RU2626065C2 - Method of measuring intensity of electric field - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: method of measuring electric field intensity relates to measurement equipment and can be used for research of electric fields of the Earth's atmosphere and outer space. Method of measuring electric field intensity based on that electric field intensity sensor with controlled dielectric (with variable dielectric permeability under effect of electric field) performs detection of electric field intensity by measuring phase shift of signal in strip transmission line, on basis of which sensor is made. In order to reduce size of sensor it can be made on basis of resonant section of transmission line, i.e. stripline resonator. To expand dynamic range of possible implementation of sensor based on system of interacting stripline resonators, which in fact represents bandpass filter with adjusting central frequency shifting phase-frequency characteristic under effect of external electric field. Due to this at frequencies of pass band signal phase shift occurs, value of which is determined by electric field intensity.

EFFECT: increased sensitivity and reduced dimensions.

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Description

The method of measuring electric field strength relates to measuring technique and can be used to study the electric fields of the earth's atmosphere and outer space.

A known method of measuring electric field strength, based on the use of a ferroelectric, placed in the studied field [M.I. Ivanov. The method of measuring the electric field / AC No. 140495, publ. 1961 bull. No. 16]. The value of the electric field is determined by the change in the degree of absorption in the ferroelectric of ultrasonic vibrations excited by means of a vibration emitter mounted on it and a receiver of these vibrations. The implementation of the described method, according to the invention, provides in some cases an increase in measurement accuracy.

There is also a method of measuring the intensity of a constant electric field, consisting in the fact that a ferro-capacitor is placed in the studied field, the dielectric constant of the material of which is changed by an auxiliary alternating field [Yu.P. Building, A.A. Balchitis, V.Yu. Lazauskas, I.K. Petrushkevichus. Device for measuring electric field strength / AC No. 203781, publ. 10/9/1967, bull. No. 21]. As a result of this effect, a bias current arises in the volume of the ferro-capacitor, which is used to judge the strength of the external (measured) electric field.

It is known that on the basis of a dielectric and a pair of strip conductors it is possible to realize a “strip resonator” used in the microwave technique. A method for calculating the Q factor of a strip resonator and other characteristics of the device is described in patent RU 2352032 “Strip resonator”, application of 10/31/2007, inventors Belyaev BA, Lexikov AA, Sergeants AM, published on 04/10/2009. as follows: At the resonant frequencies of the structure, when, for example, half the wavelength of the electromagnetic wave is laid along the length of each strip conductor, both conductors in the resonator have the same distribution of high-frequency currents and voltages along their length, i.e., current It is divided into two conductors in the cavity, which reduces losses and improves the quality factor.

The main disadvantage of the described methods for measuring the electric field is the low sensitivity and large size of the sensor, which introduces an error in the measurement of the field.

The technical result realized when using the proposed method is to increase the sensitivity and reduce the size of the sensor.

The indicated technical result is achieved in that in a sensor of electric field strength containing a dielectric with a dielectric constant changing under the influence of an electric field, then a controlled dielectric ("voltage-controllable dielectric"), it is new that registration of electric field strength is carried out by measuring shear phase of the electromagnetic wave propagating in the strip transmission line, on the basis of which the sensor is made. Here, by the phase shift of the signal is meant the delay time of the quasimochromatic wave packet, which is associated with the method of measuring the phase shift.

The differences of the proposed method from the closest analogue are that the registration of the electric field is carried out by measuring the phase shift of the signal in a strip transmission line containing a controlled dielectric. This difference allows us to conclude that the proposed technical solution meets the criterion of "novelty." Signs that distinguish the claimed technical solution from the prototype are not identified in other technical solutions when studying this and related areas of technology and, therefore, provide the claimed solution with the criterion of "inventive step".

The invention is illustrated by the following drawings:

FIG. 1 is a design of an electric field strength sensor based on a strip line containing a controlled dielectric;

FIG. 2 is a design of an electric field strength sensor based on a strip resonator containing a controlled dielectric;

FIG. 3 - amplitude-frequency (AFC) and phase-frequency (PFC) characteristics of a band-pass filter at two values of the dielectric constant of the substrate;

FIG. 4 is a design of a specific implementation of a sensor based on coupled strip resonators;

FIG. 5 - calculated dependence of the phase shift of the signal at the output of the strip bandpass filter with liquid crystal filling on the intensity of the external electric field.

It is well known that for a transmission segment of a strip line (PL) coordinated with the signal source and receiver with a length l, the phase incursion of the transmitted signal is equal to its electric length

where λ is the wavelength of the high-frequency signal in vacuum, ε is the effective dielectric constant of the dielectric PL, depending on the strength of the external electric field. In this case

From formula (2) it follows that if the insulator of the submarine contains a controlled dielectric, then the registration of the external electric field can be carried out by measuring the phase shift of the electromagnetic wave in the submarine.

In FIG. 1 shows the simplest design of an electric field strength sensor based on the proposed method. The device comprises a stripe transmission line connected to the input and output ports 2. matched in wave impedance to the source (not shown) and the signal receiver (not shown). The strip line (hereinafter also referred to as PL) is formed by strip conductor 1, conducting base 4, and dielectric substrate (insulator) 3, consisting of a material whose dielectric constant depends on the applied electric field. The lower side of the substrate is metallized and together with the body forms a grounded base 4.

The sensor based on the proposed method works as follows. Under the influence of the measured electric field, the effective dielectric constant of the insulator of the submarine changes. In this case, a change in the propagation velocity of the electromagnetic wave in it occurs, which leads to an additional phase shift at the output of the submarine, by measuring which the magnitude of the electric field can be determined. An important advantage of this measurement method is that its sensitivity can be increased by increasing the length of the submarine, since this increases the phase shift of the signal, which is proportional to this length (2).

The size of the sensor can be significantly reduced by using a transmission line section that is resonant at the operating frequency, i.e. strip resonator.

Methods for calculating the parameters of a strip resonator are available in patent RU 2352031.

Let us consider a controlled phase shift of a segment of a strip transmission line of length l under resonance conditions. It is known [G.S. Gorelik, Oscillations and waves, State Publishing House of Physics and Mathematics, Moscow: 1959, p. 102] that the frequency dependence of the phase in resonance is determined by the formula

, несложно найти величину управляемого сдвига фазы, вызванного сдвигом частоты резонатора за счет изменения электрического поля, путем дифференцирования формулы (3)where Q is the quality factor of resonance, ω ₀ is the resonant frequency. Expressing the resonant frequency through the length of the PL segment - l, the speed of light in vacuum - s, and the effective dielectric ε:

, it is easy to find the magnitude of the controlled phase shift caused by the frequency shift of the resonator due to a change in the electric field, by differentiating the formula (3)

Since near the resonance ω≈ω ₀ , for the resonator

For a consistent transmission line under the same conditions

Thus, it can be seen from formulas (5) and (6) that the phase shift controlled by an external electric field, i.e. the sensitivity of the sensor in the "resonant" device is approximately Q times greater than in the matched line, or with the same sensitivity, the "resonant" device can be made Q times smaller. It is important to note that in a real device, the Q value is the loaded Q-factor of the resonator.

In FIG. 2 shows the construction of an electric field sensor based on a strip resonator. The device comprises a segment of a strip transmission line (strip conductor) 1, a resonant length at the operating frequency (in this case, a strip resonator formed by a strip conductor 1, a dielectric substrate (insulator) 3 and a conductive base 4), which is connected to the input and output through the capacitance connection 5, the value of which determines its loaded Q factor. The resonator is connected to the input and output ports 2 and is made on a dielectric substrate (insulator) 3, consisting of a controlled dielectric.

As a controlled dielectric, ferroelectrics, liquid crystals, and other materials known from the prior art can be selected.

Under the influence of the measured electric field, a change in the dielectric constant of the material occurs, which is accompanied by a change in the resonant frequency of the resonator and a shift in the phase-frequency characteristic. It is obvious that the signal at a frequency f ₀ undergoes a certain phase shift, the magnitude of which will depend on the strength of the applied electric field.

Thus, with the same sensitivity, the “resonant” sensor will have significantly smaller dimensions. However, despite the high sensitivity and miniature size, the dynamic range of such a device remains small, due to the narrow bandwidth of the working frequencies of a single resonator, which is determined by its quality factor.

To expand the dynamic range, you can use a system of interacting strip resonators, which, in fact, is a band-pass filter, the frequency of which is tuned by an external electric field. A device based on the proposed method works as follows. In FIG. Figure 3 shows the typical frequency response (L) and phase response (ϕ) of the filter with a solid line, and the dashed line shows the same when tuning the center frequency by a certain amount not exceeding the bandwidth. It can be seen that in some frequency band the frequency response remains uniform, and the phase response is sufficiently linear, with a phase shift Δϕ occurring at each frequency from this interval.

Let us determine how the phase shift Δϕ of such a device depends on the tuning of its center frequency by δf. We find the phase shift Δϕ of the signal passing through the resonant circuit at the frequency ω, when the resonant frequency of the latter changes from ω ₀₁ = ω-δω to ω ₀₂ = ω + δω when δω << ω. We introduce the notation Δω / ω = δ; then, based on formula (3)

Transforming the difference of arctangents, we obtain

Since δ << 1, then with a high degree of accuracy

From formula (9) it is seen that the phase shift in the system of interacting strip resonators in the device is greater, the higher the resonance Q factor and the greater the shift in the central frequency of the passband, however, it should be borne in mind that in a real device Q is loaded Q factor. Obviously, the phase shift is proportional to the number of resonators in the device, i.e. for a system consisting of N resonators

Thus, it is obvious that by increasing the bandwidth, it is possible to expand the dynamic range of such a sensor while maintaining high sensitivity.

The sensor based on the proposed method works as follows. In the sensor, made on the basis of a system of interacting strip resonators, in which a dielectric controlled by a field is selected, the central frequency of the passband of the filter, as well as the phase response, is shifted by an external electric field (Fig. 3). By measuring the phase shift at a selected frequency, for example, f ₀ , it is possible to determine the magnitude of the external electric field by the phase shift. Obviously, the wider the bandwidth of the device, the greater will be the dynamic range of measurement of electric field strength.

The choice of the material of the controlled dielectric is determined by the energy loss in the dielectric, the quality factor of the system, and the variability of the dielectric constant.

In the example below, a liquid crystal (LC) with an anisotropy of dielectric constant, which coincides in direction with the electric field vector, is selected.

In the technology of creating elements for microwave electronics (phase shifters and filters), it is known to use ferroelectric thin films with a strong dependence of 8 on E. In [Z. Yuan, Y. Lin, J. Weaver, X. Chen, CL Chen, Applier Physics Letters, Vol. 87, 152901 (2005)] demonstrated an 80% change in the dielectric constant in the range of the applied field from 0 to 8 V / μm. The material is Mn: BSTO (BSTO designation for ceramic ferroelectric Ba _1-x Sr _x TiO ₃ ). In [J. Park, J. Lu, S. Stemmer, RA York, Journal of Applied Phsyics, Vol. 97, 084110 (2005)] shows a strong dependence of the dielectric constant on the electric field for a ferroelectric (Ba, Sr) TiO ₃ (BST) in a wide frequency range.

As is clear from the disclosed invention, ferroelectric films can be used as a controlled dielectric.

In FIG. 4 shows an example of a specific implementation of an electric field sensor based on the proposed method. In such a device, the role of a controlled dielectric (dielectric substrate (insulator) 3) is played by a layer of liquid crystal (hereinafter also referred to as LC). Due to the presence of dielectric constant anisotropy in an LC, the tensor components of which depend on the director’s orientation, in this design it becomes possible to control the dielectric constant by an external electric field.

The sensor is based on the structure of a strip filter, consisting of five interacting strip resonators.

The input and output of the device is connected through ports 2 to external transmission lines with a wave impedance of 50 Ohms through strip conductors (resonators) 6, which have a distributed electromagnetic connection with resonators formed by strip conductors 1. The dielectric substrate (insulator) 3 is in the gap formed by a grounded base 4 and a thin quartz substrate 7, on the inner surface of which regular strip conductors of electromagnetically coupled resonators 6 are formed.

With the right choice of lengths and connections of the resonators of the sensor, it is possible to form a uniform passband at the sensor, centered on the resonant frequency. When the external electric field orthogonal to the plane of the substrate is equal to zero, the interaction with the "walls" is oriented by the director of the LC in the plane of its layer. In this case, the dielectric constant of the LC is minimal with respect to the polarization of the microwave electric field in the microstrip resonator. With a nonzero external electric field, an electric field is induced directly below the strip conductor 1, which rotates the director of the LC to the direction of the lines of force of the microwave electric field of the resonators, as a result, the value of 8 increases, reaching a maximum when the director is set perpendicular to the LC layer.

In the program of electrodynamic modeling, the design of the sensor was calculated based on the proposed method. The sensor had the following design parameters. The number of identical NS resonators, the width of the strip conductors of the resonators is 1.2 mm, their length is 15.5 mm, the range of variation of the dielectric constant of the LC under the influence of an external electric field is 2.8-3.1 (i.e., the anisotropy of the LCD is Δε = 0.3), the thickness of the layer of the LCD dielectric is 0.5 mm . The operating frequency of the sensor was 6 GHz with a maximum value of the controlled phase shift at this frequency ≈720 °. To measure the phase difference in such a wide range, an amplitude-modulated signal can be used, while a coarse measurement of the phase shift is performed at a low signal modulation frequency, and accurate at a working frequency. This allows you to expand the measurement range of the phase shift.

In FIG. 5 shows the calculated dependence of the obtained phase shift of such a sensor (shown in Fig. 4) depending on the intensity of the applied electric field. In the calculation, the experimentally measured dependence of the dielectric constant 6 of the used LC on the strength of the applied electric field was used. Estimates showed that with a phase measurement accuracy of ± 0.05 °, the sensitivity of the sensor can reach ≈3 V / m. This sensitivity is significantly higher than that of the closest analogues, and it can be increased even more by increasing the number of resonators in the sensor and using a liquid crystal with greater anisotropy. Using bridge phase shift meters, the sensitivity of the sensor based on the proposed method can be significantly improved.

Thus, the proposed method for measuring the electric field strength allows you to create sensors based on it, with high sensitivity and small size.

Claims (4)

1. The method of measuring the electric field strength, which consists in the fact that in the electric field strength sensor containing a controlled dielectric, characterized in that the registration of the electric field strength is performed by measuring the phase shift of the electromagnetic signal propagating in the strip transmission line. 2. A method of measuring electric field strength according to claim 1, characterized in that the sensor is made on the basis of a resonant segment of a strip transmission line. 3. The method of measuring electric field strength according to claim 2, characterized in that the sensor is made in the form of a system of coupled strip resonators. 4. A method of measuring electric field strength according to any one of paragraphs. 1-3, characterized in that as a controlled dielectric selected liquid crystal with a longitudinal component of the dielectric constant, depending on the electric field strength.

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