Ultrasonic Propagation in Highly Attenuating Insulation Materials.

Experiments have been performed to demonstrate that ultrasound in the 100-400 kHz frequency range can be used to propagate signals through various types of industrial insulation. This is despite the fact that they are highly attenuating to ultrasonic signals due to scattering and viscoelastic effects. The experiments used a combination of piezocomposite transducers and pulse compression processing. This combination allowed signal-to-noise levels to be enhanced so that signals reflected from the surface of an insulated and cladded steel pipe could be obtained.

A simple, low-cost conductive composite material for 3D printing of electronic sensors.

3D printing technology can produce complex objects directly from computer aided digital designs. The technology has traditionally been used by large companies to produce fit and form concept prototypes ('rapid prototyping') before production. In recent years however there has been a move to adopt the technology as full-scale manufacturing solution. The advent of low-cost, desktop 3D printers such as the RepRap and Fab@Home has meant a wider user base are now able to have access to desktop manufacturing platforms enabling them to produce highly customised products for personal use and sale. This uptake in usage has been coupled with a demand for printing technology and materials able to print functional elements such as electronic sensors. Here we present formulation of a simple conductive thermoplastic composite we term 'carbomorph' and demonstrate how it can be used in an unmodified low-cost 3D printer to print electronic sensors able to sense mechanical flexing and capacitance changes. We show how this capability can be used to produce custom sensing devices and user interface devices along with printed objects with embedded sensing capability. This advance in low-cost 3D printing with offer a new paradigm in the 3D printing field with printed sensors and electronics embedded inside 3D printed objects in a single build process without requiring complex or expensive materials incorporating additives such as carbon nanotubes.

Through-transmission imaging of solids in air using ultrasonic gas-jet waveguides.

An ultrasonic waveguide has been produced in air by using a gas jet. This uses the fact that a lower acoustic velocity can be produced within the jet, relative to the air surrounding it. The lower velocity is achieved by mixing carbon dioxide with air within the jet at a concentration that is a compromise between lower acoustic velocity and increasing attenuation. Using a capacitance transducer placed within the flowing gas, it is shown that improvements in the beam width can result when the gas jet is used. Air-coupled images of solid samples have been produced in through transmission, which demonstrate that an improved lateral resolution can result when a comparison is made to images from conventional air-coupled testing.

High-resolution, air-coupled ultrasonic imaging of thin materials.

This paper describes the use of a focused air-coupled capacitance transducer combined with pulse compression techniques to form high-resolution images of thin materials in air. The focusing of the device is achieved by using an off-axis parabolic mirror. The lateral resolution of the focused transducer, operating over a bandwidth of 1.2 MHz, was found to be less than 0.5 mm. A combination of the focused transducer as a source and a planar receiver in through-transmission mode has been developed for the measurement of different features in paper products, with a lateral resolution in through-transmission imaging of approximately 0.4 mm. Images in air of thin samples such as bank notes, high-quality writing paper, stamps, and sealed joints were obtained without contact to the sample.

Radiated fields of capacitive micromachined ultrasonic transducers in air.

This paper presents a study of the radiated ultrasonic fields of capacitive micromachined ultrasonic transducers (often referred to as cMUTs) in air. These fields were modeled theoretically and then compared to the experimental near-field amplitude variations and directivity patterns of square cMUTs. The good agreement between theory and experiment indicates that the devices can be approximated to plane piston radiators. The fields of multiple elements driven in phase on the same silicon substrate are presented, where again comparison is made to theory. The results indicate that individual elements are unaffected by radiation through the silicon substrate from adjacent devices. It will also be demonstrated that it is possible to use the knowledge of these fields to develop air-coupled ultrasonic surface imaging systems.