Overview of the winning approaches in BCI Controlled Robot Contest in World Robot Contest 2021:Calibration-free SSVEP

Recently,steady-state visual evoked potential(SSVEP)has become one of the most popular electroencephalography paradigms due to its high information transfer rate.Several approaches have been proposed to improve the performance of SSVEP.The calibration-free scenario is significant in SSVEP-based brain-computer interface systems,where the subject is the first time to use the system.The participating teams proposed several effective calibration-free algorithm frameworks in the SSVEP competition(calibration-free)of the BCI Controlled Robot Contest in World Robot Contest 2021.This paper introduces the approaches used in the algorithms of the top five teams in the final.The results of the five subjects in the final proved the effectiveness of the approaches.This paper discusses the effectiveness of each approach in improving the system performance in the calibration-free scenario and gives suggestions on how to use these approaches in a real-world system.

A calibration-free model for laser-induced breakdown spectroscopy using non-gated detectors

Calibration-free(CF)laser-induced breakdown spectroscopy(LIBS)is normally only applicable for gated detectors due to its dependence on the assumption of a steady-state plasma.However,most currently available LIBS systems are equipped with non-gated detectors such as chargecoupled device(CCD),which degrades the accuracy of CF method.In this paper,the reason for the less satisfactory quantification performance of CF for LIBS with non-gated detectors was clarified and a time-integration calibration-free(TICF)model was proposed for applications with non-gated detectors.It was based on an assumed temporal profile of plasma properties,including temperature and electron density,obtained from another pre-experiment.The line intensity at different time during the signal collection time window was estimated with self-absorption correction according to the temporal profile of the plasma properties.The proposed model was validated on titanium alloys and compared with traditional CF.The accuracy of elemental concentration measurement was improved significantly:the average relative error of aluminum and vanadium decreased from 6.07%and 22.34%to 2.01%and 1.92%,respectively.The quantification results showed that TICF method was able to extend the applicability of CF to LIBS with non-gated detectors.

Accurate quantitative CF-LIBS analysis of both major and minor elements in alloys via iterative correction of plasma temperature and spectral intensity

The chemical composition of alloys directly determines their mechanical behaviors and application fields.Accurate and rapid analysis of both major and minor elements in alloys plays a key role in metallurgy quality control and material classification processes.A quantitative calibration-free laser-induced breakdown spectroscopy(CF-LIBS)analysis method,which carries out combined correction of plasma temperature and spectral intensity by using a secondorder iterative algorithm and two boundary standard samples,is proposed to realize accurate composition measurements.Experimental results show that,compared to conventional CF-LIBS analysis,the relative errors for major elements Cu and Zn and minor element Pb in the copperlead alloys has been reduced from 12%,26%and 32%to 1.8%,2.7%and 13.4%,respectively.The measurement accuracy for all elements has been improved substantially.

An improved wall shear stress measurement technique using sandwiched hot-film sensors

In this letter we present a novel wall shear stress measurement technique for a turbulent boundary layer using sandwiched hot-film sensors. Under certain conditions, satisfactory results can be obtained using only the heat generated by one of the hot-film and a calibration of the sensors is not required. Two thin Nickel films with the same size were used in this study, separated by an electrical insulating layer. The upper film served as a sensor and the bottom one served as a guard heater. The two Nickel films were operated at a same temperature, so that the Joule heat flux generated by the sensor film transferred to the air with a minimum loss or gain depending on the uncertainties in the film temperature measurements. Analytical solution of the shear stress based on the aforementioned heat flux was obtained. The preliminary results were promising and the estimated wall shear stresses agreed reasonablywell with the directly measured values （with errors less than 20%） in a fully developed turbulent pipe flow. The proposed technique can be improved to further increase precisions.

Overview of recognition methods for SSVEP-based BCIs in World Robot Contest 2022: MATLAB undergraduate group

The steady-state visual evoked potential(SSVEP)-based speller has emerged as a widely adopted paradigm in current brain–computer interface(BCI) systems due to its rapid processing and consistent performance across different individuals. Calibration-free SSVEP algorithms, as opposed to their calibration-based counterparts, offer clear and intuitive mathematical principles, making them accessible to novice developers. During the World Robot Contest(WRC)2022, participants in the undergraduate category utilized various approaches to accomplish target detection in the calibration-free setting, successfully implementing the algorithms using MATLAB.The winning approach achieved an average information transfer rate of 198.94 bits/min in the final test, which is notably high given the calibration-free scenario. This paper presents an introduction to the underlying principles of the selected methods, accompanied by a comparison of their effectiveness through analysis of results from both the final test and offline experiments. Additionally, we propose that the youth competition of WRC could serve as an ideal starting point for beginners interested in studying and developing their own BCI systems.

A 14-bit 100-MS/s 85.2-dB SFDR pipelined ADC without calibration

This paper describes a 14-bit 100-MS/s calibration-free pipelined analog-to-digital converter （ADC）. Choices for stage resolution as well as circuit topology are carefully considered to obtain high linearity without any calibration algorithm. An adjusted timing diagram with an additional clock phase is proposed to give residue voltage more settling time and minimize its distortion. The ADC employs an LVDS clock input buffer with low-jitter consideration to ensure good performance at high sampling rate. Implemented in a 0.18-μm CMOS technology, the ADC prototype achieves a spurious free dynamic range （SFDR） of 85.2 dB and signal-to-noise-and-distortion ratio （SNDR） of 63.4 dB with a 19.1-MHz input signal, while consuming 412-mW power at 2.0-V supply and occupying an area of 2.9 × 3.7 mm^2.

A 14-bit 80 MS/s CMOS ADC with 84.8 dB SFDR and 72 dB SNDR

This paper presents a design of 14-bit 80 Msample/s pipelined ADC implemented in 0.35μm CMOS. A charge-sharing correction is proposed to remove the signal-dependent charge-injection,together with a low-jitter clock circuit,guaranteeing the high dynamic performance for the ADC.A scheme of capacitor-switching and a symmetrical layout technique minimizes capacitor mismatch,ensuring the overall linearity.The measured results show that the calibration-free ADC achieves an effective number of bits of 11.6-bit,spurious free dynamic range （SFDR） of 84.8 dB,signal-to-noise-and-distortion ratio（SNDR） of 72 dB,differential nonlinearity of＋0.63/—0.6 LSB and integrated nonlinearity of＋ 1.3/-0.9 LSB at 36.7 MHz input and maintains over 75 dB SFDR and 59 dB SNDR up to 200 MHz.