Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2001-06-25
2003-12-16
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C333S158000
Reexamination Certificate
active
06664708
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a device and method for the contactless detection of external electric and magnetic fields.
BACKGROUND OF THE INVENTION
As is widely known, piezoelectric materials possess the special property of becoming electrically polarized under mechanical pressure. The converse effect is known as well. Such properties have given rise to the development of various piezoelectric sensors and detectors.
The mentioned converse approach enables piezoelectric elements to be utilized for sensing electric voltage applied thereto. In such sensors, the voltage applied to the element results in respective mechanical deformation of the element, which can be registered.
U.S. Pat. No. 4,340,872 describes a controllable piezoelectric crystal delay line. An input signal is transmitted through input lines to an input transducer and an output signal is received through output lines from an output transducer. The input signal is converted to a surface acoustic wave (SAW) propagating along the surface of the piezoelectric crystal. Control electrodes are applied to surfaces of the piezoelectric crystal and are connected to control lines. A control signal (an electric voltage) is applied to the control lines, and thus an electric field applied to the piezoelectric crystal alters its longitudinal dimension and, consequently, controls the propagation distance between the input transducer and the output transducer. By varying the propagation distance between the transducers, the control signal continuously varies the propagation delay of SAW. Thus, the time delay between the input and output signals is a function (i.e., a measure) of the control voltage applied to the driven lines. However, the device of US'872 provides for measuring an electrical field using contacts, i.e., without guarantying desired safety.
EP 810724 describes a tunable piezoelectric delay line comprising a SAW conducting piezoelectric substrate, two transducers and an additional electrode. This device is claimed to be used as a voltage sensor. The delay line is tuned by applying electric voltage to the additional electrode manufactured as a capacitive MOS structure (a semiconductor plate) which is superimposed on the piezoelectric substrate between the transducers of the delay line. The electroconductivity of the semiconductor plate electrode is controlled by the electric field effect. Since the SAW velocity depends on the electroconductivity of the adjacent electrode, the application of voltage to the MOS structure controls the delay time of the delay line. The structure described in EP 810724 is quite complex to prepare and, besides that, has low sensitivity to the applied electrical voltage. Another drawback of the device is its inapplicability to cases where non-contact detection of electric field or voltage is required, since in the device, the voltage of interest has to be applied to the semiconductor plate via electrical contacts.
Technique aimed at measuring external fields are also disclosed in the following publications: DE 19514342, WO 97/09624, and WO 93/13495.
According to the technique disclosed in DE 19514342, a current transformer assembly is used for determining voltage by measuring an electric current flowing in a high-voltage power line (electrical wire). However, for example, in the case of line disruption, this technique does not allow to determine the presence of a high voltage unambiguously.
According to WO 97/09624, a voltmeter utilizing an impedance voltage divider is used, being inserted between an electrical conductor whose electrical potential is to be measured relative to an electrical base potential, and this base potential. A surface-wave device is used as a part of the voltmeter, and has the function of measuring an electric voltage occurring across the voltage divider, namely, a voltage whose electric field has a valuable effect on the wave propagation in the surface-wave device. This technique, however, is not a contactless one.
WO 93/13495 discloses the use of a passive surface-wave sensor that can be wirelessly interrogated and used for measuring an external temperature field. The description of this technique focuses on the kinds of interrogation signals and a code used in an acoustic line, presenting no specific construction of a measuring device suitable to be used with this technique. The interrogation signals are frequency-modulated, and the acoustic line is chirped-coded and located in a particular place, where some external temperature field is to be fixed or measured.
Thus, practically, no solution has been found so far in the relevant prior art for the non-contact detection of electric fields or voltages, i.e., for safe measurement. This problem prevents performing a quick and safe test to determine whether a required voltage exists between electric wires in a power supply line, or in other hard-to-reach points.
Another modification of a delay line, such as a so-called resonator delay line is also known in the art. It comprises a transducer placed on a substrate and two systems of reflectors disposed bilaterally of the transducer.
U.S. Pat. No. 5,469,170 describes a system of passive SAW-identification tags to be placed on a plurality of articles, wherein the tags operate with the aid of a chirp transducer. The passive SAW-ID tag device is provided with a piezoelectric substrate having bus bars, spaced electrode taps between the bus bars and a built-in antenna, connected with an input SAW transducer matched to an input chirp signal generated by a nearby located chirp transmitter (an interrogating transmitter). The SAW-ID tags are intended for identifying articles and do not perform any additional function.
SUMMARY OF THE INVENTION
The main idea of the present invention consists of utilizing an effect, other than the converse piezoelectric effect. The converse piezoelectric effect is the linear effect consisting of the mechanical deformation of a piezoelectric element caused by an external electrical field to which the element is exposed. The effect utilized in the present invention is a non-linear effect and consists of a change in the velocity of propagation of a wave in a substrate capable of transporting the wave therethrough, wherein said change is caused by the application of an external electric or magnetic field. This physical effect, the so-called electroacoustic effect, is described, for example, in the following publications: “
Physical properties of crystals”,
J. F. Nye, Oxford, At the Clarendon Press, 1957; and R. B. Thompson and C. F. Quata, J. Appl. Phys. 42, 907 (1970).
Magneto-static and magneto-elastic waves can be created in magnetic materials (such as ferrites) when a micro-strip transducer mounted on a surface thereof is excited by an electromagnetic signal. Delay lines, functionally analogous to those known with respect to piezoelectric substrates, are described also for the magnetic materials. Moreover, the wave propagation characteristics, such as phase and group velocities and attenuation, depend on an external magnetic field to which the materials are exposed. The above properties are described, for example, in a monograph “
Spin waves and magnetic excitations”.
Edited by A. Borovik-Romanov, S. K. Sinha. North Holland. Amsterdam-New-York-Tokyo, 1988.
The present invention is particularly useful for the non-contact detection of the existence of an external electric or magnetic field in the vicinity of a high-voltage electric line. It should be understood that if the external field to be detected is an electric field, a piezoelectric or electrostriction substrate is used and said wave is an acoustic wave. If the external field to be detected is a magnetic field, the substrate is made of a magnetic material and said wave is a magnetic wave. The term “magnetic wave” used herein signifies a magneto-static or magneto-elastic wave in magnetic materials.
The inventors have found that when dealing with the detection of an external electric or magnetic field, the above-indicated non-linear effect of the change in the velocity o
Kozlov Anatolii
Levin Marik
Shlimak Issai
Sondomirsky Vladimir
Dougherty Thomas M.
Voltage Vision Ltd.
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