Low-Cost Scalable PCB-Based 2-D Transducer Arrays for Volumetric Photoacoustic Imaging.

Photoacoustic (PA) imaging provides deep tissue molecular imaging of chromophores with optical absorption contrast and ultrasonic resolution. Present PA imaging techniques are predominantly limited to one 2D plane per acquisition. 2D ultrasound transducers, required for real-time 3D PA imaging, are high-cost, complex to fabricate and have limited scalability in design. We present novel PCB-based 2D matrix ultrasound transducer arrays that are capable of being bulk manufactured at low-cost without using laborious ultrasound fabrication tools. The 2D ultrasound array specifications are easily scalable with respect to widely available PCB design and fabrication tools at low cost. To demonstrate scalability, we fabricated low (11 MHz) frequency 8x8 matrix array and high (40 MHz) frequency 4x4 matrix array by directly bonding an undiced polyvinylidene fluoride (PVDF) piezoelectric material of desired thickness to the custom designed PCB substrate. Characterization results demonstrate wideband PA receive sensitivity for both low (87%) and high (188%) frequency arrays. Volumetric PA imaging results of light absorbing targets inside optical scattering medium demonstrate improved spatial resolution and field of view with increase in aperture size.

Unusual Presentation of Reversible Transient Vision Loss After Caesarean Section Under Subarachnoid Block: A Case Report.

A transient vision loss is not commonly encountered during the postoperative period following a caesarean section. Although numerous causes have been suggested for transient vision loss, when loss of vision is associated with seizures and headaches, the differential diagnoses include hemolysis, elevated liver enzymes, low platelet syndrome, reversible cerebral vasoconstriction syndrome, posterior reversible encephalopathy syndrome (PRES), dural venous thrombosis, and central retinal arteriolar occlusion. We report a case of a 35-year-old patient who underwent an elective caesarean section under spinal anaesthesia and developed a headache followed by loss of vision and seizures during the postoperative period. An MRI scan of the brain on the same day revealed subtle hyperintensity in bilateral parieto-occipital lobes in the cortical and subcortical areas and bilateral cerebral hemispheres, which indicates PRES. Rapid and complete resolution of symptoms was observed with supportive treatment. Therefore, prompt suspicion and effective management of PRES are of paramount importance to prevent short- and long-term neurological deficits.

Effect of Tourniquet Deflation on Intracranial Pressure Measured by Ultrasound of the Optic Nerve Sheath Diameter in Patients Undergoing Orthopedic Surgery Under Spinal Anesthesia: An Observational Study.

Background Orthopedic surgeries of the lower extremities frequently require exsanguination and the use of pneumatic tourniquets. However, the deflation of the tourniquet is accompanied by predominant metabolic changes such as an increase in PaCO2. Prior studies have reported the existence of a correlation between tourniquet deflation and an increase in intracranial pressure in patients undergoing surgery under general anesthesia. However, there is a dearth of literature demonstrating such relationships among patients undergoing surgery under subarachnoid block in the Indian setting. The present research was conducted to study the variations in intracranial pressure after the deflation of the tourniquet by measuring the optic nerve sheath diameter (ONSD) using ultrasound among patients undergoing orthopedic surgery of the lower limb under spinal anesthesia at a tertiary care hospital in eastern India. Methodology After obtaining clearance from the Institutional Ethics Committee, this prospective observational study was conducted among 45 patients undergoing orthopedic surgeries of the lower limb using a pneumatic tourniquet. Changes in intracranial pressure following tourniquet deflation were recorded by measuring ONSD by ultrasound in these patients. Heart rate (HR), mean arterial pressure (MAP), SpO2, EtCO2, and ONSD were noted 15 minutes before administration of subarachnoid block (T0), just before tourniquet deflation (T1) and at 5, 10, and 15 minutes after tourniquet deflation (T5, T10, and T15, respectively). Results The ONSD varied significantly at each point of observation (p < 0.05). The ONSDs at 5 and 10 minutes after the deflation of the tourniquet were significantly greater than that at T0 (p = 0.002). EtCO2 showed a significant increase compared to baseline values at every point of observation intraoperatively whereas MAP showed a significant decrease (p < 0.05). For all parameters (ONSD, HR, systolic blood pressure, diastolic blood pressure, MAP, and EtCO2), the most significant change in observation was noted at T10, i.e., 10 minutes after the deflation of the tourniquet.   Conclusions The significant finding in this study was that the ONSD measurements recorded by ultrasound were increased after the deflation of the tourniquet and that this change can be attributed to an increase in EtCO2. However, the results obtained cannot be validated outside the present research owing to the observational nature of the study and limited sample size. Thus, it is difficult to arrive at a definitive conclusion. Further large-scale multicentric studies may be needed to substantiate the findings of this study.

A tip-coupled, two-cantilever, non-resonant microsystem for direct measurement of liquid viscosity.

We report a non-resonant piezoelectric microelectromechanical cantilever system for the measurement of liquid viscosity. The system consists of two PiezoMEMS cantilevers in-line, with their free ends facing each other. The system is immersed in the fluid under test for viscosity measurement. One of the cantilevers is actuated using the embedded piezoelectric thin film to oscillate at a pre-selected non-resonant frequency. The second cantilever, the passive one, starts to oscillate due to the fluid-mediated energy transfer. The relative response of the passive cantilever is used as the metric for the fluid's kinematic viscosity. The fabricated cantilevers are tested as viscosity sensors by carrying out experiments in fluids with different viscosities. The viscometer can measure viscosity at a single frequency of choice, and hence some important considerations for frequency selection are discussed. A discussion on the energy coupling between the active and the passive cantilevers is presented. The novel PiezoMEMS viscometer architecture proposed in this work will overcome several challenges faced by state-of-the-art resonance MEMS viscometers, by enabling faster and direct measurement, straightforward calibration, and the possibility of shear rate-dependent viscosity measurement.

Electric current-assisted manipulation of liquid metals using a stylus at micro-and nano-scales.

A novel methodology, based on wetting and electromigration, for transporting liquid metal, over long distances, at micro-and nano-scale using a stylus is reported. The mechanism is analogous to a dropper that uses 'suction and release' actions to 'collect and dispense' liquid. In our methodology, a stylus coated with a thin metal film acts like the dropper that collects liquid metal from a reservoir upon application of an electric current, holds the liquid metal via wetting while carrying the liquid metal over large distances away from the reservoir and drops it on the target location by reversing the direction of electric current. Essentially, the working principle of the technique relies on the directionality of electromigration force and adhesive force due to wetting. The working of the technique is demonstrated by using an Au-coated Si micropillar as the stylus, liquid Ga as the liquid metal to be transported, and a Kleindiek-based position micro-manipulator to traverse the stylus from the liquid reservoir to the target location. For demonstrating the potential applications, the technique is utilized for closing a micro-gap by dispensing a minuscule amount of liquid Ga and conformally coating the desired segment of the patterned thin films with liquid Ga. This study confirms the promising potential of the developed technique for reversible, controlled manipulation of liquid metal at small length scales.

Manipulating liquid metal flow for creating standalone structures with micro-and nano-scale features in a single step.

Standalone structures with periodic surface undulations or ripples can be spontaneously created upon flowing a liquid metal, e.g. Ga, over a metallic film, e.g. Pt, Au, etc, through a complex 'wetting-reaction'-driven process. Due to the ability of 3-dimensional patterning at the small length scale in a single step, the liquid metal 'ripple' flow is a promising non-conventional patterning technique. Herein, we examine the effect of a few process parameters, such as distance away from the liquid reservoir, size of the liquid reservoir, and the geometry, thickness, and width of substrate metal film, on the nature of the ripple flow to produce finer patterns with feature sizes of ≤ 2µm. The height and the pitch of the pattern decrease with distance from the liquid reservoir and decrease in the reservoir volume. Furthermore, a decrease in the thickness and width of the substrate film also leads to a decrease in the height and pitch of the ripples. Finally, the application of an external electric field also controls the ripple patterns. By optimizing various parameters, standalone ripple structures of Ga with the height and pitch of ≤ 500 nm are created. As potential applications, the ripple patterns with micro-and nano-scopic features are demonstrated to produce a diffraction grating and a die for micro-stamping.

Spontaneous Formation of Structures with Micro- and Nano-Scopic Periodic Ripple Patterns.

We report the first study on the formation of structures with micro- and nano-scopic periodic surface patterns created by the spontaneous flow of liquid metal over thin metallic solid films. Minute details of the flow of liquid gallium over gold are captured in situ at very high magnifications using a scanning electron microscope, and a series of experiments and microstructural characterization are performed to understand the underlying principles of the liquid flow and the pattern formation. This phenomenon is solely driven by wetting, with little influence of gravity, and is aided by a tenacious semi-solidus envelope of the intermetallic compound formed due to the reaction between the liquid metal and the metallic substrate. This complex flow creates highly periodic patterns with features ranging from hundreds of nanometers to tens of micrometers, which can be tuned a priori. We propose a model capturing the essential mechanics of the ripple formation and apply it to simulate the formation of a single ripple, along with its essential asymmetry, that forms the basis for generating the observed patterns.

The mechanics of acoustic signal evolution in field crickets.

Field crickets (Family Gryllidae, Subfamily Gryllinae) typically produce tonal calls with carrier frequencies in the range 3-8 kHz. In this study, we explored the use of a finite element model (FEM) of the stridulatory apparatus of a field cricket, Gryllus bimaculatus, based on experimental measurements of resonator geometry and mechanical properties, to predict the measured call carrier frequencies of eight other field cricket species, ranging between 3 and 7 kHz. The model allowed accurate predictions of carrier frequencies for all eight species to within a few hundred hertz from morphological measurements of their resonators. We then used the model to explore the plausible evolutionary design space for field cricket call carrier frequency along the axes of resonator size and thickness, and mapped the locations of the nine experimentally measured species in this design space. Although the nine species spanned the evolutionarily conserved spectrum of carrier frequency and body size in field crickets, they were clustered in a small region of the available design space. We then explored the reasons for this apparent evolutionary constraint on field cricket carrier frequencies at both the lower and higher limit. We found that body size and sound radiation efficiency were the main constraints at the lower limits, whereas the energetics of stridulation using the clockwork mechanism may pose a constraint at higher frequencies.

A Prospective, Comparative Study to Evaluate the Diagnostic Accuracy of Mallampati Grading in Supine and Sitting Positions for Prediction of Difficult Airway.

Background & aim Difficult airway is a major concern for all anaesthesiologists because failure to secure airway could lead to devastating complications or may increase morbidity and mortality. Airway assessment, therefore, is of paramount importance and anticipating a difficult airway prior to anesthetic administration, could help us in better preparation as well as avoidance of life-threatening complications. There are various tests available to assess the airway, out of which, modified Mallampati test (MLPT) is one of the common, easy and reliable methods to predict difficult airway. Mallampati test, usually is done with patient in sitting position. However, in certain group of patients in whom sitting position is not possible (suspected cervical spine injury, pelvic injury, patients in shock, etc.), the Mallampati test can be done in supine position. Few studies were available which concluded that Mallampati test in supine position was not only reliable but also superior to sitting position, whereas, few other studies contradicted this opinion. We, therefore, wanted to address this issue and tried to find out whether Mallampati test in supine position could offer better diagnostic accuracy or not. Materials & methods Mallampati test (MLPT) in sitting position was done in 100 patients initially in preoperative period and subsequently in supine position inside operating room prior to induction of anesthesia. During laryngoscopy, Cormack-Lehane (CL) grading was noted in all patients. Correlation of Mallampati test in sitting and supine position with Cormack-Lehane grading was obtained. A receiver operating characteristics (ROC) analysis was done to determine the area under the curve, the sensitivity and the specificity. Positive predictive value (PPV) and negative predictive value (NPV) were also calculated to analyse the diagnostic accuracy of Mallampati score (MLPT) in sitting and supine position. Results A toal of 22.2% of patients had difficult intubation (CL grade 3) although MLPT of these patients in sitting position anticipated a non-difficult airway (MLPT 1 and 2) and there was no significant correlation between MLPT grade in sitting position with the Cormack-Lehane grade. In comparison to sitting position, MLPT in supine position had significant correlation with the Cormack-Lehane grading and all patients with supine MLPT 1 and 2 (non-difficult airway) had easy intubation (CL grade 1 and 2). ROC analysis also showed that MLPT grade in supine position had superior correlation and better diagnostic accuracy than MLPT in sitting position for assessment of airway as indicated by higher sensitivity and better positive as well as negative predictive values. Conclusion Mallampati test done in supine position has far greater sensitivity and is superior in predicting difficult intubation as compared to MLPT done in conventional sitting position.

Introducing Water Electrolithography.

High-resolution patterning with remarkable customizability has stimulated the invention of numerous scanning probe lithography (SPL) techniques. However, frequent tip damage, substrate-film deterioration, low throughput, and debris amassing in the patterned region are the inherent impediments that have precluded obtaining patterns with high repeatability using SPL. Hence, SPL still has not got wider acceptance for industrial fabrication and technological applications. Here, we introduce a novel SPL technique, named water electrolithography (W-ELG), for patterning at the microscale and potentially at the nanoscale also. The technique operates in the non-contact mode and is based on the selective etching, via an electrochemical process, of a metallic film (e.g., Cr) submerged into water. Here, the working of W-ELG is demonstrated by scribing a pattern into the Cr film by a traversing cathode tip along a preset locus. A numerical analysis establishing the working principles and optimization strategies of W-ELG is also presented. The tip-sample distance and tip-diameter are identified as the critical parameters controlling the pattern creation. W-ELG achieved a throughput of 1.5 × 107 µm2/h, which is the highest among the existing SPL techniques, while drawing 4 µm wide lines, and is also immune to deleterious issues of tip damage, debris amassment, etc. Therefore, the resolution of these inherent impediments of SPL in W-ELG sets the stage for a paradigm shift that may now translate the SPL from academic exploration to industrial fabrications.

Self-Resolving Mobitz Type II Second-Degree Heart Block (Atypical Wenckebach Block) After Cesarean Section Under Subarachnoid Block: A Case Report.

The majority of the perioperative arrhythmias in patients undergoing cesarean section under spinal anesthesia are benign. We report a case of a 30-year-old full-term parturient with a history of an uneventful previous cesarean section. She had no preexisting comorbidities. She subsequently underwent another emergency cesarean section three years later due to abdominal pain and scar tenderness indicative of impending rupture. Two hours after an uneventful surgery, the patient developed epigastric pain with a prolonged PR interval (280 ms) and intermittent second-degree AV block with two consecutive blocked P waves, which was consistent with Mobitz type II second-degree heart block (atypical Wenckebach block). However, she remained hemodynamically stable throughout. Serial electrocardiogram (ECG) did not demonstrate any evidence of ST-T wave changes, and normal troponin I and echocardiography excluded myocardial ischemia as a potential cause for the arrhythmia. Normal serum electrolytes and the resolution of the sensorimotor block caused by the spinal anesthesia excluded other known causes for such ECG changes. The PR interval gradually decreased to 240 ms on the second postoperative day and normalized to 200 ms on the fifth postoperative day. Such patients, especially those with a wide QRS complex, are susceptible to developing dangerous ventricular arrhythmias that can adversely affect circulatory function. Close vigil is the key to avoiding adverse perioperative outcomes.

First example of engineered ß-cyclodextrinylated MEMS devices for volatile pheromone sensing of olive fruit pests.

Olive oil is more preferred than other vegetable oils because of the increasing health concern among people throughout the world. The major hindrance in large-scale production of olive oil is olive fruit pests which cause serious economic damage to the olive orchards. This requires careful monitoring and timely application of suitable remedies before pest infestation. Herein we demonstrate efficacious utilization of covalently functionalized ß-cyclodextrinylated MEMS devices for selective and sensitive detection of female sex pheromone of olive fruit pest, Bactocera oleae. Two of the MEMS devices, silicon dioxide surface-micromachined cantilever arrays and zinc oxide surface-microfabricated interdigitated circuits, have been used to selectively capture the major pheromone component, 1,7-dioxaspiro[5,5]undecane. The non-covalent capture of olive pheromones inside the ß-cyclodextrin cavity leads to the reduction of resonant frequency of the cantilevers, whereas an increase in resistance has been found in case of zinc oxide derived MEMS devices. Sensitivity of the MEMS devices towards the olive pheromone was found to be directly correlated with the increasing availability of ß-cyclodextrin moieties over the surface of the devices and thus the detection limit of the devices has been achieved to a value as low as 0.297 ppq of the olive pheromone when the devices were functionalized with one of the standardized protocols. Overall, the reversible usability and potential capability of the suitably functionalized MEMS devices to selectively detect the presence of female sex pheromone of olive fruit fly before the onset of pest infestation in an orchard makes the technology quite attractive for viable commercial application.

On-chip silicon photonics based grating assisted vibration sensor.

We present a compact, highly sensitive and scalable on-chip photonic vibration measurement scheme for vibration sensing. The scheme uses a silicon photonic diffraction-grating based sensor integrated underneath a silicon cantilever. We demonstrate a static and dynamic measurement sensitivity (ΔT/Δgap) of 0.6 % change in intensity per nm displacement. The electrostatically driven dynamic response measurement of the grating based sensor shows an excellent agreement with commercial Laser Doppler Vibrometer (LDV) measurement. We demonstrate the thermo-mechanical noise measurement on the cantilever in ambience, which is verified using LDV. A minimum displacement of 1.9 pm is measured with a displacement sensitivity of 10 µW/nm for a measurement bandwidth of 16 Hz. The demonstrated sensitivity is 2 orders of magnitude better than that obtained from measurements of static displacement. We also present a detailed 2D-FDTD simulation and optimization of the grating-based sensor to achieve maximum displacement sensitivity.

Effectiveness of Granisetron in Prevention of Hypotension Following Spinal Anaesthesia in Patients Undergoing Elective Caesarean Section.

BACKGROUND AND AIM: Spinal anesthesia is the most common type of anesthesia administered for caesarean section and it is frequently associated with hypotension. When post-spinal hypotension is accompanied with bradycardia, the condition may become more complicated. Numerous pharmacological agents have therefore been tried for prevention of hypotension and 5HT3 antagonists are the latest in the armamentarium. However, studies have shown conflicting evidence regardings the effectiveness of 5HT3 inhibitors (ondansetron and granisetron) in preventing spinal hypotension. We have tried to address this controversy and also wanted to explore the adverse effects of granisetron on the foetus, if any. MATERIALS AND METHODS: Two hundred patients were included in the study and divided into two groups of 100 patients each. Group S patients received 5ml of 0.9% normal saline while Group G patients received IV granisetron 1mg (diluted to 5ml) 10 minutes prior to administration of spinal anesthesia. Analysis of variance (ANOVA) test was used for comparing the data, Student t-test was applied to compare the difference between the two means and Chi-Square test was used to test significance of difference of proportions. RESULTS: The incidence of hypotension in Group S was 69%, whereas it was 37% in Group G (p<0.001), hence patients of Group S required a significantly higher (p=0.001) amount of mephentermine. Haemodynamic parameters were well maintained throughout the study period in patients of Group G. The neonatal outcome was assessed by Apgar score at 0 minutes, one minute, and five minutes after delivery, and it was comparable between the two study groups. CONCLUSION: Intravenous granisetron 1mg if administered before administering spinal anesthesia can effectively attenuate hypotension in parturients without any adverse effects on the mother and the neonate.

A Photoacoustic Imaging Device Using Piezoelectric Micromachined Ultrasound Transducers (PMUTs).

A linear piezoelectric micromachined ultrasound transducer (PMUT) array was fabricated and integrated into a device for photoacoustic imaging (PAI) of tissue phantoms. The PMUT contained 65 array elements, with each element having 60 diaphragms of [Formula: see text] diameter and [Formula: see text] pitch. A lead zirconate titanate (PZT) thin film was used as the piezoelectric layer. The in-air vibration response of the PMUT array elements showed a first mode resonance between 6 and 8 MHz. Hydrophone measurements showed 16.2 kPa average peak ultrasound pressure output at 7.5 mm from one element excited with 5 Vpp input. A receive sensitivity of ~0.48 mV/kPa was observed for a PMUT array element with 0 dB gain. The PMUT array was bonded to a custom-printed circuit board to enable compact integration with an optical fiber bundle for PAI. A broad photoacoustic bandwidth of ~89% was observed for the photoacoustic response captured from absorbing pencil lead targets. Linear scanning of a single element of a PMUT array was performed on different tissue phantoms embedded with light-absorbing targets to successfully demonstrate B-mode PAI using PMUTs.

Comparative analysis of APACHE-II and P-POSSUM scoring systems in predicting postoperative mortality in patients undergoing emergency laparotomy.

BACKGROUND: Laparotomy remains one of the commonest emergency surgical procedures. Early prognostic evaluation would aid in selecting the high-risk patients for an aggressive treatment. Awareness about risks could potentially contribute to the quality of perioperative care and optimum utilization of resources. Portsmouth modification of Physiological and operative severity for the enumeration of mortality and morbidity (P-POSSUM) and the acute physiology and chronic health evaluation II (APACHE-II) have been the most widely used scoring systems for emergency laparotomies. It is always better to have a single scoring system to predict outcomes and audit healthcare organizations. AIM: To compare the ability of APACHE-II and P-POSSUM to predict postoperative morbidity and mortality in patients undergoing emergency laparotomy. METHODS: All patients undergoing emergency laparotomy at the Tata Main Hospital, Jamshedpur between December 2013 and November 2014 were included in the study. In this observational study, P-POSSUM and APACHE-II scoring were done, and the outcome analysis evaluated with mortality being the primary outcome. RESULTS: For P-POSSUM, at a cut off value of 63 to predict mortality using receiver operating characteristics curve analysis, the area under the curve was 0.989; and for APACHE-II, at the cut off value of 24, the area under the curve was 0.965. CONCLUSION: Because the ability of APACHE-II to predict mortality was similar to P-POSSUM and APACHE-II does not need scoring for intra-operative findings and histopathology reports, APACHE-II can be used pre-operatively to assess the risk in patients undergoing emergency laparotomy. However, for audit purposes, either of the two scoring systems can be used.

Thin Film PZT-Based PMUT Arrays for Deterministic Particle Manipulation.

Lead zirconate titanate (PZT)-based piezoelectric micromachined ultrasonic transducers (PMUTs) for particle manipulation applications were designed, fabricated, characterized, and tested. The PMUTs had a diaphragm diameter of 60 [Formula: see text], a resonant frequency of ~8 MHz, and an operational bandwidth (BW) of 62.5%. Acoustic pressure output in water was 9.5 kPa at 7.5 mm distance from a PMUT element excited with a unipolar waveform at 5 Vpp . The element consisted of 20 diaphragms connected electrically in parallel. Particle trapping of 4 [Formula: see text] silica beads was shown to be possible with 5 Vpp unipolar excitation. Trapping of multiple beads by a single element and deterministic control of particles via acoustophoresis without the assistance of microfluidic flow were demonstrated. It was found that the particles move toward diaphragm areas of highest pressure, in agreement with literature and simulations. Unique bead patterns were generated at different driving frequencies and were formed at frequencies up to 60 MHz, much higher than the operational BW. Levitation planes were generated above the 30 MHz driving frequency.

Reversible defect engineering in graphene grain boundaries.

Research efforts in large area graphene synthesis have been focused on increasing grain size. Here, it is shown that, beyond 1 µm grain size, grain boundary engineering determines the electronic properties of the monolayer. It is established by chemical vapor deposition experiments and first-principle calculations that there is a thermodynamic correlation between the vapor phase chemistry and carbon potential at grain boundaries and triple junctions. As a result, boundary formation can be controlled, and well-formed boundaries can be intentionally made defective, reversibly. In 100 µm long channels this aspect is demonstrated by reversibly changing room temperature electronic mobilities from 1000 to 20,000 cm2 V-1 s-1. Water permeation experiments show that changes are localized to grain boundaries. Electron microscopy is further used to correlate the global vapor phase conditions and the boundary defect types. Such thermodynamic control is essential to enable consistent growth and control of two-dimensional layer properties over large areas.

Over 15 MA/cm2 of critical current density in 4.8 µm thick, Zr-doped (Gd,Y)Ba2Cu3Ox superconductor at 30 K, 3T.

An Advanced MOCVD (A-MOCVD) reactor was used to deposit 4.8 µm thick (Gd,Y)BaCuO tapes with 15 mol% Zr addition in a single pass. A record-high critical current density (J c ) of 15.11 MA/cm2 has been measured over a bridge at 30 K, 3T, corresponding to an equivalent (I c ) value of 8705 A/12 mm width. This corresponds to a lift factor in critical current of ~11 which is the highest ever reported to the best of author's knowledge. The measured critical current densities at 3T (B||c) and 30, 40 and 50 K, respectively, are 15.11, 9.70 and 6.26 MA/cm2, corresponding to equivalent Ic values of 8705, 5586 and 3606 A/12 mm and engineering current densities (J e ) of 7068, 4535 and 2928 A/mm2. The engineering current density (J e ) at 40 K, 3T is 7 times higher than that of the commercial HTS tapes available with 7.5 mol% Zr addition. Such record-high performance in thick films (>1 µm) is a clear demonstration that growing thick REBCO films with high critical current density (J c ) is possible, contrary to the usual findings of strong J c degradation with film thickness. This achievement was possible due to a combination of strong temperature control and uniform laminar flow achieved in the A-MOCVD system, coupled with optimization of BaZrO3 nanorod growth parameters.

Evaluation of High Frequency Piezoelectric Micromachined Ultrasound Transducers for Photoacoustic Imaging.

In this work, the design, fabrication, and characterization of piezoelectric micromachined ultrasound transducer (PMUT) arrays for photoacoustic imaging applications are reported. An 80-element linear PMUT array with each element having 53 PMUT cells of 125 µm cell diameter were fabricated using 650 nm thick lead zirconate titanate (PZT) as the active piezoelectric layer. The PMUTs are designed to operate at ~10 MHz resonant frequency. The PMUT elements are validated for photoacoustic imaging using an agar gel phantom with embedded pencil leads as the imaging target. Photoacoustic A-line response of the targets captured by single PMUT element shows ~7 MHz center frequency with ~4.8 MHz bandwidth. B-mode images reconstructed from A-lines recorded during the linear scanning of a single element clearly imaged all the targets, thus validating the potential of the fabricated PMUTs for photoacoustic imaging.