Development of a planar multi-body model of the human knee joint

The aim of this work is to develop a dynamic model for the biological human knee joint. The model is formulated in the framework of multibody systems methodologies, as a system of two bodies, the femur and the tibia. For the purpose of describing the formulation, the relative motion of the tibia with respect to the femur is considered. Due to their higher stiffness compared to that of the articular cartilages, the femur and tibia are considered as rigid bodies. The femur and tibia cartilages are considered to be deformable structures with specific material characteristics. The rotation and gliding motions of the tibia relative to the femur can not be modeled with any conventional kinematic joint, but rather in terms of the action of the knee ligaments and potential contact between the bones. Based on medical imaging techniques, the femur and tibia profiles in the sagittal plane are extracted and used to define the interface geometric conditions for contact. When a contact is detected, a continuous non-linear contact force law is applied which calculates the contact forces developed at the interface as a function of the relative indentation between the two bodies. The four basic cruciate and collateral ligaments present in the knee are also taken into account in the proposed knee joint model, which are modeled as non-linear elastic springs. The forces produced in the ligaments, together with the contact forces, are introduced into the system’s equations of motion as external forces. In addition, an external force is applied on the center of mass of the tibia, in order to actuate the system mimicking a normal gait motion. Finally, numerical results obtained from computational simulations are used to address the assumptions and procedures adopted in this study.Fundação para a Ciência e a Tecnologia (FCT

Higher-order virtual ground fence design for filtering power plane noise

The virtual ground fence (VGF) has been recently proposed to filter power plane noise in GHz frequency range. The VGF has distinct advantages over existing approaches, such as power islands and electromagnetic bandgap structures: the IR drop is not increased; transmission-line return-path discontinuities can be avoided; and the design procedure is simple. The basic VGF is created by using quarter-wave resonators referenced to the power or the ground plane. At the design frequency, the resonator creates an ac short circuit between the power and ground planes. An array of such resonators then can be placed in electrically short intervals to create a virtual ground fence. Power plane noise will then ideally be shorted to ground at the location of the VGF. The operation principle is then similar to the series resonance of a decoupling capacitor, which is usually ineffective in the GHz frequency range

Non-overlapping power/ground planes for localized power distribution network design

Power/ground planes are used for low IR-drop and inductance, but they also cause switching noise coupling globally across chip packages and printed circuit boards. The switching noise coupling is a concern for mixed-signal boards, high-speed I/Os, and electromagnetic compatibility. In GHz frequency regime, switching noise cannot be controlled by off-chip discrete decoupling capacitors due to their inductance. In this paper we introduce the non-overlapping power/ground planes design methodology for filtering of GHz power plane noise. Unlike existing approaches, our approach is simple, has wide bandwidth, and does not increase IR-drop or inductance

Determination of dielectric thickness, constant, and loss tangent from cavity resonators

For high-speed digital and high-frequency analog applications, accurate determination of material properties are critical. Technological tolerances on printed circuit boards and packages result in variations of the dielectric thickness, constant, and loss tangent. These properties may also change depending on the process and location on the panel. Hence a methodology is needed where these properties can be measured using test coupons on a panel. Previous research focuses on the determination of dielectric constant and loss tangent using coupons in the form of resonators or transmission lines. However, dielectric thickness also shows significant variation from vendor-supplied values. In this paper, we present a new method that allows to extract the dielectric thickness from resonator measurements as well, hence providing a unique capability for non-destructive monitoring of geometrical as well as electrical properties of printed circuit boards and packages

Mixed-Port Scattering and Hybrid Parameters for High-Speed Differential Lines

High-speed transmission lines are commonly routed as differential lines to control sensitivity to noise on the reference planes at higher speeds. Differential lines are typically characterized in terms of mixed-mode scattering parameters, as they provide insight into the behavior of differential and common signals, as well as the mode conversion among them. These mixed-mode scattering parameters can be mathematically obtained from single-ended parameters, which can, for example, be measured with a four-port vector network analyzer. There has been recent efforts to develop extended or modified versions of mixed-mode scattering parameters, especially for tightly-coupled lines. This can be a point of confusion in interpreting the behavior of differential lines. In this paper, we introduce the mixed-port scattering and hybrid parameters, which do not suffer from any such ambiguous definitions. Mixed-port hybrid parameters are the most natural way to represent any four-port differential circuit, as they are based on intuitive differential and common-port excitations of the network. They also enable extraction of the current division factor experimentally, which is a critical parameter for electromagnetic interference analysis of differential lines. Mixed-port scattering parameters are also defined based on common and differential port excitations, allowing a simpler interpretation than their mixed-mode counterparts, without the need for defining even, odd, common, or differential-mode impedances. As such, mixed-port scattering and hybrid parameters can be used to analyze the performance of a general differential network, certainly including coupled or asymmetrical lines, without any ambiguity

Stress analysis and fixation problems in joint replacement

The aims and scopes of stress analyses, and the three most commonly applied methods (i.e. experimental strain-gauge techniques, analytical `closed-form' solutions, and finite element methods) are discussed with particular reference to total hip replacemen

Closed-form network representations of frequency-dependent RLGC parameters

In this paper, equivalent circuit representations for frequency-dependent RLGC (resistance, inductance, conductance and capacitance) parameters of interconnects are presented. Several novel approaches are proposed and compared with each other to model the frequency-dependent behaviour of interconnects due to substrate and conductor losses. The network representations are obtained by network synthesis of suitable non-rational immittances based on analytical methods. Due to the closed-form description of the circuit elements, which consist of positive-valued resistors, inductors, and capacitors, the proposed models can be conveniently implemented in generic circuit simulators

Nonoverlapping Power/Ground Planes for Suppression of Power Plane Noise

Providing low IR-drop and inductance are two major roles of power and ground (PG) planes in chip packages and boards. However, planes can also cause switching noise coupling, especially when they resonate. This is a concern for mixed-signal boards, high-speed I/Os, and electromagnetic compatibility. Discrete decoupling capacitors are ineffective to control switching noise at gigahertz frequency regime due to their inductance. To filter such high-frequency noise, a possible approach is modifying the shape of the PG planes, such as in power islands or electromagnetic bandgap structures. In this paper, we introduce the nonoverlapping PG planes design methodology for filtering of gigahertz power plane noise. Unlike existing approaches, our approach is simple and has wide bandwidth, while avoiding narrow inductive bridges that increase IR-drop