Resonance spectroscopy has two main industrial applications:

• firstly, on a production-line, testing the quality of 100% of the production - it has a short time to test (typically a few seconds) and low-cost per test;
• secondly, Cambridge Ultrasonics believes the method can be used for in-service monitoring of structures, both concrete and steel, such as bridges, roads, offshore oil production structures, power stations, it offers a low annual cost and it should quickly find regions of the structure undergoing significant change that might jeopardise the structural integrity.

Continuous sine wave excitation is used to drive an ultrasonic transducer in contact with a test sample during a resonance spectroscopy inspection. The response of the test sample is detected by a receiver at a second location on the surface. Both the amplitude and the relative phase of the received signal are recorded over a range of discreet test frequencies so that spectra of amplitude and phase are recorded. Test frequencies covering 100 Hz to 10 MHz have been used in experiments.

Ultrasonic resonance spectroscopy has application to inspecting the quality of a wide range of industrial components, for example: aerospace, concrete and metallic. One of the advantages of the technique over pulse-echo examination is the ability to inspect a whole component with one test - virtually all other
inspection methods require scanning of the surface which is relatively slow and expensive. It has been shown in this project that the combination of resonance spectroscopy, creating data (spectra), and an artificial neural network, deciding quality (using spectra), results in an inspection system with the following qualities:

• Capable of inspecting whole components quickly.
• Simple testing procedure - because only a single test is made.
• Output of the neural network can be as simple as either Pass or Fail.
• Operators do not make decisions about the quality of inspected samples -eliminating a source of error.
• The neural network is able to interpret spectra and decide correctly on quality when an operator is unable.
• The method has good potential for automation due to its simplicity.
• Suitable for use in a mass-production environment at a low cost per inspection with 100% testing.

This way of applying resonance spectroscopy should find application where many identical components are to be tested. With further development it may be possible to use the technique on unique objects in the field.

The technique has been applied successfully, giving accurate assessments of the quality of a diverse range of test samples when spectra have been interpreted using artificial neural network software - the success-rate in correctly assessing quality has been encouragingly high (in the range 82% to 100%) - to be an attractive inspection method from a commercial point of view requires success-rates close to 100% but it is generally accepted that success-rates above 90% are good. Volumetric flaws in the range 0.04% to 3% were detected in tests on concrete paving slabs. When interpretation was un-aided, that is to say using human judgment alone, or when human judgment has been assisted by predictions using a finite element approach then interpretation has been mainly unsuccessful. This lack of success was notable in the case of concrete components and structures, which possibly present an added difficulty due to the coarse-grained internal structure of concrete tested. However, a statistically significant number of finer-grained concrete paving slabs was successfully classified for quality using a neural network and aging experiments on coarse-grained concrete samples were partially successful so it is impossible at this stage to draw far-reaching conclusions because there is a need for more research. The range of success achieved on concrete samples serves not only to illustrate the difficulty of testing this material but also the importance of using a neural network to interpret experimental results. The main disadvantage of the neural network approach is the cost of creating a set of data with which to train the neural network - a network requires many different examples of spectra to represent all possible cases of both unacceptable and acceptable quality of samples.

Encouraging results were obtained using ultrasonic resonance spectroscopy covering a wide range of industrially important components including: forgings, pressings, brazings, bolts and composites. Success-rates of 96% were typical for classifications using a neural network and in some cases 100% success was achieved (although this was for only a small number of samples).

Resonance spectroscopy has also been applied to certain aerospace materials using welded aluminium and an aluminium honeycomb with surfaces made of woven carbon fibres. Whilst it has been possible to classify defective zones successfully, with a high success rate approaching 100%, an improvement in sensitivity to smaller flaws is needed before resonance spectroscopy meets the stringent requirements for aerospace quality inspection. There is optimism that
this improvement is possible.

A novel lock-in amplifier has been used successfully with various transducers to collect spectra from all of the test samples. The novel features designed into this lock-in amplifier enable it to collect spectra quickly and with good accuracy.

Partners in the project were: Cambridge Ultrasonics (Instrumentation Innovation, GB - co-ordinator), Alcatel Espace (F), Taywood Engineering (GB), TechSonic (F), University of Uppsala (S); associated
partners: I So Test Engineering (I), High Point Rendel (GB) and King's College London (GB). The work was supported by the European Commission and the Petroleum Science and Technology
Institute (now Centre for Marine & Petroleum Technology GB).

Figure captions:

• Resonance test in action on a pre-cast concrete paving slab. A success-rate of 87% was achieved in correctly assessing the quality of these highly irregular mass-produced parts.
• Spectrum compared for two nominally identical pre-cast concrete paving slabs showing differences due to material properties.
• Equipment developed in the project (plug-in board comprising the lock-in amplifier).
• Sketch to illustrate the driving signal applied to a test sample in a resonance test.
• Sketch to illustrate the time taken to establish steady-state resonances in a test sample. Note
  that the received signal does not start until after the transmitted signal has started and it takes a further time before steady-state resonance has been established (constant amplitude).
  

At the end of last year Carrbridge Ultrasonics' service for visualising ultrasound was promoted in the press. The response has been strong from a variety of organisations all with problems of ultrasonic propagation.

Respect for commercial confidentiality does not allow us to describe recent investigations but in the past a manufacturer of ultrasonic medical imaging systems evaluated its phased-array using our equipment. Whilst performance was generally very impressive there was one side-lobe that appeared in the visualised images - it shouldn't have been so strong. Its presence could easily cause an image artefact, which, in-turn, could result in incorrect diagnosis. The archive printouts of hydrophone scans were located (they occupied several filing cabinets) and eventually the correct data were found. Sure enough it was no optical artefact but the side-lobe had been overlooked in the mountain of information generated by the hydrophone tests. Some redesign work was needed.

The image shows ultrasound emerging from a transducer above a pellicular hydrophone. Colour is used to represent grey scale in this computer generated image. Enhancement procedures allow more information to be extracted from images. Shown below the schlierent image is the output of the hydrophone on an oscilloscope. Contact us for quick, low-cost evaluations of your transducers or for equipment rental.

The European parliament has allocated 9 BEcu (about GBP 6B) for the present Framework 4 for assisting R&D in Europe. Businesses can receive up to 50% of their actual costs for R&D projects from one of the Commission' 5 many research programmes. Most technology-based businesses could benefit from participating - particularly small and medium size. You must submit a proposal for your project to be supported. Compared with national programmes, where lobbying is often the key, success in Europe requires the proposal document to be of high quality and there are many hidden pitfalls.

Cambridge Ultrasonics has many man-years of experience in European projects and a good success-rate with its proposals. All of our projects have been praised technically: two of them have been funded, two that were not funded initially were recommended for incorporating into a new project that was funded leaving one other - that's either 40% success or 80% success, depending on how you count success.

It came as a surprise to learn that our success-rate is higher than the average (now about 10%) and a bigger surprise to learn that a significant proportion of proposals are rejected by the European Commission for failing to meet certain conditions of presentation - as many as 25% of proposals fail this initial screening.

We found that many organisations, particularly small companies, find the whole procedure so confusing that they don't apply and lose out on opportunities to get support for developing new products and services.

Enter Rapido - this is the section of Cambridge Ultrasonics that writes proposals and reports; Rapido is offering a new service to help with proposals and setting a strategy for improving your business' success in getting financial support from the European Commission. We can:

• Come to your premises and give a presentation on how to write a winning proposal.
• Help formulate your strategy and proposal with a brainstorming session at your premises.
• Write, print and submit proposals on your behalf based upon your technical ideas - as much help as you want.
• Assist with finding suitable partners including searching the internet, press releases and registering your interest with the European Commission.

Contact us and ask for Rapido.