Design and Numerical Investigation of an Octagonal Graphene Terahertz Metasurface Absorber with Enhanced Sensitivity for Biosensing Applications

Studies in terahertz (THz) imaging have revealed a significant difference between skin cancer (basal cell carcinoma) and healthy tissue. Since water has strong absorptions at THz frequencies and tumours tend to have different water content from normal tissue, a likely contrast mechanism is variation in water content. Thus, we have previously devised a finite difference time-domain (FDTD) model which is able to closely simulate the interaction of THz radiation with water. In this work we investigate the interaction of THz radiation with normal human skin on the forearm and palm of the hand in vivo. We conduct the first ever systematic in vivo study of the response of THz radiation to normal skin. We take in vivo reflection measurements of normal skin on the forearm and palm of the hand of 20 volunteers. We compare individual examples of THz responses with the mean response for the areas of skin under investigation. Using the in vivo data, we demonstrate that the FDTD model can be applied to biological tissue. In particular, we successfully simulate the interaction of THz radiation with the volar forearm. Understanding the interaction of THz radiation with normal skin will form a step towards developing improved imaging algorithms for diagnostic detection of skin cancer and other tissue disorders using THz radiation.

An efficient and miniaturized ultra-thin tunable UWB graphene metasurface absorber for terahertz gap regime

Studies in terahertz (THz) imaging have revealed a significant difference between skin cancer (basal cell carcinoma) and healthy tissue. Since water has strong absorptions at THz frequencies and tumor affects the water content of tissue, a likely contrast mechanism is variation in water content. Modeling the propagation of a THz pulse through water is the first step toward understanding the origin of contrast in terahertz pulsed images of skin cancer. In this letter, we develop a finite-difference-time-domain simulation to model the propagation of a THz pulse and incorporate double Debye theory to model the behavior of water subject to THz radiation. Furthermore, we apply this model to skin.

Terahertz narrowband perfect metasurface absorber based on micro-ring-shaped GaAs array for enhanced refractive index sensing

Simple SummaryIn order to realize rapid and complete pre-screening in the pathological examination of gastric cancer and assist in quickly determining the boundary between cancerous and healthy cells, we developed a fast-scanning near-field terahertz (THz) imaging system. This imaging system is compact, low-cost, and easy to operate. THz examination does not need any processing after sectioning, and the diagnostic results are directly displayed in images within one minute. Compared with the H&E staining method, THz imaging diagnosis uses a quantitative absorption coefficient to distinguish cancer tissue and healthy tissue, which makes the automation of the tissue sampling pre-screening procedure possible and will save valuable time to help quickly define cancer tissue. At the same time, the spatial resolution of our near-field imaging system reaches λ/17. Using THz imaging to accurately define the margins of cancer can not only conserve healthy tissues but also minimize the number of second surgical procedures, which would save a lot of additional hospital resources.The distinguishable absorption contrast among healthy gastric tissues, carcinoma in situ and cancer tissues in the THz frequency range is one of the keys to realizing gastric cancer diagnosis by THz imaging. Based on microwave devices and a sub-wavelength fiber, we developed a fast-scanning THz imaging system combined with the principle of surface plasmon resonance enhancement. This imaging system has a near-field λ/17 spatial resolution and imaging S/N ratio as high as 108:1, and the image results are directly displayed within 1 min. We also successfully demonstrated the image diagnostic capability on sliced tissues from eight patients with gastric cancer. The results indicate that THz absorption images can not only clearly distinguish cancer tissue from healthy tissues but also accurately define the margins of cancer. Through a medical statistical study of 40 sliced tissues from 40 patients, we prove that THz imaging can be used as a standalone method to diagnose gastric cancer tissues with a diagnostic specificity and sensitivity of 100%. Compared with the H&E staining method, THz imaging diagnosis makes the automation of tissue-sampling pre-screening procedure possible and assists in quickly determining the boundary between cancerous and healthy tissues.

Terahertz(THz) imaging provided a good contrast between skin cancer (basal cell carcinoma BCC) and healthy tissue in vitro and ex vivo owing to the high water content and strong absorption of cancer tissue at THz frequencies .Modeling the propagation of a THz pulse through BCC would contribute to revealing the diagnostic and potential therapeutic application value of THz radiation. In this letter, the healthy skin and BCC were modeled as Double Debye dispersive media and the model was incorporated into the FDTD method to simulate the propagation of a THz pulse. Furthermore, absorption properties were revealed by calculating average SAR value of the horizontal distribution and vertical distribution, which would help investigate the response below the skin surface.

Laser hyperthermia therapy (HT) has emerged as a well-established method for treating cancer, yet it poses unique challenges in comprehending heat transfer dynamics within both healthy and cancerous tissues due to their intricate nature. This study investigates laser HT therapy as a promising avenue for addressing skin cancer. Employing two distinct near-infrared (NIR) laser beams at 980 nm, we analyze temperature variations within tumors, employing Pennes’ bioheat transfer equation as our fundamental investigative framework. Furthermore, our study delves into the influence of Ytterbium nanoparticles (YbNPs) on predicting temperature distributions in healthy and cancerous skin tissues. Our findings reveal that the application of YbNPs using a Gaussian beam shape results in a notable maximum temperature increase of 5 °C within the tumor compared to nanoparticle-free heating. Similarly, utilizing a flat top beam alongside YbNPs induces a temperature rise of 3 °C. While this research provides valuable insights into utilizing YbNPs with a Gaussian laser beam configuration for skin cancer treatment, a more thorough understanding could be attained through additional details on experimental parameters such as setup, exposure duration, and specific implications for skin cancer therapy.

Characterization of healthy and cancerous human skin tissue utilizing Stokes–Mueller​ polarimetry technique

A CPW-fed antenna sensor with high quality factor is designed to identify the skin cancer. The proposed antenna operates in the ISM band at 2.47 GHz frequency. The proposed antenna aims to exploit the variations in dielectric constants of skin, fat, and muscle tissues to enable non-invasive and early detection of skin cancer. The antenna design process involves considerations for achieving a high frequency shift and quality factor to discern subtle variations in dielectric properties. Electromagnetic simulations, utilizing advanced numerical techniques are employed to analyze the antenna's performance in different tissue environments. The proposed antenna design is optimized for enhancing its sensitivity to changes in the dielectric constants associated with healthy and cancerous skin tissues. To validate the antenna's effectiveness, experimental setups using tissue-mimicking phantoms are utilized. This research not only emphasizes the technical aspects of antenna design but also underscores the potential clinical applications for non-invasive skin cancer detection.

A narrow-band metasurface absorber (MSA) based on InSb micro-cylinder arrays has been proposed and investigated numerically, which could be believed to be applicable for both temperature and refractive index (RI) sensing in terahertz (THz) region. Distinct from previous designs, the proposed narrow-band MSA is only consisted of a sub-wavelength periodic micro-cylinder array based on the InSb material possessing an extremely thermosensitive relative permittivity which varies with the external environment temperature, and a gold ground-plane deposited on a glass substrate. Numerical simulation results indicate that the proposed MSA can achieve an absorbance of 99.9% at 1.8985 THz and the corresponding Q-factor is about 120.9 at room temperature (300 K). It is inferred that the narrow-band perfect absorption of the MSA could be contributed to the surface plasmon polariton (SPP) resonance mode excitation. Furthermore, the absorption property of the designed MSA is found to be highly sensitive to the RI value variations of the surrounding mediums and fluctuations of external environment temperature. Thus, the proposed MSA can be not only operated as a temperature sensor with a sensitivity of 2.13 GHz/K, but also a RI sensor with a sensitivity of 960 GHz/RIU (refractive index unit). Due to its high sensing performance, it can be believed that the narrow-band MSA has great potential applications in chemical, biological or other optoelectronic related areas.

Currently, oncological diseases are a serious problem in medicine, requiring the development of effective diagnostic and treatment methods. Stomach cancer is the fifth most common and the third most lethal cancer among oncological diseases. The main method of treating stomach cancer is surgical resection, the success of which depends on the scope of the intervention. It is important to remove the tumor with minimal damage to the stomach, since increasing the scope of the operation reduces the life expectancy of patients. The difficulty of diagnosing stomach cancer is associated with the lack of clear boundaries of the cancerous tissue. To determine the optimal volume of resection, a high-quality surgical analysis and clarification of the boundaries of the affected area of ​​the stomach are required. This requires effective methods for differentiating healthy and cancerous stomach tissue. The aim of the study is to develop a method for intraoperative diagnostics of human gastric cancer based on terahertz (THz) dielectric spectroscopy using terahertz time-domain spectroscopy in reflection mode, It was shown that using the dispersion of the real part of the permittivity and relaxation coefficients according to the Debye model (the dielectric permittivity at the high-frequency limit ε∞, the coefficients ε1 and ε2, the relaxation times τ1, and τ2)), it is possible to distinguish healthy and cancerous gastric tissue according to 6 criteria. The proposed method allows diagnosing malignant tumors of the stomach at early stages due to a significant difference in the optical properties of cancer and healthy tissues in the THz frequency range and strong absorption of THz radiation by hydroxyl groups actively accumulating in malignant tumors. THz radiation is non-ionizing, which allows it to be used for diagnostics and visualization of the disease without harm to health. Thus, THz dielectric spectroscopy is an innovative and relevant method for diagnosing gastric cancer and can potentially become a new "gold standard" of intraoperative diagnostics.

Terahertz (THz) refers to electromagnetic waves with frequency from 0.1 to 10 THz, which lies between millimeter waves and infrared light. This paper proposes an ultra-thin metasurface absorber which is perfectly suited to be the signal coupling part of terahertz focal plane array (FPA) detector. The absorptance of the proposed metasurface is higher than 80% from 4.46 to 5.76 THz (25.4%) while the thickness is merely 1.12 µm (0.018 λ). Since the metasurface absorber will be applied to terahertz FPA detector which requires planar array formation, it is divided into meta-atoms. Each meta-atom consists of the same unit cell layout, and air gaps are introduced between adjacent meta-atoms to enhance the thermal isolation, which is crucial for FPA detector to obtain desired imaging results. Due to the symmetrical layout of meta-atoms, absorptance keeps stable for different polarized waves, moreover, good absorptance could also be achieved for incidence angles range of ± 30 °. Spectral measurements show good agreement with the simulation. As a result, features of ultra-thin thickness, polarization insensitivity, and high absorptance make the proposed metasurface absorber well suited to highly efficient coupling of terahertz signals in FPA detector.

Comparison of atmospheric transmission in the bands ranging from terahertz (THz) to infrared (IR) bands using MODTRAN and available literature data show that THz radiation is not dramatically attenuated in adverse conditions when compared to IR bands especially at long distances. Favorable THz bands and mechanisms for detection of low IR signature target under adverse conditions in these bands are determined. In this study, a set of experiments are conducted to compare THz detection mechanisms, which are THz detectors and IR microbolometer cameras. Typically, IR Microbolometer cameras are not sensitive enough to detect THz waves and their sensitivity needs to be improved. While THz microbolometer cameras are being continuously improved the use of a THz to IR converter intermediary component allows a cost-effective solution to the problem. A THz to IR converter based on a metasurface absorber is studied in this regard. The effectiveness of the device is simulated and the temperature difference that can be detected with the IR microbolometer camera is modeled based on heat transfer equations.

Biological Effects of Low Dose Radiation (LDR) on Peri-Tumoral and Tumoral Areas with Squamous Cell Skin Cancer

This paper introduces a metasurface absorber (MSA) sensor designed for fuel adulteration detection in the sub-terahertz (THz) range. The MSA features mirror-symmetric separated half-circle (MSSHC)-shaped resonators, a gold ground plane, and a dielectric layer, operating effectively within the 4.4–5.4 THz frequency range. It achieves notable absorption peaks at 4.94 THz. The resonance frequencies can be finely tuned by adjusting the geometric dimensions, ensuring optimal absorption. The MSA detects various additives in diesel, gasoline, and octane by monitoring shifts in resonance frequencies corresponding to changes in the oil’s refractive index (RI). The absorber demonstrates a Q-factor of 304.35, a figure of merit (FOM) of 7.15 RIU−1, and a maximum sensitivity of 120 GHz/RIU in diesel detection. This innovative concept holds significant potential as an efficient fuel oil sensor within the automotive industry. Its structural tunability, high sensitivity, and practical design render it a promising sensor for chemical detection and biosensing applications in the THz regime.