DC-Biased Piezoelectret Film Transducers for Airborne Ultrasound

Abstract

Ultrasonic senders with DC-biased piezoelectret films were built and characterized. The generated sound pressure of the transducers is inversely proportional to the distance from the transducer and proportional to transducer size, AC-voltage, square of the frequency, and effective d 33 -coefficient of the films. With polypropylene films and DCvoltages of 1000 V, effective d 33 -coefficients of more than 750 pC/N are obtained. For an applied signal AC-voltage of 46 V rms , a transducer area of 1.8 cm 2 , and a distance of 60 mm, sound pressures exceeding 10 Pa were measured in the frequency range above 100 kHz. With stacks of 2 and 3 piezoelectret film layers, effective d 33 -coefficients up to 1500 pC/N and sound pressures of about 20 and 40 Pa, respectively, could be obtained at frequencies between 60 and 120 kHz. This represents, for otherwise equal parameters, an increase by about a factor of four compared to previous piezoelectret transducers.

A Flexible Piezoelectret Actuator/Sensor Patch for Mechanical Human–Machine Interfaces

“…For example, the applied electrical field of 0.33 V/μm (50 V for a 150 μm thick piezoelectret film) produces very weak sensation feelings for the fingertip in all tested frequencies as shown in Figure f. At 0.66 V/μm, an appreciable vibration sensation is detected with the sensation feelings, similar to that produced by a previously reported commercial PVDF actuator under 150–250 V (50–75 V/μm). , The comparisons with other previously reported actuators are summarized in Table S2 and Figure g, and this work shows low electrical field requirement (driving voltage per thickness) and high piezoelectric coefficient ( d 33 ) ,,− as the result of large charges stored by the FEP electret films and soft property of Ecoflex spacer. , …”

Flexible PET/EVA-based piezoelectret generator for energy harvesting in harsh environments

“…Flexible piezoelectret, known of high piezoelectric coefficient (d33), light-weight and lowcost, etc, has extensive transducer applications, such as energy harvesters [25][26][27][28] and loudspeakers 29 . Since the electric dipole-like charges are produced inside the materials, 25 the piezoelectret generators, one kind of electrostatic generators, have the potential to be excellent energy harvester candidates that still can perform well in harsh environments.…”

Cellular Polypropylene Piezoelectret for Human Body Energy Harvesting and Health Monitoring

“…Cellular polypropylene piezoelectret, which is flexible, light‐weight, inexpensive, and has the similar property with traditional piezoelectric materials, was first proposed by Kari Kirjavainen and co‐workers in 1990 . In the past 25 years, cellular polypropylene has been applied in many transducer applications, like loudspeakers and energy harvesters, because of its rather small specific acoustic impedance and relative high piezoelectric coefficient ( d 33 ) …”