P. Pallav

Elliptical-Tukey Chirp Signal for High-Resolution, Air-Coupled Ultrasonic Imaging

A new signal processing method, which uses a modified chirp signal for air-coupled ultrasonic imaging, is described. A combination of the elliptical and Tukey window functions has been shown to give a better performance than the Hanning windowing used in most pulse- compression algorithms for air-coupled applications. The elliptical-Tukey chirp signal provides an improvement in both the resolution of images and signal-to-noise ratios. In addition, this type of signal also reduces the level of signal voltages required to drive the source transducer while maintaining the performance of the system. This approach, thus, may have wide interest in all forms of wide bandwidth ultrasonic imaging.

A near-infrared (NIR) Technique for imaging food materials.

The results of imaging experiments in food materials are presented, using near-infrared wavelengths. The technique uses a modulated source and a lock-in amplifier detection circuit to give a high sensitivity to changes in through-transmission signal levels. This is shown to lead to a set of images, whereby the internal content of various foods can be imaged. Examples are presented of the detection of foreign bodies, both metallic and nonmetallic, to illustrate the imaging performance.

Air-coupled ultrasonic spectroscopy of highly damping materials using pulse compression

Air-coupled ultrasonic spectroscopy is described, whereby the output from a pulse compression system is used. It is demonstrated that the cross-correlation operation used within a pulse-compression system preserves amplitude and phase information. This approach allows the signal-to-noise ratio and, hence, signal-detection capability to be improved by the cross-correlation, while allowing noncontact spectral information for solid samples to be obtained. Results are presented for chocolate samples, where measurements of interest to the food industry have been obtained.

Dual-mode combined infra red and air-coupled ultrasonic technique for real-time industrial process control with special reference to the food industry

This paper describes the use of air‐coupled ultrasound and Near Infra red (NIR) as complimentary techniques for food quality assessment. A major study has been performed, in collaboration with four industrial food companies, to investigate the use of air‐coupled ultrasound and NIR to both detect foreign bodies, and to measure certain parameters of interest, such as the amount of a certain additive. The research has demonstrated that air‐coupled ultrasound can be used in on‐line situations, measuring food materials such as chocolate and cheese. It is also capable of performing measurements on moving sealed metal cans containing food, and is able to detect foreign bodies with the top removed, as encountered just before sealing. NIR has been used as a complimentary technique to test food materials where propagation of air‐coupled ultrasound was found to be difficult. This could be due to the presence of air pockets within the food material, as in the case of bread dough.

NEAR INFRARED (NIR) IMAGING FOR NDE

A novel application of near infrared (NIR) signals is presented, which can be used to provide images of many different materials and objects. It is effectively a very low cost non‐ionising alternative to many applications currently being investigated using electromagnetic waves at other frequencies, such as THz and X‐ray imaging. This alternative technique can be realised by very simple and inexpensive electronics and is inherently far more portable and easy to use. Transmission imaging results from this technique are presented from examples industrial quality control, food inspection and various security applications, and the results compared to existing techniques. In addition, this technique can be used in through‐transmission mode on biological and medical samples, and images are presented that differentiate between not only flesh and bone, but also various types of soft tissue.

NEAR INFRARED (NIR) SPECTRAL IMAGING FOR NDE

A novel technique of NIR imaging is presented that gives access to most of the applications currently published as being solely suitable for terahertz waves. This technique also affords the means to provide simultaneous insitu chemical‐bond analysis and simultaneously combine chemical/spectral identification with imaging. The two separate features of the technique can be combined in a data fusion that produces a conventional image with chemical data etc superimposed (e.g. via false colours on the image) by imaging software. The technique itself uses NIR beams wavelengths found in ordinary domestic remote controls (circa 850 nm) and various signal recovery techniques commonly found in astronomy. This alternative technique can be realised by very simple and inexpensive electronics and is inherently far more portable and easy to use and no special sources are required. Transmission imaging results from this technique are presented from several industrial examples and various security applications and are com...

A novel low cost alternative to THz for security and defence applications

A novel technique of NIR imaging is presented that gives access to most of the applications currently published as being solely suitable for Terahertz (THz) waves. The technique uses NIR beams wavelengths found in ordinary domestic remote controls (circa 850 nm) and various signal recovery techniques commonly found in astronomy. This alternative technique can be realised by very simple and inexpensive electronics and is inherently far more portable and easy to use and no special sources are required. Transmission imaging results from this technique are presented from several industrial examples and various security applications and are compared and contrasted directly with their THz-derived counterparts. It would appear possible to very cheaply and simply emulate the performance of commercial terahertz systems at a fraction of the cost and with greatly reduced processing times Another advantage is that apart from imaging, this technique affords the means to provide simultaneous in-situ chemical-bond analysis for stand-off detection of certain chemical signatures - for example, those found in drugs and explosives (both molecular and oxidiser based). Also, unlike THz, this technique can penetrate bulk water and high humidity atmospheres and be used in transmission mode on biological and medical samples. Several results are presented of non-ionising X-ray type images that even differentiate between separate types of soft tissue