108 as shown in 1104 and 1106 can be tracked by processor 103 through position sensing system 105 a control signal is generated if the distance between finger 108 and display 104 is less than the threshold value three ultrasonic sensors are depicted in fig1 more or less ultrasonic sensors may be used ultrasonic sensors may be arranged in a two dimensional array ultrasonic sensors can also be disposed beneath display 104 and also be disposed outside the display area in the front surface of mobile device 102 fig1 is a schematic diagram of an exemplary position sensing system 105 in accordance with a third embodiment an array of temperature sensor 118 as shown exemplarily in 1202 is disposed beneath display 102 temperature sensors 118 measures temperature distribution or map in a plane beneath display 104 each of temperature sensors is disposed in a substrate unit the substrate units are disposed underneath display 104 the operations of mobile device 102 generate heat which is called self heating in this disclosure the temperature sensors measure the temperature of each of the substrate units the measured temperatures form a temperature map overlapping the display plane the temperature map is measured according to a predetermined frequency and is transmitted to processor 103 in real time base the self heating leads to the measured temperatures at levels higher than an ambient temperature the heat is transferred to the ambient through display 104 each of the substrate units is associated with a resistance of heat transfer the resistance is affected by an object in the heat transfer path and also by the distance of the object to the substrate unit.