Possibility of Gravitational Force
Shielding
Received 9 September 1992
A possibility of gravitational force shielding by bulk
YBa2Cu3O7-x superconductor
Shielding properties of single-phase dense bulk
superconducting ceramics of YBa2Cu3O7-x against the gravitational
force were studied at temperatures below 77 K. A small non-conducting
and non-magnetic sample weighing 5.48 g was placed over a levitating
superconducting disk and the loss of weight was measured with high
precision using an electro-optical balance system. The sample was
found to lose from 0.05 to 0.3% of its weight, depending on the
rotation speed of the superconducting disk. Partial loss of weight
might be the result of a certain state of energy which exists inside
the crystal structure of the superconductor at low temperatures. The
unusual state of energy might have changed a regular interaction
between electromagnetic, nuclear and gravitational forces inside a
solid body and is responsible for the gravity shielding effect.
1.) Introduction
High-temperature ceramic oxide superconductors as well
as conventional ones can be used as effective shields against
electromagnetic fields at low temperatures due to the Meissner effect.
But physical phenomena inside metal superconductors and ceramic ones
might be entirely different, as well as the mechanisms of
superconductivity. It is well-known that the current carriers in both
types of superconductors have a charge of 2-. But the energy state in
the structure of ceramic superconductors seems to be of a different
nature, as compared to metallic ones. The internal state of energy of
ceramic superconductors can be influenced by several parameters
forming a crystal lattice with a defined order.
Various physical properties of ceramic superconductors,
such as thermal conductivity, lattice distances, optical reflection
etc. show abnormal changes near the transition temperature. No
overwhelming theory has yet been proposed to explain the mechanism of
superconductivity and the abnormal behaviour of high-Tc oxide ceramic
materials at low temperatures.
The aim of this study was initially to investigate the
shielding properties of dense y-based bulk superconductors against
electromagnetic fields of various frequencies and intensities in a
wide range of temperatures. But an unusual behaviour of the ceramic
material observed during the first stage of this work initiated a
separate set of experiments dealing with the shielding of the
gravitational force.
2.) Experimental
Superconducting single-phase YBa2Cu3O7-x compound was
prepared in a form of a disk with a diameter of 145 mm and a thickness
of 6 mm. The preparation procedure consisted of mixing the initial
oxides followed by calcining the powder at 930C in air, grinding,
pressing the disk at 150 MPa and sintering it in oxygen at 930C for 12
h with slow cooling down to room temperature.
The disk was placed over a toroidal solenoid and kept at
a temperature below 77 K using liquid helium and its vapours. The disk
was usually first submerged into liquid helium and kept there for
several minutes, then the power was connected to the toroidal solenoid
and the disk raised over the surface of the helium. This massive disk
maintained its temperature below 60 K for about 2.5 min.
Two coils with rotating magnetic fields, similar to
those used in regular electric motors, were placed on both sides of
the disk, as shown in fig. 1. The disk levitated above the toroidal
magnet and was able to rotate around its central axis at a variable
speed. The frequency of the electromagnetic field in all three
solenoids was varied from 50 to 106 Hz. A sample made of silicon
dioxide hanging on a thread was placed over the disk at a distance of
about 15 mm from it, and was separated from the He vapours by a thin
transparent plastic foil. The weight of the sample was measured with
high precision using an electro-optical comparing balance.
The phase and crystal structure of the superconductor
were studied by X-ray diffraction analysis (XRD) and under a scanning
electron microscope (SEM). The electrical resistivity of the
superconductor was measured by the four-probe method using an AC
current and gold contacts.
3.) Results
As determined by XRD-analysis, the sintered disk was
pure single-phase orthorhombic 123-compound with random orientation
and lattice parameters: a=0.381 nm, b=0.385 nm, c=1.165 nm. SEM
investigations showed that the material was extremely dense with no
open porosity and consisted of small grains with pure grain boundaries
free from phase segregation.
The transition temperature Tc measured from the
resistive transition was 92 K with a width of 0.7 K.
The superconducting ceramic disk revealed a weak but
clearly detectable shielding effect against the gravitational force at
the temperatures from 20 to 70 K. The sample with the initial weight
of 5.47834 g was found to loose about 0.05% of its weight when placed
over the levitating disk without any rotation. When the rotation speed
of the disk increased, the weight of the sample became unstable and
gave fluctuations from -2.5 to +5.4% of the initial value [Editors
note: subsequent communication with the authors confirmed that this
refers to a deviation to the 0.05% weight loss, or a weight loss range
of 0.049% to 0.053%].
At certain speeds of rotation and at certain frequencies
of electromagnetic field in the rotation magnets the weight of the
sample stabilized and decreased by 0.3%. The readings in the stable
regions were recorded several times with good reproducibility.
The levitating superconducting disk was found to rise by
up to 7 mm when its rotation moment increased. Test measurements
without the superconducting shielding disk. but with all operating
solenoids connected to the power supply, had no effect on the weight
of the sample.
Every precaution was taken to prevent the influence of
static electricity and air flow on the sample or the supporting
thread. Also, the electro-optical balance was shielded from the
possible influence of electromagnetic fields.
4.) Discussion
There exist several types of levitation which can be
explained by different physical phenomena. Free flotation of the
objects can be caused by aerodynamic, acoustic, and optical forces,
and can also be generated by electrostatic or magnetic fields or by
radio-frequency radiation, as analyzed in detail in ref. [2].
In the present work, a typical superconducting
levitation due to the Meissner effect is used to lift a
superconducting disk by an alternating electromagnetic field. The
rotating magnetic field at the position of the hanging sample
generates an AC field which is partly shielded by the sample.
Therefore, part of the AC magnetic field is expelled from the sample.
Since the AC field decreases with increasing height, the expulsion
results in a levitation force. Magnetic levitation counteracts the
gravitational force and decreases the weight of the sample. This
explanation can be given for the case when the superconducting disk is
rotated by the magnetic field. But it becomes rather difficult to
explain the loss of weight when the field is switched off and the disk
is still rotating, and the weight of the sample remains decreased till
the rotation speed of the disk decreases.
Another possible explanation of the observed phenomenon
could be the levitation of the sample in the radio-frequency (RF)
field generated by the solenoids on both sides of the superconducting
disk. The RF rotating field penetrates a specimen to a certain skin
depth and induces small currents in the surface of the sample. The RF
field is then partly screened from the interior and the sample is
expelled from the RF field. This interpretation also seems quite
reasonable because the maximum loss of weight of the sample was
observed only at high frequencies of the magnetic field up to 106 Hz.
Still, the explanation is not adequate for the conditions of the
experiment when 50 Hz electric current was used and also when the
rotation solenoids were off and the superconducting disk was immobile.
Partial acoustic levitation, usually caused by a
high-intensity ultrasonic field with a frequency of 20 to 40 kHz,
seems hardly probable in the present case, as no special transducers
generating standing waves were applied and the intensity of ultrasonic
radiation from the solenoids was relatively low.
The interaction of an external magnetic field with a
bulk ceramic superconductor is defined by several parameters, and the
main ones are: the temperature, the coherence length, the flux
pinning, the frequency and the force of the field, and the penetration
depth. All these factors are interrelated in a complex way. It is
known that the coherence length for Y-Ba-Cu-O at 77 K in a zero field
is much smaller than the penetration length [1], but these parameters
depend on the temperature [3-5] and can change considerably under
certain conditions.
The lifting force in a superconductor levitating over a
permanent magnet was studied by several authors [6-8], but the
interaction of the ceramic superconductor with the alternating field
was not studied in detail.
Intergrain boundaries were always regarded only as
obstacles for the current, and it is known that the magnetic field
penetrates inside a superconductor mainly along the grain boundaries.
According to our experience, this penetrating field interacts with the
superconducting grain boundaries in such a way that its further
propagation inside the material is still possible along the grain
boundaries but the intensity of the field is greatly reduced.
When the wavelengths of the external magnetic fields
having various directions become comparable to the coherence length
and to the interplane distances, they interact with the whole atomic
structure inside the superconductor. The rotation of the
superconducting body moves the grains and grain boundaries in the
field, causing various disturbances of the magnetic fields because of
the hysteresis effect These disturbances can also be influenced by the
great number of Josephson junctions which exist inside the bulk
superconducting disk and are responsible for the corresponding
effects.
These disturbances change the standard interaction of
magnetic, nuclear and gravitational fields inside a solid body, and
the superconductor might obtain its own new gravitational momentum
which yields a small gravitation shielding effect. It is well known
that any physical body rotating around its vertical axis loses a part
of its weight. Under certain conditions, the rotation of magnetic
fields around the body might have a similar effect. In the present
work the superconducting disk has its own rotation momentum and
current carriers with the charge of minus two, and is moving in a
high-frequency magnetic field. It might be possible that such a system
modifies the magnetic field in such a way that it counteracts the
gravitational force.
5.) Conclusion
A bulk sintered ceramic disk of YBa2Cu3O7-x reveals a
small shielding effect against the gravitational force at temperatures
below 60 K. This effect increases when the disk is rotated around its
central axis and depends on several parameters. The shieldmg effect
depends on the temperature of the Y-Ba-Cu-0 superconducting disk and
the maximum effect was observed at temperatures below 40 K.
The shielding force depends on the rotational speed of
the disk and has a tendency to increase with the speed of rotation.
Fluctuations of the weight noticed in the experiment might be due to
inhomogeneity and uneven density of the superconducting disk.
The shielding force depends on the frequency of the
electromagnetic field, both in the supporting and rotation magnet
systems, and shows a resonance behaviour at frequencies over l05 Hz.
The gravity shielding effect might be the result of a
certain state of energy which exists inside the crystal structure of
the superconductor at low temperatures. This unusual state of energy
might change the regular interaction between electromagnetic, nuclear
and gravitational force fields inside a superconductor, and is
responsible for the observed phenomenon.
References
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by E. Podkletnov and R. Nieminen
Tampere University of Technology
Institute of Materials Science
P.O. Box 589, SF-33101
Tampere, Finland
Revised manuscript received 13 October 1992