Low-frequency Highly Directional Air Coupled Ultrasound Sensor

Air coupled ultrasonic transducers are used for non-contact nondestructive evaluation of the properties of materials or structures. To obtain high resolution measurements, these transducers should have highly directional transmit and receive beams and good depth resolution. To achieve this, most transducers operate at ultrasonic frequencies greater than 100 kHz. However, there are many applications were these higher ultrasonic frequencies cannot be used due the high attenuation rates of a material. In these cases, lower ultrasonic frequencies are more suited. However, traditional air coupled transducers have poor resolution at these low frequencies due to wide beam widths and long duration transmit pulses. In this paper, we present a novel air coupled ultrasonic sensor. It has a highly directional transmit and receive beams and improved depth resolution for frequencies from about 25-65 kHz.