Kousuke Takeuchi

Characteristics of Surface Acoustic Wave on AlN Thin Films.

A surface acoustic wave (SAW) on a (001) plane of hexagonal aluminum nitride (AlN) deposited on R-plane sapphire ( (1\bar12)Al2O3) with an inclination of about 26 degrees to the substrate was analyzed. A Rayleigh wave and shear-horizontal-type (SH-type) wave were found. The phase velocity of these was 5400-5800 m/s and 6100-6600 m/s, respectively. To confirm this results, the propagating characteristics of both SAW modes were measured by input admittance of single interdigital transducers (IDT) and by transmission characteristics between two IDTs. The phase velocity of the Rayleigh wave and the SH-type wave was 5600 m/s and 6500 m/s, respectively, and the propagation loss was 0 dB/λ and 0.04 dB/λ, respectively. These measured characteristics approximately agree with the results of the simulation.

Highly Accurate CO2 Gas Sensor Using a Modulation-Type Pyroelectric Infrared Detector

We have developed a highly accurate CO2 gas sensor which utilizes a pyroelectric infrared (IR) detector containing a solid state chopper and an optical filter. We have improved the noise of the IR detector and the dependence of the sensitivity on the optical filter characteristics. The noise of the IR detector is suppressed by optimization of the gate resistance value and by development of a new structure for IR sensing to compensate for extraneous noise. The magnitude of the noise is improved about one-half compared with the magnitude in the conventional detector. The sensitivity to CO2 has been raised by investigating the optimum conditions of the optical filter. The accuracy of the CO2 gas sensor using the new IR detector is ±0.03% at a 5% CO2 gas concentration and ±0.12% at a 20% concentration.

New High-Phase-Velocity Leaky Surface Acoustic Wave Mode on LiTaO3 and LiNbO3

A new high-phase-velocity leaky surface acoustic wave (SAW) mode, which was predicted by computer simulation, was confirmed experimentally to exist on both LiTaO3 and LiNbO3. The Euler angles of the propagation direction are (90°, 90°, 31°) on LiTaO3 and (90°, 90°, 37°) on LiNbO3. One-port SAW resonators were produced to confirm these modes. The phase velocity of the mode on LiTaO3 (90°, 90°, 31°) is 6250 m/s, and that on LiNbO3 (90°, 90°, 37°) is 7170 m/s. The temperature coefficient of the resonance frequency on LiTaO3 (90°, 90°, 31°) is -30 ppm/°C, and that on LiNbO3 (90°, 90°, 37°) is -30 ppm/°C.

A New-Structure IR Gas Sensor

We developed a new-structure IR gas sensor using a new type of pyroelectric IR detector with a solid-state chopper and an optical filter in the same package. This gas sensor enables high accuracy and high reliability due to the new structure (DEA Structure) and the new IR detector. The accuracy of the measurement is ±0.5% in the range of a 0~20% concentration of CO2 gas. The change of the output signal is within ±0.8% for 1500 hours. The characteristics (especially long-term operation) are superior to those of the conventional NDIR-type gas sensor.

Modulation Type Pyroelectric IR Detector

We have developed a new type of pyroelectric IR detector which contains a sensing part and a solid state chopper with two bimorph vibrators and two slit plates in the same package. This new detector (M-type IR detector) features high reliability, small volume and low electric power consumption compared with conventional pyroelectric IR detectors using a rotating chopper. The output voltage and noise voltage of the M-type IR detector have been investigated theoretically and experimentally. It was confirmed that a good performance can be achieved in the M-type IR detector by optimizing the relative position of the two slit plates and the aperture diameter of the shield box.

Investigation of the Characteristics of a Piezoelectric Chopper for a Modulation-Type Pyroelectric Infrared Detector

The characteristics of a piezoelectric chopper utilizing a slit plate for a modulation-type pyroelectric infrared detector (M-type IR detector) were investigated. First, we discuss how the accuracy of the signal of the M-type IR detector is affected by the emissivity of the slit plate, for applications to noncontact temperature measurement. Then, the accuracy of the measurement can be improved by an optimum emissivity of the slit plate against changes in operating gate-source voltage of the field-effect transistor, when the ambient temperature of the detector is changed rapidly. Next, we study the change in the detecting area caused by the diffraction effect from the use of the slit plate by means of numerical simulation and experiments. The expansion of the detecting area due to the diffraction can be improved by an optimum design of the can structure.

Characteristics of a liquid crystal IR chopper for pyroelectric IR sensors

Abstract We have developed an IR chopper utilizing the electro-optical effect of liquid crystals for pyroelectric sensors. This IR chopper primarily consists of liquid crystals and Si substrates with wire-grid polarizers. We have investigated theoretically the relationship between the characteristics of this IR chopper and its structure. It is confirmed that the theoretical calculations of the IR modulation degree are in approximate agreement with the experimental results. Under the condition that the IR radiation is emitted from a blackbody whose surface temperature is 150 °C, a degree of modulation of 7.4% is obtained.

Modulation-type pyroelectric infrared detector and its application

Abstract We have developed a new type of pyroelectric infrared (IR) detector that contains a sensing part and a solid-state chopper with two bimorph vibrators and two slit plates in the same package. This detector (M-type IR detector) features high reliability, small volume and low electric-power consumption compared with conventional pyroelectric IR detectors using a rotating chopper. In addition, two applications using an M-type IR detector have been investigated. One application is a new type of gas sensor, and the other is non-contact temperature measurement. For the gas sensor, the measurement accuracy is ±0.12% over a 0–20% gas concentration range. The non-contact temperature measurement system is used in a permanent-wave machine. In this system, the temperature of the hair can be accurately measured and automatically controlled. The accuracy of measurement is ±0.15°C over the temperature range 34–64°C.

Modulation Type Pyroelectric Infrared Sensor Using LiTaO3 Single Crystal

A pyroelectric infrared sensor with a solid state chopper was developed. Ordinarily, the incident rays of pyroelectric IR sensors must be periodically interrupted by means of a chopper, which consists of a motor and a revolving plate, in order to generate a continuous output voltage for temperature measurement. We have developed a new pyroelectric infrared sensor structure by replacing the chopper with a solid state setup consisting of a bimorph vibrator and a grate-type slit plate.