An official website of the United States government
This paper presents a mid-air thermal interface enabled by a piezoelectric micromachined ultrasonic transducer (pMUT) array. The two-stage thermal actuating process consists of an ultrasound-transmission process via a pMUT array and an ultrasound-absorption process via porous fabric. The pMUT design employs sputtered potassium sodium niobate (K,Na)NbO3 (KNN) thin film with a high piezoelectric coefficient (d31 ~ 8-10 C/m2) as piezoelectric layer for enhanced acoustic pressure. Testing results show that the prototype pMUT array has a resonant frequency around 97.6 kHz, and it can generate 1970 Pa of focal pressure at 15 mm away under the 10.6 Vp-p excitation. As a result, fabric temperature in the central focal area can rise from 24.2℃ to 31.7℃ after 320 seconds with an average temperature variation rate of 0.023℃/s. Moreover, thermal sensations on the human palms have been realized by the heat conduction through the fabric-skin contact. As such, this work highlights the promising application of pMUT array with high acoustic pressure for human-machine interface, particularly mid-air thermal display.
more »
« less
Design Approaches and Electromechanical Modeling of Conformable Piezoelectric‐Based Ultrasound Systems
Abstract Painless, needleless delivery of drugs through the skin can be realized through aphenomenon called sonophoresis by applying an ultrasound field to the biological tissue. Development of wearable embodiments of such systems demands comprehensive characterization of both the physical mechanism of sonophoresisas well as wearability parameters. Here, we present a framework for analyzing disk‐type piezoelectric transducers in a polymeric substrate to create acoustic cavitation in a fluid coupling medium for sonophoresis applications. The device design and operating parameters such as the working frequency, applied voltage range, acoustic pressure distribution, and transducer spacing were determine dusing a finite element methods (FEM),and verified with experimental measurements. The influence of the surrounding water and tank reflections on the acoustic pressure field, and the interaction between the elements in the array structure were also studied.Finally, the impact of skin and the substrate geometry on the acoustic pressure fields was characterized to simulate the invivo use‐case of the system. These analytical models can be used to guide critical parameters for device design such as the separation distance of the piezoelectric transducer from the skin boundary. We envision that this tool boxwill support rapid design iteration for realization of wearable ultrasound systems.
more »
« less
- Award ID(s):
- 2044688
- PAR ID:
- 10641225
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Sensor Research
- Volume:
- 3
- Issue:
- 10
- ISSN:
- 2751-1219
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Ultrasound is a safe, noninvasive diagnostic technique used to measure internal structures such as blood vessels and the velocity of blood flow in the human body. The ability to continuously measure blood flow in major cerebral arteries would enable the early detection of medical problems such as stroke. However, current ultrasound technology consists of rigid, hand-held probes that are arduous to use, sensitive to movement, and are primarily designed for intermittent, instead of continuous use. Here, we describe the design of a wearable ultrasound patch for continuously measuring blood flow velocity through the middle cerebral artery (MCA) that can be assessed from the temple region of the head. The wearable ultrasound patch is composed of an array of piezoelectric elements that are wired together using flexible electrical conductors and encapsulated in an elastic substrate. To improve ultrasound energy transfer, a soft and conformal composite matching layer is introduced. The matching layer consists of gallium-based liquid metal (LM) microdroplets dispersed in a silicone elastomer. The acoustic impedance of the matching layer can be tuned by varying the volume loading of LM. The wearable ultrasound patch will provide new opportunities to continuously measure blood flow velocity and ultimately enable early detection of medical problems such as stroke.more » « less
-
Abstract Ultrasound is a safe, noninvasive diagnostic technique used to measure internal structures such as tissues, organs, and arterial and venous blood flow. Skin‐mounted wearable ultrasound devices can enable long‐term continuous monitoring of patients to provide solutions to critical healthcare needs. However, stretchable ultrasound devices that are composed of ultrasonic transducers embedded in an elastomer matrix are incompatible with existing rigid acoustic matching layers, leading to reduced energy transmission and reduced imaging resolution. Here, a systematic study of soft composites with liquid metal (LM) fillers dispersed in elastomers reveals key strategies to tune the acoustic impedance of soft materials. Experiments supported by theoretical models demonstrate that the increase in acoustic impedance is primarily driven by the increase in density with negligible changes to the speed of sound through the material. By controlling the volume loading and particle size of the LM fillers, a material is created that achieves a high acoustic impedance 4.8 Mrayl, (> 440% increase over the polymer matrix) with low modulus (< 1 MPa) and high stretchability (> 100% strain). When the device is mechanically strained, a small decrease is observed in acoustic impedance (< 15%) with negligible decrease in sound transmittance and impact on attenuation for all droplet sizes. The stretchable acoustic matching layer is then integrated with a wearable ultrasound device and the ability to measure motion is demonstrated using a phantom model as is performed in Doppler ultrasound.more » « less
-
Abstract Conformable electronics are regarded as the next generation of personal healthcare monitoring and remote diagnosis devices. In recent years, piezoelectric‐based conformable ultrasound electronics (cUSE) have been intensively studied due to their unique capabilities, including nonradiative monitoring, soft tissue imaging, deep signal decoding, wireless power transfer, portability, and compatibility. This review provides a comprehensive understanding of cUSE for use in biomedical and healthcare monitoring systems and a summary of their recent advancements. Following an introduction to the fundamentals of piezoelectrics and ultrasound transducers, the critical parameters for transducer design are discussed. Next, five types of cUSE with their advantages and limitations are highlighted, and the fabrication of cUSE using advanced technologies is discussed. In addition, the working function, acoustic performance, and accomplishments in various applications are thoroughly summarized. It is noted that application considerations must be given to the tradeoffs between material selection, manufacturing processes, acoustic performance, mechanical integrity, and the entire integrated system. Finally, current challenges and directions for the development of cUSE are highlighted, and research flow is provided as the roadmap for future research. In conclusion, these advances in the fields of piezoelectric materials, ultrasound transducers, and conformable electronics spark an emerging era of biomedicine and personal healthcare.more » « less
-
Chan, Jenna F; Rajaraman, Swaminathan (Ed.)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.more » « less
