We present an air-coupled ultrasonic imaging system based on a 40 kHz 8×8 phased-array for three-dimensional real-time localization of multiple objects in the far-field. By attaching a waveguide to the array, the effective inter-element spacing is reduced to half wavelength. This enables grating lobe free transmit and receive beamforming with a uniform rectangular array of efficient low-cost transducers. The system further includes custom transceiver electronics, an FPGA Systemon- Chip and a PC for GPU accelerated frequency domain signal processing, consisting of matched filtering, conventional beamforming and envelope extraction using Nvidia CUDA and OpenGL for visualization. The uniform rectangular layout allows utilizing multiple transmit and receive methods, known from medical imaging applications. Thus, the system is dynamically adaptable to maximize the frame rate or detection range. One implemented method demonstrates the real-time capability by transmitting a hemispherical pulse with a single transducer to irradiate the surroundings simultaneously, whereas all transducers are used for echo reception. The imaging properties, such as axial and lateral resolution, field of view and range of view, are characterized in an anechoic chamber. The object localization is validated for a horizontal and vertical field of view of ±80° and a range of view of 0.5m to 3m with 29 frames per second. Using the same system, a comparison between the hemispherical pulse method and the dynamic transmit beamforming method, which transmits multiple sequential beamformed pulses for long-range localization, is provided.

Polymers with electrically charged internal air cavities (ferroelectrets) reveal a pronounced piezoelectric response and are regarded as soft electroactive multi-functional materials. This work presents preliminary results on the preparation and piezoelectric effect of ferroelectrets based on the polylactic acid (PLA) polymer. A distinctive feature of the manufactured films is that they are biodegradable. After a microstructure modification of carbon dioxide (CO₂) foamed PLA sheets by hot-pressing treatment and corona polarization, these cellular films reveal large piezoelectric $d_{33}$ and $d_{31}$ responses in both quasi-static and dynamic modes. For freshly charged films, the maximum quasi-static piezoelectric coefficients are about 600 pC/N ($d_{33}$ ) and 44 pC/N ($d_{31}$ ) for a relatively thick film of 360 μm and a nominal porosity of about 60%. During the first 20 days after polarization, the piezoelectric activity decreases by half compared to the primary value, but then remains almost unchanged for a long time. Due to an already established inherent biocompatibility of PLA polymers, these eco-friendly ferroelectrets can be potentially used in various biological applications such as biosensors and microenergy harvesters embedded in tissue and artificial muscles.

Control over the intensity, shape, direction and phase of coherent light is essential in numerous fields, from gravitational wave astronomy, quantum metrology and ultrafast sciences to semiconductor fabrication. Modern photonics, however, can involve parameter regimes where the wavelength or high optical powers involved restrict control due to absorption, light-induced damage or optical nonlinearity in solid media. Here we propose to circumvent these constraints using gaseous media tailored by high-intensity ultrasound waves. We demonstrate an implementation of this approach by efficiently deflecting ultrashort laser pulses using ultrasound waves in ambient air, without the use of transmissive solid media. At optical peak powers of 20 GW, exceeding previous limits of solid-based acousto-optic modulation by about three orders of magnitude, we reach a deflection efficiency greater than 50% while preserving excellent beam quality. Our approach is not limited to laser pulse deflection; gas-phase photonic schemes controlled by sonic waves could potentially be useful for realizing a new class of optical elements such as lenses or waveguides, which are effectively invulnerable against damage and can operate in new spectral regions.

Despite limited scientific evidence, there is an increasing interest in soft robotic gloves to optimize hand- and finger-related functional abilities following a neurological event. This review maps evidence on the effects and effectiveness of soft robotic gloves for hand rehabilitation and, whenever possible, patients’ satisfaction. A systematized search of the literature was conducted using keywords structured around three areas: technology attributes, anatomy, and rehabilitation. A total of 272 titles, abstracts, and keywords were initially retrieved, and data were extracted out of 13 articles. Six articles investigated the effects of wearing a soft robotic glove and eight studied the effect or effectiveness of an intervention with it. Some statistically significant and meaningful beneficial effects were confirmed with the 29 outcome measures used. Finally, 11 articles also confirmed users’ satisfaction with regard to the soft robotic glove, while some articles also noticed an increased engagement in the rehabilitation program with this technology. Despite the heterogeneity across studies, soft robotic gloves stand out as a safe and promising technology to improve hand- and finger-related dexterity and functional performance. However, strengthened evidence of the effects or effectiveness of such devices is needed before their transition from laboratory to clinical practice.

Sparse spiral phased arrays are advantageous for many emerging air-coupled ultrasonic applications, since grating lobes are prevented without being constrained to the half-wavelength element spacing requirement of well-known dense arrays. As a result, the limitation on the maximum transducer diameter is omitted and the aperture can be enlarged for improving the beamforming precision without requiring the number of transducers to be increased. We demonstrate that in-air imaging, in particular, benefits from these features, enabling large-volume, unambiguous and high-resolution image formation. Therefore, we created an air-coupled ultrasonic phased array based on the Fermat spiral, capable of transmit, receive and pulse-echo operation, as well as 3D imaging. The array consists of 64 piezoelectric 40-kHz transducers (Murata MA40S4S), spanning an aperture of 200 mm. First, we provide an application-independent numerical and experimental characterization of the conventional beamforming performance of all operation modes for varying focal directions and distances. Second, we examine the resulting imaging capabilities using the single line transmission technique. Apart from the high maximum sound pressure level of 152 dB, we validate that unambiguous high-accuracy 3D imaging is possible in a wide field of view (±80°), long range (20 cm to 5 m+) and with a high angular resolution of up to 2.3°. Additionally, we demonstrate that object shapes and patterns of multiple reflectors are recognizable in the images generated using a simple threshold for separation. In total, the imaging capabilities achieved are promising to open up further possibilities, e.g. robust object classification in harsh environments based on ultrasonic images.