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We have successfully demonstrated a novel, passive layer-free, curved piezoelectric micromachined ultrasound transducer (PMUT) array, using a sacrificial curved glass template and 30% scandium-doped aluminum nitride (Sc-AlN) as the active layer. The PMUTs were fabricated using a curved, suspended borosilicate glass template created via a chip-scale glass-blowing technique, onto which electrodes and the piezoelectric layer were deposited. The glass layer was thereafter selectively removed. We characterized the performance of a 13 × 13 curved PMUT (cPMUT) array using an electrical impedance analyzer, a Laser Doppler Vibrometer (LDV), and hydrophone pressure measurements. Our results reveal a device resonance frequency of approximately 1.8 MHz in air, with LDV analysis indicating a significantly enhanced low-frequency response of 1.68 nm/V—a fivefold improvement over conventional curved PMUTs with a passive layer. Additionally, acoustic characterization in water showed that this array generates an acoustic pressure of approximately 80 kPa at a 4.4 mm focal distance, with a beam width of 5 mm, and achieves a spatial peak pulse average intensity (ISPPA) of 216 mW/cm2 when driven off-resonance. Furthermore, we demonstrate 20-degree steering capability using our data acquisition system. These advancements highlight significant potential for enhancing the precision and efficacy of medical imaging and therapeutic applications, particularly in ultrasonic diagnostics and treatments. 

Ultrasound has been extensively used and investigated in medical applications, such as medical imaging [1] and drug delivery [2], because of advantages such as noninvasiveness, good penetration, good sensitivity, and ease of use. Prior to the development of piezoelectric micromachined ultrasound transducers (pMUTs), conventional transducers were made of piezoelectric ceramics, such as lead zirconate titanate [3]. These materials when operated in thickness mode exhibit a large impedance mismatch between the transducer surface and medium resulting in lower bandwidth unless augmented with one or more matching layers. With the development of MEMS technology, improvements in MUTs have been realized in several aspects, such as wide bandwidth without the addition of matching layers [4], smaller cell size, therefore higher operating frequency and better resolution, and easier fabrication of large arrays at lower cost [5]. Despite lower electromechanical coupling coefficient, the low-power consumption feature makes pMUTs good candidates for a variety of applications, including intrabody communication [6] and fingerprint sensing [7]. 

The receive sensitivity of lead zirconate titanate (PZT) piezoelectric micromachined ultrasound transducers (PMUTs) was improved by applying a DC bias during operation. The PMUT receive sensitivity is governed by the voltage piezoelectric coefficient, h31,f. With applied DC biases (up to 15 V) on a 2 μm PbZr0.52Ti0.48O3 film, e31,f increased 1.6 times, permittivity decreased by a factor of 0.6, and the voltage coefficient increased by ~2.5 times. For released PMUT devices, the ultrasound receive sensitivity improved by 2.5 times and the photoacoustic signal improved 1.9 times with 15 V applied DC bias. B-mode photoacoustic imaging experiments showed that with DC bias, the PMUT received clearer photoacoustic signals from pencil leads at 4.3 cm, compared to 3.7 cm without DC bias. 

Abstract Studying brain‐wide hemodynamic responses to different stimuli at high spatiotemporal resolutions can help gain new insights into the mechanisms of neuro‐ diseases and ‐disorders. Nonetheless, this task is challenging, primarily due to the complexity of neurovascular coupling, which encompasses interdependent hemodynamic parameters including cerebral blood volume (CBV), cerebral blood flow (CBF), and cerebral oxygen saturation (SO₂). The current brain imaging technologies exhibit inherent limitations in resolution, sensitivity, and imaging depth, restricting their capacity to comprehensively capture the intricacies of cerebral functions. To address this, a multimodal functional ultrasound and photoacoustic (fUSPA) imaging platform is reported, which integrates ultrafast ultrasound and multispectral photoacoustic imaging methods in a compact head‐mountable device, to quantitatively map individual dynamics of CBV, CBF, and SO₂as well as contrast agent enhanced brain imaging at high spatiotemporal resolutions. Following systematic characterization, the fUSPA system is applied to study brain‐wide cerebrovascular reactivity (CVR) at single‐vessel resolution via relative changes in CBV, CBF, and SO₂in response to hypercapnia stimulation. These results show that cortical veins and arteries exhibit differences in CVR in the stimulated state and consistent anti‐correlation in CBV oscillations during the resting state, demonstrating the multiparametric fUSPA system's unique capabilities in investigating complex mechanisms of brain functions.