Peter William Lorraine

Ultrasonic transducer with lens having electrorheological fluid therein for dynamically focusing and steering ultrasound energy

An ultrasonic transducer having a transducer element which generates ultrasonic energy propagating along a transducer axis with a predetermined speed of propagation, and a lens acoustically coupled to the transducer element and having an input face positioned to receive the ultrasonic energy, wherein the lens includes electrorheological fluid with voltage dependent acoustic properties therein for enabling the speed of propagation to be selectively controlled as the ultrasonic energy passes through the lens. The transducer may include a focusing lens, a steering lens, or a combination thereof for selectively controlling the focusing and/or steering of the ultrasonic energy within a region of interest in an object to be inspected therewith. A voltage control device is used to controllably apply voltage to the lens to control the propagation speed as the ultrasonic energy passes therethrough. Acoustic matching and backing layers are also provided with electrorheological fluid having voltage dependent acoustic properties therein which enable the acoustic properties thereof to be selectively altered through the use of a voltage control device for selectively applying voltage thereto.

Experimental verification of the effects of optical wavelength on the amplitude of laser generated ultrasound in polymer-matrix composites

Laser ultrasound is now integrated into the manufacturing process of some of the most modern aircraft for the inspection of composite parts. Unfortunately, for some material and process combinations, laser-ultrasound suffers from a lack of sensitivity. In laser-ultrasound generation, optical penetration depth plays a very important role. It was shown that changing the generation wavelength from the 10.6 microm of the CO2 laser to the 3-4 microm range can significantly improve generation efficiency. In this paper, ultrasonic displacements are compared to measurements of optical penetration depth in different polymer-matrix composites. Ultrasonic waves were generated using an optical parametric oscillator operating in the 3.0-3.5 microm band and optical penetration depth spectra were evaluated using quantitative photoacoustic spectroscopy. The relative amplitudes of the generated ultrasonic waves track closely the optical penetration depth spectra. These results experimentally demonstrate the importance of optical penetration in the laser-ultrasound generation process.

Experimental comparison between optical spectroscopy and laser-ultrasound generation in polymer-matrix composites

Laser ultrasound is a technique based on lasers to generate and detect ultrasound. The generation mechanism involves several parameters among which one of the most important is the optical penetration depth. This letter presents a comparison between the amplitude of ultrasonic waves generated by an optical parametric oscillator and optical penetration depth spectra measured by photoacoustic spectroscopy in the 3.0 to 3.5 μm wavelength range for three different composite samples. The laser-ultrasound amplitude spectra closely track the photoacoustic spectra. The results presented in this letter experimentally demonstrate why the 3.0–3.5 μm wavelength range generates more efficiently generates ultrasonic waves in the ultrasonic frequency range of interest for the inspection of polymer-matrix composites than the 10.6 μm wavelength of the CO2 laser.

Method for fabricating high density ultrasound array

A high yield method of fabricating an ultrasound array having densely packed ultrasound elements with smooth surface finishes includes the steps of: 1) applying an acoustic matching material to opposites faces (or surfaces) of a piezo electric material ceramic block; 2) cutting the block in a plane perpendicular to the two faces of the block so as to form a plurality of wafers having the acoustic matching material disposed on opposite ends; 3) assembling the wafers to form a laminated body having respective portions of the matching layer on opposite surfaces and with the wafers each being separated from an adjacent wafer by a selected gap distance and bonded together by a polymeric adhesive material; 4) cutting the laminated body along a longitudinal axis so as to form a first laminate body subassembly and a second laminate body subassembly, each of the subassemblies having a front surface having the acoustic matching material disposed thereon and a back surface where the laminate body was cut; 5) applying a backing layer to each laminate body subassembly; and 6) removing the polymeric adhesive material disposed between the wafers, whereby each subassembly comprises an ultrasound array having transducer elements separated by the selected array gap distance.

High Resolution Laser Ultrasound Detection of Metal Defects

The standard for sensitive detection and resolution of defects in metal components is scanned focused immersion inspection to produce C-scans. Laser ultrasound, although successfully applied to composite inspection, has previously not produced comparable results in this arena.

Progress on the development of an advanced laser ultrasound generation source for inspecting polymer-matrix composites

Laser ultrasound is proving to be a cost effective means for inspecting composite components. In this paper, we report the progress made towards the development of a new source for the laser-ultrasound inspection of composite parts. Previously, it was experimentally demonstrated that an optical parametric oscillator having a wavelength between 3 and 4 μm is significantly more efficient per energy unit to generate ultrasonic waves than a CO2 laser. Two factors explain the better performances of the OPO: the short pulse duration and the operating wavelength range that corresponds to larger optical penetration depths than the one corresponding to the CO2 laser wavelength. In this paper, these two factors are analyzed separately and their individual contributions to improvement in generation efficiency over the CO2 laser are quantitatively estimated using a numerical model. Also, the effect of optical penetration depth is experimentally explored by comparing ultrasonic amplitude of waves generated using an op...

Large-Scale Laser Ultrasonic Facility for Aerospace Applications

The use of composite materials for aerospace applications has markedly increased over the past two decades. Typically, a large percentage of composite aircraft components are fatigue and fracture critical, necessitating 100% inspection coverage. For composite materials, ultrasonic testing is the method of choice for detecting manufacturing defects which could lead to catastrophic failure during flight. As composite usage and part complexity increase, greater demands are placed on ultrasonic inspection systems. Projections of future composite usage (e.g. Joint Strike Fighter (JSF) program) show that the inspection workload may push current conventional automated ultrasonic inspection systems beyond practical limits. Conventional systems are typically slow, require significant setup time for highly contoured parts, and are generally inappropriate for in-service inspections where access is limited to a single side. Laser ultrasonic testing (Laser UT™) on the other hand offers many advantages over conventional automated ultrasonic systems: (1) the method is non-contact, requiring no couplants, (2) it can rapidly scan large areas, (3) it is able to inspect at angles far off normal, (4) it does not require expensive part fixtures, and (5) prior knowledge of the surface contour is not required. The optical scanning techniques used in make it capable of testing complex composite structures at speeds that cannot be matched by conventional mechanical scanning systems. These advantages in turn will reduce inspection costs and increase production throughput by as much as a factor of 10. Figure 1 illustrates the time savings of Laser UT™ over conventional UT as a function of part complexity.

A new laser source for ultrasound generation in composites

Laser ultrasound is proving to be a cost-effective means for inspecting composite components. Ultrasound is typically generated with a pulse of 10.6 micron light from a TEA CO2 laser. In this paper, we report on experimental progress towards a new source laser with improved characteristics.

7.5-MHz pediatric phased array transesophageal endoscope

This work extends the clinical benefits of phased array transesophageal echocardiography with high detail and contrast resolution to include neonatal patients. We have built several prototype, 64‐element, 7.5‐MHz phased array transducers housed in 6.2‐mm endoscope shafts for use with commercially available imaging systems. The acoustic design is standard, but the miniaturized packaging of the electrical connections was quite challenging. The endoscopes demonstrate very good structural resolution and excellent sensitivity for color flow imaging and continuous‐wave Doppler. They have been used on patients as small as 1.9 kg, frequently as an anatomical guide during catheter‐based interventions and during congenital heart surgery. Array test data and representative clinical studies are shown.

Laser Ultrasound Imaging of Lamb Waves in Thin Plates

Laser ultrasound offers many advantages over conventional piezoelectric ultrasound including the potential for rapid wide-area scanning, non-contacting (no couplant) generation and sensing, and large bandwidth [1,2]. Ultrasonic surface waves may be easily generated by a laser and can travel extended distances when the part is not immersed and loss to a surrounding water bath is eliminated. In addition, the geometric attenuation is significantly less as the sound energy spreads out in a circular annulus rather than in a spherical shell giving rise to an amplitude decay proportional to r −1/2.We have shown that synthetic focusing of laser ultrasound data [3] permits us to use this information to create images of near-surface defects outside the scan area. A single scan line can be used to image the complete surface of part with high speed, resolution, and sensitivity (Figure 1).