Acoustic emissions are detected by reflecting microwave radar signals off of an object, receiving reflected radar signals, generating an intermediate frequency, and filtering the intermediate frequency to remove low frequency signals associated with object movement and not acoustic emissions. A microwave Doppler radar detector provides the signals, a band-pass filter filters the intermediate frequency signal, and resulting signal is collected and analyzed to establish a relationship between the acoustic emission and the filtered signal. One application described is detecting tool wear using a microwave Doppler-based acoustic emission sensor and predicting tool wear based on the detected acoustic emission.