Air-Coupled Ultrasonic Ferroelectret Receiver with Additional DC Voltage

Highly sensitive air-coupled ultrasonic sensors are essential for various applications such as testing of composite materials. One of the major challenges for the development of air-coupled ultrasonic sensors is the impedance matching to air. With a lower acoustic impedance than the usual piezoelectric materials, charged cellular polypropylene film (cPP) offers better matching to air with a similar piezoelectric coefficient. The piezoelectric behaviour demonstrated by cPP comes from polarized air cells that create a permanent internal voltage. The sensitivity of the sensor varies with the application of an additional DC bias voltage. Thus, this work presents a cPP ultrasonic sensor with an improvement of up to 15 ± 1 dB on the signal-to-noise ratio

A Human−Computer Interface Replacing Mouse and Keyboard for Individuals with Limited Upper Limb Mobility

People with physical disabilities in their upper extremities face serious issues in using classical input devices due to lacking movement possibilities and precision. This article suggests an alternative input concept and presents corresponding input devices. The proposed interface combines an inertial measurement unit and force sensing resistors, which can replace mouse and keyboard. Head motions are mapped to mouse pointer positions, while mouse button actions are triggered by contracting mastication muscles. The contact pressures of each fingertip are acquired to replace the conventional keyboard. To allow for complex text entry, the sensory concept is complemented by an ambiguous keyboard layout with ten keys. The related word prediction function provides disambiguation at word level. Haptic feedback is provided to users corresponding to their virtual keystrokes for enhanced closed-loop interactions. This alternative input system enables text input as well as the emulation of a two-button mouse

Two-dimensional flexural ultrasonic phased array for flow measurement

The arrival time detection probability and the measurement range of transit-time ultrasonic flow meters are undermined by the sound drift effect. One solution to this problem is utilizing a phased-array beam steering technique to compensate the bend of the ultrasonic beams. The design, the fabrication and the characterization of two-dimensional flexural ultrasonic phased arrays is investigated in this paper. A meter body with an inner diameter of 146 mmis machined to accommodate the arrays, and flow tests are carried out at different flow rates ranging from 0 to 2500 m3/h. Experimental results indicate that, with the increase of flow rate, the optimum steering angle of arrays increases from 30° to 40.5° when ultrasonic beams travel upstream and decreases from 30° to 22.5° when ultrasonic beams travel downstream. This proof-of-concept design demonstrates the potential of the flexural ultrasonic phased array as an accurate, economic, efficient, and robust solution for gas flow measurement

Frequency-Dependent Ultrasonic Stimulation of Poly(N-isopropylacrylamide) Microgels in Water

As a novel stimulus, we use high-frequency ultrasonic waves to provide the required energy for breaking hydrogen bonds between Poly(N-isopropylacrylamide) (PNIPAM) and water molecules while the solution temperature is maintained below the volume phase transition temperature (VPTT = 32 °C). Ultrasonic waves propagate through the solution and their energy will be absorbed due to the liquid viscosity. The absorbed energy partially leads to the generation of a streaming flow and the rest will be spent to break the hydrogen bonds. Therefore, the microgels collapse and become insoluble in water and agglomerate, resulting in solution turbidity. We use turbidity to quantify the ultrasound energy absorption and show that the acousto-response of PNIPAM microgels is a temporal phenomenon that depends on the duration of the actuation. Increasing the solution concentration leads to a faster turbidity evolution. Furthermore, an increase in ultrasound frequency leads to an increase in the breakage of more hydrogen bonds within a certain time and thus faster turbidity evolution. This is due to the increase in ultrasound energy absorption by liquids at higher frequencies

Highly Efficient Piezoelectrets through Ultra-Soft Elastomeric Spacers

Piezoelectrets are artificial ferroelectrics that are produced from non-polar air-filled porous polymers by symmetry breaking through high-voltage-induced Paschen breakdown in air. A new strategy for three-layer polymer sandwiches is introduced by separating the electrical from the mechanical response. A 3D-printed grid of periodically spaced thermoplastic polyurethane (TPU) spacers and air channels was sandwiched between two thin fluoroethylene propylene (FEP) films. After corona charging, the air-filled sections acted as electroactive elements, while the ultra-soft TPU sections determined the mechanical stiffness. Due to the ultra-soft TPU sections, very high quasi-static (22,000 pC N⁻¹) and dynamic (7500 pC N⁻¹) d₃₃ coefficients were achieved. The isothermal stability of the d₃₃ coefficients showed a strong dependence on poling temperature. Furthermore, the thermally stimulated discharge currents revealed well-known instability of positive charge carriers in FEP, thereby offering the possibility of stabilization by high-temperature poling. The dependences of the dynamic d₃₃ coefficient on seismic mass and acceleration showed high coefficients, even at accelerations approaching that of gravity. An advanced analytical model rationalizes the magnitude of the obtained quasi-static d₃₃ coefficients of the suggested structure indicating a potential for further optimization

Ferroelectret energy harvesting with 3D‐printed air‐spaced cantilever design

Vibrational energy harvesters of air-spaced cantilever design, utilizing ferroelectrets as the electroactive element, are a very recent concept. Such systems, based on the d₃₁ piezoelectric effect are further studied with harvesters of improved design, partially implemented by additive manufacturing. The focus of the present work is on the dependence of frequency response, resonance frequency, and generated power on the distance of the ferroelectret from the cantilever beam and on the pre-stressing of the ferroelectret. Experimental data are compared with both analytical and numerical evaluations. It is found that the power generated can be increased by one to two orders of magnitude by proper choice of distance. A suitable pre-stress yields another increase of power by a factor of 2 to 10 and linearizes the response.Thus, normalized output powers more than 1000μW referred to an acceleration of 9.81 ms² and a seismic mass of 3.5 g, can be achieved, which significantly exceeds previous results of cantilever-based energy harvesters

Acousto-Optic Modulation in Ambient Air

Control over intensity, shape, direction and phase of coherent light is a cornerstone of 20 photonics. Modern laser optics, however, frequently demands parameter regimes where either the wavelength or the optical power restricts control e.g. due to absorption or damage. Limitations are imposed by the properties of solid media, upon which most photonic control schemes rely. We propose to circumvent these limitations using gas media tailored by high-intensity ultrasound waves. We demonstrate a first implementation of this approach by modulating ultrashort laser 25 pulses using ultrasound waves in ambient air, entirely omitting transmissive solid media. At peak powers of 20 GW exceeding the limits of solid-based acousto-optical modulation by about three orders of magnitude, we reach a diffraction efficiency greater than 50% while preserving excellent beam quality. Our results open a route towards versatile gas-phase Sono-Photonic methods, i.e. gas-based photonic systems controlled by sonic waves.Comment: 20 pages, including 11 pages of main text and 9 pages of supplementary text, 3 figures, 3 supplemtary figures, 1 supplementary tabl

Performance Simulation of Unforced Choice Paradigms in Parametric Psychometric Procedures

This paper shows an implementation of the Psi andUML (Updated Maximum Likelihood) methods to incorporate unforced choice paradigms (nAUC) and simulation results for repeatability, efficiency and accuracy. Parametric methods like Psi and UML promise higher accuracy and efficiency compared to classic and non-parametric methods and support fixed sets of stimuli. Unforced choice paradigms have shown similar erformance as forced choice paradigms but are expected to create less confusion for test subjects for low stimuli intensities. An implementation of an unsure test person is presented. Psi and UML methods are compared to the Unforced Weighted Up-Down method (UWUD) in two Monte Carlo simulations. Considered measures are Variation Coefficient for repeatability, Sweat Factor for efficiency and threshold bias for accuracy. Psi and UML seem suitable to be combined with nAUC paradigms. Variation coefficients are smaller than 0.08 (Psi) and 0.15 (UML) for YN, 2AFC and 3AFC paradigms. UML-based procedures show a bias less than 2 %, while Psi-based procedures exhibit paradigm-dependent bias up to 10 %. Psi is at least twice as efficient as UML for 40 simulated trials. Because of large bias and poor repeatability, only the combination of UWUD with a 3AUC-paradigm shows results comparable to parametric procedures with nAUC paradigms