[MicroAcoustic instruments Inc.]

Micromachined Air-Coupled Capacitance Transducer

Background

Ultrasonic transducers have a wide range of applications, including non-destructive testing of materials (NDT), biomedical imaging, and industrial process control. In most applications, conventional ultrasonic transducers require the use of a liquid couplant between the transducer and the materials to be inspected. This need for a liquid couplant has serious disadvantages in a variety of applications. For example, some materials such as carbon-fibre epoxy composites and paper can be damaged by absorption of liquid couplants; whereas other objects in need of routine inspection (such as airplanes) are too large for inspection in water baths and use water-jet transducers as a cumbersome alternative.

One way of eliminating liquid couplants is to couple the ultrasonic waves from the transducer to the material through an intervening layer of air or gas (i.e. without contact). However, this approach has been limited by the large acoustic-impedance mismatches that exist between gases and materials. These large mismatches make it difficult to transfer sufficient ultrasonic energy into the materials for inspection. Certain designs of piezoelectric transducer have demonstrated a limited ability to couple energy through an air-layer, but they themselves have enormous impedance mismatches with air, and can only respond over a very narrow range of frequencies. Such drawbacks of the piezoelectric air-coupled transducer have limited its widespread application.

Description of the Technology

The recently developed Micromachined Air-Coupled Capacitance Transducer has overcome the past limitations in air-coupled ultrasonics and has opened up a wide range of new applications that were not previously possible. This novel transducer was developed by Dr. David Schindel at Queen's University, Canada, and Dr. David Hutchins at Warwick University, England, and employs integrated circuit (IC) manufacturing techniques (or micromachining) in its unique capacitive design. The device has a wideband frequency response, a high sensitivity, and reproducible responses from transducer to transducer. Most importantly, the patented technology has many applications within and beyond existing uses of conventional ultrasound transducers.

MicroAcoustic's Broadband Air-coupled
Transducer (BAT®), right. Ultrasound
emerges from the bright circular region at centre.

Applications

There are two main areas of application for the micromachined air-coupled capacitance transducer. The first area (as mentioned) involves non-contact inspection of solid and liquid materials through an intermediary air/gas layer. The main advantages here are the elimination of liquid couplants and the potential for rapid inspection of large structures and sheet materials. Examples of the latter include plastics, glass-epoxy composites, carbon-epoxy composites (both thick and thin), paper and wood products, and metals.

The second main area of application involves reflection (or "in-air") applications, where the ultrasonic air-waves are simply reflected from the surfaces of solids or liquids. In this case, the small wavelengths of ultrasound in air allow high resolution imaging of materials surfaces (e.g. 25micron resolution at a frequency of 2MHz). Alternatively, properties of gases themselves and any particulates contained therein can also be investigated.

Specific application examples: non-contact distance sensing and level-detection; robotic imaging and room surveillance; gauging and imaging of manufactured parts; process control; non-contact NDT and materials characterization (such as aerospace components); gas and particulate analysis; gas flow measurements; environmental monitoring; scientific reference instrumentation; and biomedical applications.

Benefits

. Wideband frequency response: 40kHz - 2.5MHz
. High sensitivity
. IC technology produces low cost, high quality units with reproducible characteristics.
. A logical extension of the manufacturing process makes it possible to carefully control ultrasound beam profiles (e.g., focusing the ultrasonic beam using a Micromachined Air-Coupled Fresnel Zone-Plate).
. Lack of transducer "ringing" provides dead times of 5-40µsec, allowing high-frequency imaging at distances close to the transducer (~5mm).

Commercial Status

PARTEQ Innovations has patent protection for the transducers as well as comprehensive patent coverage for various air-coupled inspection techniques. Over 40 technical publications have been published demonstrating the feasibility of this technology in a wide range of new air-coupled applications. Dr. David Schindel (the inventor) has formed MicroAcoustic Instruments Incorporated for the purpose of developing and commercializing the technology, and various transducers and associated electronics are now available for sale. MicroAcoustic and PARTEQ are also actively seeking sub-licensees to help manufacture and commercialize the technology for various mass-markets and other unique areas of application.

>> View MicroAcoustic technical publications here

Contacts

Business/Technical Contact:
Dr. David Schindel, Physicist, P.Eng.
MicroAcoustic Instruments Inc.
460 Wilbrod Street, Suite 2
Ottawa, ON
Canada K1N 6M8

Phone: (613) 237-0867
Fax: (613) 237-9296
Email: schindel@microacoustic.com

PARTEQ Contact:
Anne Vivian-Scott
Manager, Commercial Development
PARTEQ Innovations
Biosciences Complex
Queen's University
Kingston, ON
Canada K7L 3N6

Phone: (613) 533-6000 ext. 75513
Fax: (613) 533-6853
Email: av4@post.queensu.ca

Go to the IAR/NRC site