Identifying Regions-of-Interest and Extracting Gold from PCBs Using MHz HIFU

Increased digitalization and technological development raises the demand for rare and precious metals (RPM). Due to their rarity, mining RPMs from the earth is becoming increasingly difficult. Traditional urban mining methods to recover RPMs from printed circuit boards (PCB) need to separate the RPMs from non-metallic substances, e.g. plastic. This separation requires toxic substances and causes unwanted and toxic by-products and emissions. The ability to identify regions-of-interest on PCBs, i.e. the gold pads, and to extract RPMs from only the desired areas would reduce the need for toxic substances. In this study, a single 12 MHz high-intensity focused-ultrasound transducer was used to 1) image a PCB to locate the gold pads, and 2) to subsequently induce inertial cavitation to remove gold from three extraction areas on the selected gold pad. The sonication was performed in water without additional chemicals. Gold removal was verified by imaging the pad with a coded-excitation scanning acoustic microscope (fc = 375 MHz). Average areas and volumes of the three extraction regions were A = (12.2 ± 0.5)·103 μm2 and V = (18 ± 2)·103 μm3, respectively. The total amount of removed gold and nickel (from beneath the gold plating) from all three extraction areas was estimated to mAu,tot = (570 ± 20) ng and mNi,tot = (440 ± 30) ng. This study constitutes a first step towards more environmentally friendly, non-toxic urban mining of RPMs.Peer reviewe

Machining of Aluminium with MHz High-Intensity Focused Ultrasound

Cavitation-induced surface erosion has been studied for decades. High-intensity focused ultrasound (HIFU) enables localized erosion, with applications in many fields. However, no research has been published on machining solely with HIFU. Compared to existing micro-machining technologies, HIFU exhibits a unique set of benefits: inexpensive, minimal maintenance due to non-contact machining without slurry, mitigated chemical load, and monitoring capability. We demonstrate controlled surface machining of mirror-polished aluminium (AW-5754) using high-frequency (12 MHz) HIFU-induced cavitation erosion. Optimal sonication parameters (transducer-sample distance, amplitude, cycles per burst, number of bursts, and pulse repetition frequency) for stationary surface erosion were first identified experimentally. These parameters served as a basis for studying the effect of sonication parameters during on-the-fly erosion, i.e., engraving lines. The effect of stage translation velocity and the number of repeated passes across the engraved line were also studied. Subsequently, the acronym of our laboratory, “ETLA”, was engraved, with a 500 µm letter height and an average line width of 53 µm.Peer reviewe

An Ultrasonically Actuated Fine-Needle Creates Cavitation in Bovine Liver

Ultrasonic cavitation is being used in medical applications as a way to influence matter, such as tissue or drug vehicles, on a micro-scale. Oscillating or collapsing cavitation bubbles provide transient mechanical force fields, which can, e.g., fractionate soft tissue or even disintegrate solid objects such as calculi. Our recent study demonstrates that an ultrasonically actuated medical needle can create cavitation phenomena inside water. However, the presence and behavior of cavitation and related bioeffects in diagnostic and therapeutic applications with ultrasonically actuated needles are not known. Using simulations, we demonstrate numerically and experimentally the cavitation phenomena near ultrasonically actuated needles. We define the cavitation onset within a liver tissue model with different total acoustic power levels. We directly visualize and quantitatively characterize cavitation events generated by the ultrasonic needle in thin fresh bovine liver sections enabled by high speed imaging. On a qualitative basis, the numerical and experimental results show a close resemblance in threshold and spatial distribution of cavitation. These findings are crucial for developing new methods and technologies employing ultrasonically actuated fine-needles such as ultrasound-enhanced fine-needle biopsy, drug delivery and histotripsy.Comment: 35 pages, 6 figures, under consideration at The Journal of the Acoustical Society of Americ

An Ultrasonically Actuated Needle Promotes the Transport of Nanoparticles and Fluids

Non-invasive therapeutic ultrasound methods, such as high-intensity focused ultrasound (HIFU), have limited access to tissue targets shadowed by bones or presence of gas. This study demonstrates that an ultrasonically actuated medical needle can be used to translate nanoparticles and fluids under the action of nonlinear phenomena, potentially overcoming some limitations of HIFU. A simulation study was first conducted to study the delivery of a tracer with an ultrasonically actuated needle (33 kHz) inside a porous medium acting as a model for soft tissue. The model was then validated experimentally in different concentrations of agarose gel showing a close match with the experimental results, when diluted soot nanoparticles (diameter < 150 nm) were employed as delivered entity. An additional simulation study demonstrated a threefold increase of the volume covered by the delivered agent in liver under a constant injection rate, when compared to without ultrasound. This method, if developed to its full potential, could serve as a cost effective way to improve safety and efficacy of drug therapies by maximizing the concentration of delivered entities within e.g. a small lesion, while minimizing exposure outside the lesion.Comment: 34 pages, 4 figures, under review in the Journal of the Acoustical Society of Americ

Ultrasonic actuation of a fine-needle improves biopsy yield

Despite the ubiquitous use over the past 150 years, the functions of the current medical needle are facilitated only by mechanical shear and cutting by the needle tip, i.e. the lancet. In this study, we demonstrate how nonlinear ultrasonics (NLU) extends the functionality of the medical needle far beyond its present capability. The NLU actions were found to be localized to the proximity of the needle tip, the SonoLancet, but the effects extend to several millimeters from the physical needle boundary. The observed nonlinear phenomena, transient cavitation, fluid streams, translation of micro- and nanoparticles and atomization, were quantitatively characterized. In the fine-needle biopsy application, the SonoLancet contributed to obtaining tissue cores with an increase in tissue yield by 3-6x in different tissue types compared to conventional needle biopsy technique using the same 21G needle. In conclusion, the SonoLancet could be of interest to several other medical applications, including drug or gene delivery, cell modulation, and minimally invasive surgical procedures.Peer reviewe