Electromagnetic Transmitter with Arduino Controlled Variable Frequencies

The deliverable for the project is an electromagnet with a frequency between 15hz and 35hz. This needs to be adjustable by changing the number within the Arduino code. I also require a receiver to detect the electromagnet and its frequency. It would be excellent if these could be programmed in Arduino as it will fit within the rest of the project. The electromagnet needs to be powered with AA batteries and last a long time (preferable days from four AA batteries). It can pulse so that it is not continuously on to make the batteries last longer. The intention is to be able to track this electromagnet as it goes through the sewer and other pipelines to find a blockage. From research I know that low power small diameter long (300mm) electromagnets have been buried meters below the ground and it is still possible to detect them. I also believe that similar technology is used in the oil and gas industry to detect pigs buried in pipelines below the seafloor. Once this part of the project is complete I will add it to my current project where the an App will be able to change the frequency via Bluetooth.