Ultrasonic applications such as non-destructive testing, biomedical imaging or range measurements are currently based on piezoelectric bulk transducers. Yet, these kinds of transducers with their mm to cm dimensions are rather impractical in fields in which both frequencies in the kHz region and small-feature sizes are required. This fact mainly relates to the inverse relationship between the resonance frequency constant and the transducers’ dimension, yielding a higher frequency and attenuation with a decreasing size. Piezoelectric micromachined ultrasonic transducers (PMUTs), in comparison, incorporate a small-scale µm design while preserving the operating frequency in the desired kHz range. This contribution presents the detailed manufacturing of such a PMUT with a multiple ring electrode‑based structure to additionally adjust the sound pressure fields. The PMUT will be characterized by its deflection in air along with the characterization of the piezoelectric material lead zirconate titanate (PZT) itself. The measurements showed a maximum polarization of 21.8 µC/cm² at 50 kV/cm, the PMUT’s displacement of 30.50 nm/V in air when all electrodes are driven, and an adjustable deflection via different electrode excitations without the need for additional hardware. The ring design also offered the possibility to emit two distinct frequencies simultaneously. These results demonstrate the potential of the designs for small-feature-size applications as they are in high demand for implantable devices, miniaturized ultrasonic-based communication or drug delivery.

The emerging desire for implantable devices assisting individuals’ medical treatments requires their connection to systems placed outside and inside the human body. Their exchange of crucial information on health parameters at different locations may allow them to optimize the patient’s therapy by evaluating the received and transmitted data. Electromagnetic communication methods are the current implementation of choice for such applications. Yet, this kind of communication is often limited to shorter distances due to their restrictions on safe electromagnetic levels, causing no damaging heat dissipation in human tissue. In contrast, employing ultrasound as an alternative method will allow for long-distance communication in the same medium by simultaneously guaranteeing safety requirements for the patient. In this contribution, we will demonstrate a proof-of-concept for which we modulate ultrasonic carrier signals with the help of a low-power consumption microcontroller TI-MSP430. For this, two identical non-focused ultrasonic transducers will be used to receive and send messages through a tissue-mimicking phantom placed in a water tank, indicating the potential of ultrasonic signals as the carrier of information.

Personalized medicine meets microimplants. Miniaturized, distributed implants may offer treatment options for diseases in which pharmaceuticals do not work for all patients or do not exist at all. In order to supply these implants efficiently with energy combinations of inductive links and ultrasonic transducers were investigated. This methodological review contributes with a comprehensive overview on the energy supply aspects of neural implants and summarizes basic mechanisms, differences and commonalities with the most widespread method, inductive coupling. It is believed that this review as seminal work can guide researchers who are not familiar with the energy supply field as well as neural engineers, neuroscientists, and clinicians to better understand strengths, weaknesses, threats, and opportunities of this methodology in innovative and novel neurotechnological applications. As figure of merit, inductive links are suggested for short distances and to couple energy into the body, while ultrasound is more efficient over larger lengths and in networks inside the body. The authors suggest planar butterfly coils, membrane‐based piezoelectric micromachined ultrasonic transducers and non‐hermetic encapsulation using silicone rubber for these envisioned neural implant networks.

Nowadays, increasing digitalization may give acoustic communication an essential role in areas where electromagnetic communication fails or can only be employed with extensive effort. Consequently, acoustic communication systems need to address the challenges of real-world applications. One key requirement are the limited energy resources that battery-powered sensor nodes possess. Besides the high energy consumption during transmission and reception, listening to the communication channel for synchronization between transmitter and receiver is a major energy consuming factor. For this purpose, we introduce a concept of wake-up receivers for acoustic communication systems, originally known from radio technology. Therefore, this contribution presents a concept of a low-power acoustic wake-up receiver implemented with a demonstrator through a 1.6 mm thick metal barrier.We exploit two fundamental resonance modes of a piezoelectric disc transducer to facilitate an acoustic wake-up. The radial vibration mode at 220 kHz enables frequency-based wake-up with a sensitivity of –87 dBm and a radial distance of 1.35 m. The thickness extension mode at 1.2 MHz generates a 100 kHz subcarrier to transmit an 8-bit Manchester-coded ID at 1.1 kbps, achieving a sensitivity of –37 dBm. Both wake-up schemes have been demonstrated to function reliably with an energy consumption of 14.3 μW.

Lead zirconate titanate (PZT) is a widely used material for applications in microsensors, actuators, and transducers. Due to its high piezoelectric coefficient, large dielectric constant, and strong polarization capability near the morphotropic phase boundary (Zr/Ti ≈ 52/48), it is considered one of the most attractive materials for micro-electromechanical systems (MEMS). These advantageous material properties strongly depend on the PZT layer’s microstructure and crystallinity, which are primarily determined by the choice of seed layer, deposition conditions, and the post-deposition annealing treatment that promotes the formation of the PZT’s perovskite phase. In this contribution, sputter-deposited PZT thin films were crystallized by conventional furnace annealing (CFA) to evaluate the effect of heating/cooling rates (1 °C·min⁻¹–7 °C·min⁻¹) within a temperature range of 450 °C to 700 °C on structural, electrical, and ferroelectric properties, with consideration of the seed layer preparation. We characterized the materials’ properties by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and measurements of the ferroelectric hysteresis, capacitance, and leakage current. All samples annealed at temperatures of at least 500 °C fully crystallized into the perovskite phase, independently of the heating/cooling rate. The best ferroelectric performance was achieved at 550 °C with a 1 °C·min⁻¹ heating/cooling rate, yielding a saturation polarization of 82.8 µC·cm⁻² and a remnant polarization of 36.9 µC·cm⁻² under a maximum applied field of 300 kV·cm⁻¹.