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] The present disclosure relates to imaging devices, and more particularly to scanning-based THz imaging devices for biomedical imaging. [Background technology]

[0002] Terahertz (THz) science and technology has been of great interest to researchers for the last two decades. The THz spectral gap between millimeter wave and infrared is the last part of the EM wave spectrum that needs to be explored for potential disclosures. And with recent advances in terahertz sources and detectors, terahertz systems are now moving from the laboratory level 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 luminescence imaging, do not have sufficient sensitivity for detecting early stages of dental caries for early prevention. Moreover, X-ray imaging is related to the stage of disease treatment or surgery, and is not reliably recommended by doctors for determining the early stage of caries.

[0004] Unlike X-rays, THz radiation has low ionization energy and can therefore be safely used in biomedical imaging applications involving humans. X-ray and THz images of human teeth have also been compared, proving that the resolution of THz images has improved enough that THz systems have the potential to be implemented in dentistry for the early detection of dental problems. Terahertz radiation has unique dielectric properties in metals and dental tissue, making it a safer and easier method of diagnosing even very small gaps when filling the inside of teeth with metal during surgery.

[0005] Although there have been a few studies that have demonstrated the feasibility of THz imaging of human teeth, many significant physical and technical problems remain in the development of clinical-level prototypes for monitoring caries at the in vivo stage. Currently, there are no proven commercial devices or in vivo imaging clinical prototypes. The major limitations in moving laboratory-level THz imaging devices to commercial disclosure are the large and complex configuration, moving mechanical components, and expensive femtosecond lasers. THz pulsed imaging is usually performed using THz time-domain spectroscopy (THz-TDS), which requires a mechanical delay stage and is therefore difficult to integrate into a portable system.

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

[0007] In view of the foregoing, the present 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 includes a THz emitter for emitting a terahertz signal, a generator coupled to the THz emitter and configured to induce the THz emitter to emit the terahertz signal, and a receiver for receiving the terahertz signal.

[0009] In at least one embodiment of the present disclosure, a 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 to induce and generate 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 covered internally by the tapered structure.

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

[0011] In at least one embodiment of the present disclosure, a 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, hi some embodiments, the THz detector is covered internally 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 resonator antenna electrically connected to the emitter and collector of the RTD, and a radiator antenna disposed above the resonator antenna. In some embodiments, the RTD is a TBRTD or multi-barrier RTD that includes AIAs / InGaAS / AIAs layers, and this structure significantly improves the overall DC-to-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 any wideband antenna. In some embodiments, the radiator antenna structure of the THz source is a tunable fractal antenna structure, and the frequency shift can be changed by reconfiguring its fractal pattern or by voltage-induced dielectric constant changes in 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 the scanning-based THz imaging device has an air-core portion, an emission aperture, and an entrance 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 taper 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 emission aperture of the first tapered structure is cut at an angle to increase the deflection angle.

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

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

[0017] In at least one embodiment of the present disclosure, a beam deflector module is disposed at an entrance opening of the first tapered structure and configured to deflect a terahertz signal emitted from the 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 galvo 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 single layer terahertz fishnet metamaterial structures. In some embodiments, the terahertz fishnet metamaterial structures include 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 disposed between the first layer and the second layer 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 between focusing, diverging, and collimating functions by changing an applied voltage.

[0022] In at least one embodiment of the present disclosure, the scanning-based THz imaging device further comprises a connector for removably connecting the THz emitter to the receiver and separating 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 enable reconstructing images of targets of different sizes.

[0023] The present disclosure also provides a method for diagnosing a disease, disorder, or condition in a subject, comprising providing a scanning-based THz imaging device of the present disclosure, emitting a terahertz signal from a terahertz emitter to a surface of a target within a subject in need thereof, receiving the terahertz signal reflected from the surface of the target with a receiver, and diagnosing a condition of the target surface by analyzing the received terahertz signal. In some embodiments, the method further comprises 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, a soft tissue (e.g., skin), hard tissue (e.g., bone), enamel, dental tubules, nerves, blood vessels of a subject. In some embodiments, the target can be a dielectric and has no water content, e.g., a tooth or bone, but the present disclosure is not limited thereto. In some embodiments, the target is a tooth and the surface is a tooth enamel surface.

[0025] In at least one embodiment of the present disclosure, the disease, disorder, or condition of interest may be, but is not limited to, dental caries (especially the early stages of caries), demineralization of tooth structures (e.g., tooth enamel), peri-implantitis, periodontal disease, gingivitis, the hardening process of dental composites, lesions of oral structures, or dental abnormalities. Since human tooth enamel is transparent at 0.4-0.55 THz, dental cavities or enamel demineralization can be monitored at the early stages themselves. However, limitations arise in terahertz sources and detectors. Some embodiments of the present disclosure provide a THz scanner using air-side emitting RTDs and beam scanning devices suitable for dental imaging.

[0026] In at least one embodiment of the present disclosure, the disease, disorder, or condition of interest may be, but is not limited to, a burn, edema, or cancer. In some embodiments, the burn is a second-degree burn or higher. In some embodiments, the cancer may 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, assembled into an array using CMOS technology, can open the possibility of low-cost terahertz biomedical imaging, and thus non-destructive cancer imaging by THz for cancer diagnosis can be achieved.

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

[0028] In some embodiments, the target is the skin edge, which has a low refractive index and absorbance at THz.

[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 increased terahertz transmission signal compared to healthy tooth structure.

[0031] In some embodiments, the margins of cancer or tumor or less dense tissue compared to healthy tissue may be detected as visible terahertz imaging at early, middle, or late stages of the target tissue.

[0032] The present disclosure further provides a method for imaging a target in an object, comprising the steps of providing a target scanning-based THz imaging device of the present disclosure, emitting a terahertz signal from a terahertz emitter to a surface of the target in a subject requiring it, receiving the terahertz signal reflected from the surface of the target with a receiver, and reconstructing an image of the subject from the received terahertz signal. In some embodiments, the target is a dielectric and does not have water.

[0033] In the portable THz imaging device for diagnosing a condition of a subject as described in the present disclosure, the THz imaging device can be manufactured as a simple, portable, real-time in-vivo THz imaging device for imaging dental tissue. Moreover, the portable THz imaging device has a high enough sensitivity to detect early stages of caries compared to common X-rays. Therefore, the THz imaging device of the present disclosure can operate at a density for early detection of dental problems, such as imaging enamel thickness with high resolution. [Brief description of the drawings]

[0034] The present disclosure can be more fully understood by reading the following description of the embodiments in conjunction with the accompanying drawings, in which: [Figure 1] FIG. 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. [Diagram 2] FIG. 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. [Diagram 3] FIG. 3 is a schematic diagram of a receiver of an apparatus for collecting terahertz signals according to one embodiment of the present disclosure. [Figure 4A] FIG. 4A is a schematic diagram of a THz source in an RTD (resonant tunneling diode) configuration with an antenna according to one embodiment of the present disclosure. [Figure 4B]FIG. 4B is a schematic diagram of a THz source in an RTD structure with an antenna according to another embodiment of the present disclosure. [Figure 4C] FIG. 4C is a schematic diagram of a THz source in an RTD structure with an antenna according to another embodiment of the present disclosure. [Figure 4D] FIG. 4D is a schematic diagram of a THz source in an RTD structure with an antenna according to another embodiment of the present disclosure. [Diagram 5] FIG. 5 is a cross-sectional view of a portion of a terahertz source according to one embodiment of the present disclosure. [Figure 6] FIG. 6 is an exemplary graph illustrating voltage vs. current density characteristics of a triple barrier RTD (TBRTD) according to one embodiment of the present disclosure. [Figure 7] FIG. 7 is an exemplary graph illustrating estimated device capacitance versus maximum oscillation frequency characteristics of a TBRTD according to one embodiment of the present disclosure. [Figure 8] FIG. 8 is a schematic diagram illustrating a frequency tunable fractal antenna of a THz source according to different embodiments of the present disclosure. [Figure 9] FIG. 9 is a schematic diagram illustrating a frequency tunable fractal antenna of a THz source according to different embodiments of the present disclosure. [Figure 10] FIG. 10 is a schematic diagram illustrating a frequency tunable fractal antenna of a THz source according to different embodiments of the present disclosure. [Figure 11] FIG. 11 is a schematic diagram illustrating a frequency tunable fractal antenna of a THz source according to different embodiments of the present disclosure. [Figure 12] FIG. 12 is an exemplary graph illustrating the frequency shift of a frequency tunable fractal antenna of a THz source according to different embodiments of the present disclosure. [Figure 13] FIG. 13 is an exemplary graph illustrating the frequency shift of a frequency tunable fractal antenna of a THz source according to different embodiments of the present disclosure. [Figure 14] FIG. 14 is a schematic diagram of a tapered structure of a THz source according to one embodiment of the present disclosure. [Figure 15A]FIG. 15A is the simulated electric field response of a hollow polymer taper structure without a metal coating. [Figure 15B] FIG. 15B is the simulated electric field response of a hollow polymer taper structure with an inner wall metal coating. [Figure 16] FIG. 16 is a schematic diagram of a device according to one embodiment of the present disclosure. [Figure 17] FIG. 17 is a schematic diagram of a device according to another embodiment of the present disclosure. [Figure 18] FIG. 18 is a schematic diagram of a device according to another embodiment of the present disclosure. [Figure 19] FIG. 19 is a schematic diagram of a tapered structure having a beveled cut on the light emitting aperture according to one embodiment of the present disclosure. [Figure 20] FIG. 20 is a schematic diagram of a physical terahertz fishnet metamaterial (TFMM) prism design of a beam deflector according to one embodiment of the present disclosure. [Figure 21] FIG. 21 is a schematic diagram of a flat TFMM prism design of a beam deflector according to one embodiment of the present disclosure. [Figure 22] FIG. 22 is a cross-sectional view of droplets of different sizes disposed between two layers of a fishnet array of a beam deflector according to one embodiment of the present disclosure. [Figure 23] FIG. 23 is a flow diagram of a process for operating a portable THz imaging device according to one embodiment of the disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] The following embodiments are used to illustrate the present disclosure. Those skilled in the art can easily conceive other advantages and effects of the present invention based on the disclosure of this specification. The present disclosure can also be implemented or applied as described in different embodiments. For different aspects and applications, the form for implementing the present disclosure can be modified or changed without departing from the scope of the present disclosure.

[0036] The subject matter will now be described with reference to the accompanying drawings. Various structures, systems, and devices are shown in the drawings in a schematic manner for purposes of explanation only, so as not to obscure the present disclosure with details well known to those skilled in the art. Nevertheless, the accompanying drawings are included to illustrate and explain exemplary embodiments of the present disclosure. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the art. A special definition of a term or phrase, i.e., a definition that is different from the ordinary meaning understood by those skilled in the art, is not implied by consistent use of the term or phrase herein. To the extent that 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 special definition will be expressly set forth herein in a definitive manner that directly and unambiguously provides the special definition of the term or phrase.

[0037] The proportionality, structure, size, and other features shown in the accompanying drawings of the present disclosure are only used to illustrate the embodiments described herein so that those skilled in the art can read and understand the present disclosure therefrom, but they are not intended to limit the scope of the present disclosure. Any changes, modifications, or adjustments of said features should all fall within the scope of the technical content of the present disclosure, unless they affect the designed purpose and effect of the present disclosure.

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

[0039] As used herein, sequential terms such as "first," "second," and the like are cited merely for convenience in describing or distinguishing limitations of elements, components, structures, regions, parts, devices, systems, and the like from one another, and are not intended to limit the scope of the disclosure or to limit the spatial order between such limitations. Furthermore, unless otherwise specified, singular terms such as "a," "an," and "the" also relate to the plural, 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, in reference to a list of one or more elements, at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each element listed in the list of elements, and not excluding any combination of elements in the list of elements. This definition also allows for elements other than those identified in the list of elements to which the phrase "at least one" refers, whether related or unrelated to the identified elements, to be optionally present. Thus, as a non-limiting 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") can refer, in one embodiment, to at least one with no B present (and optionally including elements other than B), optionally including more than one A. In another embodiment, at least one with no A present (and optionally including elements other than A), optionally including more than one B. In yet another embodiment, it refers to containing at least one, and optionally more than one, A, and containing at least one, and optionally more than one, B (and optionally other elements).

[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 include any vertebrate, including, but not limited to, humans, mammals, reptiles, amphibians, and / or fish. Advantageously, however, the subject is a mammal, such as a human, or an animal mammal, such as a domesticated mammal, such as a dog, cat, horse, etc., or a production mammal, such as a cow, sheep, pig, etc. The term "patient" may be interchangeable with "subject."

[0043] As used herein, the term "signal" refers to radiation emitted from a source or reflected from an object, including, but not limited to, a beam, a terahertz beam, a signal, and a terahertz signal. In at least one embodiment of the present disclosure, a signal can be a transmission and a reflection.

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

[0045] FIG. 1 illustrates an embodiment of a 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, the receiver 30, and the generator 40 may be fully electronically controlled and may communicate electrically with each other via wires or wirelessly. In some embodiments, the device 10 further comprises a connector 50 for detachably connecting the THz emitter 20 and the receiver 30 at a distance.

[0046] In at least one embodiment, the THz emitter 20 may be configured to face the receiver 30, and the target 60 may be disposed between the THz emitter 20 and the receiver 30. In this manner, the receiver 30 may collect the emitted terahertz signal that has passed through the target 60 after emitting the terahertz signal from the terahertz emitter 20.

[0047] In at least one embodiment, the THz emitter 20 is connected to a generator 40 that can induce the THz emitter 20 to emit a terahertz signal that can strike and be reflected from a surface of the target 60. The reflected terahertz signal can be collected by the receiver 30 such that the 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 allow for reconstructing images of targets 60 having different sizes. The detailed configuration of the emitter 20 and the receiver 30 are described further below.

[0049] FIG. 2 shows an embodiment of a THz emitter 20 for emitting a terahertz signal of 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 disposed on the top surface 27 of the cover 24. In at least one embodiment, the THz source 21 is disposed 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 disposed on the bottom surface 26 (the terahertz source 721 and tapered structure 722 shown in FIG. 16). In some embodiments, the tapered structure 22 may have a smaller opening for emitting a signal and a larger opening covering the THz source 21 for collecting the 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 include a beam deflector 231 and one or more deflector electrodes 232. In some embodiments, the beam deflector 231 is disposed at the center of the top surface 27 of the cover 24 and is electrically connected to the deflector electrodes 232. In some other embodiments, the location of the beam deflector 231 may not be at the center of the top surface 27 of the cover 24 but may be at any location according to actual needs. In some embodiments, the deflector electrodes 232 may extend outward from the beam deflector 231 to an edge of the top surface 27 of the cover 24.

[0051] In some embodiments, the shape of the cover 24 of the THz emitter 20 may be fabricated as, but not limited to, a cube, a cuboid, a cylinder, or other suitable shapes according to actual needs.

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

[0053] Referring to FIG. 4A, an embodiment of a THz source 21 of the present disclosure is shown. The terahertz source 21 includes a substrate 211, an RTD structure 212, a spacer layer 213, a resonator antenna 214, and a radiating antenna 215, with the spacer layer 213 acting as a separator between the resonator antenna 214 and the radiating antenna 215. For example, the RTD structure 212 is disposed on the substrate 211. The spacer layer 213 is disposed on the RTD structure 212. The resonator antenna 214 is disposed on the RTD structure 212 and embedded in the spacer layer 213. And the radiating antenna 215 is disposed on the spacer layer 213. In some embodiments, the RTD structure 212 is disposed on the substrate by using conventional MBE (molecular beam epitaxy) and MOCVD (metal organic chemical vapor deposition) deposition. In some embodiments, the substrate 211 is made of indium phosphide (InP) and the RTD structure 212 is fabricated as an AlAs / InGaAs / AlAs structure.

[0054] 4B and 4C show an embodiment of a THz source 21 of the present 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, and a radiating antenna 215, with the spacer layer 213 acting as a separator between the resonator antenna 214 and the radiating antenna 215. In FIG. 4B, the radiating antenna 215 and the spacer layer 213 have been removed to more clearly show the resonator antenna 214. The RTD structure 212 includes an RTD 212a disposed on a buffer layer 212b. In some embodiments, the buffer layer 212b is an In 0.53 Ga 0.47The RTD 212a may be made of As. In some embodiments, the RTD 212a may be a triple barrier resonant tunneling diode (TBRTD). In some embodiments, the passivation layer 216 may be made of silicon dioxide. In some embodiments, the buffer layer 212b is disposed on the substrate 211. The passivation layer 216 is disposed on the buffer layer 212b. The RTD 212a is embedded in the passivation layer 216. The main portion of the resonator antenna 214 is disposed on the passivation layer 216. In some embodiments, the top electrode of the resonator antenna 214 is electrically connected to the emitter end of the RTD 212a, and the bottom electrode of the resonator antenna 214 is electrically connected to the collector end of the RTD 212a. In some embodiments, the top electrode of the resonator antenna 214 is embedded in the passivation layer 216, and the bottom electrode of the resonator antenna 214 is disposed on the buffer layer 212b and embedded in or covered by the passivation layer 216. In some embodiments, the spacer layer 213 is disposed on the passivation layer 216 and the resonator antenna 214, and the radiator antenna 215 is disposed on the spacer layer 213.

[0055] In at least one embodiment, the resonator antenna 214 and / or the radiator antenna 215 can be a spiral antenna structure or any wideband or tunable antenna. In some embodiments, the resonator antenna 214 and the radiator antenna 215 are fractal antennas shaped according to the same fractal curve or pattern. Thus, the radiator antenna 215 has the same shape and size as the main part of the resonator antenna 214. Also, the radiator antenna 215 and the main part of the resonator antenna 214 are aligned one above the other. For example, the resonator antenna 214 and the radiator antenna 215 shown in FIG. 4(B) and FIG. 4(C) are both shaped according to a Hilbert curve. In some embodiments, the resonator antenna 214 and the radiator antenna 215 may be shaped according to another fractal curve or pattern, such as a Koch curve, a Peano curve, a Sierpinski gasket, or a Minkowski geometry.

[0056] Referring to FIG. 4D, an embodiment of the terahertz source 21 of the present disclosure is shown, which is an alternative design compared to those of FIG. 4B and FIG. 4C. The main part of the resonator antenna 214 of the THz source 21 is fabricated on the substrate 211 or the buffer layer 212b. In FIG. 4D, in order to more clearly show the RTD 212a and the resonator antenna 214, the spacer layer 213 and the radiating antenna 215 are removed, and only a small part of the passivation layer 216 is shown. In fact, the passivation layer 216 of the terahertz source 21 can have approximately the same size as its counterpart in FIG. 4B, so that the passivation layer 216 covers the resonator antenna 214. The terahertz source 21 also includes a spacer layer 213 disposed on the passivation layer 216 and a radiating antenna 215 fabricated on the spacer layer 213. Resonant tunneling diodes are suitable for the terahertz source 21 and detector 31 in the portable device 10 of the present disclosure due to their simple design, conventional semiconductor fabrication methods, and integration advantages over other terahertz sources. Resonant tunneling diodes can both emit terahertz radiation and detect terahertz radiation when biased in different regions. The RTD structure 212 can emit terahertz radiation when biased in the negative differential region (NDR) and detect terahertz radiation when operated in the 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 lower at 0.4 THz to 0.5 THz compared to other ranges of the terahertz spectrum. Thus, 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 with a slot resonator antenna (shown in FIG. 4A) or other antenna structure (shown in FIG. 4B) to couple the generated terahertz radiation into free space via a silicon lens attached to the backside of the substrate. Such configurations use hemispherical or hyper-hemispherical silicon lenses, but these silicon lenses are expensive and difficult to package. Thus, in some embodiments, the radiating antenna 215 is disposed on the 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 vibrations can be inductively coupled to the patch antenna and can emit radiation in the upward direction, thus eliminating the use of a silicon lens 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] Thus, in some embodiments, the radiator antenna 215 may be formed as a helical antenna structure (as shown in FIG. 4A) or a similar type of wideband antenna structure (as shown in FIG. 4B) on top of the spacer layer 213 of the THz source 21 to emit (or receive) terahertz signals without the use of a silicon lens. The free space coupling (or receiving) efficiency of the antenna structure on top of the spacer layer can be enhanced by careful design of the antenna geometry and optimizing the dielectric thickness, although the present disclosure is not limited thereto.

[0061] 5 is a cross-sectional view of a portion of a terahertz source 500 according to one embodiment of the present disclosure. The THz source 500 includes all of the components and layers of the THz source 21 shown in FIGS. 4B and 4C. The terahertz source 500 also includes a bottom contact layer 510 disposed between the buffer layer 212b and the TBRTD 160, a top contact layer 520 formed on the TBRTD 160, a bottom contact metal 515 formed on the bottom contact layer 510, and a top contact metal 525 formed on the top contact layer 520. The bottom contact metal 515 and the top contact metal 525 may be formed by sputtering gold and may be terminals of the resonator antenna 214.

[0062] 5, the TBRTD 160 has a nine-layer stack including, from bottom to top, a collector layer 161, a spacer 162, a collector barrier 163, a quantum well (collector well) 164, a primary 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 top contact layer 520 to the buffer layer 212b in FIG. 5. [Table 1] In a traditional double barrier RTD or DBRTD, the emitter and collector barriers are identical (same barrier material and thickness) and the device structure is symmetrical, avoiding rapid thermal leakage currents and increasing the tunneling current.

[0063] In contrast, the triple barrier of the TBRTD 160 provided by the present disclosure includes more quantum wells and barriers, increasing the well charge and peak current, and reducing the peak voltage. Furthermore, the TBRTD 160 includes a non-identical primary barrier 165. As shown in Table 1, the collector barrier 163 and the emitter barrier 167 have the same material and thickness, but the primary barrier 165 is formed of a different material and has a different thickness. Furthermore, 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 is In 0.52 Al 0.48 The collector barrier 163 and the emitter barrier 167 are made of AlAs. All other layers shown in Table 1 are made of In. 0.53 Ga 0.47 The TBRTD 160 employs a combination of InGaAs / InAlAs / AlAs materials because this material system provides better RTD characteristics. The spacers 162 and 168 are made of undoped In to avoid diffusion of charge carriers from the highly doped layers. 0.53 Ga 0.47 As.

[0065] TBRTD160 is 440kA / cm 2The simulated peak current density of 1000 MHz and DC-RF conversion efficiency up to 19.75% are shown. The theoretically calculated maximum extractable output power of TBRTD160 is about 250 μW at 0.95 THz for a device area of ​​1 μm2, which is much higher than the previously reported output power of conventional TBRTDs. The non-identical triple barrier structure of TBRTD160 shows a ΔV of 0.41 V and a ΔI of 0.0033 A, where ΔV and ΔI are the voltage and current of the negative differential resistance (NDR) region of TBRTD160, respectively. The peak-to-valley current ratio (PVCR) is about 4.71. Compared with the conventional TBRTD, the peak current and peak voltage of TBRTD160 are reduced without compromising the PVCR, and the DC-RF conversion efficiency is also increased at the same time. The maximum oscillation frequency of TBRTD160 is 0.95 THz. The theoretically estimated parasitic capacitance of TBRTD160 is cn=21.3 fF. The series resistance of the TBRTD160 is Rs = 3.25 Ω. The reciprocal of the negative conductance of the TBRTD160 is Rn = 18.66 Ω.

[0066] Figure 6 shows the 1 μm 2 1 is an exemplary graph showing numerically simulated voltage vs. current density characteristics of a TBRTD 160 having a device area of

[0067] Figure 7 shows the 1 μm 2 1 is an exemplary graph showing maximum oscillation frequency characteristics versus estimated device capacitance for a TBRTD 160 having a device area of ​​100 .mu.m.

[0068] In some embodiments, the resonator antenna 214 and the radiator antenna 215 of the THz source 500 may be fractal antennas, as fractal technology allows for the integration of small antennas and multiple bands. Fractal antennas have desirable properties such as space filling, self-similarity, fractional dimensions, infinite complexity, mechanical simplicity, and robustness, which make them unique for more efficiently achieving advantages such as miniaturization, wideband, and multi-band properties. The space-filling properties are used to reduce antenna size. The self-similarity is used to achieve multi-band resonator antennas. The number of repetitions of the geometric shapes of the resonator antenna 214 and the radiator antenna 215 is based on their operating wavelengths.

[0069] Additionally, the radiator antenna 215 of the THz source 500 may be a fractal antenna that is reconfigurable 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 wireless communication.

[0070] In some embodiments, for large frequency shifts, large sections of electrical length or large segments of the fractal pattern can simply be disconnected 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, more electrical length or more fractal patterns can be connected to the radiator antenna 215, thus increasing the overall size of the radiator antenna 215 and generating a downward frequency shift. The radiator antenna 215 can include at least one switch embedded in the fractal curve or fractal pattern of the radiator antenna 215. The at least one switch can 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 shifts. For example, in an embodiment, the radiator antenna 215 can be switched between a one-segment fractal curve 800 shown in FIG. 8 and a two-segment fractal curve 900 shown in FIG. 9. When the radiator antenna 215 is switched to the one-segment fractal curve 800 of Fig. 8, its reflection coefficient S11 is plotted as curve 1210 of Fig. 12. When the radiator antenna 215 is switched to the two-segment fractal curve 900 of Fig. 9, its reflection coefficient S11 is plotted as curve 1220 shown in Fig. 12.

[0071] In some embodiments, for medium frequency shifts, fewer fractal patterns or shorter electrical lengths can be disconnected from or connected to the radiator antenna 215 by controlling the switches embedded in the radiator antenna 215. This effect can decrease the electrical length of the radiator antenna 215 and increase the operating frequency, or vice versa. For example, in some embodiments, the radiator antenna 215 can be further switched between the fractal curve 1000 shown in FIG. 10 and the fractal curve 1100 shown in FIG. 11. When the radiator antenna 215 switches from the fractal curve 900 in FIG. 9 to the fractal curve 1000 in FIG. 10, three arms are disconnected from each fractal segment and the electrical length is increased. The resulting reflection coefficient S11 is plotted as the curve 1230 shown in FIG. 12. A downward (leftward) frequency shift of about 0.02 THz is observed. If the radiator antenna 215 is switched to the fractal curve 1100 of Figure 11 with a larger cut and electrical length reduction, the reflection coefficient S11 is plotted as the curve 1240 shown in Figure 12. Here, an upward (rightward) frequency shift is observed.

[0072] In some embodiments, similar to the radiator antenna 215, the resonator 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 resonator antenna 214 to reconfigure the resonator antenna 214 for large and medium frequency shifts.

[0073] In some embodiments, both the resonator antenna 214 and the radiator antenna 215 include switches for large and medium frequency shifts.

[0074] In some embodiments, for fine frequency shifting or continuous frequency tuning, the spacer layer 213 beneath the radiator antenna 215 may include a ferroelectric material, such as a polymer dispersed liquid crystal (PDLC), whose dielectric constant changes when an electric field applied to the ferroelectric material changes. Unlike the previously described 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 much more continuous and minute changes in the operating frequency.

[0075] An example of this frequency shift due to dielectric constant change using a spacer layer 213 of PDLC on a radiating antenna 215 is shown in Figure 13, where the frequency shift is due to the liquid crystal in the spacer layer 213 changing from an ordinary polarization state (corresponding to curve 1310) to an extraordinary polarization state (corresponding to curve 1320). The operating frequency of the radiating antenna 215 changes in proportion to the dielectric constant of the PDLC in the spacer layer 213.

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

[0077] In some embodiments, the substrate 211, buffer layer 212b or passivation layer 216 under the resonator antenna 214, and the spacer layer 213 under the radiating antenna 215 may both comprise a ferroelectric material such as PDLC for fine frequency shifting or continuous frequency tuning of the resonator antenna 214 and the radiating antenna 215.

[0078] 14 shows an embodiment of the tapered structure 22 or 32 of the THz source of 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 with an entrance opening at the proximal end and an emission opening at the distal end, the entrance opening being larger than the emission opening. For example, the tapered structure 22 covers the terahertz source 21 with the entrance opening side of the tapered structure 22, and the tapered structure 32 covers the terahertz detector 31 with the exit 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 by several methods, such as increasing the source power, decreasing the transmission loss, improving the impedance matching, and using a large aperture diameter and a short probe length. However, increasing the THz source power and improving the impedance matching can increase the cost and complexity of the imaging system. Also, a larger aperture diameter can lead to a decrease in image resolution. Therefore, in some embodiments, decreasing the transmission loss of the terahertz wave in the waveguide and the probe structure is a suitable method to achieve a strong electric field localization at the tapered tip.

[0080] In order to reduce the transmission loss of the terahertz signal, it is preferable to select an appropriate material for forming the tapered structure. The terahertz transmission loss is

number

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

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

[0083] Therefore, by coating a metal on the hollow polymer taper structure, the metal-coated hollow polymer taper structure may have the ability to confine the terahertz signal or input beam through a sub-wavelength aperture and achieve sub-wavelength resolution terahertz images while performing near-field image scanning by an electronically controlled beam deflector. In some embodiments, the metal coated on the hollow polymer taper is silver, or any other metal that can achieve the same effect as above.

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

[0085] FIG. 16 shows an embodiment of the device 70 of the present disclosure. The electro-optic beam deflector may be made of a tunable metamaterial or metasurface (e.g., the design of the beam deflector 110 or 120 shown in FIGS. 20-22) and fabricated on a thin substrate to form the beam deflector module 723 of the device 70 (the beam deflector module 23 shown in FIG. 2), the thin substrate having extremely low absorption at the terahertz frequency of interest. The terahertz source 721 is covered by a tapered structure 722 at the entrance aperture 725 side to emit the terahertz signal 71. The beam deflector module 723 is attached to 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 arranged perpendicular to the direction of the terahertz signal 71 and hits the target 75 located between the THz source 721 and the THz detector 731. The outgoing terahertz signal 72 is then reflected from the surface of the target 75 as a reflected terahertz signal 73. The reflected terahertz signal 73 is finally collected by a tapered structure 732 and received by a THz detector 731.

[0086] The beam deflector module 723 of some embodiments is fabricated using an 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 a beam deflector module 723 fabricated with a phase change material is controlled by an applied bias voltage, the phase front of the propagating wave can be tilted so that the direction of the terahertz beam can be steered, focused, or collimated.

[0087] FIG. 17 shows an embodiment of the device 80 of the present disclosure. The electro-optic beam deflector may be made of a tunable metamaterial or metasurface (e.g., the design of the beam deflector 110 or 120 shown in FIGS. 20-22) and processed on the curved surface to form a beam deflector module 823 that can focus and deflect the terahertz signal 81. The terahertz source 821 is covered by a tapered structure 822 at the entrance aperture 825 side to emit the terahertz signal 81. In some embodiments, the beam deflector module 823 is partially attached to the emission aperture 824 of the tapered structure 822 so that the terahertz signal 81 exiting from the emission aperture 824 can be focused and deflected by the beam deflector module 823 and impinge on the target 85, which does not need to be located 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 finally collected by the tapered structure 832 and received by the THz detector 831 .

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

[0089] Referring to FIG. 18, an embodiment of the device 90 of the present disclosure is shown. The beam deflector module 923 is similar to the beam deflector module 823, but is not formed on a curved surface. Also, the beam deflector module 923 can be made of tunable metamaterials or metasurfaces (e.g., the design of the beam deflector 110 or 120 shown in FIGS. 20-22). Instead, the beam deflector module 923 is formed on a flat surface. The terahertz source 921 of the device 90 is not covered by the entrance opening 925 of the tapered structure 922, and the beam deflector module 923 is not attached to the emission opening 924 of the tapered structure 922. The terahertz signal 91 emitted from the terahertz source 921 impinges on the beam deflector module 923 at a certain angle, and based on the bias voltage applied to the beam deflector module 923, the reflection angle of the terahertz signal 91 can be controlled by the beam deflector module 923. In some embodiments, the beam deflector module 923 may comprise an electro-optic beam deflector or a galvo mirror.

[0090] Therefore, the angle of incidence of the reflected terahertz signal 91 incident on the opening 925 of the tapered structure 922 is changed, and the terahertz signal 92 exits from the exit opening 924 of the tapered structure 922 to collide with the target 95. The exiting 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 above-described configuration of the device 90, the angle of incidence 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] 19 shows an embodiment of a tapered structure 101 having a sloped cut on the emission aperture 102 of the present disclosure. To achieve scanning of near-field terahertz radiation, the output aperture 102 of the tapered structure 101 may be cut at an angle to increase the deflection angle such that the surface 104 of the output aperture 102 is sloped with respect to the surface 105 of the input aperture 103 of the tapered structure 101. The terahertz signal leaves the output aperture 102 with a sloped cut in different directions due to the change in the reflection angle / anti-resonant reflection pattern within the tapered structure 101.

[0092] FIG. 20 illustrates an embodiment of a physical terahertz fishnet metamaterial (TFMM) prism design of the beam deflector 110 of the present 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 FIG. 16-18. The beam deflector 110 is a TFMM prism for beam steering purposes similar to the normal prism design, except that the fishnet is an anisotropic material that allows only normal incident beams (e.g., incident terahertz signals). In some embodiments, to achieve larger angle beam steering to generate larger 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, and each of the multiple stages 112 may be formed by at least three fishnet layers 111. Thus, beam bending may 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 FIG. 21, an embodiment of a flat TFMM prism design of the beam deflector 120 of the present disclosure is shown. The flat prism design of the beam deflector 120 can be one of the proposed electro-optic modulator designs in the beam deflector modules 723, 823, or 923 shown in FIGS. 16-18. In at least one embodiment, the challenge of fabricating a multi-layer TFMM prism using a flat prism structure can be mitigated by combining the concept of beam steering based on OPD with the 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 FIG. 21. Different external fields can be applied to each of the fishnet rows that are not connected to each other (i.e., fishnet rows 121, 122, 123, and 124) to generate a large OPD that varies along the direction perpendicular to the incident beam. Therefore, if a material is capable of producing a large ODP that varies along a direction perpendicular to an incident beam, such as a terahertz signal, the beam deflector 120 does not need to be in the form of a physical prism to steer the beam.

[0094] FIG. 22 shows another embodiment for creating the electro-optic modulator design of the beam deflector module 723, 823, or 923 shown in FIGS. 16-18. FIG. 22 shows a cross-sectional view of an embodiment of droplets 133 of different sizes disposed between two layers of a fishnet row. With this design, the flat prism 120 shown in FIG. 21 can be produced by inducing refractive index changes between cells with different droplet sizes including an upper fishnet layer 131, a lower fishnet layer 132, and multiple droplets 133. For example, each fishnet row shown in FIG. 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 disposed between the upper fishnet layer 131 and the lower fishnet layer 132. In some embodiments, the 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 droplets 133, the more droplet layers). Thus, a gradient refractive index structure may be constructed by varying the droplet size between each of the fishnet columns of the cut TFMM array. In some embodiments, the droplets 133 may be composed of a 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 refractive index change, the fishnet structure of the beam deflector can be used as a single electrode to apply a separate electric field on 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 molded with different curves can operate with positive refractive index, but may be constrained by the diffraction limit. Gradient plano lenses infiltrated with materials such as non-uniform LC cells can produce optical effects like triangular prisms, but may be limited by the refractive index of the material. Thus, at least one embodiment of the present disclosure provides an actively controlled metamaterial lens of a beam deflector that can overcome these problems by transforming the lens to perform different functions, such as from focusing to diverging, to collimating, or achieving near-field or sub-wavelength focusing by changing the applied voltage. In some embodiments, the beam deflector is designed by using UV-curable PDLC as a dielectric substrate, and the material exposed with different UV intensities can cause the LC droplets inside the polymer to form with different sizes.

[0097] Because the ordinary and extraordinary refractive indices of PDLC can vary depending on the average size of the liquid crystal droplets within the polymer host medium, the material can be exposed with ever-increasing doses to achieve a prismatic effect. Based on the above concepts, in some embodiments, the beam deflector may be fabricated as a tunable flat lens, a prism with active steering, or even a more complex lens design, depending on the configuration of the PDLC substrate.

[0098] FIG. 23 shows a flow chart of a process for operating the portable THz imaging device of the present disclosure. First, in step S10, a generator connected to a THz emitter induces the THz emitter to radiate a terahertz signal to a 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 of interest diagnosed by the portable THz imaging device may be a patient's tooth and the target surface may be a tooth enamel surface. In some embodiments, diagnosis with the portable THz imaging device may be performed by a series of scans from the left side back relative to the midline of the mouth: left buccal, left occlusal, labial, incisal, right buccal, right occlusal, and lingual.

[0100] In some embodiments, the dental condition diagnosed may be caries, early detection of demineralized dental enamel, monitoring the hardening process of dental composites, and identification of dental abnormalities.

[0101] In the portable THz imaging device for diagnosing the condition of a target of interest as described in the present disclosure, the THz imaging device can be manufactured as a simple, portable, real-time in-vivo THz imaging device for imaging dental tissue. Moreover, the portable THz imaging device has a high enough sensitivity to detect early stages of caries compared to common X-rays. Therefore, the THz imaging device of the present disclosure can operate at a density for early detection of dental problems, such as imaging enamel thickness with high resolution.

[0102] The present disclosure has been described using exemplary embodiments to illustrate the principles, features, and effectiveness of the present disclosure, but is not intended to limit the scope of implementation of the present disclosure. The present disclosure may be modified and altered by those skilled in the art without departing from the spirit and scope of the present disclosure. However, any equivalent modifications and alterations achieved according to the disclosure of the present disclosure should be considered to be within the scope of the present disclosure. The scope of the present disclosure should be defined by the appended claims.

Claims

1. 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; a receiver for receiving the terahertz signal; The THz emitter comprises: 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 to induce and generate a focused near-field beam profile at a distal end; a beam deflector module coupled to the first cover and configured to deflect or modulate a terahertz signal for scanning; The receiver includes: A second cover; a second tapered structure disposed within the second cover; a THz detector disposed within the second cover and covered by the second tapered structure; Scanning-based THz imaging device.

2. The THz source includes: a resonant tunneling diode (RTD) having an emitter and a collector; When electrically connected to the emitter and collector of the RTD, and a radiator antenna disposed above the resonator antenna.

3. 2. The scanning-based THz imaging device of claim 1, wherein the RTD is a TBRTD or a multi-barrier RTD including AIAs / InGaAS / AIAs layers, and the TBRTD or the multi-barrier RTD is configured to improve overall DC-RF conversion efficiency and reduce peak current-voltage.

4. 3. The scanning-based THz imaging device of claim 2, wherein the radiator antenna is a tunable fractal antenna structure configured to vary the frequency shift by reconfiguration of a fractal pattern of the tunable fractal antenna structure or by voltage-induced dielectric constant changes in the radiator antenna.

5. The scanning-based THz imaging device of claim 1 , wherein the first tapered structure has an air core, an emission aperture, and an entrance aperture.

6. The scanning-based THz imaging device of claim 5 , wherein the air-core portion has an inner wall coated with a metallic material for directing and generating the focused near-field beam profile at the radiating aperture of the first tapered structure.

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

8. The scanning-based THz imaging device of claim 5 , wherein the beam deflector module is disposed at the emission aperture of the tapered structure and configured to transmit the terahertz signal.

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

10. 6. The scanning-based THz imaging device of claim 5, wherein the beam deflector module is disposed at the entrance aperture of the first tapered structure and configured to deflect the terahertz signal emitted from the THz emitter and enter the tapered structure.

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

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

13. 10. The scanning-based THz imaging device of 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 terahertz fishnet metamaterial structure comprises: A first layer; and a second layer opposite the first layer; and and a plurality of droplets disposed between the first layer and the second layer forming a plurality of droplet layers.

15. The scanning-based THz imaging device of 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. 2. The scanning-based THz imaging device of 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 across the metamaterial array.

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

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

19. Providing a scanning-based THz imaging device according to claim 1; emitting a terahertz signal from a terahertz radiator to a target within a subject in need thereof; receiving a terahertz signal reflected from the target with a receiver; and diagnosing a condition of the target by analyzing the received terahertz signal. A method for diagnosing a disease, disorder, or condition in a subject.

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

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

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

23. Providing a scanning-based THz imaging device according to claim 1; emitting a terahertz signal from a terahertz radiator onto a surface of a target within a subject; receiving a terahertz signal reflected from a surface of the target with a receiver; and reconstructing an image of the object from the received terahertz signals. A method for imaging a target at an object.

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

Images