Flexible transparent CMUT arrays for photoacoustic tomography

Abstract

This paper reports the fabrication and characterization of the first flexible transparent capacitive micromachined ultrasound transducer (CMUT) array for through-illumination photoacoustic tomography. Fabricated based on an adhesive wafer bonding technique and a PDMS backfill approach, the array has a maximum transparency of 67% in visible light range and can be bent to a radius of curvature of less than 5 mm without the structural layers being damaged. With a center frequency of 3.5 MHz, 80% fractional bandwidth, and noise equivalent pressure (NEP) of 62 mPa/ H z , the array was successfully used in limited-view photoacoustic tomography of a 100 µm wire target, demonstrating lateral and axial resolutions of 293 µm and 382 µm, respectively, with 46 dB signal-to-noise ratio. Additionally, deep tissue photoacoustic tomography was also demonstrated on a blood tube within a chicken tissue using the fabricated CMUT arrays.

Ultrafast Orthogonal Row–Column Electronic Scanning (uFORCES) With Bias-Switchable Top-Orthogonal-to-Bottom Electrode 2-D Arrays

“…Lead magnesium niobate (PMN) with low lead titanate (PT) doping is a electrostrictive material that is naturally unpolarized at around room temperature and becomes polarized by applying a DC bias voltage (PMN38, TRS Technology). These materials can also be made transparent/translucent when polished on both sides that potentially can be used in through-illumination photoacoustic applications [26], [27]. Capacitive micromachined ultrasound transducer (CMUT) is another bias-sensitive transducer that uses electrostatic forces between two clamped plates to generate acoustics which some of their applications in TOBE configurations have been demonstrated recently [8].…”

A wearable cardiac ultrasound imager

“…To quantify the device spatial resolutions using the wide-beam compounding strategy, we measured full widths at half maximum from the point spread function curves 28 extracted from the images (Fig. 2a , third and fourth columns and the bottom row and Supplementary Fig.…”

Recent Advances in Flexible Ultrasonic Transducers: From Materials Optimization to Imaging Applications

“…Mahyar et al proposed a flexible transparent CMUT array with a center frequency of 3.5 MHz, an 80% fractional bandwidth and a noise equivalent pressure (NEP) of 62 . The flexible CMUT array was fabricated based on an adhesive bonding technique with benzocyclobutene (BCB) as both the adhesive and sidewall layers, ITO as the electrodes, silicon nitride as the membrane, and PDMS as the flexible backing layers [ 15 ]. The fabrication processes, optical microscopy images, photographs, NEP and frequency spectrum of the transparent flexible CMUT array are shown in Figure 6 c.…”

“…Mahyar et al bonded a 64-element CMUT array to a flexible PCB to detect PA signals, as shown in Figure 9 b. The PAI system with a flexible CMUT array showed an SNR of 46 dB with an axial and lateral resolution of 382 μm and 293 μm, respectively [ 15 ]. Liu et al used a single-element US transducer with a 6.7 MHz center frequency and 86.3% −3 dB fractional bandwidth in a PAI system, as shown in Figure 9 c [ 26 ].…”

“…The mismatch between the transducers’ rigid surfaces and irregular surfaces of the target tissues would generate an irregular, thick coupling layer between the above two surfaces, which leads to distortions and sensitivity loss. Compared to rigid US transducers, flexible US transducers provide the advantages of being thin, compact and lightweight and having the ability to conform to any complex surface [ 15 , 16 , 17 ]. Due to the superiority of the self-alignment to the target surface, even with curved or complex geometries, the flexible US transducer could detect the maximized transmitted US energy.…”