Hasan Koruk

An assessment of the performance of impedance tube method

The impedance tube method is widely used for measuring sound absorption (or reflection) coefficients of acoustic materials as a function of frequency. However, the sound absorption coefficients obtained using the impedance tube method may have some variations due to the dimensions (limits) of an impedance tube, sample preparation and sample mounting. This paper assesses the performance of the two-microphone impedance tube method as a function of frequency for different tube dimensions and materials and presents suggestions for increasing the reliability and repeatability of impedance tube measurements. First, after summarizing a systematic way for measuring acoustic transfer functions, sound absorption coefficients of a variety of materials ranging from conventional absorbing acoustic materials to samples with thin films are measured using two tubes with different tube diameter and microphone spacing. Uncertainty of sound absorption coefficients for various materials is discussed, and the frequency limits of impedance tubes are assessed. Then, a method for minimizing uncertainty due to sample mounting is proposed and the main findings are discussed.

Acoustic particle palpation for measuring tissue elasticity.

We propose acoustic particle palpation-the use of sound to press a population of acoustic particles against an interface-as a method for measuring the qualitative and quantitative mechanical properties of materials. We tested the feasibility of this method by emitting ultrasound pulses across a tunnel of an elastic material filled with microbubbles. Ultrasound stimulated the microbubble cloud to move in the direction of wave propagation, press against the distal surface, and cause deformations relevant for elasticity measurements. Shear waves propagated away from the palpation site with a velocity that was used to estimate the materials Youngs modulus.

On Measuring Dynamic Properties of Damping Materials Using Oberst Beam Method

The Oberst Beam Method is widely used for the measurement of the mechanical properties of damping materials. This method is a classical method based on a multilayer cantilever beam which consists of a base beam and one or two layers of other materials. The base beam is almost always made of a lightly damped material such as steel and aluminum. If the Oberst Beam Method (OBM) is to be used, it is essential to establish a very accurate measurement methodology. In this respect, the response and the excitation sensors in the Oberst test rig are generally non-contact type. Although the drawbacks of contacting type of transducers are eliminated by this way, there are other critical issues when OBM is used. It is therefore essential to be aware of the parameters that might adversely affect the measured data and also to avoid them as much as possible. Consequently, all the parameters affecting the result need to be optimized in order to obtain the material properties with high accuracy. Although the OBM is referenced in some standards and widely used in scientific studies, detailed information in the literature on how to perform a successful Oberst Beam experiment is very limited. This is the main subject this paper aims to address. In this paper, after setting up the Oberst test rig the effects of various parameters on measured data using an Oberst test rig are examined in an attempt to improve the accuracy of the estimated material properties. Then repeatability measurements are performed and the main parameters affecting the quality of the measured data are identified. After that, extensive tests are performed so as to determine the effect of the amplitude of the excitation force, adverse effects of electromagnetic excitation and the effects of length of the test specimen. Furthermore, it is found that the small differences between individual samples may also affect the results significantly. Finally, some suggestions are given to the potential users of the OBM so as to avoid undesirable effects of certain parameters during such measurements.Copyright

Assessment of Modal Strain Energy Method: Advantages and Limitations

The Modal Strain Energy Method (MSEM) is widely used in practice for the prediction of damping levels in structures. MSEM is based on a fundamental assumption that the damped and the undamped mode shapes of a structure are identical. Therefore, when MSEM is to be used, it is essential to ensure that this assumption is an acceptable assumption. However, detailed information on the accuracy of the method as a function of the system parameters including modal (or mode shape) complexity is quite limited. In this paper, the performance of MSEM is assessed in terms of the damping levels of the structure, proportionality of damping distribution and/or the modal complexity. To do so, an effective finite element based MSE approach is proposed first. Then, a proportionally damped structure with different damping levels is modeled and the performance of MSEM is assessed as a function of the structural damping level. After that, a non-proportionally damped structure is studied in order to examine the performance of the method with respect to mode shape complexity. In all cases, a more accurate reference method, based on complex eigenvalue approach, is used for comparison purposes. Furthermore, a few definitions of mode shape complexity are utilized in order to quantify the mode shape complexity. The results show that as long as the mode shapes are real or close to being real, MSEM can predict the damping levels as well as the natural frequencies of a damped structure with good accuracy. However, the accuracy that can be achieved with MSEM decreases as mode shape complexity increases.Copyright

Acoustic Streaming in a Soft Tissue Microenvironment

We demonstrated that sound can push fluid through a tissue-mimicking material. Although acoustic streaming in tissue has been proposed as a mechanism for biomedical ultrasound applications, such as neuromodulation and enhanced drug penetration, streaming in tissue or acoustic phantoms has not been directly observed. We developed a material that mimics the porous structure of tissue and used a dye and a video camera to track fluid movement. When applied above an acoustic intensity threshold, a continuous focused ultrasound beam (spatial peak time average intensity: 238 W/cm2, centre frequency: 5 MHz) was found to push the dye axially, that is, in the direction of wave propagation and in the radial direction. Dye clearance increased with ultrasound intensity and was modelled using an adapted version of Eckarts acoustic streaming velocity equation. No microstructural changes were observed in the sonicated region when assessed using scanning electron microscopy. Our study indicates that acoustic streaming can occur in soft porous materials and provides a mechanistic basis for future use of streaming for therapeutic or diagnostic purposes.

The effects of ultrasound parameters and microbubble concentration on acoustic particle palpation

The elasticity of tissue-an indicator of disease progression-can be imaged by ultrasound elasticity imaging technologies. An acoustic particle palpation (APP) has recently been developed-the use of ultrasonically driven acoustic particles (e.g., microbubbles)-as an alternative method of tissue deformation. APP has the potential to improve the resolution, contrast, and depth of ultrasound elasticity imaging; but the tissue displacement dynamics and its dependence on acoustic pressure, center frequency, and microbubble concentration remains unknown. Here, displacements of at least 1 μm were produced by applying ultrasound onto a microbubble solution (concentration: 10 × 106 microbubbles ml-1) placed within a tunnel surrounded by a 5% gelatin phantom. Displacements of more than 10 μm were produced using a 1, 3.5, or 5 MHz center frequency pulse with peak-rarefactional pressures of 470, 785, and 1210 kPa, respectively. The deformation of the distal wall varied spatially and temporally according to the different parameters investigated. At low pressures, the deformation increased over several milliseconds until it was held at a nearly constant value. At high pressures, a large deformation occurred within a millisecond followed by a sharp decrease and long stabilization. Ultrasound exposure in the presence of microbubbles produced tissue deformation (p < 0.05) while without microbubbles, no deformation was observed.

Displacement of a bubble by acoustic radiation force into a fluid–tissue interface

Microbubbles in an ultrasound beam experience a primary Bjerknes force, which pushes the microbubbles against a fluid-tissue interface and deforms the tissue. This interaction has been used to measure tissue elasticity and is a common interaction in many therapeutic and diagnostic applications, but the mechanisms of deformation, and how the deformation dynamic depends on the bubble and ultrasound parameters, remain unknown. In this study, a mathematical model is proposed for the displacement of a bubble onto a fluid-tissue interface and the tissue deformation in response to the primary Bjerknes force. First, a model was derived for static loading and the models prediction of bubble-mediated tissue displacement and stresses in tissue were explored. Second, the model was updated for dynamic loading. The results showed that the bubble is both displaced by the applied force and changes its shape. The bubble displacement changes nonlinearly with the applied force. The stress values in tissue are quite high for a distance within one radius of the bubble from the bubble surface. The model proposed here is permissible in human tissue and can be used for biomedical ultrasound applications, including material characterization.

Noninvasive and localized acoustic micropumping—An in vitro study of an ultrasound method that enhances drug distribution through a physiologically-relevant material

Acoustic streaming—the displacement of fluid by sound—has been proposed as the mechanism for therapeutic effects, such as drug distribution enhancement, yet there have been no direct observation or characterization of this effect in soft tissue, making it difficult to optimize and control. We aimed to directly observe ultrasound-induced streaming during sonication in a tissue-mimicking material. We hypothesized that existing ultrasound phantoms (e.g., polyacrylamide (PAA) and gelatin) mimic the acoustic properties of tissue, but not the tissue microenvironment. Scanning electron microscopy revealed that gelatin and PAA had closed pores suggesting that they can’t support acoustic streaming. In contrast, macroporous acrylamide (MPPA), a new phantom we created, had interconnected pores resembling the interstitial space of soft tissue. The focal point of a focused ultrasound (FUS) transducer was placed at the distal surface of the MPPA phantom. A model drug (Bromophenol blue) was injected in and around the fo...

Investigation of Modal Properties of AlSi7 Foam Produced by Powder Metallurgy Technique

Abstract The modal properties of aluminum-based (AlSi7) metallic foam, produced by powder metallurgy technique, as a function of foam density (and thus pore size and amount of porosity) were investigated. In the experimental studies, 1 wt.-% TiH2 and 7 wt.-% Si powders were added to aluminum powder and they were mixed in a three dimensional turbola mixer for 30 minutes. Mixed powders were compacted, extruded and rolled to produce the precursor samples. AlSi7 foam samples with the dimensions of 18.7 cm × 2.6 cm × 1.6 cm were produced after foaming at 690 °C. After all, the natural frequencies and the modal loss factors of a few foam samples with different pore distributions and/or densities were determined using the frequency response functions measured on the test samples. The results show that the densities of the foam samples decrease with increasing pore size and amount of porosity, and the modal loss factors of foam samples increase as foam density decreases.

A Low Cost Velocity Measurement System Design for Rotary Machinery

Today, as the importance of system automation increases, measurement systems become more and more important. Consequently, in many applications, from washing machines, motorized vehicles, robots to nuclear turbine reactors, velocity measurement is inevitable. In industry, velocity is widespreadly needed to be measured. Besides that researchers through the globe need such measurement devices in their studies. On the other hand, to be able to make a correct measurement, it may be needed to pay much on measuring equipments while the economical issue is sometimes the reason for the research does not continue on or even not begin. So, it has always been a practical problem for both industry and researchers not to be able to measure the rotating velocity of machinery with both sufficient precision and low cost. In this paper, a very low cost but still precise velocity measurement system design is introduced, explained and discussed. First, building up of the sensor circuit and basic components of the system are introduced. Then, data acquisition and signal processing of the system are explained. Finally, advantages of the system are discussed and some conclusions are given.Copyright