Magnetic sensor could allow pigeon-style GPS

A variety of migrating birds, as well as bats and even hamsters successfully use a 'magnetic sense' to navigate on long journeys. Now, a new type of sensor developed by scientists in the US could make it possible for humans do the same trick.
Magnetic global positioning works by matching precise measurements of the Earth's magnetic field with a database of measurements from across the globe.
The magnetic field is like that of a giant bar magnet placed along the globe's axis. Magnetic field lines emerge from the southern half of the globe and re-enter the northern half. To use the field to calculate geographic position requires two measurements – of its angle and its strength.
The Earth's field is strongest at the poles and weakest at the equator. The angle at which it meets the Earth's surface is unique for a particular location, making it possible to refer to the survey data to work out where you are. Measuring both properties improves accuracy.
The sensor developed by researchers at Virginia Tech University, US, exploits a property called the 'giant magnetoelectric effect', where a material changes its electrical properties under the influence of a magnetic field.
The core of the sensor is made from layers of lead zirconium titanate, which has the largest magnetoelectric effect of any material. This means it can detect the tiny variations in field strength and angle needed for magnetic GPS.
3D measurements
To use the device as a geomagnetic sensor, the researchers apply a small alternating current to a coil wrapped around the core and measure the voltage generated from the core as a result. This voltage is proportional to the change in the Earth's magnetic field.
"For GPS applications, we need to take measurements in 3D so we can calculate both the magnetic field and the inclination," team member Junyi Zhai told New Scientist. "We therefore use three sensors, each one perpendicular to the other two to achieve this." The device is roughly cubic and 10cm to a side..
To determine location, the researchers compare the values of the magnetic field and angles obtained to data from the United States Geological Survey, which has tabulated the Earth's mean field and its inclinations at many points over much of the Earth's surface.
Although less accurate than satellite GPS, the new sensor's use of the magnetic field means it is more reliable in certain situations. For example, in remote areas that have no satellite reception, or in bad weather conditions where the connection is temporarily lost.
The researchers say the accuracy of the technique is "quite good", but that it is limited by the grid of values from the US Geological Survey. A more accurate survey of the field across the world would improve accuracy.
"The idea of using the ME sensors for GPS applications is truly novel," says Gopalan Srinivasan, who researches magnetoelectric devices at Oakland University, US. He adds that technical issues with the epoxy used to glue the core together, and its response to temperature will need to be ironed out in any device intended for production.
Journal reference: Applied Physics Letters (DOI: