Computer-controlled Positioning System Research Articles

Scale model observations of coupled vertical modes in a translationally invariant wedge.

Scale-model tank experiments offer a controlled environment in which to make underwater acoustic propagation measurements that can provide high-quality data for comparison with numerical models. This paper presents results from a scale model experiment for a translationally invariant wedge with a 10° slope fabricated from closed-cell polyurethane foam to investigate three-dimensional (3-D) propagation effects. A computer controlled positioning system accurately located a receiving hydrophone in 3-D space to create a dense field of synthetic vertical line arrays, which are subsequently used to mode filter the measured pressure field. The resulting mode amplitudes show the modal propagation zone, the modal shadow zone, and the classical intra-mode interference pattern resulting from rays launched up and along the slope. The observed features of the measured data are compared to three different propagation models: an exact, closed-form solution for a point source in wedge with pressure release boundaries, a 3-D ray trace model, and an adiabatic model. Examination of the mode amplitudes produced by the models reveals how the effects of vertical mode coupling can be observed in the measured data.

A new approach in physical modeling for velocity anisotropy study

Special automated equipment is constructed for ultrasonic velocity measurements at various incidence angles of waves that is necessary for estimation of anisotropy parameters of rocks. The equipment includes hydraulic press for simulation of vertical pressure in the Earth, at a range up to 40 MPa and computer controlled positioning system that provides precise independent positioning of ultrasonic source and receiver. This setup enables us to perform reliable velocity measurements at the angle interval from 15° to 90° and additional single measurement at 0°. The minimum step of a transducer position in 15°-90° range is 8.1'. As an example on anisotropy study, we perform physical modeling of wave propagation in artificial sample of transversely isotropic (TI) symmetry, which represents a model of fractured rock. Using experimental setup, we acquire P-wave velocity data for plate-stack model with vertical axis of symmetry formed by acrylic 1 mm thick sheet plates. Using measured velocities, we estimate Thomsen’s anisotropy parameters e and δ, and get dependence between the velocity of P-waves and symmetry axis of the model. . In our oncoming research, the upgraded Ultrasonic Measuring System will be supplemented by multicomponent transducers similar to those described in Chichinina et al. (2009), which allow simultaneous recording of P, SV and SH waves at each data point.

Use of wide-element one-dimensional receiving arrays to measure two-dimensional lateral pressure distribution of ultrasound beams

Measurement of acoustic fields is an important aspect of ultrasound research and development. The corresponding data is usually collected by a raster scan using a single point receiver moved by a computer-controlled positioning system. A faster approach could be based on the use of a 1D linear multi-element array with several tens or hundreds of small elements, which is moved in a direction perpendicular to the beam axis. The drawback of such an approach is difficulty in making small, closely-positioned receiving elements that provide sufficient signal-to-noise ratio. The current paper presents an alternative design for a 1D linear array: instead of using small elements, here it is suggested to use narrow but long elements, with a width on the order of a half wavelength or less and a length larger than the extent of the ultrasound beam being studied. The drawback of the proposed long-element arrays is absence of resolution in the direction along the element. This problem is solved by incrementally rotating the array either around the axis parallel to the array surface and perpendicular to the elements or around the axis perpendicular to the array surface. [Work supported by RSF 14-15-00665, NIH R01 EB007643, and NIH R21 EB016118.]

Examining the intra-modal interference in an idealized oceanic wedge using scale-model experiments and acoustic propagation modeling

Scale-model tank experiments are beneficial because they offer a controlled environment in which to make underwater acoustic propagation measurements that can provide high-quality data for comparison with numerical models. This talk presents results from a 1:7500 scale model experiment for a wedge with a 10° slope fabricated from closed-cell polyurethane foam to investigate three-dimensional (3D) propagation effects. A 333 μs second long pulse allows the acoustic field to obtain a steady-state, continuous-wave signal. A computer controlled positioning system accurately moves the receiving hydrophone in 3D space to create a dense field of vertical line arrays, which are used to mode filter the measured time series. The single-mode fields show the classical interference pattern resulting from rays launched up and along the slope. The measured data are compared to an exact, closed-form solution for a point source in wedge with impenetrable boundaries. The finite size of the source and the departure from the ...

Measurements and modeling of three-dimensional acoustic propagation in a scale-model canyon

Scale-model acoustic propagation experiments were conducted in a laboratory tank to investigate three-dimensional (3D) propagation effects induced by range-dependent bathymetry. The model bathymetry, patterned after measured bathymetric data, represents a portion of the Hudson Canyon at 1:7500 scale and was fabricated from closed-cell polyurethane foam using a computer-numerically controlled (CNC) milling machine. In the measurement apparatus, a computer-controlled positioning system precisely locates the receiving hydrophone which permits the creation of synthetic horizontal line arrays. Results are shown for propagation paths along and across the axis of the canyon. The measurements are explained using both a hybrid method known as vertical modes/horizontal parabolic equation and a 3D ray model known as Bellhop3D. For propagation along the canyon axis, horizontal focusing is observed and discussed in the context of normal modes. For the across canyon propagation, the reflective foam walls of the canyon ...

Testing and verification of a scale-model acoustic propagation system.

This paper discusses the design and operation of a measurement apparatus used to conduct scale-model underwater acoustic propagation experiments, presents experimental results for an idealized waveguide, and compares the measured results to data generated by two-dimensional (2D) and three-dimensional (3D) numerical models. The main objective of this paper is to demonstrate the capability of the apparatus for a simple waveguide that primarily exhibits 2D acoustic propagation. The apparatus contains a computer-controlled positioning system that accurately moves a receiving transducer in the water layer above a scale-model bathymetry while a stationary source transducer emits broadband pulsed waveforms. Experimental results are shown for a 2.133 m × 1.219 m bathymetric part possessing a flat-bottom bathymetry with a translationally invariant wedge of 10° slope along one edge. Beamformed results from a synthetic horizontal line array indicate the presence of strong in-plane arrivals along with weaker diffracted and horizontally refracted arrivals. A simulated annealing inversion method is applied to infer values for five waveguide parameters with the largest measurement uncertainty. The inferred values are then used in a 2D method of images model and a 3D adiabatic normal-mode model to simulate the measured acoustic data.

Measurement of the electric potential at the surface of nonuniformly charged polypropylene nonwoven media

The aim of this paper is to establish the conditions in which the vibrating capacitive probe of an electrostatic voltmeter could be employed for mapping the electric potential at the surface of non-uniformly charged insulating bodies. A first set of experiments are performed on polypropylene non-woven media (thickness: 0.4 mm; fiber diameter: 20 μm) in ambient air. In a second set of experiments the non-uniformity of charge is simulated using five copper strips (width: 2 mm or 3 mm; distance between strips: 2 mm). All the strips are connected to a high-voltage supply (Vs = 1000 V). The sample carrier is attached to a computer-controlled positioning system that transfers it under the capacitive probe (TREK, model 3451) of an electrostatic voltmeter (TREK, model 1341B). The measurements are performed at various relative speeds Vb between the sample and the probe, and for various sample rates Fe. A first set of experiments point out that the electric potential displayed by the electrostatic voltmeter depends on the spacing h between the sample and the probe. The diameter D of the spot “seen” by the probe is approximately D ≈ 8h/3. From the second set of experiments performed with the test plate, it can be concluded that the surface potential can be measured with the media in motion, but the accuracy is limited by the spatial resolution defined by k = Vb/Fe.

Measurements of three-dimensional acoustic propagation in a scale-model canyon

Scale-model acoustic propagation experiments were conducted in a laboratory tank to investigate three-dimensional (3D) propagation effects induced by range-dependent bathymetry. The model bathymetry, patterned after measured bathymetric data, represents a portion of the Hudson Canyon at 1:7500 scale and was fabricated from closed-cell polyurethane foam using a computer-numerically controlled (CNC) milling machine. In the measurement apparatus, a computer-controlled positioning system locates the receiving hydrophone at user-defined points in 3D space while the stationary source hydrophone emits broadband pulsed waveforms. Precise control of the receiving hydrophone permits the creation of synthetic arrays from which horizontal and vertical beamforming is performed. Results are shown for propagation paths along and across the axis of the canyon where the received time series are post-processed to estimate travel times, transmission loss, and horizontal and vertical arrival angles. [Work supported by ONR.]

Characterization of Pressure Fields of Focused Transducers at TÜBİTAK UME

Field radiated by HIFU (High Intensity Focused Ultrasound) has been investigated by measuring its pressure field and mapping in 2-D and 3-D. A new ultrasound pressure measurement system has been designed and constructed at TÜBİTAK UME (The Scientific and Technological Research Council of Turkey, the National Metrology Institute). System consists of a water tank, positioning system, measurement devices and a controlling program. The hydrophone was attached to a 3-axis, computer-controlled positioning system for alignment with the ultrasound source. The signal was captured and analyzed by the commercially available LabVIEW 8.1 software. The measurements of the ultrasound field were carried out with a needle hydrophone. For each waveform, p, p+ and p-pressures have been calculated. Wave behaviors produced by the KZK model and from experiments look like similar in general. In p, p+, p- the focal point, zero point after the primary peak (focus) and extremum points in the near field well match.

Results from a scale model acoustic propagation experiment over a translationally invariant wedge

A 1:7500 scale underwater acoustic propagation experiment was conducted in a laboratory tank to investigate three-dimensional (3D) propagation effects, with the objective of providing benchmark quality data for comparison with numerical models. A computer controlled positioning system accurately moves the receiving hydrophone in 3D space while a stationary source hydrophone emits band-limited pulse waveforms between 200 kHz and 1 MHz. The received time series can be post-processed to estimate travel time, transmission loss, and vertical and horizontal arrival angle. Experimental results are shown for a 1.22 × 2.13 m bathymetric part possessing both a flat bottom bathymetry and a translationally invariant wedge with a 10° slope. Comparisons between the experimental data and numerical models are also shown. [Work supported by ONR.]

A novel high-throughput irradiator for in vitro radiation sensitivity bioassays

This paper describes the development and characterization of a fully automated in vitro cell irradiator using an electronic brachytherapy source to perform radiation sensitivity bioassays. This novel irradiator allows complex variable dose and dose rate schemes to be delivered to multiple wells of 96-well culture plates used in standard biological assays. The Xoft Axxent® eBx™ was chosen as the x-ray source due to its ability to vary tube current up to 300 µA for a 50 kVp spectrum using clinical surface applicators. Translation of the multiwell plate across the fixed radiation field is achieved using a precision motor driven computer controlled positioning system. A series of measurements was performed to characterize dosimetric performance of the system. Measurements have shown that the radiation output measured with an end window ionization chamber is stable between operating currents of 50–300 µA. In addition, radiochromic film was used to characterize the field flatness and symmetry. The average field flatness in the in-plane and cross-plane direction was 2.9 ±1.0% and 4.0 ±1.7%, respectively. The average symmetry in the in-plane and cross-plane direction was 1.8 ±0.9% and 1.6 ±0.5%, respectively. The optimal focal spot resolution at the cellular plane was determined by measuring sequential irradiations on radiochromic film for three different well spacing schemes. It was determined that the current system can irradiate every other well with negligible impact on the radiation field characteristics. Finally, a performance comparison between this system and a common cabinet irradiator is presented.

TH‐F‐105‐04: Development of a Novel High‐Throughput Variable Dose Rate Irradiator for in Vitro Radiobiology Research

Purpose : Modern biology research often depends upon high‐throughput assays that are incompatible with traditional irradiation techniques due to dose inhomogeneity and dose rate limitations of the most common irradiator systems. To overcome these limitations, we sought to develop a high‐throughput, variable dose rate irradiator for in vitro radiobiology research. Methods: The Xoft Axxent eBx™ was chosen as the x‐ray source for its ability to vary current up to 300 μA, allowing delivery of a variety of doses over a range of dose rates to be applied to a 96‐well cell culture plate. This system delivers a 50kVp spectrum using standard surface applicators. Field flatness was achieved using a 10‐mm diameter surface applicator equipped with a flattening filter that is used for treating skin cancers. Additional collimation was designed to prevent dose contamination into adjacent wells. Dose uniformity was verified using EBT3 Gafchromic film and analyzed using ImageJ, while dose verification was achieved using TLD‐100 measurements and MCNP5 Monte Carlo simulations. Results : Translation of the well plate across the fixed radiation field is achieved using a precision motor‐driven computer controlled positioning system. An Exradin A20 ion chamber has been incorporated into this system to provide periodic air‐kerma rate verification during the irradiation cycle using newly proposed dosimetry formalism for this source. Ion chamber measurements of air‐kerma rate at the skin applicator exit window indicate achievable dose rates of 6–36 mGy/s while the dose uniformity profile of the 10mm Xoft skin applicator was maintained within 3.2% inside the cell culture well. Conclusions: This work indicates significant potential for the development of a high‐throughput, variable dose rate irradiator for in vitro radiobiology research using the Xoft Axxent eBx™ skin applicator system. This irradiator provides a powerful tool by increasing the efficiency and number of assay techniques available for the radiobiology researcher.

Quantitative Volumetric Perfusion Mapping of the Microvasculature Using Contrast Ultrasound

Contrast-enhanced ultrasound imaging has demonstrated significant potential as a noninvasive technology for monitoring blood flow in the microvasculature. With the application of nondestructive contrast imaging pulse sequences combined with a clearance-refill approach, it is possible to create quantitative time-to-refill maps of tissue correlating to blood perfusion rate. One limitation to standard two-dimensional (2D) perfusion imaging is that the narrow elevational beamwidth of 1- or 1.5-D ultrasound transducers provides information in only a single slice of tissue, and thus it is difficult to image exactly the same plane from study to study. We hypothesize that inhomogeneity in vascularization, such as that common in many types of tumors, makes serial perfusion estimates inconsistent unless the same region can be imaged repeatedly. Our objective was to evaluate error in 2D quantitative perfusion estimation in an in vivo sample volume because of differences in transducer positioning. To mitigate observed errors due to imaging plane misalignment, we propose and demonstrate the application of quantitative 3-dimensional (3D) perfusion imaging. We also evaluate the effect of contrast agent concentration and infusion rate on perfusion estimates. Contrast-enhanced destruction-reperfusion imaging was performed using parametric mapping of refill times and custom software for image alignment to compensate for tissue motion. Imaging was performed in rats using a Siemens Sequoia 512 imaging system with a 15L8 transducer. A custom 3D perfusion mapping system was designed by incorporating a computer-controlled positioning system to move the transducer in the elevational direction, and the Sequoia was interfaced to the motion system for timing of the destruction-reperfusion sequence and data acquisition. Perfusion estimates were acquired from rat kidneys as a function of imaging plane and in response to the vasoactive drug dopamine. Our results indicate that perfusion estimates generated by 2D imaging in the rat kidney have mean standard deviations on the order of 10%, and as high as 22%, because of differences in initial transducer position. This difference was larger than changes in kidney perfusion induced by dopamine. With application of 3D perfusion mapping, repeatability in perfusion estimated in the kidney is reduced to a standard deviation of less than 3%, despite random initial transducer positioning. Varying contrast agent administration rate was also observed to bias measured perfusion time, especially at low concentrations; however, we observed that contrast administration rates between 2.7 × 10(8) and 3.9 × 10(8) bubbles/min provided results that were consistent within 3% for the contrast agent type evaluated. Three-dimensional perfusion imaging allows a significant reduction in the error caused by transducer positioning, and significantly improves the reliability of quantitative perfusion time estimates in a rat kidney model. When performing perfusion imaging, it is important to use appropriate and consistent contrast agent infusion rates to avoid bias.

Fused deposition modelling using direct extrusion

In the present work, a process based on the principle of polymer extrusion is developed: the extruder deposition process (EDP). This system uses a screw extruder to deposit the material on a computer-controlled positioning system to build components. Experiments (Box–Behnken technique is used for experimental design) are carried out to study the influence of three process variables: nozzle temperature, chamber temperature and road gap on bond strength (inter-road and interlayer) and surface finish. Surface roughness and ultimate tensile strength values are measured for test specimens. Analysis of variance (ANOVA) is used to determine the significance of process variables. It is concluded that the developed EDP eliminates many of the shortcomings of the systems developed based on the principles of extrusion and produces components having higher bond strength than that achieved in commercial fused deposition modelling (FDM) systems.

Derivation of sonograph quality parameters by the use of Point Spread Function analysis

A measuring system evaluating a Point Spread Function generated in an ultrasonographic image by scanning a spherical target was developed. The target is moved in measuring bath filled by water over scanned volume via 3D computer controlled positioning system. A video signal obtained is converted to digital form and analyzed by original software to derive various objective parameters of the imager as follows: Focal areas in both the azimuth and the elevation directions, Ultrasound scanning lines visualisation, Manufacturer preloaded TGC, Width of the scanning plane, Side lobe levels and Amplification uniformity in the azimuth direction. The method was verified by testing 18 different equipments in 282 measurements. Samples of particular measurement results in form of graphical outputs are included. Medical and physiological impacts of this approach are discussed.

An automated system for producing uniform surface deposits of dry particles.

A laboratory system has been constructed that uniformly deposits dry particles onto any type of test surface. Devised as a quality assurance tool for the purpose of evaluating surface sampling methods for lead, it also may be used to generate test surfaces for any contaminant that uses particles or dust as a transport mechanism. Additionally, it may be used to spike surfaces for studies concerning particle transport, resuspension, reentrainment, and exposure. The electromechanical system includes a rugged aluminum chamber housing deposition equipment, a computer-controlled positioning system, and a 0.61 x 0.61 m target surface area (2 x 2 ft). Media used to evaluate the system have included glass beads of various size fractions (physical diameters between 30 and 500 microm), and Arizona Test Dust (aerodynamic diameters between 1 and 80 microm). Presieved particle size fractions may be used individually to study the effects of monodisperse particles, or may be mixed to create custom polydisperse size distributions. Using arrays of 16 coupons placed on the surface to collect representative samples from every test, the uniformity of the particle deposition can be quantified. The system achieved an average coefficient of variation of less than 20% for the 16 coupons for the particle types and sizes mentioned above and for a variety of total surface loadings (0.3-19 g/m2). Calculations of the system's repeatability (as the average coefficient of variation of mass gains for individual coupon locations compared across multiple identically configured runs) yielded approximately 10 +/- 5% (one standard deviation). Tests of the system's accuracy, defined as the absolute percentage difference between predicted surface loadings and actual loadings, yielded 3.7 +/- 1.3% (one standard deviation).

High-resolution measurements of the specific absorption rate produced by small antennas in lossy media

We describe a thermistor-based technique for measurement of the specific absorption rate (SAR) of radio frequency energy from a small antenna in lossy matter with high spatial resolution. The apparatus employs a small thermistor probe, that is moved about the antenna using a computer-controlled positioning system. The antenna is excited by pulses of radio frequency energy, and the SAR is obtained from the measured rate of temperature increase. We present a simplified thermal model to account for heating of the thermistor by the applied electromagnetic energy, which is a major potential artifact in the method. The apparatus is useful for studies of radio frequency ablation of tissue or near-field exposure in models of the body by transmitters.

Five axis programmable positioning system for underwater acoustic measurements at Penn State

To facilitate underwater acoustic measurements at Penn State, a five axis computer controlled positioning system has been developed by the author and installed in the new water tank facilities at the Applied Research Laboratory. Providing linear motion in three directions and rotations about two axes, the system allows an acoustic transducer to be positioned and oriented at virtually any position and direction within the water tank. Motion is controlled along each axis via programmable controllers (indexers) which are in turned accessed by a computer via RS 232. Resolution in the linear directions is 0.005 in. Angular resolution is 0.18°. Working in conjunction with the appropriate data-acquisition hardware and software, the positioning system allows the entire measurement procedure to be automated. Although designed initially for use in monostatic and bistatic surface scattering experiments, the system is also being used for other interesting underwater experiments, including bottom sediment studies, and the effects of thermal gradients on acoustic signals.

Ocean acoustics turbulence study: Acoustic scattering from a buoyant axisymmetric plume

Limited in situ measurements from high-frequency underwater acoustic echosounders have suggested that there may be circumstances in which acoustic scattering from ocean temperature variability is sufficiently intense to be observable over volume reverberation due to biologics. A new laboratory program, the ocean acoustics turbulence study (OATS), has been undertaken to quantify such scattering. The laboratory employs a very precise computer-controlled positioning system and allows a scattering geometry from a near forward-scattering angle, 5°, to a near backscattering angle, 160°. This article reports on results of an initial set of experiments utilizing a 1-MHz, 1-cycle transmitted pulse scattering from a temperature anomaly field produced by a laminar buoyant plume. The objective of this experiment is to compare observations of acoustic scattering from the temperature anomaly with that predicted by the Bragg scattering condition. A parameter regime is chosen such that the laminar plume has an approximately axisymmetric and Gaussian temperature profile. For the two-dimensional axisymmetric case, the Bragg scattering condition allows prediction of an acoustically derived two-dimensional Fourier transform of the temperature field. The acoustically derived two-dimensional Fourier transform and the one derived directly from in situ temperature measurements are in good agreement, except at the higher frequency range of the bandwidth of the scattered signal. Discussion of the possibility of inverting such measurements for a direct calculation of the temperature field is presented.

Corneal Lathing Using the Excimer Laser and a Computer-Controlled Positioning System: Part II-Variable Trephination of Corneal Buttons

A new system is presented that allows a variable trephination of donor corneas for the preparation of corneal buttons used in penetrating keratoplasty. With the help of a computer-controlled positioning system that uses high-precision micropositioning elements (both translation and rotational stages) the donor cornea is removed, epithelial side up, in a fixation device in front of a focused excimer laser beam (ArF, lambda = 193 nm). User friendly computer software allows the surgeon to select a variety of parameters (diameter, shape, angle of trephination) of the corneal graft. Histological and electron microscopical data of human corneas trephined with this "Excimer Laser Corneal Shaping System" are presented.