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Constant on -time control (COT) has been widely adopted in buck converters because of its simplicity, fast transient response, and high light-load efficiency. However, the increasing power demands of CPUs and AI/ML engines is pushing voltage regulators to support higher output currents, which typically requires the use of multiphase operation. However, since most high-performance COT schemes utilize ripple as a control variable, the ripple cancellation point in multiphase designs imposes difficult stability concerns, limiting performance, and robustness. In this article, a novel ultrafast transient COT (UFTCOT) control scheme is proposed to enable fast and robust operation even in multiphase converters. The small-signal models of the proposed control scheme are derived based on a describing function technique, whose theoretical results are compared, along with simulation and measurement results, to contrast the proposed UFTCOT technique to exiting approaches.

The ripple-based constant on-time (COT) control with ripple compensation has been widely adopted in buck converters in the recent years because of its simplicity, fast transient response, and high light-load efficiency. However, this control has the potential issues of instability and excessive load transient response with wide input/output voltage range conditions in the power management integrated circuit (PMIC) applications. In this article, an accurate adaptive COT control scheme is proposed to solve these problems. The control scheme achieves accurate output voltage, and nearly constant quality factor and well transient response over a wide-range operation with simple circuit. The small-signal model is also derived based on the describing function (DF) technique for design optimization. Finally, the simulations and experimental verifications were conducted to verify the proposed concepts.

Flexible asymmetric supercapacitor is fabricated with three dimensional(3D) Fe2O3/Ni(OH)2 composite brush anode and Ni(OH)2/MoO2 honeycomb cathode. Particularly for 3D composite brush anode, a layer of thin Fe2O3 film is firmly adhered on a 3D Ni brush current collector with the assist of Ni(OH)2, functioning as both adherence layer and pseudocapacitive active material. The unique 3D Ni brush current collector possesses large surface area and stretching architecture, which facilitate to achieve the composite anode with high gravimetric capacitance of 2158 F/g. In terms of cathode, Ni(OH)2 and MoO2 have a synergistic effect to improve the specific capacitance, and the resulting Ni(OH)2/MoO2 honeycomb cathode shows a very high gravimetric capacitance up to 3264 F/g. The asymmetric supercapacitor(ASC) has balanced cathode and anode, and exhibits an ultrahigh gravimetric capacitance of 1427 F/g and an energy density of 476 Wh/kg. The energy density of ASC is 3–4 times higher than those of other reported aqueous electrolyte-based supercapacitors and even comparable to that of commercial lithium ion batteries. The device also shows marginal capacitance degradation after 1000 cycles’ bending test, demonstrating its potency in the application of flexible energy storage devices.

A mixed ionic (Li1.3Al0.3Ti1.7(PO4)3: LATP) and electronic conductor (porous carbon: C) hybrid layer can effectively enhance the electrochemical performance of cathode materials. In this work, a sustainable low-temperature synthesis strategy (≤200 °C) combining ball milling and solvent-recrystallization of lithium iodide is first proposed to prepare the LATP/C coated LiNi1/3Co1/3Mn1/3O2 (LNCMO) material. The characterizations of structures and morphology reveal that LATP and porous carbon powder are mixed into the ethanol dissolved lithium iodide by a simple ball milling process, then the lithium iodide is recrystallized to serve as a binder when ethanol is vaporized at a low temperature to coat uniform thickness and homogeneously distributed LATP/C on the surface of LNCMO cathode. The charge-discharge results illustrate that the cycling performance and rate discharge capability of the active materials coated with LATP/C are significantly superior to the bare LNCMO. AC impedance analysis confirms that lower charge transfer resistance and higher Li+ ion diffusion coefficient are achieved in cathode materials. This work successfully exploited a novel low-temperature cathode coating method based on lithium iodide solvent-recrystallization and obtained results comparable to high-temperature processes without suffering from side reaction problems.

Open in a separate window Size- and shape-dependent features of plasmonic nanocrystals govern the development of their applications. In the past decades, gold nanostructures, such as gold nanorods and nanoshells, have been well studied and applied for sensing, bioimaging, and photothermal generation. However, knowledge of copper chalcogenide, a new generation of plasmonic nanomaterials, is limited, especially about their preparation and size- and shape-dependent photothermal properties. In this work, controllable size and shape Cu2–xS nanocrystals (NCs) are synthesized by a facile aqueous route. Using low-molecular-weight polyethylenimine (PEI) as the reducing and capping agents, the size and shape of Cu2–xS NCs can be controlled with lengths from 6.5 to 46.5 nm and the aspect ratio from 2.2 to 7.5 by adjusting the concentration of PEI. The plasmonic peak of Cu2–xS experiences a redshift (from 1145 to 1369 nm) when the length increases from 6.5 to 44.5 nm. Under the irradiation of 1064 nm laser with 1.33 W/cm2, an excellent photothermal conversion rate (from 34.9 to 49.0%) is obtained. The characterization of Cu2–xS NCs is conducted with a UV–vis spectrometer, transmission electron microscopy, powder X-ray diffraction measurements, and 1064 nm laser.

Flyback converters with universal serial bus power delivery (USB-PD) specification are widely used in low-power adapter application. The wide output voltage range operation of USB-PD makes the loop gain vary under different working conditions. To ensure stability in all working conditions, the loop gain has to be compensated based on the worst case of control-to-output transfer function. However, in other conditions, the crossover frequencies of loop gain are sacrificed, resulting in poor transient responses. This paper proposes an adaptive variable-frequency peak current mode control with constant crossover frequency to mitigate the tradeoff between stability and transient response while possessing the variable frequency characteristic to improve light load efficiency. The adaptive control law is derived from the proposed small-signal model. Experimental and simulation results verify the analysis. The proposed control reduces the output voltage variation at load transient by 43% and 34% at 5 and 20 V output voltage, respectively.

A facile and environmental-friendly method is developed to coat nickel films on fabrics using Gantrez as the functional molecule and Ag+ as the catalyst, and nickel cloth and nickel brush are synthesized by this method. Nanohemisphere structures are grown on the nickel fabrics by diffusion controlled electroless deposition method subsequently. The nickel fabrics with nanohemispheres have high and balanced electrochemical performance with 1.5 M NaOH as the electrolyte. At the current density of 5 mA/cm2, the nanoarchitectured nickel cloth and nickel brush show a specific capacitance of 2.31 F/cm2 and 6.82 F/cm2, respectively. The nanoarchitectured nickel brush has a high rate capability and cyclic capability with 92% capacitance retention as the current density changes from 3 mA/cm2 to 20 mA/cm2, and 113% capacitance retention after 10,000 charge-discharge cycles. Furthermore, 98% capacitance retention of the nickel brush is measured after the bending test with a radius of 3 mm for 800 cycles.

Recently, a flyback converter with universal serial bus power delivery (USB-PD) specification is widely used in low-power adaptor application. However, the wide output-voltage-range operation of USB-PD makes the stability issue of the flyback converter more severe. This paper provides a brief discussion of two stability improvement methods for the peak-current-mode-controlled flyback converter at variable frequency and completely interprets those detailed techniques. Simulation validates the performances of the two methods. Furthermore, a control circuit and a flyback converter are built for experimental validation of the two stability improvement methods. Finally, some comments are also summarized.

Flyback converter with variable-frequency peak-current-mode (VFPCM) control is widely used in low-power adaptor and recently proposed universal serial bus power delivery application. The control scheme achieves high efficiency for the entire load range by reducing the switching frequency at light load. In the present study, an accurate unified small-signal model for VFPCM control in continuous conduction mode (CCM) and discontinuous conduction mode (DCM) is proposed. Based on the model, a compensation strategy is proposed to overcome the unstable problem in a wide range of operations and give engineers insight. Experimental and simulation results verify the proposed model and compensation strategy.

Flyback converter is widely used in low-power adaptor applications. To achieve high efficiency for the entire load range of operations, the variable-frequency peak-current-mode (VFPCM) control is often used in the flyback converter to reduce switching frequency at light load. Since there is no small-signal model being developed for the VFPCM control to overcome the unstable problem in a wide range of operations, the present study proposes a novel, accurate small-signal model for VFPCM control operated in continuous-conduction mode. Control behavior and design are analyzed and compared with constant-frequency peak-current-mode control to give engineers insight. A control IC and a flyback converter are built for the experimental validation of the proposed model. Experimental and simulation results verify the proposed model.

Among the biomedical imaging modalities, photoacoustic computed tomography (PACT) was one of the emerging hybrid techniques in recent years. In designing the PACT imaging system, a finite-bandwidth transducer is one of the limited factors for the overall performance. As the target size is inversely proportional to the dominant frequency components of the generated photoacoustic (PA) signal, a broad bandwidth transducer is desired for different scales’ imaging. In this paper, a monolithic multiband capacitive micromachined ultrasonic transducer (CMUT) array was designed and fabricated for the reception of the wideband PA signals so as to provide high-resolution images with high-frequency CMUT arrays and present the high signal-to-noise-ratio major structure with low-frequency CMUT arrays. To demonstrate its performance, a phantom experiment was conducted to show and evaluate the various qualities of multiresolution images. In addition, an in vivo mouse model experiment was also carried out for revealing the multiscale PA imaging capability with the multiband CMUTs on biological tissues. From the obtained results, the images from different CMUT arrays could show the structures of the mouse brain in different scales. In addition, the images from the high-frequency CMUT arrays were able to reveal the major blood vasculatures, whereas the images from low-frequency CMUT arrays showed the gross macroscopic anatomy of the brain with higher contrast.

In this study, dual-responsive polymeric nanocapsules, in which the state (swelling or collapse) can be repeatedly controlled by external stimuli (i.e., temperature and light), have been designed and prepared through distillation–precipitation polymerization. Temperature sensitive monomers of N-isopropylacrylamide are cross-linked by photoresponsive bis(methacryloylamino) onto a silica nanospherical template to form a core–shell (SiO2–PNIPAM/Azo) structure. The silica core is then removed by hydrofluoric acid to produce PNIPAM/Azo nanocapsules (P/ANCs) of diameter ∼238 nm at ∼25 °C. The size of the nanocapsule is temperature responsive and, as such, its diameter could be reduced to ∼182 nm on increasing the temperature to 40 °C. In addition, the permeability of nanocapsules can be adjusted by UV irradiation. The cis–trans transformation of modified azobenzene allowed us to perform both the encapsulation and controlled release of molecules. Rhodamine B (RhB) was successfully encapsulated using the photomec...

A SiC trench metal-oxide-semiconductor field-effect transistor (MOSFET) with a self-biased p-shield (SBS-MOS) is proposed and comprehensively studied. The p-shield region is used to reduce the high oxide field at the OFF-state, which would otherwise be detrimental to the device long-term reliability. A self-biasing network is designed to raise the potential of the p-shield in the SBS-MOS, so that the parasitic junction field effect transistor (JFET) is driven synchronously with the MOS-gate. Mixed-mode numerical simulations are carried out to study the performance of the proposed device. The SBS-MOS boasts a reduced specific ON-resistance ( R ON-SP ) compared with the trench MOSFET with a grounded p-shield (GS-MOS), by the reduction of the JFET resistance and/or further down-scaling of the cell size. To synchronously drive the JFET region, only a slightly larger gate charge is required for the SBS-MOS. Therefore, a low OFF-state oxide field, a low R ON-SP and a low Q GD are simultaneously achieved in the proposed SBS-MOS.

The high OFF-state oxide field in the SiC trench MOSFET is a threat for its long term reliability, and thus hinders the wide acceptance of the SiC trench MOSFETs. In this paper, an SiC trench MOSFET with protruded p-bases (PB-MOS) is proposed, which features protruded p-bases to shield the gate oxide at the trench bottom against the high OFF-state drain voltage. Numerical device simulations based on Sentaurus TCAD verify the benefits of the structure. The OFF-state oxide field ( ${ {E}}_{\text {ox-m}}$ ) in the PB-MOS is 1.7 MV/cm, which is dramatically lower compared to the high ${ {E}}_{\text {ox-m}}$ of 8.6 MV/cm in the conventional trench MOSFET (C-MOS). The above benefit is achieved without sacrificing device performances. The reverse transfer capacitance ( ${ {C}}_{\text{rss}}$ ) of the PB-MOS is around ten times lower than that in the C-MOS. Both the gate charge ( ${ {Q}}_{\text{G}}$ ) and the gate-to-drain charge ( ${ {Q}}_{\text{GD}}$ ) of the PB-MOS are significantly improved compared to the C-MOS. A low specific ON-resistance ( ${ {R}}_{\text{ON}}$ ) is maintained in the PB-MOS by using additional JFET doping to compensate the JFET effect. As a result, the PB-MOS presents much better figures of merit ${ {Q}}_{\text{G}} \cdot { {R}}_{\text{ON}}$ and ${ {Q}}_{\text{GD}} \cdot { {R}}_{\text{ON}}$ than those of the C-MOS. The PB-MOS achieves a much faster switching speed than the C-MOS, and consequently exhibits an appreciable reduction in the switching energy loss.

We propose a SiC trench/planar MOSFET (TP-MOS) which features a trench channel and a planar channel in one half-cell. Numerical simulations with Sentaurus TCAD have been carried out to study the proposed device architecture. Compared with traditional planar MOSFET (P-MOS), the TP-MOS has a much lower ${R} _{\mathrm {ON}}$ owing to the increased channel density. Unlike traditional trench MOSFET (T-MOS) which enables a higher channel density at the price of a high bottom-oxide field in the high-voltage OFF-state, the TP-MOS features bottom p-bases as in the P-MOS that protect the gate oxide from high electric field. The OFF-state oxide field in the TP-MOS is found to be even lower than the P-MOS. In addition, the TP-MOS boasts a low feedback capacitance ( ${C} _{\mathrm {rss}})$ and gate-to-drain charge ( ${Q} _{\mathrm {GD}})$ , since the coupling between the gate and the drain is suppressed by the collective effects of the top p-bases and the bottom p-bases. The ${Q} _{\mathrm {G}}$ of the TP-MOS is nearly the same as the P-MOS, and is much smaller than the T-MOS. Superior figures of merit ( ${Q} _{\mathrm {G}}\times {R} _{\mathrm {ON}}$ and ${Q} _{\mathrm {GD}}\times {R} _{\mathrm {ON}})$ are achieved in the TP-MOS.

This paper is to develop analytical models for the underwater capacitive micromachined ultrasonic transducer (CMUT) to understand its large deflection effect from the water pressure. To accurately model the displacement profile of the CMUT under the water pressure, Von Karman equations and the perturbation method are employed to calculate the membrane deformation from a uniform pressure. The equations for an annular-ring plate model are first applied to calculate the displacement profile of the uniform CMUT membrane. The lateral force due to the membrane elongation is considered in the proposed model, which is used to calculate the displacement profiles for both conventional and collapse mode CMUTs under different external pressures. When compared with finite-element method results, the proposed model can predict the displacement profiles of the conventional-mode CMUT under water pressure ranging from 0.8 to 4 MPa with an error of

Multiscale surfaces enriched with different scales of features are becoming widely used in many fields such as MEMS and optics industries. Due to the complexity of the multiple scale geometries, a single sensor or a single measurement can hardly obtain the holistic information of these surfaces. Multiple measurement method can solve this problem while it will introduce a lot of challenges for multiscale data fusion for the measurement results. This paper presents a framework of a data fusion algorithm for precision measurement of multiscale surfaces. The method makes use of iterative closest point based method to precisely register the datasets obtained in multiple measurements, and a Gaussian zero-order regression filter is used to separate the geometric features in different scales. Hence, the datasets are fused based on an edge intensity data fusion algorithm within the same wavelength. Finally, the fused datasets of different wavelengths were merged and replaced to the corresponding area in the large scale measurement to form a new surface with holistic multiscale information. The effectiveness of the proposed method has been verified on a v-grooved surface through a series of simulation experiments

Capacitive Micromachined Ultrasonic Transducer (CMUT) is a promising ultrasonic transducer in medical diagnosis and therapeutic applications that demand a high output pressure. The concept of a CMUT with an annular embossed pattern on a membrane working in collapse mode is proposed to further improve the output pressure. To evaluate the performance of an embossed CMUT cell, both the embossed and uniform membrane CMUT cells were fabricated in the same die with a customized six-mask sacrificial release process. An annular nickel pattern with the dimension of 3 &mu, m&nbsp, &times, 2 &mu, m (width &times, height) was formed on a full top electrode CMUT to realize an embossed CMUT cell. Experimental characterization was carried out with optical, electrical, and acoustic instruments on the embossed and uniform CMUT cells. The embossed CMUT cell achieved 27.1% improvement of output pressure in comparison to the uniform CMUT cell biased at 170 V voltage. The fractional bandwidths of the embossed and uniform CMUT cells were 52.5% and 41.8%, respectively. It substantiated that the embossed pattern should be placed at the vibrating center of the membrane for achieving a higher output pressure. The experimental characterization indicated that the embossed CMUT cell has better operational performance than the uniform CMUT cell in collapse region.

Recently, flyback converter with Universal Serial Bus Power Delivery (USB-PD) specification is widely used in low-power adaptor application. However, the wide output-voltage-range operation of USB-PD makes the stability issue of flyback converter more severe. This paper provides a brief overview of two stability improvement methods for variable-frequency peak-current mode (VFPCM) controlled flyback converter while possessing the variable frequency characteristic for high efficiency and completely interprets those detail techniques. Simulation validates the performances of the two methods. Furthermore, a control circuit and a flyback converter are built for experimental validation of NVFPCM control with constant crossover frequency. Finally, some comments are also summarized.

Among the biomedical imaging modalities, photoacoustic computed tomography (PACT) was one of the emerging hybrid techniques in recent years. In designing the PACT imaging system, a finite-bandwidth transducer is one of the limited factors for the overall performance. As the target size is inversely proportional to the dominant frequency components of the generated photoacoustic (PA) signal, a broad bandwidth transducer is desired for different scales' imaging. In this paper, a monolithic multiband capacitive micromachined ultrasonic transducer (CMUT) array was designed and fabricated for the reception of the wideband PA signals so as to provide high-resolution images with high-frequency CMUT arrays and present the high signal-to-noise-ratio major structure with low-frequency CMUT arrays. To demonstrate its performance, a phantom experiment was conducted to show and evaluate the various qualities of multiresolution images. In addition, an in vivo mouse model experiment was also carried out for revealing the multiscale PA imaging capability with the multiband CMUTs on biological tissues. From the obtained results, the images from different CMUT arrays could show the structures of the mouse brain in different scales. In addition, the images from the high-frequency CMUT arrays were able to reveal the major blood vasculatures, whereas the images from low-frequency CMUT arrays showed the gross macroscopic anatomy of the brain with higher contrast.

Based on the synergy of a theoretical one-dimensional (1D) mass-spring-damper model and the experimental validation of fabricated capacitive MEMS microphones fabricated by the PolyMUMPs process, we identify the existence of a critical diaphragm radius which represents the inflection point on the microphone's sensitivity-radius curve. To overcome this miniaturization barrier, we propose a new microphone structure with four folded microbeams. The corresponding sensitivity remains the same, while the radius reduces by 17% in comparison with the previous design.

A capacitive micromachined ultrasonic transducer (CMUT) with a graphene membrane is reported. The CMUT membranes were commonly made from very thin silicon nitride or metal material. To date, no graphene CMUT has been successfully used. In this reported work, a photomask were used for the cavity pattern to make a 1μm layer EPON SU-8 photoresist on the silicon substrate. Then a single-layer graphene were tranferred directly to be attached to the EPON SU-8 cavity layer to form the CMUT with a graphene membrane. The resonance frequency was measured to be 95 MHz in air.

This paper presents fabrication methods using graphene as a membrane that was thermally bonded on top of the CMUT cavity formed by patterned photoresist. The impedance measurement result showed graphene CMUT exhibit high resonance frequency when membrane size remains large. Previously we had also reported such a graphene CMUT with stiction problem caused by a graphene transfer technique. In the newly fabricated CMUT, different methods are used to protect the graphene membrane and stiction problem was solved by bonding in air. The resonant frequencies of the fabricated graphene CMUT with membrane sizes of 500µm and 90µm are found to be 45MHz and 63MHz respectively in air.

Capacitive Micromachined Ultrasonic Transducer (CMUT) is a new type of ultrasound wave generator and detector. Analytical method is intuitive to understand the mechanism and physical effects through modeling of CMUT. To optimize the design procedures of CMUT membrane undergoing large deflection, a new analytical model with the consideration of the lateral force using Von Karman equations is proposed. This model is capable of calculating the membrane profile of the CMUT since it includes the effect of the lateral force. The calculated results match well with the simulated results and the maximum deflection error in the center of the CMUT is less than 1% of the simulation results. The lateral force increases with the deflection of the membrane and it can be found that with the introduction of the lateral force, the proposed model can accurately estimate the membrane large defection profile in both single and double-layer membrane cases. The capacitance of the CMUT can be derived when the deflection profile of the membrane is available.

Capacitive micromachined ultrasonic transducers (CMUTs) have emerged as a competitive alternative to piezoelectric ultrasonic transducers, especially in medical ultrasound imaging and therapeutic ultrasound applications, which require high output pressure. However, as compared with piezoelectric ultrasonic transducers, the output pressure capability of CMUTs remains to be improved. In this paper, a novel structure is proposed by forming an embossed vibrating membrane on a CMUT cell operating in the collapse mode to increase the maximum output pressure. By using a beam model in undamped conditions and finite-element analysis simulations, the proposed embossed structure showed improvement on the maximum output pressure of the CMUT cell when the embossed pattern was placed on the estimated location of the peak deflection. As compared with a uniform membrane CMUT cell worked in the collapse mode, the proposed CMUT cell can yield the maximum output pressure by 51.1% and 88.1% enhancement with a single embossed pattern made of Si3N4 and nickel, respectively. The maximum output pressures were improved by 34.9% (a single Si3N4 embossed pattern) and 46.7% (a single nickel embossed pattern) with the uniform membrane when the center frequencies of both original and embossed CMUT designs were similar.

A novel fluidic strain sensor is proposed with the use of a mixture of glycerin with aqueous sodium chloride encapsulated within an elastomer as a mean for piezoresistive large strain measurement. Electrochemical impedance spectroscopy (EIS) is conducted for strain response measurement and equivalent circuit analysis is applied for explaining the strain-affected ion transportation behavior of the sensor. The applied strain has caused an increase in both the resistance to charge transfer (Rct) and the resistance of the salt solution which is reflected in an increase in the resistance of the system (Rsys). A parabolic relationship between the real part of the impedance (Zre) and the true strain (ɛ) for an applied strain of up to about 30% is verified. In addition, a novel fluid encapsulation technique by applying oxygen plasma surface modification is introduced. Aqueous sodium chloride is successfully encapsulated within an elastomeric casing with a pattern and this sensor is capable of measuring large strain of even up to about 40%. This method is suggested as an industrial fabrication technique for the strain sensor. The use of ionic liquids for green chemistry has been suggested for years and its use as an electrical conductive media in large strain sensor technology is found to be direct and environmentally friendly.

In this paper, an improved design of a capacitive micromachined ultrasonic transducer (CMUT) is presented. The design improvement aims to address the reliability issues of a CMUT and to extend the device operation beyond the contact (collapse) voltage. The major design novelty is the isolation posts in the vacuum cavities of the CMUT cells instead of full-coverage insulation layers in conventional CMUTs. This eliminates the contact voltage drifting due to charging caused by the insulation layer, and enables repeatable CMUT operation in the post-contact regime. Ultrasonic tests of the CMUTs with isolation posts (PostCMUTs) in air (electrical input impedance and capacitance vs. bias voltage) and immersion (transmission and reception) indicate acoustic performance similar to that obtained from conventional CMUTs while no undesired side effects of this new design is observed.

Microchannels (0.05–1 mm) improve gas routing in proton exchange membrane fuel cells, but add to the complexities of water management. This work microfabricates experimental structures with distributed water injection as well as with heating and temperature sensing capabilities to study water formation and transport. The samples feature optical access to allow visualization and distributed thermometry for investigation of two-phase flow transport phenomena in the microchannels. The temperature evolution along the channel is observed that the temperature downstream of the distributed water injection decreases as the pressure drop increases. As the water injection rate is lower than 200 μl/min, there exists a turning point where temperature increases as the pressure drop increases further. These micromachined structures with integrated temperature sensors and heaters are key to the experimental investigation as well as visualization of two-phase flow and water transport phenomena in microchannels for fuel cell applications.

Polymer Electrolyte Membrane (PEM) fuel cells incorporating microchannels ( D