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Piezoelectric Energy-Harvesting Systems
Published in Kenji Uchino, Micro Mechatronics, 2019
Piezoelectric materials generally convert mechanical energy to electrical energy with relatively high voltage, which means output impedance is relatively high at an off-resonance frequency. On the other hand, energy storage devices such as a rechargeable battery have low input impedance (10–100 Ω). Thus, a large portion of the excited electrical energy is reflected back if we connect the battery immediately after the rectified voltage. In order to improve energy transfer efficiency, electrical impedance matching is required.
Lab-on-a-Chip-Based Devices for Rapid and Accurate Measurement of Nanomaterial Toxicity
Published in Suresh C. Pillai, Yvonne Lang, Toxicity of Nanomaterials, 2019
Mehenur Sarwar, Amirali Nilchian, Chen-zhong Li
Electric impedance is representative of resistance in an alternating current (AC) circuit. The term impedance refers to the frequency-dependent resistance to the flow of current through circuit elements such as a capacitor, resistor, or inductor. Calculating electrical resistance for a simplified DC circuit (assuming all circuit elements are an ideal resistor) is as easy as dividing voltage by current (R = V/I). An ideal resistor has a frequency-independent resistance value, which follows Ohm’s Law at all voltage and current levels. However, most real applications comprise intricate circuit design including several electronic compartments with non-ideal and complex behaviour. Hence, impedance replaces resistance as a more general circuit parameter.
Critical examination of ultrasonic transducer characteristics and calibration methods
Published in Research in Nondestructive Evaluation, 2019
Electrical impedance is extended from electrical resistance and has a complex value. This is widely used in eddy-current testing and is represented by Z = Rz + i Xz, where real resistance Rz (in the x direction in an impedance diagram), i2 = –1, and imaginary component Xz (in the y direction). An inductor of L henry has Xz = + 2πfL (in ohms with frequency f in Hz) and a capacitance C farad has Xz = –(1/2πfC) (also in ohms). In terms of Z, a piezoelectric transducer primarily behaves as a capacitor, and its frequency dependence is inversely proportional to frequency. For example, a V103 (1) transducer has C = 432 pF and Z = 737 Ω at 0.5 MHz (or 57.3 dB) in reference to 0 dB at 1 Ω. Also for an R15 (0.15) transducer, C = 188 pF and Z = 1.69 kΩ (64.6 dB) also at 0.5 MHz. In a Z – f plot (Z in dB and f in logarithmic scale), most piezoelectric transducers show nearly straight lines with the slope of –1. Z of a transducer can be measured by passing ac signals and by dividing applied voltage by (complex) current flowing through it. The applied ac signal can be a broadband pulse or sinewave wavelets of varying frequency. Here, both methods are utilized.