Robert Snee Gilmore

High frequency focused ultrasonic transducer for invasive tissue characterization

A broadband 25 to 50 MHz spherically focused ultrasonic transducer is placed on the tip of a catheter such that ultrasonic images of arteries and plaque are produced by introducing the catheter into arteries of patients. The high frequency transducer has thin piezoelectric polymer film as the transducing element and is adhered to a depression in the reduced cross section catheter tip. A coaxial cable in the catheter connects the transducer to an external signal source and a display for the received signals. The diagnosis and characterization of arterial disease is most often coupled with a therapeutic technique such as balloon angioplasty.

Silicon and silicon dioxide thermal bonding for silicon‐on‐insulator applications

There has been a good deal of interest recently in the applicability of thermal bonding to silicon‐on‐insultator (SOI) technology. Thermal bonding (also called direct bonding) is accomplished by mating polished, properly hydrolyzed silicon and/or silicon dioxide surfaces, which are then annealed to promote diffusion bonding. In order to produce high‐quality SOI layers it must be demonstrated that the interface betweeen the wafers is void‐free over the entire surface of the wafer (4‐in. wafers in our study). We have found that the standard annealing step which has been used by other groups to form the wafer bond must be followed by a hyperbaric, high‐temperature annealing cycle in order to produce interfaces which are completely void‐free. In addition, we have found that mating the wafers in a controlled atmosphere is necessary to insure that voids do not remain after the thermal processing is complete. We shall present transmission electron micrographs which reveal the morphology of the bonded interface o...

A Multizone Technique for Billet Inspection

An ultrasonic inspection system has been developed in response to FAA recommendations for improved inspection of titanium billet [1]. This prototype system — called Multizone — has been transitioned to the factory floor and has inspected 1,000,000+ pounds of Ti billet in 1993–94. It is a real-time, PC based platform that employs custom built analog electronics using up to 8 parallel (non-multiplexed) channels, each with a remote pulser/receiver matched to the ultrasonic transducer. Scanned helically, the billet is divided into concentric zones with a focused transducer used to acquire peak detected C-Scan image data for each zone. The depth of each zone is established by the depth of focus of that transducer. C-Scan image data from all channels are displayed simultaneously on a 1024×1280 CRT and scroll as the inspection advances along the billet length. The data are written to optical storage upon completion of the inspection. The analog electronics are fully synchronous and could provide a baseline system for the acquisition of full waveforms. Custom post scan analysis software has been developed to detect flaws using signal to noise based algorithms. This software provides more reproducible results than conventional systems and greatly reduces operator fatigue and the chance for error. This paper will discuss the system architecture and operation. A companion paper in this volume discusses inspection results. [2]

Ultrasonic phase velocity and elastic modulus in isotopically enhanced manufactured diamonds

We have performed ultrasonic pulse‐echo experiments to measure the longitudinal and transverse acoustic velocities in nine single‐crystal manufactured diamonds. The 13C concentration in the samples ranged from nearly 0% to 99%. Small (4%–5%) but distinct decreases in both the longitudinal and transverse 〈100〉 phase velocities with increasing 13C content were observed. Using these velocities and density data, values for the cubic elastic moduli c11 and c44 were determined. Within experimental uncertainty (typically <0.5%), c11 remained constant with 13C content. However, c44 was observed to decrease by 2% over the range 0%–99% 13C. Phase velocities in 〈111〉‐oriented samples remained nearly constant with isotope content, implying a 2%–6% increase in 13C diamond’s effective elastic constants 1/3(c11+2c12+4c44) and 1/3(c11−c12+c44) over those of 12C diamond. Together with experimentally determined densities and crystalline orientations and the above results for c11 and c44, the 〈111〉 velocities were used to n...

Discriminating porosity in composites using thermal depth imaging

Porosity evaluation in composites has been extensively studied with ultrasonics. There are far fewer examples of porosity evaluation using thermal imaging. One reason for this dearth of work has been the qualitative nature of most thermal characterization. In this paper we use quantitative thermal depth imaging to identify, for the first time, the characteristic signature of planes of dense porosity in composites. The observations are compared with results from thermal theory and modeling of porosity and with ultrasonic characterization. This approach should eventually lead to a quantitative thermal evaluation of volume % porosity in composites.

5 Industrial ultrasonic imaging/microscopy

Summary Ultrasonic imaging and scanned acoustic microscopy are terms used to describe similar imaging processes at different magnifications and frequencies. (A typical ultrasonic imaging/microscopy system is shown schematically in Fig. 1). Both processes form images by acquiring spatially correlated measurements of the interaction of high-frequency sound waves with materials. With the exception of the interference measurement, called V(z) , and the gigahertz frequencies used by the higher-frequency scanning acoustic microscopes, it is difficult to establish operational differences between them. This is especially true since almost all commercial ultrasonic imaging systems use transducers producing focused beams and can display magnified high-resolution images. Ultrasonic C-Scan imaging was developed largely by the ultrasonic nondestructive testing industry. The development was gradual and evolutionary. Over a 50-year period, better and better broadband transducers, electronics, and scanners were developed for operation at progressively higher frequencies, now ranging from 1.0 to 100 MHz. Conversely, scanning acoustic microscopes made a relatively sudden appearance 20 years ago on the campus of Stanford University. The first scanning acoustic microscopes operated at gigahertz frequencies and used microwave electronics that produced acoustic tone-bursts with many wavelengths per pulse. Three factors control resolution in an acoustic image: • Diameter of the acoustic beam or its point spread function (PSF) • Size and spacing of the pixels making up the image • Signal-to-noise ratio (contrast) of the feature being resolved The beam diameter, or PSF, is controlled by the frequency of the ultrasonic pulse and the focal convergence of the beam (or focal length to diameter ratio, Z/d ). In the coupling fluid, the Z/d ratio is determined by the transducer diameter and lens, but in the material, the Z/d is established by the materials ultrasonic velocities. Pixels are the squares of color or gray scale that make up computer displays of scanned images. Following Nyquists criterion, the resolution of those images is twice the size and spacing of the pixels. It follows, therefore, that to support the resolution of an ultrasonic beam, the pixels must be no larger than half that beam diameter. Finally, the contrast of the feature being studied must be (at least) a clear shade of gray above the background produced by the image noise. The noise can be due to the material or the electronics. Written to support industrial ultrasonic inspection of materials, this discussion will emphasize the similarities between imaging and microscopy rather than the differences. The roles of the focusing lens, the pulse frequency and the material being imaged, with respect to the final resolution of an acoustic image, will be considered in detail. It will be shown that additional improvements in resolution can be achieved with image processing. Finally, applications studies in metals, ceramics, composites, attachment methods, coatings, and electronic assemblies will be used to demonstrate specific roles for imaging/microscopy in nondestructive testing.

Microstructure and sound velocity of Ti-N-O synthetic inclusions in Ti-6Al-4V

The ultrasonic properties of titanium-nitrogen-oxygen inclusions within Ti-6A1-4V (Ti64) blocks were measured and related to inclusion chemistry. Sound velocities were measured on Ti-N-O alloy samples that had been prepared by powder metallurgy and ingot-melting techniques. The contributions to sound velocity from oxygen and nitrogen contents were determined. Then, Ti64 blocks were hot isostatic pressing (HIP) bonded to contain inclusions of the Ti-N-O alloys. The signal-to-noise ratios of reflections from uncracked inclusions were found to be an increasing function of inclusion interstitial content and were related to changes in sound velocity with inclusion chemistry. Measurements were made of the reflectance of titanium-nitrogen inclusions in titanium and Ti64.

Broadband Acoustic Microscopy: Scanned Images with Amplitude and Velocity Information

Since the introduction of the mechanically scanned acoustic microscope by Lemons and Quate,1 a world-wide effort has taken place to make this device2 one of the most widely used tools for materials characterization and development. With the exception of work by Tsai,2,3 and the pulse compression acoustic microscopy by Ni-koonahad, Yue, and Ash2 most studies have utilized acoustic pulses containing many wavelengths, resulting in narrow bandwidth systems. Calculations for material properties therefore require amplitude and phase measurements at different heights of the acoustic transducer above the sample. Algorithms for the use of these V(z) data have become highly sophisticated as reported in the work of Weglein, Kushibiki, Chubachi, Bertoni, Kino, Laing, Kuri-Yakub, Ash, Wickramasinghe, and others.2 This work continues to develop methods for time and frequency domain observations of broadband acoustic pulses. These observations permit material properties to be determined with the acoustic transducer at a constant height above the sample. The necessary data can be acquired during uninterrupted mechanical scanning by digitizing the reflected waveforms from the sample. One of the advantages of this approach is that scanned broadband systems are, and historically have been, widely used for industrial quality control.

Design and Fabrication of Forged Ti-6Al-4V Blocks with Synthetic Ti-N Inclusions for Estimation of Detectability by Ultrasonic Signal-To-Noise

In the work described subsequently, synthetic “hard alpha” inclusions have been fabricated within Ti-6A1-4V (Ti64) forgings. Several compositions of synthetic hard alpha were made by arc melting Ti sponge and TiN powder. Small solid cylinders of the titanium-nitrogen alloys were made by electro-discharge machining (e. d. m.) the arc-melted ingots to diameters of 0.031, 0.047, 0.062, and 0.078 inches, respectively, with heights equal to the respective diameter. Sets of eight or sixteen each identical cylinders were hot isostatic press (HIP) bonded within forged Ti64 blocks to yield uncracked inclusions with sharp interfaces with the Ti64 matrix. Detectability of the uncracked hard alpha was estimated as a function of flaw size, orientation, and nitrogen content from ultrasonic signal to noise ratios determined from C-Scan images of the blocks. Relationships of detectability to physical properties of hard alpha, and methodologies of signal to noise determinations are discussed.

SNR-based estimations for subsurface ultrasonic POD

Focused beams and C-Scan imaging for ultrasonic inspection have significantly improved the detection capability and the probability of detection (POD) for small and weakly reflecting flaws. As with most NDE sensor technologies, ultrasonic flaw detection relies on flaw signals exceeding any electronic and/or material noise, which in combination may obscure them. For reliable detection, where flaw signals are clearly discriminated from noise, the detection signal-to-noise ratio (SNR) is often specified to be at least 2.5 to 3.0, depending on the inspection procedure, the uniformity of the noise, and the method used to calculate the SNR. Almost all POD discussions, including those describing the reliability of RADAR and SONAR systems [1], begin with schematic plots of the probability density functions for flaw signals and noise signals [2,3,4]. Such schematics include thresholds, located between the two distributions, establishing the POD for the flaw signals falling above threshold, and also a Probability o...