A location system comprising: an acoustic sensor ; and a location device for determining the location of the acoustic sensor, the location device comprising: an ultrasound transducer array arranged to transmit a plurality of ultrasound beams and receive corresponding reflected echo signals; a controller arrangement , said arrangement comprising: a transmit controller for controlling transmitted signals of the transducer array to provide a transmit beam comprising a transmission from each transducer of the array; a receive controller for analyzing the received reflected signals, wherein the controller arrangement is adapted to implement a location process which comprises, for each of the plurality of transmitted ultrasound beams, performing a frequency analysis of the received reflected signals to identify if there is a signal reflected from the acoustic sensor and to identify a location area of said acoustic sensor, and to derive a progressively more accurate final location, by adapting the transmit beam pattern or type, within said location area from the plurality of frequency analyses. an acoustic sensor ; and a location device for determining the location of the acoustic sensor, the location device comprising: an ultrasound transducer array arranged to transmit a plurality of ultrasound beams and receive corresponding reflected echo signals; a controller arrangement , said arrangement comprising: a transmit controller for controlling transmitted signals of the transducer array to provide a transmit beam comprising a transmission from each transducer of the array; a receive controller for analyzing the received reflected signals, wherein the controller arrangement is adapted to implement a location process which comprises, for each of the plurality of transmitted ultrasound beams, performing a frequency analysis of the received reflected signals to identify if there is a signal reflected from the acoustic sensor and to identify a location area of said acoustic sensor, and to derive a progressively more accurate final location, by adapting the transmit beam pattern or type, within said location area from the plurality of frequency analyses. an ultrasound transducer array arranged to transmit a plurality of ultrasound beams and receive corresponding reflected echo signals; a controller arrangement , said arrangement comprising: a transmit controller for controlling transmitted signals of the transducer array to provide a transmit beam comprising a transmission from each transducer of the array; a receive controller for analyzing the received reflected signals, a transmit controller for controlling transmitted signals of the transducer array to provide a transmit beam comprising a transmission from each transducer of the array; a receive controller for analyzing the received reflected signals, wherein the controller arrangement is adapted to implement a location process which comprises, for each of the plurality of transmitted ultrasound beams, performing a frequency analysis of the received reflected signals to identify if there is a signal reflected from the acoustic sensor and to identify a location area of said acoustic sensor, and to derive a progressively more accurate final location, by adapting the transmit beam pattern or type, within said location area from the plurality of frequency analyses. <EOS>