Search

A scaling law is demonstrated in the conductivity of gated two-dimensional (2D) materials with tunable concentrations of ionized impurity scatterers. Experimental data is shown to collapse onto a single 2D conductivity scaling (2DCS) curve when the mobility is scaled by r, the relative impurity-induced scattering, and the gate voltage is shifted by V s , a consequence of impurity-induced doping. This 2DCS analysis is demonstrated first in an encapsulated 2D black phosphorus multilayer at T = 100 K with charge trap densities programmed by a gate bias upon cooldown, and next in a Bi2Se3 2D monolayer at room temperature exposed to varying concentrations of gas adsorbates. The observed scaling can be explained using a conductivity model with screened ionized impurity scatterers. The slope of the r vs. V s plot defines a disorder-charge specific scattering rate Γ q = d r / d V s equivalent to a scattering strength per unit impurity charge density: Γ q > 0 indicates a preponderance of positively charged impurities with Γ q < 0 for negatively charged. This 2DCS analysis is expected to be applicable in arbitrary 2D materials systems with tunable impurity density, which will advance 2D materials characterization and improve performance of 2D sensors and transistors.

In this paper, the FEM simulation package FLUX2D is utilized as a tool to design a proportional solenoid for the hydraulic proportional suspension damper. The hydraulic proportional suspension damper can be used in vehicle semi-active suspension system due to its adjustable output damping force. In addition, the proportional solenoid plays the most significant role to achieve such a variable output damping force. From previous literatures, three different structures of proportional solenoid will be discussed in this paper. The first one utilizes the stepped conical armature design. Its advantages include low cost, easy manufacturing. However, the limited available linear stroke as well as the poor linearity are its major faults. The second structure uses a special tube consisting of three metal rings that are welded together. Between two magnetic steel rings, there is a non-magnetic copper ring serving to guide the magnetic flux and to produce a linear force/stroke relation. Clearly, higher cost and complex manufacturing process are its major disadvantages. However, larger available linear stroke and good linearity are two promising advantages. In this paper, the third design of proportional solenoid is adopted. The construction of the proportional solenoid is divided into several parts. After assembling these parts together, a ring of air gap with a well-designed geometrical shape exists which can be used to replace the non-magnetic copper ring. Without the copper ring, the expensive and complex welding process can be omitted. Meanwhile, the large available linear stroke as well as good linearity are both preserved. Finally, an experimental test device for measuring the force/stroke relation of proportional solenoid is implemented in this study. It is observed that the simulation results agree quite well with the experimental results.