Eugene Malyarenko

Ultrasonic Lamb wave diffraction tomography.

Ultrasonic guided waves, Lamb waves, allow large sections of aircraft structures to be rapidly inspected. Unlike conventional ultrasonic C-scan imaging that requires access to the whole inspected area, tomographic algorithms work with data collected over the perimeter. Because the velocity of Lamb waves depends on thickness the travel times of the fundamental modes can be converted into a thickness map of inspected region. Lamb waves cannot penetrate through holes and other strongly scattering defects and the assumption of straight wave paths, essential for many tomographic algorithms, fails. Diffraction tomography is a way to incorporate scattering effects into tomographic algorithms in order to improve image quality and resolution. This work describes the iterative reconstruction procedure developed for Lamb wave tomography and allowing for ray bending correction for imaging of moderately scattering objects.

Ultrasonic Lamb wave tomography

Nondestructive evaluation (NDE) of aerospace structures using traditional methods is a complex, time-consuming process critical to maintaining mission readiness and flight safety. Limited access to corrosion-prone structure and the restricted applicability of available NDE techniques for the detection of hidden corrosion or other damage often compound the challenge. In this paper we discuss our recent work using ultrasonic Lamb wave tomography to address this pressing NDE technology need. Lamb waves are ultrasonic guided waves, which allow large sections of aircraft structures to be rapidly inspected for structural flaws such as disbonds, corrosion and delaminations. Because the velocity of Lamb waves depends on thickness, for example, the travel times of the fundamental Lamb modes can be converted into a thickness map of the inspection region. However, extracting quantitative information from Lamb wave data has always involved highly trained personnel with a detailed knowledge of mechanical waveguide physics. Our work focuses on tomographic reconstruction to produce quantitative maps that can be easily interpreted by technicians or fed directly into structural integrity and lifetime prediction codes. Laboratory measurements discussed here demonstrate that Lamb wave tomography using a square perimeter array of transducers with algebraic reconstruction tomography is appropriate for detecting flaws in aircraft materials. The speed and fidelity of the reconstruction algorithms as well as practical considerations for person-portable array-based systems are discussed in this paper.

Fan beam and double crosshole Lamb wave tomography for mapping flaws in aging aircraft structures.

As the worldwide aviation fleet continues to age, methods for accurately predicting the presence of structural flaws-such as hidden corrosion and disbonds-that compromise airworthiness become increasingly necessary. Ultrasonic guided waves, Lamb waves, allow large sections of aircraft structures to be rapidly inspected. However, extracting quantitative information from Lamb wave data has always involved highly trained personnel with a detailed knowledge of mechanical waveguide physics. The work summarized here focuses on a variety of different tomographic reconstruction techniques to graphically represent the Lamb wave data in quantitative maps that can be easily interpreted by technicians. Because the velocity of Lamb waves depends on thickness, for example, the traveltimes of the fundamental Lamb modes can be converted into a thickness map of the inspection region. This article describes two potentially practical implementations of Lamb wave tomographic imaging techniques that can be optimized for in-the-field testing of large-area aircraft structures. Laboratory measurements discussed here demonstrate that Lamb wave tomography using either a ring of transducers with fan beam reconstructions, or a square array of transducers with algebraic reconstruction tomography, is appropriate for detecting flaws in multilayer aircraft materials. The speed and fidelity of the reconstruction algorithms as well as practical considerations for person-portable array-based systems are discussed in this article.

Contact scanning Lamb wave tomography

Lamb waves are guided ultrasonic waves capable of propagating relatively long distances in platelike structures such as airframe skins, storage tanks, and pressure vessels. Their propagation depends on frequency thickness and material properties, and, because structural flaws present changes in effective thickness and/or material properties, Lamb waves can be employed to assess the integrity of these structures. For structures with large surface areas, a full integrity evaluation can be a time‐consuming operation, but with Lamb wave techniques, this evaluation can be performed with waves propagating along one dimension of the inspection area as the probing transducers are moved in the perpendicular dimension. Such an approach yields information about the presence of flaws within the scanned area. Then, in order to quantitatively characterize the flaws, Lamb wave measurements can be made for a number of projections and an image of the flawed region can be reconstructed tomographically. Contact scanning Lam...

High-resolution ultrasonic thermometer for radiation dosimetry

This paper describes recent developments in the area of high-precision ultrasonic thermometry with the potential to provide on-site direct determination of radiation doses administered for cancer treatment. Conventional calorimeters used for this purpose measure radiation-induced heating in a water phantom at one point in space by means of immersed thermistors and are subject to various thermal disturbances due to Ohmic heating and interactions of the radiation with the sensor probes. By contrast, the method described here is based on a high-resolution ultrasonic system that determines the change of the speed of sound due to small temperature changes in an acoustic propagation path in the radiation-heated water, thereby avoiding such undesired thermal effects. The thermometer is able to measure tens of microkelvin changes in the water temperature averaged over the acoustic path of about 60 cm at room temperature, with root-mean-squared noise of about 5 microK. Both incandescent and ionizing radiation heating data are presented for analog and digital implementations of a laboratory prototype. This application of the ultrasonic technique opens up possibilities for a new approach to performing therapy-level radiation dosimetry for medical clinics and standards laboratories.

Blind test of Lamb wave diffraction tomography

Lamb waves are guided ultrasonic waves capable of propagating relatively long distances in plates and laminated structures, such as airframe skins, storage tanks and pressure vessels. Their propagation properties in these media depend on the vibrational frequency as well as on the thickness and material properties of the structure. Structural flaws such as disbonds, corrosion and fatigue cracks represent changes in effective thickness and local material properties, and therefore measurement of variations in Lamb wave propagation can be employed to assess the integrity of these structures. Lamb wave measurements can be made for a number of relative transducer positions (projections) and an image of the flawed region can be reconstructed tomographically to give a quantitative map of a quantity of interest, e.g. thickness loss due to corrosion. As a test of the Lamb wave scanning apparatus and diffraction tomography reconstruction algorithms, we have undertaken an experiment which is double-blind in the medi...

Ultrasonic Lamb wave tomographic scanning

Lamb waves are guided ultrasonic waves capable of propagating relatively long distances in plate-like structures such as airframe skins. Their propagation depends on frequency-thickness and material properties, and because structural flaws present changes in effective thickness and/or material properties Lamb waves can be employed to assess the integrity of these structures. For aging aircraft structures a full integrity evaluation can be a time- consuming operation, but with Lamb wave techniques this evaluation can be performed with waves propagating along one dimension of the inspection area as the probing transducer pair is moved in the perpendicular dimension. Such an approach yields information about the presence of flaws within the scanned area. Then, in order to quantitatively characterize the flaws, Lamb wave measurements can be made for a number of projections and an image of the flawed region can be reconstructed tomographically. In this paper, contact scanning Lamb wave tomography for metallic aircraft structures with flaws is discussed as a practical technique for quantitative nondestructive evaluation.

Advantages and Limitations of Using Matrix Pencil Method for the Modal Analysis of Medical Percussion Signals

Although clinical percussion remains one of the most widespread traditional noninvasive methods for diagnosing pulmonary disease, the available analysis of physical characteristics of the percussion sound using modern signal processing techniques is still quite limited. The majority of existing literature on the subject reports either time-domain or spectral analysis methods. However, Fourier analysis, which represents the signal as a sum of infinite periodic harmonics, is not naturally suited for decomposition of short and aperiodic percussion signals. Broadening of the spectral peaks due to damping leads to their overlapping and masking of the lower amplitude peaks, which could be important for the fine-level signal classification. In this study, an attempt is made to automatically decompose percussion signals into a sum of exponentially damped harmonics, which in this case form a more natural basis than Fourier harmonics and thus allow for a more robust representation of the signal in the parametric space. The damped harmonic decomposition of percussion signals recorded on healthy volunteers in clinical setting is performed using the matrix pencil method, which proves to be quite robust in the presence of noise and well suited for the task.

TH‐E‐224A‐05: Absorbed Radiation Dose Measurement with a μK‐Resolution Ultrasonic Thermometer

Purpose: To develop a μK‐resolution ultrasonicthermometer for non‐invasive measurements of absorbed radiationdose in water and to characterize the intensity profile of radiation beams used for medical treatment.Method and Materials: Subtle temperature changes in water were measured by monitoring the phase of an ultrasonic disturbance propagating in it. The current system includes a thermally insulated water tank, an ultrasonic transducer, a frequency counter, and a Pulsed Phase‐Locked Loop connected to a PC. The alpha‐prototype was initially tested and characterized experimentally with time‐controlled light pulses, and was subsequently evaluated with radiation heating from a therapy‐level Co‐60 source. The system was subjected to 30 one‐minute, 50% duty cycle radiation exposures; the temperature history was recorded and analyzed. Results: Preliminary Fourier analysis of the temperature changes caused by periodic radiation heating showed that the absorbed dose rate corresponds to 1.80 Gy/min, deduced from a 0.43 mK (±3% 1 ) per cycle temperature rise in water. The estimated nominal dose rate at 81.6 cm from the source and 3.2 cm below the water surface is estimated to be 1.65 Gy/min. The discrepancy can be attributed to the non‐standard water tank size and incomplete temperature calibration of the alpha prototype at test time. We expect to resolve these issues by equipping the system with a standard water tank and implementing a more advanced calibration procedure. Conclusions: The alpha prototype has been tested in Co‐60 radiation and produced reasonable results. The feedback from these tests has recently been incorporated into the design of a beta prototype. The new system routinely detects less than 10 μK temperature changes in water and shows great promise for precise dose measurements and beam profile characterization. The new calibration procedure does not require external sensors and makes the system more portable and fully self‐contained. Research sponsored by NIST.

Development of a method to image blood flow beneath the skull or tissue using ultrasonic speckle reflections

The interest of our study is the in-vivo transcranial visualization of blood flow without removal of the skull. The strong attenuation, scattering, and distortion by the skull bones (or other tissues) make it difficult to use currently existing methods. However, blood flow can still be detected by using the ultrasonic speckle reflections from the blood cells and platelets (or contrast agents) moving with the blood. The methodology specifically targets these random temporal changes, imaging the owing region and eliminating static components. This process analyzed over multiple exposures allows an image of the blood flow to be obtained, even with negative acoustic effects of the skull in play. Experimental results show this methodology is able to produce both 2D and 3D images of the owing region, and eliminates those regions of static acoustic sources as predicted. Images produced of the owing region are found to agree with the physical size of the vessel analogues, and also found to provide a qualitative measure on the amount of flow through the vessels.