Other

California Institute of Technology

Siimpel Corporation

Thomas R Vanzandt

Stephen J Manion

Roman Gutierrez

Robert J Calvet

William J Kaiser

Thomas W Kenny

Christopher I Walker

Edouard G H Schmidtlin

David Crisp

A fiber optic collimator comprises an optical fiber with an angled end face, a ferrule and a plano-convex lens. An end portion of the optical fiber is inserted in the ferrule. The plano-convex lens collimates a beam of light from the optical fiber.

Fiber optic collimator and collimator array

The invention concerns methods and apparatus for improving the performance of a force-balance accelerometer based upon a conventional, single-coil, velocity geophone. Specifically, the operating temperature range is increased through the use of both a temperature-compensating reference impedance, and a new electronic circuit architecture. Two specific types of temperature-compensating reference impedances are disclosed. One is a pure DC-resistance, with the temperature coefficient of the DC resistance matching that of a single coil of a conventional geophone. A second reference impedance adds a series reactance which closely matches the ratio of total impedance to DC-resistance, and the temperature coefficient of this ratio, with that of the geophone coil. A method is also described which provides for decreased magnitude of a reference impedance required in an accelerometer. This allows for a significant reduction in the physical size of the reference impedance. The reduction in size reduces the physical size of the impedance and the sensitivity of the accelerometer to external time-varying magnetic fields.

Method and apparatus for improving performance of a force balance accelerometer based on a single-coil velocity geophone

Force-balance feedback geophone apparatus and methods for characterization of the geophone apparatus. Control inputs ( ) provide for switching ( ) of a force-balance feedback geophone between operational states, thereby allowing for in situ determination of geophone characteristics. Feedback circuit modification provides for increased bandwidth and a series RC circuit in the reference resistance provides for increased damping without significantly affecting low frequency performance.

Method and apparatus for controlling damping and in situ determination of frequency response for high bandwidth force-balance single-coil geophone

The invention converts a conventional velocity geophone to a force-balance accelerometer. A single, spring supported geophone coil, in conjunction with a permanent magnet assembly fixed to the geophone housing, is used as both an electromagnetic velocity sensor and a force actuator. An electronic circuit is used to implement a force-balance feedback control system. The electromotive force associated with the velocity of the coil is detected and used as an input to the feedback control system. The output of the control system is applied to the same coil in such a manner as to provide negative feedback. In the presence of accelerations, the coil velocity with respect to the geophone housing is reduced essentially to zero. Thus, the force related to the external acceleration acting on the coil-mass, is balanced by the applied force. Specifically, the current applied by the control system to the same coil is proportional to the acceleration of the housing.

Single-coil force balance velocity geophone

An uncoated interdigitated transducer is cooled from a temperature above the dew point to a temperature below the dew point, while a parameter of a signal of the transducer is measured. The reduction in temperature causes a monotonic change in transducer signal because that signal is sensitive primarily to the water loading of the transducer surface as water forms on that surface due to the reduction in temperature. As the dew point is approached with temperature reduction, the slope of the curve of transducer signal with respect to temperature, remains relatively constant. However, as the dew point is reached the slope of that curve increases and because of changes in the structure of the water layer on the surface of the transducer, at the dew point the transducer responds with a clear shift in the rate at which the transducer signal changes. The temperature at which the second derivative of signal vs. temperature peaks can be readily used to identify with extreme accuracy, the precise dew point. The measurement technique employed by the present invention is relatively immune to surface contamination which remains significantly unchanged during the brief measurement period.

Growing community of inventors

Redondo Beach, CA, United States of America

Thomas R Vanzandt