No abstract

A diffractive grating is a well-known optical component and is extensively used in many applications. This research work explores application of the diffractive grating in a photoconductive antenna (PCA) of a terahertz time domain spectroscopy (THz-TDS) system, by utilizing benefits of a sub-wavelength grating structure. The grating PCA structure was modeled and simulated by COMSOL Multiphysics software (COMSOL, Inc., Burlington, MA, USA). Performance of the proposed PCA design is studied in terms of its induced photocurrent. The effects of geometrical parameters of the grating are also investigated and analyzed through its optical and electrical responses. Thanks to the increase in absorption of the incident laser’s electric field, the simulation results show a 63% increment of the induced photocurrent in the grating PCA, compared with the conventional planar PCA.

In B-mode imaging of the dependent or compressed breast, wave incidence at steep angles can change propagation directions and induce areas of signal dropout. To evaluate the image anomalies in reasonable simulation times, we performed full-wave studies for center frequencies of 1 and 4 MHz. Speed of sound and density of skin, typical coupling gel, and adipose tissue were assigned to the test couplant. Compared with commercial gel, skin-like couplant reduced the dropout area at 1 and 4 MHz by 57.1% and 96.7%, respectively, consistent with a decreased average beam deflection in the breast. Conversely, the adipose-like couplant increased the dropout area from that of simulated commercial gel by 26.5% and 36.7% at 1 and 4 MHz, respectively. In addition, the skin-like couplant resulted in the greatest beam deflection inside the breast among all couplants. The findings could aid the use of three-dimensional simulations to design ultrasound couplants for beam passage through tissue boundaries at steep angles to improve corrections of signal dropout and defocusing and in compound imaging.

Lactose plays a significant role in daily lives as a constituent of various food and pharmaceutical products. Yet, lactose intolerance conditions demand low-lactose and lactose-free products in the market. These increasing nutritional claims and labels on food products entail simple and reliable methods of analysis that can be used for meeting quality standards, nutritional claims and legal requirements. In this study, terahertz time–domain spectroscopy (THz-TDS) was employed to analyse α-lactose monohydrate qualitatively and quantitatively in food products. Both absorption spectra and absorption coefficient spectra were investigated for their prediction performance. Regression models for lactose quantification using peak area and height of the absorption peaks 0.53 and 1.37 THz were developed and assessed in infant formula samples. Satisfactory prediction results were achieved in ideal conditions with pure standards, but not in all predictions of infant formula samples. Reasons and further implications are discussed.