Patch-type capacitive micromachined ultrasonic transducer for ultrasonic power and data transfer

Abstract

Ultrasonic power and data transfer is a promising technology for implantable medical devices because of its non-invasiveness, deep penetration depth, and potential for a high-power transmission rate with a low specific absorption rate. However, ultrasound-powered implantable devices still suffer from low power transfer efficiency due to beam misalignment and are limited to short-term use due to the bulkiness of the transmitting transducers. Here, we report the first proof of concept for adaptive positioning and targeting of ultrasound-based implantable devices through ultrasound image guidance. A lightweight patch-type ultrasonic transducer array is fabricated to enable ultrasound imaging and beam-forming during long-term operation. The uniform performance of the array is established through the silicon micromachining process. We demonstrate the complete scheme of imaging, positioning, and targeted power transfer in an ex vivo environment, achieving precise targeting of moving implanted devices through real-time ultrasound imaging. Enhanced power transfer efficiency through the use of patch-type ultrasonic transducers can enhance patient comfort and minimize invasive procedures, opening new applications for ultrasonic-powered implantable devices.

Fig. 1

Overview of adaptive ultrasonic power and data transfer using a patch-type CMUT array a Application scenario of focused acoustic power transfer using a conventional handheld ultrasound transducer and a patch-type CMUT. b Photograph of the patch-type CMUT array attached to a human hand. c A conceptual schematic showing the components of the patch-type CMUT array. d k-Wave simulation of a focused ultrasound beam generated from a 1D array composed of different aperture sizes. e The −6 dB beam width of simulated beams measured at a depth of 10 cm

Fig. 2

Characterization of the fabricated CMUTs a A cross-sectional SEM image of a single CMUT cell. Scale bar = 1 μm. b A 3D optical profile of the deflections of circular cells in a single element of CMUT. c A photograph of the packaged CMUT patch. d Electrical input impedance of a single channel of the CMUT array. e 6-element modeling of electrical impedance at a bias voltage of 70 V. f Uniformity of center frequencies of 32 channels in air. g Pitch-catch impulse response of 70 V-biased single CMUT channel. h Transmit and receive sensitivity of a single channel. i Transmit pressures before and after the encapsulation

Fig. 3

Ultrasound imaging, beam steering, and data transfer using the patch-type CMUT a Profile of the string phantom. b B-mode images of the string phantom located at the depths of 1 cm, 2 cm, and 3 cm. c Lateral and axial resolution of the point spread function at different depths. d Signal-to-noise of the point spread function at different depths. e Beam profiles of the 1D CMUT array during beam steering. f Impulse response of the 1D CMUT array, which shows the bit-rate of the system. g Acoustic pressure measured at the focal point at 1 cm depth. h Transmitted ultrasound signals received by the hydrophone

Fig. 4

Imaging stability of the patch-type CMUT a Long-term stability of focused ultrasound beam at 12-hour intervals over one day. b The −3 dB full width at half maximum measured at a depth of 2 cm over one day. c Long-term B-mode imaging of the IMD at 12-hour intervals over one day. d Lateral and axial resolution of the point spread function at 2 cm depth over one day

Fig. 5

Ex vivo power and data transfer using the patch-type CMUT on the chicken breast a A schematic diagram of ultrasound-guided power transmission. b Equivalent circuit modeling of the proposed ultrasound system. c Electrical input impedance of the implanted piezoelectric disk that is used to receive ultrasound signal. d Ultrasound B-mode image of the implanted piezoelectric device. e Transmitted waveform and received signals for power transfer. f Bit-coded ultrasound signal received by the implanted piezoelectric device for data transfer