Husain N. Shekhani

Losses in piezoelectrics derived from a new equivalent circuit

Miniaturization of piezoelectric devices such as ultrasonic motors, transformers, and sound projectors requires high power density maintained in the piezoelectric materials. During operation, heat generation due to material losses, however, hinders the realization of high power density. As a result, it is very important to understand the loss mechanisms in piezoelectric materials to successfully realize device miniaturization and at the same time maintain a good device performance. There are three fundamental losses in piezoelectric materials: dielectric, elastic, and piezoelectric. The first two components have been intensively investigated, whereas piezoelectric loss has not received much attention, which leaves some phenomena inexplicable. To verify its significance, in this paper, a new methodology has been presented to calculate the dielectric, elastic and piezoelectric losses based on a new equivalent circuit (EC) deduced from the revised Hamilton’s Principle. The improvement of the new methodology lies in the fact that all the three losses, including the piezoelectric loss, have been fully taken in consideration. The derivations and the calculation results indicate that the piezoelectric loss is not only non-negligible, but is also larger than other two components for hard PZT materials. The significance of the piezoelectric loss component has been therefore verified. During the above verification process, an elegant and concise measuring procedure of all the losses, including piezoelectric component, has been presented from an EC aspect for the first time. The calculation and measurement also indicate that the largest mechanical quality factor exists at a frequency between resonance and antiresonance, which may suggest a new optimal working frequency for piezoelectric devices from the loss reduction viewpoint.

Advanced methodology for measuring the extensive elastic compliance and mechanical loss directly in k31 mode piezoelectric ceramic plates

Dielectric, elastic, and piezoelectric constants, and their corresponding losses are defined under constant conditions of two categories; namely, intensive (i.e., E, electric field or T, stress), and extensive (i.e., D, dielectric displacement or x, strain) ones. So far, only the intensive parameters and losses could be measured directly in a k31 mode sample. Their corresponding extensive parameters could be calculated indirectly using the coupling factor and “K” matrix. However, the extensive loss parameters, calculated through this indirect method, could have large uncertainty, due to the error propagation in calculation. In order to overcome this issue, extensive losses should be measured separately from the measurable intensive ones in lead-zirconate-titanate (PZT) k31 mode rectangular plate ceramics. We propose a new mechanical-excitation methodology, using a non-destructive testing approach by means of a partial electrode configuration, instead of the conventional full electrode configuration. For t...

Driving frequency optimization of a piezoelectric transducer and the power supply development.

Piezoelectric transducers are commonly operated at their resonance frequency. However, from a power dissipation standpoint, this is not the ideal driving frequency. In this paper, an optimized driving frequency in between the resonance and antiresonance frequencies is proposed for the piezo-transducer. First, the optimum driving frequency is characterized using a constant vibration velocity measurement method. The actual input power reveals the lowest power dissipation frequency between the resonance and the antiresonance frequencies, where the transducer behaves inductive. The electrical parameters of the transducer are then determined by an equivalent circuit formulation, which is useful for the electrical circuit analysis of the driver design. A Class E resonant inverter is used to design a capacitive output impedance driver at the optimized frequency by utilizing a series capacitor. Compared with the traditional resonance drive, driving at the optimized frequency reduces the required power by approximately half according to the measurements performed.

Thermal diffusivity measurements using insulating and isothermal boundary conditions

Many methods exist to measure thermal diffusivity using either steady state or transient techniques. Steady state methods yield large experimental error and inaccuracies. Transient techniques, namely, the laser flash method, are expensive and require specialized equipment and advanced data analysis. In this paper, a novel experimental setup is devised to evaluate thermal diffusivity. In this experiment hot isothermal and insulating boundary conditions are imposed on a flat disk sample. The transient temperature profile of the insulated side of the sample is analytically similar to a classic time constant formulation. The thermal diffusivity is proportional to the inverse time constant. This method hosts a variety of advantages over other methods such as accuracy comparable to other methods, low cost, integrated modeling of interface effects, and small sample size. Several materials with low to medium thermal diffusivity (0.1 → 3 mm(2)/s) have been measured. The diameter of the sample is 32 mm and its thickness ranges from 2 to 6.5 mm. The thermal diffusivity measurements in this experiment have an accuracy of 5% or better in comparison to the literature values.