D. I. Bolef

Sensitivity Enhancement by the Use of Acoustic Resonators in cw Ultrasonic Spectroscopy

The role of an acoustic resonator in the study of cw acoustic magnetic resonance (AMR) effects is discussed. From the expression for the frequency response of a resonator consisting of an isolated sample, one can calculate absorption and dispersion sensitivities and determine the conditions under which a pure absorption or pure dispersion AMR signal may be observed. The calculation is extended to the case of a sample and transducer. The primary effect of the transducer is to shift the frequency of the isolated sample mechanical resonance without materially altering the mechanical resonance lineshape or associated AMR sensitivities.

Frequency Modulation CW Technique for the Measurement of Very Small Changes in Ultrasonic Velocity

An improved continuous wave technique capable of measuring changes in ultrasonic velocity of 1 part in 107 or better is described. The technique utilizes frequency modulation of the cw carrier signal and subsequent lock‐in amplification.

cw Microwave Spectrometer for Ultrasonic Paramagnetic Resonance

A description and detailed analysis of an acoustic cw microwave spectrometer is given. The spectrometer, although designed specifically to measure the small changes in acoustic velocity and attenuation characteristic of ultrasonic paramagnetic resonance, can be used also to measure absolute values of acoustic velocity and attenuation over wide ranges of frequency and temperature. The use of a calibrator in producing a known reference signal is described.

Deformation Potential and Piezoelectric Ultrasonic Phonon‐Charge Carrier Coupling in Indium Antimonide

The interaction of ultrasonic phonons with charge carriers in nearly intrinsic InSb via deformation potential and piezoelectric coupling mechanisms has been investigated at 296 K in magnetic fields of 0 to 11 kOe and over a frequency range of 10 to 200 MHz. The single crystal InSb was p type with an average acceptor concentration of (1.45±0.05)×1016 cm−3. The experiment permitted an ultrasonic determination of the electron and hole mobilities. The values obtained were μn0 = (58 000±4000) cm2 V−1 sec−1 and μp0 = (720±80) cm2 V−1 sec−1. Values of the deformation potential and piezoelectric coupling constants obtained were | Cn+Cp | = (5.8±0.4) eV and e14 = | 0.076±0.010 | C/m2.

Self‐Modulated Mode of Operation of a Marginal Oscillator Ultrasonic Spectrometer

A new, self‐modulated mode of operation of the marginal oscillator ultrasonic spectrometer, in which no external modulation is required, is described and analyzed. In this mode, the system consisting of an oscillator‐coupling network‐acoustic resonator is induced to oscillate simultaneously at two frequencies. Small changes in acoustic attenuation are reflected as changes in the amplitude or frequency of the detected beat frequency signal resulting from the interference of the two oscillations. Applications to magnetoacoustic phenomena are reported.

CW Transmission Spectrometer for Direct Detection of Nuclear Acoustic Resonance Utilizing Magnetic Field or Frequency Modulation

A continuous wave transmission spectrometer operating in the radio frequency range has been developed for direct detection of nuclear acoustic resonance (NAR) in solids. The inherent flexibility of a spectrometer of this type makes possible studies over a wider range of frequencies and ultrasonic powers than is attainable by the more conventional marginal oscillator acoustic spectrometer. With the transmission spectrometer one can observe both absorption and dispersion of acoustic waves, while with the marginal oscillator one is limited to NAR absorption only. An additional feature is the ease of operation of the transmission spectrometer as compared to the marginal oscillator technique. Both magnetic field and frequency modulation have been used with the transmission spectrometer. Certain advantages of frequency modulation, especially with respect to investigations in bulk conductors, are cited.

Elastic constants of tungsten between 4.2 and 77 K

The elastic constants of single‐crystal tungsten between 4.2 and 77 K have been measured utilizing a sampled continuous‐wave technique. The sensitivity of the present technique is such that the temperature dependence Cij(T) below 77 K is explicitly observed for the first time. A diffuse anomaly in CL(T), where CL = 1/2 (C11+C12)+C44, is observed in the temperature range 15–22 K.

Technique for the Study of Highly Attenuated Ultrasonic Waves in Gases

The sampled‐cw ultrasonic technique is applied to the study of highly attenuated waves in gases. Phase velocity and attenuation are obtained from a measurement of the reflection coefficient at the solid‐gas interface of a gas‐immersed crystal resonator.

Dispersion of Finite Amplitude Ultrasonic Waves in InSb

The dispersion of finite‐amplitude ultrasonic standing waves in single crystal InSb is reported. The observed dispersion was found to be proportional to the square of the voltage applied to the transducer, in agreement with the predictions of a simple model which is proposed to account for the effect. An enhanced sensitivity to the detection of harmonics of the ultrasonic wave results from the use of a standing wave technique.

Use of a distributed processing data‐acquisition system to control an acoustic spectrometer

A powerful data‐acquisition and processing system, which retains the low per‐station cost of a microcomputer‐based system while providing the resources for easy data reduction, is presented. The system uses microcomputer‐based real‐time data‐collection stations and a larger central computer for data‐reduction tasks. An application to the control of a continuous‐wave ultrasonic spectrometer is shown. In particular, the precision measurement of acoustic velocity as a function of temperature is presented for single‐crystal vanadium with a low concentration of interstitial hydrogen.