Differential transmission lines with surface plasmon polaritons at low frequencies

Abstract

A new kind of differential microstrip lines by introducing periodic subwavelength corrugation in the edge, which is able to support low-frequency spoof surface plasmon polaritions, is proposed. The surface current distribution of the subwavelength periodic corrugated microstrip is numerically analysed. A kind of differential to singleended microstrip coupling circuit is designed to investigate the ability of suppressing the crosstalk of such a subwavelength periodic corrugated differential pair. Experimental results show that such a structure can be utilised to effectively suppress crosstalk, and to reduce the transformation between differential-mode and commonmode signals.Introduction: Decreasing device size and increasing distribution density are two main methods to cut the cost of circuit manufacture. Recently, the rate of the signal transmission has been increasing rapidly, and the wiring layout has been more dense. As a result, the interference between adjacent routes is much more serious, and the interaction between the electromagnetic (EM) signal and the subwavelength scale structure has become an important subject.Surface plasmon polaritons (SPPs) are EM excitations propagating along a metal-dielectric interface. Since the EM fields can be strongly confined to the near vicinity of the interface [1], it attracts intensive interest in various areas [2]. Owing to its property of high confinement of the modal field, the SPPs structure has become the prior method of the highly integrated optical circuit and the subwavelength optical device.At low frequencies, however, metals behave no longer like a plasma but resemble a perfect electric conductor (PEC), as their plasma frequencies are often in the ultraviolet part of the EM spectrum, and as a result, SPPs are highly delocalised on metal surfaces. To engineer a surface plasmon at lower frequency, Pendry [3] suggested a scheme in which the penetration of the fields into the metal can be increased by cutting holes or grooves on a scale much smaller than the wavelength of probing radiation in metal surfaces, and the frequency of existing surface plasmons, which is called spoof SPPs, can be tailored at will. Such spoof SPPs possess an effective plasma frequency only determined by its geometric dimension [4,5] and provides a new way to transmit tetrahertz and microwave signals effectively. A differential pair is widely used in the integrated circuit to transmit two complementary signals, and consequently such a differential pair has much smaller crosstalk compared with traditional microstrips. However, because of the high density of routes distribution, the crosstalk between adjacent routes becomes more serious. In this Letter, we utilise the concept of low frequency spoof SPPs in the designing of differential microstrip lines by introducing periodic subwavelength corrugations at the edge of the differential microstrip, and study its transmission properties and the efficiency of crosstalk suppression both theoretically and experimentally.

Spatial k-dispersion engineering of spoof surface plasmon polaritons for customized absorption

“…At microwave frequencies, the corrugated metal strips with near-zero thickness have been demonstrated to support spoof SPPs 36 37 38 39 40 41 . Here we employed such strips to construct the desired plasmonic structures.…”

“…The SPPs naturally exist at optical frequencies, but suitably structured metamaterials have been developed to excite the spoof SPPs at low frequencies 33 34 35 . In particular, recent study on the corrugated plasmonic strips with nearly zero thickness 36 37 38 39 40 41 is promising for the required structures in this work. We took such derivative structures as an effective validation for the concept of spatial k -dispersion engineering for achieving the customized absorption over a broad frequency band, and also implemented experimental demonstrations.…”

Differential surface plasmon polaritons transmission line with controllable common mode rejection

“…In the past few years, differential topology is widely adopted in constructing microwave/millimeter-wave circuits due to inherent superior signal-to-noise ratio and high immunity to environmental noise and electromagnetic interference 16 – 19 . Most of differential circuits have been constructed with conventional planar transmission lines (T-lines) such as microstrip and coplanar waveguide (CPW) and only few is concerned with plasmonic T-lines 20 . Recent results show the advantage of crosstalk suppression of SPP T-lines facilitates the improvement of signal integrity in circuits on PCB and chip level 20 , 21 .…”

“…Most of differential circuits have been constructed with conventional planar transmission lines (T-lines) such as microstrip and coplanar waveguide (CPW) and only few is concerned with plasmonic T-lines 20 . Recent results show the advantage of crosstalk suppression of SPP T-lines facilitates the improvement of signal integrity in circuits on PCB and chip level 20 , 21 . However, to the author’s best knowledge, the common mode suppression has not been mentioned so far.…”

Surface plasmon wave application in microwave modulator induced by switchable metamaterial

“…They are termed as spoof SPPs (SSPPs) . Among them, ultrathin corrugated metallic strip structure is very attractive and reported recently . The approach to achieve conversion from guided wave to SSPPs and its wave manipulation has been well studied.…”