Yuan Gao

Chipless radio frequency identification (RFID) is a low-cost RFID solution that has the potential to replace traditional barcodes in short-range applications. In this paper, a novel frequency-coded chipless RFID tag is designed at Ku-band (12.4-18 GHz). Compared to previous designs, the proposed tag has a more compact design by multiplexing one tag antenna for both transmitting and receiving purposes. In addition, the tag is designed on a substrate with ground plane, which reduces the undesired effect of the background detuning. To demonstrate the performance of the proposed chipless RFID tag, four 3-bit tags are designed in simulation, with having two of them manufactured and tested. Simulations and measurements are performed for codes of 000 and 111, and the results verify the validity of the proposed design. Finally, the sensitivity of the tag response to fabrication errors and orientation are discussed and demonstrated with simulations.

In this paper, we first review the most common measurement methods, previously used, for assessing the complex permittivity of human skin, namely, open-ended coaxial and waveguide probe reflectometry methods. We then outline and emphasize their useful features and shortcomings that can adversely affect the measurements. Then, an approach utilizing an open-ended waveguide probe with an engineered ground plane and a thin dielectric layer in front of the aperture to prevent skin protrusion is proposed. This approach utilizes a full-wave electromagnetic model that accurately describes the interaction of a layered skin with this probe. Furthermore, comprehensive analyses were performed to investigate the important sources of modeling and measurement errors and their influences on the calculated skin complex permittivity. The results of these analyses have shown that the proposed method can achieve $~ $85% and $~ $95% calculation accuracy for skin relative (to free space) dielectric constant and relative dielectric loss factor, respectively. Finally, a series of in vivo measurement was performed in the Ka-band (26.5-40 GHz) on several different locations of three human subjects using this proposed method. In addition, it is demonstrated that the homogeneous skin model cannot be used for areas of the body where the stratum corneum (SC) layer is relatively thick (e.g., palm). Finally, the effect of a thick SC layer on the relative complex permittivity calculation was discussed, and a modified method to determine the relative complex permittivity of the layered skin was proposed and verified by simulations.

Circular geometries are often encountered in nondestructive testing and evaluation applications. Circular synthetic aperture radar imaging technique, capable of producing high-resolution images, has great utility for this purpose. However, in many such applications, scanning only a portion of the circular geometry (i.e., scanning domain), called the subaperture, may only be possible or sufficient for a particular inspection need. Consequently, in subaperture imaging, for an imaging aspect angle and aspect angle measurement interval, we must determine the expected image resolution. In this paper, for an arbitrary area of interest, we analyze the image spatial resolution obtained from a generally defined aspect angle and aspect angle measurement interval. Using resolution as the criteria, we use this method to determine the boundary between small and large subapertures, which also show to produce markedly different range and cross-range resolutions as a function of aspect angle and aspect angle measurement interval. Moreover, the optimum aspect angle and aspect angle measurement interval for this fixed area of interest are defined based on these analyses. Finally, the results of these analyses and images obtained from simulations are compared and corroborated with relevant experimental results at X-band (8.2-12.4 GHz).

Translational position error in imaging systems can cause significant imaging quality degradation or image distortion. In this study, effects of translational position error in microwave SAR imaging system is investigated and evaluated by defining three image quality metrics. Extensive simulations are performed, in X-Band (8.2-12.4 GHz), to show the relationship between image quality and translational position error. Simulation results show that the imaging quality degrades with increasing position errors, and the sensitivity to translational position error increases as the standoff distance decreases. Measurements are also performed in X-Band for a 1D SAR imaging system. The measured results show good agreement with the simulated results. The methodology proposed in this study could be used to evaluate the feasibility or help define the required specifications of a microwave SAR imaging system for a specific application.

Accurate skin degree-of-burn assessment is critically important and can assist burn technicians and physicians to make appropriate treatment decisions. Millimeter wave imaging is a potential diagnosis tool capable of distinguishing between healthy and burned skin as the dielectric properties of the latter is significantly different from that of the former. In this paper, the layered model of human skin is used along with numerical electromagnetic simulations, at V-band (50-75 GHz), to demonstrate the potential for such diagnosis. In addition, an image of a burned pig skin is produced at V-band showing the potential of this methodology at millimeter wave frequencies.