Multiple dipole line trap system

The present disclosure includes dipole line trap system, a method for tuning a natural frequency of a dipole line trap system, and seismometer. One embodiment of the dipole line trap system may comprise a first axis unit. The first axis unit may comprise a first group of at least three cylindrical diametric magnets mounted in parallel around a first open region, and a first diamagnetic object in the first open region. In some embodiments, the first axis unit may comprise four cylindrical diametric magnets mounted in parallel around the first open region. In some embodiments, the first axis unit may have a natural frequency of less than 1 Hz.

BACKGROUND

The present disclosure relates to sensors, and more specifically, to sensors comprising multiple dipole line trap systems.

Inertial sensors generally refer to a type of sensor that measures and reports a specific force, angular rate, or an orientation of an object. Inertial sensors typically consist of a combination of accelerometers, gyroscopes, and/or magnetometers.

Tiltmeters generally refer to a type of sensor that measures small changes from the vertical plane. Precision tiltmeters are useful for detecting sagging and/or oscillations in structures or of the ground. Common applications for such precision tiltmeters include monitoring the ground tilt at fracking sites or other regions with changing underground pressures, and monitoring motion of underground magma or gas that can deform the surface of a volcano prior to an eruption.

Seismometers generally refer to a type of sensor designed to measure vibrations, such as those from earthquakes, volcanic activities, landslides activities, and civic activities. Seismometers may be used for tsunami monitoring, structural health monitoring, seismic alarms, or to monitor man-made activities such as explosions. Existing seismometers rely on a suspended oscillator to detect the vibrations. This includes physical pendula, spring-mass systems, cantilevers, and geophones.

Infrasound generally refers to vibrations that occur a frequency less than audible frequency e.g., less than about 20 Hz. Infrasound detectors, in turn, are sensors designed to detect and measure infrasound. Infrasound detectors may be used to monitor: (i) natural events, such as thunder, wind, waves, waterfalls, aurora, large meteors, upper atmosphere disturbances, (ii) natural disasters, such as tremors, earthquakes, landslides, avalanches, fracturing icebergs, tornados, volcanic eruptions, and tsunamis; (iii) civil activity, such as bridge and building movements and wind farms; (iv) human activities, such as traffic, aircraft, explosions, trains, and fireworks; (5) animal activities, such as motion and vocalization from elephants and other large mammals or large herds of small animals, (6) surveillance, such as the detection of missile launches; and (7) engineering, such as monitoring machine operations.

Cylindrical diametric magnets (CDMs) are a type of cylindrical magnet with magnetization along its diameter. The article by O. Gunawan, Y. Virgus, and K. Fai Tai entitledA parallel dipole line systemin Appl. Phys. Lett. 106, 062407 (2015) presents a study of a parallel linear distribution of transverse dipole system, which can be realized using a pair of cylindrical diametric magnets. The system can serve as a trap for a cylindrical diamagnetic object, can produce a one-dimensional camelback potential profile at its center plane, can yield a technique for measuring magnetic susceptibility of the trapped object, and can serve as a system to implement highly sensitive Hall measurement utilizing rotating parallel dipole line system and lock-in detection.

SUMMARY

According to embodiments of the present disclosure, a dipole line trap system comprising a first axis unit. The first axis unit may comprise a first group of at least three cylindrical diametric magnets mounted in parallel around a first open region, and a first diamagnetic object in the first open region. In some embodiments, the first axis unit may comprise four cylindrical diametric magnets mounted in parallel around the first open region. In some embodiments, the first axis unit may have a natural frequency of less than 1 Hz.

According to embodiments of the present disclosure, a method for tuning a natural frequency of a dipole line trap system. The dipole line trap system may comprise at least three diametrically magnetized cylindrical magnets mounted in parallel around an open region and having spacings therebetween; and a diamagnetic object in the open region. The method for tuning may comprise changing the spacings between the at least three diametrically magnetized cylindrical magnets relative to the other diametrically magnetized cylindrical magnets. In some embodiments, the at least three diametrically magnetized cylindrical magnets may include a magnetization angle, and the method of tuning may further comprise changing one or more of the magnetization angles relative to the other magnetization angles.

According to embodiments of the present disclosure, a seismometer comprising at least two cylindrical diametric magnets, and a diamagnetic rod levitated by the two cylindrical diametric magnets. Some embodiments may further comprise an electrode adapted to control a position of the diamagnetic rod using electrostatic forces. Some embodiments may further comprise an electronics system adapted to provide negative feedback to bias the diamagnetic rod toward a center position.

DETAILED DESCRIPTION

Aspects of the present disclosure relate to sensors; more particular aspects relate to sensors comprising multiple dipole line trap systems. While the present disclosure is not necessarily limited to such applications, various aspects of the disclosure may be appreciated through a discussion of various examples using this context.

Many remote sensing systems and devices are enhanced by sensitivity to low frequencies e.g., less than about 20 Hz. For example, in teleseismic monitoring applications, sensitivity to the low frequency components of earthquake oscillations may enhance detection range as the low frequency oscillations of earthquakes typically travel the greatest distances. Similarly, sensitivity to low frequencies may help for structural monitoring applications as the resonant motions of large buildings, bridges, and ships typically occur at low frequencies.

Accordingly, one aspect of the disclosure is a parallel dipole line (PDL) trap system comprising multiple (“N”) CDMs surrounding a diamagnetic object, where “N” is two or more. Specific embodiments with N=3, 4, 5, and 6 are described in more detail below. Laboratory experiments have shown that such PDL trap systems may be configured to have a very low natural frequency to about 0.1 Hz, and as a result, may be well adapted for use as a low frequency sensor. Systems comprising PDL trap systems consistent with some embodiments may be desirable for use as inertial sensors, tiltmeters, and seismometers used to measure acceleration, velocity, infrasound, and/or displacement due to earthquakes, ground movement, and/or structural loading. Additionally, systems comprising PDL trap systems may be desirable to measure and/or infer other physical properties of systems, such as a pressure or fluid viscosity.

Another aspect of the disclosure is a method of tuning the natural frequency of a PDL trap system and/or the camelback-shaped magnetic potential of the PDL trap system. This method may include controlling the dimensions of the PDL trap system, such as the rad(ii) of the CDMs and the separation(s) of the CDMs that comprise the PDL trap system. Yet another aspect of the disclosure is a method for tuning of the sensitivity of PDL trap system, such that the trapped inertial mass (e.g., a diametric object) moves a greater or lesser distance for a given input (e.g., a tilt angle).

One feature and advantage of some embodiments is that they may neither use nor require an attachment between the inertial mass and a housing. This feature and advantage may be desirable because the attachment(s) used by many prior art devices will restrict relative motion between the inertial mass and the housing, preventing extremely sensitive detection of some motions. Those skilled in the art will appreciate that this feature and advantage may be particularly beneficial as applied to seismometers, infrasound detectors, and gravity field strength detectors.

Another feature and advantage of some embodiments is that they may contain and levitate the inertial mass regardless of the orientation/rotation of the PDL trap system, thereby extending the versatility of the resulting sensors. Those skilled in the art will appreciate that this feature and advantage may be beneficial in environments and applications where the movement and/or orientation of the resulting sensor(s) cannot be limited to a single plane, such as inertial sensors used in certain transportation systems. Some embodiments may further enhance containment of the inertial mass by adding a non-magnetic wall or window at the ends of the respective systems.

One specific embodiment of the disclosure is a broadband seismometer. For seismic monitoring applications, a broadband seismometer having a very low natural frequency (e.g., down to 0.01 Hz) is very desirable to detect long distance seismic events (e.g., at a distance greater than about 1000 km). The information coming from a network of such broadband seismometers may be used to determine the characteristics of the earthquake, such as its epicenter, magnitude, and focal mechanism. This embodiment may comprise one to three axis units. Each axis unit, in turn, may comprise two or more CDMs that cooperate to form a levitation trap for a diamagnetic object, such as a graphite cylinder. Each axis unit may also be positioned at a tilted angle to a horizontal plane. By combining outputs from the tilted axis units, a Cartesian north-west-vertical (seeFIG.16) motion can be calculated. This embodiment may operate in two ways: (i) a passive way, in which the seismic vibration may be detected by measuring the position of the levitating diamagnetic object; and (ii) an active way, in which electrostatic actuators may be used to keep the diamagnetic object in the center of the sensor, and in which seismic vibration is detected as the voltage bias needed to stabilize the diamagnetic object.

A second specific embodiment of a broadband seismometer may comprise a set of two to four CDMs arranged to form a PDL trap system, and a diamagnetic object (such as a graphite cylinder) at the center of the trap. The CDMs may be active or passive depending whether negative feedback is desired to position the diamagnetic object in the center of the PDL trap system. The position of the diamagnetic object may be detected using a split photodetector. A set of capacitive electrodes surrounding the diamagnetic object may be used to apply electrostatic force to provide the negative feedback actuation force.

Turning now to the figures,FIG.1is a perspective view of a system100consisting of two CDMs aligned in parallel. This system100produces the camelback magnetic potential110depicted inFIG.1.

FIG.2is a side view of a triple dipole line (TDL) magnetic trap system200, consistent with some embodiments. The TDL system200inFIG.2comprises three CDMs205held in parallel and in an equilateral triangle configuration by a rigid housing (not shown) with transverse magnetization angles. The appropriate transverse magnetization angles may depend on the vertical gap of the system200. As depicted, the transverse magnetization angles for example system200are at 60, 180, and 300 degrees from the horizontal. This TDL system200may further comprise a diamagnetic material210, such as graphite cylinder, in a gap215between the CDMs205. The resulting azimuthal magnetic configuration may exhibit an equilibrium state such that the CDMs205may relax and stick together within a fixture (not shown. SeeFIG.15for one suitable embodiment) without needing additional physical supports.

One feature and advantage of the TDL system200inFIG.2is that, for the right combination of magnetization, magnetic susceptibility, and system dimensions, the diamagnetic material210may levitate against the force of gravity in the central gap215, and this levitation may be independent of the exact orientation of the three CDMs205relative to vertical as long as their respective cylindrical axes are approximately horizontal (e.g., so the diamagnetic cylinder210does not fall out of the ends of the gap215). That is, the diamagnetic material210may levitate in the gap215even if the system200is not exactly horizontal.

The TDL trap system200inFIG.2may have two parameters that can be tuned to obtain a desired natural frequency: (i) a vertical gap (gv) distance shown inFIG.2, and (ii) a horizontal gap (gh) distance shown inFIG.2.FIG.3is a contour plot300showing the natural frequency of the TDL system200ofFIG.2as a function of the vertical gap (gv) and the horizontal gap (gh) for a TDL system using standard CDM magnets with magnetization of M=1.1×106A/m and magnet radius of R=3.18 mm. and length L=25.4 mm. As can be seen inFIG.3, a high natural frequency may be obtained when the horizontal gap is small and the vertical gap is large, and a low natural frequency may be obtained when the horizontal gap is large and the vertical gap is small. The bottom-right region310inFIG.3corresponds to an unstable equilibrium of the diamagnetic material210e.g., when it falls out of the TDL trap system200. As can be seen inFIG.3, a natural frequency as low as 0.05 Hz can be achieved.

The oscillation frequency may be further lowered in some embodiments by adding another magnet to form quadruple dipole line (QDL) system.FIG.4Ashows a side view of a QDL magnetic trap system400, consistent with some embodiments. The QDL system400embodiment inFIG.4Acomprises four CDMs405held in parallel and in a trapezoid configuration by a rigid housing (not shown), and a cylinder of diamagnetic cylinder410trapped in a gap415between the CDMs405. As shown inFIG.4A, each CDM405in this embodiment may have its magnetization angle tilted with respect to the magnetization angle of the other CDMs405such that the system400forms a stable configuration, e.g., at angle θ1and θ2(e.g., as shown, at approximately 60, 120, 240, and 300 degrees from the horizontal). The total potential energy (per unit length) of the resulting QDL system400may be calculated as:

The resulting magnetic field of the QDL system400may be a superposition of magnetic fields from the four magnetic sources (i.e., the four CDMs405) with magnetization M oriented at angles θ1and θ2as shown inFIG.4A. These parameters may be tuned in some embodiments to trap the diamagnetic cylinder410such that it is equidistant from the two pairs of CDMs405in the x-direction (i.e., horizontal direction perpendicular to the cylinders of the CDMs405) and slightly below center of the two pairs of upper and lower CDMs405in the y-direction. That is, for a symmetric configuration of a QDL system400, the x-direction magnetizations of the upper CDMs405may be opposite to those of the lower CDMs405. In the y-direction, however, the restoring force (or spring constant) of the system400may not be canceled out completely (i.e., such that the diamagnetic cylinder410is exactly in the center of the system400) due to gravity forces.

One feature and advantage of the QDL system400embodiment inFIG.4Ais that there may be three adjustable gap parameters: (i) a lower horizontal gap gh1; (ii) a upper horizontal gap gh2; and (iii) and a vertical gap gv. These gap parameters may be tuned to achieve a very low natural oscillation frequency down to approximately 0.01 Hz. These gap parameters may also be tuned to achieve a desired stiffness coefficient of the camelback magnetic potential of the system400. This stiffness coefficient, in turn, may affect how far the diamagnetic cylinder410moves in response to a given input i.e., the sensitivity of the QDL system400to motion.

FIG.4Bis a plot450illustrating a natural frequency of the QDL system400inFIG.4Awith respect to gvand ga1. The plot550was created using system parameters of M=1.1×106A/m for a neodymium alloy (e.g., NdFeB), magnet sizes radius R=3.15 mm and length L=8R, and separations gv=1 mm and ga2=1 mm. The darkest region495in that plot450corresponds to an unstable equilibrium of the diamagnetic cylinder410(e.g., when the diamagnetic cylinder410falls out of the QDL trap system400). From this plot450, the gap parameters that can achieve a desired natural frequency may be determined. As can seen inFIG.4B, a natural frequency as low as about 0.01 Hz may be achieved.

FIG.5Ais a plot500showing experimental data of the QDL trap system400inFIG.4Awith varying vertical gap gv. As can be seen inFIG.5A, reducing the vertical gap gvcan lower the resulting natural frequency significantly. This effect may occur because the magnetic field from the top pair of CDMs405pushes down on the magnetic field from the bottom pair of CDMs, causing the camel back potential from the bottom pair of CDMs to flatten in the middle. Because the frequency of oscillation of the levitating diamagnetic cylinder is proportional to the square root of second spatial derivative of this potential, the flatter potential produces a lower oscillation frequency.

FIG.5Bis a plot550comparing the natural frequencies of a two-magnet PDL ofFIG.1to the four-magnet QDL400inFIG.4A. This plot550was created using the parameters of M=1.1×106Am2for a neodymium alloys (e.g., NdFeB), magnet sizes R=3.15 mm and L=8R, and separations gv=1 mm and ga2=1 mm. The oscillation frequencies of a graphite cylinder410are given in Hertz. As can be seen inFIG.5B, the natural frequency for the QDL system400may be made significantly lower than even the theoretical limit of two-magnet system ofFIG.2. This lowering of the natural frequency, in turn, may allow for detection of extremely-low frequency motion such as tele-seismic signal, infrasound, etc.

FIG.6is a side view of a higher order multiple dipole line trap system600with five CDM magnets (N=5), consistent with some embodiments.FIG.7is a side view of a higher order multiple dipole line trap system with six CDM magnets (N=6), consistent with some embodiments. In bothFIGS.5and6, suitable transverse magnetization angles are also depicted.

FIGS.8A and8Bare front and side views of an illustrative first inertial sensor800, consistent with some embodiments. The first inertial sensor800may comprise four CDM magnets805and a diamagnetic cylinder810. The first sensor800may detect a position of the diamagnetic cylinder810using a position detector840. The position detector840may comprise a light source842located above the diamagnetic cylinder810and a split photodetector844located below the diamagnetic cylinder810.

In operation, the light source842may comprise a small LED that provides constant illumination. The two parts of the split photodetectors844may independently measure a current level of illumination that it receives from the light source842(i.e., a maximum amount of light minus an amount of light currently blocked by the diamagnetic cylinder810). The position of the diamagnetic cylinder810can thus be determined from the difference in output from the two photodetectors844e.g., by using a differential amplifier848to convert the difference in output of the split photodetectors844into a voltage signal proportional the difference in output.

FIGS.9A and9Bare front and side views of an illustrative second inertial sensor900, consistent with some embodiments and particularly desirable for use as an active seismometer. This second inertial sensor900may comprise three CDM magnets910arranged in a plane and a levitating diamagnetic object (test mass)910. The levitating diamagnetic mass910, in turn, may comprise a diamagnetic slab912suspended from or supported by two diamagnetic cylinders914. The test mass910(i.e., dielectric slab912and the diamagnetic cylinders914) may be levitated and trapped at a center position of the sensor900by the camelback potential of the CDM magnets905. The second inertial sensor900may further have a light source942and a split photo detector944, which may generate an output proportional to a current position of the test mass910, in a manner similar to the light source842and the split photodetector844discussed in more detail with reference toFIGS.8A-8B.

The embodiment inFIGS.9A-9B, however, may further comprise an electronics control module960adapted to generate an electric potential in metal electrodes985. These metal electrodes985may also pull the test mass910toward the center position of the sensor900when energized by a voltage from the electronics control module960. The control module960in this embodiment may include a proportional-integral-differential (PID) module that aims to stabilize the test mass910in the center of the system900(e.g., if the test mass910moves to the left, the right electrode985will be energized to pull the test mass910back to the center position). In this way, in the presence of a seismic signal or vibration, the response of the PID controller may act as an active negative (i.e., in the opposite direction of the seismic acceleration) feedback force, in addition to the passive feedback from the CDM magnets910. Moreover, the response of the PID controller (i.e., its voltage output) will be proportional to a seismic acceleration signal. Accordingly, one feature and advantage of the second sensor900is that it may generate outputs indicative of both a current position and an acceleration of the test mass910.

Another feature and advantage of the second sensor900embodiment is that the large size of the dielectric slab912may allow for either smaller voltage or stronger force for negative feedback. That is, if one of the electrodes985is energized by a voltage V, the dielectric slab will be pulled by a force:

F=12⁢V2⁢dC/dx=12⁢(εr-1)⁢ε0⁢wd⁢V2
where w is the width of the electrode and εris the relative dielectric constant of the dielectric slab, ε0is the vacuum dielectric permittivity and d is the distance between the top and bottom electrode. In this way, the second sensor900embodiment may allow for use in applications where the sensor will experience strong vibrations.

FIGS.10A,10B, and10Care top, side, and front views of an illustrative third sensor1000, consistent with some embodiments. This sensor1000may also be particularly desirable for use as a seismometer. InFIGS.10A-10C, the sensor1000may comprise two dipole line magnets1005that serve as a trap, a diamagnetic cylinder (e.g., graphite)1010; a split photo detector1044on a bottom side; a light source1042on a top side adapted to illuminate the diamagnetic cylinder1010; a glass cover1070with Transparent Conducting Oxide (TCO) surface electrodes1072on a bottom surface, and an electronics module1060to both detect the position of the diamagnetic cylinder1010and to energize the electrodes1072.

In operation, the glass cover1070may have two segments of the TCO surface electrodes1072on the left and right. The two segments may act as electrodes of a circuit, with the CDM magnets1005serving as ground. If one of the surface electrodes1072is energized with a high voltage, it will pull the diamagnetic cylinder1010towards it via electrostatic interaction. The surface electrodes1072may be controlled by the electronics module1060. The electronics module1060may include a PID component adapted such that its resulting output voltage will tend to hold the diamagnetic cylinder1010in the center of the sensor1000. In this way, the surface electrodes1072and the electronics module may cooperate to create negative feedback. Moreover, when used in active seismometer applications, the voltage applied to the surface electrodes1072may be proportional to the ground acceleration, which becomes a first seismic signal output. A position of the diamagnetic cylinder1010is detected by the split photodetector1044, which becomes a second seismic signal output. In this way, the third sensor1000may detect both position and acceleration.

FIGS.11A and11Bare front and side views, andFIG.11Cis a partial perspective view, of an illustrative fourth sensor1100, consistent with some embodiments. The sensor1100may comprise four CDM magnets1105; a diamagnetic cylinder (e.g., graphite)1110; a split photo detector1144; a light source1142; four pairs of surface electrodes1170covering the CDM magnets1105; and an electronics module1160to detect the position and to energize the electrodes. As described in more detail with reference toFIG.4A, this embodiment may be desirable as the four PDL magnets1105may allow for a lower natural frequency, as compared to the embodiment inFIGS.10A and10B, due to interaction of the top and bottom PDL magnets1105. This, in turn, may be beneficial for use as a seismometer adapted to operate at a very low frequency.

The surface electrodes1170inFIGS.11A-11Cmay be made of thin film metal or conducting tape, and may be cast onto the respective surfaces of the CDM magnets1105. In some embodiments, there may be two sets of surface electrodes (1170-1and1170-2) for the opposite side of the diamagnetic cylinder1110. For each set of surface electrodes1170, there may be a respective ground electrode and bias electrode. Similar to the configuration described with reference toFIGS.9A-9B and10A-10C, an active seismometer application may be implemented using negative feedback and the PID controller of the electronics module1060. The voltage applied to the surface electrodes1170by the PID controller may be proportional to the ground acceleration which becomes the seismic signal output.

InFIGS.11A-11C, the CDM magnets1105may all be aligned to the horizontal plane. Thus, they may be adapted to measure horizontal motions (e.g., north and east axis of seismometer). To further detect vertical motion, other embodiments may tilt the system as shown inFIGS.12and13A-13Cwhile applying a voltage bias to one of the electrodes to pull the diamagnetic cylinder towards it so that the diamagnetic cylinder remains at the center. In this way, the sensor may also be sensitive to the vertical motion.

FIG.12is a side view of an active sensor1200comprising four CDM magnets in a tilted configuration, consistent with some embodiments. In the basic magnetic trap configurations outlined with reference toFIGS.1-11C, the CDM magnets are aligned to the horizontal plane, thus are optimized to measure horizontal motions (e.g., north and east axis of seismometer). To detect the vertical motion, some embodiments may tilt the axis units as shown inFIG.12by an angle θ to the horizontal. Some embodiments may additionally apply a voltage bias to one of the surface electrodes to pull the diamagnetic object toward it so the diamagnetic object remains at the center of the system. In this way the sensor1200is also sensitive to the vertical motion.

FIGS.13A-13Care top and side views of another sensor1300that is sensitive to the vertical motion, consistent with some embodiments. The sensor1300consists of a pair of dipole line magnets1305with an increasing gap from g1to g2. Sensor1300may also have a light source1342to illuminate a diamagnetic object1310, a glass cover1380to contain the levitating diamagnetic object1310, and a split photodetector1344at the bottom. The light source1342may cast a shadow on the split photodetector1344and the position of the diamagnetic object1310may be detected by an electronics module as discussed in more detail with reference toFIGS.8A-8B.

In this embodiment, due to the variable gap configuration with one end of the magnet pair more separated or open then the other end, the camelback magnetic potential may be tilted to one side as shown inFIG.13and the diamagnetic object1310may rest at the minimum towards the more open side. To compensate this, the PDL trap can be tilted higher on-the more open side as shown below so that the diamagnetic object1310remains in the center.

The total confinement potential of this system may be given as:

UT=χ2⁢μ0⁢B⁡(y0,𝓏)2+ρ⁢g⁡(y0⁢cos⁢θ+𝓏sinθ)
Where χ is the magnetic susceptibility, μ0is the magnetic permeability, B is the total magnetic field at the graphite, ρ is the mass density of the graphite, g is acceleration of gravity, y0is the height of the graphite and z is the horizontal position of the graphite along the tilted plane. The energy potential in the tilted PDL trap is shown inFIG.13D.

This system1300may have sensitivity with respect to the vertical motion, as shown in the simulation results depicted inFIGS.13E-13F. If there is a vertical motion that increases the acceleration (e.g., by 5%) the graphite will move to the left. For an example of a typical PDL trap with length and diameter of 1″×0.25″ we obtain a sensitivity of 69 μm for every percent change in g.

To decouple the three-dimensional motion in the ground frame of reference with cartesian coordinates x, y, z, some embodiments may employ a set of three sensors and a linear transformation calculation as discussed in more detail with reference toFIGS.15A-15B

FIGS.14A-14Care side, top, and front views of another sensor1400that is sensitive to the vertical motion, consistent with some embodiments. This variation of the passive sensor with variable gap and tilted configuration has four CDM magnets that form a multiple dipole line trap. The top pair of CDM magnets modify the magnetic confinement potential to be flatter and have a lower resonant frequency. This way, this sensor1400can detect lower vibration frequency.

As best shown inFIGS.13A and14B, the two cylindrical magnets in sensors1300and1400in the vertical detection case are not parallel. That is, in such tilted embodiments, the cylindrical magnets may have one end more open than the other end (e.g., g2>g1).

FIGS.15A-15Bare side and top views of a complete sensor unit1500, consistent with some embodiments. The complete unit1500comprises three sensor modules1525sitting on an adjustable base platform1530, an electronics module1560, and rigid enclosure1570made of metal for electrical noise suppression. The electronics module1560may contain a position detector circuit, PID controller, a digitizer, and a microcomputer with internet or Wi-Fi capability to stream the data to the seismic data server. The enclosure1570may sit on three adjustable legs1575for optimum alignment with the horizontal plane and so that the sensor modules1525have a level base and are centered.

To achieve a fully three-dimensional motion detection in x, y and z axes (or North, West and Z in the coordinate axis ofFIG.16), this embodiment places three tilted three sensor modules1525(active or passive type) as shown in the figures above. Each of these sensor modules1525may yield seismic signals: u, v, and w. The passive sensor typically yields a displacement signal while the active sensor yields acceleration.

By arranging each sensor module1525in a tilted fashion as shown inFIGS.15A-15B, along tilted axes: u, v and w, the signals in the standard Cartesian coordinate system (x, y, z or North, West and Z in the coordinate axis inFIG.16) can be calculated. The coordinate systems is shown inFIG.16and the transformation matrix is given below. The dipole line traps are assumed to be oriented with a tilt from the x, y plane equal to θ and an equal azimuthal spacing of 120° from the x axis.

While aspects of the present disclosure has been described with reference to a number of specific embodiments, other variations are within its scope. For example, some embodiments may also utilize ring-shaped magnets, instead of CDM magnets. These embodiments may levitate a spherically shaped diamagnet just above a central hole. These embodiments may be desirable for use as motion sensors or accelerometers, where the spherical diamagnet acts as a fixed internal mass and the motion of the environment is sensed by the relative motion of the magnets and housing. Ring magnets may also be desirable because they can be configured to automatically measure two-dimensional motions, as they are symmetric in two horizontal dimensions. Some embodiments using ring-shaped magnets may also include a relatively small tilt so that the diamagnet sphere does not fall out of the trap.

GENERAL