Power consumption is forecast by the International Technology Roadmap of Semiconductors (ITRS) to pose long-term technical challenges for the semiconductor industry. The purpose of this paper is threefold: (1) to provide an overview of strategies for powering MEMS via non-regenerative and regenerative power supplies; (2) to review the fundamentals of piezoelectric energy harvesting, along with recent advancements, and (3) to discuss future trends and applications for piezoelectric energy harvesting technology. The paper concludes with a discussion of research needs that are critical for the enhancement of piezoelectric energy harvesting devices.

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Powering MEMS portable devices—a review of non-regenerative and regenerative power supply systems with special emphasis on piezoelectric energy harvesting systems

Recent development in lead-free perovskite piezoelectric bulk materials

An apparatus for cleansing wounds in which irrigant fluid from a reservoir connected to a conformable wound dressing and wound exudate from the dressing are recirculated by a device for moving fluid through a flow path which passes through the dressing and a means for fluid cleansing and back to the dressing. The cleansing means (which may be a single-phase, e.g. microfiltration, system or a two-phase, e.g. dialytic system) removes materials deleterious to wound healing, and the cleansed fluid, still containing materials that are beneficial in promoting wound healing, is returned to the wound bed. The dressing and a method of treatment using the apparatus.

Apparatus for aspirating, irrigating and cleansing wounds

Ultrasound applicators able to both image a treatment site and administer ultrasound therapy include an array of transducer elements that can be focused. In several embodiments, an electronically phased array is used for controlling the focal point of an ultrasound beam. The ultrasound beam produced thereby can also be electronically steered. To reduce the quality factor or Q of the array when the array is used for imaging, an electronic switch is selectively closed, placing a resistance in parallel with each of the array elements. A flexible array is employed in several embodiments and is selectively bent or flexed to vary its radius of curvature and thus control the focal point and/or a direction of focus of the array. In another embodiment, each of the transducer elements comprising the array are individually mechanically pivotable to steer the ultrasonic beam produced by the transducer elements.

Ultrasound transducers for imaging and therapy

In some examples, nerves surrounding arteries or leading to organs are targeted with energy sources to correct or modulate physiologic processes. In some examples, different types of energy sources are utilized singly or combined with one another. In some examples, bioactive agents or devices activated by the energy sources are delivered to the region of interest and the energy is enhanced by such agents or the agents are enhanced by the energy sources.

Energetic modulation of nerves

Large-area flexible piezoelectric composite transducer elements and large-area arrays of such transducer elements have sufficient flexibility to conform to the contours of the human anatomy, e.g., the hip, spine. These transducer elements and arrays support at least 2.0 mm deflection under flexural bending, facilitating the more efficient coupling and transfer of acoustic energy to the body. The two techniques for fabrication processing are the spiral fiber method and the dice-and-fill method. The transducer system incorporates a flexible matching layer and a flexible housing fabricated with the same polymer component used in the array and matching layer. The resulting flexible transducer system allows for medical therapeutic applications as promoting the healing of bone fractures and tissue wounds at any section or multiple sections of the human anatomy, and can be extended to medical diagnostic ultrasound and nondestructive testing applications.

Arrays made from flexible transducer elements

A high-displacement piezoelectric actuator, employing spiral geometry of a curved piezoelectric strip is described. The monolithic actuators are fabricated using a layered manufacturing technique, fused deposition of ceramics, which is capable of prototyping electroceramic components with complex shapes. The spiral actuators (2–3 cm in diameter) consisted of 4–5 turns of a lead zirconate titanate ceramic strip with an effective length up to 28 cm. The width was varied from 0.9 to 1.75 mm with a height of 3 mm. When driven by the electric field applied across the width of the spiral wall, the tip of the actuator was found to displace in both radial and tangential directions. The tangential displacement of the tip was about 210 μm under the field of 5 kV/cm. Both the displacement and resonant frequency of the spirals could be tailored by changing the effective length and wall width. The blocking force of the actuator in tangential direction was about 1 N under the field of 5 kV/cm. These properties are advantageous for high-displacement low-force applications where bimorph or monomorph actuators are currently employed.

High-displacement spiral piezoelectric actuators

Multi-frequency harmonic arrays: initial experience with a novel transducer concept for nonlinear contrast imaging.

This paper discusses the fabrication and characterization of a single-element ultrasonic transducer with a lead-free piezoelectric active element. A piezoelectric ceramic with composition of 0.88Bi0.5Na0.5TiO3–0.08Bi0.5K0.5TiO3– 0.04Bi0.5Li0.5TiO3 was chosen as the active element of the transducer. This composition exhibited a thickness coupling coefficient (kt) of 0.45, a dielectric constant of 440 (at 1 kHz), and a longitudinal piezoelectric coefficient (d33) of 84 pC?N–1. To make the transducer, the ceramic was sandwiched between an epoxy–tungsten backing layer and a silver epoxy matching layer. An epoxy lens was also incorporated into the transducer?s design to focus the ultrasound beam. The focused transducer with a center frequency of about 23 MHz demonstrated a –6-dB bandwidth of 55% and an insertion loss of –32 dB; the –20-dB pulsed length was measured to be 150 ns. A phantom made of copper wires (30 μm in diameter) was utilized to investigate the imaging capability of the transducer. The results indicated that the fabricated transducer, with a lateral resolution of 260 μm and a relatively high depolarization temperature, could be considered as a candidate for replacement of lead-based ultrasonic transducers.

Fabrication and evaluation of a single-element Bi 0.5 Na 0.5 TiO 3 -based ultrasonic transducer

Advanced Cerametrics Inc. has conceived of and developed the Viscous-Suspension-Spinning Process (VSSP) to produce continuous fine filaments of nearly any powdered ceramic material. VSSP lead zirconate titanate (PZT) fiber tows with 100 and 790 filaments have been spun in continuous lengths exceeding 1700 meters. Sintered PZT filaments typically are 10-25 microns in diameter and have moderate flexibility. Prior to carrier burnout and sintering, VSSP PZT fibers can be formed into 2D and 3D shapes using conventional textile and composite forming processes. While the extension of PZT is on the order of 20 microns per linear inch, a woven, wound or braided structure can contain very long lengths of PZT fiber and generate comparatively large output strokes from relatively small volumes. These structures are intended for applications such as bipolar actuators for fiber optic assembly and repair, vibration and noise damping for aircraft, rotorcraft, automobiles and home appliances, vibration generators and ultrasonic transducers for medical and industrial imaging. Fiber and component cost savings over current technologies, such as the dice-and-fill method for transducer production, and the range of unique structures possible with continuous VSSP PZT fiber are discussed. Recent results have yielded 1-3 type composites (25 vol% PZT) with d 33 = 340 pC/N, K = 470, and g 33 = 80 mV/N, k t = 0.54, k p = 0.19, d h = 50.1pC/N and g h = 13 mV/N.

Bahram Jadidian

Papers

Arrays made from flexible transducer elements

High-displacement spiral piezoelectric actuators

Multi-frequency harmonic arrays: initial experience with a novel transducer concept for nonlinear contrast imaging.

Fabrication and evaluation of a single-element Bi 0.5 Na 0.5 TiO 3 -based ultrasonic transducer

Production of continuous piezoelectric ceramic fibers for smart materials and active control devices