Robert E. Anderson

Mechanical Impedance Measurements of Soils

A method of measuring the mechanical impedance of the earth is described, and some experimentally measured impedances as functions of water content, soil character, and source diameter are given. A comparison of the measured impedance with some previous theoretical work is also included.

Scattering of Acoustic Pulses by a Solid Sphere in Air

The diffraction of an acoustical pulse in air by a solid sphere is studied by the use of a one cycle sine wave pulse. A generator was designed and built to produce pulses of this type. This generator delivered a gating pulse to an electronic gate to which the sinusoidal signal was applied. The gating pulse was adjustable in time position, width, and repetition frequency but was synchronized with the sinusoidal signal. Accordingly all pulses transmitted by the gate were identical, and could be separated in time by as much as 10 seconds. The gated pulse used was a single cycle of a 10 000‐cycle sine wave, successive pulses being one second apart. The Fourier analysis of this pulsed sine wave was found. A speaker was built that would give a reasonable reproduction of this pulsed sine wave. A microphone with the necessary quality was available and was used together with necessary amplifiers and an oscilloscope to record the pulses. The pulsed sine wave was scattered by a one and one half inch diameter solid brass sphere and experimental data found every ten degrees about the sphere. Scattering by the sphere at one scattering angle was computed and compared to the experimental results.