Haekwan Oh

Development of a high-sensitivity strain measurement system based on a SH SAW sensor

A strain measurement system based on a shear horizontal surface acoustic wave (SH SAW) was developed. The developed system is composed of a SAW microsensor, a printed circuit board (PCB), an adhesive and a strain gauge. When a compression force is applied to the PCB by the strain gauge, the PCB is bent so that external strain energy can be evenly delivered to the microsensor without any detachment of the sensor from the board. When a stretching force is applied to the PCB under the condition that one side of the PCB is fixed and the other side is modulated, the actual length of the SAW delay line between the two interdigital transducers (IDTs) is increased. The increase in the delay line length causes a change in the time for the propagating SAW to reach the output IDT. If strain energy is applied to the piezoelectric substrate, the substrate density is changed, which then changes the propagation velocity of the SAW. Coupling-of-modes modeling was conducted prior to fabrication to determine the optimal device parameters. Depending on the strain, the frequency difference was linearly modulated. The obtained sensitivity for stretching was 17.3 kHz/% for the SH wave mode and split electrode. And the obtained sensitivity for bending was 46.1 kHz/% for the SH wave mode and split electrode. The SH wave showed about 15% higher sensitivity than the Rayleigh wave, and the dog-bone PCB showed about 8% higher sensitivity than the rectangular PCB. The obtained sensitivity was about five times higher than that of existing SAW-based strain sensors.

Enhanced Sensitivity of Novel Surface Acoustic Wave Microelectromechanical System-Interdigital Transducer Gyroscope

In this paper, we present a novel microelectromechanical system-interdigital transducer (MEMS-IDT) surface acoustic wave (SAW) gyroscope with an 80 MHz central frequency on a 128 YX LiNbO3 wafer. The developed MEMS-IDT gyroscope is composed of a two-port SAW resonator, a dual delay line oscillator, and metallic dots. The SAW resonator provides a stable standing wave, and the vibrating metallic dot at an antinode of the standing wave induces the second SAW in the normal direction of its vibrating axis. The dual delay line oscillator detects the Coriolis force by comparing the resonant frequencies between two oscillators through the interference effect. The coupling of mode (COM) modeling was used to extract the optimal design parameters prior to fabrication. In the electrical testing by the network analyzer, the fabricated SAW resonator and delay lines showed low insertion loss and similar operation frequencies between a resonator and delay lines. When the device was rotated, the resonant frequency differences between two oscillators linearly varied owing to the Coriolis force. The obtained sensitivity was approximately 119 Hz deg 1 s 1 in the angular rate range of 0 –1000 deg/s. Satisfactory linearity and superior directivity were also observed in the test. # 2009 The Japan Society of Applied Physics DOI: 10.1143/JJAP.48.06FK09

The development of a wireless Love wave biosensor on 41° YX LiNbO3

This paper presents a novel wireless Love-wave-based biosensor using a polymethyl methacrylate (PMMA) waveguide and protein A receptor layers on a 41? YX LiNbO3 piezoelectric substrate for immunoglobulin G (IgG) detection. A 440?MHz reflective delay line composed of single-phase unidirectional transducers (SPUDTs) and three shorted grating reflectors was fabricated as the sensor element. A theoretical modeling was performed to describe the wave propagation of Love wave devices on a 41? YX LiNbO3 piezoelectric substrate with large piezoelectricity. The fabricated devices were wirelessly characterized by using the network analyzer as the reader unit. The resultant reflection peaks showed large signal/noise ratio, sharp peaks, and few spurious signals. The binding of the IgG to the protein A receptor layer induced large phase shifts of the reflection peaks due to the mass loading effect. Good linearity, reproducibility, and high sensitivity were observed in the IgG concentration range 1?65?nM. Unique advantages such as high sensitivity and a simple wireless measurement method over other currently available biosensors are also presented.

Enhanced sensitivity of a surface acoustic wave gyroscope using a progressive wave

A surface acoustic wave (SAW)-based gyroscope with an 80 MHz central frequency was developed on two different piezoelectric substrates (128° YX LiNbO3 and ST-X quartz). A sensor was developed that contained two SAW oscillators. One oscillator was used as the sensing element and had metallic dots in the cavity between the input and output interdigital transducers (IDTs). The other oscillator was used as a reference element. Two oscillators were formed to extract the Coriolis effect by comparing the oscillation frequencies between these two delay lines, and metallic dots were used to induce a Coriolis force. Three different IDT structures were used to obtain a stable progressive SAW. Coupling of modes modeling was conducted prior to fabrication for determining the optimal device parameters. The device was fabricated and then measured on a rate table in accordance with the results of simulation. When the device was subjected to an angular rotation, the oscillation frequencies of the two oscillators were observed to differ. Depending on the angular velocity, the frequency difference was linearly modulated. The obtained sensitivity was approximately 62.57 Hz deg−1 s−1 at angular rates in the range 0–1000 deg s−1 in the case of the LiNbO3 substrate and single-phase unidirectional transducer and combed electrode structure. The dependence of the device performance on the piezoelectric substrate, IDT structure, and temperatures was also characterized. The developed device has good resistance to mechanical shock and stability to temperature.

Development of a carbon nanotube-based touchscreen capable of multi-touch and multi-force sensing

A force sensing touchscreen, which detects touch point and touch force simultaneously by sensing a change in electric capacitance, was designed and fabricated. It was made with single-walled carbon nanotubes (SWCNTs) which have better mechanical and chemical characteristics than the indium-tin-oxide transparent electrodes used in most contemporary touchscreen devices. The SWCNTs, with a transmittance of about 85% and electric conductivity of 400 Ω per square; were coated and patterned on glass and polyethyleneterephthalate (PET) film substrates. The constructed force sensing touchscreen has a total size and thickness of 62 mm × 100 mm × 1.4 mm, and is composed of 11 driving line and 19 receiving line channels. The gap between the channels was designed to be 20 µm, taking visibility into consideration, and patterned by a photolithography and plasma etching processes. The mutual capacitance formed by the upper and lower transparent electrodes was initially about 2.8 pF and, on applying a 500 gf force with a 3 mm diameter tip, it showed a 25% capacitance variation. Furthermore, the touchscreen can detect multiple touches and forces simultaneously and is unaffected by touch material characteristics, such as conductance or non-conductance.

Wireless and simultaneous detections of multiple bio-molecules in a single sensor using Love wave biosensor.

A Love wave-based biosensor with a 440 MHz center frequency was developed for the simultaneous detection of two different analytes of Cartilage Oligomeric Matrix Protein (COMP) and rabbit immunoglobulin G (IgG) in a single sensor. The developed biosensor consists of one-port surface acoustic wave (SAW) reflective delay lines on a 41° YX LiNbO3 piezoelectric substrate, a poly(methyl methacrylate) (PMMA) waveguide layer, and two different sensitive films. The Love wave biosensor was wirelessly characterized using two antennas and a network analyzer. The binding of the analytes to the sensitive layers induced a large change in the time positions of the original reflection peaks mainly due to the mass loading effect. The assessed time shifts in the reflection peaks were matched well with the predicted values from coupling of mode (COM) modeling. The sensitivities evaluated from the sensitive films were ∼15 deg/μg/mL for the rabbit IgG and ∼1.8 deg/ng/mL for COMP.

Enhanced Sensitivity of Wireless Chemical Sensor Based on Love Wave Mode

A 440 MHz wireless and passive Love-wave-based chemical sensor was developed for CO2 detection. The developed device was composed of a reflective delay line patterned on 41° YX LiNbO3 piezoelectric substrate, a poly(methyl methacrylate) (PMMA) waveguide layer, and Teflon AF 2400 sensitive film. A theoretical model is presented to describe wave propagation in Love wave devices with large piezoelectricity and to allow the design of an optimized structure. In wireless device testing using a network analyzer, infusion of CO2 into the testing chamber induced large phase shifts of the reflection peaks owing to the interaction between the sensing film and the test gas (CO2). Good linearity and repeatability were observed at CO2 concentrations of 0–350 ppm. The obtained sensitivity from the Love wave device was approximately 7.07° ppm-1. The gas response properties of the fabricated Love-wave sensor in terms of linearity and sensitivity were provided, and a comparison to surface acoustic wave devices was also discussed.

Development of a New Wireless Chemical Sensor for CO 2 detection

We developed a 440 MHz surface acoustic wave wireless gas senor for CO2 detection and wireless measurement system. The sensor consists of a SAW reflective delay line structured by single phase unidirectional transducers (SPUDTs) and three shorted grating reflectors, and a Teflon AF 2400 thin film sensitive to CO2 gas deposited onto substrate between reflectors. The fabricated SAW device was wirelessly characterized by network analyzer. Adsorption of CO2 gas onto the sensitive film induced a large phase shifts of the reflection peaks depending on the CO2 concentration. The obtained sensitivity was 1.987 ppm.

Development of a Polymer Coating-Based Microlens Array on Isotropically Wet-Etched Quartz Substrates for Maskless Lithography Application

A polymer coating-based microlens array (MLA) was developed on an isotropically wet-etched quartz substrate for maskless photolithography application. The developed MLA showed excellent light focusing ability and uniformity, and a dense fill factor. The obtained focal length ranged from 32.2 to 45.4 µm depending on the curvature of quartz and the thickness of an ultraviolet (UV) adhesive. A small spot size of 1.55 µm and an uniformly focused beam intensity were obtained at the focal plane, confirming that the fabricated MLA has excellent uniformity and good focal ability. The fabricated MLA was applied to UV lithography. Beams were well focused onto a photoresist when UV passed through the MLA. Depending on the variable distance from the MLA, beam size on the photoresist was controlled. Variable micropatterns were realized on the photoresist. Even at high a temperature, the interface between quartz and the UV adhesive was thermally stable and lens performance characteristics remained unchanged.

Wirelessly Driven and Battery-Free Love Wave Biosensor Based on Dinitrophenyl Immobilization

A Love wave-based wireless immunosensor with a 440 MHz operating frequency was developed on a 41� YX LiNbO3 piezoelectric substrate. The developed sensor was composed of a shear horizontal surface acoustic wave (SH SAW) reflective delay line, a poly(methyl methacrylate) (PMMA) waveguide layer, and a 2,4-dinitrophenyl (DNP) receptor layer that specifically responds to an anti-DNP immunoglobulin G (IgG). Fabricated devices were wirelessly tested using a network analyzer. Four reflection peaks with large signal/noise (S/N) ratios and sharp reflection peaks were observed in the time domain, and are attributed to three shorted grating reflectors and DNPbound gold film. With 10 mW radio frequency (RF) power from the network analyzer, a readout distance of � 1 m was observed. The binding of IgG to DNP receptor molecules induced a change in the Love wave velocity owing to a mass loading effect, resulting in phase shifts of the original reflection peaks. The phase shifts increased linearly with increasing IgG concentration. Fast response time and long-term stability of the developed sensor in a liquid environment were observed. The phase shifts depending on different PMMA thicknesses were also investigated to identify the optimal PMMA waveguide thickness. # 2009 The Japan Society of Applied Physics