Aiming at the strong capacitive impedance of piezoelectric stack actuators, the principle to improve the dynamic performance of piezoelectric stack actuators through increasing the peak values of the output current and output power of power amplifiers are explored. Based on the error-amplified principle, the method that enlarges the output voltage of the dynamic power amplifiers through using a high-voltage operational amplifier in series with the power booster section, as well as the method that improves the peak values of the output current and output power through paralleling multiple power booster units utilizing the class AB quasi-complementary symmetry power amplifier circuits, are proposed and analyzed. Utilizing the proposed principle and method, a high-voltage and high-power amplifier for driving piezoelectric stack actuators is developed, simulated, and tested. The research results indicate that the developed power amplifier not only can break through the limit that each single power booster unit can only achieve the power output <125 W, but also can disperse the current and power averagely among the power booster units in parallel, which are beneficial to realizing the high power output with good static and dynamic performance and enhancing the reliability of the power amplifier.

In this article, in order to linearize the hysteresis behavior of stack piezoelectric ceramic actuators (SPCAs), the feedforward linearization method based on the BoucWen model and the hybrid linearization method combining the feedforward method and PI feedback loop are proposed and explored. The rapid control prototypes of the linearization controllers for the SPCA are established and tested. The research results show that both the feedforward and hybrid linearization methods can linearize the hysteresis behavior and the SPCAs with linearization controllers can be regarded as linear actuators. However, the linearization accuracy using the feedforward method is confined by the modeling error of the BoucWen model. Although the proposed hybrid method combining the feedforward method and the PI feedback loop can reach higher linearization accuracy than that with the feedforward method, the hybrid method will result in high frequency components in the additional voltage, which will have a serious impact on the lifespan of the controlled SPCA. Utilizing the linearization methods proposed in this article, the open-loop and closed-loop controls for the tip displacement of a piezoelectric-driven microgripper are realized, which indicates that the proposed linearization methods can simplify the control of SPCAs and SPCA-based systems with high accuracy.

In this article, based on the classical laminated plate theory, a new static deflection model for CPUAs subjected to voltage is established and the bonding layer is taken into account as an individual layer. According to the established analytical model, the influences of the structural parameters and material properties of the CPUA on the transverse deflection are numerically simulated and the static and dynamic characteristics of the CPUA are experimentally tested. The research results show that the predicted static deflections of the CPUA by the established deflection model in this article agree well with the measured results, the established static deflection model considering the bonding layer is more accurate than the existing model neglecting the bonding layer, and the maximum relative error is reduced by 8.45%. The static deflections of the CPUA are apparently affected by the structural parameters and the material properties, which indicate that the performance of the CPUA can be optimized by the structural parameters and material properties. Because the hysteresis of the piezoelectric material is not considered when establishing the static deflection model, the apparent error exists when utilizing the static deflection model to predict the dynamic characteristics of the CPUA.

A tip-sensitive fibre-optic Bragg grating ultrasonic hydrophone (TSFBGUH) with high spatial resolution for measuring high-intensity focused ultrasound (HIFU) fields is reported. When measuring a HIFU field, the sensitive axis of the TSFBGUH with a flexible fibre-optic sensor holder should be in parallel with the acoustic axis of the HIFU transducer to ensure the measured ultrasound impinges on the tip of the TSFBGUH. The TSFBGUH system has been established and tested. The experimental results show that the acoustic pressure sensitivity of the TSFBGUH system is about 31.3 mV/MPa within the measurement range of 10 MHz and the noise equivalent pressure is about 10.4 kPa.Introduction: High-intensity focused ultrasounds (HIFUs) have been used to cure cancers non-invasively by destroying tumours through heating and acoustic cavitations. To ensure the treatment safety, the acoustic pressure distributions and the size of the focal regions of HIFU fields need to be measured and characterised accurately. At present, HIFU fields are commonly measured and characterised by piezoelectric needle hydrophones, fibre-optic hydrophones etc. [1][2][3][4]. The fibre-optic hydrophones possess the merits of simple configuration, miniaturisation and immunity to electromagnetic interference. The fibre-optic Bragg gratings (FBGs) have been developed into various sensors for measuring static pressures [5], ultrasonic pressures [6-13] and other physical parameters. The FBG hydrophones, possessing the capability of multiplexing and withstanding high acoustic pressure, have attracted much interest [9-13]. All the above-mentioned FBG hydrophones sensed ultrasounds through the lateral side of FBGs, which could break the hydrophones by the ultrasonic wave and limit the spatial resolution [2,8]. Up to now, we have not found the literature about the tip-sensitive FBG hydrophones for measuring HIFU fields.In this Letter, a tip-sensitive FBG ultrasonic hydrophone (TSFBGUH) for measuring HIFU fields is described. The TSFBGUH system and the experimental setup have been built to measure the HIFU fields generated by a 0.965 MHz HIFU transducer in continuous mode.

SummaryIn this paper, a bilateral prediction and intersection calculation autofocus method for automated microscopy, which obtains the in-focus position by calculating the intersection of the predicted left and right focus measure curves located respectively in the left and right sides of the peak position of the focus measure curve, is proposed and performed. According to the autofocus method, the area including the peak position of the focus measure curve and its left and right neighbourhoods should be determined firstly, and the left and right neighbourhoods are considered as the left and right sampling areas. The left and right focus measure curves are predicted by appropriate predicting models according to the two sample sequences, which comprise the focus values by evaluating the sampled images in the left sampling area and right sampling area, respectively and their corresponding sampling positions. The intersection of the predicted left and right focus measure curves is calculated and can be considered as the in-focus position. The autofocus can be realized by moving the focus plane of the microscope to the intersection of the predicted left and right focus measure curves. The proposed bilateral prediction and intersection calculation autofocus method is experimentally verified in an automated light microscopy for implementing microassembly and micromanipulation. The theoretical analyses have shown that the proposed bilateral prediction and intersection calculation autofocus method can not only effectively avoid the principle error caused by assuming the symmetrical focus measure curve in the autofocus methods based on curve fitting, but also eliminate the possible waver search near the peak position in the modified fast climbing servo method. The experimental results have shown that the proposed bilateral prediction and intersection calculation autofocus method possesses the merits as follows: (1) the focusing accuracy is high and slightly affected by the sampling step size and (2) the focusing speed is higher than those of the 7-point hill-climbing search method and the quadratic curve fitting method with a determinate focusing accuracy.