Considerations on the Equivalent Electric Models of a UHF RFID Helical Antenna Yarn

Abstract

The aim of this paper is to present different ways to extract electrical models of an antenna specifically designed for Radio Frequency IDentification (RFID) Ultra High Frequency (UHF) communications. More precisely the models are extracted from a helical dipole designed to operate in the European RFID band and in the context of smart textiles. This kind of antenna was chosen because its electrical properties and radiation pattern are relatively robust with respect of stretching deformation. After presenting the antenna's design, two strategies to extract antenna models are discussed and then compared. The first method is taking into account the antenna's physical dimensions and shape, and the second one, which is a general method relevant to any other antenna geometry, is based on the rational approximation of the antenna's frequency response.

The influence of structure uniformity on resonant frequency of ultra-high frequency radio frequency identification tag thread With normal mode helix dipole antenna

“…That is say, the method of simplifying the tag antenna geometry structure as NMHDA in this work is feasible. Additionally, according to Benouakta's work, 5,15 the resonant frequency decrease with an increase of relative permittivity of carrying yarn. Therefore, the simulated resonant frequency is little more than the measured one.…”

“…However, compared with the influence of structural parameters on the resonant frequency, the dielectric properties of the carrying yarn have a negligible influence on the resonant frequency in previous work. 5,9,14,15 Thus, the carrying yarn was not considered to simplify the model of UHF RFID tag thread with NMHDA and reduce computing cost in this work. And then, the tag antenna was simplified as NMHDA.…”

Physical relationship between resonant frequency and structure parameters of a normal mode helix dipole antenna for an ultra-high frequency radio frequency identification tag thread

“…When the value of the helical pitch and the single arm length of the NHMDA are determined, Equation (12) only includes three unknown variables, that is, the helical radius r, resonant frequency f, and reactance parameter Z(S). According to the above discussion in the Validation section, the measured results fit well with Equation ( 12), and only a pair of values for the helical radius and resonant frequency of the NMHDA, that is, {r i , f i }, is needed to determine parameter Z(S) in Equation (12). According to Table 2, Equation ( 12) has the worst accuracy in the case of the NMHDA with a helical pitch of 1.0 mm and a single arm length of 43.0 mm.…”

“…Previous works ignored the distributed capacitance caused by the geometry simplification (helix to straight line), which led to reactance deviation of over 50 Ω or even 100 Ω 6,12 before and after the model simplification. The impedance of the common chip (Alien Higgs-4) is 27.38 – j 200.76 Ω at 915 MHz.…”

“…For a NMHDA with constant single arm length, the distributed capacitance is mainly related to the conductor radius and the helical pitch. 13 This work is derived in the case of a constant conductor radius, and according to previous equivalent circuit and simulation results, 12 the reactance deviation caused by distributed capacitance is nearly constant in the UHF range. Therefore, the reactance parameter Z ( S ) is introduced to modify the impedance from the lumped inductor, and then the lumped inductor, Z m-lump ( r , S , f , l , Z ), is rewritten as …”