Suspension of electromagnetic receiver coil
An electromagnetic receiver system with an EM receiver coil is for measuring EM signals while transported by a vehicle, e.g. a helicopter. A base part serves for connection to a towing system. A coil support is fixed to the electrical conductor of the EM receiver coil. A suspension system has gimbal axles defining gimbal axes arranged in one plane. The gimbal axles are arranged within a periphery of the EM receiver coil. A central element is connected to the gimbal axles, such that the axes intersect in an EM receiver coil central part. Joints allow the receiver coil to pivot around the first and second axes. Springs provide a self-righting effect on the coil around the axes. A precise calibration of centre of mass of the suspended receiver coil can be obtained by adding masses to cause the centre of mass to coincide with the geometric intersection between the axes.
1. An EM receiver system for measuring EM signals while being transported by an associated vehicle, comprising
a base part arranged for connection to the associated vehicle,
a EM receiver coil comprising a plurality of windings of an electrical conductor and being arranged for measuring an EM signal, further comprising a coil support fixed to the electrical conductor,
a suspension system comprising
first and second gimbal axles defining first and second gimbal axes arranged in one plane,
wherein the first and second gimbal axles are arranged within a periphery defined by the EM receiver coil,
a central element arranged in a central part of the EM receiver coil and connected to both of the first and second gimbal axles, so that the first and second gimbal axes intersect in a central part of the EM receiver coil,
a first set of joints fixed to the coil support and a second set of joints fixed to the base part, so as to allow the EM receiver coil to pivot around the first and second gimbal axes, and
a spring system serving to provide a self-righting effect on the EM receiver coil around each of the first and second gimbal axes.
2. The EM receiver system according to claim 1 , comprising at least one part, such as the coil support, arranged to receive a mass, so as to allow adjustment of a centre of mass of the EM receiver coil to coincide with a point of intersection of the first and second gimbal axles.
3. The EM receiver system according to claim 1 , wherein the central element comprises a sandwich element formed by a fibre reinforced polymer and a foam, wherein the sandwich element serves to fix relative positions of the first and second gimbal axes.
4. The EM receiver system according to claim 1 , wherein each of the first and second gimbal axles are formed by respective aluminium oxide pipes.
5. The EM receiver system according to claim 1 , wherein the coil support is formed by a foam structure surrounding the electrically conducting windings forming the EM receiver coil.
6. The EM receiver system according to claim 1 , wherein the base part is formed by a structure being a fibre reinforced polymer and a foam sandwich structure.
7. The EM receiver system according to claim 1 , wherein the spring system is adjusted so as to provide a natural oscillation frequency for the EM receiver coil around each of the first and second gimbal axes which is within 0.1-10.0 Hz.
8. The EM receiver system according to claim 1 , wherein the spring system comprises a set of springs on each of the first and second gimbal axles.
9. The EM receiver system according to claim 1 , wherein each joint of the first and second sets of joints comprises ball bearings.
10. The EM receiver system according to claim 1 , wherein the plurality of windings of electrical conductor of the EM receiver coil form a ring with a circular shape.
11. The EM receiver system according to claim 10 , wherein said ring has a height within a factor of 0.05 to 0.5 of a diameter of said ring.
12. The EM receiver system according to claim 1 , further comprising a third gimbal axle defining a third gimbal axis arranged in relation to the first and second gimbal axles, wherein the third gimbal axle is arranged in a central part of the EM receiver coil.
13. The EM receiver system according to claim 12 , comprising at least one spring serving to provide a self-righting effect on the EM receiver coil around the third gimbal axis.
14. An EM signal measurement system comprising
an EM receiver system according to claim 1 , and
a towing system arranged for connection to the base part of the EM receiver system, so as to allow the EM receiver system to be towed by a moving vehicle.
15. The EM signal measurement system according to claim 14 , further comprising:
an EM signal recording system connected to the EM receiver coil so as to receive an electric signal indicative of an EM signal received by the coil and to store a time series of data accordingly.
16. The EM signal measurement system according to claim 14 , further comprising:
an EM transmitter coil arranged for generating EM pulses, wherein the towing system is arranged for carrying the EM transmitter coil, and
an electric generator system arranged for connection to the EM transmitter coil, wherein
the electric generator system is arranged to generate electric pulses with at least one pulse rate within 0.1-60 Hz.
17. A method for measuring EM signals, the method comprising:
providing (P_EMS) an EM receiver system according to claim 1 ,
connecting (C_MV) the base part of the EM receiver system to a mobile vehicle,
towing (T_EMS) the EM receiver system by means of the mobile vehicle, and
recording (RC_EM) EM signals received by the EM receiver coil during towing.