This paper presents methods of promoting the sensitivity of Microelectromechanical Systems (MEMS) vector hydrophone by increasing the sensing area of cilium and perfect insulative Parylene membrane. First, a low-density sphere is integrated with the cilium to compose a “lollipop shape,” which can considerably increase the sensing area. A mathematic model on the sensitivity of the “lollipop-shaped” MEMS vector hydrophone is presented, and the influences of different structural parameters on the sensitivity are analyzed via simulation. Second, the MEMS vector hydrophone is encapsulated through the conformal deposition of insulative Parylene membrane, which enables underwater acoustic monitoring without any typed sound-transparent encapsulation. Finally, the characterization results demonstrate that the sensitivity reaches up to −183 dB (500 Hz 0dB at 1 V/$\mu \text{Pa}$ ), which is increased by more than 10 dB, comparing with the previous cilium-shaped MEMS vector hydrophone. Besides, the frequency response takes on a sensitivity increment of 6 dB per octave. The working frequency band is 20–500 Hz and the concave point depth of 8-shaped directivity is beyond 30 dB, indicating that the hydrophone is promising in underwater acoustic application.

Miniaturized magnetic soft robotic catheters offer significant potential in minimally invasive surgery by enabling remote active steering and reduced radiation exposure. However, existing magnetic catheters are limited by the absence of in-situ biomechanical force sensing, which is crucial for controlling the contact force exerted on surrounding tissues during surgical procedures. Here, we report an in-situ force sensing strategy for small-scale magnetic robotic catheters. A coaxial integration of ring-shaped permanent and fibre-based force sensors at the catheter's distal end enables both active steering and precise force measurement. The force sensor is designed to be sensitive exclusively to contact forces perpendicular to its plane, achieving a sensitivity of 0.69 nm/kPa (or 0.38 nm/mN). By manipulating magnetic field patterns, the catheter can actively generate and control contact forces to tissues, using real-time feedback from the force sensor. We demonstrate the system's force-sensing and force-control capability in isolated organs and tissue phantom during passage, verifying the catheter's high force sensitivity and high steerability. The feedback-loop force control enhances procedural safety and efficacy for minimally invasive surgery, making it especially suitable for procedures such as transbronchial microwave ablation of lung nodules and cardiac ablation for atrial fibrillation.

For the purpose of acquiring precise underwater 3D spatial orientation, a ‘fitness-wheel-shaped’ MEMS vector hydrophone (FWVH) is developed, which achieves monitoring of a tri-axial acoustic pressure differential via appropriate constructional design and strain readout. Compared to the previously reported T-structure-combined vector hydrophone (TSVH) which has a nonlinear relationship between output and external force, using the FWVH it is feasible in principle to achieve a tri-axial match, which make it promising in accurate acoustic orientation. A theoretic model for sensitivity is developed, where torque moment is taken into consideration to match the simulation and practical results. Superior to 3D force sensors, bandwidth is taken as the key index for the FWVH and is designed in detail with a compromise of sensitivity. In view of the bandwidth, the parameters are determined for detecting the signal in the range 20–300 Hz. A vibration test demonstrates tri-axial resonance frequencies. Finally, the frequency response curve of the FWVH shows that tri-axial sensitivities are consistent, agreeing with the analysis and simulation results, which reach −174 dB (0 dB referring to 1 V µ Pa ⁻¹ ) at 300 Hz.

Since the sensitivity and frequency band of the micro-electro-mechanical system (MEMS) bionic vector hydrophone restrain each other, a single hydrophone can not simultaneously meet the high sensitivity and wide frequency band requirements. Therefore, in this paper, based on a single MEMS bionic vector hydrophone, a 2 × 2 four-unit array microstructure on a chip has been proposed to realize both high sensitivity and wide frequency band, which consists of four four-beam-cilium structures with different cilium lengths of 10000, 8000, 6000, and 3000 um, respectively. The array structure sizes are determined by the theoretical and simulation analysis, and then the array structure is fabricated integrally by the MEMS manufacturing technology. Finally, this paper presents the experimental characterization of the packaged array hydrophone in a standing wave tube to validate the theory and the simulation. The test results show that the array hydrophone has high sensitivity and good frequency response, exhibiting the highest sensitivity of -189 dB (without pre-amplifier, 0 dB reference 1 V/uPa) and frequency band of 20-5000 Hz, both bearing witness to a good directivity in the shape of 8. The improvements of the hydrophone performance broaden its application scope.

Similar to the vital performance factors, the receiving sensitivity and the bandwidth exist interactively in the micro-electromechanical systems (MEMS)-based vector hydrophones. Some existing methods can improve the sensitivity of the hydrophone, but these improvements are usually gained at a cost of the bandwidth. However, the cup-shaped MEMS vector hydrophone that is presented in this paper can improve its sensitivity while retaining a sufficient bandwidth. The cup-shaped structure acts as a new sensing unit in the MEMS vector hydrophone, replacing the bionic columnar hair that was previously used for sensing. The relationships between the parameters of the cup-shaped structure and the sensitivity of the vector hydrophone were determined by a theoretical deduction. In addition, simulation analyses were performed, and optimized structural parameters were obtained in this work. ANSYS 15.0 simulation was used to derive the optimum characteristics for the cup-shaped structure. The results of the calibration experiments showed that the sensitivity reached up to −188.5 dB (gain of 40 dB, 1 kHz, 0 [email protected] V/μPa), and the bandwidth was in the 20 Hz–1 kHz range, which is sufficient for an underwater acoustic detection at low frequencies. This work has, thus, proved that the cup-shaped vector hydrophone has superior properties for the engineering applications.

In order to eliminate polyurethane hat resonance frequency intervention and reduce fluid influence, a whisker-inspired MEMS vector hydrophone (WIVH) encapsulated with parylene is proposed to broaden frequency bandwidth and improve sensitivity-frequency response performance, compared to the lateral line-inspired MEMS vector hydrophone (LLIVH). Parylene that is conformally deposited on the device surface replaces polyurethane encapsulating hat and silicone oil existing in current encapsulation technology. The main advantage of WIVH as demonstrated by modelling and characterization is the enhanced bandwidth response, which is the critical factor in hydrophone design. Acoustic pressure gradient properties of the WIVH and LLIVH are analyzed to demonstrate the influence of the polyurethane hat. The interactions of the parylene membrane with fluid and the influences on vibrating performance are also investigated. Resonance measurement and sensitivity-frequency response analysis demonstrate the frequency bandwidth of the WIVH could be extended twice compared to that of the LLIVH. Moreover, the WIVH is proved to act as a typical pressure gradient hydrophone with an increment of 6 dB per octave in the linear region.