Chunsheng Yang

Graphene oxide doped conducting polymer nanocomposite film for electrode-tissue interface

One of the most significant components for implantable bioelectronic devices is the interface between the microelectrodes and the tissue or cells for disease diagnosis or treatment. To make the devices work efficiently and safely in vivo, the electrode-tissue interface should not only be confined in micro scale, but also possesses excellent electrochemical characteristic, stability and biocompatibility. Considering the enhancement of many composite materials by combining graphene oxide (GO) for its multiple advantages, we dope graphene oxide into poly(3,4-ethylenedioxythiophene) (PEDOT) forming a composite film by electrochemical deposition for electrode site modification. As a consequence, not only the enlargement of efficient surface area, but also the development of impedance, charge storage capacity and charge injection limit contribute to the excellent electrochemical performance. Furthermore, the stability and biocompatibility are confirmed by numerously repeated usage test and cell proliferation and attachment examination, respectively. As electrode-tissue interface, this biomaterial opens a new gate for tissue engineering and implantable electrophysiological devices.

A flexible and biocompatible triboelectric nanogenerator with tunable internal resistance for powering wearable devices.

Recently, triboelectric energy nanogenerators (TENGs) have been paid the most attention by many researchers to convert mechanical energy into electrical energy. TENGs usually have a simple structure and a high output voltage. However, their high internal resistance results in low output power. In this work, we propose a flexible triboelectric energy nanogenerator with the double-side tribological layers of polydimethlysiloxane (PDMS) and PDMS/multiwall carbon nanotube (MWCNT). MWCNTs with different concentrations have been doped into PDMS to tune the internal resistance of triboelectric nanogenerator and optimize its output power. The dimension of the fabricated prototype is ~3.6 cm3. Three-axial force sensor is used to monitor the applied vertical forces on the device under vertical contact-separation working mode. The Prototype with 10 wt% MWCNT (Prototype I) produces higher output voltage than one with 2 wt% MWCNT (Prototype II) due to its higher dielectric parameter measured by LRC impedance analyzer. The triboelectric output voltages of Prototype I and Prototype II are 30 V and 25 V under the vertical force of 3.0 N, respectively. Their maximum triboelectric output powers are ~130 μW at 6 MΩ and ~120 μW at 8.6 MΩ under vertical forces, respectively.

PDMS-Based Low Cost Flexible Dry Electrode for Long-Term EEG Measurement

In this paper, a novel flexible dry electrode for long-term electroencephalogram (EEG) measurement is presented. Though the standard wet electrodes (Ag/AgCl) were used widely, they have their own drawbacks, such as the need for conductive gel and skin preparation, which causes the user discomfort and is unsafe, and cannot fit the long-term EEG measurement. To overcome these drawbacks of the wet electrodes, a novel flexible dry electrode made of Polydimethysiloxane is proposed; it works without conductive gel and skin preparation. More importantly, this flexible dry electrode with pins structure can directly measure the EEG of hairy sites through hair. The impedances in frequency and time domains are tested to characterize the performance of the proposed dry electrode. In addition, to estimate signal quality, the average correlation and the power spectrum are presented between different electrodes. This flexible dry electrode can meet the requirement of high quality EEG measurement.

A flexible triboelectric-piezoelectric hybrid nanogenerator based on P(VDF-TrFE) nanofibers and PDMS/MWCNT for wearable devices

This paper studied and realized a flexible nanogenerator based on P(VDF-TrFE) nanofibers and PDMS/MWCNT thin composite membrane, which worked under triboelectric and piezoelectric hybrid mechanisms. The P(VDF-TrFE) nanofibers as a piezoelectric functional layer and a triboelectric friction layer are formed by electrospinning process. In order to improve the performance of triboelectric nanogenerator, the multiwall carbon nanotubes (MWCNT) is doped into PDMS patterned films as the other flexible friction layer to increase the initial capacitance. The flexible nanogenerator is fabricated by low cost MEMS processes. Its output performance is characterized in detail and structural optimization is performed. The device’s output peak-peak voltage, power and power density under triboelectric mechanism are 25 V, 98.56 μW and 1.98 mW/cm3 under the pressure force of 5 N, respectively. The output peak-peak voltage, power and power density under piezoelectric working principle are 2.5 V, 9.74 μW, and 0.689 mW/cm3 under the same condition, respectively. We believe that the proposed flexible, biocompatible, lightweight, low cost nanogenerator will supply effective power energy sustainably for wearable devices in practical applications.

A micro-tensile method for measuring mechanical properties of MEMS materials

Mechanical properties of micro-electro-mechanical systems (MEMS) materials are increasingly important with the wide use of miniaturized systems. This paper proposes a new method for measuring mechanical properties of thin films. This method is suitable for thin films with large strain (>5%) and can be applied to samples with different thicknesses. The S-shaped support springs of the test chip are able to improve the measurement accuracy. Specimens of Ni thin film, with a gauge section 50 µm wide, 100 µm long and 5 µm thick, were tested. The measured Youngs modulus of Ni thin film is about 32 GPa and the tensile strength is about 750 MPa.

Fabrication and analysis of high-performance piezoelectric MEMS generators

In this paper, we have designed a fabrication process for microgenerators by bonding a piezoelectric ceramic Pb(Zr,Ti)O3?(PZT) plate to a silicon on insulator (SOI) wafer. The key techniques of the process include the low-temperature bonding technique using conductive epoxy resin, thinning of the bulk PZT using mechanical lapping and wet-etching combined method, and the micromachining of bulk ceramics by dicing. Through the development and optimization of the process, a piezoelectric MEMS power generator array was successfully fabricated. The typical device is selected to characterize the output performance of the microgenerators, while the composite beam dimension of PZT and silicon layer is about 3080 ?m???800 ?m???31 ?m and the dimension of Ni proof mass is about 900 ?m?? 800 ?m???450 ?m. The experimental results show that the output voltage, output power and power density of this device are 2.72 VP-P, 11.56 ?W and 28?856.7 ?W cm?3?at the resonant frequency of 514.1 Hz when it matches an optimal resistive load of 70 k? under the excitation of 1g acceleration. The output performance of this device is higher, compared with that of other reported MEMS power generators, which demonstrates that this novel technique has great potential to fabricate high-performance piezoelectric MEMS energy harvester.

An axial flux electromagnetic micromotor

In this paper, the principle, design, fabrication and performance of an axial flux electromagnetic micromotor are described. The stator of the micromotors consists of six levels of copper windings and an alumina filling using a modified LIGA (Lithographic Galvanoforming Abforming)-like technology. The rotor is a disc made of SmCo permanent magnetic alloy using the electro discharge machining (EDM) technique and it is magnetized with pairs of magnetic poles using a specially designed apparatus. The rotor and the stator are assembled together to form the micromotor. The dimensions of the assembled motors are 1 mm and 2 mm in diameter and about 1.5 mm thick. The rotation speed of the micromotors can be adjusted from several hundreds to over ten thousand rpm and the rotation is reversible. The output torques of the micromotor are measured to be 1.5 µN m and 2.8 µN m for motors with diameters of 1 mm and 2 mm, respectively.

A generator with nonlinear spring oscillator to provide vibrations of multi-frequency

A piezoelectric generator with nonlinear spring oscillator is proposed to provide multiple resonant modes for operation and improve conversion efficiency. In order to scavenge the vibration energy of multiple frequencies from a certain vibration source, two types of nonlinear springs have been employed and tested. The maximum output power of 5, 17.83, and 23.39 μW for the nonlinear spring of 8.3 N/m with 1 g acceleration has been obtained under the resonant frequency of 89, 104, and 130 Hz, respectively. Its total output power of 46.22 μW is obviously larger than the one of 28.35 μW for traditional second-order spring-mass linear system.

Deep reactive ion etching of commercial PMMA in O2/CHF3, and O2/Ar-based discharges

The reactive ion etching of PMMA in O2, O2/CHF3 and O2/Ar discharges has been examined as a function of bias voltage, flow rate and composition of the gas mixtures. Etching in O2, O2/CHF3 and O2/Ar plasmas (with a flow ratio of Ar/O2 ≤ 50%) shows higher ion-enhanced chemical etching dependence than in O2/Ar (with a flow ratio of Ar/O2 ≥ 50%). In Ar/O2 plasmas, with an increasing proportion of Ar, the dominant process changed from an ion-enhanced chemical process with high values of etch rate to a physical sputtering etch process. PMMA etched in O2 (10 sccm)/Ar (40 sccm) produced a smooth and vertical sidewall. With an increasing amount of CHF3, the etch rates of PMMA show a larger dependence on physical sputtering and a gradual decrease. When the depth of PMMA etched in O2 (25 sccm)/CHF3 (25 sccm) is about 100 µm the profile is vertical, but the sidewall surface is rough.

A transparent and biocompatible single-friction-surface triboelectric and piezoelectric generator and body movement sensor

With the development of wearable electronics, flexible energy devices are now paid more attention, aiming at efficiently converting a variety of physical motion energy of the human body into electricity. This work innovatively proposes a flexible and biocompatible single-friction-surface triboelectric and piezoelectric hybrid generator (TPG) with good transparency. The novel TPG uses Al:ZnO (AZO) as transparent electrodes, P(VDF-TrFE) as the piezoelectric functional layer and PDMS with micro-fabricated pyramids as the triboelectric layer. The proposed TPG can effectively harvest bending and movement energy from human skin under piezoelectric and triboelectric mechanisms. The typical stress–strain curve and transmittance testing of TPG indicates that TPG has outstanding stretchability and transmittance. The generator has an open-circuit output voltage of 25 V under the triboelectric mechanism and a piezoelectric open-circuit output voltage of 2.5 V under the piezoelectric method. The total output voltage and power density of this device are 26 V and 751.1 mW m−2, respectively. In addition, this device would scavenge the mechanical energy from the different parts of the body, such as the human neck, finger, elbow and ankle into electric energy with various signal forms owing to the different contacting moving modes on the friction surface, which will be deployed as a body moving sensor.