# State of the Art Review about Bio-Inspired Design and Applications: An Aerospace Perspective
## 4 Applications of Bio-Inspiration in the Aerospace Industry
### Sensors  
The implementation of sensors in aerospace engineering plays a crucial role in determining an aerial vehicle's response towards its surrounding stimuli. An early application of bio-inspired sensors can be traced back to 2003. The problems regarding the installation of environment perception sensors on small-scale aerial vehicles like MAVs and UAVs were the issue [6]. Small winged insects have particular neurons for the same purpose called elementary motion detectors, which helps them form a safe path through lit obstacles. Two micro-bots were mounted by optic flow sensors, to implement optical motion detection. Experiments revealed that this enabled one of the microbots to perceive a safe distance from the ground even after altering speeds and enabled the other to fixate itself on a contrasting target. The functioning of the International Space Station and the crew aboard can be in imminent danger in the event of a leak in the station's walls [77]. To counter this, various pressure sensors inspired by the sensory capabilities of a swarm of bees are distributed throughout the station to pick up signals in case of a pressure loss. In the event of a pressure loss, a swarm of pressure sensors around the region of failure is activated. An ultralight indoor aerial vehicle, inspired by flies' flight, was capable of autonomously steering the aircraft [78]. A fly's ability of trajectory control was incorporated into the system of the plane as well. Another study based on a bio-inspired optic flow sensor-enabled a MAV to perform tasks such as take-off and leveling mid-flight [7]. Optic flow sensors were tested on serial vehicles for perception sensing of indoor and outdoor environments to assess their sensitivity to illumination [10]. The study proved the sensors to show sound visual processing under natural conditions. A low-cost optical sensor based on the compound eye of a fly was developed, which helped gauge the angular position of a distant edge with a minimum accuracy of 160 times, concerning the particular interceptor angle [79]. A bio-inspired optical device was developed based on a fly's ability to gauge speed, landing, and obstacles based on elementary motion detection [80]. A sensor similar to the compound eye was developed to mimic the large field of view and the exceptional ability of the insect to process light. This helped with terrain navigation and auto landing, with a 360-degree FOV. Figure 23 indicates the sensor developed inspired by a compound eye of a fly. Figure 22: Computer-aided design of the arm wing structure mimicking a Bat’s wing [75]. A NODKA sensor was also implemented to locate a contrasting target, precisely an edge [81]. This optical sensor (refer Figure 24), inspired by insects' rapid eye movements such as a housefly was mounted onto a MAV and detected an opposite edge at an exceptional resolution. A bio-inspired pressure sensor installed chordwise on an unmanned aerial system was used to control the aircraft attitude using a trained artificial neural network [82]. A pressure sensor inspired by mechanoreceptors embedded in a bird's wing was implemented in a MAV to establish roll control in a turbulent environment by showing the correlation between the pressure variation on the wing surface and pitch angle variation of the upstream flow [83]. A bat possesses several sensory hairs on its wings. Influenced by these structures, a UAV was set up with strain sensors that controlled roll motions, and pressure sensors (chordwise) were able to control pitch motions [84]. A bio-inspired pressure sensor's robustness to detect airflow installed strategically on the leading edge of a small UAV wing was indicated by numerical analysis. It showed promising results under the change in external stimulus [85]. A quadcopter design inspired from the lobula giant movement detector neurons (LGMD) in locusts was designed to detect possible collisions [86].