Examples are directed toward systems and methods relating to security screening. For example, a screening system includes a sensor array to sense a gravitational field caused by an item, and a conveyor to convey the item through sensing positions for scanning by the sensor array. A controller acquires weight measurement information from sensor elements, and gravitational measurement information from the sensor array. The conveyor incrementally advances the item through additional sensing positions to acquire weight measurement information and gravitational measurement information. The controller performs tomographic reconstruction to generate a tomographic image of the item, using a generated weight map as a static weight input vector and using a generated mass map as a static mass input vector for the tomographic reconstruction.

An accelerometer/gravitometer based on coherent oscillatory matterwaves (COMW). The accelerometer includes a pair of COMW generator systems, each with an oscillator and a respective resonator to stabilize the oscillator output. One of the resonators can be aligned with acceleration, while the other is transverse to the acceleration. The COMW generator outputs can be compared to derive a measurement of acceleration.

An accelerometer/gravitometer based on coherent oscillatory matterwaves (COMW). The accelerometer includes a pair of COMW generator systems, each with an oscillator and a respective resonator to stabilize the oscillator output. One of the resonators can be aligned with acceleration, while the other is transverse to the acceleration. The COMW generator outputs can be compared to derive a measurement of acceleration.

A closed-loop coherent oscillator matterwave (COMW) system generates a COMW. Atoms tunnel into a COMW oscillator to populate the COMW generated and emitted by the oscillator. A detuned light-field-based COMW splitter divides the emitted COMW between an output COMW and a regulator COMW. A COMW resonator, including detuned light-field mirrors, receives the regulator COMW and returns a feedback COMW. A COMW sensor evaluates the intensity of the feedback COMW. A controller adjusts the oscillator based on the evaluation to optimize the COMW output of the system.

A gravimeter probe includes a spring structure, a proof mass, movable comb fingers, fixed comb fingers, and an outer frame. A fixed end of the spring structure is arranged on the outer frame and a free end thereof is connected to the proof mass. The movable comb fingers are arranged on upper and lower surfaces of the proof mass, and the fixed comb fingers are correspondingly arranged on the outer frame. Each of the movable comb fingers and the fixed comb fingers has a special-shaped comb finger structure. The special-shaped comb finger structure includes a comb finger bottom portion and a comb finger top portion, and the width of the comb finger bottom portion is smaller than the width of the comb finger top portion.

A gravimeter probe includes a spring structure, a proof mass, movable comb fingers, fixed comb fingers, and an outer frame. A fixed end of the spring structure is arranged on the outer frame and a free end thereof is connected to the proof mass. The movable comb fingers are arranged on upper and lower surfaces of the proof mass, and the fixed comb fingers are correspondingly arranged on the outer frame. Each of the movable comb fingers and the fixed comb fingers has a special-shaped comb finger structure. The special-shaped comb finger structure includes a comb finger bottom portion and a comb finger top portion, and the width of the comb finger bottom portion is smaller than the width of the comb finger top portion.

A capacitance sensing assembly is provided. The capacitance sensing assembly includes an op-amp arranged with four complex impedance circuits and a sensing capacitor connected to the fourth complex impedance circuit and ground; or to the non-inverting input of the op-amp, the fourth complex impedance circuit, ground and the second terminal of the fourth complex impedance circuit, wherein the fourth complex impedance circuit is connected in parallel to the sensing capacitor. The complex impedance circuits are configured to increase a gradient of a phase to frequency response curve of the capacitance sensing assembly relative to that of an all-pass filter with a second electrode of a capacitor connected to the non-inverting input of the op-amp and the ground without the fourth complex impedance circuit.

A capacitance sensing assembly is provided. The capacitance sensing assembly includes an op-amp arranged with four complex impedance circuits and a sensing capacitor connected to the fourth complex impedance circuit and ground; or to the non-inverting input of the op-amp, the fourth complex impedance circuit, ground and the second terminal of the fourth complex impedance circuit, wherein the fourth complex impedance circuit is connected in parallel to the sensing capacitor. The complex impedance circuits are configured to increase a gradient of a phase to frequency response curve of the capacitance sensing assembly relative to that of an all-pass filter with a second electrode of a capacitor connected to the non-inverting input of the op-amp and the ground without the fourth complex impedance circuit.

The invention discloses a superconducting gravity gradiometer and a sensitivity improvement method thereof including a pair of superconducting test masses, a pair of negative-stiffness superconducting coils, a pair of positive-stiffness superconducting coils, and a superconducting circuit coupling the test masses into two-degree-of-freedom superconducting magnetic spring oscillators. Superconducting wires are used to connect the negative-stiffness superconducting coils in series to form a superconducting loop, the differential mode stiffness of the two-degree-of-freedom superconducting magnetic spring oscillators is reduced, and the ratio of the common mode stiffness to the differential mode stiffness is increased. When using the method of the invention to configure the magnetic spring oscillator of a superconducting gravity gradiometer, when configuring a vertical diagonal component superconducting gravity gradiometer with a full magnetic suspension for the test mass, the sensitivity of gradient measurement is significantly improved.

The invention discloses a superconducting gravity gradiometer and a sensitivity improvement method thereof including a pair of superconducting test masses, a pair of negative-stiffness superconducting coils, a pair of positive-stiffness superconducting coils, and a superconducting circuit coupling the test masses into two-degree-of-freedom superconducting magnetic spring oscillators. Superconducting wires are used to connect the negative-stiffness superconducting coils in series to form a superconducting loop, the differential mode stiffness of the two-degree-of-freedom superconducting magnetic spring oscillators is reduced, and the ratio of the common mode stiffness to the differential mode stiffness is increased. When using the method of the invention to configure the magnetic spring oscillator of a superconducting gravity gradiometer, when configuring a vertical diagonal component superconducting gravity gradiometer with a full magnetic suspension for the test mass, the sensitivity of gradient measurement is significantly improved.