Randall D. Peters

Linear rotary differential capacitance transducer

A bridge-type capacitance transducer is disclosed. The transducer utilizes a coaxially mounted circular stator and circular rotor to form the capacitance bridge. An excitation voltage is applied to the bridge. The output voltage of the bridge is conditioned by synchronous detection so as to yield a signal proportional to the degree of rotation of the rotor.

Ultrasonic Third‐Harmonic Generation in Strontium Titanate Single Crystals

The ultrasonic harmonic generation technique employing fundamental and third harmonic wave amplitude measurements has been used to study the nonlinear elastic properties of SrTiO3 single crystals. A complete set of nonlinearity parameters calculated from room temperature data support the values recently reported for the harmonic generation technique in which fundamental and second‐harmonic amplitudes were measured. The temperature variation of the third‐order elastic constant C111 in the range 103°–300°K was also measured by third‐harmonic generation methods and was found to agree well with the corresponding second‐harmonic result. The experimental technique in most cases involved overlapped pulses in the pulse‐echo wave train, and the results were found to agree well with measurements for the first pulse in the normal pulse‐echo pattern.

The not-so-simple harmonic oscillator

A model inspired by the behavior of a simple harmonic oscillator subject to dry sliding friction is applied to the damping of a variety of mechanical oscillators. In contrast to the conventional model of damping in mechanical systems, the new model predicts a logarithmic decrement of the motion which is quadratic in the period. This prediction agrees well with the observed period dependence of the long-period physical pendulum which was the primary focus of this investigation.

Symmetric differential capacitive pressure sensor

Differential capacitive sensors are common to pressure gauges. Previous sensors of the bridge type have utilized only two variable (active) components, resulting in a half‐bridge electrical equivalent circuit. There are numerous advantages of a symmetric full bridge, using four active components. The symmetry improves linearity and increases signal to noise ratio, especially when supported by electronics based on synchronous detection. Another advantage of symmetry is invariance to scaling, through immunity to stray capacitance. This feature is especially important in relationship to the current trend toward micro‐electro‐mechanical systems. A crude, inexpensive, macroscopic prototype of the present design was built with attention to high sensitivity. Constructed with a thin aluminized Mylar diaphragm, this device can readily resolve pressure changes smaller than 10−2 Pa.

THIRD HARMONIC OF AN INITIALLY SINUSOIDAL ULTRASONIC WAVE IN COPPER

The amplitude of the third harmonic of an initially sinusoidal ultrasonic wave is measured in the [100] direction in copper, both directly and by a pulse overlap technique. The value of the third‐order elastic constant C111=−16 × 1012 dyn/cm2 is obtained from measurements of third harmonic amplitudes of the order of 10−3 A. The contribution of the fourth‐order constant C1111 to these amplitudes appears to be negligible.

Nanoposition sensors with superior linear response to position and unlimited travel ranges

With the advancement in nanotechnology, the ability of positioning/measuring at subnanometer scale has been one of the most critical issues for the nanofabrication industry and researchers using scanning probe microscopy. Commercial nanopositioners have achieved direct measurements at the scale of 0.01 nm with capacitive sensing metrology. However, the commercial sensors have small dynamic ranges (up to only a few hundred micrometers) and are relatively large in size (centimeters in the transverse directions to the motion), which is necessary for healthy signal detections but making it difficult to use on smaller devices. This limits applications in which large materials (on the scale of centimeters or greater) are handled with needs of subnanometer resolutions. What has been done in the past is to combine the fine and coarse translation stages with different dynamic ranges to simultaneously achieve long travel range and high spatial resolution. In this paper, we present a novel capacitive position sensing metrology with ultrawide dynamic range from subnanometer to literally any practically desired length for a translation stage. This sensor will greatly simplify the task and enhance the performance of direct metrology in a hybrid translational stage covering translation tasks from subnanometer to centimeters.

Capacitive angle sensor with infinite range

A variant of the linear rotary differential capacitance transducer has been used to build an angle sensor which is essentially linear over an infinite range, while maintaining microradian resolution. This capability is realized by ganging two of the transducers on a common axle, in quadrature. By sequentially monitoring the output from the pair of transducers with a personal computer, estimates of axle position are obtained through a switching algorithm.

Mechanically adjustable balance and sensitive tilt meter

A torsion balance has been modified by clamping the fibre, under tension, at both the top and the bottom of the instrument housing. Operating with the centre of mass of the boom displaced from the near vertical fibre, the instrument is influenced by the Earths gravitational field as well as by the shear modulus of the fibre. This causes the restoring constant of the balance to depend on the angle of tilt between the fibre direction and local vertical. The contribution from the Earths field either adds to or subtracts from that of the shear modulus, according to the direction of tilt. The result is an instrument of variable sensitivity when used as a force-measuring device. It can also be configured to function as a highly sensitive tilt meter.

Variable Gap Capacitive Detector for the Measurement of Ultrasonic Displacement Amplitudes in Solids

A variable gap capacitive detector has been developed for displacement amplitude measurements of longitudinal ultrasonic waves in the frequency range 5 to 100 MHz. The gap spacing is controlled by differential gas pressure. With this device it is possible to maintain a constant detector capacitance for measurements of the temperature dependence of the third order elastic constants. This improves the precision of the measurements considerably.

Student-friendly precision pendulum

This “simple” Kater pendulum permits students to easily measure Earth’s gravitational field, g≈9.8 m/s2, to a few parts in 10,000. Although an inexpensive commercial instrument will be soon available for purchase, enterprising students are capable of building their own pendulum using the information provided.