Knitted ECG electrodes in relaxed fitting garments

A wide range of signal quality indices (SQIs) related to statistical methods, are used to guide the optimisation process of knitted textile electrodes for ECG recordings. The electrode structure and composition as well as their integration into a garment are evaluated in view of a fully knitted garment. The dry electrodes with the best SQIs are obtained by using conductive yarn only with a compact knit structure and a medium level of roughness. The best SQIs for the e-garment were obtained by sewing electrodes at their edges only, into the knitted garment. This implementation outperforms the intarsia and double-knit method as it allows the garment some independent movement from the electrodes, reducing motion artifacts. Tests done on a healthy volunteer demonstrate excellent system performance under gentle ambulation. The advantage of using SQIs in the optimisation process of dry textile ECG electrodes is that they offer a quantitative benchmark against which to compare other approaches. The fully knitted clothing allows for more relaxed e-garments when gentle ambulation is considered

Room-Temperature Terahertz Detection and Imaging by Using Strained-Silicon MODFETs

This chapter reports on an experimental and theoretical study of Schottky-gated strained-Si modulation-doped field-effect transistors (MODFETs) with different sub-micron gate lengths (100, 250, and 500 nm). Room-temperature detection of terahertz (THz) radiation by the strained-Si MODFETs was performed at two frequencies (0.15 and 0.3 THz). A technology computer-aided design (TCAD) analysis based on a two-dimensional hydrodynamic model (HDM) was used to investigate the transistor response to THz radiation excitation. TCAD simulation was validated through comparison with DC and low-frequency AC measurements. It was found that the photoresponse of the transistors can be improved by applying a constant drain-to-source bias. This enhancement was observed both theoretically and experimentally. The HDM model satisfactorily describes the experimental dependence of the photoresponse on the excitation frequency, the gate bias, and the drain-to-source current bias. The coupling of the incoming THz radiation to the MODFETs was studied at 0.15 and 0.3 THz. Finally, to demonstrate the suitability of strained-Si MODFET for terahertz applications, an image sensor within a pixel-by-pixel terahertz imaging system for the inspection of hidden objects was used

Effect of the Front and Back Illumination on Sub-Terahertz Detection Using n-Channel Strained-Silicon MODFETs

[EN] Plasma waves in semiconductor gated 2-D systems can be used to efficiently detect Terahertz (THz) electromagnetic radiation. This work reports on the response of a strained-Si Modulation-doped Field-Effect Transistor (MODFET) under front and back sub-THz illumination. The response of the MODFET has been characterized using a two-tones solid-state continuous wave source at 0.15 and 0.30 THz. The DC drain-to-source voltage of 500-nm gate length transistors transducing the sub-THz radiation (photovoltaic mode) exhibited a non-resonant response in agreement with literature results. Two configurations of the illumination were investigated: (i) front side illumination in which the transistor was shined on its top side, and (ii) back illumination side where the device received the sub-THz radiation on its bottom side, i.e., on the Si substrate. Under excitation at 0.15 THz clear evidence of the coupling of terahertz radiation by the bonding wires was found, this coupling leads to a stronger response under front illumination than under back illumination. When the radiation is shifted to 0.3 THz, as a result of a lesser efficient coupling of the EM radiation through the bonding wires, the response under front illumination was considerably weakened while it was strengthened under back illumination. Electromagnetic simulations explained this behavior as the magnitude of the induced electric field in the channel of the MODFET was considerably stronger under back illumination.This research was funded by the Ministerio de Ciencia, Investigacion y Universidades of Spain andFEDER (ERDF: European Regional Development Fund) under the Research Grants numbers RTI2018-097180-B-100 and TEC2016-78028-C3-3-P and FEDER/Junta de Castilla y Leon Research Grant number SA256P18. Also by Conselleria d'Educacio, lnvestigacio, Cultura i Esport, Generalitat Valenciana (Spain) through the grant AIC0/2019/018. The APC received no external funding.Delgado-Notario, JA.; Calvo-Gallego, J.; Velázquez-Pérez, JE.; Ferrando Bataller, M.; Fobelets, K.; Meziani, YM. (2020). Effect of the Front and Back Illumination on Sub-Terahertz Detection Using n-Channel Strained-Silicon MODFETs. Applied Sciences. 10(17):1-9. https://doi.org/10.3390/app10175959S191017Lewis, R. A. (2019). A review of terahertz detectors. Journal of Physics D: Applied Physics, 52(43), 433001. doi:10.1088/1361-6463/ab31d5Dragoman, D., & Dragoman, M. (2004). Terahertz fields and applications. Progress in Quantum Electronics, 28(1), 1-66. doi:10.1016/s0079-6727(03)00058-2Mittleman, D. M. (2017). Perspective: Terahertz science and technology. Journal of Applied Physics, 122(23), 230901. doi:10.1063/1.5007683Pawar, A. Y., Sonawane, D. D., Erande, K. B., & Derle, D. V. (2013). Terahertz technology and its applications. Drug Invention Today, 5(2), 157-163. doi:10.1016/j.dit.2013.03.009Federici, J., & Moeller, L. (2010). Review of terahertz and subterahertz wireless communications. Journal of Applied Physics, 107(11), 111101. doi:10.1063/1.3386413Federici, J. F., Schulkin, B., Huang, F., Gary, D., Barat, R., Oliveira, F., & Zimdars, D. (2005). THz imaging and sensing for security applications—explosives, weapons and drugs. Semiconductor Science and Technology, 20(7), S266-S280. doi:10.1088/0268-1242/20/7/018Dyakonov, M., & Shur, M. (1993). Shallow water analogy for a ballistic field effect transistor: New mechanism of plasma wave generation by dc current. Physical Review Letters, 71(15), 2465-2468. doi:10.1103/physrevlett.71.2465Dyakonov, M., & Shur, M. (1996). Detection, mixing, and frequency multiplication of terahertz radiation by two-dimensional electronic fluid. IEEE Transactions on Electron Devices, 43(3), 380-387. doi:10.1109/16.485650Tauk, R., Teppe, F., Boubanga, S., Coquillat, D., Knap, W., Meziani, Y. M., … Shur, M. S. (2006). Plasma wave detection of terahertz radiation by silicon field effects transistors: Responsivity and noise equivalent power. Applied Physics Letters, 89(25), 253511. doi:10.1063/1.2410215Rumyantsev, S. L., Fobelets, K., Veksler, D., Hackbarth, T., & Shur, M. S. (2008). Strained-Si modulation doped field effect transistors as detectors of terahertz and sub-terahertz radiation. Semiconductor Science and Technology, 23(10), 105001. doi:10.1088/0268-1242/23/10/105001Javadi, E., Delgado-Notario, J. A., Masoumi, N., Shahabadi, M., Velázquez-Pérez, J. E., & Meziani, Y. M. (2018). Continuous Wave Terahertz Sensing Using GaN HEMTs. physica status solidi (a), 215(11), 1700607. doi:10.1002/pssa.201700607Delgado-Notario, J. A., Clericò, V., Diez, E., Velázquez-Pérez, J. E., Taniguchi, T., Watanabe, K., … Meziani, Y. M. (2020). Asymmetric dual-grating gates graphene FET for detection of terahertz radiations. APL Photonics, 5(6), 066102. doi:10.1063/5.0007249Lewis, R. A. (2014). A review of terahertz sources. Journal of Physics D: Applied Physics, 47(37), 374001. doi:10.1088/0022-3727/47/37/374001Delgado-Notario, J., Velazquez-Perez, J., Meziani, Y., & Fobelets, K. (2018). Sub-THz Imaging Using Non-Resonant HEMT Detectors. Sensors, 18(2), 543. doi:10.3390/s18020543Gaspari, V., Fobelets, K., Velazquez-Perez, J. E., Ferguson, R., Michelakis, K., Despotopoulos, S., & Papavassilliou, C. (2004). Effect of temperature on the transfer characteristic of a 0.5 μm-gate Si:SiGe depletion-mode n-MODFET. Applied Surface Science, 224(1-4), 390-393. doi:10.1016/j.apsusc.2003.08.066Fobelets, K., Jeamsaksiri, W., Papavasilliou, C., Vilches, T., Gaspari, V., Velazquez-Perez, J. E., … König, U. (2004). Comparison of sub-micron Si:SiGe heterojunction nFETs to Si nMOSFET in present-day technologies. Solid-State Electronics, 48(8), 1401-1406. doi:10.1016/j.sse.2004.01.017Delgado Notario, J. A., Javadi, E., Calvo-Gallego, J., Diez, E., Velázquez, J. E., Meziani, Y. M., & Fobelets, K. (2016). Sub-Micron Gate Length Field Effect Transistors as Broad Band Detectors of Terahertz Radiation. International Journal of High Speed Electronics and Systems, 25(03n04), 1640020. doi:10.1142/s0129156416400206Sakowicz, M., Łusakowski, J., Karpierz, K., Grynberg, M., Gwarek, W., Boubanga, S., … Studart, N. (2010). A High Mobility Field-Effect Transistor as an Antenna for sub-THz Radiation. doi:10.1063/1.3295528Knap, W., Teppe, F., Meziani, Y., Dyakonova, N., Lusakowski, J., Boeuf, F., … Shur, M. S. (2004). Plasma wave detection of sub-terahertz and terahertz radiation by silicon field-effect transistors. Applied Physics Letters, 85(4), 675-677. doi:10.1063/1.177503

Responsivity enhancement of a strained silicon field-effect transistor detector at 0.3 THz using the terajet effect

[EN] We report on the enhancement of responsivity by more than one order of magnitude of a silicon-based sub-terahertz detector when a mesoscopic dielectric particle was used to localize incident radiation to a sub-wavelength volume and focus it directly onto the detector. A strained-silicon modulation field-effect transistor was used as a direct detector on an incident terahertz beam at 0.3 THz. A systematic study in which Teflon cubes were placed in front of the detector to focus the terahertz beam was performed. In this study, cubes with different sizes were investigated, and an enhancement of the responsivity up to 11 dB was observed for a cube with an edge length of 3.45 mm (or 3.45 lambda). Electromagnetic simulation results were in good agreement with the experimental ones and demonstrated that the size of the mesoscopic particle plays an important role in focalizing the electric field within an area below the diffraction limit. This approach provides an efficient, uncostly, and easy to implement method to substantially improve the responsivity and noise equivalent power of sub-terahertz detectors.Tomsk Polytechnic University Development Program; Ministerio de Ciencia, Innovacion y Universidades (PID2019-107885GB-C32, RTI2018-097180-B-100, TEC2016-78028-C3-3-P); Junta de Castilla y Leon (SA121P20, SA256P18); Conselleria d'Educacio, Investigacio, Cultura i Esport (AIC0/2019/018); European Regional Development Fund; Fundacja na rzeczNauki Polskiej (CENTERA-IRA MAB/2018/9)Minin, IV.; Minin, OV.; Salvador-Sánchez, J.; Delgado-Notario, JA.; Calvo-Gallego, J.; Ferrando Bataller, M.; Fobelets, K.... (2021). Responsivity enhancement of a strained silicon field-effect transistor detector at 0.3 THz using the terajet effect. Optics Letters. 46(13):3061-3064. https://doi.org/10.1364/OL.43117530613064461

Analogue micropower FET techniques review

Accepted versio

Ambulatory Monitoring Using Knitted 3D Helical Coils

We present a highly sensitive wearable angular position sensor to measure joint movement. The sensor is a 3D helical coil knitted in the sleeve of a garment by circularly knitting thin insulated metal wire and yarn simultaneously. The sensing mechanism is based on the variation of the mutual inductance between windings. A 167 μH change is measured for knee movement from fully stretched to completely bent. A double cross coupled FET pair transforms the low-Q coils into a high-Q system giving a maximum frequency variation of 145 kHz for knee bending

Respiratory Inductive Plethysmography System for Knitted Helical Coils

Three-dimensional knitted helical coils are very sensitive inductive sensors that can be used to monitor breathing. Their inductance is high and the quality factor relatively low. A read-out circuit is designed and tested to track the inductance variations during circumference changes of a phantom chest. The challenge of the low-quality factors of the coil is resolved by designing a double cross-coupled FET pair with low capacitance. A digital counter records the frequency. A microprocessor samples the signal every 250 ms to minimize power consumption

Simultaneous Breathing and ECG Measurements with e-Knits

Simultaneous recording of breathing and heart rate signals was carried out on a healthy volunteer with a fully knitted, non-sports-type garment. Breathing was recorded using two knitted respiratory inductive plethysmography (RIP) sensors. Electrocardiogram (ECG) recordings were obtained from three knitted electrodes. The knitted garment design was customised for the specific requirements of RIP and ECG by adapting the needle size and/or introducing knit-in-elastic in the sensor areas. RIP was read out using an in-house-developed cross-coupled complementary oscillator circuit. The ECG was recorded using the commercial OpenBCI board. The sensors produced excellent signal quality that allowed for simple signal processing to extract information on heart and breathing rates, showing good correlation between the two

n-Si–p-Si1−xGex nanowire arrays for thermoelectric power generation

The output power of a discrete assembly of n-Si–p-Si1−xGex (0 ⩽ x ⩽ 0.4) thermoelectric generators is measured as a function of load resistance. The influence of Ge content and nanowire structures on the performance of thermoelectric devices is evaluated in measurements around room temperature. The nanowire arrays are etched using a metal induced local oxidation and etching process, based on self-assembled Ag nanoparticles and HF. The use of nanowires and SiGe with dimensions smaller than 30 μm, is beneficial for an improvement of, at least, a factor of 10 in the output power. However, better performance improvements can be obtained by optimising the thermal and electrical contact resistances at the interfaces. Optimisation of the electrical contact results in a performance boost by a factor of 25