Self-powered wideband ultrasonic sensor based on capacitive triboelectric technology with ultralow detection limits and superior frequency resolution

The ultrasound-driven triboelectric nanogenerator with a vibratory membrane layer (USD-VM-TENG) has emerged as a promising self-powered wideband ultrasonic sensor. However, the inherent high detection limit (DL) of existing designs constrains broader applications. Furthermore, an incomplete understanding of the membrane layer's ultrasound-driven vibration characteristics (USD-VC) hinders deeper insights into the device's performance and further optimization. In this study, 3D dynamic laser scanning technology is applied to experimentally reveal the broadband USD-VC of the membrane layer for the first time, guiding the innovative design of a cavity-free USD-VM-TENG (CF-USD-VM-TENG). Despite being generally deemed unsuitable for the contact-separation mode of TENGs, the cavity-free structure eliminates the ultrasound-driven contact process and enables contact electrification independently of ultrasonic excitation. As a result, this design adapts exceptionally well to the membrane layer's diverse higher-order vibration behaviors across a broad ultrasonic frequency range, substantially reducing the device's average DL by 1–2 orders of magnitude compared to conventional USD-VM-TENGs with cavity structures. The optimized CF-USD-VM-TENG achieves an ultralow DL down to 37.1 Pa@20 kHz. Its calibrated wideband output characteristics and superior frequency resolution of 0.001 kHz offer valuable insights for the device's further development. Furthermore, it enables an operating frequency up to 25 MHz, along with operating stability and durability (100 million cycles over 20 days). The CF-USD-VM-TENG is successfully demonstrated to extend the ultrasonic sensing applications of TENGs by enabling the detection and recognition of low-intensity, broadband ultrasonic signals. This work paves the way for further advancements of TENGs in ultrasound-related applications.