Jin-Jyh Su

A System for Seismocardiography-Based Identification of Quiescent Heart Phases: Implications for Cardiac Imaging

Seismocardiography (SCG), a representation of mechanical heart motion, may more accurately determine periods of cardiac quiescence within a cardiac cycle than the electrically derived electrocardiogram (EKG) and, thus, may have implications for gating in cardiac computed tomography. We designed and implemented a system to synchronously acquire echocardiography, EKG, and SCG data. The device was used to study the variability between EKG and SCG and characterize the relationship between the mechanical and electrical activity of the heart. For each cardiac cycle, the feature of the SCG indicating Aortic Valve Closure was identified and its time position with respect to the EKG was observed. This position was found to vary for different heart rates and between two human subjects. A color map showing the magnitude of the SCG acceleration and computed velocity was derived, allowing for direct visualization of quiescent phases of the cardiac cycle with respect to heart rate.

Bio-inspired fluidic thermal angular accelerometer

This paper reports on a bio-inspired angular accelerometer based on a two-mask microfluidic process using a PDMS mold. The sensor is inspired by the semicircular canals in mammalian vestibular systems and pairs a fluid-filled microtorus with a thermal detection principle based on thermal convection. With inherent linear acceleration insensitivity, the sensor features a sensitivity of 29.8μV/deg/s2=1.7mV/rad/s2, a dynamic range of 14,000deg/s2 and a detection limit of ~20deg/s2.

A trimodal system for the acquisition of synchronous echocardiography, electrocardiography, and seismocardiography data

A novel system was developed to acquire synchronous echocardiography, electrocardiography (EKG), and seismocardiography (SCG) data. The system was developed to facilitate the study of the relationship between the mechanical and electrical characteristics of the heart. The system has both a hardware and software component. The hardware component consists of an application-specific device designed and built to acquire both SCG and EKG signals simultaneously. The software component consists of a package developed to record and synchronize data from both the device and a clinical ultrasound machine. A feasibility test was performed by simultaneous acquisition of a synchronous dataset from a human subject.

Thermally actuated silicon tuning fork resonators for sensing applications in air

This paper introduces an electrothermally actuated, piezoresistively detected, silicon-based tuning fork geometry as a suitable platform for resonant sensing applications in air. Operated at their fundamental tuning fork mode (fTF ≈ 400 kHz), in which the two tines oscillate with 180° phase shift to each other, the devices exhibit Q-factors of 4000-4200 in air. By properly choosing the locations of the integrated excitation resistors as well as the four piezoresistors forming a Wheatstone bridge, output signals stemming from low-frequency out-of-plane vibration modes of the microstructure are successfully suppressed. As a result, the tuning forks can be easily embedded into an amplifying feedback loop, achieving short-term frequency stabilities in air as low as 0.02 ppm (0.008 Hz) for gate times of 1 sec. Coated with a chemically sensitive polymer film, the tuning forks were used as mass-sensitive sensors with detection limits in the low-ppm range for toluene.

On the relative sensitivity of mass-sensitive chemical microsensors

In this work, the chemical sensitivity of mass-sensitive chemical microsensors with a uniform layer sandwich structure vibrating in their lateral or in-plane flexural modes is investigated. It is experimentally verified that the relative chemical sensitivity of such resonant microsensors is -to a first order- independent of the microstructures in-plane dimensions and the flexural eigenmode used, and only depends on the layer thicknesses and densities as well as the sorption properties of the sensing film. Important implications for the design of mass-sensitive chemical microsensors are discussed, whereby the designer can focus on the layer stack to optimize the chemical sensitivity and on the in-plane dimensions and mode shape to optimize the resonators frequency stability.

Cantilever-based resonant gas sensors with integrated recesses for localized sensing layer deposition

This work presents mass-sensitive hammerhead resonators with integrated recesses as a gas-phase chemical microsensor platform. Recesses are etched into the head region of the resonator to locally deposit chemically sensitive polymers by ink-jet printing. This permits the sensing films to be confined to areas that (a) are most effective in detecting mass loading and (b) are not strained during the in-plane vibrations of the resonator. As a result of the second point, even 5-μm thick polymer coatings on resonators with a 9-12 μm silicon thickness barely affect the Q-factor in air. This translates into higher frequency stability and ultimately higher sensor resolution compared to uniformly coated devices.

Assessing polymer sorption kinetics using micromachined resonators

This paper introduces a new approach to investigate polymer sorption kinetics by weighing the polymer films using micromachined in-plane resonators. A custom gas-testing setup enables fast analyte concentration changes, which are necessary to study analyte diffusion into thin polymer coatings deposited on top of the microresonators. Short-term frequency stabilities of the microresonators in the 10−8 range in air yield sub-picogram mass resolution and enable real-time measurement of analyte uptake into µm-thick films with time constants ranging from seconds to minutes. As an example, the diffusion of alcohols and aromatic hydro-carbons into poly(epichlorohydrin) and poly(isobuty-lene) films, which are of interest for chemical sensing applications, has been investigated.

Pulsed operation of InGaZnO TFTs for VOC sensing applications

In this work, the detection of volatile organic compounds (VOCs) using amorphous indium gallium zinc oxide (a-InGaZnO) thin film transistors (TFTs) is explored. Pulsemode biasing to improve the long-term stability of these TFTs when exposed to the environment and under bias stress is proposed. Coated with a non-conducting polyepichlorohydrin (PECH) film, the TFTs under constant voltage bias exhibit a reversible response to varying ethanol concentrations in the gas phase. Furthermore, by lowering the duty cycle (δ) using bias pulses, the drain current decay under voltage bias can be reduced, thus extending the devices operational lifetime.