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Cambridge Ultrasonics
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Consultancy service in physics, electronics, maths & ultrasonics

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Above - piezoelectric ceramic diced to make a sparse array for use in medical applications.

Above - a 1-D phased array of 16 elements produces circular wavefronts that combine to create: plane waves (close to the array), steered plane waves (intermediate) and a focus (right-most).

Experimental photograph of ultrasonic waves (1.5 MHz) focussed to a caustic (dotted white lines).

Medical

3-D cardiac imaging

A major multinational business wanted to  enter the medical scanner market. It wanted to leap-frog the competition and to aim for the high value, real-time, 3-D imaging market, with particular interest in cardiac imaging. Initially, Cambridge Ultrasonics was asked to use its visualization expertise to verify the correct operation of the 2-D sparse arrays under-development by the client. During brainstorming sessions with the client and a university-partner Cambridge Ultrasonics made an increasing contribution to the system design, particularly the use of novel signal-processing based upon the physics of waves arriving at the transducer to compress data to get improved real-time refresh speeds.

Testing phased-array

Another example is a major manufacturer of foetal (fetal) medical scanners that wanted to assess its transducers. Cambridge Ultrasonics was asked to take its visualization system to the client's premises so that the client's entire R&D team could see (for the first time) the output of the transducers they had designed. One of the client's foetal scanners, with a phased array of 128-elements, was connected to our visualization system with the transducer put in a water tank where the waves from the 128-element array were rendered visible using Cambridge Ultrasonics' equipment. The results were nothing short of spectacular. The scanner was able to create many different beams by electronic beam steering. Cambridge Ultrasonics' visualization system was able to visualize all the beams, showing the sharpness of the focus, the position of the focus and how the focus was scanned - all in real-time.

Indeed, the visualization was so good it also showed a secondary, slightly blurred focus under certain conditions, several centimetres away from the intended focus. A secondary focus can cause a problem if it touches any bone, for example the mother's pelvis. Bone gives a strong reflection and some of the reflected waves could get back to the phased array and be collected and contribute to forming the image of the foetus. The computer controlling the position of the focus of the phased array would wrongly ascribe the reflection from the pelvis to the position of the intended focus, which might be inside the foetus. The reflection from the pelvis would therefore distort the image of the foetus making it appear to be deformed. Apart from causing distress to parents seeing a distorted image of their foetus a rogue focus might exceptionally result in some form of intervention from the medical staff, resulting in unnecessary treatment of the foetus.

The client was faced with a costly recall and replacement of the transducer but the quality of its product was improved. If the client had checked its transducer during development using a visualization technique the problem could have been identified earlier and the cost of rectifying the fault would have been very much lower.

Plate waves in transducers

Wave propagation in solid materials can be very complex. Medical scanner transducers are made from solids and the ultrasonic waves propagate through a variety of layers inside the transducer. It is possible for unusual waves to be created when an ultrasonic pulse enters plate-like layers, for example Stoneley waves can be generated. A major international manufacturer asked Cambridge Ultrasonics to investigate the possible creation of plate waves and how these might leak out of the plate.

Our visualization system quickly showed that plate waves were indeed created in the front polymer layer of the transducer. Ultrasonic waves had to be incident over a narrow range of angles for plate waves to be created. Energy from the plate waves then leaked out into the surrounding medium in a characteristic pattern.