An encoder for an active speed sensor includes a non-metallic body embedded with magnetized ferrous particles generating a magnetic field. The rare earth magnet comprises rare earth magnet particles. The golf putter includes a weight having an alignment point to be used as an aid in aligning the golf putter. Flexibility in the selection of a wavelength can be obtained by holographically imprinting multiple sets of wavelength selection elements. The compounds have general formula \u03a8:An example is.