Showing papers by "Arif Sanli Ergun published in 2001"

Influence of the Electrode Size and Location on the Performance of a CMUT

Abstract: The collapse voltage of micromachined capacitive ultrasonic transducers (CMUT) depends on the size, thickness, type, and position of the metal electrode within the membrane. This paper reports the result of a finite element study of this effect. The program (ANSYS 5.7) is used to model a circular membrane on top of a Si substrate covered by a Si3N4 insulation layer. We find that the collapse voltage increases in proportion to the metal thickness for constant membrane thickness. The collapse voltage of a membrane with a thin metal electrode decreases as the metal plate moves closer to the bottom of the membrane; whereas, for electrodes with larger metal thickness, the collapse voltage has a peak intermediate value. Decreasing the outer radius of the metal plate results in an asymptotic increase of the collapse voltage. For a finite metal thickness, an initial decrease in the collapse voltage is seen as the outer radius decreases. The collapse voltages of half-metallized and full-metallized structures are almost equal for typical metal plate thickness. The asymptotic increase of the collapse voltage is seen for ring shaped metal plates as the inner radius is varied from the center to the outer radius. In summary, we find that the influence of the metal electrode on the collapse voltage is a very important parameter in determining optimum performance of a CMUT.

A new detection method for capacitive micromachined ultrasonic transducers

Abstract: Capacitive micromachined ultrasonic transducers (cMUT) have become an alternative to piezoelectric transducers in the past few years. They consist of many small circular membranes that are connected in parallel. In this work, we report a new detection method for cMUTs. We model the membranes as capacitors and the interconnections between the membranes as inductors. This kind of LC network is called an artificial transmission line. The vibrations of the membranes modulate the electrical length of the transmission line, which is proportional to the frequency of the signal through it. By measuring the electrical length of the artificial line at a high RF frequency (in the gigahertz range), the vibrations of the membranes can be detected in a very sensitive manner. For the devices we measured, we calculated the minimum detectable displacement to be in the order of 10/sup -5/ /spl Aring///spl radic/Hz with a possible improvement to 10/sup -7/ /spl Aring///spl radic/Hz.

Micro-machined coupled capacitor devices

Abstract: The present invention provides an apparatus and method for a new class of micro-machined electromechanical devices that make use of vibrating membranes The electromechanical devices include two or more electrodes which are positioned with a membrane A gap exists between the membrane and each electrode which may vary for each electrode In general, one electrode is used as an input electrode which receives an electrical signal that causes vibration of the membrane The vibration of the membrane is then coupled to a receiving or an output electrode A DC bias voltage is applied to the electrodes to set or modify a width of a gap in the electromechanical device The electromechanical device could be designed as a transformer, a capacitor, a resonator or a filter In addition, the device includes a control voltage to dynamically change the coupling between the input electrode and the output electrode(s)

Acoustic sensing using radio frequency detection and capacitive micromachined ultrasonic transducers

Abstract: Broadband acoustic sensing over several decades of frequency has traditionally been difficult to achieve. Conventional condenser and electret microphones depend on membrane and cavity resonances to achieve their maximum sensitivity. However, such resonant phenomena are inherently narrowband and limit the applicable frequency range of the acoustic sensor. New microphones using capacitive micromachined ultrasonic transducer (CMUT) technology and radio frequency (RF) detection achieve a relatively flat acoustic frequency response from frequencies below one hertz to hundreds of kilohertz. In this detection method, a high-frequency carrier signal is launched down a capacitively-loaded transmission line consisting of capacitive micromachined membranes and interconnects. The resulting phase modulation of the carrier due to impinging sound pressure can be measured. Preliminary experiments demonstrate microphone sensitivities of 50 dB/Pa/Hz/spl plusmn/3 dB over a frequency range of 0.1 Hz to 300 kHz. Calculations reveal that sensitivities on the order of 100 dB/Pa/Hz greater than the sensitivity of the human ear, may be possible with a 1 cm/sup 2/ device and a carrier frequency of several gigahertz.