A novel biasing scheme having the potential to dynamically control the effective cavity heights of two fabricated, multiple moving membrane capacitive micromachined ultrasonic transducers (M 3 -CMUTs) has been developed. With this unique approach it is may be possible to avoid design trade-off requirements of the ultrasonic transducers that affect both receiving and transmitting operating modes. Each of these M 3 -CMUTs has two vibrating membranes suspended over a fixed bottom electrode. The two air-coupled M 3 -CMUT devices with the resonant frequencies of 1MHz single cell and 1.5MHz array device were fabricated. Finite Element Analysis (FEA) was carried out to investigate the effect of an additional middle membrane on the effective cavity height and device performance. Experimental validation was then completed with the transducers operating under both positive and negative biasing conditions of middle membrane, while keeping the top membrane at selected positive biasing voltages to realize a dynamically controlled range of effective cavity heights. The new biasing scheme may facilitate dynamic tunning of resonant frequencies of transmitter and receiver transducers through the variation of effective cavity height for improved performance.

Two sets of multiple moving membrane capacitive micromachined ultrasonic transducers (M-3-CMUTs) are designed and fabricated for a range of middle membrane radii, from 35 - 49 mu m and 34 - 44 mu m. All other design parameters were kept identical within each set of experiments to enable a fair comparison. To study the dynamic control range of the designed M-3-CMUTs, their performance was first evaluated through COMSOL simulation yielding results on the resonant frequency and corresponding cavity height. This was followed by fabrication of the same designs using multiuser microelectromechanical systems processes (MUMPs). The development of these prototypes enabled the comprehensive electrical characterization of the designs with responses that are demonstrated to be in full agreement with the simulation results. The middle membrane radii of the M-3-CMUTs impact the collapse voltage of these devices in addition to affecting the measured resonant frequencies when tested devices within the same measurement conditions. A 20 kHz increase in resonant frequency shift was recorded when the middle membrane radius of these devices was increased from 7 mu m to 10 mu m while operating under a 20V top membrane bias and -3V to -5V middle membrane bias. These observations indicate that the middle membrane radius has influence on the dynamic control of effective cavity height in M3-CMUTs, which enables the expansion of the devices' cavity heights beyond that of conventional capacitive micromachined transducers. This finding has potential in applications with a need for acoustic power where dynamic control of the cavity height could serve as a solution, such as in medical imaging.

The design fabrication and development of a 67.5 kHz capacitive micromachined ultrasonic transducer (CMUT) suited for Martian anemometry is presented in this paper. To have low signal attenuation under Martian conditions, the device operating frequency is limited to 100 kHz. This is due to the low-density carbon dioxide (CO2) atmosphere and acoustic impedance mismatch transduction losses. CMUTs capable of generating frequencies less than 100 kHz need either large Silicon area or higher operating voltages. This is a problem for the battery operation and portability of devices. The devices presented in this paper are designed and fabricated using low cost commercially available surface micromachining technique. COMSOL Multiphysics and MATLAB simulations were used to analyze the device critical design parameters and investigate the operability of devices. Simulation results show that the designed single cell 170- $\mu \text{m}$ radius membrane has a resonant frequency ~65 kHz. The device exhibits a static displacement of 105nm under 20 V DC bias. Using the developed single cell model, a $3\times 10$ array CMUT anemometer was fabricated and evaluated that generates a ~65 kHz acoustic signal in lab environment. This proposed CMUT anemometer can operate for a supply < 38 V. The device performance was evaluated using a commercial air-coupled capacitive microphone named CAP1. Successful transmit-receive of ultrasound from the developed 2D array to CAP1 for separation in the range of 1–15 cm was performed. The experiment results performed in lab environment show the speed of sound and the atmospheric attenuation can be accurately measured using this developed technology with a ±5% accuracy.

This paper presents a theoretical model and an experimental validation of a two-port multiple moving membrane capacitive micromachined ultrasonic transducer. The developed transducer includes a stack of two flexible membranes suspended on a fixed electrode. The transducer is fabricated utilizing a sacrificial technique, PolyMUMPs, and with a resonant frequency of 1.8 MHz. Electrical measurements are conducted using an impedance analyzer in order to investigate the influence of the transducer's additional moving membrane on the device effective cavity height. This, consequently, influences the transducer acoustic power generation. The deigned two port transducer enables a dynamic change in the effective cavity height through adjusting the applied DC bias voltage. The experimental results validate this hypothesis and are shown in agreement with the theoretical results.

The CMUT devices presented in this paper were fabricated using a commercially available MEMSCAPs PolyMUMPs process. The moveable membrane evolves from the available single layer polysilicon. COMSOL simulations were used to model and investigate the effects of a 140 μm and 105 μm radius membranes that are 1.5 μm and 2 μm thick respectively. The results for two different structures designed to operate below 350 kHz are demonstrated in this work. Simulations show that both the devices presented show displacement of over 40 nm. The device snap shut was observed beyond 40 V. This frequency range is suitable to have high SNR and accurate distance measurements. Reducing the size of CMUT devices for the proposed frequency range was a challenge, sorted in this paper. A device capable to generate ultrasound close to 50kHZ is also presented.

An artificial olfactory system, capable of detecting and discriminating different volatile organic compounds, has a vast potential to solve several sensing challenges. The conducting polymers are a well-researched class of materials that have a demonstrated sensitivity to a wide range of volatile compounds. This work, presented here, demonstrates an olfaction system developed with the integration of gas sensitive conducting polymers into an array of Si-foundry based floating gate metal oxide semiconductor (FGMOS) sensors. The design of the sensor and the post silicon processing steps required to ensure compatibility of this silicon system with the conducting polymers is presented. The system's response to several different analytes have been measured and analyzed. A statistical method, principle component analysis (PCA), is used to extract information from the experimental data. The PCA analysis confirms successful detection and discrimination of the tested analytes.

An integrated dielectrophoresis cytometer has been designed and implemented using a standard 0.35 mu m CMOS technology. This design makes use of differential ring oscillators. The frequency difference between the two oscillators, in presence of a cell, is detected by an XOR gate. The frequency difference is then measured by a frequency counter. This sensor has similar to 14 aF capacitance sensitivity at similar to 1.4 GHz. It is used for detection of 10-20 mu m polystyrene spheres and Chinese Hamster Ovary cells using coplanar microelectrodes on top of the CMOS chip. The design demonstrates that it is possible to differentiate between particles experiencing an altitude change resulting from either a positive or negative dielectrophoretic force in a microfluidic channel. The total area occupied by the DEP system is 0.6 mm(2). This sensor can be used in high throughput applications with a density of more than 160 DEP sensor units in 1 cm(2). The sensor integrates all the required parts of a DEP cytometer-excluding the pumping system and frequency counter-, making a semi-integrated lab on chip system for single cell detection and analysis. (C) 2017 Published by Elsevier B.V.

Differential 3-stage and 5-stage, ring oscillator based capacitance sensors were designed and integrated using 0.35 μm CMOS technology. The sensor operates at 0.7 GHz and 1.4 GHz and achieves ~14 aF capacitive sensitivity. The use of CMOS technology makes the integration of the sensing circuit, and the detection microelectrodes on chip possible. A hybrid system was developed where a Plexiglas microfluidic system was mounted on top of the CMOS chip. This created a complete Lab-on-Chip cytometer sensor that was used to detect individual polystyrene spheres (10-15 μm) and Chinese hamster ovary (CHO) cells. The integration of sensing circuitry with the microfluidic parts reduces the sensor size and weight significantly when compared with previous designs.

A multiple moving membrane capacitive micromachined ultrasonic transducer has been developed. This transducer cell structure includes a second flexible plate suspended between the transducer top plate and the fixed bottom electrode. The added plate influences the transducer top plate deflection map and, therefore, the transducer properties. Three series of individual air-coupled, dual deflectable plate transducers and two 1 x 27 element transducer arrays were fabricated using multiuser microelectromechanical systems (MEMS) processes (MUMPs). Each set of transducers included devices with middle plate radii from 22% to 65% of the corresponding transducer top plate radius. The effect of the transducer middle plate configuration has been investigated. Electrical, optical, and acoustic characterizations were conducted and the results were compared with the simulation findings. It was found that the transducer top plate amplitude of vibration is significantly enhanced with a wider middle deflectable plate. The electrical and optical measurement results are shown to be in good agreement with simulation results. The acoustic measurement results indicated a 37% increase in the amplitude of transmitted signal by the 1-MHz air-couple transducer when its middle plate radius was increased by 35%. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

A novel air-coupled multiple moving membrane-capacitive micromachined ultrasonic transducer ( [Formula: see text]-CMUT) with individually biased deflectable plates has been developed. Unlike the conventional capacitive micromachined ultrasonic transducer, this device cell structure includes an additional deflectable plate that is suspended underneath the transducer top plate. This added flexible plate contributes to the device signal transmission and reception. It is demonstrated that due to the presence of this added moving plate, the transducer is capable of operating under inverse bias condition, where the driving voltage is sandwiched between two grounded electrodes. COMSOL electromechanical simulations were conducted to investigate the influence of the transducer additional moving plate. A set of three individuals and an array of [Formula: see text]-CMUT transducers were fabricated using a sacrificial technique and with resonant frequencies ranging from 0.8 to 2.1 MHz. Electrical, optical, and pitch-catch acoustic measurements were performed to characterize the transducers properties under inverse bias condition. The experimental results are shown to be in good agreement with the simulation results for all of the fabricated transducers. It is shown that these transducers are fully functional under both normal and inverse bias conditions without any degradation in the transducer performance.

The development of chemically diverse arrays of sensing elements has gained the attention of researchers due to their anticipated capacity to mimic the function of olfactory receptors in the mammalian olfactory system.

Multiple moving membrane capacitive micromachined ultrasonic transducers (M3-CMUTs) employ a multiple vibrating plate configuration. The presence of an additional plate improves the transducer properties. In this letter, the device displacement amplitude is further enhanced through eliminating the transducer fixed electrode and employing a deflectable plate as the bottom electrode. A set of air-coupled transducers with the effective plate radius of 65 μm has been fabricated. Electrical and optical measurements were conducted. It is demonstrated that the transducer with a deflectable bottom electrode exhibits larger top plate displacement amplitude compared with the conventional CMUTs as well as the M3-CMUT with a fixed bottom electrode. A maximum of a 57% and 4% increase in the plate displacement is achieved at a dc bias level of 27 V for the transducer with vibrating bottom electrode compared with the conventional CMUT and M3-CMUT with a fixed bottom electrode, respectively.

A robust capacitive micromachined ultrasonic transducer has been developed. In this novel configuration, a stack of two deflectable membranes are suspended over a fixed bottom electrode. Similar to conventional capacitive ultrasonic transducers, a generated electrostatic force between the electrodes causes the membranes to deflect and vibrate. However, in this new configuration the transducer effective cavity height is reduced due to the deflection of two membranes. Therefore, the transducer spring constant is more susceptible to bias voltage, which in return reduces the required bias voltage. The transducers have been produced employing a MEMS sacrificial technique where two different membrane anchoring (curved- and flat- anchors) structures, with similar membrane radii were fabricated. Highly doped polysilicon was used as the membrane material. The resonant frequencies of the two transducers have been investigated. It was found that the transducers with curved membrane anchors exhibits a larger resonant frequency shift compared to the transducers with flat membranes for a given bias voltage. Comparison has been made between the spring constant of the flat membrane transducer and that of a conventional single membrane transducer. It is shown that the multiple moving membrane transducer exhibits a larger reduction in the spring constant compared to the conventional transducer, when driven with the same bias voltage. This results in a transducer with a higher power generation capability and sensitivity.

A novel capacitive micromachined ultrasonic transducer is designed and fabricated. This transducer employs a stack of two deflectable membranes suspended over a fixed bottom electrode. In this configuration, the two moving membranes deflect simultaneously in response to a bias voltage, which results in a smaller effective cavity height compared with the conventional capacitive transducers. Electromechanical and acoustic analyses are conducted to investigate the transducer properties. A set of seven transducers with radii ranging from 30 to 55 μm were fabricated utilizing a sacrificial microelectromechanical system fabrication technology. Electrical measurements were performed and were compared with results from physical deflection measurements utilizing an optical vibrometer system. The results have been compared with analytical models as well as characterization of a set of five conventional, single membrane, transducers fabricated with the same technology. These experiments indicate a good agreement between the model and measured data. A larger membrane deflection and smaller cavity height are achieved from the double membrane devices. Therefore, this type of device may enhance the transducer acoustic power generation capability as well as increasing its sensitivity both of which result from the reduction in the transducer effective cavity height.

A 2-D multiple moving membrane capacitive micromachined ultrasonic transducer (M3-CMUT) array has been developed for air-coupled detection purposes in the megahertz frequency range. The transducer includes an array of 6×6 M3-CMUT elements. This transducer benefits from a novel configuration where a stack of two vibrating membranes suspended over a fixed grounded electrode are involved in the signal transmission and detection. Using this configuration, the amplitude of membrane vibration is increased and that enhances the transducer power output and sensitivity. Electrical and acoustic characterization of this transducer array is presented in this paper.

Multiple moving membrane, capacitive micromachined ultrasonic transducers (M3-CMUTs) benefit from a multiple vibrating membrane configuration that enhances the transducer properties. In this work, further improvement in the device displacement amplitude is achieved through eliminating the transducer fixed electrode. Two M3-CMUT devices have been fabricated and their electrical impedances are compared. It is demonstrated that the 50 μm radius transducer without the fixed electrode shows a 70% increase in the membrane displacement amplitude at a DC voltage of 20 V compared with the M3-CMUT with a fixed bottom electrode of the same dimension.

A 6 x 6 element multiple moving membrane capacitive micromachined ultrasonic transducer (M-3-CMUT) array has been developed for air-coupled detection purposes in the low megahertz frequency range. Unlike conventional capacitive MEMS transducers, the developed transducer array employs a novel cell configuration where more than one flexible membrane contributes in the transducer signal transmission and detection. In this structure, a stack of two vibrating membranes is suspended over a fixed grounded bottom electrode. The transducer array has been fabricated through employing a MEMS sacrificial technique, with the top and middle membrane radii of 65 and 42 mu m, respectively. The electrical, optical and acoustic evaluation results of this transducer array are presented in this paper. It is shown that using this configuration, the amplitude of membrane displacement is increased which enhances the transducer power output and sensitivity for a given bias condition. The experimental results demonstrate that this transducer array structure can be highly beneficial in high performance imaging application systems. (C) 2014 Elsevier B.V. All rights reserved.

Ultrasound technology is a very well-known effective technique used in Non-Destructive Testing (NDT). Of the advantages, one can name its relatively low cost and that it is safe. At high frequencies it offers the capability of generating high resolution imagery. Unfortunately at high frequencies ultrasound waves are highly attenuated in air and within materials attenuation also worsens as the frequency increases. Additionally, transmission in air results on a considerable impedance mismatch between the propagating medium and the materials under inspection. Thus a coupling medium is used that limits its applications to materials that can be either immersed in water or be in touch with coupling gel. In this paper we explore the use of 25 KHz frequency transducers used in air with no coupling material. We trade the benefits of high resolution imaging for effective fault detection with a system that offers its own benefits. By choosing such a low frequency we alleviate in part the attenuation of high frequency sound waves within the material and air but by not using a coupling medium the transmitted power to the sample is highly attenuated. Our main application, detection of faults within the insulation material of power cables requires such a system. We report that detection is possible.