Gravity Gradiometer Impedance Simulation Circuit
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Solution Overview
Problem
Existing gravity gradiometers face challenges in distinguishing spatial variations of the gravitational field from temporal fluctuations during airborne measurements, leading to noise interference due to unwanted accelerations from aircraft movements, which complicates the detection of gravity gradients.
Innovation Solution
A gravity gradiometer design incorporating a sensor mass with a pivotal coupling and an electronic circuit that simulates impedance to generate low thermal noise, allowing for fine-tuning of resonance behavior and damping of oscillations, thereby reducing noise interference and enhancing sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the gravity gradiometer is mounted in an aircraft for airborne measurements, then the measurement coverage and exploration capability are improved, but unwanted accelerations from aircraft movements introduce noise that swamps the actual gravity gradient signals
Solution Approach 1:
The patent uses the unwanted accelerations from aircraft movements as a beneficial reference signal. By measuring these accelerations with accelerometers and using them as reference inputs in the H∞ filter, the system converts the harmful noise into useful information for noise cancellation, allowing airborne measurements to achieve sufficient precision for exploring subsurface structures
Solution Approach 2:
The patent introduces accelerometers as intermediary devices that measure the aircraft movements and transmit this information to the signal processing system. The H∞ filter acts as an intermediary that processes both the gravity gradiometer signals and accelerometer reference signals, separating the desired gravity gradient information from the unwanted aircraft motion noise
2Measurement precision
If the sensor masses are operated at resonance frequency to increase sensitivity, then the detection capability is improved, but the bandwidth is reduced which limits spatial resolution
Solution Approach 1:
The patent implements active feedback control that dynamically adjusts the operating parameters of the sensor masses. The electronic circuitry provides real-time damping control and resonance frequency tuning, allowing the system to adaptively optimize the balance between sensitivity and bandwidth based on measurement conditions, rather than being fixed at a single operating point
3Measurement precision
If two sensor masses are used to eliminate unwanted accelerations, then the noise rejection is improved, but the device complexity and difficulty of balancing increase
Solution Approach 1:
The patent combines multiple sensor masses into a single integrated sensor assembly that functions as one unit. The sensor masses are mounted on a common support structure with shared pivot axes, and the electronic circuitry processes their signals together, reducing the overall system complexity while maintaining the noise rejection benefits of multiple masses
Solution Approach 2:
The patent uses identical or near-identical sensor mass designs that can be manufactured and calibrated to have matching dynamic properties. This copying approach simplifies the balancing process, as the sensor masses can be produced with consistent characteristics, reducing the complexity of individual mass adjustment while achieving the required noise cancellation performance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces thermal noise and improves the sensitivity of gravity gradient measurements by fine-tuning the resonance frequency and damping of sensor masses, enabling more accurate detection of spatial variations in the gravitational field.
Implementation Method 1
at least one sensor mass for movement in response to a gravity gradient
Implementation Method 2
an electronic circuit for simulating an impedance... whereby between the first amplifier input terminal and the amplifier output terminal in use the impedance of approximately is simulated
Implementation Method 3
the angular frequency of the rotation is chosen so that the sensor masses oscillate at or near resonance frequency
Implementation Method 4
for influencing the movement of the at least one sensor mass... damping of oscillations
Data Source
AI summary
The present invention provides a gravity gradiometer for measuring components of the gravity gradient tensor. The gravity gradiometer includes at least one sensor mass for movement in response to a gravity gradient and a sensor and actuator unit for generating an electrical signal in response to the movement of the at least one sensor mass and for influencing the movement of the at least one sensor mass. The gravity gradiometer also includes an electronic circuit for simulating an impedance. The electrical circuit is arranged for amplifying the electrical signal received from the sensor and actuator unit and for directing an actuating signal to the sensor and actuator unit. The electronic circuit includes a differential amplifiers having first and second amplifier input terminals and an amplifier output terminal and impedances Z1, Z2, Z3, at least one of the impedances have an imaginary impedance component.