Multiple solutions and corresponding power output of a nonlinear bistable piezoelectric energy harvester

We examine multiple responses of a vibrational energy harvester composed of a vertical beam and a tip mass. The beam is excited horizontally by a harmonic inertial force while mechanical vibrational energy is converted to electrical power through a piezoelectric patch. The mechanical resonator can be described by single or double well potentials depending on the gravity force from the tip mass. By changing the tip mass we examine the appearance of various solutions and their basins of attraction. Identification of particular solutions of the energy harvester is important as each solution may provide a different level of power output

Regular and chaotic vibration in a piezoelectric energy harvester

We examine regular and chaotic responses of a vibrational energy harvester composed of a vertical beam and a tip mass. The beam is excited horizontally by a harmonic inertial force while mechanical vibrational energy is converted to electrical power through a piezoelectric patch. The mechanical resonator can be described by single or double well potentials depending on the gravity force from the tip mass. By changing the tip mass we examine bifurcations from single well oscillations, to regular and chaotic vibrations between the potential wells. The appearance of chaotic responses in the energy harvesting system is illustrated by the bifurcation diagram, the corresponding Fourier spectra, the phase portraits, and is confirmed by the 0–1 test. The appearance of chaotic vibrations reduces the level of harvested energy

Computer-Aided Acoustical Simulation of Pathological Knee Joints, Part I: in vitro

Previous studies have shown that different pathological knee joints produce unique acoustical characteristics.In‐vitro simulation of acoustical signature was attempted using bovine knee joints placed in a “flexing” machine. Mechanical destruction was induced on the articular cartilage surface, and the noise produced during rubbing was picked up by a sensitive condensermicrophone, amplified, recorded, and converted into digital form. A computer program was written to perform various statistical analysis. Cartilage surface roughness was measured with a profilometer and a spatial waveform roughness distribution curve was plotted out. Preliminary results show that the unique acoustical characteristics of the various knee‐joint diseases can be simulated fairly well with this technique. This study therefore provides a rough diagnostic indication of the degree of roughness of the various types of knee‐joint diseases. [Work supported by NIH.] © 1976 Acoustical Society of Americ

Computer-Aided Acoustical Simulation of Pathological Knee Joints, Part II: in vivo

Suitable models of pathological knee‐joint diseases were created on rabbits using biological‐surgical techniques. At regular intervals during the progress of the disease, acoustical signatures were retrieved during flexion and extension of the knee joints. The noise was recorded on tape and digitized using an A/D converter. With the use of an IBM computer various statistical analysis were performed. The rabbits were sacrificed at regular intervals during the experiment and the roughness measured with a profilometer. The spatial waveform was recorded and statistically analyzed. Preliminary results showed that close correlation exists between the degree of roughness of the “diseased” cartilage and the acoustical signature emitted. This study verifies the strong correlation between the knee‐joint cartilage pathological condition and the acoustical noise emitted during extension and flexion. [Work supported by NIH.] © 1976 Acoustical Society of Americ