Report on the National Electroacoustics Institute “O. M. Corbino” (I.N.E.A.C.), Rome, Italy
Authors: Bolt R. H. , Giacomini A. 
Published: September 2005

Dedicated to the late O. M. Corbino in 1939, this institute lost, during the war, its original building and most of its facilities, which included newly constructed reverberation and free-field rooms for large-scale acoustics research. Most of the comprehensive acoustics library was salvaged, together with some pieces of equipment. Operations were renewed in 1945 in a portion of the Italian National Research Council building at Piazzale delle Scienze, Rome. The group numbers about ten research scientists, some of whom are members of the staff of the University of Rome, and about ten service personnel. The program features mainly ultrasonics, vibration studies of solids, and acoustic instrumentation.

The ultrasonics program is characterized by the exploitation of light diffraction methods for measurement. In some recent developments, the usually employed standing waves between a quartz crystal and a reflector have been replaced by a pair of oppositely directed parallel beams of progressive waves from two quartz plates driven at the same frequency by a common source. The new device is free from the high precision requirements for parallelism and operates continuously over a fairly wide range of frequencies without mechanical adjustment.

Ultrasonic velocity and absorption in several liquids and liquid mixtures are being studied from 1 to 10 megacycles, as a function of temperature. Velocity is now determined by measurement of wave-lengths in a progressive beam which is illuminated stroboscopically by the two-crystal cell described above. For absorption measurements, a monochromatic light line is passed through a single progressive ultrasonic beam and masked to allow a single-order diffraction line to fall on a photo-cell. The measured light intensity is proportional (within certain limits which can be checked) to the ultrasonic intensity which can then be measured as a function of distance to determine absorption.

Dynamic properties of wood and metal are being studied by vibrating small samples and measuring the elastic and damping coefficients from resonant behavior. The basic tool is a condenser which drives the sample by electrostatic force and which also frequency modulates a high frequency carrier to provide a measure of vibration amplitude. The output is presented oscillographically to display force and displacement on the two axes of the scope. Samples are suspended on fine stretched wires and driven in transverse or longitudinal modes of vibration. These simple and effective means for studying internal damping and elasticity as dependent upon composition and temperature should prove useful in solid-state physics studies.

Instrumentation studies include tube resonance methods of acoustic impedance measurement, frequency dividers, and multipliers for stable sound and ultrasonic sources, earphone testing, and microphone calibration.

The I.N.E.A.C. has issued some eighty reports and papers, which have appeared in Ricerca Scientifica, Alta Frequenza, Atti dell 'Accademia Nazionale dei Lincei, Journal of the Acoustical Society of America, and other journals. A Bibliography, annotated with abstracts or summaries of several of the papers, is included in this report.