Ultrasonic distance measurement system with a well defined and adjustable detection area

One major problem of ultrasonic distance measurement is the strongly object dependent detection range: objects providing strong echoes (e.g. well aligned planes) can be detected in a much wider distance than "small objects" reflecting only a fractional amount of the incoming sound energy (e.g. edges). In conventional sensor constructions not only the maximum measurable distance along the sensor axis varies, but also the field of detection where measurement values are delivered. As a consequence, the decision if an object is located inside or outside a defined area is hardly possible without a priori knowledge of the object's reflection properties. This work presents a measurement principle that provides a well defined and object independent detection area that moreover can be dynamically adjusted to achieve high resolution for algorithms based on contact-less ultrasonic "touching" of objects.