagnetic ribbon, coated with a layer of polyurethane and alumina, having a large and nonlinear permeability that supports higher-order harmonics in response to a time varying magnetic field. The hypochlorite ions induce swelling in the coating, with the resultant stress altering the harmonic signature of the sensor from which the sodium hypochlorite concentration can be determined. The wireless, passive nature of the sensor platform enables long-term monitoring of bleach concentrations in the environment. The sensor platform can be extended to other chemical analytes of interest as desired.

A Wireless, Passive, Magnetically-soft Harmonic Sensor for Monitoring Sodium Hypochlorite Concentrations in Water

A wireless, passive, remote-query sensor for monitoring sodium hypochlorite (bleach) solutions is reported. The sensor is comprised of a magnetically-soft ferromagnetic ribbon, coated with a layer of polyurethane and alumina, having a large and nonlinear permeability that supports higher-order harmonics in response to a time varying magnetic field. The hypochlorite ions induce swelling in the coating, with the resultant stress altering the harmonic signature of the sensor from which the sodium hypochlorite concentration can be determined. The wireless, passive nature of the sensor platform enables long-term monitoring of bleach concentrations in the environment. The sensor platform can be extended to other chemical analytes of interest as desired.

The complex frequencies of long-period seismic events as probes of fluid composition beneath volcanoes

Summary Long-period (LP) events have been widely observed in relation to magmatic and hydrothermal activities in volcanic areas. LP waveforms characterized by their harmonic signature have been interpreted as oscillations of a fluid-filled resonator, and mixtures of liquid and gas in the form of bubbly liquids have been mainly assumed for the fluid. To investigate the characteristic properties of the resonator system, we analyse waveforms of LP events observed at four different volcanoes in Hawaii, Alaska, Colombia and Japan using a newly developed spectral method. This method allows an estimation of the complex frequencies of decaying sinusoids based on an autoregressive model. The results of our analysis show a wide variety of Q factors, ranging from tens to several hundred. We compare these complex frequencies with those predicted by the fluid-filled crack model for various mixtures of liquid, gas and ash. Although the oscillations of LP events with Q smaller than 50 can be explained by various combinations of liquids and gases, we find that ash-laden gases are required to explain long-lasting oscillations with Q larger than 100. The complex frequencies of LP events yield useful information on the types of fluids. Temporal and spatial variations of the complex frequencies can be used as probes of fluid composition beneath volcanoes.

Harmonic ‘signatures’ of microorganisms

The frequency/amplitude effect of various microorganisms exposed to periodic (time varying) electric fields, when proximate to immersed electrodes, has been studied using a novel analytical instrument. The harmonic distribution, in complex signals caused by cells exposed to harmonic free waveforms and occupying part of the electrode/suspension interface volume, was shown to be almost entirely due to the change in the standing interfacial transfer function by the (dielectrically nonlinear) presence of cells. Thus, the characteristic interfacial non-linearity is viewed as variable, being uniquely modulated by the presence of particular cells in the interfacial region. Little can be attributed to bulk (far field) effects. The tendency for subtle (characteristic) signal distortion to occur as a function of particulate (cell or molecular) occupancy of the near electrode interfacial region under controlled current conditions leads to the method of sample characterisation by harmonic (Fourier) analysis. We report here, as a sequel to our original studies (Hutchings et al., 1993; Hutchings and Blake-Coleman, 1993), preliminary results of the harmonic analysis of microbial suspensions under controlled signal conditions using a three-electrode configuration. These data provide three-dimensional graphical representations producing harmonic ‘surfaces’ for various microorganisms. Thus, cell type differences are characterised by their ‘harmonic signature’. The visual distinction provided by these ‘surface’ forming three-dimensional plots is striking and gives a convincing impression of the ability to identify and enumerate specific microorganisms by acquisition of cell-modulated electrode interfacial Fourier spectra.

A nonlinear coherence function and its application to machine diagnostics

The harmonic content in dynamic measurements from rotating machinery contains much subtle information concerning equipment operational condition and component degradation. For this reason, the power density spectrum (PSD) has long been employed to assess the relative magnitude of fault-related spectral contributions. Measurements on high-performance rocket engine turbomachinery suffer from severe noise contamination from numerous extraneous sources, which impedes rotating element diagnostic evaluation. It is thus difficult to determine whether an apparent high-level harmonic contribution is indeed related to the fundamental rotational frequency, f1, or possibly due to an independent source. The ordinary PSD, being an absolute value, is of no assistance to this problem. In an effort to relate synchronous speed characteristics with an arbitrary harmonic component, an unique coherence spectrum was devised which we call the hyper-coherence function. The hyper-coherence function, Hn(f1), defines the nonlinear correlation between waves at the fundamental frequency and harmonics at nf1, n = 1,2…. The computation is straightforward by FFT methods, and results in a line spectrum of correlation coefficients as a function of harmonic number. This paper presents the hyper-coherence as a multiple-ordered correlation function and illustrates its utility through application to several idealized signals, and the assessment of an apparent high-amplitude harmonic signature in rocket engine vibration measurements.