Engineering From ears to engineering Sometimes the solutions to engineering questions have already been answered – by ! Rather than ‘reinvent the wheel,’ therefore, Professor James Windmill and his lab team at the University of Strathclyde choose to learn from some of the remarkable feats of engineering found in the natural world. In particular, his research focuses on using ideas from hearing to develop new microphones and transducers for use in fields as wide-ranging as medicine and materials science.

odern microphones, such any other ; the insect with the highest as those used in hearing frequency call – a genus of katydid dubbed aids, and transducers such ‘Supersonus,’ from the South American as ultrasound scanners, rainforest; and the loudest (relative to its are remarkably sensitive. size) animal on earth – a water boatman that However, they still struggle to deal with generates a mating call by rubbing its penis Missues such as background noise, which may against its abdomen. need to be removed by downstream digital processing, or identifying the direction To elucidate the mechanisms of hearing from which a sound originates. Electronics in an insect, Prof Windmill’s lab use an engineer Prof Windmill’s highly multi- array of techniques, including behavioural disciplinary team provide solutions to these observation, microscopy and X-ray problems, taking their inspiration from the microtomography, 3D laser vibrometry, and natural world, in particular the . electrical examination of the signals passing through the auditory nerve. The results are INSPIRING INSECTS translated into a three-dimensional computer With about a million species known to model of the ear’s structure, which can science, insects are an extremely varied then be used to simulate how it responds group of organisms, and have evolved a to sound. Comparing their experimental diverse array of different hearing organs. data with the computer models gives the Previous research into insect hearing has researchers a thorough understanding of how largely focused on the noisiest groups: the the organism’s hearing works – both in terms grasshoppers, crickets, locusts, and cicadas; of its mechanics, and downstream signal however, Prof Windmill’s research covers a processing at the neural level. wide range of other insects including and moths. In the course of their work, Prof Then, the baton is passed to the engineers, Windmill and colleagues have discovered physicists, mathematicians and material some remarkable insects, including a moth, scientists of the team who develop new the greater wax moth, with the ability to microphones (instruments for sensing hear sounds up to 300 kilohertz, higher than acoustic and ultrasonic waves) and

Comparing their experimental data with the computer models gives the researchers a thorough understanding of how the organism’s hearing works

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RESEARCH OBJECTIVES Prof Windmill’s research focuses on How did you first become aware of in the human inner ear works. But the the investigation of hearing systems the potential of biological systems to locust was doing this all on the eardrum. in insects to inspire the development inform engineering questions? This led me to realise that there could be of new acoustic and ultrasonic sensors My background is electronic engineering, many interesting insect hearing systems and systems. He is also interested which led to a PhD that involved sensing at phenomena that we could use to inspire in sustainable engineering through the nanoscale. I wanted to do something engineering. the process of remanufacturing, the Above: Multi-band silicon piezoelectric MEMS a little different following my PhD, and development of new biomedical directional microphone inspired by ochracea that led me to biological research into What impact do you think the advent sensors, and the use of ultrasound in Right: MEMS directional microphone in a 3D-printed insect hearing systems as a postdoctoral of 3D printing will have on this kind of manufacturing. housing (UK five-pence coin for scale) researcher. This gave me the opportunity research? to discover just how many different The main impact is speed for the FUNDING hearing systems there are in the insect researcher. A device can be computer European Research Council - https://erc. transducers (instruments that can both world. I went back into an engineering designed, 3D printed, then tested and europa.eu/ generate and sense sound – such as are used department as an academic, but I wanted characterised in hours, or at the most a in hospital ultrasound scanners) based on to continue biological research as well few days. Working with standard silicon COLLABORATORS these findings. as develop my engineering work. So the microfabrication, particularly for smaller • Dr Fernando Montealegre-Z, University natural thing to do was to bring the two labs and institutions, can stretch this of Lincoln, UK NAVIGATING BY SOUND together. process out to months. So, 3D printing • Dr Jerome Sueur, Muséum national While larger animals can detect the direction provides a research team with many d’Histoire naturelle de Paris, France of a sound source by the difference in timing acoustic sensors for use in hearing aids. Until Lepidoptera have tympanal ears, and many What techniques do you use to study iterations in the same time that standard • Prof Michael Greenfield, Université and amplitude as sound waves are received recently, the sensors were built from silicon use ultrasound for mating. To enable them such tiny organisms? microsystem fabrication provides just one. François-Rabelais, Tours, France at each of their two ears, for smaller animals using standard Microelectromechanical to hone in on the mating call of their own We use a variety of microscopy But there are some notes of caution. 3D such as insects, the distance between their Systems (MEMS, or ‘micromachine’) species, these moths are able to physically techniques to study their morphology, printing has many challenges as there are BIO two hearing organs is likely too small for this techniques – but now the team are moving adapt the response of their eardrums to focus including optical and scanning electron many things it’s difficult to do with this Prof James Windmill is a Professor of to work. Thus, smaller organisms have come into the realm of 3D-printing. This is enabling on particular frequencies of sound. microscopy, and more recently technology. And, standard microsystem Electronic and Electrical Engineering up with a variety of innovative techniques that them to more easily design complex three- X-ray 3D microtomography. We use fabrication is very easy to scale up to at the University of Strathclyde. He are now coming to the interest of engineers. dimensional structures and to use more There are many situations in which this electrophysiological techniques to produce millions of the same unit, while gained a PhD in nanotechnology from flexible materials, simulating more closely property could be useful: for instance, a measure auditory nerve signals, and have generally 3D printing isn’t. the University of Plymouth (UK) in 2002, Ormia ochracea is a tiny, nocturnal which the mechanical properties of biological hearing aid could focus on the frequency also worked with colleagues to study the and then worked as a researcher on lays its eggs on crickets. It therefore needs structures. range of human speech and fade out behaviour of some insects. We use a 3D What benefits and challenges are insect auditory systems at the School of to locate its hosts in the dark, which the ‘noise’ from other sources. Like the microscanning laser Doppler vibrometer there from working in such an Biological Sciences, University of Bristol it does by the sound of the male cricket’s More recently, Prof Windmill, with colleagues Lepidoptera, our own ears, and those of to measure how things move, i.e., how interdisciplinary team? (UK), from 2003 to 2008. He joined mating call. Since the mid-nineties, it has from the Université François Rabelais de many animals, do this automatically through does an insect eardrum move in response The major benefits are that the University of Strathclyde been known that the Ormia’s two tympanic Tours, France, has identified a tiny moth, a feedback system – the nature of the sounds to sound. We need the vibrometer researchers not only bring different as a lecturer in 2008. He is an membranes (ear drums) which are located Achroia grisella, the lesser wax moth, which is heard changes the response of the ear. Until because the insect hearing systems skills and expertise, but have academic member of the Centre around the base of their front legs, are able to determine the directionality of sound now, however, engineered microphones have usually move only tiny amounts, typically been trained to think and utilise for Ultrasonic Engineering at directly coupled to each other by a strut. with just one ear, which has a maximum relied on downstream digital processing of nanometers or less. Finally, we tie this different scientific methods. For Strathclyde, and has featured in In effect, the structure forms a tiny, highly response to sound arising from a particular all the sound signals received, which can all together using powerful computer example, biologists may want to more than 50 journal publications. sensitive see-saw which rocks if the sound angle. These moths then use their behaviour cause time delays as well as using energy and modelling to explore and explain how explore something that already exists in He is also the managing editor of the waves reaching the two tympanic membranes – scanning with their head to search for the increasing the total size of the microphone these auditory systems function. nature, and engineers are used to creating Journal of Remanufacturing (Springer). are in any way different in intensity or timing. source of a sound, and then maintaining the system. something to solve a problem. Add to this This ingenious system amplifies minute same angle between themselves and the What is your favorite or most exciting physicists, mathematicians and materials CONTACT differences in sound reaching the two sound as they move – to locate their singing Now Prof Windmill’s team, after studying biological discovery so far? scientists, and the mix can produce very Prof James Windmill membranes, enabling the insect to detect the partners for mating. the hearing system of the large yellow My favourite is the discovery of travelling intriguing ideas. Of course, it can be very Electronic and Electrical Engineering direction a sound is coming from. underwing (Noctua pronuba), have waves on the tympanal membrane challenging, as you must ensure that Royal College Building BLOCKING OUT THE NOISE developed a MEMS microphone which can (eardrum) of the locust. This was my first everyone has some understanding of University of Strathclyde In Prof Windmill’s lab, their three-dimensional In fact, it is in the butterflies and moths adapt its sensitivity to different frequencies discovery, and led to my first biological what the others are doing, why, and also 204 George St, Glasgow G1 1XW computer models and simulations of the (Lepidoptera) that the greatest number of depending on the sound received. This may sciences paper. The waves appear on how. But the experience is then a great UK Ormia system have been used to develop tiny ‘acoustic’ insects are found. Around 55% of be particularly good news to users of hearing one side of the eardrum, and then their positive, as the researchers can use what aids or cochlear implants who struggle with direction and the point they stop moving they've learnt from others in their own E: [email protected] background noise. Thanks to Prof Windmill’s changes depending on the sound work. T: +44 (0)141 548 2694 multidisciplinary team and the combination frequency. This allows the locust to W: www.strath.ac.uk/staff/ A hearing aid could focus on the of fundamental biology with applied distinguish different frequencies, and is windmilljamesdr/ engineering, the amazing adaptations very similar to how the basilar membrane www.sasatin.eu frequency range of human speech and of the insect world could be coming to a www.cue.ac.uk fade out the ‘noise’ from other sources microphone near you.

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