In general, search coils come in two types: Concentric and Wide scan. Concentric are preferred for discriminating while wide scan coils are less affected by ground mineralization. All search coils are electro-statically shielded and waterproof.
Larger search coils will give better detection depth with larger targets and better ground coverage but sensitivity to smaller objects may be sacrificed. Smaller search coils will offer greater sensitivity to smaller objects and improved target separation in trashy soil.
A third style, the Printed Spiral, is made only by Tesoro for use with pulse induction circuitry. It offers good sensitivity to a broader range of target sizes and improved sensitivity to less conductive targets such as fine gold chains.