Scanning-based THz near-field imaging device

Abstract

A simple, portable, real-time in-vivo THz imaging device is provided for imaging targets in a subject, such as teeth. The scanning-based THz imaging device is also highly sensitive compared to typical X-ray imaging devices. Thus, the scanning-based THz imaging device has the potential to operate at a density for early detection problems such as dental caries or demineralization of dental enamel. A method for diagnosing or imaging targets in a subject is also provided by using the scanning-based THz imaging device of the present disclosure.

Description

[Technical Field]

[0001] This disclosure relates to an imaging device, and more particularly to a scanning-based THz imaging device for biomedical imaging. [Background technology]

[0002] Terahertz (THz) science and technology have been a subject of great interest among researchers over the past two decades. The THz spectral gap between millimeter waves and infrared radiation is the last segment of the EM wave spectrum that needs to be investigated for potential disclosures. Furthermore, recent advances in terahertz sources and detectors have led to the current transition of terahertz systems from laboratory to commercial systems.

[0003] The common imaging practice in dentistry is X-ray imaging, which is not only harmful to patients but also requires large and expensive equipment. Conventional dental imaging techniques, such as X-ray and infrared emission imaging, do not have sufficient sensitivity for detecting the early stages of dental caries for early prevention. Furthermore, X-ray imaging is associated with the stage of disease treatment or surgery and is not reliably recommended by physicians for determining the early stages of caries.

[0004] Unlike X-rays, THz rays have low ionization energy, making them safe for use in biomedical imaging of humans. Comparisons of X-ray and THz images of human teeth have demonstrated that the significant improvement in THz image resolution has given terahertz systems the potential to be implemented in dentistry for the early detection of dental problems. Terahertz rays have unique dielectric properties in metals and dental tissues, making surgical procedures safer and easier, even for diagnosing very small gaps when filling teeth with metal.

[0005] While a few studies have demonstrated the feasibility of THz imaging of human teeth, many significant physical and technical challenges remain in developing clinical-level prototypes for monitoring caries in vivo. Currently, there are no demonstrated commercially available devices or in vivo imaging clinical prototypes. Major limitations in transitioning laboratory-level THz imaging devices to commercial disclosure include large and complex configurations, moving mechanical components, and expensive femtosecond lasers. THz pulse imaging is typically performed using THz time-domain spectroscopy (THz-TDS), which requires a mechanical delay stage, making it difficult to integrate into portable systems.

[0006] Therefore, in dentistry, a simple, portable, real-time bio-THz imaging device is highly desirable for early and rapid diagnosis of dental problems in a faster and safer manner. [Overview of the Initiative]

[0007] In light of the foregoing, this disclosure provides a simple and portable THz imaging system for both industrial and biomedical imaging.

[0008] In at least one embodiment of the present disclosure, a scanning-based THz imaging device comprises a THz emitter for emitting a terahertz signal, a generator coupled to the THz emitter and configured to induce the THz emitter to emit a terahertz signal, and a receiver for receiving the terahertz signal.

[0009] In at least one embodiment of the present disclosure, the THz emitter of a scanning-based THz imaging device includes a first cover; a first tapered structure disposed within the first cover and having a distal end and a proximal end opposite the distal end; a THz source disposed within the first cover and covered by the first tapered structure for inducing and generating a focused near-field beam profile at the distal end of the first tapered structure; and a beam deflector module coupled to the first cover. In some embodiments, the THz source is inwardly covered by the tapered structure.

[0010] In at least one embodiment of the present disclosure, a generator in a scanning-based THz imaging device is coupled to a THz emitter and configured to induce the THz emitter to emit a terahertz signal.

[0011] In at least one embodiment of the present disclosure, the receiver of a scanning-based THz imaging device comprises a second cover, a second tapered structure disposed within the second cover, and a THz detector disposed within the second cover and covered by the second tapered structure. In some embodiments, the THz detector is inwardly covered by the tapered structure.

[0012] In at least one embodiment of the present disclosure, the THz source comprises an RTD having an emitter and a collector, a resonant antenna electrically connected to the emitter and collector of the RTD, and an arrangement on the resonant antenna. Radiator It includes an antenna. In some embodiments, the RTD is a TBRTD or multi-barrier RTD containing an AIAs / InGaAS / AIAs layer, which significantly improves the overall DC-RF conversion efficiency and reduces the peak current-voltage.

[0013] In at least one embodiment of the present disclosure, the THz source has a radiator antenna. In some embodiments, the radiator antenna structure of the THz source is a spiral antenna structure or an arbitrary broadband antenna. In some embodiments, the radiator antenna structure of the THz source is a tunable fractal antenna structure, and the frequency shift can be altered by reconfiguring its fractal pattern or by voltage-induced dielectric constant changes within the antenna to achieve more continuous and minute frequency changes.

[0014] In at least one embodiment of the present disclosure, the first tapered structure of a scanning-based THz imaging device has an air core portion, a radiating aperture, and an inlet aperture. In some embodiments, the air core portion has an inner wall coated with a metallic material to induce and generate a focused near-field beam profile at the exit of the tapered end, and this near-field operation allows the spatial image resolution to exceed the diffraction limit and further improve the overall image resolution. In some embodiments, the radiating aperture of the first tapered structure is cut at a certain angle to increase the deflection angle.

[0015] In at least one embodiment of the present disclosure, the beam deflector module is positioned in a tapered radiating aperture and configured to transmit a terahertz signal.

[0016] In at least one embodiment of the present disclosure, the beam deflector module is fabricated on a curved surface to focus and deflect a terahertz signal, and the beam deflector module is positioned in a radiating aperture of a first tapered structure.

[0017] In at least one embodiment of the present disclosure, a beam deflector module is positioned at the entrance opening of a first tapered structure and is configured to deflect a terahertz signal emitted from a THz emitter and enter the tapered structure.

[0018] In at least one embodiment of the present disclosure, the beam deflector module comprises an electro-optic beam deflector or a Garbo mirror.

[0019] In at least one embodiment of the present disclosure, the beam deflector module is a physical terahertz fishnet metamaterial prism having a stacked fishnet structure.

[0020] In at least one embodiment of the present disclosure, the beam deflector module is a flat terahertz fishnet metamaterial prism having an array of signal layer terahertz fishnet metamaterial structures. In some embodiments, the terahertz fishnet metamaterial structure includes a first layer and a second layer opposite the first layer. In some embodiments, the array of single-layer terahertz fishnet metamaterial structures includes a plurality of droplets arranged between the first and second layers to form a plurality of droplet layers. In some embodiments, the droplets are composed of a liquid crystal material, and the size of the droplets is controlled by ultraviolet radiation to form a refractive index gradient.

[0021] In at least one embodiment of the present disclosure, the beam deflector module is an actively controlled metamaterial lens for converting functions between focusing, diverging, and collimating functions by changing the applied voltage.

[0022] In at least one embodiment of the present disclosure, a scan-based THz imaging device detachably connects a THz emitter to a receiver and further comprises a connector for isolating the THz emitter at a distance from the receiver. In some embodiments, the distance between the THz emitter and the receiver is adjusted by the connector to allow for the reconstruction of images of targets of different sizes.

[0023] The present disclosure also provides a method for diagnosing a target disease, disorder, or condition, comprising the steps of providing a scanning-based THz imaging device of the present disclosure; emitting a terahertz signal from a terahertz emitter onto the surface of a target within a subject that requires it; receiving, with a receiver, the terahertz signal reflected from the surface of the target; and diagnosing the condition of the target surface by analyzing the received terahertz signal. In some embodiments, the method further comprises the step of reconstructing an image of the target.

[0024] In at least one embodiment of the present disclosure, the target can be, but is not limited to, soft tissue (e.g., skin), hard tissue (e.g., bone), enamel, dental tubules, nerves, blood vessels of the subject. In some embodiments, the target may be a dielectric and have no water content, for example, a tooth or bone, but the present disclosure is not limited thereto. In some embodiments, the target is a tooth and the surface is the enamel surface of the tooth.

[0025] In at least one embodiment of the present disclosure, the target disease, disorder, or condition can be, but is not limited to, dental caries (especially in the initial stage), demineralization of tooth structure (e.g., tooth enamel), peri-implantitis, periodontal disease, gingivitis, the curing process of dental composites, lesions of the oral structure, or tooth abnormalities. Since human tooth enamel is transparent at 0.4 - 0.55 THz, dental caries or demineralization of enamel can be monitored at the initial stage itself. However, there are limitations in terahertz sources and detectors. Some embodiments of the present disclosure provide a THz scanner that uses an air-side emitting RTD and a beam scanning device suitable for dental imaging.

[0026] In at least one embodiment of the present disclosure, the target disease, disorder, or condition can be, but is not limited to, burns, edema, or cancer. In some embodiments, the burn is a second-degree or higher burn. In some embodiments, the cancer can be, but is not limited to, skin cancer, bone cancer, oral cancer, oral lymphoma, mucosal melanoma, oral sarcoma, oral squamous cell carcinoma, or adenocarcinoma. Cancer detection or cancer classification is one of the major biomedical applications; however, currently available THz cameras are not only expensive but also have poor resolution. Therefore, the transceiver design of the present disclosure can be assembled into an array using COMS technology, opening up the possibility of low-cost terahertz biomedical imaging, and as a result, achieving non-destructive cancer imaging using THz for cancer diagnosis.

[0027] In some embodiments, the terahertz radiation of a target with caries is greater than that of a target without caries.

[0028] In some embodiments, the target is a skin edge with a low refractive index and terahertz absorbance.

[0029] In some embodiments, the absorption of terahertz radiation in diseased tissue is greater than the absorption of terahertz radiation in healthy tissue.

[0030] In some embodiments, demineralized enamel exhibits an increase in the terahertz transmission signal compared to healthy tooth structure.

[0031] In some embodiments, compared to healthy tissue, the edge of cancer or tumor or low-density tissue may be detected as visible terahertz imaging at the initial, intermediate, or late stage of the target tissue.

[0032] This disclosure further provides a method for imaging a target in a subject, comprising the steps of: providing a scan-based THz imaging device of the target disclosure; emitting a terahertz signal from a terahertz radiator onto the surface of a target in a subject requiring it; receiving the terahertz signal reflected from the surface of the target in a receiver; and reconstructing an image of the subject using the received terahertz signal. In some embodiments, the target is a dielectric and does not contain water.

[0033] In a portable THz imaging device for diagnosing the condition of a subject as described in this disclosure, the THz imaging device may be manufactured as a simple, portable, real-time in vivo THz imaging device for imaging dental tissue. Furthermore, the portable THz imaging device has a sensitivity that is far more than sufficient to detect the early stages of caries compared to conventional X-rays. Thus, the THz imaging device of this disclosure can operate at a density for early detection of dental problems, such as imaging enamel thickness with high resolution. [Brief explanation of the drawing]

[0034] This disclosure can be better understood by referring to the attached drawings and reading the following description of embodiments. [Figure 1] Figure 1 is a schematic diagram of a device for reconstructing a real-time image of a target according to one embodiment of the present disclosure. [Figure 2] Figure 2 is a schematic diagram of a THz emitter of a device for emitting a terahertz signal according to one embodiment of the present disclosure. [Figure 3] Figure 3 is a schematic diagram of a receiver for an apparatus for collecting terahertz signals according to one embodiment of the present disclosure. [Figure 4A] Figure 4A is a schematic diagram of a THz source in an RTD (resonant tunneling diode) structure having an antenna according to one embodiment of the present disclosure. [Figure 4B]Figure 4B is a schematic diagram of a THz source in an RTD structure having an antenna according to another embodiment of the present disclosure. [Figure 4C] Figure 4C is a schematic diagram of a THz source in an RTD structure having an antenna according to another embodiment of the present disclosure. [Figure 4D] Figure 4D is a schematic diagram of a THz source in an RTD structure having an antenna according to another embodiment of the present disclosure. [Figure 5] Figure 5 is a cross-sectional view of a portion of a terahertz source according to one embodiment of the present disclosure. [Figure 6] Figure 6 is an exemplary graph showing the voltage-to-current density characteristics of a triple-barrier RTD (TBRTD) according to one embodiment of the present disclosure. [Figure 7] Figure 7 is an exemplary graph showing the estimated device capacitance versus maximum oscillation frequency characteristics of a TBRTD according to one embodiment of the present disclosure. [Figure 8] Figure 8 is a schematic diagram showing a frequency-adjustable fractal antenna for a THz source according to a different embodiment of the present disclosure. [Figure 9] Figure 9 is a schematic diagram showing a frequency-adjustable fractal antenna for a THz source according to a different embodiment of the present disclosure. [Figure 10] Figure 10 is a schematic diagram showing a frequency-adjustable fractal antenna for a THz source according to a different embodiment of the present disclosure. [Figure 11] Figure 11 is a schematic diagram showing a frequency-adjustable fractal antenna for a THz source according to a different embodiment of the present disclosure. [Figure 12] Figure 12 is an exemplary graph showing the frequency shift of a frequency-adjustable fractal antenna for a THz source according to a different embodiment of the present disclosure. [Figure 13] Figure 13 is an exemplary graph showing the frequency shift of a frequency-adjustable fractal antenna for a THz source according to a different embodiment of the present disclosure. [Figure 14] Figure 14 is a schematic diagram of the tapered structure of a THz source according to one embodiment of the present disclosure. [Figure 15A]Figure 15A shows the simulated electric field response of a hollow polymer tapered structure without metal coating. [Figure 15B] Figure 15B shows the simulated electric field response of a hollow polymer tapered structure with an inner wall metal coating. [Figure 16] Figure 16 is a schematic diagram of a device according to one embodiment of the present disclosure. [Figure 17] Figure 17 is a schematic diagram of a device according to another embodiment of the present disclosure. [Figure 18] Figure 18 is a schematic diagram of a device according to another embodiment of the present disclosure. [Figure 19] Figure 19 is a schematic diagram of a tapered structure having an inclined cut on the light-emitting aperture according to one embodiment of the present disclosure. [Figure 20] Figure 20 is a schematic diagram of a physical terahertz fishnet metamaterial (TFMM) prism design for a beam deflector according to one embodiment of the present disclosure. [Figure 21] Figure 21 is a schematic diagram of a flat TFMM prism design for a beam deflector according to one embodiment of the present disclosure. [Figure 22] Figure 22 is a cross-sectional view of droplets of different sizes placed between two layers of a fishnet row in a beam deflector according to one embodiment of the present disclosure. [Figure 23] Figure 23 is a flowchart of the process for operating a portable THz imaging device according to one embodiment of the present disclosure. [Modes for carrying out the invention]

[0035] The following embodiments are used to illustrate the present disclosure. Those skilled in the art will readily conceive of other advantages and effects of the invention based on the disclosure herein. The present disclosure can also be implemented or applied as described in different embodiments. For different aspects and uses, it is possible to modify or change the form to carry out the present disclosure without departing from the scope of the present disclosure.

[0036] The subject matter is described here with reference to the accompanying drawings. Various structures, systems, and devices are schematically shown in the drawings for illustrative purposes only, so as not to obscure the disclosure with details familiar to those skilled in the art. Nevertheless, the accompanying drawings are included to illustrate and describe exemplary embodiments of the disclosure. Words and phrases used herein should be understood and interpreted as having meanings consistent with those understood by those skilled in the art. No special definition of a term or phrase, i.e., a definition different from its ordinary meaning as understood by those skilled in the art, is implied by the consistent use of the term or phrase herein. Wherever a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by those skilled in the art, such a special definition is expressly provided herein in a definitive form that directly and clearly provides the special definition of the term or phrase.

[0037] The proportions, structures, sizes, and other features shown in the drawings accompanying this disclosure are used solely to illustrate the embodiments described herein, so that those skilled in the art can read and understand this disclosure from there; however, they are not intended to limit the scope of this disclosure. Any changes, modifications, or adjustments to such features, as long as they do not affect the purpose and effect for which this disclosure is designed, should all fall within the scope of the technical content of this disclosure.

[0038] As used herein, the terms “includes,” “contains,” “have,” “contains,” and any other variations thereof are intended to include non-exclusive inclusions. For example, when an object is described as “comprises,” it may further include other elements, components, structures, areas, parts, devices, systems, steps, or connections, unless otherwise specified, and should not exclude other limitations.

[0039] As used herein, consecutive terms such as “first,” “second,” etc., are cited solely for the convenience of describing or distinguishing between limitations such as elements, components, structures, areas, parts, devices, systems, etc., and are not intended to limit the scope of the disclosure or the spatial order between such limitations. Furthermore, unless otherwise specified, singular terms such as “one,” “one,” and “it” also relate to plural forms, and terms such as “or,” and “and / or” may be used interchangeably.

[0040] As used herein, the phrase “at least one” should be understood to mean, with respect to a list of one or more elements, at least one element selected from any one or more elements in the list of elements, but not necessarily including at least one of each element enumerated in the list of elements, nor excluding any combination of elements in the list of elements. This definition also allows for the optional presence of elements other than those identified in the list of elements to which the phrase “at least one” refers, whether related to or unrelated to the identified element. Thus, as an unrestrictive example, “at least one of A and B” (or equivalently, “at least one of A or B,” or equivalently, “at least one of A and / or B”) may, in one embodiment, refer to at least one containing more than one A of any choice, where B is absent (and optionally containing elements other than B). In another embodiment, at least one containing more than one B of any choice, where A is absent (and optionally containing elements other than A). In yet another embodiment, this means including at least one A of any choice, and at least one B of any choice, and including other elements of any choice.

[0041] As used herein, the terms “one or more” and “at least one” may have the same meaning and include one, two, three, or more.

[0042] As used herein, the term “subject” may encompass any vertebrate (including, but not limited to, humans, mammals, reptiles, amphibians, and / or fish). However, advantageously, the subject may be a mammal, e.g., a human; or an animal mammal, e.g., a domesticated mammal, e.g., a dog, cat, horse; or a production mammal, e.g., a cow, sheep, pig. The term “patient” may be interchangeable with “subject.”

[0043] As used herein, the term “signal” means radiation emitted from a light source or reflected from an object, and includes, but is not limited to, beams, terahertz beams, signals, and terahertz signals. In at least one embodiment of this disclosure, the signal may be transmitted or reflected.

[0044] As used herein, the terms “distal end” and “proximal end” refer to the ends of a structure that are further from and closer to the THz source, respectively. For example, the proximal end of a tapered structure is closer to the THz source located within the tapered structure compared to the distal end of the tapered structure.

[0045] Figure 1 illustrates an embodiment of the device 10 of the present disclosure configured to reconstruct a real-time image of a target 60 (e.g., a tooth). Specifically, the device 10 comprises a THz emitter 20, a receiver 30, and a generator 40. The aforementioned components can operate independently or individually. Furthermore, these components, including the THz emitter 20, receiver 30, and generator 40, may be fully electronically controlled and may communicate electrically with each other via wired or wireless connections. In some embodiments, the device 10 further comprises a connector 50 for detachably connecting the THz emitter 20 and receiver 30 at a distance from each other.

[0046] In at least one embodiment, the THz emitter 20 is configured to face the receiver 30, and the target 60 may be positioned between the THz emitter 20 and the receiver 30. In this way, the receiver 30 can collect the emitted terahertz signal after it has passed through the target 60, following the emission of the terahertz signal from the terahertz emitter 20.

[0047] In at least one embodiment, the THz emitter 20 is connected to a generator 40 which can induce the THz emitter 20 to emit a terahertz signal, which can then strike and reflect off the surface of a target 60. The reflected terahertz signal can be collected by a receiver 30 so that device 10 can reconstruct a real-time image of the target 60.

[0048] In at least one embodiment, the connector 50 may adjust the distance between the THz emitter 20 and the receiver 30 to enable the reconstruction of images of targets 60 having different sizes. The detailed configurations of the transmitter 20 and receiver 30 will be described further later.

[0049] Figure 2 shows an embodiment of a THz emitter 20 for emitting a terahertz signal according to the present disclosure. The terahertz emitter 20 comprises a cover 24, a terahertz source 21 and a tapered structure 22 integrated inside the cover, and a beam deflector module 23 positioned on the top surface 27 of the cover 24. In at least one embodiment, the THz source 21 is positioned on the bottom surface 26 inside the cover 24 of the THz emitter 20, and the tapered structure 22 covering the THz source 21 is also positioned on the bottom surface 26 (which is the terahertz source 721 and tapered structure 722 shown in Figure 16). In some embodiments, the tapered structure 22 may have a smaller aperture for emitting a signal and a larger aperture covering the THz source 21 for collecting a signal. A detailed configuration of the terahertz source 21 will be described later.

[0050] In at least one embodiment, the beam deflector module 23 may comprise a beam deflector 231 and one or more deflector electrodes 232. In some embodiments, the beam deflector 231 is located in the center of the upper surface 27 of the cover 24 and is electrically connected to the deflector electrodes 232. In some other embodiments, the position of the beam deflector 231 may be any position depending on the actual need, rather than being in the center of the upper surface 27 of the cover 24. In some embodiments, the deflector electrodes 232 may extend outward from the beam deflector 231 to the edge of the upper surface 27 of the cover 24.

[0051] In some embodiments, the shape of the cover 24 of the THz emitter 20 may be machined as a cube, a cylinder, or other suitable shape depending on the actual need, but is not limited thereto.

[0052] Figure 3 shows an embodiment of a receiver 30 for collecting terahertz signals according to the present disclosure. The receiver 30 comprises a cover 34 similar to the cover 24 of the THz radiator 20, a THz detector 31, and a tapered structure 32 similar to the tapered structure 22 of the THz radiator 20. In at least one embodiment, the THz detector 31 is located on the bottom surface 36 inside the cover 34 of the receiver 30, and the tapered structure 32 covering the THz detector 31 is also located on the bottom surface 36. In some embodiments, the configuration between the THz detector 31 and the tapered structure 32 is reversed compared to the configuration between the THz source 21 and the tapered structure 22 shown in Figure 2, namely, the THz detector 31 is covered by a smaller opening in the tapered structure 32, and the larger opening of the tapered structure 32 is directed towards the top surface 37 of the cover 34 to collect terahertz signals.

[0053] Referring to Figure 4A, an embodiment of the THz source 21 of this disclosure is shown. The terahertz source 21 comprises a substrate 211, an RTD structure 212, a spacer layer 213, a resonator antenna 214, Radiator The spacer layer 213 is equipped with an antenna 215 and a resonator antenna 214. RadiatorIt functions as a separator between the antenna 215 and the spacer layer 213. For example, the RTD structure 212 is placed on the substrate 211. The spacer layer 213 is placed on the RTD structure 212. The resonant antenna 214 is placed on the RTD structure 212 and embedded in the spacer layer 213. Radiator Antenna 215 is positioned. In some embodiments, the RTD structure 212 is positioned on a substrate by using conventional MBE (molecular beam epitaxy) and MOCVD (metal-organic chemical vapor deposition) deposition. In some embodiments, the substrate 211 is made from indium phosphide (InP), and the RTD structure 212 is fabricated as an AlAs / InGaAs / AlAs structure.

[0054] Figures 4B and 4C show embodiments of the Terahertz source 21 of this disclosure. The Terahertz source 21 comprises a substrate 211, an RTD structure 212, a spacer layer 213, a resonator antenna 214, a passivation layer 216, Radiator The spacer layer 213 is equipped with an antenna 215 and a resonator antenna 214. Radiator It functions as a separator between it and antenna 215. In Figure 4B, to show the resonant antenna 214 more clearly, Radiator Antenna 215 and spacer layer 213 have been removed. The RTD structure 212 includes an RTD 212a placed on a buffer layer 212b. In some embodiments, the buffer layer 212b is In 0.53 Ga 0.47It can be fabricated from As. In some embodiments, the RTD212a may be a triple-barrier resonant tunneling diode (TBRTD). In some embodiments, the passivation layer 216 may be fabricated from silicon dioxide. In some embodiments, the buffer layer 212b is placed on the substrate 211. The passivation layer 216 is placed on top of the buffer layer 212b. The RTD212a is embedded in the passivation layer 216. The main part of the resonant antenna 214 is placed on the passivation layer 216. In some embodiments, the upper electrode of the resonant antenna 214 is electrically connected to the emitter terminal of the RTD212a, and the lower electrode of the resonant antenna 214 is electrically connected to the collector terminal of the RTD212a. In some embodiments, the upper electrode of the resonant antenna 214 is embedded in the passivation layer 216, and the lower electrode of the resonant antenna 214 is located on the buffer layer 212b and is embedded in or covered by the passivation layer 216. In some embodiments, the spacer layer 213 is located on the passivation layer 216 and the resonant antenna 214. Radiator Antenna 215 is placed on spacer layer 213.

[0055] In at least one embodiment, a resonant antenna 214 and / or Radiator Antenna 215 may be a spiral antenna structure or any broadband antenna or tunable antenna. In some embodiments, the resonator antenna 214 and the radiator antenna 215 are fractal antennas formed according to the same fractal curve or fractal pattern. Therefore, Radiator Antenna 215 has the same shape and size as the main part of the resonator antenna 214. Furthermore, the radiator antenna 215 and the main body of the resonator antenna 214 are positioned vertically. For example, the resonator antenna 214 and shown in Figures 4(B) and 4(C) Radiator The antennas 215 all have a shape that follows the Hilbert curve. In some embodiments, the resonator antenna 214 and RadiatorThe antenna 215 may be shaped according to another fractal curve or fractal pattern such as a Koch curve, a Pino curve, a Sierpinski gasket, or a Minkowski geometric shape.

[0056] Referring to Figure 4D, an embodiment of the terahertz source 21 of this disclosure is shown, which is an alternative design compared to those in Figures 4B and 4C. The main part of the resonator antenna 214 of the THz source 21 is fabricated on the substrate 211 or buffer layer 212b. In Figure 4D, to more clearly show the RTD 212a and the resonator antenna 214, a spacer layer 213 and Radiator Antenna 215 has been removed, and only a small portion of the passivation layer 216 is shown. In fact, the passivation layer 216 of the terahertz source 21 can be approximately the same size as its counterpart in Figure 4B, and as a result, the passivation layer 216 covers the resonator antenna 214. The terahertz source 21 also has a spacer layer 213 placed on the passivation layer 216 and fabricated on the spacer layer 213. Radiator The device comprises an antenna 215. Resonant tunneling diodes are suitable as terahertz sources 21 and detectors 31 in the portable device 10 of this disclosure due to their simple design, conventional semiconductor manufacturing methods, and superior integration advantages over other terahertz sources. Resonant tunneling diodes can perform both terahertz emission and detection when terahertz emission is biased in different regions. The RTD structure 212 can emit terahertz emission when terahertz emission is biased in a negative differential region (NDR) and can detect terahertz emission when operating in a nonlinear region of the voltage-current response.

[0057] In some embodiments, the RTD structure 212 of the THz source 21 may be configured to emit and sense terahertz radiation in the range of 0.4 THz to 0.5 THz. Dental tissue can exhibit better imaging contrast in this terahertz range, and atmospheric water absorption is low at 0.4 THz to 0.5 THz compared to other ranges of the terahertz spectrum. Therefore, the proposed portable THz scanner can perform dental imaging in situ or in vivo, even in high-humidity atmospheres such as the human mouth.

[0058] In at least one embodiment, the RTD structure is fabricated using a slot resonator antenna (shown in Figure 4A) or other antenna structure (shown in Figure 4B) to connect the generated terahertz radiation to free space via a silicon lens mounted on the back surface of the substrate. Such configurations use hemispherical or hyperhemispherical silicon lenses, but these silicon lenses are expensive and difficult to package. Therefore, in some embodiments, Radiator Antenna 215 is placed on spacer layer 213.

[0059] By using a square patch antenna on top of the dielectric covering the slot resonator antenna 214 of the RTD structure 212, the generated terahertz oscillations can be inductively coupled to the patch antenna, allowing radiation to be emitted upward, thus eliminating the need for silicon lenses in the THz source. However, the efficiency achieved is only about 25% at 510 GHz due to the structural limitations of the square patch antenna used.

[0060] Therefore, in some embodiments, the radiator antenna 215 may be formed on top of the spacer layer 213 of the THz source 21 as a helical antenna structure (as shown in Figure 4A) or a similar type of broadband antenna structure (as shown in Figure 4B) to emit (or receive) terahertz signals without using a silicon lens. The free-space coupling (or receiving) efficiency of the antenna structure on top of the spacer layer can be increased by carefully designing the antenna geometry and optimizing the dielectric thickness, but is not limited to this disclosure.

[0061] Figure 5 is a cross-sectional view of a portion of a terahertz source 500 according to one embodiment of the present disclosure. The terahertz source 500 includes all the components and layers of the terahertz source 21 shown in Figures 4B and 4C. The terahertz source 500 further includes a lower contact layer 510 disposed between the buffer layer 212b and the TBRTD 160, an upper contact layer 520 formed on the TBRTD 160, a lower contact metal 515 formed on the lower contact layer 510, and an upper contact metal 525 formed on the upper contact layer 520. The lower contact metal 515 and the upper contact metal 525 may be formed by sputtering gold, or they may be terminal portions of the resonator antenna 214.

[0062] As shown in Figure 5, the TBRTD160 has a stack of nine layers, from bottom to top: a collector layer 161, a spacer 162, a collector barrier 163, a quantum well (collector well) 164, a main barrier 165, another quantum well (emitter well) 166, an emitter barrier 167, a spacer 168, and an emitter layer 169. Table 1 below lists the material, thickness, and molar concentration of silicon doping for each layer from the upper contact layer 520 to the buffer layer 212b in Figure 5. [Table 1] In a traditional double-barrier RTD or DBRTD, the emitter and collector barriers are the same (same barrier material and thickness), the device structure is symmetric, avoiding rapid thermionic leakage current and increasing tunneling current.

[0063] In contrast, the triple barrier of the TBRTD160 provided by the present disclosure includes more quantum wells and barriers, increasing well charge and peak current and decreasing peak voltage. Further, the TBRTD160 includes a non-identical main barrier 165. As shown in Table 1, the collector barrier 163 and the emitter barrier 167 have the same material and thickness, but the main barrier 165 is formed of a different material and has a different thickness. Further, the collector well 164 and the emitter well 166 are also asymmetric because their thicknesses are different. Thus, the aforementioned asymmetric structure increases the tunneling current and increases the maximum operating frequency limit.

[0064] As shown in Table 1, the main barrier 165 consists of In 0.52 Al 0.48 As. The collector barrier 163 and the emitter barrier 167 consist of AlAs. All the other layers shown in Table 1 consist of In 0.53 Ga 0.47 As. The TBRTD160 employs a combination of InGaAs / InAlAs / AlAs materials because this material system provides better RTD characteristics. The spacers 162 and 168 are undoped In 0.53 Ga 0.47 As to avoid the diffusion of charge carriers from the highly doped layers.

[0065] The TBRTD160 has 440 kA / cm 2The simulated peak current density and DC-RF conversion efficiency up to 19.75% are shown. The theoretically calculated maximum extractable output power of the TBRTD160 is approximately 250 μW at 0.95 THz for a device area of ​​1 μm², which is significantly higher than the output power of conventional TBRTDs previously reported. The non-identical triple barrier structure of the TBRTD160 exhibits a ΔV of 0.41 V and a ΔI of 0.0033 A, where ΔV and ΔI are the voltage and current in the negative differential resistance (NDR) region of the TBRTD160, respectively. The peak-to-valley current ratio (PVCR) is approximately 4.71. Compared to conventional TBRTDs, the peak current and peak voltage of the TBRTD160 are reduced without compromising the PVCR, while simultaneously increasing the DC-RF conversion efficiency. The maximum oscillation frequency of the TBRTD160 is 0.95 THz. The theoretically estimated parasitic capacitance of the TBRTD160 is cn = 21.3 fF. The series resistance of the TBRTD160 is Rs = 3.25Ω. The reciprocal of the negative conductance of the TBRTD160 is Rn = 18.66Ω.

[0066] Figure 6 shows 1 μm 2 This is an exemplary graph showing the numerically simulated voltage-to-current density characteristics of the TBRTD160, which has a device area of ​​[device area value].

[0067] Figure 7 shows 1 μm 2 This is an exemplary graph showing the maximum oscillation frequency characteristics for the estimated device capacitance of the TBRTD160, which has a device area.

[0068] In some embodiments, the resonator antenna 214 and radiator antenna 215 of the THz source 500 may be fractal antennas, as fractal technology enables small antennas and the integration of multiple bands. Fractal antennas possess desirable properties such as space filling, self-similarity, fractional dimensions, infinite complexity, mechanical simplicity, and robustness, which make fractal antennas unique in achieving advantages such as miniaturization, broadband, and multiband characteristics more efficiently. Space-filling properties are used to reduce antenna size. Self-similarity is used to achieve multiband resonator antennas. Resonator antenna 214 and Radiator The number of repetitions of the geometric shape of antenna 215 is based on their operating wavelengths.

[0069] Furthermore, the radiator antenna 215 of the THz source 500 may be a reconfigurable fractal antenna to extend its operating frequency range. The radiator antenna 215 can be adjusted to achieve either reconfigurability or tunability in a desired frequency range for radio communication.

[0070] In some embodiments, for large frequency shifts, sections with large electrical length or segments with large fractal patterns can be simply cut from the radiator antenna 215, thus reducing the overall size of the radiator antenna 215 and generating an upward frequency shift. On the other hand, for larger electrical length or larger fractal patterns Radiator It can be connected to antenna 215, and therefore, RadiatorThe overall size of antenna 215 is increased to generate a downward frequency shift. The radiator antenna 215 may include at least one switch embedded in the fractal curve or fractal pattern of the radiator antenna 215. The at least one switch may be implemented by a diode or transistor for connecting and disconnecting one or more sections or segments of the radiator antenna 215 to reconfigure the radiator antenna 215 for frequency shift. For example, in one embodiment, the radiator antenna 215 may be switched between a one-segment fractal curve 800 shown in Figure 8 and a two-segment fractal curve 900 shown in Figure 9. When the radiator antenna 215 is switched to the one-segment fractal curve 800 in Figure 8, its reflection coefficient S11 is plotted as curve 1210 in Figure 12. When the radiator antenna 215 is switched to the two-segment fractal curve 900 in Figure 9, its reflection coefficient S11 is plotted as curve 1220 in Figure 12.

[0071] In some embodiments, for a medium frequency shift, a switch embedded in the radiator antenna 215 can be controlled to cut off or connect fewer fractal patterns or shorter electrical lengths from the radiator antenna 215. This effect can reduce the electrical length of the radiator antenna 215 and increase the operating frequency, or vice versa. For example, in one embodiment, the radiator antenna 215 can be further switched between fractal curve 1000 shown in Figure 10 and fractal curve 1100 shown in Figure 11. When the radiator antenna 215 switches from fractal curve 900 in Figure 9 to fractal curve 1000 in Figure 10, three arms are cut off from each fractal segment, and the electrical length increases. The resulting reflection coefficient S11 is plotted as curve 1230 shown in Figure 12. A downward (leftward) frequency shift of approximately 0.02 THz is observed. RadiatorWhen antenna 215 switches to the fractal curve 1100 in Figure 11, which has a larger cutoff and electrical length reduction, the reflection coefficient S11 is plotted as curve 1240 shown in Figure 12. Here, an upward (rightward) frequency shift is observed.

[0072] In some embodiments, Radiator Similar to antenna 215, the resonant antenna 214 may include at least one switch, implemented by a diode or transistor, for connecting and disconnecting one or more sections, segments, or arms of the resonant antenna 214 to reconfigure the resonant antenna 214 for large and intermediate frequency shifts.

[0073] In some embodiments, the resonator antenna 214 and Radiator Both antennas 215 include switches for high and medium frequency shifts.

[0074] In some embodiments, for fine frequency shift or continuous frequency tuning, Radiator The spacer layer 213 beneath the antenna 215 may contain a ferroelectric material such as polymer-dispersed liquid crystal (PDLC), whose dielectric constant changes when the electric field applied to the ferroelectric material changes. Unlike the aforementioned reconstruction of fractal patterns, where the frequency shift is more discrete and highly dependent on the fractal pattern, voltage-induced dielectric constant changes in the radiator antenna 215 can result in a much more continuous and minute change in the operating frequency.

[0075] Radiator Figure 13 shows an example of this frequency shift due to a change in dielectric constant using a spacer layer 213 made of PDLC on antenna 215, where the frequency shift is caused by the liquid crystal in the spacer layer 213 changing from a normal polarization state (corresponding to curve 1310) to an abnormal polarization state (corresponding to curve 1320). Radiator The operating frequency of antenna 215 changes in proportion to the dielectric constant of the PDLC in the spacer layer 213.

[0076] In some embodiments, the substrate 211, buffer layer 212b, or passivation layer 216 beneath the resonant antenna 214 may include a ferroelectric material such as PDLC for fine frequency shift or continuous frequency tuning of the resonant antenna 214.

[0077] In some embodiments, the substrate 211 beneath the resonant antenna 214, the buffer layer 212b or the passivation layer 216, and Radiator The spacer layer 213 below antenna 215 is for both resonator antenna 214 and Radiator The antenna 215 may include a ferroelectric material such as PDLC for fine frequency shifting or continuous frequency tuning.

[0078] Figure 14 shows embodiments of the tapered structure 22 or 32 of the THz source according to the present disclosure. The tapered structure 22 of the THz emitter 20 and the tapered structure 32 of the receiver 30 are hollow polymer tapered structures having an inlet opening at the proximal end and a radiating opening at the distal end, the inlet opening being larger than the radiating opening. For example, the tapered structure 22 covers the terahertz source 21 with the inlet opening side of the tapered structure 22, and the tapered structure 32 covers the terahertz detector 31 with the outlet opening side of the tapered structure 32. In some embodiments, the tapered structure 22 or 23 of the THz source is a tapered waveguide structure.

[0079] The electric field at the tapered tip (i.e., the exit aperture of the tapered structure) is strongly influenced by the probe design. The electric field strength can be increased in several ways, including by increasing source power, reducing transmission loss, improving impedance matching, and by using larger aperture diameters and shorter probe lengths. However, increasing THz source power and improving impedance matching can increase the cost and complexity of the imaging system. Furthermore, larger aperture diameters can lead to decreased image resolution. Therefore, in some embodiments, reducing the transmission loss of terahertz waves within the waveguide and probe structure is a preferred method for achieving strong electric field localization at the tapered tip.

[0080] To reduce the transmission loss of terahertz signals, it is preferable to select an appropriate material that forms a tapered structure. Terahertz transmission loss is

number

[0081] Figures 15A and 15B show the simulated electric field responses of hollow polymer tapered structures with and without metal coating, respectively. The cross-sectional electric field profile of the hollow HDPE (high-density polyethylene) tapered structure 61 is shown in Figure 15A. This indicates that the local electric field at the tapered tip (i.e., the radiating aperture) of the hollow HDPE tapered structure 61 is not significant, due to resonance of the input THz signal occurring in the air core and leakage waves observed outside the hollow tapered structure without metal coating, resulting from mismatch in waveguide conditions at the air core and internal HDPE interface.

[0082] In some embodiments, the hollow core of the tapered structure of the present disclosure has a metal-coated inner wall, forming a metal-coated hollow polymer tapered structure that helps induce and generate a focused near-field beam profile at the exit of the tapered end. This near-field operation allows the spatial image resolution to exceed the diffraction limit, further improving the overall image resolution. Referring to Figure 15B, the simulated electric field response of the metal-coated hollow polymer tapered structure of the present disclosure is shown. The metal-coated hollow polymer tapered structure 62 exhibits stronger electric field enhancement at the subwavelength aperture compared to the hollow HDPE tapered structure 61 shown in Figure 15A. The input terahertz radiation at the inlet aperture of the metal-coated hollow polymer tapered structure is guided inside the tapered structure without excessive loss of terahertz radiation energy due to structural resonance and leakage.

[0083] Therefore, by coating a hollow polymer tapered structure with a metal, the metal-coated hollow polymer tapered structure may have the ability to confine a terahertz signal or input beam through a subwavelength aperture while performing near-field image scanning by an electronically controlled beam deflector, thereby achieving subwavelength resolution terahertz images. In some embodiments, the metal coated on the hollow polymer tapered structure is silver, or any other metal capable of achieving the same effect as described above.

[0084] To perform subwavelength resolution scanning on a target surface, the present disclosure provides several means for driving or bending near-field terahertz radiation from a subwavelength aperture.

[0085] Figure 16 shows an embodiment of the device 70 of the present disclosure. The electro-optic beam deflector is fabricated from a tunable metamaterial or metasurface (e.g., the design of the beam deflector 110 or 120 shown in Figures 20-22) and may be fabricated on a thin substrate to form the beam deflector module 723 of the device 70 (the beam deflector module 23 shown in Figure 2), the thin substrate having very low absorption at the terahertz frequency of interest. The terahertz source 721 is covered by a tapered structure 722 on the inlet aperture 725 side to emit a terahertz signal 71. The beam deflector module 723 is mounted on the exit aperture 724 of the tapered structure 722, and the exit terahertz signal 72 emitted from the exit aperture 724 passes through the beam deflector module 723 positioned perpendicular to the direction of the terahertz signal 71 and collides with a target 75 located between the THz source 721 and the THz detector 731. Next, the outgoing terahertz signal 72 is reflected from the surface of the target 75 as a reflected terahertz signal 73. The reflected terahertz signal 73 is finally collected by the tapered structure 732 and received by the THz detector 731.

[0086] In some embodiments, the beam deflector module 723 is manufactured using electrically controlled phase-change material. The direction of the terahertz signal does not change when no voltage is applied to the beam deflector module 723. When the beam deflector module 723, fabricated from phase-change material, is controlled by an applied bias voltage, the phase plane of the propagating wave can be tilted so that the direction of the terahertz beam can be steered, focused, or collimated.

[0087] Figure 17 shows an embodiment of the device 80 of the present disclosure. The electro-optic beam deflector is fabricated from a tunable metamaterial or metasurface (e.g., the design of beam deflectors 110 or 120 shown in Figures 20-22) and may be machined onto a curved surface to form a beam deflector module 823 capable of focusing and deflecting a terahertz signal 81. The terahertz source 821 is covered by a tapered structure 822 on the inlet aperture 825 side to radiate a terahertz signal 81. In some embodiments, the beam deflector module 823 is partially mounted on the radiating aperture 824 of the tapered structure 822 so that the terahertz signal 81 emanating from the radiating aperture 824 can be focused and deflected by the beam deflector module 823 and strike a target 85 that does not need to be placed between the THz source 821 and the THz detector 831. The focused terahertz signal 82 is then reflected from the surface of the target 85 as a reflected terahertz signal 83. The reflected terahertz signal 83 is ultimately collected by the tapered structure 832 and received by the THz detector 831.

[0088] In at least one embodiment, the beam deflector module 823 functions like a curved electro-optic mirror surface that can focus, collimate, diverge, and / or deflect terahertz signals along the optical axis as the bias voltage applied to the beam deflector module 823 changes. In some embodiments, the refractive index of the electro-optic material of the beam deflector module 823 may change along with the bias voltage applied to the beam deflector module 823. This can change the reflection angle of the terahertz signals incident on the electro-optic surface, allowing the terahertz signals to be focused off-axis from the electro-optic mirror.

[0089] Referring to Figure 18, an embodiment of the device 90 of this disclosure is shown. The beam deflector module 923 is similar to the beam deflector module 823 but is not formed on a curved surface. The beam deflector module 923 can also be made of an adjustable metamaterial or metasurface (e.g., the design of beam deflectors 110 or 120 shown in Figures 20-22). Alternatively, the beam deflector module 923 is formed on a flat surface. The terahertz source 921 of the device 90 is not covered by the inlet opening 925 of the tapered structure 922, and the beam deflector module 923 is not attached to the radiating aperture 924 of the tapered structure 922. The terahertz signal 91 emitted from the terahertz source 921 collides with the beam deflector module 923 at a constant angle, and the reflection angle of the terahertz signal 91 can be controlled by the beam deflector module 923 based on a bias voltage applied to the beam deflector module 923. In some embodiments, the beam deflector module 923 may include an electro-optic beam deflector or a Garbo mirror.

[0090] Therefore, the incident angle of the reflected terahertz signal 91 incident on the aperture 925 of the tapered structure 922 changes, and the terahertz signal 92 exits the exit aperture 924 of the tapered structure 922 and is emitted so as to collide with the target 95. The departing terahertz signal 92 is then reflected from the surface of the target 95 as a reflected terahertz signal 93. The reflected terahertz signal 93 is finally collected by the tapered structure 932 and received by the THz detector 931. With the configuration of the apparatus 90 as described above, the incident angle of the terahertz signal 91 incident on the tapered structure 922 can be changed, and the reflection angle can be changed inside the tapered structure 922.

[0091] Figure 19 shows an embodiment of a tapered structure 101 having a beveled cut on the emission aperture 102 of the present disclosure. To achieve scanning of near-field terahertz radiation, the exit aperture 102 of the tapered structure 101 may be cut at an angle such that the surface 104 of the exit aperture 102 is beveled with respect to the surface 105 of the entrance aperture 103 of the tapered structure 101, thereby increasing the deflection angle. The terahertz signal exits the exit aperture 102 beveled in different directions due to the change in the reflection angle / anti-resonance reflection pattern within the tapered structure 101.

[0092] Figure 20 shows an embodiment of the physical terahertz fishnet metamaterial (TFMM) prism design of the beam deflector 110 of this disclosure. The physical prism design of the beam deflector 110 may be one of the electro-optic modulator designs in the beam deflector modules 723, 823, or 923 shown in Figures 16-18. The beam deflector 110 is a TFMM prism for beam steering purposes similar to a normal prism design, except that the fishnet is an anisotropic material that allows only perpendicularly incident beams (e.g., incident terahertz signals). In some embodiments, to achieve larger angular beam steering and generate a large optical path difference (OPD), the beam deflector 110 may be formed as a TFMM prism in which multiple fishnet layers 111 are stacked to form multiple stages 112, each of which may be formed by at least three fishnet layers 111. Thus, beam bending can be achieved by the optical path length difference due to the relative geometric shape change (or thickness) between adjacent stages 112. The angle and uniformity of the output beam profile may depend on the number of fishnet layers 111, the relative geometry between the stages 112, and / or the operating frequency.

[0093] Referring to Figure 21, an embodiment of the flat TFMM prism design for the beam deflector 120 of this disclosure is shown. The flat prism design for the beam deflector 120 may be one of the proposed electro-optic modulator designs in beam deflector modules 723, 823, or 923 shown in Figures 16-18. In at least one embodiment, the challenges of fabricating a multilayer TFMM prism using a flat prism structure can be mitigated by combining the concept of beam steering based on OPD with a large refractive index change of the metamaterial near its resonant frequency. For example, the beam deflector 120 may be fabricated as an array of single-layer terahertz fishnet metamaterial structures, as shown in Figure 21. Different external fields can be applied to each of the fishnet rows (i.e., fishnet rows 121, 122, 123, and 124) that are not connected to each other, in order to generate a large OPD that changes along the direction perpendicular to the incident beam. Therefore, if the material can generate a large ODP that changes along a direction perpendicular to the incident beam, such as a terahertz signal, it is not necessary to make the beam deflector 120 into a physical prism shape to steer the beam.

[0094] Figure 22 shows another embodiment for creating the electro-optic modulator design for the beam deflector modules 723, 823, or 923 shown in Figures 16-18. Figure 22 shows a cross-sectional view of an embodiment in which droplets 133 of different sizes are arranged between two layers of fishnet rows. With this design, the flat prism 120 shown in Figure 21 can be produced by inducing refractive index changes between different cells containing an upper fishnet layer 131, a lower fishnet layer 132, and multiple droplets 133. For example, each fishnet row shown in Figure 21 (i.e., fishnet rows 121, 122, 123, 124) may include an upper fishnet layer 131 and a lower fishnet layer 132. Multiple droplets 133 may be arranged between the upper fishnet layer 131 and the lower fishnet layer 132. In some embodiments, multiple droplets 133 may be formed as droplet layers, and the number of droplet layers between the upper fishnet layer 131 and the lower fishnet layer 132 may depend on the size of the droplets 133 (e.g., the smaller the size of the droplet 133, the more droplet layers there are). Thus, a gradient refractive index structure can be constructed by varying the droplet size between each of the fishnet rows of the cut TFMM array. In some embodiments, the droplets 133 may be composed of liquid crystal (LC) material, and the size of the LC droplets 133 may be controlled by ultraviolet (UV) radiation to determine the refractive index gradient.

[0095] In some embodiments, the droplet size of the polymer-dispersed liquid crystal (PDLC) can be controlled by a grayscale mask to form a gradient structure. The fishnet structure can increase the effective refractive index. Since the TFMM can produce a large change in refractive index, the fishnet structure of the beam deflector can be used as a separate electrode to apply a separate electric field to the PDLC, resulting in a refractive index gradient along the direction perpendicular to the incident beam, which is equivalent to a real prism.

[0096] Conventional lenses shaped with different curves can operate with positive refractive indices, but may be limited by the diffraction limit. Gradient flat lenses impregnated with materials such as non-uniform LC cells can produce triangular prism-like optical effects, but may be limited by the refractive index of the material. Therefore, at least one embodiment of the present disclosure provides an actively controlled metamaterial lens for a beam deflector, which can overcome these problems by transforming the lens to perform different functions, such as from focusing to diverging, collimating, or achieving near-field or subwavelength focusing by changing the applied voltage. In some embodiments, the beam deflector is designed by using UV-curable PDLC as a dielectric substrate, where the material exposed to different UV intensities can cause LC droplets of different sizes to form inside the polymer.

[0097] Since the normal and abnormal refractive indices of PDLCs can vary depending on the average size of the liquid crystal droplets in the polymer host medium, the material can be exposed with a constantly increasing dose to achieve a prism effect. In some embodiments, based on the above concept, the beam deflector may be fabricated as a tunable flat lens, a prism with active steering, or a more complex lens design, depending on the configuration of the PDLC substrate.

[0098] Figure 23 shows a flowchart of the process for operating the portable THz imaging device of this disclosure. First, in step S10, a generator connected to the THz emitter guides the THz emitter to emit a terahertz signal onto the surface of a target. Second, in step S20, a receiver receives the terahertz signal reflected from the surface of the target. Then, in step S30, the portable terahertz imaging device can analyze the received terahertz signal to diagnose the condition of the surface of the target. Finally, in step S40, an image of the target can be reconstructed.

[0099] The target being diagnosed by the portable THz imaging device may be the patient's teeth, and the target surface may be the enamel surface of the tooth. In some embodiments, the diagnosis using the portable THz imaging device may be performed by a series of scans from left to right, posteriorly, with respect to the midline of the mouth, including the left buccal, left occlusal, labial, incisal, right buccal, right occlusal, and lingual sides.

[0100] In some embodiments, the diagnosed state of a tooth may include caries, early detection of demineralized enamel, monitoring of the hardening process of dental composite materials, and identification of tooth abnormalities.

[0101] In a portable THz imaging device for diagnosing the condition of a target subject as described in this disclosure, the THz imaging device may be manufactured as a simple, portable, real-time in vivo THz imaging device for imaging dental tissue. Furthermore, the portable THz imaging device has a sensitivity that is far more than sufficient to detect the early stages of caries compared to conventional X-rays. Thus, the THz imaging device of this disclosure can operate at a density for early detection of dental problems, such as imaging enamel thickness with high resolution.

[0102] This disclosure has been described using exemplary embodiments to illustrate the principles, features, and effectiveness of the disclosure, but is not intended to limit the scope of implementation of the disclosure. Various changes and modifications can be made to this disclosure by those skilled in the art without departing from the spirit and scope of its premises. However, any equivalent changes and modifications achieved in accordance with the disclosure should be deemed to fall within the scope of the disclosure. The scope of this disclosure should be defined by the appended claims.

Claims

1. A THz emitter for radiating a terahertz signal upwards, A radiator antenna integrated with and coupled to the THz emitter and configured to guide the THz emitter to emit a terahertz signal, Includes a receiver that receives the terahertz signal, The aforementioned THz emitter is The first cover and, A first tapered structure is disposed within the first cover and has a distal end and a proximal end opposite to the distal end, and has coated side walls. A THz source is disposed within the first cover and covered by the first tapered structure, which induces and generates a focused near-field beam profile at the distal end. The system includes a beam deflector module connected to the first cover and configured to deflect or modulate a terahertz signal for scanning, The aforementioned receiver is The second cover, A second tapered structure disposed within the second cover, The system includes a THz detector disposed within the second cover and covered by the second tapered structure having coated sidewalls, The THz detector is covered by a smaller opening in the second tapered structure. The larger opening of the second tapered structure is directed toward the upper surface of the second cover toward the target, Scanning-based THz imaging device.

2. The aforementioned THz source is A resonant tunneling diode (RTD) having an emitter and a collector, A resonant antenna electrically connected to the emitter and collector of the RTD, A scanning-based THz imaging device according to claim 1, comprising a radiator antenna positioned on the resonant antenna and separated by a dielectric layer.

3. The scanning-based THz imaging device according to claim 2, wherein the RTD is a TBRTD or multi-barrier RTD comprising quantum well / barrier / well layers of semiconductor material having non-uniform thickness and constituent material, and the TBRTD or multi-barrier RTD is configured to improve overall DC-RF conversion efficiency and reduce peak current-voltage.

4. The scanning-based THz imaging device according to claim 2, wherein the radiator antenna laminated on the dielectric layer is a tunable fractal antenna structure configured to change the frequency shift by reconstructing the fractal pattern of the tunable fractal antenna structure or by a voltage-induced dielectric constant change of the dielectric layer in the radiator antenna.

5. The scan-based THz imaging device according to claim 1, wherein the first tapered structure having a coated sidewall comprises an air core for minimizing transmission loss and enhancing THz signal localization, a radiating aperture, and an incoming aperture.

6. The scan-based THz imaging device according to claim 5, wherein the air core has an inner wall coated with a metallic material for inducing and generating a focused beam at near-field distance in the radiating aperture of the first tapered structure.

7. The scanning-based THz imaging device according to claim 5, wherein the radiating aperture of the first tapered structure is cut at one angle to increase the deflection angle.

8. The scanning-based THz imaging device according to claim 5, wherein the beam deflector module is positioned in the tapered radiating aperture and configured to transmit the terahertz signal to manipulate the optical axis of the THz beam.

9. The scanning-based THz imaging device according to claim 5, wherein the beam deflector module is fabricated on a curved surface for focusing and deflecting the terahertz signal at near-field distance, and the beam deflector module is positioned in the radiating aperture of the first tapered structure.

10. The scanning-based THz imaging device according to claim 5, wherein the beam deflector module is positioned at the entrance aperture of the first tapered structure and is configured to deflect the terahertz signal emitted from the THz emitter and to change the angle of incidence entering the tapered structure.

11. The scanning-based THz imaging device according to claim 10, wherein the beam deflector module comprises an electro-optic beam deflector or a Garbo mirror.

12. The scanning-based THz imaging device according to claim 1, wherein the beam deflector module is a physical terahertz fishnet metamaterial prism having a stacked fishnet structure.

13. The scanning-based THz imaging device according to claim 1, wherein the beam deflector module is a flat terahertz fishnet metamaterial prism having an array of single-layer terahertz fishnet metamaterial structures.

14. The aforementioned single-layer terahertz fishnet metamaterial structure is The first layer and, A second layer opposite the first layer, A scanning-based THz imaging device according to claim 13, comprising a plurality of droplets disposed between a first layer and a second layer to form a plurality of droplet layers.

15. The scanning-based THz imaging device according to claim 14, wherein the droplets are composed of a liquid crystal material, and the size of the droplets is controlled by ultraviolet radiation to produce different refractive indices.

16. The scanning-based THz imaging device according to claim 1, wherein the beam deflector module is an actively controlled metamaterial lens / beam deflector for converting functions between focusing, diverging, collimating, beam deflection, or any combination of two or more functions by changing the applied voltage between metamaterial arrays.

17. The scanning-based THz imaging device according to claim 1, further comprising a connector for detachably connecting the THz emitter to the receiver and for separating the THz emitter at a distance from the receiver.

18. The scan-based THz imaging device according to claim 17, wherein the connector is configured to adjust the distance between the THz emitter and the receiver.

19. The steps of providing a scanning-based THz imaging device according to claim 1, The steps include: emitting a terahertz signal from a terahertz radiator to a target within the subject where it is needed; The steps include receiving the terahertz signal reflected from the target with a receiver, The steps include, A method for scanning targets within a given area.

20. The method according to claim 19, further comprising the step of reconstructing the image of the target.

21. The method according to claim 19, wherein the target is a dielectric and does not contain water.

22. The method according to claim 19, wherein the disease, disorder, or condition of interest is selected from the group consisting of dental caries, tooth demineralization, peri-implantitis, periodontal disease, gingivitis, hardening processes of dental composites, lesions of oral structures, tooth abnormalities, burns, edema, and cancer.

23. The steps of providing a scanning-based THz imaging device according to claim 1, The steps include: emitting a terahertz signal from a terahertz radiator onto the surface of a target within the subject to be used; The steps include: receiving the terahertz signal reflected from the surface of the target with a receiver, The steps include: reconstructing an image of a subject using a received terahertz signal; A method for imaging a target within an object.

24. The method according to claim 23, wherein the target is a dielectric and does not contain water.

Images