Acoustic Characterization of Polydimethylsiloxane for Microscale Acoustofluidics

We present a protocol for the design, fabrication and characterisation of laser-induced ultrasound transmitters with a specific, user-defined frequency response for the purpose of ultrasound tomography of large-volume biomedical samples. Using an analytic solution to the photoacoustic equation and measurements of the optical and acoustic properties of the materials used in the transmitters, we arrive at a required mixture of carbon black and polydimethylsiloxane to achieve the desired frequency response. After an in-depth explanation of the fabrication and characterisation approaches we show the performance of the fabricated transmitter, which has a centre frequency of 0.9 MHz, 200% bandwidth and 45.8 opening angle, multi-kPa pressures over a large depth range in water.

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“…Taking the mean values of the fitted parameters of the power law in Eq. (16) gives us

and

, in line with values found in literature [29] , [30] .…”

Section: Resultssupporting

confidence: 90%

Laser-induced ultrasound transmitters for large-volume ultrasound tomography

et al. 2022

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“…Deviations of the UTT values from the UEIS values, may in part be explained by the fact that the UTT technique uses a frequency pulse with a width of 1 MHz around the center frequency 1.90 MHz, while UEIS is based on an entire frequency spectrum from 500 Hz to 5 MHz using a single frequency at a time. However, while different models exist, which assumes a frequency-dependence of the elastic moduli of PMMA [12], similar to the frequency dependencies measured in PDMS [9], we do find it sufficient in the UEIS method to neglect the frequency-dependence of the PMMA complex-valued elastic moduli.…”

Section: B Ueis-fitted Materials Parameters For Gluesupporting

confidence: 57%

Determination of the complex-valued elastic moduli of polymers by electrical impedance spectroscopy for ultrasound applications

Bodé¹,

Lickert²,

Augustsson³

et al. 2022

Preprint

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A method is presented for the determination of complex-valued compression and shear elastic moduli of polymers for ultrasound applications. The resulting values, which are scarcely reported in the literature, are found with uncertainties typically around 1% (real part) and 6% (imaginary part). The method involves a setup consisting of a cm-radius, mm-thick polymer ring glued concentrically to a disk-shaped piezoelectric transducer. The ultrasound electrical impedance spectrum of the transducer is computed numerically and fitted to measured values as an inverse problem in a wide frequency range, typically from 500 Hz to 5 MHz, both on and off resonance. The method was validated experimentally by ultrasonic through-transmission around 1.9 MHz. Experimentally, the method is arguably simple and low cost, and it is not limited to specific geometries and crystal symmetries. Moreover, by involving off-resonance frequencies, it allows for determining the imaginary parts of the elastic moduli, equivalent to attenuation coefficients. Finally, the method has no obvious frequency limitations before severe attenuation sets in above 100 MHz.

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“…The first one occurs at the edge of the cavity, and the second one is 30 µm farther at the interface between the PDMS film and the air [ 18 ]. Considering the longitudinal velocity of PDMS (v) is about 1028 m/s [ 19 ], the two reflection disturbances should act on the vibration plate after 2 d 1 / v = 0.58 µs and 2( d 1 + d 2 )/ v = 0.64 µs of the generation, respectively, which means that if they existed, both should appear after 3 µs. However, as shown in the insert of Figure 6 , only a low-frequency wave (0.5 MHz) can be seen, which is possibly due to the thermal expansion of the PDMS [ 20 ].…”

Section: Resultsmentioning

confidence: 99%

“…Therefore, it can be deduced that the 300 µm PDMS backing structure can attenuate the reflected wave by at least 55 dB. This is much higher than the 7 dB attenuation of longitudinal waves in bulk [ 19 ], suggesting a complex propagation in the cylinder.…”

Section: Resultsmentioning

confidence: 99%

Development of Broadband High-Frequency Piezoelectric Micromachined Ultrasonic Transducer Array

Wang

et al. 2021

Sensors

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Piezoelectric micromachined ultrasonic transducers (PMUT) are promising elements to fabricate a two-dimensional (2D) array with a pitch small enough (approximately half wavelength) to form and receive arbitrary acoustic beams for medical imaging. However, PMUT arrays have so far failed to combine the wide, high-frequency bandwidth needed to achieve a high axial resolution. In this paper, a polydimethylsiloxane (PDMS) backing structure is introduced into the PMUTs to improve the device bandwidth while keeping a sub-wavelength (λ) pitch. We implement this backing on a 16 × 8 array with 75 µm pitch (3λ/4) with a 15 MHz working frequency. Adding the backing nearly doubles the bandwidth to 92% (−6 dB) and has little influence on the impulse response sensitivity. By widening the transducer bandwidth, this backing may enable using PMUT ultrasonic arrays for high-resolution 3D imaging.

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Acoustic Characterization of Polydimethylsiloxane for Microscale Acoustofluidics

Cited by 26 publications

References 44 publications

Laser-induced ultrasound transmitters for large-volume ultrasound tomography

Laser-induced ultrasound transmitters for large-volume ultrasound tomography

Determination of the complex-valued elastic moduli of polymers by electrical impedance spectroscopy for ultrasound applications

Development of Broadband High-Frequency Piezoelectric Micromachined Ultrasonic Transducer Array

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