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This paper presents a microfabricated nozzleless acoustic droplet ejector with electrically tunable droplet size as a new tool for on-demand picking and placing semiconductor chips for semiconductor packaging. The ejector is based on a 2-mm-thick lead zirconate titanate (PZT) sheet with a planar annular-ring air-cavity acoustic Fresnel lens on top. When driven with sinusoidal pulsed voltage signals of 1.16 MHz, the ejector generates focused ultrasound with 1-mm focal diameter and 5-mm focal depth at 22 mm focal length in sodium polytungstate (SPT) solution. A finite-element-method (FEM) simulation model calculating the acoustic-field-induced fluid motion during the droplet ejection process has been developed, and verified by experiments, in which the device ejects SPT droplets whose diameter is from 850 to 2, $490~\mu \text{m}$ , controlled by the driving pulse width and voltage. The ejected droplets are able to carry 400- $\mu \text{m}$ -thick square silicon chips with side length from 700 to 3, $100~\mu \text{m}$ . A polyester channel-embedded guiding cover for semi-automatic loading of silicon chips to the ejection site is designed to avoid manual placement of the silicon chips. With the proof-of-concept system, we demonstrate ejecting silicon chips out of SPT surface onto a nearby paper, assembling them into arrays with good repeatability. [2020-0337]

Focused ultrasound (FUS) has proven its efficacy in non-invasive, radiation-free cancer treatment. However, the commonly used low-frequency high-intensity focused ultrasound (HIFU) destroys both cancerous and healthy tissues non-specifically through extreme heat and inertial cavitation with low spatial resolution. To address this issue, we evaluate the therapeutic effects of pulsed (60 Hz pulse repetition frequency, 1.45 ms pulse width) high-frequency (20.7 MHz) medium-intensity (spatial-peak pulse-average intensity ISPPA < 279.1 W/cm2, spatial-peak temporal-average intensity ISPTA < 24.3 W/cm2) focused ultrasound (pHFMIFU) for selective cancer treatment without thermal damage and with low risk of inertial cavitation (mechanical index < 0.66), in an in vivo subcutaneous B16F10 melanoma tumor growth model in mice. The pHFMIFU with $104~\mu \text{m}$ focal diameter is generated by a microfabricated self-focusing acoustic transducer (SFAT) with a Fresnel acoustic lens. A three-axis positioning system has been developed for automatic scanning of the transducer to cover a larger treatment volume, while a water-cooling system is custom-built for dissipating non-acoustic heat from the transducer surface. Initial testing revealed that pHFMIFU treatment can be applied to a living animal while maintaining skin temperature under 35.6 °C without damaging normal skin and tissue. After eleven days of treatment with pHFMIFU, the treated tumors were significantly smaller with large areas of necrosis and apoptosis in the treatment field compared to untreated controls. Potential mechanisms of this selective, non-thermal killing effect, as well as possible causes of and solutions to the variation in treatment results, have been analyzed and proposed. The pHFMIFU could potentially be used as a new therapeutic modality for safer cancer treatment especially in critical body regions, due to its cancer-specific effects and high spatial resolution.

This paper describes a novel acoustic transducer with dual functionality based on 1-mm-thick lead zirconate titanate (PZT) substrate with a modified air-cavity Fresnel acoustic lens on top. Designed to let ultrasound waves focus over an annular ring region, the lens generates a long depth-of-focus Bessel-like focal beam and multiple trapping zones based on quasi-Airy beams and bottle beams. With 2.32 MHz sinusoidal driving signal at 150 $\text{V}_{\mathrm {pp}}$ , the transducer produces a focal zone with 9.9 mm depth-of-focus and 0.8 MPa peak pressure at a focal length of 31.33 mm. With 2.32 MHz continuous sinusoidal drive at 30–35 $\text{V}_{\mathrm {pp}}$ , the transducer is able to trap multiple polyethylene microspheres (350–1, $000~\mu \text{m}$ in diameter and 1.025–1.130 g/cm3 in density) in water either simultaneously (when suspended by mechanical agitation or released from water surface) or sequentially (when placed one after another with a pipette). The largest particles the transducer could trap are two 1-mm-diameter microspheres stuck together (1.07 mg in weight, lifted by buoyancy and $0.257~\mu \text{N}$ acoustic-field-induced force). When the transducer is moved laterally, some firmly trapped microspheres follow along the transducer’s movement, while being trapped. When trapped, some microspheres can rotate due to the rotation torque generated by the quasi-Airy beams. [2020-0184]

This paper reports a highly sensitive piezoelectric microelectromechanical systems (MEMS) resonant microphone array (RMA) for detection and classification of wheezing in lung sounds. The RMA is composed of eight width-stepped cantilever resonant microphones with Mel-distributed resonance frequencies from 230 to 630 Hz, the main frequency range of wheezing. At the resonance frequencies, the unamplified sensitivities of the microphones in the RMA are between 86 and 265 mV Pa−1, while the signal-to-noise ratios (SNRs) for 1 Pa sound pressure are between 86.6 and 98.0 dBA. Over 200–650 Hz, the unamplified sensitivities are between 35 and 265 mV Pa−1, while the SNRs are between 79 and 98 dBA. Wheezing feature in lung sounds recorded by the RMA is more distinguishable than that recorded by a reference microphone with traditional flat sensitivity, and thus, the automatic classification accuracy of wheezing is higher with the lung sounds recorded by the RMA than with those by the reference microphone, when tested with deep learning algorithms on computer or with simple machine learning algorithms on low-power wireless chip set for wearable applications.

The Breakthrough Starshot Initiative, established in 2016, aims to propel an ultra-lightweight spacecraft to Alpha Centauri using radiation pressure from a high-power, ground-based laser. Nanopatterned silicon nitride has been proposed as a candidate material for the laser sail. In this work, we design and fabricate a silicon nitride photonic crystal with high reflectivity around a laser wavelength of 1064 nm. We demonstrate the ability to shift the resonant features of the laser sail using titanium dioxide coatings and increase the longwave infrared emissivity using polymer coatings. We also characterize the response of the sail to temperature and optical power.

This paper reports a piezoelectric MEMS resonant microphone array for wheezing detection in lung sounds. The microphone array is composed of resonant cantilevers with serpentine support beams, and each of the resonant microphones has an unamplified sensitivity between 34.6 and 131.4 mV/Pa at the resonant frequencies, over a frequency range of 150 - 700 Hz (where wheezing spectral density is most prominent). With the high sensitivity and signal-to-noise ratio, wheezing is distinguished in both frequency domain and time domain, and as high as 97.73% identification accuracy is achieved on automatic classification through deep machine learning, when the resonant microphone array is used to record lung sounds.

This paper presents piezoelectric MEMS microphone arrays for automatic detection of wheezing in lung sound. Very high unamplified sensitivities of 36.3 – 78.2 mV/Pa have been obtained at the resonant frequencies of the microphone array between 200 and 500 Hz where wheezing is typically prominent. Consequently, the acoustic feature of wheezing was distinguished better in both time domain and frequency domain in comparison with a flat-band reference microphone. With this advantage, as high as 97.44% identification accuracy of lung sounds with and without wheezing was achieved, while the same algorithm based on a commercial reference microphone yielded 89.74% accuracy.

This paper presents a novel way of ejecting particles (Polystyrene microspheres) carried by liquid droplets through and from agarose-gel-filled Petri dish with high-intensity focused-ultrasound generated from self-focusing acoustic transducers working on the 3rd, 5th and 9th harmonic resonant frequencies of 1-mm-thick lead zirconate titanate (PZT) sheets. With different designs, the ejection spot area (related to focal size) is varied, so that the number of particles per ejection may be precisely controlled.

This paper describes acoustic thruster and lifter capable of generating propulsion force on-demand from synthetic air jets generated by acoustic waves passing through orifices on a thin plastic (shaped with laser-machining) covering a sound source (audio speaker). The orifice array pattern was optimized through experiments to produce large thrust force. By varying driving condition and operating frequency, the transducer that weighs 603 mg can rotate, or jump 2.8 mm high and 100 mm far, propelled by the air jets. When tested as an acoustic lifter, the transducer is capable of lifting a plastic piece of 299 mg and rotating a metal piece of 20.4 g. The device could also be driven with acoustic signal instead of electrical power.

This paper reports a novel acoustic tweezers with multi-foci linear Fresnel lens that was designed to create a large Bessel beam zone for contactless, non-invasive object trapping in liquid. The tweezers was built on a 1-mm-thick lead zirconate titanate (PZT) substrate with rectangular air-cavity Fresnel lens having multiple focal lengths. With 25 V pp continuous 2.32 MHz sinusoidal drive, the acoustic tweezers is capable of trapping a silicon chip of $5.30\times 0.67\times 0.51\ \text{mm}^{3}$ in size and 3.98 mg in mass along with two $500-\mu\mathrm{m}$ -diameter Polyethylene microspheres.

This paper describes a single-element planar focusing ultrasonic transducer with electrically tunable focal size, through modifying the design of a self-focusing acoustic transducer (SFAT). The transudcer is built on a 1-mm-thlck lead zirconate titanate (PZT) with (1) Fresnel acoustic lens formed with annular rings of air cavities on the top and (2) patterned annular ring electrodes on the bottom. By controlling the number of Fresnel rings being driven from the center, we were able to tune the focal size between 371 and 866 µm, while keeping the focal length at 6 mm, with 2.32 MHz pulsed ultrasound. When tested as a droplet ejector, the transducer ejected water droplets with diameter between 294 and 560 µm (between 13.3 and 92.0 nL in volume), depending on which set of electrodes are actuated.

This paper reports a nozzle-less, heatless droplet ejector capable of ejecting large liquid droplets of 285 μm in diameter with a volume of 12.1 nL. The ejector is built on a 1 mm thick lead zirconate titanate (PZT) sheet covered by Fresnel acoustic lens formed with annular rings of air cavities. With 450 V pp pulsed 2.2 MHz sinusoidal drive, the ejector produces a focused high-intensity acoustic beam at the top surface of liquid contained in a reservoir, and is able to eject liquid droplets from the liquid surface located 5 mm away from the ejector. The ejector consistently ejects one droplet per pulse with a driving pulse width of 18.18 μs, and the highest ejection rate is estimated to be 222 Hz. When the ejector is driven with a pulse of 81.81 μs width, the ejected droplet travels 30 cm upwards before falling down due to gravity and the corresponding initial velocity of the ejected droplet is calculated to be 2.42 m/s.

This paper reports a stackable dual layer coil based on ZnO sacrificial layer and thermal-release-tape transfer technique for electromagnetic energy harvester. The power density of electromagnetic energy harvester can be improved significantly using multilayer coil with high coil turns. Five of microfabricated dual-layer coil plates are stacked for 450 turns for an electromagnetic vibration-energy harvester, which produces 116 μW from 3.6 g vibration at resonant frequency of 160 Hz.

This paper reports a microfabricated ultrasonic transducer based on a piezoelectrically actuated dome-shaped diaphragm supported at the center of a flat square diaphragm. The dome-shaped diaphragm is fabricated by silicon isotropic wet etching while the whole diaphragm including the flat square diaphragm is released by KOH etching with a novel dicing-based front-to-back alignment method. Shadow masks are used for patterned film depositions on 3D dome diaphragm. With 30 Vpp drive voltage, the transducer produces sound pressure level (SPL) as high as 88.21 dB between 10 and 40 kHz when measured at 5 mm away in an open field. The linearity of the sound output as a function of input voltage is measured to be very good. In addition, post-process laser cutting was utilized to form a cantilever-like diaphragm structure, which boosted the maximum SPL to 95.12 dB without degrading the linearity.

This paper reports an electromagnetic vibration-energy harvester with low resonant frequency based on liquid spring composed of ferrofluid. Cylinder magnet array formed by four disc NdFeB magnets is suspended by ferrofluid in a laser-machined acrylic tube which is wrapped by flexible planar coil fabricated with microfabrication process. The magnet array and coil are aligned automatically by the ferrofluid. Restoring force when the magnet array is deviated from the balance position is proportional to the deviated distance, which makes the ferrofluid work as a liquid spring obeying Hook's law. Experimental results show that the electromagnetic energy harvester occupying 1.8 cc and weighing 5 g has a resonant frequency of 16 Hz and generates an induced electromotive force of Vrms = 2.58 mV (delivering 79 nW power into matched load of 21 Ω) from 3 g acceleration at 16 Hz.