a radically new principle of operation seismic detector of nano-scale vibrations

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IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 17, NO. 2, JUNE 2007 629 A Radically New Principle of Operation Seismic Detector of Nano-Scale Vibrations Samvel G. Gevorgyan, Vardan S. Gevorgyan, Hovsep G. Shirinyan, Gagik H. Karapetyan, and Albert G. Sarkisyan Abstract—A new class broad-band, nano-scale shift position sensor is created and tested. It maybe used as an additional sensor in seismographs/accelerometers/vibrometers. It enables to extend band and enhance sensitivity of the technique available on market by 10–100 times, depending on model of the base product. Combined with such sensor traditional technique may enable to study quasi-static deformations and low-order free oscillations of Earth crust precursor to earthquakes—perhaps unnoticeable to other methods. It may permit to detect also gravity waves, and study peculiarities of tidal motion and tsunami. It may allow to transfer mechanical vibrations of constructions & buildings, with amplitudes over 1 nm, into detectable signal in a frequency range starting from quasi-static movements. It is based on detection of position changes of a vibrating metallic plate placed near the flat coil—being used as a pick-up in a stable tunnel diode oscillator. Frequency of oscillator is used as a detecting parameter, and the measuring effect is determined by a distortion of a MHz-range testing field configuration near the coil by a vibrating plate, leading to magnetic inductance changes of a coil with a resolution 10 pH. This results in the changes of oscillator frequency. We discuss initial-test data of such position sensor, installed in a Russian SM-3 seismometer, as the additional pick-up component, showing its advantages compared to traditional. We discuss also future of such new position sensor related with substitution of a normal-metallic coil by the superconductive one & replacement of a tunnel diode by S/I/S structure—as less-powered active element in oscillator. These may strongly improve stability of oscillator, and hence, enhance resolution of the seismic detectors. Index Terms—Detector for gravity waves search, nano-scale shift position sensor, position sensing and controlling element for probe microscopes and seismic detectors, single-layer flat-coil oscillator. Manuscript received April 3, 2007. This work was supported in part by the Armenian National Foundation of Science & Advanced Technologies (NFSAT) and by the U.S. Civilian Research & Development Foundation (CRDF) under Grant ISIPA 01-04. This study was supported also by the Armenian Foundation for Basic Research under Grant 04-0046. S. G. Gevorgyan is with the Department of Physics, Yerevan State Univer- sity, Yerevan 375025 Armenia. He is also with the Institute for Physical Re- search, National Academy of Sciences, Ashtarak-2, 378410 Armenia (e-mail: [email protected]; [email protected]). V. S. Gevorgyan is with the International Scientific-Educational Centre, National Academy of Sciences, Yerevan, 375019, Armenia. He is also with the Yerevan State University, Yerevan 375025 Armenia, and with the Institute for Physical Research, National Academy of Sciences, Ashtarak-2, 378410 Armenia. H. G. Shirinyan is with the Institute for Physical Research, National Academy of Sciences, Ashtarak-2, 378410 Armenia. He is also with the Yerevan State University, Yerevan 375025 Armenia (e-mail: [email protected]). G. H. Karapetyan are with the Institute for Physical Research, National Academy of Sciences, Ashtarak-2, 378410 Armenia. A. G. Sarkisyan is with the International Scientific-Educational Centre, Na- tional Academy of Sciences, Yerevan, 375019, Armenia. He is also with the Yerevan State University, Yerevan 375025 Armenia (e-mail: [email protected]). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TASC.2007.898678 I. INTRODUCTION B ASICALLY, there are two different types of seismic sen- sors: inertial seismometers, which measure ground motion relative to inertial reference (suspended inert mass), & strain- meters (or extensometers), that detect shift between two points of ground [1]. Although strain-meters are conceptually simpler than inertial seismometers, their technical realization is much more difficult. Besides, as ground motion relative to reference is usually larger than differential motion within a test-canal of reasonable dimensions, inertial seismometers usually are more sensitive to earthquakes. But, at low frequencies it becomes in- creasingly difficult to maintain an inert reference fixed, and for detection of quasi-static deformations and low-order free oscil- lations of Earth crust, tidal motions and for observation of me- chanical vibrations of buildings, constructions & machines, the strain-meters may exceed noticeably inertial seismometers. We offer here how to overcome such serious lack of acting seismographs/accelerometers/vibrometers by use of the single- layer open-flat-coil (OFC) oscillator-based sensitive platform technology, described in details by us in [2], [3]. II. TRADITIONAL INERTIAL SEISMOMETER Inertial seismometer converts ground motion into electrical signal, but its properties can not be described by a single-scale factor, such as the output volts per millimeter of the ground mo- tion (as occur in case of position sensor). Its response to ground motion depends not only on the amplitude of motion (how large it is), but also, on its time scale (how sudden it is). That is why the suspended seismic mass has to be kept in place by certain restoring force (electromagnetic, mechanical, or any other na- ture). But, when ground motion is slow, the mass will move with the rest of a seismometer, and the output signal even for a large motion will thus be negligibly smaller. Such a system is so a high-pass filter for the ground shift. This must be taken into account if ground motion is reconstructed from the recorded signal. This is why creation of seismic detectors, which may give large output signals both for the fast and slow ground motion (regardless of the rate of motion—as behave themselves posi- tion sensors), still remains among the prime important problems in seismology (and not only). Thus, we discuss below a new inertial seismic detector cre- ated by use of the OFC-oscillator method developed by our group. The method enabled to create a new position sensor of nano-scale shifts operating down to liquid— temperatures. It may be used, in particular, as a super broad-band and more sensitive additional pick-up element in seismographs available on market—to enhance their characteristics. That may permit 1051-8223/$25.00 © 2007 IEEE

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Page 1: A Radically New Principle of Operation Seismic Detector of Nano-Scale Vibrations

IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 17, NO. 2, JUNE 2007 629

A Radically New Principle of Operation SeismicDetector of Nano-Scale Vibrations

Samvel G. Gevorgyan, Vardan S. Gevorgyan, Hovsep G. Shirinyan, Gagik H. Karapetyan, and Albert G. Sarkisyan

Abstract—A new class broad-band, nano-scale shift positionsensor is created and tested. It maybe used as an additionalsensor in seismographs/accelerometers/vibrometers. It enables toextend band and enhance sensitivity of the technique available onmarket by 10–100 times, depending on model of the base product.Combined with such sensor traditional technique may enable tostudy quasi-static deformations and low-order free oscillations ofEarth crust precursor to earthquakes—perhaps unnoticeable toother methods. It may permit to detect also gravity waves, andstudy peculiarities of tidal motion and tsunami. It may allow totransfer mechanical vibrations of constructions & buildings, withamplitudes over 1 nm, into detectable signal in a frequency rangestarting from quasi-static movements. It is based on detection ofposition changes of a vibrating metallic plate placed near the flatcoil—being used as a pick-up in a stable tunnel diode oscillator.Frequency of oscillator is used as a detecting parameter, and themeasuring effect is determined by a distortion of a MHz-rangetesting field configuration near the coil by a vibrating plate,leading to magnetic inductance changes of a coil with a resolution

10 pH. This results in the changes of oscillator frequency. Wediscuss initial-test data of such position sensor, installed in aRussian SM-3 seismometer, as the additional pick-up component,showing its advantages compared to traditional. We discuss alsofuture of such new position sensor related with substitution of anormal-metallic coil by the superconductive one & replacement ofa tunnel diode by S/I/S structure—as less-powered active elementin oscillator. These may strongly improve stability of oscillator,and hence, enhance resolution of the seismic detectors.

Index Terms—Detector for gravity waves search, nano-scale shiftposition sensor, position sensing and controlling element for probemicroscopes and seismic detectors, single-layer flat-coil oscillator.

Manuscript received April 3, 2007. This work was supported in part by theArmenian National Foundation of Science & Advanced Technologies (NFSAT)and by the U.S. Civilian Research & Development Foundation (CRDF) underGrant ISIPA 01-04. This study was supported also by the Armenian Foundationfor Basic Research under Grant 04-0046.

S. G. Gevorgyan is with the Department of Physics, Yerevan State Univer-sity, Yerevan 375025 Armenia. He is also with the Institute for Physical Re-search, National Academy of Sciences, Ashtarak-2, 378410 Armenia (e-mail:[email protected]; [email protected]).

V. S. Gevorgyan is with the International Scientific-Educational Centre,National Academy of Sciences, Yerevan, 375019, Armenia. He is also withthe Yerevan State University, Yerevan 375025 Armenia, and with the Institutefor Physical Research, National Academy of Sciences, Ashtarak-2, 378410Armenia.

H. G. Shirinyan is with the Institute for Physical Research, National Academyof Sciences, Ashtarak-2, 378410 Armenia. He is also with the Yerevan StateUniversity, Yerevan 375025 Armenia (e-mail: [email protected]).

G. H. Karapetyan are with the Institute for Physical Research, NationalAcademy of Sciences, Ashtarak-2, 378410 Armenia.

A. G. Sarkisyan is with the International Scientific-Educational Centre, Na-tional Academy of Sciences, Yerevan, 375019, Armenia. He is also with theYerevan State University, Yerevan 375025 Armenia (e-mail: [email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TASC.2007.898678

I. INTRODUCTION

BASICALLY, there are two different types of seismic sen-sors: inertial seismometers, which measure ground motion

relative to inertial reference (suspended inert mass), & strain-meters (or extensometers), that detect shift between two pointsof ground [1]. Although strain-meters are conceptually simplerthan inertial seismometers, their technical realization is muchmore difficult. Besides, as ground motion relative to referenceis usually larger than differential motion within a test-canal ofreasonable dimensions, inertial seismometers usually are moresensitive to earthquakes. But, at low frequencies it becomes in-creasingly difficult to maintain an inert reference fixed, and fordetection of quasi-static deformations and low-order free oscil-lations of Earth crust, tidal motions and for observation of me-chanical vibrations of buildings, constructions & machines, thestrain-meters may exceed noticeably inertial seismometers.

We offer here how to overcome such serious lack of actingseismographs/accelerometers/vibrometers by use of the single-layer open-flat-coil (OFC) oscillator-based sensitive platformtechnology, described in details by us in [2], [3].

II. TRADITIONAL INERTIAL SEISMOMETER

Inertial seismometer converts ground motion into electricalsignal, but its properties can not be described by a single-scalefactor, such as the output volts per millimeter of the ground mo-tion (as occur in case of position sensor). Its response to groundmotion depends not only on the amplitude of motion (how largeit is), but also, on its time scale (how sudden it is). That is whythe suspended seismic mass has to be kept in place by certainrestoring force (electromagnetic, mechanical, or any other na-ture). But, when ground motion is slow, the mass will movewith the rest of a seismometer, and the output signal even fora large motion will thus be negligibly smaller. Such a systemis so a high-pass filter for the ground shift. This must be takeninto account if ground motion is reconstructed from the recordedsignal. This is why creation of seismic detectors, which may givelarge output signals both for the fast and slow ground motion(regardless of the rate of motion—as behave themselves posi-tion sensors), still remains among the prime important problemsin seismology (and not only).

Thus, we discuss below a new inertial seismic detector cre-ated by use of the OFC-oscillator method developed by ourgroup. The method enabled to create a new position sensor ofnano-scale shifts operating down to liquid— temperatures.It may be used, in particular, as a super broad-band and moresensitive additional pick-up element in seismographs availableon market—to enhance their characteristics. That may permit

1051-8223/$25.00 © 2007 IEEE

Page 2: A Radically New Principle of Operation Seismic Detector of Nano-Scale Vibrations

630 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 17, NO. 2, JUNE 2007

Fig. 1. (a) Top view of the known Russian SM-3 seismograph (with a screwednormal-metallic plate on its vibrating pendulum), originally designed to detectmechanical vibrations in a range up to 50 Hz; (b) front-view of the new positionsensor assembled inside the setup of SM-3 seismograph.

to reveal & study small vibrations precursor to earthquakes, aswell as to detect low-powered nuclear weapon tests.

III. PRINCIPLE OF OPERATION OF NEW SEISMIC DETECTOR

To this end, a model of such a new position sensor has beencreated & installed in a setup of a known Russian seismometerof SM-3 type (Fig. 1(a)). In such ‘hybrid SM-3’ device, flat coilserves as a pick-up circuit in a stable os-cillator drived by a low-power tunnel diode (TD). Actually, 2similar flat-coil oscillators are mounted in ‘hybrid SM-3’. Oneis used as a position detector, the 2nd—to detect backgroundat all times (bottom & top oscillators shown in Fig. 1(b) re-spectively). Mounted in SM-3 position sensor is extra to itsown vibro-sensor, based on excitation of electromotive force(EMF) in a solenoid (Fig. 1(a)). In case of position sensor, mea-suring effect is proportional to changes of mutual distance be-tween the flat coil & metallic plate vibrating parallel to coil face

Fig. 2. Schematics of the single-layer open-flat-coil (OFC) oscillator based po-sition sensor, used in a new seismic detector.

( , Fig. 2). This finally results in the changes of oscillator fre-quency.

So, our seismic detector converts ground motion into shift of asingle-layer flat-coil based oscillator frequency—due to groundshaking. Measuring signal appears as a result of the coil motion(fixed on seismograph’s pedestal) relative to the metallic plate(fixed on a suspended pendulum), positioned near the coil face.Fig. 2 illustrates the schematics of such new principle of actionposition sensor, & based on it new seismic detector ( is theshock force, —amplitude of vibration).

IV. FLAT COIL-BASED TEST METHOD AND ITS ADVANTAGES

A single-layer flat-coil-oscillator technique (Fig. 3) is a fineinstrument for doing MHz-range measurements [2]–[4]. Dueto flat shape of the coil even a little shift of the position ofa normal-metallic plate, placed near coil, may lead to strongdistortion of a testing radio-frequency field distributionaround the coil. Replacement of the solenoid coil by a flat onein ‘LC-resonator’ technique made coil’s filling factor maximalpossible ( 1) for flat objects [2], while its value for solenoid is

. These features, and high stability of TD-oscil-lator –10 Hz, —dependingon model and working temperature of the oscillator in a range4–300 K [2], [5]–[7]) enabled to improve the resolution of thetests in flat objects by 3–4 orders of a value. As a result, 6 ordersof the relative resolution is reached in OFC-oscillator method[2], which enabled to detect some fine effects in HTS materialsby this technique [8], [9]. Frequency of oscillator is a detectingparameter in this method, and the measuring effect arises froma distortion of the testing rf-field’s configuration near the coilface, which leads to changes of an oscillator frequency.

V. SEISMIC DETECTOR BASED ON A FLAT-COIL TECHNIQUE:RESULTS, DISCUSSION, FUTURE PERSPECTIVES

A. Results

Since EMF-based vibro-sensors (included, SM-3’s ownsensor) & created position sensor are different nature deviceswith different outputs (EMF-based sensor converts groundmotion into output volts, while our position sensor convertsthe same motion into shift of oscillator frequency), there areno reasonable direct ways to compare them correctly. Whatwe can, that is only to compare their responses over respective

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GEVORGYAN et al.: NEW PRINCIPLE OF OPERATION SEISMIC DETECTOR OF NANO-SCALE VIBRATIONS 631

Fig. 3. Schematics of a single-layer open-flat-coil (OFC) oscillator methodwith a plate-like HTS specimen. Side insets: technological details of design ofthe measuring (� � 25–30 mm), and coupling (� � 15 mm) coils.

noises during the same shaking. Therefore, we tried to detectand compare signal-to-noise ratios for these two sensors at thesame experiment, against the same 1–2 Hz time-scale vibration.

Thus, comparative-test data of such an experiment we bringin Fig. 4. As follows from test-data presented in Figure, detectedby a new position sensor background vibration of our researchlaboratory (‘hybrid SM-3’ was safely screwed to tile floor of ourexperimental room during the tests, positioned on the 2jobnndfloor) is about 400 Hz (that corresponds to amplitude of me-chanical vibrations of the floor 40 nm [3]). Besides, Fig. 4(a)demonstrates that background vibration of the research buildingis almost 4 times larger at working days, compared to week-endsand nights. However, even shakings at nights are 50–100 timeslarger from the noise level of the test oscillator, which is about1–2 Hz according to data shown in Fig. 4(b).

The rocking of experimental room might be caused by the in-dustrial pumping of environment, and also by background vibra-tion of Earth crust, and also, by the shaking of a technical natureduring the tests. In this regard, a fine signal shown in Fig. 4(b),detected by new position sensor (due to beating of test oscillatorwith a signal arrived from close-located broad-casting station),is an additional evidence of its high ability.

Presently, an acting experimental seismic station is under cre-ation in Yerevan State University, based on above-tested ‘hy-brid SM-3’ seismograph, capable of providing LabVIEW envi-ronment based computer data acquisition and processing (seeFig. 5), as well as online data transfer via the web-site of theArmenian NFSAT organization (http://www.nfsat.am).

B. Discussion

So, comparison of signal-to-noise ratios for new andSM-3-sensor (both installed in the same seismograph) permitsto conclude that the new sensor is more sensitive by 2 ordersof a value. Besides, because our new sensor permits to detectposition shifts, it may enable to detect the start of oscillatingprocesses at very low frequencies (beginning at quasi-staticshifts)—in contrast to EMF-based sensors. This may becomecrucial for detection of low-order free oscillations of the Earthcrust, and for observation of few hours duration tidal motionsand tsunami shaping. That is why, one may use it to reveal

Fig. 4. (a) Comparative test data of the flat-coil-oscillator based position sensorand the EMF-based vibro-sensor (both installed inside the same SM-3 seis-mometer). (b) Noise level (stability) of the used TD-oscillator, enabling to esti-mate signal-to-noise level reached in a created position sensor.

& study the origin of formation of the earthquakes in ad-vance—practically impossible for similar other methods. Ouroffer holds considerable potential for meeting technical needsof the seismic services supported by the governments of thecountries positioned in main World seismically-active regions.

C. Future Perspectives

There are ways how to improve resolution of such a new po-sition sensor, and hence, capabilities of the acting presently in-ertial seismometers—even by several orders of a value. To thisend, the pick-up coil, or/and active element of oscillator shouldbe made of the superconductive material (HTS, or LTS—forhigher stability). First and relatively easier way relates to re-placement of normal-metallic coil by the superconductive one.

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632 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 17, NO. 2, JUNE 2007

Fig. 5. LabVIEW signals of the created inertial seismic detector, which is basedon a single-layer open-flat-coil (OFC) oscillator sensitive test-method.

This may improve TD-oscillator stability by 1–2 orders of avalue [7]. Next possibility relates to substitution of tunnel diodeby superconductive S/I/S structure—as less-powered active ele-ment for the oscillator, with a few orders of a value less steep-ness of its I-V curve negative differential resistance [10]. Thismay raise oscillator stability by another 2–3 orders of a value[7]. But, even these two modifications are enough to enhancestability of TD-oscillator, and hence, to increase the signal-to-noise ratio of such a new position sensor-based seismic detectorby 3–5 orders of a value. Note that resolution of such sensorrises exponentially when normal-metallic plate is moved closerto the coil [3]. This makes easy adjustment of sensitivity of suchsensor, for various practical usages.

VI. CONCLUSION

We created a new-class super broad-band, nano-scale shift &cheap position sensor. It enables to extend frequency band, andenhance resolution of available on the market vibrometers/seis-mographs by 10–100 times, depending on the model of the baseproduct (such as, the American KS-1/KS-54000 & FBA-23; Eu-ropean GS-13 & STS-1/STS-2, and Russian SM-3—its sensorwas compared with the created sensor). Test-model of the newsensor permits to transfer vibrations of buildings and construc-tions with amplitudes superior to 1 nm into detectable electricalsignal. Such high is the achieved resolution, because due tomuch higher precision one may measure the frequency, com-pared with the inductance or capacitance, oscillators are mostsuitable sensors for high-precision detection. This is why a sim-ilar position sensor, based on the inductance-change detectionof the lithographically-made single-layer flat coil, shows by 3orders less resolution [11].

Except of usage of the present sensor in seismic prediction& protection, it may be applied also in geophysics, in securitysystems, military science, in micro- and nano-electronics, etc.:

in security systems (for protection of bank funds andState-priority objects, for safety take-off/landing of air-crafts, etc.);in geophysics & town-planning (for gas and oil prospectingand to reveal weak vibrations of buildings and construc-tions);in micro- and nano-electronics (as the position sensing andcontrolling tools, for creation of NG-microscopes with along-range action ‘magnetic-field’ probes (ASC’06 Prog #2EF03);in military science, engineering & Intelligence (to detectthe onset and amount of attacking soldiery of enemy armforces in the absence of direct visibility, as well as to revealand detect low-powered nuclear weapon tests);in basic research (for high-precision measurements of theCasimir Force and very little friction related with it).

Besides, High- or/and Low- superconductive coil-based3D analog of such new position sensor, seems, may be usefulfor sub-Angstrom spatial-resolution gravity-wave detection.

REFERENCES

[1] M. Bath, Introduction to Seismology. New York: John Wiley & Sons,1973.

[2] S. G. Gevorgyan, T. Kiss, A. A. Movsisyan, H. G. Shirinyan, Y.Hanayama, H. Katsube, T. Ohyama, M. Takeo, T. Matsushita, and K.Funaki, “Highly sensitive open-flat coil magnetometer for the �(H;T)measurements in plate-like high- T cuprates,” Rev. Sci. Instrum., vol.71, no. 3, pp. 1488–1494, 2000.

[3] S. G. Gevorgyan, T. Kiss, T. Ohyama, A. A. Movsisyan, H. G.Shirinyan, V. S. Gevorgyan, T. Matsushita, M. Takeo, and K. Funaki,“Calibration of the open-flat coil-based tunnel diode oscillator tech-nique (OFC-magnetometer) for quantitative extraction of physicalcharacteristics of superconductive state,” Physica C: “Superconduc-tivity and Its Applications”, vol. 366, no. 1, pp. 6–12, 2001.

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[6] C. T. Van Degrift, “Tunnel diode oscillator for low temperature mea-surements with an accuracy of about 10 ,” Rev. Sci. Instrum., vol. 46,no. 5, p. 599, 1975.

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[9] S. G. Gevorgyan, T. Kiss, M. Inoue, A. A. Movsisyan, H. G.Shirinyan, T. Harayama, T. Matsushita, T. Nishizaki, N. Kobayashi,and M. Takeo, “Peculiarities of the magnetic phase diagram insmall-size untwinned YBa Cu O crystal constructed by highlysensitive OFC-magnetometer,” Physica C: “Superconductivityand Its Applications”, vol. 378–381, no. P1, pp. 531–536, 2002.

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