Hironobu Yamada

Chemical sensing plate with a laser-terahertz monitoring system

A new type of laser-terahertz emission system for noncontact investigations of chemical solutions has been developed. The system monitors terahertz emission from a sensing plate, which consists of silicon oxide and silicon thin film layers on a sapphire substrate. Sensing of chemical solutions with pH values between 1.68 and 10.01 was demonstrated. The amplitude of the terahertz emission from the sensing plate increased with increasing pH value. This change in the amplitude was caused by a change in the depletion layers of the silicon thin film when protons were adsorbed on the surface of the sensing plate. This study demonstrates that full noncontact monitoring of chemical solutions is possible using the laser-terahertz emission system.

A Terahertz Chemical Microscope to Visualize Chemical Concentrations in Microfluidic Chips

Here, a new type of terahertz chemical microscope (TCM) is proposed and developed, and the first demonstration of imaging the chemical concentration in fluid channels is reported. Fluid samples flow through channels possessing a semiconductor sensing plate as a bottom wall. Terahertz (THz) waves are radiated from the sensing plate as a result of femtosecond laser illumination. Because the amplitude of the THz radiation depends on the concentration of ions adsorbed on the surface of the plate, the ion distribution in the fluid channels can be visualized by scanning the laser across the plate. An image showing separated solutions with two different proton concentrations is successfully observed as the first demonstration of this instrument.

Highly Sensitive Measurement of Moisture Content Using HTS-SQUID

We developed a highly sensitive magnetic system for measuring moisture content using an HTS-SQUID sensor. The system consists mainly of an exposure coil, a Dewar flask containing HTS-SQUID immersed in liquid nitrogen, a cancellation coil, a lock-in amplifier, magnetically shielded box, and FLL circuit. The cancellation coil was used to eliminate the applied magnetic field at the sensor position, and then a cancellation ratio of more than -40 dB was obtained. By the high performance, the subject can be exposed to a powerful magnetic field strength in the order of muT, and a weak magnetic signal of less than tens of pT from the subject can be detected. Using a magnetic vector analysis technique, more precise measurement of moisture content is realized.

Dual-Gate Field-Effect Transistor Hydrogen Gas Sensor with Thermal Compensation

We developed a dual-gate field-effect transistor (FET) hydrogen gas sensor for application to hydrogen vehicles. The dual-gate FET hydrogen sensor was integrated with a Pt-gate FET to detect hydrogen and a Ti-gate FET as the reference sensor in the same Si chip. The Ti-FET had the same structure as the Pt-FET except for the gate metal. The Pt-FET showed a good response to hydrogen gas above 10 ppm in air, while the Ti-FET did not show any response to hydrogen gas. The differential output voltage between the Pt-FET and the Ti-FET was stable in the temperature range from room temperature to 80 °C because of the same temperature dependence of the current–voltage (I–V) characteristics. In addition, the temperature of the integrated hydrogen sensor was controlled by an integrated system consisting of a heater and a thermometer at any given temperature under severe weather conditions.

Detection of the weak magnetic properties change of stainless-steel welding parts by low frequency magnetic imaging

Differences in weld quality resulting from variations in welding conditions were detected via low frequency magnetic imaging. This magnetic imaging was obtained using a recently developed measurement system, consisting of an exposure coil, a magnetoresistive (MR) sensor, and a lock-in amplifier. A wide area of stainless-steel sample was exposed to the magnetic field via an induction coil, and the MR sensor measured the generated magnetic field from the sample. The frequency of the magnetic field ranged from 20Hzto1kHz. A cylindrical stainless-steel sample was fabricated by rolling a stainless-steel sheet and welding each edge by an arc welder with argon gas, while the welding condition was changed by controlling the argon gas flow. The magnitude and phase shift of the generated magnetic field from the sample was measured by scanning the MR sensor on the sample surface. The change in magnetic properties caused by the welding condition change was successfully imaged.

Non-Contact Thickness Gauge for Conductive Materials Using HTS SQUID System

Eddy current testing using high-TC superconductive (HTS) superconducting quantum interference devices (SQUID), was developed to realize non-contact thickness gauge measurement of conductive materials, due to their high-sensitivity to magnetic fields generated by eddy currents. A HTS SQUID pulsed eddy current system with Fourier transform analysis is proposed and demonstrated. Aluminum plates (10 x 10 mm) with thicknesses in the range of 1 to 10 mm were used as test samples. The intrinsic responses G A(f) of the samples were successfully extracted. The slopes of these responses were estimated by linear fitting, and plotted as a function of sample thickness. The G A(f) slopes decrease with increasing thickness of the test samples. The analysed data suggests that this system can be used as a non-contact thickness gauge for conductive materials.

Hydrogen Response Mechanism of a Proton Pumping Gate FET Gas Sensor

We developed a new type hydrogen sensor for a proton pumping gate FET with a triple layer of Pd / proton conducting polymer / Pt. Compared with conventional type FET with a single catalytic metal gate, the selectivity was improved. Furthermore, two different output signals of DC and AC modulation were obtained. According to increments of the upper gate voltage to a lower gate, the sensitivity was increased. When modulation voltage was added to the upper gate voltage, AC modulation output was obtained. The response mechanism of the new type FET was investigated using several hydrogen gases and with modulation conditions. Consequently, the hydrogen response mechanism can be explained by a hydrogen dissociation reaction occurring at the upper gate, and the hydrogen gas and generated proton can pass through the proton conducting polymer, and finally an equilibrium hydrogen reaction occurs at the lower gate. These complex mechanisms can be controlled by the gate bias and modulation voltage.

Laser-Terahertz Emission Readout of Chemical Sensors

A new type of laser-terahertz emission system for the non-contact investigation of the chemical solutions has been developed. This system monitors the terahertz emission from a sensing plate, which consists of a silicon oxide and a silicon thin film layers on the sapphire substrate. The sensing of chemical solutions with the pH value between 1.68 and 10.01 was demonstrated. The amplitude of terahertz emission from the sensing plate increased with increasing the pH value. This change in the amplitude was caused by the change of the depletion layers of the silicon thin film when protons adsorbed at the surface of the sensing plate. This result indicates that fully non-contact monitoring of chemical solutions can be possible using the laser-terahertz emission system.

Laser-terahertz emission from the chemical sensing plate

A new type of sensing system to measure the concentration of the protons in the solutions by means of the laser-terahertz emission and detection was proposed and developed. The simple layered structures of SiO2/Si thin films on a sapphire substrate were prepared as a chemical sensing plate. The system measure the amplitude of the terahertz emission from the depletion layer of SiO2/Si interface by irradiating the femtosecond laser pulses with the center wavelength of 790 nm. The solution was contacted with the SiO2 surface and the Si thin film layer was electrically grounded. An Ag/AgCl reference electrode was used to control the potential of the solution. When the proton was adsorbed on the surface of the plate, the surface electric dipole was formed at the surface, which changes the local field of the depletion layer. Thus the peak amplitude of terahertz emission was changed depending on the number of the proton adsorbed on the surface of the plate. Actually, we demonstrated that the peak amplitude of terahertz emission from the sensing plate increased by increasing the pH values of the test solution when the bias voltage of the solution was 0 V. (pH values indicate the concentration of the proton in the solution) and the sensitivity was about 31 muV/pH.