For animals, being able to listen to sounds in the environment opens up a new world; a new way to sense their surroundings. Many animals have evolved to use sound for detecting prey and predators, finding and courting with potential mates, 'seeing' the world with echolocation, and reaching a level of complexity to enable speech. In many cases, having an acute auditory sense can really be a matter of life and death. Unsurprisingly, the importance of detecting the sounds emitted by friends and foe has driven the evolution of remarkable acoustic sensors. When we can hear a pin drop, we do so because that ability, a long time ago, could have saved our lives. This level of sensitivity, in humans, mammals, and insects among others has reached a point where some animals can detect sound that is in some respects only just distinguishable from noise - from the thermal buffeting to which every sensor is ultimately restricted. In order to achieve this, animals have evolved many tricks to enhance their auditory capability. Mammals and insects use sensors full of molecular motors, consuming energy to provide amplification of weak sounds that enter their ears. This feedback also gives a sensor the ability to selectively filter signals; to change the range of frequencies to which they are sensitive. In this regard, a biological acoustic sensor can be adapted perfectly to the animal's needs: to lock into the sound from a desirable mate or to form an image of their world when eyes are not enough. Insects in particular employ a wide range of exquisite sensors. For example, the mosquito uses a brush-like antenna projected away from its head into the air, which oscillates when sound is present. At the base of this antenna is some 16000 neurones (that can both sense and generate force), a truly remarkable number. Why the need for so many? Strangely enough, with so many neurones sensing and feeding back a force to the antenna, some very complex dynamic behaviour can occur. Sound can be amplified, frequencies accepted or rejected, and signals can be 'locked' to zoom in on the source. This project is inspired by these sensors. Can we learn from the way insects like the mosquito process sound? Can we harness their ability to make new sensors and actuators that can hear like they do? Over the course of this fellowship, we will investigate the way in which bundles of cells operate to achieve their exquisite sensitivity. What happens when a sensor is composed of relatively simple components, but behaves more than the sum of its parts? We will image the activity of neurones in insects and develop hypotheses on how they work collectively. We aim to proceed by searching for ways in which to implement their properties in real engineered sensors. Many transducers used industrially, and in other scientific fields, are in fact arrays of many sensors and actuators, coupled together. By knowing the mechanisms of cellular arrays in animals such as the mosquito, we will aim to achieve the level of sophistication, sensitivity and functionality of insect hearing in real systems. These bio-inspired sensors have the potential to improve the industrial use of acoustic sensors and actuators, from medical ultrasound imaging, non-destructive testing of materials, and even robot guidance.
I have discovered a variety of unusual and interesting phenomena in the ears of various insects that is providing both insight into how and why hearing has evolved in nature, and as part of an inspiration for novel directional microphones, a project that is now being funded by the EPSRC in collaboration with Dr James Windmill and the Institute for Hearing Research (MRC). We have gained new insight into how the ears of mosquitoes, moths, and locusts (among others) work in analysing sound. I have also contributed significantly to advances in ultrasonic transducer design, increasing our understanding of how to build ultrasonic sensors used in biomedical and manufacturing contexts.