High Mechanical Resonance Frequencies Research Articles

Johnson-noise-limited cancellation-free microwave impedance microscopy with monolithic silicon cantilever probes

Microwave impedance microscopy (MIM) is an emerging scanning probe technique for nanoscale complex permittivity mapping and has made significant impacts in diverse fields. To date, the most significant hurdles that limit its widespread use are the requirements of specialized microwave probes and high-precision cancellation circuits. Here, we show that forgoing both elements not only is feasible but also enhances performance. Using monolithic silicon cantilever probes and a cancellation-free architecture, we demonstrate Johnson-noise-limited, drift-free MIM operation with 15 nm spatial resolution, minimal topography crosstalk, and an unprecedented sensitivity of 0.26 zF/√Hz. We accomplish this by taking advantage of the high mechanical resonant frequency and spatial resolution of silicon probes, the inherent common-mode phase noise rejection of self-referenced homodyne detection, and the exceptional stability of the streamlined architecture. Our approach makes MIM drastically more accessible and paves the way for advanced operation modes as well as integration with complementary techniques.

A reconfigurable ladder-shaped THz metamaterial integrated with a microelectromechanical cantilever array

We experimentally demonstrate a microelectromechanically reconfigurable ladder-shaped metamaterial (LS-MM) operating in a terahertz (THz) range. Ultrasmall cantilever actuators with a beam length of 14 μm are employed to independently reshape each unit cell of the LS-MM, correspondingly switching the transmission response of THz waves. The microelectromechanically driven LS-MM achieves a tuning contrast of 60.1% in transmittance at 0.78 THz and a 0.9-rad delay in the transmission phase shift at 1.35 THz through the off-to-on reconfiguration. In particular, the cantilever actuator has a high mechanical resonant frequency of 585 kHz owing to its small size. The microelectromechanically driven LS-MM advantageously offers a pathway for applications requiring fast tunable transmission modulations, such as high-resolution THz imaging and wireless communications.

Fast-Response Sensitivity-Enhanced All-Fiber Fabry–Pérot High-Pressure Sensor for Internal Combustion Engines

A novel fast-response sensitivity-enhanced high-temperature all-fiber Fabry–Pérot high-pressure sensor formed with a hard-core diaphragm is proposed and demonstrated. The structure can effectively improve device pressure sensitivity and eliminate additional reflection interference from the outer surface. Theoretical and experimental results show that sensor pressure sensitivity increased to approximately two times the original value when the diaphragm thickness is decreased from 5 mm to 11 μm. Moreover, simulation analysis indicates that sensors with different diaphragm thicknesses, from 10 μm to 2 mm, all possess high mechanical resonant frequency exceeding 100 kHz. In addition, a sensor was tested based on an intensity demodulation method and demonstrated a stable pressure sensitivity of 0.23 V/MPa, a hysteresis of less than 1.5%, and repeatability accuracy of less than 0.8% in the range of 40–200 °C. Field dynamic tests in a diesel engine demonstrated that the fiber sensor not only has an excellent dynamic characteristic but is also consistent with a commercial Kistler sensor.

Nonlinear Identification with Constraints in Frequency Domain of Electric Direct Drive with Multi-Resonant Mechanical Part

Knowledge of a direct-drive model with a complex mechanical part is important in the synthesis of control algorithms and in the predictive maintenance of digital twins. The identification of two-mass drive systems with one low mechanical resonance frequency is often described in the literature. This paper presents an identification workflow of a multi-resonant mechanical part in direct drive with up to three high-frequency mechanical resonances. In many methods, the identification of a discrete time (DT) model is applied, and its results are transformed into a continuous-time (CT) representation. The transformation from a DT model to a CT model has limitations due to nonlinear mapping of discrete to continuous frequencies. This problem may be overcome by identification of CT models in the frequency domain. This requires usage of a discrete Fourier transform to obtain frequency response data as complex numbers. The main work presented in this paper is the appropriate fitting of a CT model of a direct-drive mechanical part to complex number datasets. Fitting to frequency response data is problematic due to the attraction of unexcited high frequency ranges, which lead to wrong identification results of multi-mass (high order) drive systems. Firstly, a CT fitting problem is a nonlinear optimization problem, and, secondly, complex numbers may be presented in several representations, which leads to changes in the formulation of the optimization problem. In this paper, several complex number representations are discussed, and their influence on the optimization process by simulation evaluation is presented. One of the best representations is then evaluated using a laboratory setup of direct drive with unknown parameters of three high mechanical resonance frequencies. The mechanical part of the examined direct drive is described by three mechanical resonances and antiresonances, which are characteristic of a four-mass drive system. The main finding is the addition of frequency boundaries in the identification procedure, which are the same as those in the frequency range of the excitation signal. Neither a linear least-square algorithm nor a nonlinear least-square algorithm is suitable for this approach. The usage of nonlinear least-square algorithm with constraints as a fitting algorithm allows one to solve the issue of modeling multi-mass direct-drive systems in the frequency domain. The second finding of this paper is a comparison of different cost functions evaluated to choose the best complex number representation for the identification of multi-mass direct-drive systems.

Einstein–de Haas effect at radio frequencies in and near magnetic equilibrium

The Einstein-de Haas (EdH) effect and its reciprocal the Barnett effect are fundamental to magnetism and uniquely yield measures of the ratio of magnetic moment to total angular momentum. These effects, small and generally difficult to observe, are enjoying a resurgence of interest as contemporary techniques enable new approaches to their study. The high mechanical resonance frequencies in nanomechanical systems offer a tremendous advantage for the observation of EdH torques in particular. At radio frequencies, the EdH effect can become comparable to or even exceed in magnitude conventional cross-product magnetic torques. In addition, the RF-EdH torque is expected to be phase-shifted by 90 degrees relative to cross-product torques, provided the magnetic system remains in quasi-static equilibrium, enabling separation in quadratures when both sources of torque are operative. Radio frequency EdH measurements are demonstrated through the full hysteresis range of micrometer scale, monocrystalline yttrium iron garnet (YIG) disks. Equilibrium behavior is observed in the vortex state at low bias field. Barkhausen-like features emerge in the in-plane EdH torque at higher fields in the vortex state, revealing magnetic disorder too weak to be visible through the in-plane cross-product torque. Beyond vortex annihilation, peaks arise in the EdH torque versus bias field, and these together with their phase signatures indicate additional utility of the Einstein-de Haas effect for the study of RF-driven spin dynamics.

An electro-thermally activated rotary micro-positioner for slider-level dual-stage positioning in hard disk drives

Slider-level micro-positioners are useful to assist a voice coil motor to perform fine head positioning over a Tb/in2 magnetic disk. Recently, a new kind of slider-level micro-positioner was developed using the thermal unimorph of the Si/SU8 composite. It has the advantages of a very small footprint and high mechanical resonant frequency, but its stroke generation is inadequate, with a 50 nm dynamic stroke at 1 kHz. There is a need for a larger thermally induced stroke. This paper presents a rotary design of an electrothermal micro-positioner to address the stroke requirements without consuming more power or decreasing the mechanical resonant frequency. Experimental studies show the present rotary design can produce a six-fold larger displacement, as compared to the previous lateral design, while possessing a 35 kHz resonant frequency. In addition, simple analytical models were developed to estimate: (i) the rotational stiffness and system’s natural frequency, (ii) thermal unimorph bending and stage rotation, and (iii) the system’s thermal time constant for this rotary electro-thermal micro-positioner. This study found that this rotary electro-thermal micro-positioner can meet the basic stroke requirement and high mechanical resonant frequency for a moving slider, but its thermal cut-off frequency needs to be increased further.

Improved design of polymeric composite electrothermal micro-actuator for high track density hard disk drives

Recently, we have developed a polymeric composite electrothermal micro-actuator for dual-stage applications in hard disk drives (HDDs). The polymer composite was demonstrated with a larger thermal expansion as compared to silicon. Yet, the previous design of polymeric composite thermal actuator was stiff, having a high mechanical resonant frequency at 33 kHz and a moderate static displacement stroke of 50 nm at 4 V. An even larger stroke above 100 nm is generally required to meet the need of HDD dual-stage systems. To meet the requirement for a large stroke, we presented an improved design of polymeric composite electrothermal micro-actuator by increasing flexibility of the composite thermal benders. As compared to the previous design, the new design doubled the displacement stroke up to 106 nm at 4 V while it maintained a high mechanical resonant frequency of 31 kHz, slightly below that of the previous design. In addition, a finite element analysis showed that electrothermal activation of the micro-actuator is rather localized and it causes only a small temperature rise of the neighbouring parts of head gimbal assembly. These good performances suggested that this improved design of thermal micro-actuator is promising for high bandwidth dual-stage positioning systems in future high track density HDDs.

Study on fast linear scanning for a new laser scanner

In the field of lidar system design, there is a need for laser scanners that offer fast linear scanning, are small size and have small a rotational inertia moment. Currently, laser scanners do not meet the above needs. A new laser scanner based on two amplified piezoelectric actuators is designed in this paper. The laser scanner has small size, high mechanical resonance frequencies and a small rotational inertia moment. The size of the mirror is 20 mm×15 mm. To achieve fast linear scanning performance, an open-loop controller is designed to compensate the hysteresis behavior and to restrain oscillations that are caused by the mechanical resonances of the scanner's mechanical structure. By comparing measured scanning waveforms, nonlinearities and scan line images between the uncontrolled and controlled scanner, it was found that the scanning linearity of linear scanning was improved The open-loop controlled laser scanner realizes linear scanning at 250 Hz with optical scan angle of ±12 mrad.

Design and input-shaping control of a novel scanner for high-speed atomic force microscopy

A novel design of a scanning unit for atomic force microscopy (AFM) is presented that enables scanning speeds three orders of magnitude faster than compared to conventional AFMs. The new scanner is designed for high mechanical resonance frequencies, based on a new scanner design, which is optimized using finite element analysis. For high-speed scanning a new controller, based on input-shaping techniques, has been developed that reduces imaging artifacts due to the scanner’s dynamics. The implementation of the new AFM system offers imaging capabilities of several thousand lines per second with a scanning range of 13 μm in both scanning directions, and the freedom to choose the fast scan-axis in any arbitrary direction in the X– Y-plane.

Fiber-Pigtailed Electrothermal MEMS Iris VOA

A high-performance variable optical attenuator, which is based on an electrothermally actuated iris with a square pupil, is demonstrated. The device is fabricated from two separate dies that are formed by deep reactive ion etching of bonded silicon-on-insulator material. The iris die is inserted into an elastic clamp on a base-plate die carrying spring-mounted fiber alignment features, allowing the iris to be held in the optical path between two expanded core fibers. A novel aperture that dynamically reduces the clearances between the shutter blades is used to achieve an extinction of 25 dB and a wavelength dependent loss of plusmn1 dB at 1550-nm wavelength. Synchronous blade motion is achieved using thermally optimized folded electrothermal actuators with undercut hot arms, which reduce the operating power to 240 mW and allow a high mechanical resonant frequency. Optical analysis is carried out using a scalar model and diffraction theory. Thermomechanical analysis is performed using a 1-D model and finite element simulation (ANSYS). Good agreement is obtained between the models and by experimentation.

DESIGN AND CHARACTERIZATION OF A NOVEL SCANNER FOR HIGH-SPEED ATOMIC FORCE MICROSCOPY

A novel design of a scanning unit for atomic force microscopy (AFM) is presented that enables scanning speeds three orders of magnitude faster than commercial AFMs. The new scanner concept is based on flexures that decouple the axes of motion and clamp the actuators on both sides in order to shorten the mechanical path lengths to a functional minimum. The positioner is designed for high mechanical resonance frequencies by optimizing the structure using finite element analysis. The implementation of the new system offers imaging capabilities of several thousand lines per second with a scanning range of 13 micrometers in both scanning directions, and the freedom to rotate the image.

On the stability of Besocke-type scanners

A widespread used construction for the coarse approach mechanism in scanning probe microscopy is the Besocke beetle type. Using stick-slip motion the scanner can thereby be positioned on the millimeter scale horizontally and vertically. This apparent advantage of a high flexibility is bought on the expense of a reduced mechanical stability. Here we present an analysis of the vibrational response of a beetle-type scanner and based on this, a very stable optimized scanner setup. In this setup, shear stack piezoelectric elements are used resulting in very high mechanical resonance frequencies and overall stability.

MEMS-based integrated head/actuator/slider for hard disk drives

We propose a new integrated head/actuator/slider concept for hard disk drives. This slider is batch fabricated on the sacrificial layer of a wafer together with an electrostatic microactuator via micromachining technology. We present the basic integrated head/actuator/slider design, the fabrication and flying-height tests of a micromachined slider body, and the design, fabrication, and testing of a prototype electrostatic microactuator. Slider warpage was analyzed and successfully suppressed to within 0.1 /spl mu/m. The slider was flown over a glass disk at heights of 26-81 nm and at linear velocities of 5-13 m/s. The test results of the electrostatic microactuator showed a stroke of 0.55 /spl mu/m, a very high mechanical resonant frequency of 34 kHz due to its low moving mass of 0.85 /spl mu/g, and a large force, estimated to be 21.3 /spl mu/N, generated by the actuator.

A stable scanning tunneling microscope designed for investigations of organic thin films in air

A new and stable scanning tunneling microscope (STM) system has been constructed for the investigation of thin organic films in air. The STM unit is made of Macor, which is machinable ceramic and has a small thermal expansion coefficient and a high mechanical stiffness. Three-dimensional coarse position adjustment (within 3 μm) is carried out using five stacked piezoelectric transducers (PZTs). A cross-type configuration is used to prevent the thermal effect of the x- and y-direction displacement mechanism. In order to achieve high resolution, x-, y-, and z-direction displacements are performed using a tube-type PZT. The z direction of the tube PZT has a high mechanical resonant frequency of 24.4 kHz. Therefore, this STM unit is mechanically rigid, and allows stable operation under mechanical disturbances (sound and mechanical vibration). Moreover, this STM unit can be controlled for 24 h or longer by using an ordinary operational amplifier, because thermal effects are compensated. The STM system can also be used to obtain information on the spatially resolved local tunneling barrier height, which is sensitive to the chemical structure of the sample. The capabilities of this newly designed STM are demonstrated with experiments investigating the morphology and tunneling barrier height of stearic acid thin films on indium-tin-oxide substrates.

A miniaturized scanning tunneling microscope with large operation range

A small sized (<1 cm3) and low mass (2.5 g) scanning tunneling microscope (STM) with automatized large range tip approach is introduced. By concentric arrangement of two piezotubes a temperature drift compensation is realized. Using a simple likewise concentric glass tube inside the inner piezotube as a frictional wire holder, an unlimited longitudinal adjustment range by stepwise inertial translation could be obtained. High mechanical resonance frequencies due to the low mass as well as the mechanical independency of the environment by purely electronic control reduce remarkably the effort for mechanical damping and make the system fast and particularly suited for special applications such as low temperature STM. Sample change and restoration of the tip position require only a few seconds.

Deformable grating optical modulator

A new type of light modulator, the deformable grating modulator, based on electrically controlling the amplitude of a micromachined phase grating is described. Mechanical motion of one quarter of a wavelength is sufficient for switching in this device. The small mechanical motion allows the use of structures with high mechanical resonance frequencies. We have developed a deformable grating modulator with a bandwidth of 1.8 MHz and a switching voltage of 3.2 V and have demonstrated modulation with 16 dB of contrast. Smaller devices with bandwidths of as much as 6.1 MHz and predicted switching voltages of less than 10 V were also fabricated.

Improved scanning ion-conductance microscope using microfabricated probes

The scanning ion-conductance microscope (SICM) is a member of the growing family of scanning probe microscopes, which includes the scanning tunneling microscope and the atomic force microscope. The SICM scans a small aperture over a sample immersed in electrolyte and measures the ionic current flowing through the aperture. This current serves as the feedback signal for standard scanning probe microscope electronics, which can then provide images of the topography of a sample surface, or the distribution of ionic current flow through the pores in a porous sample. The resolution of this microscope is essentially set by the size of the aperture. We have developed silicon microfabricated probes for the SICM that greatly improve its performance. Previous SICMs used fragile glass micropipettes as probes. The new microfabricated probes are end caps for a 1.5 mm glass capillary. A hollow tip is fabricated in the center of a silicon membrane. An aperture is formed at the tip apex using microfabrication techniques including photolithography and etching, giving typical minimum diameters of 250 nm. Unlike the glass micropipettes used previously, the new tips are compact and hence mechanically robust. The tips are mounted on a flexible membrane that allows the tip to deflect away from the surface in case of a collision with the sample surface. In addition, the microfabricated probes have been designed to have a high mechanical resonant frequency, allowing scan speeds up to 50 times faster than used with glass micropipette probes. With these new probes we have imaged the surface topography of a plastic diffraction grating, and the ion flow through porous polycarbonate membrane filters. Finally, the new microfabricated probe was designed as a general probe that may be adapted for use in other scanning probe microscopes.