A device and a method for detecting an actuator by sonicating the actuator with sound waves through a sensor. The device is used in particular in a safety application. The sensor and actuator can be moved relative to each other. The sensor includes a sound wave transmitter, a sound wave receiver and a computing unit. The sound wave transmitter is designed to send sound waves in the direction of the actuator. The sound wave receiver, in turn, is designed to pick up the sound waves reflected by the actuator and convert them into an analog signal. The computing unit converts the analog signal into a digital signal and detects the actuator by comparing it with a reference signal.

A detection apparatus is provided. The detection apparatus includes a hardware processor programmed to at least calculate a first echo intensity of a first reception signal generated from a reception wave reflected on reflection objects, calculate a second echo intensity of a second reception signal generated from a reception wave reflected on the reflection objects, a signal duration of the second reception signal being shorter than that of the first reception signal, generate a first frequency distribution of the first echo intensity, generate a second frequency distribution of the second echo intensity, and extract a density of the reflection objects or an index of density of the reflection objects based on a comparison of the first frequency distribution and the second frequency distribution.

A detection apparatus is provided. The detection apparatus includes a hardware processor programmed to at least calculate a first echo intensity of a first reception signal generated from a reception wave reflected on a reflection object, calculate a second echo intensity of a second reception signal generated from a reception wave reflected on the reflection object, a signal duration of the second reception signal being shorter than that of the first reception signal, and detect a target from a comparison of the first echo intensity and the second echo intensity.

A sonar system and method for measuring relative velocity between a transducer and a scattering surface or volume is disclosed. The system utilizes phased array or piston transducers that project acoustic beams in different directions. Each projection consists of multiple sub-waveforms of different center frequencies that are either frequency steered into different directions such that the acoustic beams ensonify different scatterers or sufficiently separated in frequency to obtain independent estimates of velocity. Each received return signal is used to estimate an independent relative velocity between the transducer and scatterers, and the estimated velocities are averaged to reduce the single-ping standard deviation of the velocity error. Different lags may be used in the different sub-waveforms, wherein shorter lags are used to ambiguity resolve longer lags such that the system ambiguity velocity is sufficiently high, and the single-ping variance decreases below what would be possible when only using a short lag.