Biomedical subjects

Steve D Sharples

Publications and source records attributed to Steve D Sharples.

3 recordsLinked to original sources

PubMed2004

Optimisation using measured Green's function for improving spatial coherence in acoustic measurements.

Aberrating materials can degrade acoustic measurements by distorting the acoustic wavefront and causing acoustic speckle (as opposed to speckle noise which is a manifestation of coherent backscatter). The amplitude and phase fluctuations associated with acoustic speckle can introduce considerable measurement uncertainty which is difficult to deal with. This paper demonstrates a new technique which optimises the spatial distribution of the generation of the ultrasound to compensate for the aberration. This technique uses experimentally measured Green's functions to allow the calculation of the field resulting from the generation wavefront during optimisation. The technique is used to improve the accuracy of velocity measurements in a steel sample using 82 MHz SAW waves. This is achieved by optimising for improved spatial coherence in the measurement region which suppresses the speckle noise. Experimental evidence of acoustic aberration arising from grain structure is shown for steel and aluminium and the measured Green's function optimisation technique is shown to overcome the resulting acoustic speckle. The technique was performed using the Adaptive Optical Scanning Acoustic Microscope (AOSAM) at Nottingham University, UK.

Journal Article↗

PubMed2004

Surface acoustic wavefront sensor using custom optics.

We have designed and had manufactured a custom surface acoustic wavefront sensor, using a standard CMOS process. Ultrasound propagating along the surface of an object perturbs the reflection of incident laser light, which has been focused onto the object using a cylindrical lens. These high-frequency angular perturbations of reflected light relate to the amplitude and phase of the ultrasound along a line on the surface of the object, and thus correspond to the acoustic wavefront. The reflected light is imaged onto a custom linear array of split photodiodes; these simultaneously detect the high-frequency perturbations at several discrete points along the line, forming an acoustic wavefront sensor. As well as a description of the device, its role within an adaptive optical scanning acoustic microscope is discussed. The sensor detects the distortions to the acoustic wavefront after it has propagated through an aberrating medium, such as a metal containing grains of random orientation. The information attained may then be used to alter the generation profile of the optical generation source of the acoustic waves, thus reducing the distortion caused by the aberration and increasing the resolution and accuracy of the system as a whole.

Journal Article↗

PubMed2003

All-optical adaptive scanning acoustic microscope.

We have constructed a fast laser-based surface acoustic wave (SAW) microscope, which may be thought of as a non-perturbing scanning acoustic microscope. The instrument is capable of rapid high resolution vector contrast imaging at several discrete frequencies, without any damage to the sample. Tailoring the generating optical distribution using computer-generated holograms allows us to both focus the acoustic waves (increasing their amplitude) and to spread the optical power over the sample surface (preventing damage). Accurate quantitative amplitude and phase (velocity) measurements and unique acoustic contrast mechanisms are possible with our instrument based on this technology due to the non-perturbing nature and the instrument geometries.However, the complexity of the optical generation profile leads to a strong dependence on material properties such as the SAW velocity and material anisotropy. We address these issues in this paper, and demonstrate how a spatial light modulator may be used to adapt the generating optical distribution to compensate for the material properties. This facilitates simpler alignment and velocity matching, and, combined with an acoustic wavefront sensor, will allow real-time adjustment of the generating source to enable imaging on anisotropic materials.

Equipment Design↗