One-Millimeter Diameter Harmonic Ball Surface Acoustic Wave Gas Sensor with Temperature Compensation by Itself

Abstract

A newly designed 1-mm diameter harmonic ball surface acoustic wave (SAW) gas sensor has a double-electrode interdigital transducer (IDT) for driving multiple frequencies. The fundamental frequency is 80 MHz. The difference in delay time between a fundamental frequency component and a high harmonics was used to compensate temperature drift. A temperature coefficient of about 0.1 ppm/°C was obtained after compensation.

Fabrication of Thin Sensitive Film of Ball Surface Acoustic Wave Sensor by Off-Axis Spin-Coating Method

“…1) is suitable as a portable gas sensor; it realizes ultrahigh sensitivity not only by velocity (delay time) measurement but also by attenuation (amplitude) measurement when ultramultiple roundtrips (e.g., >100 turns) of the collimated SAW along the equator of the ball is achieved. [7][8][9][10][11][12][13][14] In fact, 0.001 vol % hydrogen gas was successfully detected from the amplitude change, 8) whereas the highest detectability of the planar SAW hydrogen sensor was only 0.1 %. 15) However, attenuation and scattering induced by the sensitive film coated on the roundtrip route must be low so as not to hinder the ultramultiple roundtrips, and thus the film must be thin (submicron thickness) and highly uniform.…”

“…1. 8,9,11,12) In the case of an organic sensitive film, although methods such as air brush, electrospray, 16,17) and spin-coating methods, 18,19) have been studied, it is not easy to fabricate a thin (<100 nm) and uniform film along the multiple roundtrip route on a three-dimensional spherical surface. In this study, we propose the ''off-axis spin-coating'' method and evaluate the performance of sensitive films using the theory of detectability.…”

Introduction of measurement techniques in ultrasonic electronics: Basic principles and recent trends

“…Force sensors [279][280][281][282][283][284][285] Object detection [286][287][288] Acceleration [289][290][291][292][293] Gyro sensors [294][295][296][297][298][299] Bio sensors 234,256,257,[300][301][302] Gas=chemical sensors 186,233,240,243,[246][247][248]250,251,253,254,261,303,304) Application of piezoelectric thin films 214,215,218,305) Microfluidic control 306) Continued on next page:…”

“…Such sensors are also applied to biosensors 234,256,257,[300][301][302] and gas=chemical sensors. 186,233,240,243,[246][247][248]250,251,253,254,261,303,304) Most of these sensors have films that undergo a chemical reaction with target substances, which cause mass loading of the piezoelectric resonators. Therefore, such a sensor is also a type of mass sensor.…”

Highly sensitive trace moisture ball surface acoustic wave sensor using SiOxfilm

“…In this work, to compensate the drift more precisely, we used the harmonic ball SAW sensor with double electrode, where excited waveform includes harmonic frequency components of odd order modes. 29,30) In the first approximation, the fractional delay time change ¦t is expressed by extending the equation shown in Ref. 29 as…”