Göksenin Yaralıoğlu

Lens Geometries for Quantitative Acoustic Microscopy

The purpose of the first Lemons-Quate acoustic microscope(1) was to image the surfaces of materials or biological cells with a high resolution. Unfortunately, competition with the optical microscope was only partially successful due to the high degree of absorption in the liquid-coupling medium at high frequencies. Increasing the resolution beyond optical limits was possible with the use of hot water(2) or cryogenic liquids,(3) at the cost of operational difficulty and system complexity. Meanwhile it was shown that the acoustic microscope can generate information that has no counterpart in the optical world.(4) The presence of leaky waves resulted in an interference mechanism known as V(z) curves. The V(z) method involves recording the reflected signal amplitude from an acoustic lens as a function of distance between the lens and the object. This recorded signal is shown to depend on elastic parameters of the object material. After underlying processes are well understood, new lens geometries or signal-processing electronics are designed to emphasize the advantage of the acoustic lens. In any case, the aim has been to increase the quantitative characterization ability of the microscope.

MEMS based blood plasma viscosity sensor without electrical connections

A MEMS based viscometer is reported. The device has a disposable cartridge and a reader. The cartridge contains microfluidic channels and a MEMS cantilever sensor. The reader contains the actuator and the readout optics and electronics. A unique feature of the system is that both the actuation and the sensing are remote; therefore, no electrical connections are required between the reader and the cartridge. The reported sensor is capable of measuring viscosity with better than 0.01 cP resolution in a range of 0.8-14.1 cP, with less than 50 μl sample requirement. This range and sensitivity are sufficient for blood plasma viscosity measurements, which are in between 1.1-1.3 cP for healthy individuals and can be elevated to 3cP in certain diseases[1].

LoC sensor array platform for real-time coagulation measurements

This paper reports a MEMS-based sensor array enabling multiple clot-time tests in one disposable microfluidic cartridge using plasma. The versatile LoC (Lab-on-Chip) platform technology is demonstrated here for real-time coagulation tests (activated Partial Thrompoblastin Time (aPTT) and Prothrombin Time (PT)). The system has a reader unit and a disposable cartridge. The reader has no electrical connections to the cartridge, which consists of multiple microfluidic channels and MEMS microcantilevers placed in each channel. Microcantilevers are made of electro-plated nickel and actuated remotely using an external electro-coil. The read-out is also conducted remotely by a laser and the phase of the MEMS oscillator is monitored real-time. The system is capable of monitoring coagulation time with a precision estimated at 0.1sec.

Portable low cost ultrasound imaging system

The applications of ultrasound in medicine have been increasing in the last decade either in diagnostics or in treatments. Ultrasound is routinely used in clinical examinations, such as pregnancy exams. On the other hand, a typical ultrasound system costs somewhere between 100k

Characterization and imaging with Lamb wave lens at gigahertz frequencies

to 250k

Mutual radiation impedance of circular CMUTs on a cylinder

because of its (1) expensive ultrasound transducers, (2) large driving electronics, (3) processing and visualization units. High cost and large volume of the ultrasound systems prevent even wider usage of these systems. It is possible to extent the use of ultrasound in clinic environment like a stethoscope, if the size and cost had been reduced orders of magnitude. The aim of this work is to develop an ultraportable and very low cost diagnostic ultrasound imaging probe; by combining inertial sensors with the probes. The manual motion of the probe by the operators hand movement enables scanning. The position of the probe is tracked using inertial sensors. Finally, the acoustic reflections are registered together by the help of position information of the probe to form an image.

Receive-Noise Analysis of Capacitive Micromachined Ultrasonic Transducers

Lamb wave lenses with conical refracting surfaces are fabricated for use at 400 MHz and 1 GHz. The conical surfaces are ground and polished with mechanical means and they are sufficiently smooth for the frequencies of interest. The wide bandwidth of transducers allow frequency tuning necessary for Lamb wave lenses, The fabricated lenses show the expected V(Z) performance. At high frequencies the attenuation in the coupling medium can be very high, but due to the smaller wavelength the resolution is better and defocus distance can be reduced. Inherently higher leaky wave sensitivity of Lamb wave lens enables a good V(Z) characterization ability at higher frequencies as compared to the conventional spherical lens. Subsurface imaging with these Lamb wave lenses gives satisfactory results for layered structures. Chosen object has leaky wave modes within the angular coverage of the lens. The images exhibit a resolution close to the diffraction limit. Experimental V(Z) curves obtained with these lenses along with images are presented

Signal to noise ratio optimization for a CMUT based medical ultrasound imaging system

In ultrasound imaging, cross coupling of transducer elements through the medium has significant effect on the frequency response, thus affecting the quality of the ultrasound image. In Side-Looking Intravascular Ultrasound (SL-IVUS) imaging a radial image of the vessel wall is formed using a transducer array in a cylindrical configuration. Recent advances in Capacitive Micromachined Ultrasound Transducer (CMUT) fabrication and integration techniques led to realization of CMUT arrays that can be wrapped into a cylinder shape and mounted on a catheter tip. In this paper, we present the calculation of radiation impedance of un-collapse CMUT arrays on a planar rigid baffle and on a cylinder using Finite Element Method (FEM) simulation. We link the crosstalk between planar CMUT elements with dips in frequency spectrum from experimental data and conclude that decreasing the cylinder radius causes downshift of the dips in frequency response. In the case of our device, these changes are too small to have detrimental effects on the array bandwidth.

Two cantilever based sytem for viscosity and density monitoring

This paper presents an analysis of thermal (Johnson) noise received from the radiation medium by otherwise noiseless capacitive micromachined ultrasonic transducer (CMUT) membranes operating in their fundamental resonance mode. Determination of thermal noise received by multiple numbers of transducers or a transducer array requires the assessment of cross-coupling through the radiation medium, as well as the self-radiation impedance of the individual transducer. We show that the total thermal noise received by the cells of a CMUT has insignificant correlation, and is independent of the radiation impedance, but is only determined by the mass of each membrane and the electromechanical transformer ratio. The proof is based on the analytical derivations for a simple transducer with two cells, and extended to transducers with numerous cells using circuit simulators. We used a first-order model, which incorporates the fundamental resonance of the CMUT. Noise power is calculated by integrating over the entire spectrum; hence, the presented figures are an upper bound for the noise. The presented analyses are valid for a transimpedance amplifier in the receive path. We use the analysis results to calculate the minimum detectable pressure of a CMUT. We also provide an analysis based on the experimental data to show that output noise power is limited by and comparable to the theoretical upper limit.

Bi-angular lens for material characterization

CMUTs offers key performance benefits compared to their piezoelectric counterparts. However, CMUTs are not widely adopted in commercial ultrasound imaging systems due to low signal to noise ratio (SNR) in the obtained images. Tunable parameters of the CMUT include the membrane material, radius, thickness, gap height, electrode size, and bias voltage. The aim of this work is to optimize these parameters to provide a solution for low SNR problem of CMUTs. In medical imaging, the device will be used in pulse echo mode for which both good receive sensitivity and high output pressure is required. Optimizing these performance metrics will end up in conflicting design parameters, such as a high gap for large pressure output whereas a small gap for better receive sensitivity. In this work, we develop a methodology for the investigation of the round-trip behavior of the transducer and try to co-optimize transmit and receive characteristics of the device to maximize the SNR of the received signal by tuning the bias voltage.