Liansheng Zheng

Bio: Liansheng Zheng is an academic researcher from Jilin University. The author has contributed to research in topics: Femtosecond & Materials science. The author has co-authored 2 publications.

Robust physiological signal monitoring by a flexible piezoresistive sensor microstructured with filamentating laser pulses

Abstract: Flexible pressure sensors are promising for biomedical diagnosis and health monitoring, but most of such sensors meet with problems of one kind or another, such as counterfeit sensitivity, poor durability, expensive fabrication cost and trade-off between sensitivity and sensing range. Herein, a high-performance flexible pressure sensor microstructured with femtosecond filamentating pulses is assembled to realize robust physiological signal monitoring. The sensing mechanism is based on the change of contact resistance between the patterned silver conductive ink thin layer and the laser filament-microstructured polydimethylsiloxane film coated with single-walled carbon nanotubes. The sensor exhibits a maximum sensitivity of 0.266 kPa−1, a broad range of up to 160 kPa and an excellent stability. Benefiting from the aforementioned advantages, the sensor is used with success to detect a variety of human physiological signals, such as real-time artery pulse and throat muscle movement. Moreover, with the assistance of principle component analysis algorithm, it is demonstrated that the sensor can unambiguously distinguish different phonations, making it high potential for application in physiological analysis systems.

Neural Network-Enabled Flexible Pressure and Temperature Sensor with Honeycomb-like Architecture for Voice Recognition

Abstract: Flexible pressure sensors have been studied as wearable voice-recognition devices to be utilized in human-machine interaction. However, the development of highly sensitive, skin-attachable, and comfortable sensing devices to achieve clear voice detection remains a considerable challenge. Herein, we present a wearable and flexible pressure and temperature sensor with a sensitive response to vibration, which can accurately recognize the human voice by combing with the artificial neural network. The device consists of a polyethylene terephthalate (PET) printed with a silver electrode, a filament-microstructured polydimethylsiloxane (PDMS) film embedded with single-walled carbon nanotubes and a polyimide (PI) film sputtered with a patterned Ti/Pt thermistor strip. The developed pressure sensor exhibited a pressure sensitivity of 0.398 kPa −1 in the low-pressure regime, and the fabricated temperature sensor shows a desirable temperature coefficient of resistance of 0.13% ∘ C in the range of 25 ∘ C to 105 ∘ C. Through training and testing the neural network model with the waveform data of the sensor obtained from human pronunciation, the vocal fold vibrations of different words can be successfully recognized, and the total recognition accuracy rate can reach 93.4%. Our results suggest that the fabricated sensor has substantial potential for application in the human-computer interface fields, such as voice control, vocal healthcare monitoring, and voice authentication.

Carrageenan-Based Hybrid Materials with Ionic Liquids for Sustainable and Recyclable Printable Pressure Sensors

Abstract: For reducing the environmental impact of electronic systems (e-waste), increasingly implemented in the scope of the digitalization of society, this work reports on the development of a sustainable pressure sensor based on the combination of natural polymer carrageenan and ionic liquid (IL) 1-butyl-3-methylimidazolium tetrachloroferrate ([Bmim][FeCl4]). Different IL contents were incorporated into the carrageenan matrix (10, 20, and 40 wt %) to evaluate the influence of IL content on the final properties of the hybrid materials. No variations are induced in the chemical structure of carrageenan by the inclusion of the IL. On the other hand, the thermal stability of the polymer decreases with increasing IL content, as well as the Young modulus that decreases from 748 MPa for pristine carrageenan to 437 MPa for the composite with 40 wt % IL content. The ionic conductivity increases up to 8.74 × 10–9 S/cm for the sample comprising 40 wt % IL. The recyclability of the developed materials has been accessed, and the potential of the blends for the development of printable pressure sensors has been demonstrated.

High-Performance Flexible Piezoresistive Sensor Based on Ti3C2Tx MXene with a Honeycomb-like Structure for Human Activity Monitoring

Abstract: Wearable and flexible pressure sensors have sparked great interest due to their unique capacity to conformally attach to the surface of the skin and quantify human activities into recordable electric signals. As a result, more and more research efforts are being devoted to developing high-sensitivity and cost-effective flexible sensors for monitoring an individual’s state of activity. Herein, a high-performance flexible piezoresistive sensor was designed and fabricated by combing 2D transition metal carbides, nitrides, and carbonitrides (MXene) with a honeycomb-like structure formed by femtosecond filamentating pulses. The sensing mechanism is attributed to the change of the connecting conductive paths between the top interdigital electrodes and the bottom microstructured films coated with MXene. The obtained sensing device demonstrates high sensitivity of 0.61 kPa−1, relatively short response time, and excellent reliability and stability. Benefiting from the aforementioned extraordinary sensing performance, the sensor can be used with success to monitor tiny physiological signals, detect large deformations during human movement, and distinguish finger gestures, thus demonstrating its broad prospects in physiological analysis systems, health monitoring systems, and human–machine interaction.

Modulation of population inversion in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi mathvariant="normal">N</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msup><mml:mrow /><mml:mo>+</mml:mo></mml:msup></mml:mrow></mml:math> by a pump-control-seed scheme

Abstract: We experimentally demonstrate an externally seeded ${\mathrm{N}}_{2}{}^{+}$ lasing action on the transition between the $B{\phantom{\rule{4pt}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{u}{}^{+}(v=0)$ and $X{\phantom{\rule{4pt}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{g}{}^{+}({v}^{\ensuremath{'}}=0)$ states at 391.4 nm by irradiating a ${\mathrm{N}}_{2}$ gas with an intense 400-nm pump laser pulse and reveal that the populations in the rotational levels of ${J}^{\ensuremath{'}}=7--17$ in the $B{\phantom{\rule{4pt}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{u}{}^{+}(v=0)$ state are responsible for the lasing based on the rotational revival structure in the lasing intensity recorded by the pump-probe measurements. By introducing additionally an 800-nm control pulse, we find that the lasing intensity is suppressed when the timing of the control pulse is set between the 400-nm pump and 400-nm seed laser pulses while it can be enhanced when the control pulse overlaps temporally the seed pulse. By solving the time-dependent Schr\"odinger equation including the continuous ionization of ${\mathrm{N}}_{2}$ and multistate coupling among the ${B}^{\phantom{\rule{4pt}{0ex}}2}{\mathrm{\ensuremath{\Sigma}}}_{u}{}^{+}$, ${A}^{\phantom{\rule{4pt}{0ex}}2}{\mathrm{\ensuremath{\Pi}}}_{u}$, and $X{\phantom{\rule{4pt}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{g}{}^{+}$ states in ${\mathrm{N}}_{2}{}^{+}$ induced by the control pulse, we show that the population inversion in ${\mathrm{N}}_{2}{}^{+}$ can be achieved by the 400-nm pump laser pulse and can be further modulated by the control pulse. We show also that the ${\mathrm{N}}_{2}{}^{+}$ lasing intensity can be suppressed or enhanced depending on the timing and intensity of the control pulse originating from the competition between the two dynamical processes, that is, the ionization of ${\mathrm{N}}_{2}$ and the population transfer among the three electronic states of ${\mathrm{N}}_{2}{}^{+}$.

A Self-Powered Strain Sensor Applied to Real-Time Monitoring for Movable Structures

Abstract: This study uses near-field electrospinning (NFES) technology to make a novel self-powered strain sensor and applies it to the real-time monitoring of a bending structure, so that the measurement equipment can be reduced in volume. A self-powered strain sensor consists of polyvinylidene difluoride (PVDF) fibers, a PDMS fixed substrate, and an aluminum electrode. PVDF fibers are spun with DMSO and acetone using NFES technology, with a diameter of about 8 μm, Young’s modulus of 1.1 GPa, and piezoelectric effect of up to 230 mV. The fixed substrate is a film made of PDMS by thermal curing, then adhered to the PDMS film surface of the sheet Al metal as an Al electrode, and then combined with PVDF fiber film, to become a self-powered strain sensor. As a result, the XRD β value of the self-powered strain sensor reaches 2112 and the sensitivity is increased by 20% over a traditional strain sensor. The cumulative angle algorithm can be applied to measure the angular change of the object over a unit of time or the cumulative displacement of the object over the entire period of motion. The experimental results demonstrate that the self-powered strain sensor combined with the angle accumulation algorithm may be applied to monitor the bending structure, thereby achieving continuous measurements of bending structure changes, and improving on traditional piezoelectric sensors, which can only be sensed once. In the future, self-powered strain sensors will have the ability to continuously measure in real-time, enabling the use of piezoelectric sensors for long-term monitoring of structural techniques.