CN113410595B - Terahertz low-pass angle filter of square ring-four split ring type - Google Patents
Terahertz low-pass angle filter of square ring-four split ring type Download PDFInfo
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- CN113410595B CN113410595B CN202110319943.0A CN202110319943A CN113410595B CN 113410595 B CN113410595 B CN 113410595B CN 202110319943 A CN202110319943 A CN 202110319943A CN 113410595 B CN113410595 B CN 113410595B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
- H01P1/00—Auxiliary devices
- H01P1/20—Frequency-selective devices, e.g. filters
- H01P1/2002—Dielectric waveguide filters
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
- H01Q15/0006—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices
- H01Q15/0086—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices having materials with a synthesized negative refractive index, e.g. metamaterials or left-handed materials
Abstract
The invention discloses a square-ring-four-split-ring terahertz low-pass angle filter, which is formed by periodically arranging a plurality of square-ring-four-split-ring rectangular periodic units, wherein the rectangular periodic units comprise two layers, namely a metal pattern layer and a medium substrate layer from top to bottom, the metal pattern layer is tightly attached to the surface of the medium layer, the metal pattern layer comprises an outer ring and an inner four-split ring, the outer ring comprises a first square ring arranged on the periphery, the inner four-split ring comprises a second square ring which is arranged inside the first square ring and is coaxially concentric, and four rectangles which are communicated with each other and penetrate through the first square ring and the second square ring, the four rectangles are arranged at the positions of four middle points of the first square ring and the second square ring, and the four rectangles do not intersect with each other, when the terahertz waves are obliquely incident on the metal pattern layer, LC resonance can be excited, and the filtering effect on the obliquely incident waves is realized.
Description
Technical Field
The invention belongs to the technology of terahertz low-pass angle filters, and particularly relates to an omnidirectional low-pass terahertz angle filter with a square ring-four-split ring structure.
Background
Terahertz (THz) waves refer to wave bands with frequency spectrums between microwave waves and infrared waves, have the characteristics of microwaves and light waves, and also have the characteristics of strong penetrating power, rich spectral information, low photon energy, low frequency bandwidth and the like, so that the terahertz (THz) waves have wide application prospects in the fields of radars, communication, detection, imaging and the like.
In electromagnetic theory, an electromagnetic wave can be characterized by several electromagnetic parameters, such as: phase, amplitude, frequency, polarization, and propagation direction, etc. In order to realize selective control of electromagnetic waves, attempts have been made to design related devices for controlling transmission of electromagnetic waves by influencing electromagnetic parameters, such as polarization converters, absorbers, and filters. A frequency domain filter: the transmission or reflection of electromagnetic waves with different frequencies can be controlled, and the selection of the electromagnetic waves with different frequencies is realized; a polarization selector: the device can control the transmission or reflection of electromagnetic waves with different polarization modes, and realize the selection of the electromagnetic waves with different polarization directions. An angle filter: the device can control the transmission or reflection of electromagnetic waves in different propagation directions, and realizes the selection of the electromagnetic waves in different propagation directions. At present, a great deal of work is already carried out to selectively control terahertz waves according to the frequency and polarization mode of the terahertz waves, such as terahertz absorbers, terahertz polarization converters and the like. In comparison, the device capable of selectively controlling the propagation direction of the terahertz wave is slow in progress, and the conventional terahertz angle filter has the problems of low transmittance of normal incident terahertz waves, poor angle selectivity, narrow working surface, complex structure, difficulty in processing and the like. Therefore, it is necessary to design a terahertz angle filter which has a simple structure, high transmittance for normal incident terahertz waves, is suitable for multiple incident planes, and has a good angle selection characteristic to meet the requirements of the terahertz angle filter on privacy protection of terahertz waves, high signal-to-noise ratio detectors, and the like.
Disclosure of Invention
The present invention is directed to solving the above problems of the prior art. The terahertz low-pass angle filter is simple in structure, high in transmission rate of normal incidence terahertz waves, good in angle selectivity, free in incidence surface and of a 'square ring-four open ring' type. The technical scheme of the invention is as follows:
a terahertz low-pass angle filter of a square ring-four open ring type is composed of a plurality of square ring-four open ring type rectangular periodic units which are arranged periodically, the rectangular periodic units are two layers, a metal pattern layer and a medium substrate layer are respectively arranged from top to bottom, the metal pattern layer is tightly attached to the surface of the medium layer, the metal pattern layer is an outer square ring and an inner four open ring, the outer square ring is a first square ring arranged on the periphery, the inner four open ring comprises a second square ring which is arranged inside the first square ring and is coaxial and concentric, and four rectangles which are communicated with each other and penetrate through the first square ring and the second square ring, the four rectangles are arranged at four midpoint positions of the first square ring and the second square ring and do not intersect with each other, wherein the outer square ring increases the reflection of oblique waves in a mode of increasing the area of a metal surface, the reflection of oblique incident waves is increased through exciting LC resonance by the inner four-opening ring, terahertz waves are incident from the side of the metal pattern layer, the incident terahertz wave is incident at the angle theta between the vector k and the normal of the square ring-four-opening ring plane, the electric field E is always kept horizontal to the y axis, the electric field E, the magnetic field H and the wave vector k are perpendicular to each other, when the terahertz waves are obliquely incident on the metal pattern layer, LC resonance can be excited, and the filtering effect on the oblique incident waves is achieved.
Further, the dielectric substrate layer is made of one of polyimide, fused quartz and silicon.
Further, the dielectric substrate layer has a dielectric constant of 2.5 to 3.75, a loss tangent of 0.0027 to 0.30, and a thickness of 10 to 100 μm.
Furthermore, the cycle length of the medium substrate layer in the x direction and the y direction is 300-500 mu m.
Further, the metal pattern layer had a thickness of 0.1 μm and an electrical conductivity of 4.561 × 107A gold layer of S/m.
Further, in the metal pattern layer, the side length b of the second square ring is 250.0 μm, and the ring thickness of the second square ring is l2Rectangular long l 23.0 μm1105.0 μm, ring thickness l of the first square ring3＝30.0μm。
The invention has the following advantages and beneficial effects:
1. the traditional terahertz angle filter is generally formed by complex structures such as photonic crystals, metal nanowire arrays or all-dielectric gratings and is difficult to be practically applied, and the terahertz angle filter is based on a metamaterial formed by a square ring-four-opening annular metal pattern layer and a dielectric substrate layer; at present, a double-opening resonant ring structure is the most widely used metamaterial structural unit with an angle filtering characteristic, a symmetrical four-opening ring structure is obtained by optimizing the double-opening resonant ring structure, filtering of oblique incident waves of any incident surface is achieved by using the rotational symmetry characteristic of the structure, the area of a metal surface is increased by adding a square ring, and reflection of oblique incident terahertz waves is increased.
2. The angle filter based on the square ring-four open ring has the impedance real part of 1.05 and the impedance imaginary part of-0.08 (close to 0) at 0.16THz, namely, the free space and the structure meet the impedance matching condition at the interface, so that the terahertz angle filter has very high transmittance to the normal incident wave at 0.16 THz. The invention has simple structure, convenient implementation and ingenious design, has outstanding practical characteristics and remarkable progress, and is suitable for large-scale popularization and application.
Drawings
FIG. 1 is a three-dimensional schematic diagram of a 4 x 4 array structure of a square-ring-four-open-ring terahertz low-pass angular filter according to a preferred embodiment of the present invention;
FIG. 2 is a schematic forward view of a basic component unit structure of a square ring-four open ring terahertz low-pass angle filter;
fig. 3 is a side schematic view of a "square ring-four open ring" type terahertz low-pass angular filter;
FIG. 4 is a schematic diagram of an incident direction of a terahertz wave in a square-ring-four-split-ring type terahertz low-pass angle filter;
fig. 5 is a transmission coefficient curve of a square ring-four open ring type terahertz low-pass angle filter at different incident angles;
fig. 6 is a graph of the operating angular domain bandwidth (i.e., the angular width of 0.707 of transmittance reduction) and the transmission coefficient of normal-incidence terahertz waves of the "square-ring-four-split-ring" type terahertz low-pass angular filter.
Detailed Description
The technical solutions in the embodiments of the present invention will be described in detail and clearly with reference to the accompanying drawings. The described embodiments are only some of the embodiments of the present invention.
The technical scheme for solving the technical problems is as follows:
the invention provides a square-ring-four-split-ring terahertz low-pass angle filter which is structurally shown in figures 1-3 and formed by periodically arranging unit structures.
The unit structure is a double-layer structure and sequentially comprises a metal pattern layer 1 and a dielectric layer 2 from top to bottom.
The metal pattern layer 1 is composed of square rings with the side length equal to the period and variable four-opening square rings. The dark color part in fig. 2 and 3 is the metal pattern layer, and the metal pattern layer is tightly attached to the surface of the dielectric layer.
The unit structure is square, and the side length of the period of the unit structure is 400.0 mu m.
The dielectric substrate layer is made of polyimide, has a dielectric constant of 3.5, a loss tangent of 0.0027 and a thickness of 50.0 mu m.
The metal pattern layer has a thickness of 0.1 μm and an electrical conductivity of 4.561 × 107A gold layer of S/m.
As shown in fig. 2, the metal pattern layer has the specific dimensions: b 250.0 μm, l2＝23.0μm，l1＝105.0μm，l3＝30.0μm。
When incident terahertz waves vertically enter the terahertz angle filter of the metamaterial structure along the-z direction, the vertically incident waves have high transmissivity due to the fact that the impedance of the metamaterial structure is matched with the impedance of free space; when terahertz waves are vertically incident, almost no electric field is excited in the metamaterial unit structure; when the terahertz wave is obliquely incident, the electric field intensity at the two openings of the metal ring is gradually increased, and the openings are equivalent to a capacitor element. When terahertz waves are vertically incident, almost no magnetic field is excited in the metamaterial unit structure; when terahertz waves are obliquely incident, the magnetic field intensity of the upper surface and the lower surface of the two semi-metal rings is gradually increased, and the metal rings are equivalent to an inductance element. Literature research shows that the split ring structure can be equivalent to an inductance-capacitance (LC) circuit, wherein the opening is equivalent to a capacitance element, the metal arm is equivalent to an inductance element, and when one of the following conditions is met, incident terahertz waves can excite LC resonance: (1) the component of an electric field vector E of the incident wave is vertical to the opening direction of the metal ring; (2) the magnetic field vector H of the incident wave has a component perpendicular to the plane of the metal ring, and if the condition (2) is satisfied, a circular current is generated in the metal ring, resulting in a magnetic field generated in the opposite direction to the original magnetic field. As can be seen from fig. 3, when the terahertz wave is perpendicularly incident (at this time, the component of the magnetic field in the direction perpendicular to the plane of the metal ring is 0), almost no surface current is generated on the metal ring; when terahertz waves are obliquely incident (at the moment, the component of the magnetic field in the direction perpendicular to the plane of the metal ring is gradually increased), the surface current on the metal ring is gradually increased, and the current flow directions on the upper metal half ring and the lower metal half ring are the same, so that a loop current is formed. In conclusion, the designed double-opening resonance ring structure meets the condition (2) that the open ring structure generates LC resonance, namely when the terahertz wave obliquely enters, the LC resonance can be excited, and the filtering effect on the obliquely incident wave is realized.
As shown in fig. 4, which is a schematic view of an incident direction of a terahertz wave, the terahertz wave is incident from the metal pattern layer side, an angle between a vector k of the incident terahertz wave and a normal of a plane of the double-opening resonant ring is θ, an electric field E is always horizontal to a y-axis, and two pairs of the electric field E, the magnetic field H and the vector k are perpendicular to each other
As shown in fig. 5, at a frequency of 0.16THz, the transmission coefficient rapidly decreases as the incident angle increases.
As shown in fig. 6, the dotted line is a schematic diagram of the transmission coefficient of the angular filter at 0.16THz as a function of the incident angle, and it can be seen that the transmission coefficient of the structure for the normal incident wave is 0.981, and the 3dB angular domain bandwidth is 9.8 °; the dotted line is a schematic diagram of the change of the transmission coefficient with the incident angle obtained after the surface metal layer of the structure is removed (namely only the polyimide substrate layer remains); comparing the two curves can be seen: at the frequency of 0.16THz, the terahertz angle filter based on the square ring-four open ring has a very obvious filtering effect on oblique incidence terahertz waves.
It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
The above examples are to be construed as merely illustrative and not limitative of the remainder of the disclosure. After reading the description of the invention, the skilled person can make various changes or modifications to the invention, and these equivalent changes and modifications also fall into the scope of the invention defined by the claims.
Claims (6)
1. A terahertz low-pass angle filter of a square ring-four open ring type is characterized by being formed by periodically arranging a plurality of square ring-four open ring type rectangular periodic units, wherein the rectangular periodic units are two layers, namely a metal pattern layer and a medium substrate layer from top to bottom, the metal pattern layer is tightly attached to the surface of the medium layer, the metal pattern layer comprises an outer square ring and an inner four open ring, the outer square ring is a first square ring arranged on the periphery, the inner four open ring comprises a second square ring which is arranged inside the first square ring and is coaxially concentric, and four rectangles which are communicated with the first square ring and penetrate through the opening of the second square ring, the four rectangles are arranged at four midpoint positions of the first square ring and the second square ring, and the four rectangles do not intersect with each other, the outer square ring increases reflection of oblique incident waves in a mode of increasing the area of a metal surface, the inner four-opening ring increases reflection of oblique incident waves in a mode of exciting LC resonance, terahertz waves are incident from the side of the metal pattern layer, the angle between the incident terahertz wave vector k and the normal line of the square ring-four-opening ring plane is theta, an electric field E is always kept horizontal to the y axis, the electric field E, the magnetic field H and the wave vector k are perpendicular to each other, when the terahertz waves are obliquely incident to the metal pattern layer, LC resonance can be excited, and the filtering effect of the oblique incident waves is achieved.
2. The terahertz low-pass angle filter of a "square ring-four open ring" type of claim 1, wherein the material of the dielectric substrate layer is one of polyimide, fused quartz, and silicon.
3. The terahertz low-pass angle filter of a square-ring-four-split-ring type as claimed in claim 1, wherein the dielectric substrate layer has a dielectric constant of 2.5-3.75, a loss tangent of 0.0027-0.30, and a thickness of 10-100 μm.
4. The square-ring four-open-ring terahertz low-pass angle filter as claimed in claim 1, wherein the period lengths of the dielectric substrate layer in x and y directions are both 300-500 μm.
5. The terahertz low-pass angle filter of the "square-four open-loop" type of claim 1, wherein the metal pattern layer has a thickness of 0.1 μm and an electrical conductivity of 4.561 x 107A gold layer of S/m.
6. The terahertz low-pass angular filter of the "square-four open ring" type according to claim 1, wherein in the metal pattern layer, the side length b of the second square ring is 250.0 μm, and the ring thickness of the second square ring is l2Rectangular long l 23.0 μm1105.0 μm, ring thickness l of the first square ring3＝30.0μm。
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