SENSOR FOR DETECTING SUBSTANCE IN LIQUID

• US 20090060790A1
• Filed: 11/19/2008
• Published: 03/05/2009
• Est. Priority Date: 06/16/2006
• Status: Active Grant

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: HADA, Takuo, OKAGUCHI, Kenjiro, KADOTA, Michio
• Granted Patent: US 8,658,097 B2
• Time in Patent Office: Days
• US Class Current: 422/68.100
• CPC Class Codes: G01N 2291/0255 (Bio)chemical reactions, e.g. on biosensors
• CPC Class Codes: G01N 2291/0256 Adsorption, desorption, surface mass change, e.g. on biosensors
• CPC Class Codes: G01N 2291/0423 Surface waves, e.g. Rayleigh waves, Love waves
• CPC Class Codes: G01N 29/022 Fluid sensors based on microsensors, e.g. quartz crystal-microbalance [QCM], surface acoustic wave [SAW] devices, tuning forks, cantilevers, flexural plate wave [FPW] devices microdevices per se B81B

Abstract

A sensor for detecting a substance in liquid includes a sensing circuit including a sensing surface acoustic wave (SAW) element in which a reaction film to react with a substance in liquid, a reference circuit including a reference SAW element including an IDT and not including a reaction film, a first signal source driving the sensing circuit, a second signal source driving the reference circuit and being independent of the first signal source, and a differential circuit arranged to output a differential output between an output of the sensing circuit and an output of the reference circuit. The frequency of a first frequency signal output from the first signal source is different from the frequency of a second frequency signal output from the second signal source, thereby making a driving frequency for the sensing SAW element and a driving frequency for the reference SAW element substantially the same as or different from one another.

Claims

1. A sensor for detecting a substance in liquid, the sensor comprising:

a sensing circuit including a sensing surface acoustic wave element, the sensing surface acoustic wave element including a piezoelectric substrate, an interdigital transducer disposed on the piezoelectric substrate, and a sensing portion in which a reaction film is arranged so as to cover the interdigital transducer and react with a detection-target substance in liquid;

a reference circuit including a reference surface acoustic wave element, the reference surface acoustic wave element including a piezoelectric substrate and an interdigital transducer disposed on the piezoelectric substrate and having no reaction film arranged so as to cover the interdigital transducer;

a first signal source arranged to drive the sensing circuit;

a second signal source arranged to drive the reference circuit and being provided independently of the first signal source; and

a differential circuit connected to the sensing circuit and the reference circuit and arranged to output a differential output between an output of the sensing circuit and an output of the reference circuit;

the first signal source is arranged to output a first frequency signal, and the second signal source is arranged to output a second frequency signal having a frequency that is different from a frequency of the first frequency signal, so as to make a driving frequency for the sensing surface acoustic wave element and a driving frequency for the reference surface acoustic wave element different from one another.

2. The sensor for detecting a substance in liquid according to claim 1, wherein the first and second frequency signals are selected so as to satisfy dP≧

0, where dP=Pr−

Ps, and where Ps is an output signal of the sensing circuit, Pr is an output signal of the reference circuit, and dP is an output signal of the differential circuit.

3. The sensor for detecting a substance in liquid according to claim 1, wherein each of the piezoelectric substrates is a 30°

to 40°

rotated Y-plate X-propagation lithium tantalate substrate.

4. The sensor for detecting a substance in liquid according to claim 1, wherein each of the sensing surface acoustic wave element and the reference surface acoustic wave element is a surface acoustic wave element that utilizes surface acoustic waves primarily including shear-horizontal waves.