Toshiaki Yokoo

Microwave Detector Using Granular-Type YBCO Superconductors

A highly sensitive microwave detector has been developed for the first time by granular-type bulk YBCO superconductors with fine particles. Particles with a size of about 1 µm, having a SNS-like grain boundary, were controlled by a coprecipitation method, followed by a sintering process. A new fabrication method for bulk superconductors was also developed to produce a precise microbridge-type structure. Sensitivity to microwave power below -40 dBm was obtained, and a direct mixing effect was obtained at a frequency of 8.6 GHz at the temperature of 77 K. It was confirmed that the Josephson effect of the detector at the SNS grain boundary formed in the sintering process for ceramics is the most responsive for microwave detection.

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.

Application of Pyroelectricity of LiTaO3 for Infrared Detectors

We developed a new structure (PEC structure) pyroelectric IR detector using LiTaO3 single crystal. The detector with this structure has good performance, high reliability and is suited to mass-production. In addition, we fabricated a new IR detector structure containing both the chopper and the pyroelectric element in the same package (M-type detector). The structure and the characteristics of these detectors are described.

The Pyroelectric Sensor

This report is an outline of pyroelectric sensors. The properties of various materials for pyroelectric sensors were investigated. Various types of construction and performance factors which give pyroelectric sensors their particular features are described. Several applications of the pyroelectric sensor are also listed. In conclusion, the future trend of the pyroelectric sensor is described.

Properties of Yb–Ba–Cu–O Superconductors Prepared by a Plasma-Arc Melting and Rapid Quenching Method

A PMQ (plasma-arc melting and rapid quenching) method has been successfully developed to obtain homogeneous and highly dense Yb-Ba-Cu-O compounds through the crystallization of the superconducting phase from the amorphouslike state. The maximum Tc of 91 K and packing density of 7.14 g/cm3 (98% of the theoretical density 7.27 g/cm3) were produced by this method. Furthermore, a large activation energy of 1.5 eV was observed by magnetic relaxation measurements.

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.

A new-structure LiTaO3 pyroelectric infrared detector

A LiTaO3 pyroelectric infrared detector with a new type of structure has been developed.The detective material is supported on an electric conductor by a special conductive adhesive which possesses low thermal conduction.In the fabrication process of the detector, the pyroelectric material is not handled in the form of thin chips, as in the conventional fabrication process. The detector is particularly suited to mass production, and should be able to be manufactured more economically than conventional pyroelectric detectors.The voltage responsivity and the specific detectivity D* (500, 10, 1) of the new type pyroelectric detector are nearly 300 V/W at 10 Hz and 2 × 108 cm√Hz/W, respectively.The pyroelectric responsitivity and D* of this new-type pyroelectric detector are calculated theoretically as a function of the thickness of the pyroelectric element, and the thickness dependence of the responsivity and D* are experimentally confirmed. The theoretical calculation has been shown to be in agreement with ...

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.

A New-Structure LiTaO3 Pyroelectric Infrared Detector

A LiTaO3 pyroelectric infrared detector with a new type of structure has been developed. The detective material is supported on an electric conductor by a special adhesive which possesses high electricel conductivity and low thermal conductivity. The pyroelectric responsivity and D* of this new-type pyroelectric detector are calculated theoretically as a function of the thickness of the pyroelectric element, and the thickness dependence of the responsivity and D* are experimentally confirmed. The theoretical calculation has been shown to be in agreement with experimental results.

Preparation of Substrates for Superconductive Devices Using Bi-System Low-Tc Single Crystals

Formation of insulating MgO thin layers has been carried out on c-planes of Bi2SnCaCu2Ox single crystals as the first attempt at preparing S/I/S structures for the first time.