Non-contact technology simplifies torque monitoring and aids efficiency.

Monitoring torque in a drive shaft is one of the best ways of assessing the performance of plant and machinery. However because drive shafts rotate, hard wiring a sensor into place usually requires the use of a delicate slip ring. An alternative solution is to use a non-contact radio frequency detector to monitor ‘Surface Acoustic Waves’ (SAWs), as Mark Ingham of Sensor Technology Ltd explains.

Torque imparts a small degree of twist into a driven shaft, which will distort SAW devices (small quartz combs) affixed to the shaft. This deformation causes a change in the resonant frequency of the combs, which can be measured via a non-contact radio frequency (RF) pick-up mounted close to the shaft. The pick-up emits an RF signal towards the shaft which is reflected back by the combs with its frequency changed in proportion to the distortion of the combs.

A SAW transducer is able to sense torque in both directions, and provides fast mechanical and electrical responses. As the method is non-contact it has also offers complete freedom from slip rings, brushes and/or complex electronics, which are often found in traditional torque measurement systems. SAW devices also have a high immunity to magnetic forces allowing their use in, for example, motors where other analogue technologies are very susceptible to electronic interference.

More detail:
In its simplest form, a SAW transducer consists of two interdigital arrays of thin metal electrodes deposited on a highly polished piezoelectric substrate such as quartz. The electrodes that comprise these arrays alternate polarities so that an RF signal of the proper frequency applied across them causes the surface of the crystal to expand and contract and this generates the surface wave.

These interdigital electrodes are generally spaced at half- or quarter-wavelength of the operating centre frequency. Since the surface wave or acoustic velocity is 10-5 of the speed of light, an acoustic wavelength is much smaller than its electromagnetic counterpart.

For example, a signal at 100Mhz with a free space wavelength of three metres would have a corresponding acoustic wavelength of about 30 microns. This results in the SAW’s unique ability to incorporate an incredible amount of signal processing or delay in a very small volume. As a result of this relationship, physical limitations exist at higher frequencies when the electrodes become too narrow to fabricate with standard photolithographic techniques and at lower frequencies when the devices become impractically large. Hence, at this time, SAW devices are most typically used from 10Mhz to about 3Ghz.

SAW-based torque sensors have been used around the world and in many fields, from test rigs to wind turbines and generators based on tidal or river flows. They are used extensively in the high tech world of the development of engines and gearboxes for Formula 1. Pharmaceutical companies employ them to monitor the pumps micro-dosing active ingredients into medicines and tablets. Torque feedback systems can be used by security firms to determine the direction their movable CCTV cameras are facing so that they can efficiently watch premises under their protection.

Today, as industrial engineers automated manufacturing and processing operations they are increasingly turning to torque monitoring to generate the vital operating and production data that maintains production and efficiency.

@sensortech #PAuto

Load cells on stage!

With theatres striving to create breath-taking spectacles and leave the audience gasping for more, there is often world-class engineering behind the scenes. Sensor Technology is developing technology to ensure safety when excited performers and heavy machinery share the same space.

If live theatre is to compete with film and television, it has to produce visual spectacles to complement the performance of the actors, singers and musicians on stage. Hollywood’s increasing reliance on CGI (computer generated imagery) has upped the ante for stage set designers, who have to work before a live audience, in restricted space and with a constant eye on the safety of the many people working frantically round the set.

Many stage props and almost all of the backdrops are lowered onto the stage from the fly tower just behind it. Usually this is done quickly between scenes, but sometimes it is during – and as part of – the actual performance. Either way, safety and reliability are essential.

“Until recently, the sets were manually controlled with a technical stage manager watching everything from the wings and giving instructions by radio to the winch operators above.” explains Tony Ingham of Sensor Technology who is helping to introduce safety systems and automation to the theatre industry.

“Speed is of the essence during scene changes, but you have to be confident the winches won’t fail – which could easily damage the set or injure a person.”

Sensor Technology is achieving this using real-time load signals from each winch. The data is monitored by a computer in the control room so that instant action can be taken if any loads move out of tolerance.

“We developed the load cells, which we have called LoadSense, a couple of years ago, originally for monitoring cargo nets carried under helicopters.” says Tony. “We were asked to develop one specific capability within the cell and were delighted to do so because we could see that the technology would transfer to many other fields – although I didn’t realise it would get to be a backstage pass to a world of greasepaint and legwarmers!”

That critical characteristic was robust, industrial-grade wireless communications, something in which Sensor Technology already has a 15 year track record from its TorqSense transducer range. In basic terms, each LoadSense has an on-board radio frequency transmitter which sends signals to the control room computer. The transmitter has to be physically robust to cope with the environment it finds itself in and capable of maintaining its signal integrity through the most corrupting of harmonic conditions.

“By working in real time, we can act instantly to any problems. For instance, if a load starts running too fast we would slow it down immediately. If a prop is heavier than expected this could suggest someone was standing on it so shouldn’t be whizzed 50 feet into the air at high speed. In fact, in this case, the computer ‘jiggles’ the load for a second or two as a warning to encourage the person to step away: If the load then returns to normal we are happy to let it rise; if it doesn’t, the floor manager is alerted by an alarm to check the situation.”

LoadSense is proving so sensitive that it can provide a feedback signal to close the control loop on a vector drive controlling the winch. Normally theatre engineers use sensorless vector drives, which offer good dynamic performance without the complications of wiring in a feedback sensor.

Sensor Technology is closing the loop which improves system integrity and enhances safety by a significant margin.

“Not that many years ago, stage scenery was fairly static, being moved only during the interval when the curtains were closed,” Tony recalls. “Then the big theatres in the West End and on Broadway started to emulate some of the things you see in the movies. Looking back, those early efforts were pretty crude, but you would say the same about long-running film franchises such as James Bond or Indiana Jones. “Nowadays, film directors can produce their spectacular images using CGI, and this has upped the ante no end for their cousins in live theatre. The computer power they turn to is not virtual reality but industrial automation.”

In fact, theatre engineers probably work in more demanding conditions than manufacturing engineers. Everything has to be right on the night, harmonic corruption is at stratospheric levels, there can be major changes at a moments notice, people run through the ‘machinery’ without a thought for personal safety.

“But with automation some order is brought to this creative chaos. In fact, the health and safety inspectors now insist on it, with lots of failsafes and feedbacks. I honestly don’t think theatre engineers would be able to achieve half of what they do without wireless communications. There would be just too many wires running all over the place and inevitably some would get broken at the most inopportune of moments.”

@sensortech #PAuto #Stagecraft

Pumps get testing time!


Having for many years used one of Sensor Technology’s novel TorqSense non-contact torque sensors as an aid to product development, Watson-Marlow Pumps Group, the world’s leading specialist in peristaltic pumping, has now chosen another of these versatile and dependable sensors for production-line testing of its most critical products.

The TorqSense sensor was selected for this demanding application because of its ease of use and because of the reliability and accuracy that has been consistently demonstrated by the similar unit in use in the development department.

Widely accepted as the world’s fastest growing pump type, peristaltic pumps such as those manufactured by Watson-Marlow have no valves, seals or glands to wear, leak or replace. The fluid contacts only the bore of the hose or tube, thus eliminating the risk of the pump contaminating the fluid, or the fluid contaminating the pump.

Peristaltic pumps have a number of advantages over other pump types: they provide superior flow rate stability, accuracy to +/-0.5%; they are ideal for viscous and abrasive fluids as well as sterile processes; have extensive chemical compatibility; and are inherently hygienic and safe to run. In all, they offer the lowest whole life cost of all pump types.

Many of Watson-Marlow’s pumps are used as components in medical and pharmaceutical equipment and, in these demanding applications, accurate information about the operating characteristics of individual pumps is often needed. To meet the needs of its customers with applications of this type, Watson-Marlow offers the option of supplying products that are 100% tested prior to despatch.

A key element of the testing is the determination of the relationship between the operating torque of the pump and the flow rate it delivers. In order to be able to measure this, a torque sensor that will deliver accurate and reliable results over long periods without adjustment or maintenance is needed. These requirements, the engineers at Watson-Marlow Pumps knew, could most conveniently be met by using a sensor from the Sensor Technology TorqSense range.

These innovative sensors, which are covered by patents, are built around surface acoustic wave (SAW) transducer, which essentially comprise a pattern of interlocking conductive fingers deposited on a piezoelectric substrate, such as quartz.

This arrangement behaves as if it were a conventional resonant circuit with a resonant frequency in the radio frequency range. When the transducer is deformed, however, the resonant frequency changes. In torque sensing applications, the transducer is fixed to the shaft in which it is required to measure the torque. As the shaft twists in response to the applied torque, it deforms the transducer. By measuring the change in resonant frequency of the transducer produced by this deformation, the torque in the shaft can be accurately determined.

Since the SAW transducers operate at radio frequencies, it is easy to couple signals to them wirelessly. Hence, the TorqSense sensors that incorporate the SAW transducer technology can be used on rotating shafts, and can provide data continuously without the need for the inherently unreliable brushes and slip rings that are often found in traditional torque measurement systems.

In the latest application at Watson-Marlow Pumps, a TorqSense sensor with a nominal maximum torque rating of 0.5 Nm is used in a production-line test rig for peristaltic pumps where it typically measures torque over the range 0.11 to 0.17 Nm while the pump drive shaft is rotating at 60 rpm. The results are displayed and recorded using a netbook PC. The test results are ultimately logged against a serial number for every pump so that, in the event of a query from the end user, the test data for the pump in question can be readily located.

“As we had anticipated, the sensor was easy to install and set up,” said Harvey Crook of Watson-Marlow Pumps, “and it’s also very easy to use on a day-to-day basis. We’ve been using it for a considerable time now, and it has proved to be totally reliable, just like its larger counterpart in our development department. Our experience shows that these innovative sensors are a convenient, versatile and cost-effective choice for both development and production line applications.”

Putting feeling into drugs safety and handling


Most applications we cover on the Read-out Signpost have to do with the actual production of product, say in a pharmaceutical process. However the products eventually end up in the hands of health professionals or patients and the correct handling of these in this area can be as important as in the earlier period of production. This application is one designed to help at this user interface.

When product integrity is paramount, packaging has a key role to play. It has to be secure enough for protection in all likely scenarios, but has to be easy to open in possibly high tension situations.

When using diagnostic fluids on ill or nervous patients, hospital staff are likely to be feeling the stress and will not take kindly to bottle tops that proves difficult to open. However they will want them to feel secure enough that they can be confident of the fluid’s sterility.

To this end specialist capping machines have been developed by Cap Coder, which not only tighten bottle caps within precisely defined tolerance but also log every detail of every bottle that is capped by one of their machines. And they have done it with a minimum of fuss, using an off-the-shelf technology and associated software.

“Our machines are essentially simple,” says Roger Brown of Cap Coder. “Filled bottles are presented to a torque head, which quickly screws on a cap. But the devil is in the details.

“A batch size is typically 10,000 bottles, which we have to cap at say one per second. Every cap has to be done up to the same torque, and we have to provide proof of this performance. Sterility has to be ensured – the machine may even be working in a high vacuum to ensure that no bacteria or other contaminants are present.

“Put all of this together and you end up with a need for a highly engineered machine.”

As the need for traceability emerged, Cap Coder realised that it would have to develop a standard solution, which while not quite identical for every machine, would be based on the same technology deployed in the same way. And because exports are the lifeblood of such an OEM, flexibility to meet different counties’ standards had to be designed in from the outset.

Even the largest bottle tops are not that big, so handling them at the speeds required can appear impossibly fiddly.

“Our philosophy is to have a simply machine design that avoids extraneous parts,” says Roger. “This lead us to the idea that we’d like the torque sensor to be wireless.”

Looking at torque sensors available on the market, one, TorqSense from Sensor Technology, stood out as meeting all criteria: simplicity, robustness, high speed and wireless. The company was contacted and design meetings set up.

Mark Ingham of Sensor Technology takes up the story: “Basically we could use TorqSense ‘as is’ for this application; we just needed to work out mounting arrangements. Similarly, the associated software was ready to go after a bit of calibration and some front end graphics.”

The sensors that attracted the attention of Cap Coder depend for their operation on surface acoustic wave (SAW) transducers. These transducers comprise two thin metal electrodes, in the form of interlocking “fingers”, on a piezoelectric substrate such as quartz. When an RF signal of the correct frequency is applied to the transducer, surface acoustic waves are set up, and the transducer behaves as a resonant circuit.

The key feature, however, is that if the substrate is deformed, the resonant frequency changes. When the transducer is attached to a motor drive shaft, the deformation of the substrate and hence the change in resonant frequency is related to the torque applied to the shaft. In other words, the transducer, in effect, becomes a frequency-dependent strain gauge.

Since the transducers operate at radio frequencies, it is easy to couple signals to them wirelessly. Hence, TorqSense sensors that incorporate the SAW transducer technology can be used on rotating shafts, and can provide data continuously without the need for the inherently unreliable brushes and slip rings that are often found in traditional torque measurement systems.

With the Cap Coder project, software was required to do two things: run the torque up to 10kgcm within tolerances of 10 percent, and record the actual value achieved. This secures the cap to the bottle at a level of tightness that will ensure security and sterility, yet is at a level that can be opened relatively easily by an adult. The logged values are saved to a hard drive to provide a permanent record for traceability purposes.

Roger explains: “Diagnostic fluids are distributed widely, typically to every hospital in the country, where they may be stored for months before use. Tracing each bottle’s origin would be practically impossible without full records being automatically produced and saved to a central location.

“We found a solution to this complex but critical problem using an out of the box technology. And what amazes me is the diversity of other fields in which TorqSense is used – its really any machine with a rotating shaft.”

Sensors sensing growth?


We have talked about Promising signs in process automation market recently, which had an American flavour,  and we also shared an article which had a British viewpoint on recovery, Manufacturing recovery firmly on track!
Here Tony Ingham of Sensor Technology answers the question Could the sensors sector be a microcosm of the whole national economy? He certainly thinks so. Here he looks at what it will take to run a small technology company in the second decade of the millennium and suggests parallels with the wider world. Yes he is talking about the British experience but surely there are also lessons to be learned in other economies large and small.

Sensing Growth Opportunities
By Tony Ingham

Tony Ingham

You might think it perverse to say something positive about the recent recession, but it had a characteristic that I have rarely seen before – in bad times or good. It helped a lot of people realise what really makes economies tick.

In previous recessions, most peoples’ reaction was to work harder on winning sales, i.e. keep doing what they had been doing and hope for an upturn. This time though, people saw the weaknesses of the whole financial sector and began to analyse how and why economies work.

There has been a realisation that there is a massive difference between fast paper profits and fundamental wealth creation. The engine room of the economy is not the City of London, it is the primary industries, such as manufacturing and agriculture. These create thousands of jobs up and down the country, rather than concentrating so much wealth into the hands of a few lucky individuals that they become divorced from economic reality.

In fact, manufacturing, engineering, science and technology have all fared relatively well over the last couple of years – most of the pain was felt in other sectors. So it is not that surprising that manufacturing is currently our strongest sector.

But the important point is that it must remain so. Manufacturing can be wonderfully profitable if managed correctly over the whole term of its products’ lifecycles. It creates masses of jobs at all levels. It creates yet more jobs in the supporting sectors such as research, development, engineering and design. Its products are easily exportable, so will suck overseas revenues into our coffers. It is also very stable; the need for capital production equipment, highly skilled staff and a sophisticated supporting infrastructure makes it relatively difficult to relocate once it is established.

At the moment, the government is full of praise for manufacturing, but this simply is not enough. This and future governments must support manufacturing and the other technical industries. It needs to develop policies that encourage and promote manufacturing, help exporters, support enterprise and finance R&D; that generate enough trained scientists, engineers, technicians and designers, that improve the social status of those that serve their country via the technology industries. It’s a big ask, but the Chinese and Indians are doing it; the Japanese and Germans did it 50 years ago and the Americans did it 50 years before them.

So where does the sensor sector fit into all this? Well sensors are now widely used across so many areas that they are a bell-weather for the whole economy.

Overall, the sensor sector weathered the downturn well. Early in the recession many car makers and other major industries shut down production for 3 months to reduce stock. But they also took the opportunity to invest in new manufacturing systems, including sensors. Furthermore, sensors are wonderfully exportable, so manufacturers often remained busy servicing clients abroad.  And while the recession was bad, the sectors that suffered the most – finance, banking etc – were not major direct purchasers of sensors.

The UK sensors sector is currently underdeveloped, so offers many opportunities for building strong manufacturing companies that could easily become world leaders and major exporters.

The sector got going on a worldwide basis in the late-1970s or early 1980s, when traditional craft-based instrument making was giving way to sophisticated manufacture of high tech sensors. Unfortunately, at this time manufacturing was definitely not in favour in the UK. Instead, the government of the day was happily clearing away what it saw as union-infested, decrepit,  smokestack industries, so that new sunrise industries could take root (in a free market, without government support). So while the UK got call centres and pension advisors, sensor manufacturing flourished in countries where capital enterprise was supported, where labour forces did not have a black name, where a growing manufacturing sector provided a domestic market.

I must at this point say that there were exceptions, notably our own company Sensor Technology which researches, designs, develops, and manufactures sensors in the centre of England. It is a self-evident truth that what we have achieved could be replicated by other sensor manufacturers, especially if general UK manufacturing grows.

There is a virtuous circle to be developed. The more sensors that are used, the greater the manufacturing volumes; this lowers unit prices and also allows investment in automated production and improved quality systems, which encourages yet more usage.

The driving forces for the development of sensor technology include miniaturisation, robust solid state controllers replacing delicate mechanisms, wireless solutions, increasing intelligence, improved connectivity and ‘open’ communications. New drivers will also emerge, and new markets will open up.

Since Sensor Technology first set out its stall, cars have gone from having a handful of sensors to literally thousands, factories have become automated, soaking up sensors, entirely new markets have opened up such as home electronics, mobile devices, medical equipment, CCTV and surveillance, etc. Future growth will be even greater, and it is there for the taking – hopefully by a strong UK sensor manufacturing industry!

Addicted to technology transfer


By Tony Ingham

Technology transfer may prove one of the cornerstone engines for growth as Britain and other countries emerge from recession over the coming months. Tony Ingham of Sensor Technology  tells us his company is virtually addicted to the habit, so we asked him to tell us how it has shaped the company’s development and what the future holds.

TorqSense in Technology Transfer

Wireless became one of the buzzwords of the late Noughties, and ‘wireless’ got our grandparents’ generation excited too in the 1940s. But between those periods the word was not much used – except at Sensor Technology around the turn of the Millennium.

We’d identified a way to measure the torque in a rotating shaft without maintaining physical contact – well, the theory of how to do it! Doing away with the traditional slip rings would be a big advantage in many potential applications, and we kept thinking of more and more reasons to develop the concept.

Sensor Technology had been founded in the 1970s to develop various instruments and by the 1990s had diversified into several parallel fields of research and development. We had a number of projects running relating to electromagnetic corruption, EMC, and its control.

Computers and electronics were getting everywhere in the 1990s, but they could be susceptible to electrical interference if they were used in proximity to virtually any sort of machine. This included the obvious places like factory floors, but also hospital wards, offices, broadcast studios, shops full of refrigerators and police command centres. EMC was a big hurdle that had to be overcome if computers were to reach their full potential. We were working hard in the field, as were many other organisations.

Sensor Technology had been investigating the use of Surface Acoustic Waves (SAWs) or Rayleigh Waves as a way of blocking interference. These waves are produced by most objects in motion and the theory was that they could be made to interact with the EMC waves and cancel them out.  It’s a technique that several teams were working on and with which some success has been achieved.

We were setting up a long running trial on a lab bench. Things had got a bit messy and we were just tidying up a bit before starting the trial, when we noticed on our instruments that SAWs react to strain.

It was hardly a eureka moment, but over the next few days the idea grew that the SAWs could be refined to act as gauges. Even this didn’t get us too excited, but then it struck us that it was a wireless connection and this opened up many practical possibilities.

A few weeks and several late nights on and we had a workable proposition. Soon we had DTi (Department of Trade & Industry) and PERA (Production Engineering Research Association) backing to run a proof of concept project. This was successful and the race was on to develop a marketable product.

We protected ourselves with patents and worked out a plan to commercialise the technology. We needed a spread of application projects to work on; some easy, some tough; some commercial, some academic; some mainstream, some specialist. Fortunately, just about every machine in the world uses a rotating shaft to transmit power so there were plenty of contenders.

Universities were fertile grounds. At University College Dublin (IRL) the technology – by now dubbed TorqSense – was used to mix solids into liquids. It doesn’t sound that demanding, but there were highly defined targets relating to achieving an even mix in minimum time and with minimum power expenditure.

I could see that there were hundreds of industrial applications for this work, but I didn’t predict what it actually turned out to be – stirring meat and other ingredients into curry sauce on an industrial scale! This may sound a bit trivial, but it represents many many industrial processes, particularly in Ireland’s food-focussed economy.

The University of Greenwich (GB) provided a project at the toughest end of the scale – monitoring the torque in high speed rotating stone saws. These need to be brought up to speed very quickly; when they first contact the stone the shock load is incredible, but to get a smooth cut surface a constant torque has to be maintained throughout the entire cutting process, with on-the-fly adjustments being made to account for variations in the stone’s density.

Industrial stone cutting is a harsh environment and the TorqSense has to perform faultlessly for hour after hour.

The technology proved itself again and again in fields as diverse as aerospace, marine, nuclear, pharmaceuticals, packaging, pumping, conveying and mixing. Soon the company shifted its focus to developing variations of the basic theme.

We designed big and small units; single-piece sensors that are simple to fit; two-part units with a small head that will fit into the tiniest space and communicate to a controller elsewhere on the machine; a pulley replacement unit for direct installation on belt and chain drives, etc , etc, etc.

Another technology transfer is now underway. We are developing a load sensor, which is being built into helicopter cargo hooks. A wireless connection feeds real time data through to the pilot, and also logs it for later management analysis.

The wireless-ness is a massive advantage, because it means the hook is legally not a part of the aircraft. Therefore users don’t need to spend time and money getting Aviation Authority approval for its installation. The datalogging means exact billing to customers, while an integral GPS means spraying or similar tasks can be done with utter precision.

The commercial flying community is very excited about the idea and coming up with more and more avenues for us to explore.

This all seems a long way from the drive shafts and industrial plant we usually deal with, but it’s a not-unusual technology transfer scenario. We come up with an idea, get something working and let people see it. Chances are someone will step out of left field and say: “That’s just what I’ve been looking for.”

• There are other applications for Sensor Technologies’ TorqSense described on the Read-out Instrument Signpost’s other blog. Use the Google Search on the left hand column with the word TorqSense


Thames to sparkle under its own power


W.S. Gilbert in one of the librettos for the famous Gilbert & Sullivan operettas prophesies:

“…they’ll set the Thames on fire
Very soon; very soon.”

Well this story, while not an exact fullfilment, strikes us as perhaps been something Mr Gilbert might have appreciated.

...the start of the future?

A small proportion of the Thames is to be illuminated using power generated by the flow of the river itself, as Kingston University tests prototypes of a new hydroelectric turbine design.

The turbine will sit on a pontoon and will provide a floating test and measurement laboratory. On this will be an array of sensors and monitors, including a TorqSense the wireless torque sensor from Sensor Technology Ltd.

“To say that this is a harsh environment for laboratory equipment is a bit of an understatement,” says Rod Bromfield, Senior Lecturer, of the Faculty of Engineering, Kingston University. “We can only use robust kit with a proven industrial pedigree.”

The turbine under test has been developed by Hales Marine Energy near Eastbourne on the English south coast and is expected to be deployable in tidal seas as well as rivers. The design application of this turbine is to sit on a submergible tank that will sit on the sea bed and can be floated up to the surface when required. Significantly, the design is almost infinitely scalable: the unit under test is 1m diameter and produces about 1kW; 5m turbines suitable for inshore deployment would generate round 20kW; smaller units would be ideal for river use.
With access to the test site being by small boat, Rod knew that his test regime had to be both simple and comprehensive.

“The critical measurement is torque, as this indicates the power we can derive from the system. We had to be certain that we would get continuous measurements over an extended period of time, because we need to map power production against actual river flow. Also for this technology to succeed in the emerging green power market it must be capable of continuous and predictable energy production.”

One of the engineering issues that Rod faced was the relatively slow revolution of the turbine, in this test below 50rpm. This helped define the choice of the TorqSense, but it is also a key feature of the Hales turbine – the slow speed means less stress on moving parts and therefore less servicing. It also minimises habitat disturbance, so that the ecological impact is low.

“When I contacted Sensor Technology I was very concerned about vertical mounting and harsh environment performance,” recalls Rod. “Fortunately there have been TorqSenses installed vertically, including several high up on vertical axis wind turbines, where they have to withstand gales, hurricanes and lashing rain.”

In a Torqsense transducer, surface waves are produced by passing an alternating voltage across the terminals of two interleaved comb-shaped arrays, laid onto one end of a piezoelectric substrate. A receiving array at the other end of the transducer converts the wave into an electric signal.

The frequency is dependent upon the spacing of the teeth in the array and as the direction of wave propagation is at right angles to the teeth, any change in its length alters the spacing of the teeth and hence the operating frequency. Tension in the transducer reduces the operating frequency while compression increases it.

To measure the torque in a rotating shaft, two saw sensors are bonded to a shaft at 45deg to the axis of rotation. When the shaft is subjected to torque, a signal is produced which is transmitted to a stationary pick up via a capacitive couple comprising two discs, one of which rotates with the shaft, the other being static.

The design of the Hales turbine is reassuringly simple, and therefore likely to survive underwater installation with long service intervals. It was developed by Paul Hales, a design engineer who has spent a career associated with the sea.  “It’s based on the traditional water wheel, but mounted on a vertical axis – on its side,” he explains.

“Using modern engineering and materials it is possible to take this effective early turbine and by turning the output shaft to the vertical to immerse the whole turbine into the tidal flow. To overcome the high resistance on the wheel blades that on one side are trying to move against the water flow, they are shaped and hinged to present a minimum resistance. The large blade area on the drive side produces very high amounts of torque (rotational force) at low speed, in the range of 10 -20rpm.
Coupled with modern permanent magnet generators that can start producing electricity rotations as low as 2rpm, my turbine can offer the possibility of tidal generation worldwide.”

Paul continues: “Water is nearly 800 times denser than air so it carries far more energy, making water turbines a very attractive alternative to wind energy. Notably seabed systems are not an impediment to shipping, nor do they have any visual impact and ecological issues are minimal for low speed systems.”

Paul says that he could envision an array of his turbines on every headland along the English Channel and at intervals down the Thames.

“Of course, that is just the start. The simplicity of the design, its robustness and low maintenance, relative ease of installation all add up to making it suitable for deployment in remote and less developed areas. Its low ecological footprint addresses many of the issues raised by environmentalists. Its continuous and utterly predictable power output overcomes the intermittency associated with wind, wave and solar power.

“When, over the test period, people stand on Richmond Bridge and watch a modest array of lights bobbing about on a buoy, they may not know it but they will be seeing the future!”

And so we get back to W. S. Gilbert:

“…they’ll set the Thames on fire
Very soon; very soon.”

See also Power from the Sea and Tidal turbine developement in Ireland & Canada published earlier this year