In this work, a compact design of an electrically tunable notch filter, based on liquid crystal (LC) technology, has been designed, manufactured, and characterized. The proposal has been achieved through particular configuration schemes with low cost inverted-microstrip structures and conventional spurlines structures due to its ease of integration. Central frequency tunability has been induced by applying low ac voltages, thus involving low power consumption. For these devices, filter responses have been approached specifically at microwave C-band frequency allocated for many satellite communications applications. Also, it has taken advantage of new highly anisotropic nematic LC mixtures at those frequency ranges. Recently, liquid crystal (LC) technology has begun to be used in nonoptical applications due to its promising features in further electronic applications ranging from kilohertz to megahertz frequencies. Intrinsic anisotropy of some LC properties, which implies different properties depending of the direction in which they are measured, allows new advanced devices to be designed with tunable features, by using these materials.The use of LC to design tunable devices at microwave frequency bands is not a new conception; nevertheless there has been an increasing interest in improving their performance, particularly in the last decade. Liquid crystals were recognized as candidates for microwave dielectric substrates in the early 1990s. 1 Although first approaches to LC devices in waveguides led to bulky and large consumption designs (due to strong magnetic fields for switching LC molecules), most of the recent prototypes, such as tunable phase shifters, 2, 3 capacitors, 4 filters, 5,6 or antennas, 7 have reported practical functions involving electric fields for orienting LC at those frequencies.Filters are very valuable devices because they represent a powerful tool for frequency response processing. They are designed in order to select or to remove bands of frequency. A band-rejection filter or band-stop filter is a filter that attenuates a frequency band, while the other frequencies remain unchanged. A notch filter is a band-rejection filter with a narrow stopband, with a high quality factor, that is mainly used to remove spurious frequencies and to filter noise signals.In this work, the design of a notch filter for about 5 GHz rejection frequency (f 0 ), based on the electric field switching of a LC, has been proposed and its feasibility has been demonstrated. Filters working at this frequency, allocated in the C-band, are intended to be used in satellite telecommunication systems or, for example, to avoid the interference a) Author to whom correspondence should be addressed. Electronic mail:vurruchi@ing.uc3m.es.between the UWB (Ultra Wide-Band) and WLAN (Wireless Local Area Networks) systems. 8 UWB systems are particularly promising for short-range high-throughput wireless communications. Multiple solutions have been proposed for providing tunability in microwave devices, such as varactors based on sem...

ABSTRACT:In this article, the design, fabrication, and characteriza-tion of a tunable microwave notch filter based on liquid crystal (LC) using inverted-microstrip technology is presented. A spiral spurline structure is used because of its good performance as a single-resonator notch filter. Based on the LC dielectric anisotropy, a voltage-controlled rejection frequency of the filter is achieved, ranging from 3.40 to 3.75 GHz, which means that the tuning range relative to the central rejection frequency is about 10%. At the same time, this device exhibits negative group delay around the rejection frequency and the measured values throughout the tuning frequency range are presented.

In this paper, the design and experimental characterization of a tunable microstrip bandpass filter based on liquid crystal technology are presented. A reshaped microstrip dual-mode filter structure has been used in order to improve the device performance. Specifically, the aim is to increase the pass-band return loss of the filter by narrowing the filter bandwidth. Simulations confirm the improvement of using this new structure, achieving a pass-band return loss increase of 1.5 dB at least. Because of the anisotropic properties of LC molecules, a filter central frequency shift from 4.688 GHz to 5.045 GHz, which means a relative tuning range of 7.3%, is measured when an external AC voltage from 0 Vrms to 15 Vrms is applied to the device.

Introducción: El tratamiento del valgo severo es complejo. El abordaje externo descrito por Keblish es ventajoso para tratar estas deformidades. Evaluamos nuestros resultados utilizando un abordaje externo en artroplastias de rodilla con genu valgo severo. Materiales y Métodos: De 795 artroplastias primarias realizadas entre enero de 2012 y marzo de 2020, analizamos 40 que tenían un abordaje externo. Todos los pacientes tenían una deformidad en valgo >20° y un ligamento colateral medial suficiente. Se incluyó a 33 mujeres (3 bilaterales) y 4 hombres, el promedio de edad era de 71 años. La causa fue fundamentalmente osteoartrosis (82%). La deformidad prequirúrgica era de 27°. Las mediciones preoperatorias eran: KSS 15 (rango 5-42) y KFS 17 (rango 0-40). El tiempo promedio de cirugía fue de 91 minutos y el seguimiento, de 37 meses. Resultados: El ángulo femorotibial posoperatorio fue de 6,2° (rango 4-40), el KSS posoperatorio fue de 79 (rango 46-95) y el KFS, de 82 (rango 60-100). Hubo tres complicaciones (7%): una infección, un mal posicionamiento de componentes y uno de neuropraxia peronea. Conclusiones: En la artroplastia de rodilla por genu valgo, este abordaje permite restituir el eje femorotibial, lograr una adecuada estabilidad de la prótesis, aun con implantes sin mayor grado de constreñimiento, con una tasa de complicaciones equiparable a la de otras técnicas.

Over the last twenty years, there has been a growing interest in the design of tunable devices at microwave frequencies by us- ing liquid crystals technology. In particular, the use of liquid crystals with high dielectric anisotropy allows manufacturing voltage-controlled devices to operate in a wide frequency range. In this work the frequency response of a liquid crystal band-pass filter with dual-mode microstrip structure has been studied in depth by using a simulation software tool. A reshap- ing of a conventional dual-mode square patch resonator bandpass filter with a square notch, studied in the literature, has been proposed with the goal of improving the filter performance. The main features achieved are a significant increase in the return loss of the filter and a narrowing of a 3-dB bandwidth. Specifically, a reduction in the filter bandwidth from 800 MHz to 600 MHz, which leads to a return loss increase from 6 dB to 12.5 dB, has been achieved. The filter centre frequency can be tuned from 4.54 GHz to 5.19 GHz.