No abstract

Loss reduction to improve the power efficiency in active integrated antenna (AIA) is a key design drive. This paper first analyzes the loss mechanism in a convention AIA structure. A new integration scheme of a GaN power amplifier (PA) transistor with an antenna without using any output matching network (OMN) and harmonic tuning network (HTN) is then proposed to construct a seamlessly integrated AIA. This is achieved by a novel design of a slot antenna with optimized input impedance at its fundamental frequency as well as for harmonic tuning, which essentially absorbs the OMN and HTN functions in the conventional Class-F power amplifier design. By eliminating these passive networks between the transistor and the antenna, the associated insertion and mismatch losses as well as the overall circuit size are reduced. For verification, two prototypes are designed, fabricated and measured, one with the integrated design and the other with a conventional design for comparison. Both AIAs operate between 3.4 and 3.6 GHz. Experimental results show that the power-added efficiency (PAE) of the seamlessly integrated AIA is over 52% within the operating band. Compared with the conventional cascaded design of a PA and an antenna, the PAE is improved by 14.2%. INDEX TERMS Amplifier integrated antenna, active antenna, Class-F power amplifier, loss reduction, seamless integration.

Objective: To evaluate the strain-rate-dependent viscoelastic properties of the intervertebral disc by in vitro experiments. Method: The biomechanical experiments were conducted from September 2019 to December 2019. The lumbar spines of sheep were purchased within 4-6 hours from the local slaughterhouse, and the intervertebral disc samples were divided into three groups. In rupture group, the samples were used to test the mechanical behavior of the intervertebral disc rupture at different strain rates. In fatigue injury group, the samples were used to test the mechanical behavior of fatigue injury on the intervertebral disc under different strain rates. In internal displacement group, the samples were used to test the internal displacement distribution of the intervertebral disc at different strain rates by applying an optimized digital image correlation (DIC) technique. Results: Both the yielding and cracking phenomenon occurs at fast and medium loading rates, while only the yielding phenomenon occurs at a slow loading rate. The yield stress, compressive strength, and elastic modulus all increase with the increase of the strain rate, while the yield strain decreases with the increase of the strain rate. The logarithm of the elastic modulus in the intervertebral disc is approximately linear with the logarithm of the strain rate under different strain rates. Both before and after fatigue loading, the stiffness in the loading and unloading curves of the intervertebral disc is inconsistent, forming a hysteresis loop, which is caused by the viscoelastic effect. The strain rate has no significant effect on the internal displacement distribution of the intervertebral disc. Based on the experimental data, the constitutive relationship of the intervertebral disc at different strain rates is obtained. The fitting curves are well coupled with the experimental data, while the fitting parameters are approximately linear with the logarithm of the strain rate. Conclusions: These experiments indicate that the strain rate has a significant effect on the mechanical behavior of the intervertebral disc rupture and fatigue injury, while the constitutive equation can predict the rate-dependent mechanical behavior of lumbar intervertebral disc under flexion very well. These results have important theoretical guiding significance for preventing lumbar disc herniation in daily life.

Abstract. Recently, personalized services finding in Smart City or Digit City is a hotspot in research area. City and urban areas contain plenty of services but some of them are difficult to extract and retrieval to people. Furthermore, with the development of the Semantic Web, more and more datasets are represented as RDF format and become part of the Linked Data, which provides a fundamentally new venue for personalized urban services retrieval in smart city applications. In this paper, we propose a personalized urban services retrieval framework which is performed by using ontology and comparing RDF-based user profiles with dataset in relation to civic services on web of data. To extract hidden information, the domain specific ontology is involved for linking entities on the web of data. The cases we envisage will show that the proposed framework can effectively return services resources with respect to the user's interests.

In the classical WPT technology, when the load coil and the receiving coil are not aligned, the receiving power will be significantly reduced. In this paper, a new type of receiving coil named spiral add planar (SAP) coil is proposed, which can make the receiving power of the load coil almost independent of its position. The T-type equivalent circuit analysis method is used to analyze the transmission performance of the WPT system. By calculating the mutual inductance between non-coaxial coils, it can be proved theoretically that when the load coils are located at different positions, the mutual inductance between the SAP coil and the load coil is more stable comparing to the spiral coil or the planar coil. In addition, this SAP coil can support multiple loads and arbitrary movement of the load within the area of the SAP coil. This paper also proposed the concept of radius ratio (that is, the ratio of the radius of the load coil to the radius of the RX coil), and found that when the radius ratio is less than 1/2, the free-positioning characteristic is good. The simulation and experimental results show that when the load coil moves within the range of the SAP coil, the volatility of its S21 value is less than ± 1 dB.