Wenjun Liao

Evaluation of breast tumor margins in vivo with intraoperative photoacoustic imaging

The use of photoacoustic effect is a promising approach for biomedical imaging in living tissues. Photoacoustic tomography (PAT) has been demonstrated to image breast cancer, brain vasculature, arthritis and seizure focus owing to its rich optical contrast and high resolution in a single imaging modality. Here we report a microelectromechanical systems (MEMS)-based intraoperative PAT (iPAT) technique, and demonstrate its ability to accurately map tumors in three-dimension and to inspect the completeness of tumor resection during surgery in a tumor-bearing mouse model. The MEMS imaging probe is small and has the potential to be conveniently used to guide surgical resection of tumors in the breast.

A Tip-Tilt-Piston Micromirror With Symmetrical Lateral-Shift-Free Piezoelectric Actuators

In this paper, we present the design, fabrication, and characterization of a high-fill-factor tip-tilt-piston micromirror actuated by four symmetrical lateral-shift-free (LSF) piezoelectric actuators. Lead zirconate titanate (PZT) is the piezoelectric material deposited using a sol-gel process. The micromirror can operate in both piston and rotation modes. At the piston mode, the measured resonant frequency is 990 Hz. An 18.3-μm piston displacement is obtained by applying 5 Vdc to four symmetrical LSF (SLSF) actuators. For the rotation mode, the measured resonant frequency is 1650 Hz and an optical deflection angle of 4.2° is measured by applying 5 Vdc to one SLSF actuator. A 2-D resonant scanning pattern is achieved when the PZT micromirror is applied with a 3 Vpp sinusoidal voltage at the resonance frequency.

DEVICE DESIGN FOR THE NOVEL HANDWRITING RECOGNITION SYSTEM

ABSTRACT A microelectromechanical systems-based handwriting system device was designed. We proposed an ominidirectional acoustical sensor microarray which can offer isotropic directional sensitivity with a high radiation acoustic power when it as a transmitter and a high array spatial gain (AG) when it as a receiver. It has been designed for use in the novel handwriting recognition system to attain a large writeable scale and to write in any direction. The proposed array device based on novel ferroelectric thin film has excellent performance, miniature size and high reliability, and could be fabricated with conventional integrated circuit process.

Ultrasonic transducer array design for medical imaging based on MEMS technologies

Piezoelectric micromachined ultrasonic transducer (pMUT) is a new approach to form high frequency arrays for real-time 3-D medical imaging. pMUT arrays based on SOI-Si bonding and PZT-coated membrane structures have been designed in this paper. After simulation, the 6×6 ultrasonic transducer array was fabricated and characterized. The total array area is approximately 2.0 mm by 2.0 mm. The micrograph of the device shows that the physical parameters are consistent with the designed value. The impedance-frequency spectrum of the pMUT was measured by HP 4194A impedance phase analyzer. Resonance frequency and effective electro-mechanical coupling coefficient can be deduced from it. The resonance frequency is 980 KHz, and the effective electro-mechanical coupling coefficient is about 4.64%. Due to its performance, it is promising for medical ultrasonic imaging applications.

Tip-tilt-piston piezoelectric micromirror with folded PZT unimorph actuators

This paper presents the design, fabrication and characterization of a novel tip-tilt-piston (TTP) scanning micromirror based on an array of folded piezoelectric unimorph actuators. The micromirror can perform rotational scan around two in-plane orthogonal axes as well as out-of-plane piston motion. The measured resonant frequencies of the fabricated micromirror are 362 Hz (piston), 685 Hz (x axis scan), 1250 Hz (y axis scan) and 19.2 kHz (fast y axis scan), respectively.

NOVEL DEVICE DESIGN FOR AN ULTRASONIC RANGING SYSTEM

ABSTRACT This paper presents design method and fabrication process of novel devices which were used in the microelectromechanical systems based ultrasonic ranging system. An acoustical transducer microarray operating in d31 mode which can offer strong directionality with a high radiation acoustic power has been developed to enhance the spatial resolution in the pulse-echo measurement in air while an acoustical transducer operating in d33 mode which has a high isotropic receive sensitivity has been designed to expand the system detection range. The proposed devices based on novel ferroelectric thin film has excellent performance, miniature size and high reliability, and could be fabricated with conventional integrated circuit process.

The study of radiation effects in emerging micro and nano electro mechanical systems (M and NEMs)

The potential of micro and nano electromechanical systems (M and NEMS) has expanded due to advances in materials and fabrication processes. A wide variety of materials are now being pursued and deployed for M and NEMS including silicon carbide (SiC), III–V materials, thinfilm piezoelectric and ferroelectric, electro-optical and 2D atomic crystals such as graphene, hexagonal boron nitride (h-BN), and molybdenum disulfide (MoS2). The miniaturization, Semiconductor Science and Technology Semicond. Sci. Technol. 32 (2017) 013005 (14pp) doi:10.1088/1361-6641/32/1/013005 15 Author to whom any correspondence should be addressed. 0268-1242/17/013005+14

PMUT array design for a handwriting input system

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Total-Ionizing-Dose Effects in Piezoresistive Micromachined Cantilevers

The novel handwriting input system (HIS) has been designed with the ferroelectrics-based micro-acoustic array, which has been fabricated using silicon based micro-machining process. This array is composed of two acoustic dipoles. It can increase output acoustic power effectively while maintaining omni-direction.

Miniature photoacoustic imaging probe using MEMS scanning micromirror

We evaluate the response of T-shaped, asymmetric, piezoresistive, micromachined cantilevers fabricated on p-type Si to 10-keV X-ray irradiation. The resonant frequency decreases by 25 ppm at 2.1 Mrad(SiO2), and partially recovers during post-irradiation annealing. An explanation of the results is proposed that is based on radiation-induced acceptor depassivation. This occurs because radiation-generated holes release hydrogen from previously passivated acceptors, causing the carrier concentration to increase, especially near the surface. Increased carrier concentration decreases Young’s modulus, resulting in a decrease in the cantilever resonant frequency. Finite element simulations show that the effect of a decreasing Young’s modulus in the surface region is consistent with the measured decrease in resonant frequency in the irradiated devices.