Cantilever Array Research Articles

Multifrequency Piezoelectric Energy Harvester Based on Polygon‐Shaped Cantilever Array

This paper focuses on numerical and experimental investigations of a novel design piezoelectric energy harvester. Investigated harvester is based on polygon‐shaped cantilever array and employs multifrequency operating principle. It consists of eight cantilevers with irregular design of cross‐sectional area. Cantilevers are connected to each other by specific angle to form polygon‐shaped structure. Moreover, seven seismic masses with additional lever arms are added in order to create additional rotation moment. Numerical investigation showed that piezoelectric polygon‐shaped energy harvester has five natural frequencies in the frequency range from 10 Hz to 240 Hz, where the first and the second bending modes of the cantilevers are dominating. Maximum output voltage density and energy density equal to 50.03 mV/mm3 and 604 μJ/mm3, respectively, were obtained during numerical simulation. Prototype of piezoelectric harvester was made and experimental investigation was performed. Experimental measurements of the electrical characteristics showed that maximum output voltage density, energy density, and output power are 37.5 mV/mm3, 815.16 μJ/mm3, and 65.24 μW, respectively.

Towards personalised rapid label free miRNA detection for cancer and liver injury diagnostics in cell lysates and blood based samples.

Advances in prevention, diagnosis and therapy are coupled to innovation and development of new medical tools, leading to improved patient prognosis. We developed an automatic biosensor platform that could provide a non-invasive, rapid and personalised diagnosis using nanomechanical cantilever sensors. miRNA are involved in gene expression and are extractable biomarkers for multiple diseases. We detected specific expression patterns of miRNA relevant to cancer and adverse drug effects directly in cell lysates or blood based samples using only a few microliters of sample within one hour. Specific miRNA hybridisation to the upper cantilever surface induces physical bending of the sensor which is detected by monitoring the position of a laser that reflects from the sensors surface. Internal reference sensors negate environmental and nonspecific effects. We showed that the sensitivity of label free cantilever nanomechanical sensing of miRNA surpasses that of surface plasmon resonance by more than three orders of magnitude. A cancer associated miRNA expression profile from cell lysates and one associated with hepatocytes derived from necrotic liver tissue in blood-based samples has been successfully detected. Our label free mechanical approach displays the capability to perform in relevant clinical samples while also obtaining comparable results to PCR based techniques. Without the need to individually extend, amplify or label each target allowing multitarget analysis from one sample.

Design of mechanical metamaterials for simultaneous vibration isolation and energy harvesting

Through finite element analysis and a 3D printing assisted experimental study, we demonstrate a design of mechanical metamaterials for simultaneous mechanical wave filtering and energy harvesting. The mechanical metamaterials compromise a square array of free-standing cantilevers featuring piezoelectric properties being attached to a primary structural frame. A complete bandgap has thus been created via the strong coupling of the bulk elastic wave propagating along the structural frame and the distributed local resonance associated with the square array of piezoelectrically active cantilevers. Operating within the stop-band, external vibration energy has been trapped and transferred into the kinetic energy of the cantilevers, which is further converted into electric energy through mechano-electrical conversion of its integrated piezoelectric elements. Therefore, two distinct functions, vibration isolation and energy harvesting, are achieved simultaneously through the designed mechanical metamaterials.

Considering Nonlinearities to Design Micro System's Vibrational Sensitivity

AbstractThis contribution analyses the impact of nonlinearities on the sensitivity of micro‐electro‐mechanical sensors measuring quantities based on a change in resonance frequency. The considered sensor is an array of cantilevers which have an integrated actuator and sensor. The mathematical model presented to describe the motion of this array is based on a coupled thermoelastic equation of motion which has a forced and a parametric excitation. Finally, a concept is presented to utilize a two‐to‐one internal resonance to increase a micro system's vibrational sensitivity. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Review Article: Active scanning probes: A versatile toolkit for fast imaging and emerging nanofabrication

With the recent advances in the field of nanotechnology, measurement and manipulation requirements at the nanoscale have become more stringent than ever before. In atomic force microscopy, high-speed performance alone is not sufficient without considerations of other aspects of the measurement task, such as the feature aspect ratio, required range, or acceptable probe-sample interaction forces. In this paper, the authors discuss these requirements and the research directions that provide the highest potential in meeting them. The authors elaborate on the efforts toward the downsizing of self-sensed and self-actuated probes as well as on upscaling by active cantilever arrays. The authors present the fabrication process of active probes along with the tip customizations carried out targeting specific application fields. As promising application in scope of nanofabrication, field emission scanning probe lithography is introduced. The authors further discuss their control and design approach. Here, microactuators, e.g., multilayer microcantilevers, and macroactuators, e.g., flexure scanners, are combined in order to simultaneously meet both the range and speed requirements of a new generation of scanning probe microscopes.

Spiral-Shaped Piezoelectric MEMS Cantilever Array for Fully Implantable Hearing Systems.

Fully implantable, self-powered hearing aids with no external unit could significantly increase the life quality of patients suffering severe hearing loss. This highly demanding concept, however, requires a strongly miniaturized device which is fully implantable in the middle/inner ear and includes the following components: frequency selective microphone or accelerometer, energy harvesting device, speech processor, and cochlear multielectrode. Here we demonstrate a low volume, piezoelectric micro-electromechanical system (MEMS) cantilever array which is sensitive, even in the lower part of the voice frequency range (300–700 Hz). The test array consisting of 16 cantilevers has been fabricated by standard bulk micromachining using a Si-on-Insulator (SOI) wafer and aluminum nitride (AlN) as a complementary metal-oxide-semiconductor (CMOS) and biocompatible piezoelectric material. The low frequency and low device footprint are ensured by Archimedean spiral geometry and Si seismic mass. Experimentally detected resonance frequencies were validated by an analytical model. The generated open circuit voltage (3–10 mV) is sufficient for the direct analog conversion of the signals for cochlear multielectrode implants.

MEMS flexible artificial basilar membrane fabricated from piezoelectric aluminum nitride on an SU-8 substrate

In this paper, we present a flexible artificial basilar membrane (FABM) that mimics the passive mechanical frequency selectivity of the basilar membrane. The FABM is composed of a cantilever array made of piezoelectric aluminum nitride (AlN) on an SU-8 substrate. We analyzed the orientations of the AlN crystals using scanning electron microscopy and x-ray diffraction. The AIN crystals are oriented in the c-axis (0 0 2) plane and effective piezoelectric coefficient was measured as 3.52 pm V−1. To characterize the frequency selectivity of the FABM, mechanical displacements were measured using a scanning laser Doppler vibrometer. When electrical and acoustic stimuli were applied, the measured resonance frequencies were in the ranges of 663.0–2369 Hz and 659.4–2375 Hz, respectively. These results demonstrate that the mechanical frequency selectivity of this piezoelectric FABM is close to the human communication frequency range (300–3000 Hz), which is a vital feature of potential auditory prostheses.

Investigation on Phase Shifting Effect on The Voltage Output of Piezoelectric Cantilever Array

This paper analyses the phase shifting of the output waveform produced by piezoelectric cantilevers under a range of vibration frequencies. The phase shift of four piezoelectric cantilevers with different resonant frequency are inspected while it is excited with the vibration from the electrodynamics shaker at a range of frequencies from 100 Hz to 500 Hz with the acceleration level (g-force) fixed at constant magnitude of 1g-level (9.81 m/s2). Time different and Lissajous pattern methods were used in this research to measure the phase shift of the output waveform. Both methods show similar result where the major phase shift happened at the resonant frequency of respective cantilevers. The phase difference remains low around 0 degrees or in other term in phase before the resonant frequency of the cantilever. When the frequency of the vibration source approaches the resonant frequency of respective cantilever, the phase different start to increase rapidly and reach 180 degree which is out of phase after the resonant frequency. This major phase shifting contributes to the significant rise of the gap in between the peaks formed when multiple piezoelectric cantilevers are connected together. As a result, it indirectly improves the output performance of the piezoelectric cantilevers array.

Development of Diamond and Silicon MEMS Sensor Arrays with Integrated Readout for Vapor Detection.

This paper reports on the development of an autonomous instrument based on an array of eight resonant microcantilevers for vapor detection. The fabricated sensors are label-free devices, allowing chemical and biological functionalization. In this work, sensors based on an array of silicon and synthetic diamond microcantilevers are sensitized with polymeric films for the detection of analytes. The main advantage of the proposed system is that sensors can be easily changed for another application or for cleaning since the developed gas cell presents removable electrical connections. We report the successful application of our electronic nose approach to detect 12 volatile organic compounds. Moreover, the response pattern of the cantilever arrays is interpreted via principal component analysis (PCA) techniques in order to identify samples.

Thermal Characterization of Dynamic Silicon Cantilever Array Sensors by Digital Holographic Microscopy.

In this paper, we apply a digital holographic microscope (DHM) in conjunction with stroboscopic acquisition synchronization. Here, the temperature-dependent decrease of the first resonance frequency (S1(T)) and Young’s elastic modulus (E1(T)) of silicon micromechanical cantilever sensors (MCSs) are measured. To perform these measurements, the MCSs are uniformly heated from T0 = 298 K to T = 450 K while being externally actuated with a piezo-actuator in a certain frequency range close to their first resonance frequencies. At each temperature, the DHM records the time-sequence of the 3D topographies for the given frequency range. Such holographic data allow for the extracting of the out-of-plane vibrations at any relevant area of the MCSs. Next, the Bode and Nyquist diagrams are used to determine the resonant frequencies with a precision of 0.1 Hz. Our results show that the decrease of resonance frequency is a direct consequence of the reduction of the silicon elastic modulus upon heating. The measured temperature dependence of the Young’s modulus is in very good accordance with the previously-reported values, validating the reliability and applicability of this method for micromechanical sensing applications.

Towards scalable capacitive cantilever arrays for emerging biomedical applications

This paper presents the design and implementation of a cantilever array device using a multi-user MEMS process for emerging point-of-care (PoC) diagnostic technologies. Each cantilever is incorporated with two capacitive sensing electrodes for the measurement of its beam deflection. A custom-made multichannel interface readout circuit was also developed using off-the-shelf elements for capacitance recording and data acquisition purposes. Herein, we demonstrate and discuss the functionality of the proposed capacitive cantilever array platform using interferometry and non-invasive rapid air-based characterization techniques. Based on simulation and experimental results, the proposed cantilever based platform can accurately measure μN-scale forces applied on each cantilever. The applicability of the proposed cantilever system was successfully investigated for PoC lung diagnostic purposes. Based on these results, the proposed system shows significant promise for use as an emerging free breathing measurement system for continuous assessment of respiratory health.

Position and orientation correction scheme for current sensing based on magnetic piezoelectric cantilevers

A position and orientation correction scheme for current sensing based on magnetic piezoelectric cantilevers is proposed in this letter, offering an insight for the improvement of measurement accuracy. In this scheme, an array of magnetic piezoelectric cantilevers, converting mechanical vibration generated by current induced magnetic force applied on magnets at the ends of cantilevers into output voltages, is utilized. A system of nonlinear equations is established in terms of amplitude of objective current, position, and orientation errors. They are derived by solving the system of equations treated as variables, instead of parameters. As a result, the measurement error caused by position and orientation errors decreased substantially. Experiments of passive current sensing for two-wire appliances prove the validity of the proposed position and orientation correction scheme. The application of the proposed scheme can be further extended to sensors based on the magnetic field sensing mechanism, for achieving higher measurement accuracy.

Multimodal cantilevers with novel piezoelectric layer topology for sensitivity enhancement.

Self-sensing techniques for atomic force microscope (AFM) cantilevers have several advantageous characteristics compared to the optical beam deflection method. The possibility of down scaling, parallelization of cantilever arrays and the absence of optical interference associated imaging artifacts have led to an increased research interest in these methods. However, for multifrequency AFM, the optimization of the transducer layout on the cantilever for higher order modes has not been addressed. To fully utilize an integrated piezoelectric transducer, this work alters the layout of the piezoelectric layer to maximize both the deflection of the cantilever and measured piezoelectric charge response for a given mode with respect to the spatial distribution of the strain. On a prototype cantilever design, significant increases in actuator and sensor sensitivities were achieved for the first four modes without any substantial increase in sensor noise. The transduction mechanism is specifically targeted at multifrequency AFM and has the potential to provide higher resolution imaging on higher order modes.

All-phononic amplification in coupled cantilever arrays based on gap soliton dynamics.

We present a mechanism of amplification of phonons by phonons on the basis of nonlinear band-gap transmission phenomenon. As a concept the idea may be applied to the various number of systems; however we introduce the specific idea of creating an amplification scenario in the chain of coupled cantilever arrays. One chain is driven at the constant frequency located in the upper band of the ladder system, thus no wave enters the system. However the frequency is specifically chosen to be very close to the maximum value of the frequency corresponding to the dispersion relation of the system. An amplification scenario happens when a counter phase pulse of the same frequency with a small amplitude is introduced to the second chain. If both signals exceed a threshold amplitude for the band-gap transmission a large amplitude soliton enters the system-therefore we have an amplifier. Although the concept may be applied in a variety of contexts, all-optical or all-magnonic systems, we choose the system of coupled cantilever arrays and represent a clear example of the application of the presented conceptual idea. Logical operations is the other probable field, where such a mechanism could be used, which might significantly broaden the horizon of the considered applications of band-gap soliton dynamics.

A Cantilever Array Sensor Platform Guided by Optical Fibers and Its Sensing Application

Abstract A cantilever array sensor platform was developed based on the optical lever method, and the cantilever array chip was also fabricated to introduce its applications on biochemical detection. Optical fibers coupled to lasers were used as the scanning light source. This sensor system had good stability, and the noise of the detection signal was about 2 nm. Meanwhile, the cantilevers of the fabricated chip had good straightness and were consistent to temperature response, and the deviations of the response sensitivity for cantilevers' temperature change were no more than 5.0%. This sensing system was used to detect Hg 2+ in aqueous solution within a concentration range of 1–200 ng mL −1 . The deflections of one array chip were close in the same concentration, and the average deviation was less than 15%. The samples with the concentrations of 1.0 and 0.2 ng mL −1 Hg 2+ were detected separately by the fabricated chip and a foreign commercial chip on the sensor platform. The result showed that it was difficult for the fabricated chip to achieve a higher detection sensitivity and necessary to improve the cantilever array production process.

Power Optimization Configuration for Piezoelectric Cantilever Arrays

This paper investigates the changes in the output of the piezoelectric cantilever arrays when connected in different configurations. In this research matching load resistance determined and optimum output was measured by connecting the piezoelectric cantilever arrays to resistance ranging from 10 Ω to 1 MΩ while excited by constant vibration source at frequency of 300 Hz and acceleration of 1-g level. The result shows that matching load resistance for one single piezoelectric cantilever is 13 KΩ. When two, three and four cantilevers are connected in series, the matching load resistance is 26 kΩ, 39 kΩ and 52 kΩ respectively. While in parallel connection, matching load resistance reduced to 6.5 kΩ, 4.5 kΩ and 3.5 kΩ for two, three, and four connected cantilevers respectively. In series configuration, the voltage output produced is much higher as compared to the piezoelectric cantilever arrays that are connected in parallel connection. The voltage output of the piezoelectric cantilever increased from 3.41V to 6.09V when it is connected in series configuration with same polarity. Whereas in term of power output, piezoelectric cantilever arrays in parallel configuration produce higher power output as compared to piezoelectric cantilever arrays in series connection. The maximum power increased from 272μW to 521μW when two cantilevers are connected in parallel configuration with same polarity.

Active Multifunctional Microelectromechanical System Metadevices: Applications in Polarization Control, Wavefront Deflection, and Holograms

Metasurfaces have provided a novel route to control the local phase of electromagnetic radiation through subwavelength scatterers where the properties of each element remain passive. A passive metasurface design can only achieve a specific functionality as it is extremely challenging to reconfigure each element that contributes toward the control of the radiation. In this work, the authors propose a different scheme based on microelectromechanical system (MEMS) to reconfigure the resonance and radiation phase via control of each dipolar element. The suspension angle of the individual bimorph cantilever in air can be precisely controlled through electrostatic actuation that determines the operative phase diagram of the metadevice. The dynamic polarization conversion is demonstrated through global control. In addition, it is proposed that a multifunctional operation such as dynamic wavefront deflection and rewritable holographic display can be accomplished by using 1D and 2D control of the cantilever array when each cantilever in the MEMS metadevice array is uniformly and accurately controlled in the large‐area samples. Such a rewritable proposition can enable myriad of applications of MEMS‐based metadevices in polarization‐division multiplexing and dynamic flat lenses.

A high accuracy cantilever array sensor for early liver cancer diagnosis.

Early liver cancer diagnosis has clinical significance in treating cancer. Joint detection of multiple biomarkers has been considered as an effective and reliable method for early cancer diagnosis. In this work, a novel biosensor based on microcantilever array was batch-fabricated for multiple liver cancer biomarkers detection with high sensitivity, high accuracy, high throughput, and high specification. A micro-cavity was designed in the free end of the cantilever for local reaction between antibody and antigen, which can dramatically reduce the effect of adsorption-induced stiffness coefficient k variation. Furthermore,the pillar arrays in the micro-cavity were designed for increasing detection upper limit. A linear relationship between the relative frequency shift and the antigen concentration was observed for three liver cancer biomarkers, alpha-fetoprotein (AFP), γ-glutamyltranspeptidase II (GGT-2), and hepatocyte growth factor (HGF). Slight cross-reaction response to different antigens ensures high specificity of the sensor. These features will promote clinical application of the cantilever sensors in early cancer diagnosis.

Large area fast-AFM scanning with active “Quattro” cantilever arrays

In this work, the fabrication and operation of an active parallel cantilever device integrating four self-sensing and self-actuating probes in an array is presented. The so called “Quattro” cantilever system is controlled by a multichannel field programmable gate array (FPGA) controller. The integrated cantilever devices are fabricated on the basis of a silicon-on-insulator wafer using surface micromachining and gas chopping plasma-etching processes [I. W. Rangelow, J. Vac. Sci. Technol., A 21, 1550 (2003)]. The unique design of the active cantilever probes provides both patterning and readout capabilities [Kaestner et al., J. Micro-Nanolithogr. MEMS 14, 031202 (2015)]. The thermomechanical actuation allows the individually operation of each cantilever in static and dynamic modes. This enables a simultaneous atomic force microscopy operation of all cantilevers in an array, while the piezoresistive read-out of the cantilever bending routinely ensures atomic resolution at a high imaging speed. The scanning probe lithography capabilities of the active cantilevers are based on the utilization of a Fowler–Nordheim field emission process of low-energy electrons (20–50 eV) for direct writing maskless lithography. The cantilever in the Quattro active cantilever array have a pitch of 125 μm (tip-to-tip distance), which allows an image size of 0.5 × 0.2 mm to be acquired within a single scan with 0.2 nm resolution in the vertical direction. Using parallel imaging, an effective scanning speed of 5.6 mm/s is achieved. The multichannel, scalable controller architecture allows four FPGA channels to scan and collect data simultaneously. A data buffer of 128 Mbits for a single frame of 4096 × 1024 pixels is applied. The designed data transfer system allows a packet size of 128 pixels to be transmitted within less than 10 μs, respectively. Thus, the entire image frame is transferred in less than 280 ms, which exceeds the required throughput in the practical cases like critical dimension-metrology and inspection. In this article, the authors are presenting the concept of the system, which combines imaging, metrology, and lithography capabilities with a low-cost of ownership. In this context, the authors are investigating the throughput capability, reproducibility, resolution, and positioning accuracy of the Quattro active cantilever system.

Microcantilevers track single-cell mass.

An array of microfluidic cantilevers measures the mass of single cells in a population over time and detects drug-induced changes in cell growth.