The Charles Stark Draper Laboratory, Inc.

Anthony Petrovich

Marc Steven Weinberg

Jonathan Jay Bernstein

Kaplesh Kumar

John R Williams

James Alan Bickford

Gregory A Kirkos

Tommy W Lee

Christopher E Dubé

Thomas E Shelvey

John M Barry

A sensor readout circuit which provides a frequency signal output including a phase detector circuit responsive to an output signal from a sensor and an input signal to the sensor and configured to detect the phase difference between the input signal and the output signal, and a drive circuit responsive to the phase detector circuit and configured to maintain a fixed phase difference between the input signal and the output signal.

Sensor readout circuit

A system and method for compensating for gradients in a dual cavity device such as but not limited to an accelerometer. A first source drives a first cavity at least two different modes, at least one mode varying with changes in cavity length. A second source drives a second cavity at least two different modes, at least one mode varying with changes in cavity length. A processor determines changes in cavity length as a function of both modes in both cavities to compensate for non-uniform behavior between the cavities.

Dual microwave cavity accelerometer

An improved microwave resonant cavity accelerometer includes a reentrant microwave resonant cavity. Preferably, the accelerometer includes first and second complementary reentrant microwave resonant cavities, each being characterized by a nominal resonant frequency. Each cavity includes a capacitive gap, and an inductive gap surrounding each capacitive gap. A coupler couples to each cavity a microwave signal substantially at the nominal resonant frequency of each cavity. In response to an acceleration force along a sensing axis, a proof mass positioned along the sensing axis differentially changes the dimensions of each cavity and establishes a resonant frequency for each cavity which varies as a function of the acceleration force. The accelerometer includes means for detecting electromagnetic energy in each cavity and determining the frequency of the detected energy. The shift in resonant frequency is used to determine the acceleration of the proof mass. By using-reentrant cavities, the sensitivity of the accelerometer to an acceleration of the proof mass is improved by a factor of about 100 for miniaturized proof masses. The accelerometer may be fabricated using micromachining techniques.

Reentrant microwave resonant cavity accelerometer

A micromechanical tuning fork gyroscope has an input axis out of the plane of the structure. In one embodiment, capacitor plates are provided in parallel strips beneath two apertured, planar proof masses suspended from a substrate by a support structure. The proof masses are paired and set in opposed vibrational motion by an electrostatic comb drive. In response to an input angular rate about the out-of-plane input axis, the proof masses translate with respect to the striped capacitors, thereby varying the capacitance between the capacitor strips and the proof masses as a function of the input rate. In another embodiment, proof mass combs of a comb drive are meshed between fixed drive combs which are electrically excited in pairs 180&deg; out of phase. As the proof masses translate in response to an angular input, the distance between the proof mass combs and the fixed combs varies, thereby varying the capacitance between the combs resulting in an unbalanced voltage on the proof masses that is detected as an indication of input rate. The out-of-plane tuning fork gyroscope can be combined with two in-plane tuning fork gyroscopes to provide a complete three-axis inertial measurement unit from a single wafer or on a single chip.

Microfabricated tuning fork gyroscope and associated three-axis inertial measurement system to sense out-of-plane rotation

A process for synthesizing advanced ceramics having superior microstructures and properties. Metal oxide powder particles are produced from solutions of soluble salts of the respective metals by a spray decomposition process. The as-formed powders are heated in an inert atmosphere at a temperature below their sintering temperature and for a time sufficient to cause the oxide powder particles to densify without sintering, and the densified powder is then compacted under high pressure and finally sintered at a temperature above that employed in the initial heating step. Products of this process possess superior magnetic and structural uniformity, excellent grain structure, and very high mechanical strength relative to ceramics prepared without using a heat treatment for densification prior to the compacting step.

Synthesis process for advanced ceramics

A resonantly vibrating or tuning fork rate sensor in which a quartz beam is instrumented with electrodes in first and second regions forming respective sense and drive electrodes wherein the piezoelectric resonance affect of the quartz material between the drive electrodes is used as a tuning element for an oscillator circuit. The electrodes are driven in a balanced voltage mode and sensed in a common mode rejection differential amplifier while leads running to the electrodes along the quartz beam are placed at positions of minimal field strength for improving the signal to noise ratio of the device. The rate sensor utilizes a multi-electrode pattern in order to make such lead placement possible. The sense pattern and drive pattern may be either in one orientation with the drive electrodes proximate to the body of the quartz resonator or in a second pattern with the sense electrodes proximate to the body. Both the drive electrodes and the sense electrodes operate on the piezoelectric principal, utilizing constriction to induce vibration from the drive electrodes and sensing the current generated from piezoelectric effect resulting from the vibrational compression which occurs out of the plane of vibration during inertial rate input. Alternatively, a capacitive electrode structure may be utilized as a pick-off.

Quartz resonant gyroscope or quartz resonant tuning fork gyroscope

A microwave resonator accelerometer including a microwave resonant cavity having a predetermined resonant frequency; the cavity including a flexible portion; a proof mass fixed to the flexible portion for changing the geometry and establishing a new resonant frequency of the cavity in response to an acceleration force on the proof mass; a microwave frequency signal at or approximately at the predetermined resonant frequency coupled to the cavity; and a discrimination circuit, responsive to the reflected microwave signal from the cavity, for discriminating a shift in the predetermined resonant frequency of the cavity to a new resonant frequency effected by the change in geometry of the cavity resulting from the acceleration force on the proof mass.

Microwave resonator accelerometer

A monolithic quartz resonator accelerometer including a monolithic quartz sensing structure with a frame, a proof mass support structure within the frame, and a resonator structure interconnecting the frame and the support structure. Further included are a proof mass fixed to the support structure, and electrodes on the resonator structure for driving the resonator at a vibration frequency which varies as a function of the acceleration of the proof mass.

Monolithic quartz resonator accelerometer

A flexure for an accelerometer includes an inner hub; an outer rim spaced from the inner hub; one of the hub and rim being mounted to the accelerometer body and the other to the proof mass of the accelerometer; at least three curved tapered beams extending between the rim and the hub with the widest beam portion proximate the rim, for flexibly supporting the proof mass and enabling relative rotational relief between the hub and rim for preventing nonlinear stretching of the beams.

Rotationally relieved flexure for accelerometer

Method and apparatus for forming rare-earth magnets and magnet precursors of fine particle sized metal alloy powders with a high degree of metal to metal intimacy and homogeneity in the particle to particle metal composition. Salts of the desired metals which may include or be selected from zirconium, samarium, iron, cobalt, copper, neodymium and boron with nitric acid in a water based solution are atomized through a nozzle, which may be ultrasonic, into fine mist droplets form metal oxide particles which condense through a heated, atmospheric environment furnace. The furnace temperature is in a range of 600.degree. to 1150.degree. C. and causes decompositon of the metal salts along with their oxidation, driving off the liquid and nitrogen components along with other carrier materials. A very fine sized powder, typically micron dimension size powder of metal oxides, in which each particle represents a homogeneous proportion of the desired metal components, is collected in the bottom of the furnace. These fine particle metal oxide powders are subsequently reduced to metal alloy powder particles of similar homogeneity in the metal proportions. The reduction reaction typically utilizes calcium hydride in a hydrogen atmosphere to convert the metal oxides to metal alloy particles. The metal alloy powder is then aligned, compacted, densified and magnetized to produce magnets of high magnetic performance.

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Tewksbury, MA, United States of America

Anthony Petrovich