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GaN SURFACE ACOUSTIC WAVE (SAW) BASED WIRELESS FIRE SENSOR

IP.com Disclosure Number: IPCOM000199104D
Publication Date: 2010-Aug-26
Document File: 8 page(s) / 542K

Publishing Venue

The IP.com Prior Art Database

Abstract

The present invention proposes a wireless fire sensor using GaN surface acoustic wave (SAW) device. The device consists of a reference SAW generator, a SAW chemical sensor and a SAW temperature sensor, all of which are GaN based and designed on the same chip. Inter digital structure on the GaN layer and RF signal generates SAW on the GaN surface by remote activation. Adsorption of a gas or chemical or a polar molecule at the surface modulates the propagation velocity. This results in the shift in frequency for the response signal. Measurement of the frequency shift gives an estimation of the chemical or gaseous species. Thus the present invention provides a wireless fire sensor based on multiple parameter measurement: chemical species and temperature to determine the presence of fire. The sensor operates at harsher conditions and has high sensitivity due to coupling of SAW with GaN based piezo- properties.

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RP13486

GaN SURFACE ACOUSTIC WAVE (SAW) BASED WIRELESS FIRE
SENSOR

BRIEF ABSTRACT

    The present invention proposes a wireless fire sensor using GaN surface acoustic wave (SAW) device. The device consists of a reference SAW generator, a SAW chemical sensor and a SAW temperature sensor, all of which are GaN based and designed on the same chip. Inter digital structure on the GaN layer and RF signal generates SAW on the GaN surface by remote activation. Adsorption of a gas or chemical or a polar molecule at the surface modulates the propagation velocity. This results in the shift in frequency for the response signal. Measurement of the frequency shift gives an estimation of the chemical or gaseous species. Thus the present invention provides a wireless fire sensor based on multiple parameter measurement: chemical species and temperature to determine the presence of fire. The sensor operates at harsher conditions and has high sensitivity due to coupling of SAW with GaN based piezo- properties.

KEYWORDS

    Wireless Surface Acoustic Wave (SAW) sensors, remotely activated SAW device, optical detection, frequency shift, delay time effect, SAW delay line and elasto- optical interaction.

DETAILED DESCRIPTION

    Surface Acoustic Wave sensors - SAW have been recognized for their efficiency and versatility in the electrical signals processing. The SAW sensors are made by a photolithographic process on a piezoelectric substrate to form an

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RP13486

interdigital transducer (IDT). A typical SAW device consists of two sets of interdigital transducers- receiver and transmitter. The (receiver) IDT provides the electric field necessary to displace the substrate and thus form an acoustic wave. The wave propagates through the substrate, where it is converted back to an electric field at the (transmitter) IDT on the other side. Surface acoustic waves have a longitudinal and a vertical shear component that can couple with a medium in contact with the device's surface. Such coupling strongly affects the amplitude and velocity of the wave. This feature enables SAW sensors to directly sense mass and mechanical properties. Adsorption of a gas or chemical or a polar molecule modulates the elasto-optic coupling which results in the modulation of refractive index or propagation velocity on the surface layer. This results in the formation of grating like structure at the top surface whose periodicity changes with the adsorption of the species or a shift in frequency of the response signal respectively. This is illustrated in Figure 1.

    In contrast to more traditional, active sensors that rely on the use of a battery or capacitor as a power source, wireless and passive SAW devices are useful in those applications where the harsh environment may prevent the presence of a human operator, or where the presence of wires and/or a power supply may be inappropriate. In the chemical industry, for example, such wireless and passive SAW sensors can be used for extended p...