Enhanced Visualization of Biopsy Needle using a MEMS Actuator Precise localization of needle tip is important for the biopsy. A mini actuator that radiates a low-intensity ultrasound burst was manufactured with MEMS technology. Interference between the radiated and diagnostic pulses was observed as bright lines in the sonography, from which the needle tip can be recognized with ease. PZT wafer sputtered with electrodes on both sides was cut into 1 mm × 1 mm dies. The PZT die was bonded between two flexible electrodes patterned on liquid crystal polymer (LCP). The whole device was dip coated with a thin layer of PDMS as water proof treatment. The fundamental resonance is at 2.06 MHz, and the PDMS thin film has a damping effect on the transducer as seen by the reduced Q factors. The visualization of the biopsy needle in a breast phantom was evaluated by an ultrasound imaging system. When the actuator was turned on, bright and clear lines in a conical shape appeared in the sonography B-mode imaging, from which the location of the actuator could be determined with ease. For more information, please refer to: Zhiyuan Shen , Yufeng Zhou, Jianmin Miao, and Vu Kien Fong, “Enhanced v isualization of fine needle under sonographic guidance using a MEMS actuator” , Sensors . 15, (2015), pp. 3107-3115.
A Wireless Accelerometer Using Micromachined Piezoelectric Sensor Vibration monitoring is often carried out for machines fault diagnosis. The state of art vibration sensors are manually and repetitively installed, which causes inconsistency in the measurement results. The long cables, large mass and size, protruding profile of the sensors interfere with the testing results. The objective of this project is to realize a miniaturized, low profile wireless battery-powered accelerometer system with a piezoelectric MEMS sensing element for machines vibration monitoring. The MEMS sensor element comprises a frame, four suspending beams, and a seismic mass. Four sets of interdigited electrodes on the four beams are for charge collection. Finite element model simulation shows that the fundamental resonance is 7.3 kHz and the charge sensitivity at 1 kHz is 0.13 pC/N. Microfabrication results The packaged wireless piezoelectric accelerometer consists of the piezoelectric sensing element, a charge amplifier and attenuator, an analog to digital converter (ADC), a programmable microcontroller (MCU), a battery, and a RF transceiver connected to an antenna. The low profile of the package, with the size of 28.50 cm 3 and weight of 67.50 g, is smaller and lighter than the commercial wireless accelerometers found on the market (2014). The effects of the device package on the dynamic response of the wireless piezoelectric accelerometer are investigated, and two mechanisms been implemented in the package to eliminate the electromagnetic interference (EMI): 1, shielding materials are inserted in the packaging; 2, the ground of the sensing element and the ground of the charge amplifier circuit are shorted to avoid the “ground loop” effect. The sensitivity frequency spectra with a c omparison among the different grounding and shielding conditions . The resonance at 7.7 kHz agrees with the numerical simulation result. The packaging did not introduce any resonance lower than the fundamental resonance of the bending-mode sensing element, which secured the maximum utilization of the dynamic frequency range provided by the sensing element. After noise suppression, t he experimentally measured charge sensitivity at 1 kHz is 31.2 mV/g. Field test: comparison between the vibration spectra detected by our accelerometer and a commercial cabled accelerometer (4525B, Triaxial DeltaTron, BK, Denmark). For more information, please refer to: Zhiyuan Shen , Yi Fan Chen, Lei Zhang, Chin Yaw Tan, and Kui Yao, “A Wireless Accelerometer Using Micromachined Piezoelectric Sensor”. ISAF-ISIF-PFM 2015 , (2015), Singapore. (Oral presentation) Kui Yao, Zhiyuan Shen , Chin Yaw Tan, Yi Fan Chen, and Lei Zhang, “A wireless piezoelectric accelerometer for vibration monitoring”. (filed) Kui Yao, Chin Yaw Tan, Szu Cheng Lai, Lei Zhang, Zhiyuan Shen , and Yifan Chen, “Ferroelectrics for wireless sensor and transducer applications”, CIMTEC 2014 - 13th International Ceramics Congress, (2014), Montecatini Terme, Italy.
Piezoelectric Energy Harvester The resonance frequency of a MEMS structure is usually quite high compared to the frequencies of the environmental vibrational sources. A mass was loaded at the centre of the in-plane poled piezoelectric diaphragm to lower its resonance. A receptance model is built to explain the resoance of the diaphragm-mass combined system. The receptance model is an approach used to predict the vibrational characteristics of a combined system from the characteristics of indiviual components. The optimized working condition of the diaphragm was tested. The diaphragm-based energy harvester shows the maximum power when it works at its anti-resonance and the load impedance matches the output impedance of the piezoelectric diaphragm. The resonance drop very fast with little mass and the drop rate becomes slow with bigger mass. The resonance frequency change predicted by the receptance model agrees with the measured results. The voltage and power received by the energy harvester crossing the optimized load versus acceleration. A power density of 22.59 μW/cm 2 was realized. The research opens the way to making use of combined system dynamics to control the vibration of piezoelectric MEMS energy harvesters. For more information, please refer to: , Zhiyuan Shen , Shuwei Liu , Jingyu Lu, Jianmin Miao, Lye Sun Who, Zhihong Wang, “Spiral electrode d33 mode piezoelectric diaphragm combined with proof mass as energy harvester” , Journal of Micromechanics and Microengineering ， 25 ， (2015), pp. 035004. , Zhiyuan Shen , Shuwei Liu, Jianmin Miao, Lye Sun Woh and Zhihong Wang, “Proof mass effects on spiral electrode d33 mode piezoelectric diaphragm-based energy harvester”, IEEE MEMS 2013 , January, (2013), Taipei. , Zhiyuan Shen , Shuwei Liu, Haobing Liu, Kottapalli Ajay Giri Prakash, Jianmin Miao, Lye Sun Woh, “Piezoelectric d33 mode diaphragm energy harvester for self-powered sensor application”, IEEE Sensors , October, (2012), Taipei.
Acoustic Transducer Dimension of the in-plane poled piezoelectric diaphragm: electrode width=60 μ m; electrode spacing=250 μ m; radius=3.5 mm. The effective coupling coefficient is 3.08 %. The quality factor Q value is 39.96. Schematic diagram of the test setup for evaluating the acoustic transmission performance of the devices. The setup was in an anechoic chamber. A BK 4196 microphone with known sensitivity as reference. Both the sensitivity and the sound pressure level (SPL= 20log(sound pressure /20 μ Pa)), peaks appear at the resonance of 13.71 kHz. The 1 kHz sensitivity of the d 33 mode diaphragm (126.21 μ V/Pa), is nearly 20 times of the sensitivity (6.5 μ V/Pa) of a d 31 mode thick film diaphragm with the same material and similar dimensions. A 3 × 3 array was fabricated. Each element can be controlled independently. Directivity pattern of the array was tested. The array has the potential to be used as a phase array. For more information, please refer to: Zhiyuan Shen , Jingyu Lu, Chee Wee Tan, Jianmin Miao, Zhihong Wang, “ d 33 mode piezoelectric diaphragm based acoustic transducer with high sensitivity” , Sensor and Actuator A: Physical , 189, (2013), pp. 93-99.
In-plane Poled Piezoelectric Diaphragm Double-sided spiral electrodes can generate an in-plane poling scheme. The diaphragm utilizes d 33 effect to generate the in-plane strain (thus a d 33 mode transducer ), which is converted to an out-of-plane displacement due to the constrained boundary condition. Due to the fact that d 33 is ~2 times the magnitude of d 31 in piezoelectric ceramics, and that the electrode spacing s can be much larger than the piezoelectric film thickness t , the sensitivity of the d 33 mode transducer can be much larger than the sensitivity of a d 31 mode transducer (sandwich structure). The polarization has a distribution in the diaphragm due to the patterned electrode. In the uniform field modeling , the 3-D diaphragm is simplified as a two dimensional model, which is then subdivided into several areas. Polarization in each area is supposed to be uniform. Areas under electrodes are unpoled and areas between electrodes are uniformly poled radially outward or inward. In the distributed material model (a),the poling electric field was simulated (b). The electric field strength in each element was compared with the coercive field of the material. The polarization in each element was adjusted to align with the electric field by executing a program code (c)(d). Fabrication process flow: (a) PZT wafer was coated with photoresist. (b) Deposition of Cr/Au. (c) Patterning of top-side electrode by lift-off process. (d) Patterning of bottom-side electrode by lift-off process. (e) PMMA substrate was drilled with through holes using a laser. (f) PDMS soft mold was molded. (g) Epoxy precursor was tape casted. (h) Soft mold was demolded. (i) PMMA and PZT were bonded. (j) Another PMMA part was bonded on the top. A diaphragm bearing double-sided electrode can be driven in several configurations. The quasi-static displacement of the diaphragm center was characterized by a laser Doppler vibrometer. A configuration (d)(4) was found to be most efficient in generating displacement. In this configuration, the stress on the top and on the bottom of the diaphragm have different polarization. A single layer device behaves as a bimorph. The impedance spectra was characterized by a impedance analyzer. Coupling coefficient and quality factor were calculated based on some characteristic frequencies on the impedance spectra. The resonances of the diaphragm follows the circular plate vibrational model. Different driving configurations can effectively excite different resonances. A single bell rings with two pitches. For more information, please refer to: Zhiyuan Shen , Mohamad Olfatnia, Jianmin Miao, and Zhihong Wang, “Displacement and resonance behaviors of a piezoelectric diaphragm driven by a double-sided spiral electrode”, Smart Materials and Structures , 21, (2012), pp. 055001.
Ming Liu and Fuqian Yang, Finite element simulation of the effect of electric boundary conditions on the spherical indentation of transversely isotropic piezoelectric films, Smart Materials and Structures 21 (2012) 105020 (10pp) Finite element simulation was used to analyze the effect of electric boundary conditions on the indentation deformation of a transversely isotropic piezoelectric film with the contact radius much larger than the film thickness. Six different combinations of electric boundary conditions were used. The simulation results showed that the indentation load is proportional to the square of the indentation depth and the indentation-induced electric potential at the contact center is a linear function of the ratio of the indentation depth to the film thickness for all six cases. The contact stiffness is proportional to the contact area and inversely proportional to the film thickness. The nominal piezoelectric charge coefficient d33 is inversely proportional to the derivative of the electric potential with respect to the indentation depth for the indentation of a piezoelectric film by a conducting indenter with a grounded, rigid substrate.
标签: piezoelectric
