| The goal of the research was to make quantitative measurements of the surface pressure on the wings of a honey bee during hovering flight using pressure sensitive paints. This is a challenging experimental problem because the expected changes in surface pressure are small (2 x 10-4 atm) and occur on the time scale of the wing beat cycle. Combinations of seven oxygen-sensitive dyes and six polymers were evaluated according to their response time, sensitivity, biocompatibility, and uniformity of the sensing layer coating on the wing surface. Pressure sensitive paints that met coating uniformity requirements were evaluated in the phosphorescence microphone, a device that replaces the diaphragm of a microphone with a thin film of pressure sensitive paint. The phosphorescence microphone was used to show that selected pressure sensitive paints could detect pressure changes as small as 6 x 10-5 atm in the frequency range of 150--3500 Hz on a background of atmospheric pressure. Once a candidate PSP was chosen, an aerodynamic phenomenon that replicated the time scales and pressure scales of insect flight without the additional complication of a moving, flexible wing was studied. A cylinder mounted in uniform flow generates vortices that are shed from alternate trailing edges. Pressure sensitive paints were used to obtain two-dimensional maps of the mean and oscillating surface pressure during the vortex shedding cycle. These experiments indicate that the sensitivity of current pressure sensitive paints is limited by photodeterioration of the sensing layer that occurs over the time course of the experiment. Although the resolution of the pressure measurements on the cylinder surface approached the expected pressure changes on the surface of a honey bee's wing during flight, photostability issues must be addressed before pressure sensitive paint techniques can be applied to the study of insect flight. A new beeswax-based pressure sensitive paint can then be used to measure the time-dependent surface pressure changes on the wings of a hovering honey bee. This pressure sensitive paint leaves the insect capable of sustained flight and renders its wings sensitive to small, rapid pressure changes. |
