Properties of Bird Feathers as Piezoelectric Transducers and as Receptors of Microwave Radiation.

An investigation was made of the properties of bird feathers as piezoelectric transducers in the audiofrequency range and as dielectric receptors of electromagnetic radiation in the microwave region. In the first case, cartridges of the ceramic and magnetic type and an electromagnetic transducer probe were used as detecting devices. Results show piezoelectric resonances in the 1-20 kHz region for the calami of feathers. The characteristics of bird feathers, as receptors of microwave fields, were studied in the 10-16 GHz region. Experiments were conducted coupling the specimen (feather) to a length of waveguide which served, together with other microwave components, as a primary detector. Microwave power radiation patterns were measured both in the presence and in the absence of the specimen. Results indicated a substantial increase in the microwave power collected in the forward direction, and a decrease of the radiation pattern beamwidth when the feather was present. Furthermore, some experimental evidence indicated the possibility of inducing piezoelectric effects in the specimen by audiofrequency pulse-modulated microwave fields. These results are important in view of the fundamental role that feathers play in the life of birds, and the influence of environmental factors on bird behavior.