Ideas - we are a source of ideas and innovation from the unique perspective of ultrasonics, physics, electronics and software. We can come up with ideas and solutions for your R&D department.
Brainstorming - we apply our knowledge and experience to your problems in short sessions, adding our specialised technical expertise your R&D department. This is a low-cost way to get a project moving.
Feasibility analysis - we take initial ideas and go away and think about them. We will do calculations and preliminary design work then prepare a report. Save money early on in a project using our experience and expertise.
Feasibility tests - we put together a quick prototype or a model and evaluate it. Our schlieren visualization service can be used to get quick results.
Transducer design - we have designed and built many transducers over the years. We can design from scratch to meet a target performance or you may have a transducer that doesn't work properly that we can debug. We can build a prototype or a production prototype and with our contacts in the industry we can even arrange sub-contractors to manufacture for you to traceable quality standards.
Systems design - transducers need drive signals, drive amplifiers, receiver amplifiers, signal processing and information needs to be displayed. We can design all the elements in the chain to whatever level of detail you require - we will stop at the point your R&D department wants to take over. We also write specifications and operating descriptions to document our work for easy hand-over. If you want a full design service we can provide it.
Transducer investigation service - in one day our schlieren service can give you an insight into the operation of your transducers that you won't get by any other method. It is quite simply one of the best ways to check the performance of your transducer at low-cost.
Project management - we manage small projects and big, collaborative European projects. If it involves ultrasound, electronic design, software design or a European dimension then you might like to consider using us as a project manager.
Lectures - we give lectures on ultrasound brimming with practical demonstrations that bring your staff up to speed quickly on the fundamental principles of ultrasonic waves and inspection systems of all kinds. Our schlieren visualization system is portable and we can bring it to you and incorporate it into the lecture (see our web-site for examples www.cambridge-en.com). We can even put your transducers into the visualization equipment and see how they are working.
Marketing and promotion service - we have started providing a low-cost marketing and promotion service for businesses covering the UK and Scandinavia. We specialise in businesses entering a new market or businesses from outside the UK wishing to enter the UK market with a new product or service.
Management consultancy and mentoring - we provide a service based around financial modelling and risk analysis of business opportunities. If you are not sure where to put your money for business development, we may be able to help you decide. You benefit from a fresh perspective on strategic decisions.

Come along and learn about ultrasound at the Cavendish Laboratory on 20th December. Do something different, have a bit of fun in Cambridge for children aged 10 and older and adults in the week before Christmas.

Event 1: "Babbling brooks, medical ultrasonic imaging and looking at ultrasound" Public lecture 16.30 to 18.00.

Event 2: "Call my bluff - in science" a panel of scientists and celebrities tries to bluff the audience in matters scientific 19.00 to 20.00.

Both events are organised by the East Anglian branch of the Institute of Physics (IoP) with younger people in mind, in the age range 10 years and upwards. The aim is to promote interest in science in general and physics in particular. David Andrews of Cambridge Ultrasonics (ex-Cavendish laboratory) will be teaming-up with Alan Walton of the Cavendish Laboratory to give a public lecture all about ultrasound, with a strong emphasis on demonstrations. If you are familiar with the Royal Institution's Christmas lectures for young people then you will know the format.

An hour later there will be a chance for all ages to pit their wits and knowledge against a panel of leading scientists and celebrities in an adaptation of the popular TV quiz “Call my bluff”. The panel will give various simple explanations of things scientific and technological, not all of them true - anyone under 18 is allowed to vote for the one they think is true. If the largest vote is for the true explanation then the audience wins a point! Will the panel be able to bluff the audience?

There will be a display area for hands-on fun between the two events. Come and see the TV car “Brum” and some robots from the TV “Robot Wars” programme with their inventors.

Professor Malcolm Longair (head of Cavendish) and Rex Garrod (robot maker and special effects for TV) will be there. See www.cambridge-en.com for more details.

The first event will not begin until 16.30 so why not make a day of it in Cambridge, do some Christmas shopping then pop-out to the Cavendish (good parking facilities) and have some fun with science at the famous Cavendish Laboratory!

More details will be placed on our web-site www.cambridge-en.com. These events are likely to be popular and limited to tickets (free) so please request your tickets if you want to come. We need your name, e-mail address, telephone number, number of younger persons coming and the number of tickets you require. Your tickets will be held at the door until 10 minutes before the start of each event - after that they will go to anyone waiting.

We’ll be there and we look forward to seeing you at the Cavendish Laboratory on 20th December.

Cambridge Ultrasonics has been asked by by one of the major UK communications companies to help in its initiative in 4-D ultrasound. The term 4-D perhaps needs to be explained: 4-D means 3-D imaging at framing speeds in excess of 10 frames/second. The technology to be used is that of 2-D piezoelectric arrays coupled to sophisticated signal processing.

Originally called in to evaluate the transmission of ultrasound from the piezoelectric arrays using our schlieren visualization system, we were soon asked to assist in the overall system design, combining our knowledge of ultrasound and signal processing to help design the signal processing.

4-D ultrasound will use some of the technology of mobile telephones, computer networks and phased arrays to create a new type of medical ultrasound scanner capable of imaging a beating heart.

The upper figure is a photograph of a 2-D transducer array made at one of the client’s research centres as a part of a collaborative European project. Each piezoelectric square is about 200 um across. The lower figure illustrates how a 1-D array can steer a beam: close to the array with no phase difference - a plane wave is constructed parallel to the array; farther away with constant phase difference between elements - a plane wave is constructed travelling at an angle to the array (example of beam steering); farthest away using a symmetric pattern of phase differences - a focus is constructed.

A 2-D array gives much greater control of the transmitted beam profile and better quality images should result.

Our attempts at forming a collaborative European project to push forward the technology of concrete inspection has not met with the support we hoped for from the European Commission. Some of you may have been following our progress in Innovation News.

Cambridge Ultrasonics has successfully put together a strong consortium with partners in Germany, Spain, Poland, Sweden and UK but our proposal narrowly failed to attract support from the European Commission. We were advised to modify the proposal and re-submit. We are currently reviewing the position with our partners in the light of recent changes in the state-of-the-art and we hope to submit a revised proposal soon.

It is possible that we will target a new programme with a primary interest in improving methods for in-service monitoring of the concrete components in nuclear power stations. Any readers interested in participating in such a programme should contact David Andrews at camben@cambridge-en.com.

Encyclopedia of Physical Science and Technology

The Encyclopedia of Physical Sciences and Technology is published by the Academic Press of San Diego, California. David R Andrews, of Cambridge Ultrasonics, was invited to write the chapter on "Ultrasonics and acoustics" for the next edition of the encyclopedia. The chapter includes sections on pulsed methods and continuous wave methods, medical imaging, arrays, materials processing and sonochemistry as well as fundamentals and musical instruments.

David was pleased to be asked to contribute to an encyclopedia that includes chapters from illustrious academics and industrialists. His chapter includes several images of ultrasonic waves rendered visible in transparent materials, to help illustrate various points in the chapter (see facing figure for example).

Compression waves of 1.5 MHz travelling in glass, grazing a free surface, create shear waves on the free surface by mode conversion. Both waves have the same frequency but the compression wave speed is higher than the speed of the shear waves. The compression waves act as sources of shear waves - these are supersonic sources for the shear waves. The result is that the shear waves are emitted at an angle to the compression waves.

Are you responsible for the quality testing of mass-produced components? Do you currently use batch testing but would you like to switch to 100% quality testing? Then you might like to consider using resonance spectroscopy.

If a manufactured component is inspected and found to be faulty there are two options to follow: repair or discard (and recycle) the component. The choice usually depends on the relative cost of manufacturing and repair. It goes almost without saying that it is likely to be cost-effective to repair a nuclear power station but it is not cost-effective to repair a mass-produced, automotive component. Resonance spectroscopy can quickly tell if a component is flawed or flaw-free, it is particularly suited to quality inspection testing where it is not economic to consider repair.

The method of resonance spectroscopy can be applied to test the quality of low-value items because it is a fast and inexpensive test. Mechanical flaws, variations in dimensions and material irregularities all cause deviations from the average response that can be detected in a resonance spectroscopy test. Interpretation of the results is a process of classifying the response as either acceptable quality (pass) or unacceptable quality (fail). This can be done automatically by computer using various kinds of software, for example an artificial neural network. Success-rates of between 90% and close to 100% have been achieved by Cambridge Ultrasonics in tests using spectroscopy equipment we designed and built ourselves; other organisations have reported success-rates approaching 100%. Achieving such high success-rates requires careful control of the training set and this is where the work is involved in using this technique. For example, the training set should include a statistically significant number of samples of all failure modes as well as samples of acceptable quality and all samples must be tested by alternative quality inspection methods (for example: X-ray, dye-penetration, conventional ultrasound) to determine their classification.

A test sample is injected with ultrasound or sound at one transducer and the response at a second transducer is measured in a resonance spectroscopy test. The spectrum is built-up by stepping over many frequencies. Interpretation is done in the frequency-domain using the frequency response of the test samples. Cracks in high symmetry samples (roller bearing or ball bearings for example) often lead to splitting of the frequencies of degenerate modes of vibration. Splitting is easier to detect in the frequency-domain.

CW excitation fills the sample under test with sound and, provided enough time is given, a steady-state standing-wave pattern is established. Information from relatively distant parts of the sample can then reach the receiver and contribute to the spectrum so a large volume of the sample is tested, eliminating surface scanning. The time to complete a full test of 1000 test frequencies on an automotive component is about one second. This short testing time and automatic interpretation by computer means that components can be tested at rates of 2,000 parts/hour or more. It is the high through-put that allows the cost per test to be kept low and this combination of benefits makes resonance spectroscopy suitable for 100% quality assurance of mass-produced parts.

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In previous issues of Hot Hints we have dealt with how to match ultrasonic pulses to a transducer: in the last issue we dealt with how to match to the time-domain variation of the pulse and in the issue before last we considered how to match to the spatial variation of a pulse. Back copies of Innovation News are available on www.cambridge-en.com.

In this issue we are going to consider something quite different. Gone are pulses of ultrasound and in are continuous waves (CW). Pulses are good at conveying information, for example where a defect is located. But when you need energy to perform some mechanical task then pulses, with their low duty cycle (on time/on+off time), are inherently inappropriate. The power needs to be on all the time (100% duty cycle).

A good source of CW ultrasound is generally a resonating structure with a high quality factor (Q). The principle of operation is very similar to an optical laser so its termed the ultrasonic laser in this article. An ultrasonic laser is pumped with mechanical energy by an active electro-mechanical device - in an optical laser the lasing material is pumped too but by a light source. The frequency of operation of an ultrasonic laser is quantised and determined by the dimensions of the resonating structure and the speed of sound; in an optical laser the frequency is quantised and determined by energy transitions of the electrons in the lasing material. An electrical feedback system is generally used to control the frequency of electrical excitation in an ultrasonic laser and the amplitude of resonance; many optical lasers need feedback control of the pumping energy too.

There are striking similarities between optical lasers and ultrasonic lasers used for CW applications. One main difference is that ultrasonic lasers have been used for much longer than optical lasers (at least since about 1920).

If the Q of the vibrating system in the ultrasonic laser is high then the sharpness can be a disadvantage becausemechanical loading, temperature and other environmental conditions can cause the centre frequency to drift and the feedback-loop may lose control.

In high power applications the design objective is generally to maximise resonant vibration. If mechanical energy leaks through the transducer’s support-frame then efficiency is reduced. A common solution is to use a nodal support (see figure). A node is a point of minimum or zero vibration. By supporting the system at a node there should be less energy lost than through any other position. The Langévin ultrasonic laser uses nodal support.
The Langévin design also has axial symmetry which gives another advantage - it allows an axial compression device, such as a threaded high tensile steel rod, to pull the vibrating components together into compression. At least one of the vibrating components must be active so that it can convert electrical excitation into mechanical vibration. Some active materials are brittle, fracturing in tension unless they are held in compression and the presence of a static compressive stress allows these brittle active materials to operate at higher strain amplitudes then would otherwise be possible.

Some sonar transmitters are Langévin resonators; at frequencies down to about 5 kHz they can exceed 1 m in length. Similar designs are found in sieve agitation systems used in the pharmaceutical industry and in ink-jet printers; in the latter case the frequency approaches 100 kHz and the size is approximately 5 cm.

The Langévin resonator has a node at the mid-point and the ends are both anti-nodes. This means that the overall length is a half a wavelength. Given the speed of sound in the device it is possible to predict the frequency for any given size. Note that the device also has two transmitting ends, which can be useful. If it is large amplitude mechanical vibrations you want with lots of power then a good starting design is the Langévin ultrasonic laser.