Sung Q Lee

Maximization of acoustic energy difference between two spaces

There has recently been an increasing interest in the generation of a sound field that is audible in one spatial region and inaudible in an adjacent region. The method proposed here ensures the control of the amplitude and phase of multiple acoustic sources in order to maximize the acoustic energy difference between two adjacent regions while also ensuring that evenly distributed source strengths are used. The performance of the method proposed is evaluated by computer simulations and experiments with real loudspeaker arrays in the shape of a circle and a sphere. The proposed method gives an improvement in the efficiency of radiation into the space in which the sound should be audible, while maintaining the acoustic pressure difference between two acoustic spaces. This is shown to give an improvement of performance compared to the contrast control method previously proposed.

Biocompatible wireless power transferring based on ultrasonic resonance devices

To increase application area of implantable devices for medical treatment including implantable cardiac defibrillator or deep brain stimulator, wireless power transfer is highly required. Previous technologies such as magnetic resonance and induction coupling have limited applications because of short transfer distance compared to device size and magnetic field intensity limitation for the safety of body exposure. The biocompatible wireless power transferring technology is proposed using ultrasonic resonance method. In power transfer through tissue, since the distance between transmitter and receiver is not adjustable, the optimum power transfer condition is changed. For efficient power transferring, operating frequency should be adjusted based on acoustic radiation and spatial pressure distribution. The ultrasonic resonance transmitter and receiver are manufactured with 50mm diameter and 250 kHz resonance frequency. In case of water medium, since it is easy to adjust frequency at fixed distance, it bring...

A Wireless 32-Channel Implantable Bidirectional Brain Machine Interface.

All neural information systems (NIS) rely on sensing neural activity to supply commands and control signals for computers, machines and a variety of prosthetic devices. Invasive systems achieve a high signal-to-noise ratio (SNR) by eliminating the volume conduction problems caused by tissue and bone. An implantable brain machine interface (BMI) using intracortical electrodes provides excellent detection of a broad range of frequency oscillatory activities through the placement of a sensor in direct contact with cortex. This paper introduces a compact-sized implantable wireless 32-channel bidirectional brain machine interface (BBMI) to be used with freely-moving primates. The system is designed to monitor brain sensorimotor rhythms and present current stimuli with a configurable duration, frequency and amplitude in real time to the brain based on the brain activity report. The battery is charged via a novel ultrasonic wireless power delivery module developed for efficient delivery of power into a deeply-implanted system. The system was successfully tested through bench tests and in vivo tests on a behaving primate to record the local field potential (LFP) oscillation and stimulate the target area at the same time.

A novel capacitive type miniature microphone with a flexure hinge diaphragm

This paper presents a novel, highly sensitive condenser microphone with a flexure hinge diaphragm. We used the finiteelement analysis (FEA) to evaluate the mechanical and acoustic performance of the condenser microphone with a hinge diaphragm. And we fabricated the miniature condenser microphones with area of 1.5 mm x 1.5 mm. From the simulation and measurement results, we confirmed that the maximum displacements at the center of flexure hinge diaphragms are several hundred times, compared with flat diaphragms. Moreover, the miniature microphones have obtained -3 dB bandwidth of nearly 20 kHz by proper design of the flexure hinge diaphragms.

Phase-coherent conduction in mesoscopic normal-metal/superconductor hybrid junctions

In this paper we report about the transport properties of mesoscopic normal-metal/superconductor (NS) hybrid systems with two different junction layouts. One is a junction fabricated by overlaying S on N wire and the other with S sandwiched between two N wires, forming an NSN structure. At zero bias all the junctions exhibited a sharp decrease of dV=dI; which is believed to arise from the interference between the disorder-scattered and the Andreev-reflected quasiparticles. A small magnetic field corresponding to one flux quantum through the normal metal region, applied in parallel with the NS junction, easily suppressed the anomalous zero-bias conductance enhancement for the sandwich-junction sample. This high sensitivity to a small magnetic field observed in our systems of mesoscopic NS junctions in a diffusive-transport regime directly confirms the electron‐holeinterference origin of the zero-bias anomaly. q 2000 Published by Elsevier Science Ltd. All rights reserved.

A Miniature Condenser Microphone for Portable Terminals Applications

This paper presents a miniature condenser microphone with a flexure hinge diaphragm for portable terminals applications. MEMS technology has been successfully applied to miniature silicon capacitive microphones, and we fabricated the smallest condenser silicon microphone in the presented reports. We used the finite-element analysis (FEA) to evaluate mechanical and acoustic performances of the condenser microphone with a flexure hinge diaphragm. From the simulation results, we confirmed that the sensitivity of a flexure hinge diaphragm can be improved about 285 times higher than a flat diaphragm. The first and second modes occurred at 15,637 Hz and 24,387 Hz, respectively. The areas of the miniature condenser microphones with a hinge diaphragm are 1.5 mm times 1.5 mm. We measured the impedance characteristics and sensitivities of the fabricated condenser microphones. The sensitivities of microphones are around 12.87 muV/Pa (-60 dB ref. 12.5 mV/Pa) at 1 kHz under a low bias voltage of 1 V, and the frequency response is flat up to 13 kHz.

Biocompatible wireless power transferring and charging based on ultrasonic resonance devices

To increase application area of implantable devices for medical treatment including implantable cardiac defibrillator or deep brain stimulator, the rechargeable battery module is highly requested. The previous Li-type battery has limited current sources, so that the patient is forced to have surgery just for changing battery. Previous technologies such as magnetic resonance and induction coupling have limited applications because of its short transfer distance compared to device size and magnetic field intensity limitation for the safety of body exposure. As an alternative, the biocompatible wireless power transferring and charging technology is proposed using ultrasonic resonance devices. For the high efficient power transferring, optimal transfer frequency is calculated based on the acoustic radiation and damping effect. Then, the optimal load resistance is selected for matching power condition in receiver. And, transmitter is designed to match the optimal transfer frequency. The ultrasonic resonance tr...

PMN-PT Single Crystal Piezo-Electric Acoustic Sensor

The MEMS (micro-electro-mechanical systems) microphone enables the manufacturing of small mechanical components on the surface of a silicon wafer. The MEMS microphones are less susceptible to vibration because of the smaller diaphragm mass and an excellent candidate for chip-scale packaging. In this paper, we present a piezoelectric MEMS microphone based on (1-x)Pb(Mg 1/3 Nb 2/3 )O 3 -xPbTiO 3 (PMN-PT) single crystal diaphragm. The PMN-PT materials exhibit extremely high piezoelectric coefficients and other desirable properties for an acoustic sensor. The piezoelectric-based microphone can offer the ability to passively sense without the power requirements. In particular, this paper introduces the design of a PMN-PT single crystal diaphragm with interdigitated electrode. We were able to fabricate miniaturized PMN-PT single crystal diaphragms. The fabricated sensor exhibits the sensitivity of 1.5mV/Pa. This implies that the PMN-PT thin film microphone has a potential of excellent acoustic characteristics.

Electronic transport properties of coupled single-electron transistors

The electronic transport properties of parallel coupled single-electron transistors (SETs) at strong coupling under asymmetrical voltage bias are investigated theoretically. The binding of electrons and holes on the two islands of the coupled SETs is found to be the key element that governs the transport characteristics. The discrete nature of bound electrons and holes leads to the satellite Coulomb blockade oscillations, the current jumps, and the Coulomb staircases, all of which are distinct transport features of the coupled SETs.

Extraction and Analysis of Respiratory Motion Using Wearable Inertial Sensor System during Trunk Motion

Respiratory activity is an essential vital sign of life that can indicate changes in typical breathing patterns and irregular body functions such as asthma and panic attacks. Many times, there is a need to monitor breathing activity while performing day-to-day functions such as standing, bending, trunk stretching or during yoga exercises. A single IMU (inertial measurement unit) can be used in measuring respiratory motion; however, breathing motion data may be influenced by a body trunk movement that occurs while recording respiratory activity. This research employs a pair of wireless, wearable IMU sensors custom-made by the Department of Electrical Engineering at San Diego State University. After appropriate sensor placement for data collection, this research applies principles of robotics, using the Denavit-Hartenberg convention, to extract relative angular motion between the two sensors. One of the obtained relative joint angles in the “Sagittal” plane predominantly yields respiratory activity. An improvised version of the proposed method and wearable, wireless sensors can be suitable to extract respiratory information while performing sports or exercises, as they do not restrict body motion or the choice of location to gather data.