Embroidered Textile Frequency-Splitting Sensor Based on Stepped-Impedance Resonators

Abstract

This paper presents an embroidered textile frequency-splitting microwave sensor based on a pair of identical stepped-impedance resonators (SIRs) loading a microstrip transmission line. The sensor is implemented by means of conductive threads. The sensing region of the proposed structure is the capacitive square patch of one of the SIRs. If such region is kept unaltered, the structure is symmetric, and the frequency response (transmission coefficient) exhibits a single transmission zero. However, if symmetry is broken (e.g., through liquid absorption in the sensing region), the frequency response of the proposed sensor exhibits two transmission zeros (frequency splitting). The difference (in frequency and magnitude) between such zeros (or notches) is intimately related to the dielectric properties of the absorbed liquids to be sensed/detected. The proposed sensing structure is applied to the detection of deionized (DI) water absorption, and to the quantification of the number of DI water drops. The maximum measured sensitivity is found to be 2.70 MHz/µl and 0.03 dB/µl for the incremental frequency and incremental magnitude of the notches.

Microwave Humidity Sensor for Early Detection of Sweat and Urine Leakage

“…Planar microwave sensors can be categorized according to the output variable as frequency-variation sensors [7][8][9][26][27][28][29][30][31][32][33][34][35], frequency-splitting sensors [4,22,[36][37][38][39], magnitude variation sensors (or coupling modulation sensors [40][41][42][43][44][45][46][47][48][49][50][51]), and phase-variation sensors [52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69]. Nevertheless, in some cases, two combined output variables are used.…”

“…Planar microwave sensors can be fabricated by means of either subtractive (e.g., photoetching or milling) or additive (e.g., inkjet-printing, screen-printing, or 3D-printing) processes. Moreover, planar microwave sensors are compatible with many other technologies such as microfluidics, micromachining, textiles, etc., and can be equipped with functional films, that make these sensors of interest in applications as diverse as liquid sensing [3][4][5][6][7], bio-sensing [8,9], gas sensing [10][11][12][13][14][15][16], wearables [17,22], measurement of physical variables (such as temperature or ambient humidity [23][24][25]), etc. Nevertheless, the most canonical application of planar microwave sensors is the dielectric characterization of materials (permittivity measurements [7], [26][27][28]).…”

Ambient health sensing on passive surfaces using metamaterials

“…However, these sensors are contact-based and therefore have limited use in ambient sensing applications. While conductive textiles have been used to build radio-frequency devices such as antennas ( 24 , 25 ), waveguides ( 26 , 27 ), couplers ( 28 ), and resonators ( 29 ), these designs do not have capabilities in contactless health sensing.…”

Balanced Microwave Transmission Lines, Circuits, and Sensors

“…This opens the possibility of implementing conformal sensors, as well as environmentally friendly (green) sensors. Additionally, planar sensors are compatible with other technologies of interest for sensing, such as microfluidics (for liquid sensing) [12], textiles (for wearables) [13], micromachining, etc., and the associated electronics needed for signal generation, post-processing, and, eventually, communication purposes, can be integrated within the sensor substrate (thereby representing a cost reduction).…”