WO2021006727A1

WO2021006727A1 - Sensor equipped with at least one magnet and a diamagnetic plate levitating above said at least one magnet and method to measure a parameter of an object using such a sensor

Info

Publication number: WO2021006727A1
Application number: PCT/NL2020/050429
Authority: WO
Inventors: Farbod ALIJANI; Peter Gerard Steeneken; Nimit KOTHARI; Ata KESKEKLER
Original assignee: Technische Universiteit Delft
Priority date: 2019-07-09
Filing date: 2020-06-29
Publication date: 2021-01-14
Also published as: NL2023462B1

Abstract

Sensor (1) equipped with at least one magnet (2, 3) and a diamagnetic plate (4) levitating above said at least one magnet (2, 3), comprising actuation means (5, 6) to bring the 5 diamagnetic plate (4) into motion, and measurement means (7, 8) to measure the motion of the diamagnetic plate (4), wherein the sensor (1) comprises computing means (12) that are connected to the measurement means (7, 8), wherein the computing means (12) are arranged to derive from a measurement 10 by the measurement means (7, 8) a resonance frequency of the diamagnetic plate (4) while being loaded with an object (11), and to compare said resonance frequency with a calibrated frequency that corresponds to the diamagnetic plate's resonance frequency when the diamagnetic plate (4) is 15 unloaded, and to derive a parameter relating to the object (11) from a comparison of said resonance frequency and calibrated frequency.

Description

Sensor equipped with at least one magnet and a diamagnetic plate levitating above said at least one magnet and method to measure a parameter of an object using such a sensor

The invention relates to a sensor equipped with at least one magnet and a diamagnetic plate levitating above said at least one magnet, comprising actuation means to bring the diamagnetic plate into motion, and measurement means to measure the motion of the diamagnetic plate. Levitating according to this specification means that the diamagnetic plate is in a stable position floating above the at least one magnet without touching it.

Such a sensor is known from DE 10 2010 012 970 A1. This known sensor comprises a diamagnetic levitating element with a convex surface. According to this citation in one embodiment a mirror is arranged on the diamagnetic floating plate. The device comprises an optical measuring device which is suitable for measuring a change in position of the diamagnetic floating body by means of light reflection at the mirror. It can be provided in particular that the mirror is arranged centrally on the side facing away from the measuring device of the diamagnetic floating body, wherein the optical measuring device is designed as a three-beam interferometer or laser interferometric vibrometer, which is arranged above the diamagnetic body. Exemplary applications include inclination measurement (inclinometer, tilt meter), determination of gravitational acceleration (gravimeter) , determination of Newtonian gravitational constants and small masses, detection of vibrations or seismometers, and obtaining information about the intensity and direction of weak gas flows. The citation further discloses that in an application for determining the gravitational acceleration the self-resonance of the levitation device is used. In this case, additional means are provided with which from below a force field can act on the diamagnetic float to make it vibrate. The excitation of the oscillation of the floating arrangement takes place sinusoidally or pulse-shaped and intermittently with a frequency in the vicinity of its natural frequency or with its natural frequency (maximum oscillation amplitude) in the direction of the gravity line of the floating body. The time course of the vibrations of the float is measured with a laser interferometric vibrometer and evaluated with computer-aid. It is further disclosed that due to the extreme demands on the resolution and accuracy, a temperature stabilization, evacuation and regular calibration of the device makes sense.

According to the instant invention a sensor and a method to measure a parameter of an object is proposed in accordance with one or more of the appended claims.

According to a first aspect of the invention the sensor comprises computing means that are connected to the measurement means, wherein the computing means are arranged to derive from a measurement by the measurement means a resonance frequency of the diamagnetic plate while being loaded with an object, and to compare said resonance frequency with a calibrated frequency that corresponds to the diamagnetic plate' s resonance frequency when the plate is unloaded, and to derive a parameter of the object from a comparison of said resonance frequency and calibrated frequency. The parameter relating to the object is the mass of the object, and optionally one or more other properties of the object selected from the group comprising stiffness, optical absorption, moment of inertia, position, temperature. With this sensor an accurate measurement on the object can be accomplished without applying the complicated shapes of the levitating plate as proposed in the prior art. A further advantage of the sensor of the invention is that it is less sensitive to disturbances by small vibrations as may be the case in the prior art device .

The sensor of the invention can be used to measure simultaneously different parameters, such as the mass of the object, as well as the stiffness, moment of inertia, temperature, power of incident radiation, by analyzing changes in the resonance frequency and utilizing knowledge of the levitating diamagnetic plate and the plate geometry and its material properties.

Although it is possible to apply electromagnets in the sensor to levitate the diamagnetic plate, it is preferred that the magnets are permanent magnets or ferromagnets . This brings the following advantages: 1. the system does not use power, and is energy efficient; 2. the diamagnetic plate stays in a levitating state when power is out since the magnets do not require power; 3. to generate a similar magnetic field with an electromagnet or electromagnets requires high currents imposing cooling requirements of the current guiding copper or superconducting wires in order to prevent their melting.

Desirably the at least one magnet is shaped or the magnets are arranged to provide that at the location of the diamagnetic plate the magnetic field maintains the diamagnetic plate stably in position. This result can be achieved by arranging that the magnetic field gradient at the location of the diamagnetic plate is relatively large. This causes that the diamagnetic plate will experience correspondingly large forces. It is possible to create magnet structures wherein the integral of these forces always points towards an equilibrium position when the plate is positioned slightly out of equilibrium. Such magnetic arrangements can for instance be created using arrays of alternating North-South pole arrangements of permanent magnets or by creating trenches in a single magnet of fixed polarity. In a preferred embodiment the magnet arrangement comprises four magnets alternatingly arranged in a square N S N S pole configuration.

The material of the diamagnetic plate is for instance graphite, graphene or bismuth, or another suitable material with a high negative magnetic susceptibility. The material of the diamagnetic plate can also be a composition of materials, wherein at least one material is diamagnetic, such as metal on graphite, metal on silicon, or can be 3D printed structures of graphite. The diamagnetic plate can further be of arbitrary shape, for instance a block shape or sphere-shaped, as long as it is structured to remain in a stable levitating position above the magnet (s) .

The levitating plate can be equipped with a power source and electronics for sensing, actuation and/or wireless transmittal of information to and from the plate related to the plate and/or an object on or in the plate. The levitating plate can also be equipped with a heater and temperature control to stabilize the temperature dependent parameters of the diamagnetic plate.

In accordance with the above-mentioned first aspect of the invention, the invention is also embodied in a method to measure a parameter of an object using a sensor equipped with at least one magnet and a diamagnetic plate levitating above said at least one magnet, comprising bringing the diamagnetic plate into motion, measuring the motion of the diamagnetic plate, and deriving from the motion of the diamagnetic plate a resonance frequency of said diamagnetic plate whilst being loaded with an object, and comparing said resonance frequency with a calibrated frequency that corresponds to the diamagnetic plate's resonance frequency when the plate is unloaded, and deriving a parameter of the object from comparing said resonance frequency and calibrated frequency .

It is preferable that the calibrated frequency is actually measured as the resonance frequency of the diamagnetic plate when the plate is in an unloaded condition. It is however possible that the calibrated frequency is preestablished by analytic calculation.

Preferably the diamagnetic plate is equipped with a receptacle to receive the object of which a parameter is to be determined. The object can be a chemical or biological or chemical substance, in the form of a solid, powder, liquid, or gas. The sensor of the invention may thus be used in a batch operation, where many objects are measured simultaneously on separate diamagnetically levitating plates. This may be relevant in an industrial process wherein the parameters of a large number of objects have to be measured.

Suitably the receptacle is an aperture or a channel within the diamagnetic plate.

In one embodiment it is preferred that the measurement means are arranged to continuously measure the resonance frequency of the diamagnetic plate to determine the time dependency of said resonance frequency so as to enable the computing means to establish the time varying parameter of the object that is loading the diamagnetic plate. This applies in particular when a parameter of a flowing fluid or gas has to be determined.

In still another embodiment the diamagnetic plate is equipped to receive two or more objects, wherein the measurement means are arranged to measure multiple resonance frequencies of the diamagnetic plate so as to enable the computing means to determine the value of the respective objects that are loading the diamagnetic plate.

Different possibilities exist in using a particular type of actuation means to bring the diamagnetic plate into motion. Suitably the actuation means are one or more selected from the group comprising an ultrasound speaker, a magnetic coil or coils around the magnets, means to produce an electrostatic force, a shaker or piezo-actuator supporting the magnets, and a (resistive-, microwave-, or an optical-) heater for heating of the diamagnetic plate.

Also different possibilities exist for measuring the motions of the diamagnetic plate. Suitably the measurement means are one or more selected from the group comprising an accelerometer, a laser Doppler vibrometer to detect reflected light from the diamagnetic plate, an optical interferometer, one or more capacitor electrodes cooperating with the diamagnetic plate as the opposite electrode of the capacitor, an ultrasound detector for measuring the position of the diamagnetic plate, or an imaging system for measuring the position of the diamagnetic plate.

Preferably the diamagnetic plate is provided with sensory equipment and/or circuitry connected to the sensory equipment. One thing and another may for instance be embodied in the form of a CMOS chip(s) with sensors that can be used to determine the resonance frequency (e.g. using an integrated accelerometer) , or to determine the temperature of the levitating diamagnetic plate independently from the surrounding temperature. In this way sensing and actuation functions can be implemented on the levitating diamagnetic plate that would be difficult to perform wirelessly, e.g. it can in addition to the mass also measure the pH of a (biological) liquid monitored with the sensor of the invention, or determine composition or spectral properties of such liquids. It can also perform actuation functions, e.g. the circuitry could include a piezoelectric generator to bring the system into resonance at its resonance frequency, and the circuitry can stabilize the temperature of the plate using a heater and thermostat system. Furthermore the circuitry can comprise an antenna to communicate sensor data wirelessly and can comprise computing/processing units to analyze the sensor data, in which case it should also have a power source.

The invention will hereinafter be further elucidated with reference to an exemplary embodiment as depicted in the attached drawing, which is not limiting as to the appended claims, and which pertains to a sensor and a method to use such a sensor for measuring a object in accordance with the invention .

In the drawing:

- figure 1 shows a sensor of the invention in a schematic side view;

- figure 2 shows a schematic top view at another sensor of the invention;

- figure 3 shows a sensor application in a schematic side view;

- figure 4 shows another sensor application for measuring a parameter of a flowing object; and

- figure 5 shows a detail view at a diamagnetic plate with receptacle to be used in the sensor according to the invention .

Whenever in the figures the same reference numerals are applied, these numerals refer to the same parts.

Making first reference to figure 1, it shows a sensor 1 equipped with two permanent magnets 2, 3 (one magnet may already suffice) and a diamagnetic plate 4 levitating above said two magnets 2, 3. The magnets are arranged to provide that at the location of the diamagnetic plate 4 a magnetic field originating from the magnets maintains the diamagnetic plate 4 stably in position.

The sensor 1 further comprises actuation means 5 to bring the diamagnetic plate 4 into motion. The actuation means are preferably selected from the group comprising an ultrasound speaker, a magnetic coil or coils around the magnets 2, 3, a shaker or piezo-actuator supporting the magnets 2, 3, or a heater for heating of the diamagnetic plate 4. In the shown embodiment the actuation means are embodied as a piezo-actuator 6.

Figure 1 further shows that the sensor 1 includes measurement means 7, 8 to measure the motion of the diamagnetic plate 4. The measurement means 7, 8 are preferably one or more selected from the group comprising an accelerometer, a laser Doppler vibrometer to detect reflected light from the diamagnetic plate 4, an optical interferometer, a capacitor electrode cooperating with the diamagnetic plate 4 as the opposite electrode of the capacitor, an ultrasound detector for measuring the position of the diamagnetic plate 4, or an imaging system for measuring the position of the diamagnetic plate 4. In the embodiment shown in figure 1 a laser Doppler vibrometer is used employing a laser light source 7 and a detector 8 for detecting light reflected by a reflective coating 4' on the diamagnetic plate 4.

In the embodiment of figure 2 a schematic top view of another sensor of the invention is shown, wherein four magnets 2, 2', 3, 3' in a square arrangement are applied, and wherein a voltage source 9 provides power to an actuator 10 below the magnets. By providing the left magnet electrodes 2 with a different voltage than the right magnet electrodes 3, an electrostatic force is generated on the levitating plate, due to its capacitive coupling to the electrodes. The four magnets 2, 2', 3, 3' are alternatingly arranged in a square N S N S pole configuration, which is an easy way of securing that at the location of the diamagnetic plate 4 a magnetic field originates from the magnets that maintains the diamagnetic plate 4 stably in position.

Turning back to figure 1 it is shown that in accordance with the invention the sensor 1 further comprises computing means 12 that are connected to the measurement means 7, 8, wherein the computing means 12 are arranged to derive from a measurement by the measurement means 7, 8 a resonance frequency of the diamagnetic plate 4 while being loaded with an object 11. The computing means 12 compares said resonance frequency with a calibrated frequency that corresponds to the diamagnetic plate's resonance frequency when the plate 4 is unloaded, and derives a parameter of the object 11 from the comparison of said resonance frequency with said calibrated frequency. The parameter relating to the object 11 is for instance the mass of the object 11, and may optionally include one or more other properties of the object 11 selected from the group comprising stiffness, optical absorption, moment of inertia, position, temperature.

Preferably the calibrated frequency is preestablished by measurement, although it is also possible to determine the calibrated frequency analytically as the resonance frequency of the diamagnetic plate 4 when the object 11 is not present on said diamagnetic plate 4. The parameter of the object can then be derived from the measurements employing knowledge of the resonance frequencies, geometries and material properties of the plate, and utilizing relations that are common to the skilled person. Reference is made to the book: Vibration Problems in Engineering, by Timoshenko, and to the book: Fundamentals of Nanomechanical Resonators, by Silvan Schmid et al . Reference is also made to https://en.wikipedia.org/wiki/Vibration of plates.

It is remarked that the measurement means 7, 8 are arranged to continuously measure the resonance frequency of the diamagnetic plate 4 to determine the time dependency of said resonance frequency so as to enable the computing means 12 to establish the time varying parameter of the object 11 that is loading the diamagnetic plate 4. This applies in particular when a parameter of a flowing fluid or gas has to be determined.

Figure 3 and figure 4 show two embodiments according to which the sensor of the invention can be applied. In figure 3 an object 13 within a liquid film 14 is supported by a diamagnetic plate 4 of the sensor 1, wherein a glass cover plate 15 covers the liquid film 14 and the object 13. In this embodiment the liquid film 14 and the object 13 are stationary, as opposed to the embodiment of figure 4, wherein the glass plate 15 is embodied with a channel 16 through which a fluid with an object 13' can be flowing. The embodiment of figure 3 aims to measure the mass of the stationary object 13, whereas the embodiment of figure 4 aims to measure the mass of a moving object 13' passing with a flowing fluid.

In general it is also possible that the diamagnetic plate 4 itself is equipped with a receptacle to receive a solid, liquid or gas of which the mass and other parameters are to be determined. Figure 5 provides a detailed view of a diamagnetic plate 4 wherein the receptacle is a channel or channels 17 within the diamagnetic plate 4. It is also possible to apply one or more apertures on the top face of the diamagnetic plate 4 to receive an object of which the mass and other parameters must be measured.

Although the invention has been discussed in the foregoing with reference to exemplary embodiments of the sensor and method of the invention, the invention is not restricted to these particular embodiments which can be varied in many ways without departing from the invention. A possible variation is for instance that the diamagnetic plate 4 is equipped to receive two or more objects, and the measurement means 7, 8 are arranged to measure multiple resonance frequencies of the diamagnetic plate 4 so as to enable to determine the parameters of the respective objects that are loading the diamagnetic plate 4. The discussed exemplary embodiments shall therefore not be used to construe the appended claims strictly in accordance therewith. On the contrary the embodiments are merely intended to explain the wording of the appended claims without intent to limit the claims to these exemplary embodiments. The scope of protection of the invention shall therefore be construed in accordance with the appended claims only, wherein a possible ambiguity in the wording of the claims shall be resolved using these exemplary embodiments.

Claims

1. Sensor (1) equipped with at least one magnet (2, 3) and a diamagnetic plate (4) levitating above said at least one magnet (2, 3), comprising actuation means (5, 6) to bring the diamagnetic plate (4) into motion, and measurement means (7, 8) to measure the motion of the diamagnetic plate (4), characterized in that the sensor (1) comprises computing means (12) that are connected to the measurement means (7, 8), wherein the computing means (12) are arranged to derive from a measurement by the measurement means (7, 8) a resonance frequency of the diamagnetic plate (4) while being loaded with an object (11), and to compare said resonance frequency with a calibrated frequency that corresponds to the diamagnetic plate's resonance frequency when the diamagnetic plate (4) is unloaded, and to derive a parameter relating to the object (11) from a comparison of said resonance frequency and calibrated frequency.

2. Sensor according to claim 1, characterized in that the parameter relating to the object (11) is the mass of the object (11), and optionally one or more other properties of the object (11) selected from the group comprising stiffness, optical absorption, moment of inertia, position, temperature.

3. Sensor according to claim 1 or 2, characterized in that the at least one magnet (2, 3) is a permanent magnet or ferromagnet .

4. Sensor according to any one of claims 1-3, characterized in that the at least one magnet (2, 3) is shaped or the magnets are arranged to provide that at the location of the diamagnetic plate (4) a magnetic field originating from the magnet (s) maintains the diamagnetic plate (4) stably in position by arranging that the magnetic field gradient at the location of the diamagnetic plate is relatively large.

5. Sensor according to any one of claims 1-4, characterized in that the magnetic field at the location of the diamagnetic plate is provided using arrays of alternating North-South pole arrangements of permanent magnets or by creating trenches in a single magnet of fixed polarity.

6. Sensor according to any one of claims 1-5, characterized in that the sensor (1) comprises four magnets

(2, 3, 2', 3' ) alternatingly arranged in a square N S N S pole configuration .

7. Sensor according to any one of claims 1-6, characterized in that the calibrated frequency is preestablished by measurement.

8. Sensor according to any one of claims 1-7, characterized in that the diamagnetic plate (4) is equipped with a receptacle (17) to receive an object of which a parameter is to be determined.

9. Sensor according to claim 8, characterized in that the receptacle is an aperture or a channel (17) within the diamagnetic plate (4) .

10. Sensor according to any one of claims 1-9, characterized in that the measurement means (7, 8) are arranged to continuously measure the resonance frequency of the diamagnetic plate (4) to determine the time dependency of said resonance frequency so as to enable the computing means (12) to establish the time varying parameter of the object (11) that is loading the diamagnetic plate (4) .

11. Sensor according to any one of claims 1-10, characterized in that the diamagnetic plate (4) is equipped to receive two or more objects, and the measurement means (7, 8) are arranged to measure multiple resonance frequencies of the diamagnetic plate (4) so as to enable to determine the parameters of the respective objects that are loading the diamagnetic plate (4) .

12. Sensor according to any one of claims 1-11, characterized in that the actuation means (5, 6) are one or more selected from the group comprising an ultrasound speaker, a magnetic coil or coils around the magnets, a shaker or piezo-actuator supporting the magnets, a heater for heating of the diamagnetic plate.

13. Sensor according to any one of claims 1-12, characterized in that the measurement means (7, 8) are one or more selected from the group comprising an accelerometer, a laser Doppler vibrometer to detect reflected light from the diamagnetic plate, an interferometer, a capacitor electrode cooperating with the diamagnetic plate as the opposite electrode of the capacitor, an ultrasound detector for measuring the position of the diamagnetic plate, an imaging system for measuring the position of the diamagnetic plate.

14. Sensor according to any one of claims 1-13, characterized in that the diamagnetic plate is provided with sensory and/or actuation equipment or circuitry connected to the sensory equipment.

15. Method to measure a parameter of an object using a

sensor (1) equipped with at least one magnet (2, 3) and a diamagnetic plate (4) levitating above said at least one magnet (2, 3), comprising bringing the diamagnetic plate (4) into motion, and measuring the motion of the diamagnetic plate (4), characterized by deriving from the motion of the diamagnetic plate (4) a resonance frequency of said diamagnetic plate (4) whilst being loaded with an object (11), and comparing said resonance frequency with a calibrated frequency that corresponds to the diamagnetic plate's resonance frequency when the diamagnetic plate (4) is unloaded, and deriving a parameter of the object from comparing said resonance frequency and calibrated frequency.

16. Method according to claim 15, characterized by determining as the parameter the mass of the object (11), and optionally one or more other properties of the object (11) selected from the group comprising stiffness, optical absorption, moment of inertia, position, temperature.

17. Method according to claim 15 or 16, characterized by providing the at least one magnet (2, 3) in the form of a permanent magnet or ferromagnet.

18. Method according to any one of claims 15-17, characterized by shaping the at least one magnet (2, 3) or arranging the magnets to provide that at the location of the diamagnetic plate (4) a magnetic field originates from the magnet (s) to maintain the diamagnetic plate (4) stably in position by arranging that the magnetic field gradient at the location of the diamagnetic plate is relatively large.

19. Method according to any one of claims 15-18, characterized by providing the magnetic field at the location of the diamagnetic plate using arrays of alternating North- South pole arrangements of permanent magnets or by creating trenches in a single magnet of fixed polarity.

20. Method according to any one of claims 15-19, characterized by providing the sensor (1) with four magnets (2, 3, 2', 3' ) alternatively arranged in a square N S N S pole configuration .

21. Method according to any one of claims 15-20, characterized by pre-establishing the calibrated frequency by measurement .

22. Method according to any one of claims 15-21, characterized by equipping the diamagnetic plate (4) with a receptacle (17) to receive an object of which a parameter is to be determined.

23. Method according to any one of claims 15-22, characterized by providing the receptacle in the form of an aperture or a channel (17) within the diamagnetic plate (4) .

24. Method according to any one of claims 15-23, characterized by continuously measuring the resonance frequency of the diamagnetic plate (4) to determine the time dependency of said resonance frequency so as to establish the time varying parameter of the object (11) that is loading the diamagnetic plate (4) .

25. Method according to any one of claims 15-24, characterized by loading the diamagnetic plate (4) with two or more objects, and measuring multiple resonance frequencies of the diamagnetic plate for determining the value of the respective parameters of the objects that are loading the diamagnetic plate (4) .

26. Method according to any one of claims 15-25, characterized by providing the diamagnetic plate with sensory and/or actuation equipment or circuitry (18) connected to the sensory equipment.