Search

A study was made of crystallite orientation in cubic ferrites when pressed in a magnetic field. One easy axis orients in the field direction, the other easy axes lying at random in or near a perpendicular plane. Experimental torque curves have the theoretically predicted shape. The magnetic field required for microwave resonance is lower than in the same nonoriented ferrite if the axis of alignment and the field are parallel. This occurs because the anisotropy field Ha is no longer randomly oriented but helps to supply part of the resonant field requirement. Values of saturation magnetization (Ms), anisotropy energy (K), and resonant field (Hr) at 14 775 mc/sec were measured on a series of oriented polycrystalline nickel cobalt ferrites. Values of the measured resonant field are compared with values obtained from Kittel's resonance relation using the independently measured values of Ms and K.

Comparatively little work has been done on the topic of radiation damage in magnetic materials, and references concerning it will be cited herein only when pertinent to this paper. While our listing is limited, a bibliography of laboratory reports on the subject is available from the Battelle Memorial Institute. Much excellent engineering information and, in a few cases, some understanding of the mechanisms involved have grown out of the work which has been done, however, and our contribution is primarily an extension of previous investigations in the field to a few types of magnetic materials heretofore neglected.

A laser interferometer for earth strain measurements has been constructed and is described. The apparatus is designed to measure displacements down to small fractions of the laser wavelength. Measurements of length change of the interferometer arm of 10 m length were obtained during normal microseismic activity and following a distant earthquake. Some representative results of this laser application are presented.

The possibility of using a laser interferometer as a geophysical strainmeter was examined. A thermally stabilized laser was used and the results compared with a quartz Benioff strainmeter. From these measurements both long‐ and short‐term stability of the laser radiation were calculated. The results indicate that the long‐term stability is sufficient to observe earth tides while the short‐term stability is better than 1:1010.

A technique is described for the automatic measurement of ultrasonic velocity changes in continuous wave experiments. An oscillator is locked to a mechanical resonance of the sample. Velocity changes appear as frequency changes of the oscillator and are easily recorded. Some typical results are given.

The formation of yttrium iron garnet, Y3Fe2-(FeO4)3, starting with (1) Fe2O3 and Y2O3 and (2) Fe3O4 and Y2O3, was studied as a function of temperature and time by means of magnetic moment and X-ray measurements. The reaction began at 600°C. and was completed at 1200°C. The perovskite phase appeared only between 600° and 800°C. Above 1200°C. only the garnet phase was present. The microwave line width and g-factor at 9303 mc. per second were also measured and related to the preparation variables.

Effort is devoted to the measurement of acoustic losses in solids, primarily single crystals, at ultrasonic frequencies. In this type of experiment a pulse of r-f energy excites a quartz transducer bonded to the sample which in turn sends a pulse of ultrasound through the sample. The acoustic pulse is reflected from the sample end, travels back to the transducer and the reciprocal effect occurs. As a basic unit for this measurement the Sperry Ultrasonic Attenuation Comparator is used. This unit is a combination transmitter-receiver capable of delivering rf pulses over the frequency range 10-200 mc, containing a 60 mc meterodyne receiver with 8 mc bandwidth, and a calibrated exponential wave generator for attenuation measurements. The attenuation is essentially the logarithm of the ratio of the amplitudes of any two echoes, the procedure is to choose two convenient ones, detect their peaks, logarithmically amplify these, and then take the difference which is plotted on the x-y plotter against the suitable parameter.

An experimental study was performed to determine if spurious products formed from multiple signal mixes were dependent upon input signal phase relationships, and if the phase position of the intermediate frequency response wa s a function of mixer bias voltages. Formations of multiple mix products due to signal and local oscillator harmonic injection were investigated using a diode mixer, and the measurement procedures and instrumentation necessary to measure the effects of signal phase relationships on these products are presented. Test results are shown which verify that variations in the phase orientations between the fundamental and harmonics of an injected signal cause radical variations in output response levels. It is also shown that the phase of output responses are a function of the mixer bias voltage.

It is the intent of this paper to present both a broad overview of the total field of interference prediction and an analysis of past and current results obtained from specific prediction efforts. The broad overview portion of the paper consists largely of a discussion of the philosophy and purpose behind interference prediction efforts. The format of this overview will be an analysis of current system and equipment level problem areas conducted to establish (1) the areas in which interference predictions provide useful results, (2) why such predictions are necessary, (3) the primary objectives of interference prediction efforts, (4) the major factors involved in constructing accurate prediction models, and (5) the need for evaluation efforts to support prediction results. An analysis of past and current interference prediction efforts will be presented from a critical, but constructive, point of view. The efforts analyzed will include those intended to model equipment emissions and susceptibility thresholds based on limited spectrum signature data; system models involving a source, antenna, propagation factors, siting effects, and a receptor; environmental models concerned with relatively large geographical areas populated with many emitter-receptor combinations; etc. Based on the purpose, objective, and need for interference prediction in a broad sense and the detailed analysis of specific prediction efforts, needed developments, and improvements for the future are presented.

The Mossbauer study of stoichiometric Ni/sub 3/Mn shows that the transformation from the disordered to the ordered state proceeds by the classical first-order nucleation and growth process. Some Ni-Mn alloys are ferromagnetic in the ordered state and weakly ferromagnetic, or paramagnetic, in the disordered state. The difference is most pronounced near the composition Ni/sub 3/Mn. The samples were partially ordered by annealing in a helium atmosphere at 450 nif- C for 10 days. The spectrum left no doubt as to the transformation process. (C.E.S.)

A tilted loop technique has been developed to reduce bearing errors in loop HF directionfinder systems used on ionospherically propagated signals. Measures of signal elevation angle-of-arrival can be obtained. Theory of operation is stated. Field tests of an experimental model have verified the theory and disclosed significant improvements over a contemporary system.

Ultrasonic attenuation and velocity measurements exhibit anomalous peaks in the region of critical‐point transformations. Measurements near the Neel point (67.3°K) in MnF2 show such anomalous behavior with temperature. A large peak in the attenuation is observed over about a 2°–3°K temperature range with its maximum occurring at the Neel point. This peak has been studied over a frequency range from 10–150 MHz. The attenuation maximum is not seen with shear waves. Recently, we have been able to observe a similar anomaly in the velocity behavior of this material using a sensitive mechanical resonance technique. Both the attenuation and velocity data show anisotropy with the change in the (001) direction about 3 times that in the (110). These measurements, as well as results from other investigators, are discussed in terms of current theories.