RSI Publication Abstracts

J.N. Caron, "Displacement and Deflection Sensitivity of Gas-coupled Laser Acoustic Detection," to be published in Laser Ultrasonics, 2008.

Ultrasound radiated from a surface can change the path of an optical beam, directed through the acoustic field and parallel to the surface, through acousto-optic interaction. Sensing of the beam motion with a position-sensitive detector produces a simple but effective non-contact ultrasound detector, designated Gas-coupled Laser Acoustic Detection, or GCLAD. Recent research has shown that the received signal is a combination of the deflection and displacement of beam. The technique proved capable of detecting displacements of the beam, created by a transducer-generated airborne ultrasound wave, of less than a micrometer. Deflections were recorded that measured less than a microradian. The presented work estimates the sensitivity of GCLAD to an ultrasonic surface displacement. The results are compared to the sensitivities of more standard ultrasound detection methods.

W.E. Vanderlinde and J.N. Caron, "Blind Deconvolution of SEM Images," Proceedings of the 33rd International Symposium for Testing and Failure Analysis, November, 2007, p. 97-102.

Blind deconvolution techniques were used to enhance scanning electron microscope (SEM) images in the range of 200,000x to 500,000x magnification. Typical SEM samples were imaged including a gold island reference standard, a plams delayered integrated circuit, and an integrated circuit cross section. Image resolution improvement up to 40% was observed. However, it was necessary to use 16-bit images with great than 120:1 signal to noise ratio, which required 10 minute frame times.

J.N. Caron, "Progress towards a portable laser-based ultrasound sensor using gas-coupled laser acoustic detection," Review of Progress in Quantitative Nondestructive Evaluation , Vol. 24, 2004.

Gas-Coupled Laser Acoustic Detection (GCLAD) has proven to be a viable alternative to interferometric detection of ultrasound for noncontact inspection of materials. Unlike other laser-based detection techniques, GCLAD operates independently of the optical properties of the sample surface. Instead, the probe laser intercepts the ultrasound wave after it has been transmitted to air. The concept is being researched as part of an efficient, ultrasound sensor, with hangar-to-hangar portability, for interrogating flight-critical aircraft structural supports. Areas of active research include improving system sensitivity and extending the frequency response out to 10 MHz. Research to this point has shown that higher frequency waveforms can be detected using this technique and provide good sensitivity. Well-resolved waveforms have been detected in the test sample at 2.25 MHz. More research is necessary to reach the goal of detecting the signal from a 10 MHz signal. Improvements in the electronic, optical and signal processing methods are being considered.

J.N. Caron, "Blind deconvolution of audio-frequency signals using the self-deconvolving data restoration algorithm," Journal of the Acoustical Society of America, Vol. 116, Issue 1, pp. 373-378, 2004.

A signal processing algorithm has been developed in which a filter function is extracted from degraded data through mathematical operations. The filter function can be used to restore much of the degraded content of the data through use of a deconvolution process. The operation can be performed without prior knowledge of the detection system, a technique known as blind deconvolution. The extraction process, designated Self-deconvolving Data Reconstruction Algorithm (SeDDaRA), is applied here to audio-frequency signals showing significant qualitative improvement. Degradation arising from the process of electronic recording and reproduction is significantly reduced.

J.N. Caron, "Multiple-beam detection using Gas-coupled Laser Acoustic Detection," Review of Progress in Quantitative Nondestructive Evaluation, vol 20, 2000.

A novel laser-based technique for the detection of ultrasound radiated from solid materials has been developed. In this approach, a probe beam is directed parallel to the surface of a sample. Ultrasonic waves in the solid are detected when an acoustic wave is radiated from the surface into the ambient air, where the density variations cause a beam deflection. Because the laser beam is not reflected from the sample surface, the technique is not dependent upon the surface optical properties of the material under investigation. It is particularly useful for testing graphite/polymer composites and other materials with poorly reflecting surfaces. Gas-coupled laser acoustic detection (GCLAD) has been used to record well-resolved through-transmission and surface-acoustic waveforms in various materials. GCLAD has also been incorporated into a C-scanning system where it has been used to image subsurface flaws in graphite/polymer composite panels. Recent studies have investigated the inspection of curved surfaces. To this end, the flanges and corner of an angled graphite-reinforced composite panel were scanned using this technique. In addition, the prospect of using surface acoustic waves (SAWs) for the interrogation of the skins on multi-layer materials has also been studied. Using GCLAD, Lamb and Rayleigh waves have been detected in composites, polymers, thin metal films, and metal plates.

J.N. Caron, N.M. Namazi, and C.J. Rollins, "Noniterative blind data restoration by use of an extracted filter function," Applied Optics, November 10, 2002, Vol 41, No. 32, p. 6884.

A signal-processing algorithm has been developed where a filter function is extracted from degraded data through mathematical operations. The filter function can then be used to restore much of the degraded content of the data through use of a deconvolution algorithm. This process can be performed without prior knowledge of the detection system, a technique known as blind deconvolution. The extraction process, designated self-deconvolving data reconstruction algorithm, has been used successfully to restore digitized photographs, digitized acoustic waveforms, and other forms of data. The process is non-iterative, computationally efficient, and requires little user input. Implementation is straightforward, allowing inclusion into many types of signal-processing software and hardware. The novelty of the invention is the application of a power law and smoothing function to the degraded data in frequency space. Two methods for determining the value of the power law are discussed. The first method assumes the power law is frequency dependent. The function derived comparing the frequency spectrum of the degraded data with the spectrum of a signal with the desired frequency response. The second method assumes this function is a constant of frequency. This approach requires little knowledge of the original data or the degradation.