Peter F. Strong

Theory of the propagation of UHF radio waves in coal mine tunnels

The theoretical study of UHF radio communication in coal mines, with particular reference to the rate of loss of signal strength along a tunnel, and from one tunnel to another around a corner is the concern of this paper. Of prime interest are the nature of the propagation mechanism and the prediction of the radio frequency that propagates with the smallest loss. The theoretical results are compared with published measurements. This work was part of an investigation of new ways to reach and extend two-way communications to the key individuals who are highly mobile within the sections and haulageways of coal mines.

Superconductivity and electron tunneling

Experiments on the tunneling of electrons through a thin dielectric layer separating two superconducting metals are reported. Data are presented for the pairs AI-Pb, Sn-Pb, and In-Sn. Particular attention is paid to the form of the tunneling current vs voltage characteristics and to the changes observed as a function of temperature. Experimental details relative to the measurement techniques, the preparation of the samples, and the preparation of the dielectric layers are presented. An analysis of the problem is presented which is based on the simple, one-dimensional model of the electron energy spectrum of a superconductor given by the theory of Bardeen, Cooper, and Schrieffer. Close quantitative agreement is obtained between the results of the calculations and the observed characteristics.

Sensitive Tiltmeter Utilizing a Diamagnetic Suspension

A tiltmeter of the horizontal pendulum type is described whose mass consists of a diamagnetic material suspended in a potential well of a suitably shaped magnetic field. The depth of the potential minimum determines the restoring force acting upon the mass and consequently the pendulous frequency and sensitivity of the instrument. In this manner the elastic forces usually supplied by fine springs or fibers are replaced by field forces and the mass is free to respond to tilts or accelerations without any trace of friction of external (Coulomb) or internal (anelastic) origin. The required amount of damping is obtained from eddy currents induced in the seismic mass by its motion in the field. The instrument requires no power to operate the suspension and it can be used over a wide range of temperatures. Under usual environmental conditions, it requires no temperature control. Some of the preliminary results obtained with the tiltmeter in measurement of earth tides are discussed.

Infrared emittance of fibrous materials

A theory of the IR emittance of fibrous materials has been developed. The theory predicts the IR spectral emittance of a matte of randomly arrayed cylindrical fibers as a function of the optical constants of the fiber material, the fiber diameter, the packing density of the fibers, the packing of the fibers within fiber bundles, the reflectance of the substrate, and the thickness of the fabric layer. Theoretical simulations were made and compared with experimental measurements of the IR emittance of polypropylene samples. Both the theory and the experimental data confirm the validity of the concept that fabrics can be tailored by a proper choice of the above parameters so as to obtain an emittance distinctly different from unity.