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Ultrasonic gas monitor developer eyes medical applications

A sensor that measures the acoustic bulk properties of gases flowing through it looks set to lower the size and costs associated with such devices in medical equipment.

Developed at Cambridgeshire-based TTP, the ultrasonic device - dubbed SonicSense - measures the speed of sound in a gas to determine its composition.

Medical applications include respiratory monitoring, capnography, anaesthesia and COPD monitoring.

Andrew Baker-Campbell, part of the team that developed SonicSense, explained that the simplest application for a medical user would be for mixing different gasses, or monitoring of the mixture of different kinds of gas.

He told The Engineer: ‘In a ventilator, when you’re supporting a patient’s breathing, you might want to mix room air or dry compressed air…with oxygen to give the patient a richer breathing mixture. Controlling the degree of addition oxygen you put in is really important: you don’t want the person to either hyper-or-hypo-ventilate.

‘The measurement essentially says “the speed of sound in the room air is this, the speed of sound of the oxygen is this”, therefore you can plot the speed of sound of a mixture of those two gasses, and by measuring the speed of sound you can infer the composition.’

It is claimed that SonicSense devices would cost between £3 and £6 each in volume production compared to approximately £120 for paramagnetic systems for oxygen, and over £240 for infrared devices that measure carbon dioxide. Prototype devices developed for existing clients have a diameter of 24mm and a depth of 18mm, a dimension TTP believe can be reduced to less than 5mm. 

SonicSense gas sensors are set for manufacture in the next 12 months when they will be incorporated into a medical device being developed by a large multinational healthcare company that cannot be named for reasons of confidentiality.

Baker-Campbell added that SonicSense devices are not restricted the medical sector and that applications are envisaged in gas safety, plus industrial monitoring and control.

Readers' comments (3)

  • Looks great, and very impressive for TTP to have developed it for the price, but "£240 for infrared devices that measure carbon dioxide" is a ludicrous over-estimate for a like with like comparison. Mass produced sensors for this (typically originally for automotive air conditioning applications) can be close to a factor of 100 lower. The higher price would be for a full, specialist, optimised specialist instrument of some sort.

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  • Firstly, thank you for your kind words about our new technology. At TTP we are really to see where we can take this and it is great to see that the article is generating a response.
    Regarding the price of the CO2 sensor, this number has come from our investigations into opportunities to replace sensitive non-dispersive infrared sensors in medical products. In these products, hundreds of pounds for a sensor module is by no means an exaggeration. I agree that there are many different designs of sensor on the market, some of which are comparable in price to our new design. And each of these designs offers their own advantages and disadvantages. A well engineered electrolytic cell, often used in the air conditioning systems you describe, can give great sensitivity for the price; however, they have a relatively short lifetime and issues with drift. We think there is a new combination of accuracy, cost and stability here which offers something compelling for the right application.

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  • I hate to carry this on, but I was referring to infra-red technology, compensated for drift, available from many suppliers, and with long lifetimes. (Electrolytic CO2 cells are still pretty untried anyway.) Part cost is low; what they sell it for will be higher, and would reflect the costs of certification. But then those would apply to any technology. I can give you comparison costs, and the names of some people to talk to, if you contact me. (I'm pretty findable!) Not denigrating your achievement in any way - it does look great, and I wonder whether there are also applications to replace industrial applications of sensors which use differential thermal conductivity etc. Lower margin than medical, but shorter lead time in terms of certification.

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